ORIGINAL PLATE FOR ON-MACHINE DEVELOPMENT TYPE LITHOGRAPHIC PRINTING PLATE, LITHOGRAPHIC PRINTING PLATE MANUFACTURING METHOD, AND LITHOGRAPHIC PRINTING METHOD

Abstract

 Provided is an on-press development type lithographic printing plate precursor having a support, an image-recording layer, and an outermost layer in this order, in which the image-recording layer contains a polymerization initiator, a polymerizable compound, and an infrared absorber, and a decomposition rate of the infrared absorber after storage for 8 hours in an environment at an ozone concentration of 150 ppb is 50% or less. Also provided are a method of preparing lithographic printing plate and a lithographic printing method in which the lithographic printing plate precursor is used.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present disclosure relates to an on-press development type lithographic printing plate precursor, a method of preparing a lithographic printing plate, and a lithographic printing method.

2. Description of the Related Art

[0002] Generally, a lithographic printing plate consists of a lipophilic image area that receives ink in a printing process and a hydrophilic non-image area that receives dampening water. Lithographic printing is a method exploiting the mutual repulsion of water and oil-based ink, in which the lipophilic image area and the hydrophilic non-image area of a lithographic printing plate are used as an ink-receiving portion and a dampening water-receiving portion (non-ink-receiving portion) respectively, the adhesiveness of ink is varied within the surface of the lithographic printing plate such that only the image area receives the ink, and then printing is performed by the transfer of the ink to a printing substrate such as paper.

[0003] In the related art, in order to prepare this lithographic printing plate, a lithographic printing plate precursor (also called PS plate) has been widely used which is obtained by providing a lipophilic photosensitive resin layer (also called image-recording layer) on a hydrophilic support. Generally, a lithographic printing plate is obtained by a plate making method of exposing a lithographic printing plate precursor through an original picture such as a lith film, then keeping a portion of an image-recording layer that will be an image area while removing other unnecessary portions of the image-recording layer by dissolving such portions in an alkaline developer or an organic solvent, and forming a non-image area by exposing the hydrophilic surface of a support.

[0004] In response to the intensifying interest in the global environment, an environmental issue of waste liquid generated by wet treatments such as a development treatment has gathered more attention.

[0005] Regarding the environmental issue described above, an attempt is made to simplify development or plate making or to remove treatments. Examples of a method of preparing lithographic printing plate in a simple way include a method called "on-press development". That is, on-press development is a method of exposing a lithographic printing plate precursor, then immediately mounting the precursor on a printer without performing development of the related art, and removing an unnecessary portion of the image-recording layer at an early stage of the ordinary printing step.

[0006] In the present disclosure, a lithographic printing plate precursor that can be used for such on-press development is called "on-press development type lithographic printing plate precursor"

[0007] Examples of the lithographic printing plate precursors in the related art include those described in JP2012-066577A.

[0008] JP2012-066577A discloses an on-press development type lithographic printing plate precursor having, in this order, a support, an image-recording layer containing a radical polymerization initiator, a radically polymerizable compound, and a binder polymer having an alkylene oxide group, and an overcoat layer containing celluloses.

SUMMARY OF THE INVENTION

[0009] An object of an embodiment of the present disclosure is to provide an on-press development type lithographic printing plate precursor in which discoloration caused by exposure to ozone is suppressed.

[0010] An object of another embodiment of the present disclosure is to provide a method of preparing a lithographic printing plate and a lithographic printing method in which the on-press development type lithographic printing plate precursor is used.

[0011] Means for achieving the above objects include the following aspects.

<1> An on-press development type lithographic printing plate precursor having a support, an image-recording layer, and an outermost layer in this order,

in which the image-recording layer contains a polymerization initiator, a polymerizable compound, and an infrared absorber, and

a decomposition rate of the infrared absorber after storage for 8 hours in an environment at an ozone concentration of 150 ppb is 50% or less.

<2> The on-press development type lithographic printing plate precursor described in <1>, in which a film thickness of the outermost layer is 0.005 µm to 2 µm.

<3> The on-press development type lithographic printing plate precursor described in <1> or <2>, in which the outermost layer has oxygen permeability.

<4> The on-press development type lithographic printing plate precursor described in any one of <1> to <3>, in which the outermost layer contains a polysaccharide.

<5> The on-press development type lithographic printing plate precursor described in any one of <1> to <4>, in which the outermost layer contains a cellulose derivative having a methoxy group substitution degree of 1 to 2.

<6> The on-press development type lithographic printing plate precursor described in any one of <1> to <5>, in which the outermost layer further contains a hydrophobic polymer.

<7> The on-press development type lithographic printing plate precursor described in any one of <1> to <6>, in which the outermost layer further contains polymer particles.

<8> The on-press development type lithographic printing plate precursor described in any one of <1> to <7>, in which the outermost layer further contains a decomposition-type infrared absorber.

<9> The on-press development type lithographic printing plate precursor described in any one of <1> to <8>, in which the polymerization initiator includes an electron-donating polymerization initiator and an electron-accepting polymerization initiator.

<10> The on-press development type lithographic printing plate precursor described in <9>, in which HOMO of the infrared absorber - HOMO of the electron-donating polymerization initiator is 0.70 eV or less.

<11> The on-press development type lithographic printing plate precursor described in <9> or <10>, in which LUMO of the electron-accepting polymerization initiator - LUMO of the infrared absorber is 0.80 eV or less.

<12> The on-press development type lithographic printing plate precursor described in any one of <1> to <11>, in which the polymerizable compound includes a polymerizable compound having functionalities of 7 or more.

<13> The on-press development type lithographic printing plate precursor described in any one of <1> to <12>, in which the polymerizable compound includes a polymerizable compound having functionalities of 10 or more.

<14> The on-press development type lithographic printing plate precursor described in any one of <1> to <13>, in which the image-recording layer further contains polymer particles.

<15> The on-press development type lithographic printing plate precursor described in <14>, in which the polymer particles are addition polymerization-type polymer particles having a hydrophilic group, and
the hydrophilic group includes a group represented by Formula Z.

[0012] In formula Z, Q represents a divalent linking group, W represents a divalent group having a hydrophilic structure or a divalent group having a hydrophobic structure, Y represents a monovalent group having a hydrophilic structure or a monovalent group having a hydrophobic structure, either W or Y has a hydrophilic structure, and * represents a bonding site with another structure.

[0013] <16> The on-press development type lithographic printing plate precursor described in any one of <1> to <15>, in which the image-recording layer further contains a color developing agent.

[0014] <17> The on-press development type lithographic printing plate precursor described in any one of <1> to <16>, in which the color developing agent is a compound represented by any of Formula (Le-1) to Formula (Le-3).

[0015] In Formula (Le-1) to Formula (Le-3), ERG's each independently represent an electron-donating group, X₁ to X₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, X₅ to X₁₀ each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, Y₁ and Y₂ each independently represent C or N, X₁ does not exist in a case where Y₁ is N, X₄ does not exist in a case where Y₂ is N, Ra₁ represents a hydrogen atom, an alkyl group, or an alkoxy group, and Rb₁ to Rb₄ each independently represent a hydrogen atom, an alkyl group, or an aryl group.

[0016] <18> The on-press development type lithographic printing plate precursor described in <16> or <17>, in which the color developing agent is a compound represented by Formula (Le-8).

[0017] In Formula (Le-8), X₁ to X₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, Y₁ and Y₂ each independently represent C or N, X₁ does not exist in a case where Y₁ is N, X₄ does not exist in a case where Y₂ is N, Rb₁ and Rb₂ each independently represent an alkyl group, an aryl group, or a heteroaryl group, and Rc₁ and Rc₂ each independently represent an aryl group or a heteroaryl group.

[0018] <19> The on-press development type lithographic printing plate precursor described in <18>, in which Rc₁ and Rc₂ each independently represent a phenyl group that has a substituent at at least one ortho position and an electron-donating group at a para position.

[0019] <20> The on-press development type lithographic printing plate precursor described in <16> or <17>, in which the color developing agent is a compound represented by Formula (Le-10).

[0020] In Formula (Le-10), Ar₁'s each independently represent an aryl group or a heteroaryl group, and Ar₂'s each independently represent an aryl group having a substituent at at least one ortho position or a heteroaryl group having a substituent at at least one ortho position.

[0021] <21> The on-press development type lithographic printing plate precursor described in <20>, in which Ar₁'s each independently represent an aryl group having an electron-donating group or a heteroaryl group having an electron-donating group, and Ar₂'s each independently represent a phenyl group having a substituent at at least one ortho position and an electron-donating group at a para position.

[0022] <22> The on-press development type lithographic printing plate precursor described in any one of <1> to <21>, in which the support has an aluminum plate and an anodic oxide film of aluminum disposed on the aluminum plate,

the anodic oxide film is at a position closer to a side of the image-recording layer than the aluminum plate and has micropores extending in a depth direction from a surface of the anodic oxide film on the side of the image-recording layer,

an average diameter of the micropores within the surface of the anodic oxide film is more than 10 nm and 100 nm or less, and

in an L*a*b* color system, a value of brightness L* of the surface of the anodic oxide film on the side of the image-recording layer is 70 to 100.

[0023] <23>The on-press development type lithographic printing plate precursor described in <22>, in which the micropores are each composed of a large diameter portion that extends to a position at a depth of 10 nm to 1,000 nm from the surface of the anodic oxide film and a small diameter portion that is in communication with a bottom portion of the large diameter portion and extends to a position at a depth of 20 nm to 2,000 nm from a communicate position,

an average diameter of the large diameter portion within the surface of the anodic oxide film is 15 nm to 100 nm, and

an average diameter of the small diameter portion at the communicate position is 13 nm or less.

[0024] <24> A method of preparing a lithographic printing plate, including a step of exposing the on-press development type lithographic printing plate precursor described in any one of <1> to <23> in the shape of an image; and
a step of supplying at least one material selected from the group consisting of a printing ink and dampening water on a printer to remove the image-recording layer in a non-image area.

[0025] <25> A lithographic printing method including a step of exposing the on-press development type lithographic printing plate precursor described in any one of <1> to <23> in a shape of an image,
a step of supplying at least one material selected from the group consisting of a printing ink and dampening water on a printer to remove the image-recording layer in a non-image area and to prepare a lithographic printing plate, and a step of performing printing by using the obtained lithographic printing plate.

[0026] According to an embodiment of the present disclosure, it is possible to provide an on-press development type lithographic printing plate precursor in which discoloration caused by exposure to ozone is suppressed.

[0027] According to another embodiment of the present disclosure, it is possible to provide a method of preparing a lithographic printing plate and a lithographic printing method in which the on-press development type lithographic printing plate precursor is used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 

Fig. 1 is a schematic cross-sectional view of an embodiment of a support.

Fig. 2 is a schematic cross-sectional view of another embodiment of a support.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, the contents of the present disclosure will be specifically described. The following configuration requirements will be described on the basis of typical embodiments of the present disclosure, but the present disclosure is not limited to such embodiments.

[0030] In the present disclosure, a numerical range expressed using "to" includes numerical values listed before and after "to" as the lower limit and the upper limit.

[0031] Regarding the numerical ranges described stepwise in the present disclosure, the upper limit or lower limit of a numerical range may be replaced with the upper limit or lower limit of another numerical range described stepwise. Furthermore, the upper limit or lower limit of a numerical range described in the present disclosure may be replaced with the values shown in Examples.

[0032] In addition, in the present disclosure, in a case where there is no description regarding whether a group (atomic group) is substituted or unsubstituted, such a group includes both a group having no substituent and a group having a substituent. For example, "alkyl group" includes not only an alkyl group having no substituent (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group).

[0033] In the present disclosure, "(meth)acryl" is a term used as a concept including both the acryl and methacryl, and "(meth)acryloyl" is a term used as a concept including both the acryloyl and methacryloyl.

[0034] In addition, the term "step" in the present disclosure means not only an independent step but also a step that cannot be clearly differentiated from other steps as long as the intended goal of the step is achieved.

[0035] In the present disclosure, "% by mass" has the same definition as "% by weight", and "part by mass" has the same definition as "part by weight".

[0036] In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.

[0037] In addition, in the present disclosure, unless otherwise specified, each of the weight-average molecular weight (Mw) and number-average molecular weight (Mn) is a molecular weight that is detected using a gel permeation chromatography (GPC) analysis device using TSKgel GMHxL, TSKgel G4000HxL, and TSKgel G2000HxL (trade names, manufactured by Tosoh Corporation) as columns, tetrahydrofuran (THF) as a solvent, and a differential refractometer, and expressed in terms of polystyrene as a standard substance.

[0038] In the present disclosure, the term "lithographic printing plate precursor" refers not only to a lithographic printing plate precursor but also to a key plate precursor. In addition, the term "lithographic printing plate" refers not only to a lithographic printing plate prepared by performing operations such as exposure and development as necessary on a lithographic printing plate precursor but also to a key plate. The key plate precursor is not necessarily subjected to the operations such as exposure and development. The key plate refers to a lithographic printing plate precursor to be mounted on a plate cylinder that is not used, in a case where monochromatic or dichromatic printing is carried out on a part of paper during, for example, color newspaper printing.

[0039] In the present disclosure, "excellent printing durability" means that a large number of sheets can be printed using a lithographic printing plate, and printing durability exhibited in a case where a UV ink used as a printing ink will be also described as "UV printing durability" hereinafter.

<<On-press development type lithographic printing plate precursor»

[0040] The on-press development type lithographic printing plate precursor according to the present disclosure (hereinafter, also simply called "lithographic printing plate precursor") has a support, an image-recording layer, and an outermost layer in this order, in which the image-recording layer contains a polymerization initiator, a polymerizable compound, and an infrared absorber, and a decomposition rate of the infrared absorber after storage for 8 hours in an environment at an ozone concentration of 150 ppb is 50% or less.

[0041] In the lithographic printing plate precursor described in JP2012-066577A having an image-recording layer containing a polymerization initiator, a polymerizable compound, and an infrared absorber, the infrared absorber in the image-recording layer is decomposed by ozone in the atmosphere and leads to a problem of discoloration of the lithographic printing plate precursor.

[0042] On the other hand, in the lithographic printing plate precursor according to the present disclosure, the decomposition rate of the infrared absorber in the image-recording layer after storage for 8 hours in an environment at an ozone concentration of 150 ppb is 50% or less. That is, this means that even in a case where the lithographic printing plate precursor according to the present disclosure is stored for 8 hours in an environment at an ozone concentration of 150 ppb, which is a high concentration in the atmosphere, 50% or more of the infrared absorber in the image-recording layer remains without being decomposed.

[0043] Having the above characteristics, the lithographic printing plate precursor according to the present disclosure is inhibited from going through discoloration caused by exposure to ozone.

[0044] The lower the decomposition rate of the infrared absorber, the further the discoloration caused by exposure to ozone is suppressed.

<Decomposition rate of infrared absorber in lithographic printing plate precursor by exposure to ozone>

[0045] In the lithographic printing plate precursor according to the present disclosure, the decomposition rate of the infrared absorber in the image-recording layer after storage for 8 hours in an environment at an ozone concentration of 150 ppb is 50% or less.

[0046] That is, after the storage of the lithographic printing plate precursor according to the present disclosure for 8 hours in an environment at an ozone concentration of 150 ppb, the amount of the decomposed infrared absorber in the image-recording layer is equal to or less than 50% of the amount of the infrared absorber before the storage.

[0047] In other words, this means that the amount of the infrared absorber remaining in the image-recording layer after the storage of the lithographic printing plate precursor according to the present disclosure for 8 hours in an environment at an ozone concentration of 150 ppb is equal to or more than 50% of the amount of the infrared absorber in the image-recording layer before the storage.

[0048] The amount of the infrared absorber is determined by analyzing an extract extracted from the lithographic printing plate precursor by using a solvent by high-performance liquid chromatography (HPLC) and quantifying the infrared absorber.

[0049] The lower the decomposition rate of the infrared absorber in the lithographic printing plate precursor, the further the discoloration caused by exposure to ozone is suppressed.

[0050] The decomposition rate of the infrared absorber is preferably 45% or less, more preferably 40% or less, even more preferably 35% or less, and particularly preferably 30% or less.

[0051] The lower limit of the decomposition rate of the infrared absorber may be 0%. For example, the lower limit may be 1% or more or 5% or more.

[0052] The decomposition rate of the infrared absorber is measured by the following method.

[0053] The lithographic printing plate precursor is cut in a square 3 cm on a side when seen from above from the side of the outermost layer. Two samples having the same shape are obtained in this way.

[0054] One of the two samples is subjected to extraction with 5 mL of acetonitrile in an ultrasonic bath for 30 minutes, and the obtained extract is subjected to HPLC analysis through a 0.20 mm filter. The peak surface area of the infrared absorber is determined by the HPLC analysis, and adopted as the amount (X) of the infrared absorber before exposure to ozone.

[0055] The other sample is put in a 100 mL vial and left to stand on a table.

[0056] The lower tube portion of a Kiriyama funnel bottle (manufactured by Kiriyama glass. CO.) is inserted into the vial containing the sample and fixed. Meanwhile, as a spacer, a stirring blade is placed on the upper opening portion of the Kiriyama funnel bottle (manufactured by Kiriyama glass. CO.). Then, an ozonizer (manufactured by Associa Ozone Co., Ltd., a refreshing ion plus CS-4 ozonizer for business use) is fixed above the stirring blade (at this time, the ozonizer is spaced from the stirring blade by about 150 mm). In this apparatus, the ozone generated from the ozonizer moves the stirring blade, forms an air stream containing ozone, and reaches the sample in the vial through the Kiriyama funnel bottle.

[0057] The sample is exposed to ozone by this apparatus. While the sample is being exposed to ozone, the ozone concentration in the vial is measured and adjusted such that the ozone concentration reaches 150 ppm. The exposure to ozone is performed at 25°C and 50% RH.

[0058] The aforementioned exposure of the sample to ozone is continued for 8 hours. After being continuously exposed to ozone for 8 hours, the sample is subjected to HPLC analysis by the same method as described above to determine the peak surface area of the infrared absorber, and the peak area is adopted as an amount (Y) of the infrared absorber after exposure to ozone.

[0059] The amount (X) of the infrared absorber before exposure to ozone and the amount (Y) of the infrared absorber after exposure to ozone determined as above are plugged into the following Equation 1 to determine a decomposition rate (Z) of the infrared absorber.

[0060] The conditions for performing the HPLC analysis are as follows.

·Device: Alliance 2695, Waters Corporation

·Column: Mightysil RP-18GP 250 mm × ϕ4.6 mm (5 µm), KANTO CHEMICAL CO., INC.

·Column temperature: 40°C

·Eluent: <A> MeOH (containing 0.1% by mass acetic acid + 0.1% by mass triethylamine), <B> H₂O (containing 0.1% by mass acetic acid + 0.1% by mass triethylamine)

·Gradient: <A/B> = 30/70 (0 min) -100/0 (28 min) - 100/0 (40 min) - 30/70 (40.1 min) equilibration

·Flow rate: 1.0 mL/min

·Injection amount: 10 mL

UV detector: PDA 2998, Waters Corporation

[0061] Next, each of the configuration requirements in the lithographic printing plate precursor according to the present disclosure will be specifically described.

<Outermost layer>

[0062] The lithographic printing plate precursor according to the present disclosure has an outermost layer on a side of the image-recording layer opposite to the side of the support.

[0063] From the viewpoint of achieving the aforementioned decomposition rate of the infrared absorber by the exposure to ozone, the outermost layer in the present disclosure is preferably an ozone blocking layer.

[0064] The ozone blocking layer is not particularly limited as long as it has an ozone blocking ability that makes it possible to achieve the aforementioned decomposition rate of the infrared absorber by the exposure to ozone.

[Water-soluble polymer]

[0065] From the viewpoint of development removability (more preferably on-press developability), the outermost layer in the present disclosure preferably contains a water-soluble polymer.

[0066] In the present disclosure, a water-soluble polymer refers to a polymer that dissolves 5 g or more in 100 g of pure water at 125°C and is not precipitated even though a solution of 5 g of the polymer in 100 g of pure water at 125°C is cooled to 25°C.

[0067] Examples of the water-soluble polymer used in the outermost layer include polyvinyl alcohol, modified polyvinyl alcohol, poly(meth)acrylamide, polyethylene glycol, poly(meth)acrylonitrile, polyvinyl pyrrolidone, a copolymer obtained by combining raw material monomers of these polymers, a copolymer obtained by combining raw material monomers of these polymers with other monomers, and the like.

[0068] The aforementioned other monomers are not particularly limited as long as they are monomers that can be copolymerized with the raw material monomers described above. Examples thereof include vinyl acetate, an alkyl (meth)acrylic acid ester such as methyl (meth)acrylate or butyl (meth)acrylate, addition polymerization-type monomers having an acid group, such as a carboxy group, a sulfo group, or a salt of these, and the like.

[0069] As the modified polyvinyl alcohol, acid-modified polyvinyl alcohol having a carboxy group or a sulfo group is preferably used. Specific examples of the modified polyvinyl alcohol include the modified polyvinyl alcohols described in JP2005-250216A and JP2006-259137A.

[0070] As the water-soluble polymer, a polysaccharide can also be used.

[0071] That is, it is preferable that the outermost layer in the present disclosure contain a polysaccharide.

[0072] The polysaccharide to be used in the outermost layer is not limited as long as it has the water solubility described above. From the viewpoint of making it possible to form an outermost layer having a high ozone blocking ability and oxygen permeability, preferred examples of the polysaccharide include a cellulose derivative.

[0073] Examples of the polysaccharide used in the outermost layer also include soybean polysaccharide, modified starch, gum Arabic, dextrin, pullulan, and the like.

[0074] Examples of the cellulose derivative include compounds formed in a case where hydrogen atoms of at least some of the hydroxy groups in cellulose are substituted with at least one group selected from the group consisting of an alkyl group, a hydroxyalkyl group, and a carboxyalkyl group. Examples of the alkyl group, the alkyl group in the hydroxyalkyl group, and the alkyl group in the carboxyalkyl group include a methyl group, an ethyl group, a propyl group, and the like.

[0075] As the cellulose derivative, among the above, compounds are more preferable which are formed in a case where hydrogen atoms of at least some of the hydroxy groups in cellulose are substituted with at least an alkyl group (preferably a methyl group). That is, as the cellulose derivative, a compound is preferable which is formed in a case where at least some of the hydroxy groups in cellulose are substituted with an alkoxy group (preferably a methoxy group).

[0076] Specifically, preferred examples of the cellulose derivative include methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, and the like. Among these, methyl cellulose and hydroxypropyl methyl cellulose are preferable.

[0077] In the cellulose derivative, a degree of substitution of the hydroxy groups with the aforementioned group (preferably a methoxy group substitution degree) is preferably 0.1 to 6.0, more preferably 1 to 4, and even more preferably 1 to 2.

[0078] That is, it is particularly preferable that the outermost layer contain a cellulose derivative having a methoxy group substitution degree of 1 to 2.

[0079] Here, the methoxy group substitution degree means the average number of hydroxyl groups substituted with methoxy groups per glucose ring unit of cellulose. The methoxy group substitution degree can be measured by the Zeisel-GC method described in J. G. Gobler, E. p. Samscl, and G. H. Beaver, Talanta, 9, 474 (1962).

[0080] One kind of water-soluble polymer may be used alone, or two or more kinds of water-soluble polymers may be used in combination.

[0081] The content of the water-soluble polymer contained in the outermost layer with respect to the total mass of the outermost layer is preferably 20% by mass to 99% by mass, more preferably 30% by mass to 98% by mass, and even more preferably 40% by mass to 97% by mass.

[0082] From the viewpoint of suppressing discoloration of the lithographic printing plate precursor caused by exposure to ozone, the content of the polysaccharide (preferably a cellulose derivative) contained in the outermost layer with respect to the total mass of the outermost layer is preferably 30% by mass to 98% by mass, more preferably 35% by mass to 98% by mass, and even more preferably 40% by mass to 97% by mass.

[Hydrophobic polymer]

[0083] The outermost layer may contain a hydrophobic polymer.

[0084] The hydrophobic polymer refers to a polymer that dissolves less than 5 g or does not dissolve in 100 g of pure water at 125°C.

[0085] Examples of the hydrophobic polymer include polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyalkyl (meth)acrylate ester (for example, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polybutyl (meth)acrylate, and the like), a copolymer obtained by combining raw material monomers of these polymers (for example, a styrene-acrylic resin or the like), and the like.

[0086] One kind of hydrophobic polymer may be used alone, or two or more kinds of hydrophobic polymers may be used in combination.

[0087] In a case where the outermost layer contains a hydrophobic polymer, the content of the hydrophobic polymer with respect to the total mass of the outermost layer is preferably 5% by mass to 70% by mass, preferably 7.5% by mass to 50% by mass, and more preferably 10% by mass to 30% by mass.

[Polymer particles]

[0088] The outermost layer may contain polymer particles.

[0089] The polymer particles mean a polymer that is in the form of particles in the outermost layer.

[0090] Even though the polymer contained in the polymer particles corresponds to the aforementioned water-soluble polymer or hydrophobic polymer, in a case where the polymer exists in the outermost layer in the form of particles, the polymer is included in the "polymer particles".

[0091] It is particularly preferable that the outermost layer contain hydrophobic polymer particles.

[0092] Whether or not polymer particles are in the outermost layer can be checked by observing the surface of the outermost layer with a scanning electron microscope (SEM).

[0093] The polymer particles are, for example, preferably in the form of microcapsules, a microgel (that is, crosslinked polymer particles), or the like, and more preferably in the form of a microgel.

[0094] In addition, it is preferable that the polymer particles have a hydrophilic group at least on the surface thereof.

[0095] That is, as the polymer particles to be incorporated into the outermost layer, a microgel having a hydrophilic group on the surface thereof is preferable. Examples of such a microgel include the microgel used in the image-recording layer that will be described later.

[0096] One kind of polymer particles may be used alone, or two or more kinds of polymer particles may be used in combination.

[0097] In a case where the outermost layer contains polymer particles, the content of the polymer particles with respect to the total mass of the outermost layer is preferably 10% by mass to 80% by mass, preferably 15% by mass to 60% by mass, and more preferably 20% by mass to 40% by mass.

[Decomposition-type infrared absorber]

[0098] From the viewpoint of improving visibility of exposed portions, the outermost layer may contain a decomposition-type infrared absorber.

[0099] The decomposition-type infrared absorber may be a compound that absorbs at least a part of light in the infrared wavelength region (that is, a wavelength region of 750 nm to 1 mm, preferably a wavelength region of 750 nm to 1,400 nm) and decomposes. The decomposition-type infrared absorber is preferably a compound having maximum absorption in a wavelength region of 750 nm to 1,400 nm.

[0100] More specifically, the decomposition-type infrared absorber is preferably a compound that decomposes due to the exposure to infrared and generates a compound having maximum absorption wavelength in a wavelength region of 500 nm to 600 nm.

[0101] From the viewpoint of improving visibility of exposed portions, the decomposition-type infrared absorber is preferably a cyanine dye having a group that decomposes by exposure to infrared (specifically, R¹ in Formulas 1-1 to 1-7).

[0102] From the viewpoint of improving visibility of exposed portions, the decomposition-type infrared absorber is more preferably a compound represented by Formula 1-1.

[0103] In Formula 1-1, R¹ represents a group that is represented by any of Formula 2 to Formula 4, R¹¹ to R¹⁸ each independently represent a hydrogen atom, a halogen atom, -R^a, -OR^b, -SR^c, or -NR^dR^e, R^a to R^e each independently represent a hydrocarbon group, A₁, A₂, and a plurality of R¹¹ to R¹⁸ may be linked to each other to form a monocyclic or polycyclic ring, A₁ and A₂ each independently represent an oxygen atom, a sulfur atom, or a nitrogen atom, n₁₁ and n₁₂ each independently represent an integer of 0 to 5, the sum of n₁₁ and n₁₂ is 2 or more, n₁₃ and n₁₄ each independently represent 0 or 1, L represents an oxygen atom, a sulfur atom, or -NR¹⁰-, R¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and Za represents a counterion that neutralizes charge.

[0104] In Formula 2 to Formula 4, R²⁰, R³⁰, R⁴¹, and R⁴² each independently represent an alkyl group or an aryl group, Zb represents a counterion that neutralizes charge, and a wavy line represents a bonding site with a group represented by L in Formula 1-1.

[0105] In a case where the compound represented by Formula 1-1 is exposed to infrared, the R¹-L bond is cleaved, L turns into =O, =S, or =NR¹⁰, and the compound is discolored.

[0106] In Formula 1-1, R¹ represents a group represented by any of Formula 2 to Formula 4.

[0107] Hereinafter, each of the group represented by Formula 2, the group represented by Formula 3, and the group represented by Formula 4 will be described.

[0108] In Formula 2, R²⁰ represents an alkyl group or an aryl group, and the portion of the wavy line represents a bonding site with the group represented by L in Formula 1-1.

[0109] As the alkyl group represented by R²⁰, an alkyl group having 1 to 30 carbon atoms is preferable, an alkyl group having 1 to 15 carbon atoms is more preferable, and an alkyl group having 1 to 10 carbon atoms is even more preferable.

[0110] The alkyl group may be linear or branched, or may have a ring structure.

[0111] The aryl group represented by R²⁰ is preferably an aryl group having 6 to 30 carbon atoms, more preferably an aryl group having 6 to 20 carbon atoms, and even more preferably an aryl group having 6 to 12 carbon atoms.

[0112] From the viewpoint of improving visibility of exposed portions, R²⁰ is preferably an alkyl group.

[0113] From the viewpoint of improving visibility of exposed portions, the alkyl group represented by R²⁰ is preferably a secondary alkyl group or a tertiary alkyl group, and more preferably a tertiary alkyl group.

[0114] Furthermore, from the viewpoint of improving visibility of exposed portions, the alkyl group represented by R²⁰ is preferably an alkyl group having 1 to 8 carbon atoms, more preferably a branched alkyl group having 3 to 10 carbon atoms, even more preferably a branched alkyl group having 3 to 6 carbon atoms, particularly preferably an isopropyl group or a tert-butyl group, and most preferably a tert-butyl group.

[0115] The alkyl group represented by R²⁰ may be a substituted alkyl group substituted with a halogen atom (for example, a chloro group) or the like.

[0116] Specific examples of the group represented by Formula 2 will be shown below. However, the present disclosure is not limited thereto. In the following structural formulas, ● represents a bonding site with the group represented by L in Formula 1-1.

[0117] In Formula 3, R³⁰ represents an alkyl group or an aryl group, and the portion of the wavy line represents a bonding site with the group represented by L in Formula 1-1.

[0118] The alkyl group and aryl group represented by R³⁰ are the same as the alkyl group and aryl group represented by R²⁰ in Formula 2, and preferred aspects thereof are also the same.

[0119] From the viewpoint of improving visibility of exposed portions, the alkyl group represented by R³⁰ is preferably a secondary alkyl group or a tertiary alkyl group, and preferably a tertiary alkyl group.

[0120] Furthermore, from the viewpoint of improving visibility of exposed portions, the alkyl group represented by R³⁰ is preferably an alkyl group having 1 to 8 carbon atoms, more preferably a branched alkyl group having 3 to 10 carbon atoms, even more preferably a branched alkyl group having 3 to 6 carbon atoms, particularly preferably an isopropyl group or a tert-butyl group, and most preferably a tert-butyl group.

[0121] In addition, from the viewpoint of improving visibility of exposed portions, the alkyl group represented by R³⁰ is preferably a substituted alkyl group, preferably a substituted alkyl group, more preferably a fluoro-substituted alkyl group, even more preferably a perfluoroalkyl group, and particularly preferably a trifluoromethyl group.

[0122] From the viewpoint of improving visibility of exposed portions, the aryl group represented by R³⁰ is preferably a substituted aryl group. Examples of the substituent include an alkyl group (preferably an alkyl group having 1 to 4 carbon atoms), an alkoxy group (preferably an alkoxy group having 1 to 4 carbon atoms), and the like.

[0123] Specific examples of the group represented by Formula 3 will be shown below. However, the present disclosure is not limited thereto. In the following structural formulas, ● represents a bonding site with the group represented by L in Formula 1-1.

[0124] In Formula 4, R⁴¹ and R⁴² each independently represent an alkyl group or an aryl group, Zb represents a counterion that neutralizes charge, and the portion of the wavy line represents a bonding site with the group represented by L in Formula 1-1.

[0125] The alkyl group and aryl group represented by R⁴¹ or R⁴² are the same as the alkyl group and aryl group represented by R²⁰ in Formula 2, and preferred aspects thereof are also the same.

[0126] From the viewpoint of improving visibility of exposed portions, R⁴¹ is preferably an alkyl group.

[0127] From the viewpoint of improving visibility of exposed portions, R⁴² is preferably an alkyl group.

[0128] From the viewpoint of improving visibility of exposed portions, the alkyl group represented by R⁴¹ is preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group.

[0129] From the viewpoint of improving visibility of exposed portions, the alkyl group represented by R⁴² is preferably a secondary alkyl group or a tertiary alkyl group, and preferably a tertiary alkyl group.

[0130] Furthermore, from the viewpoint of improving visibility of exposed portions, the alkyl group represented by R⁴² is preferably an alkyl group having 1 to 8 carbon atoms, more preferably a branched alkyl group having 3 to 10 carbon atoms, even more preferably a branched alkyl group having 3 to 6 carbon atoms, particularly preferably an isopropyl group or a tert-butyl group, and most preferably a tert-butyl group.

[0131] Zb in Formula 4 may be a counterion that neutralizes charge, and may be included in Za in Formula 1-1 in the entirety of the compound.

[0132] Zb is preferably a sulfonate ion, a carboxylate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, a p-toluenesulfonate ion, or a perchlorate ion, and more preferably a tetrafluoroborate ion.

[0133] Specific examples of the group represented by Formula 4 will be shown below. However, the present disclosure is not limited thereto. In the following structural formulas, ● represents a bonding site with the group represented by L in Formula 1-1.

[0134] L in Formula 1-1 is preferably an oxygen atom or -NR¹⁰-, and particularly preferably an oxygen atom.

[0135] Furthermore, R¹⁰ in -NR¹⁰- is preferably an alkyl group. The alkyl group represented by R¹⁰ is preferably an alkyl group having 1 to 10 carbon atoms. The alkyl group represented by R¹⁰ may be linear or branched, or may have a ring structure.

[0136] Among the alkyl groups represented by R¹⁰, a methyl group, a tert-butyl group, or a cyclohexyl group is preferable.

[0137] In a case where R¹⁰ in -NR¹⁰- represents an aryl group, the aryl group is preferably an aryl group having 6 to 30 carbon atoms, more preferably an aryl group having 6 to 20 carbon atoms, and even more preferably an aryl group having 6 to 12 carbon atoms. These aryl groups may have a substituent.

[0138] In Formula 1-1, R¹¹ to R¹⁸ preferably each independently represent a hydrogen atom, -R^a, -OR^b, -SR^c, or -NR^dR^e.

[0139] The hydrocarbon group represented by R^a to R^e is preferably a hydrocarbon group having 1 to 30 carbon atoms, more preferably a hydrocarbon group having 1 to 15 carbon atoms, and even more preferably a hydrocarbon group having 1 to 10 carbon atoms. The hydrocarbon group represented by R^a to R^e may be linear or branched, or may have a ring structure.

[0140] As the hydrocarbon group represented by R^a to R^e, an alkyl group is particularly preferable.

[0141] The aforementioned alkyl group is preferably an alkyl group having 1 to 30 carbon atoms, more preferably an alkyl group having 1 to 15 carbon atoms, and even more preferably an alkyl group having 1 to 10 carbon atoms.

[0142] The alkyl group may be linear or branched, or may have a ring structure.

[0143] Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a hexadecyl group, an octadecyl group, an eicosyl group, an isopropyl group, an isobutyl group, an s-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a 1-methylbutyl group, an isohexyl group, a 2-ethylhexyl group, a 2-methylhexyl group, a cyclohexyl group, a cyclopentyl group, and a 2-norbornyl group.

[0144] Among these alkyl groups, a methyl group, an ethyl group, a propyl group, or a butyl group is preferable.

[0145] The above alkyl group may have a substituent.

[0146] Examples of the substituent include an alkoxy group, an aryloxy group, an amino group, an alkylthio group, an arylthio group, a halogen atom, a carboxy group, a carboxylate group, a sulfo group, a sulfonate group, an alkyloxycarbonyl group, an aryloxycarbonyl group, groups obtained by combining these, and the like.

[0147] R¹¹ to R¹⁴ in Formula 1-1 preferably each independently represent a hydrogen atom or -R^a (that is, a hydrocarbon group), more preferably each independently represent a hydrogen atom or an alkyl group, and even more preferably each independently represent a hydrogen atom except in the cases described below.

[0148] Particularly, each of R¹¹ and R¹³ bonded to the carbon atom that is bonded to the carbon atom to which L is bonded is preferably an alkyl group. It is more preferable that R¹¹ and R¹³ be linked to each other to form a ring. The ring to be formed in this way may be a monocyclic or polycyclic ring. Specifically, examples of the ring to be formed include a monocyclic ring such as a cyclopentene ring, a cyclopentadiene ring, a cyclohexene ring, or a cyclohexadiene ring, and a polycyclic ring such as an indene ring or an indole ring.

[0149] Furthermore, it is preferable that R¹² bonded to the carbon atom to which A₁⁺ is bonded be linked to R¹⁵ or R¹⁶ (preferably R¹⁶) to form a ring, and R¹⁴ bonded to the carbon atom to which A₂ is bonded be linked to R¹⁷ or R¹⁸ (preferably R¹⁸) to form a ring.

[0150] In Formula 1-1, n₁₃ is preferably 1, and R¹⁶ is preferably -R^a (that is, a hydrocarbon group).

[0151] Furthermore, it is preferable that R¹⁶ be linked to R¹² bonded to the carbon atom to which A₁⁺ is bonded, so as to form a ring. As the ring to be formed, an indolium ring, a pyrylium ring, a thiopyrylium ring, a benzoxazoline ring, or a benzimidazoline ring is preferable, and an indolium ring is more preferable from the viewpoint of improving visibility of exposed portions. These rings may further have a substituent.

[0152] In Formula 1-1, n₁₄ is preferably 1, and R¹⁸ is preferably -R^a (that is, a hydrocarbon group).

[0153] Furthermore, it is preferable that R¹⁸ be linked to R¹⁴ bonded to the carbon atom to which A₂ is bonded, so as to form a ring. As the ring to be formed, an indole ring, a pyran ring, a thiopyran ring, a benzoxazole ring, or a benzimidazole ring is preferable, and an indole ring is more preferable from the viewpoint of improving visibility of exposed portions. These rings may further have a substituent.

[0154] It is preferable that R¹⁶ and R¹⁸ in Formula 1-1 be the same group. In a case where R¹⁶ and R¹⁸ each form a ring, it is preferable that the formed rings have the same structure except for A₁⁺ and A₂.

[0155] It is preferable that R¹⁵ and R¹⁷ in Formula 1-1 be the same group. Furthermore, R¹⁵ and R¹⁷ are preferably -R^a (that is, a hydrocarbon group), more preferably an alkyl group, and even more preferably a substituted alkyl group.

[0156] From the viewpoint of improving water solubility, R¹⁵ and R¹⁷ in the compound represented by Formula 1-1 are preferably a substituted alkyl group.

[0157] Examples of the substituted alkyl group represented by R¹⁵ or R¹⁷ include a group represented by any of Formula (a1) to Formula (a4).



        -R^W2-CO₂M     (a2)

        -R^W3-PO₃M₂     (a3)

        -R^W4-SO₃M     (a4)

[0158] In Formula (a1) to Formula (a4), R^W0 represents an alkylene group having 2 to 6 carbon atoms, W represents a single bond or an oxygen atom, and n_W1 represents an integer of 1 to 45, R^W1 represents an alkyl group having 1 to 12 carbon atoms or -C(=O)-R^W5, R^W5 represents an alkyl group having 1 to 12 carbon atoms, R^W2 to R^W4 each independently represent a single bond or an alkylene group having 1 to 12 carbon atoms, and M represents a hydrogen atom, a sodium atom, a potassium atom, or an onium group.

[0159] Specific examples of the alkylene group represented by R^W0 in Formula (a1) include an ethylene group, a n-propylene group, an isopropylene group, a n-butylene group, an isobutylene group, a n-pentylene group, an isopentylene group, a n-hexyl group, an isohexyl group, and the like. Among these, an ethylene group, a n-propylene group, an isopropylene group, or a n-butylene group is preferable, and a n-propylene group is particularly preferable.
n_W1 is preferably 1 to 10, more preferably 1 to 5, and particularly preferably 1 to 3.

[0160] Specific examples of the alkyl group represented by R^W1 include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, a neopentyl group, a n-hexyl group, a n-octyl group, a n-dodecyl group, and the like. Among these, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, or a tert-butyl group is preferable, a methyl group or an ethyl group is more preferable, and a methyl group is particularly preferable.

[0161] The alkyl group represented by R^W5 is the same as the alkyl group represented by R^W1. Preferred aspects of the alkyl group represented by R^W5 are the same as preferred aspects of the alkyl group represented by R^W1.

[0162] Specific examples of the group represented by Formula (a1) will be shown below. However, the present disclosure is not limited thereto. In the following structural formulas, Me represents a methyl group, Et represents an ethyl group, and * represents a bonding site.

[0163] Specific examples of the alkylene group represented by R^W2 to R^W4 in Formula (a2) to Formula (a4) include a methylene group, an ethylene group, a n-propylene group, an isopropylene group, a n-butylene group, an isobutylene group, a n-pentylene group, an isopentylene group, a n-hexyl group, an isohexyl group, a n-octylene group, a n-dodecylene group, and the like. Among these, an ethylene group, a n-propylene group, an isopropylene group, or a n-butylene group is preferable, and an ethylene group or a n-propylene group is particularly preferable.

[0164] In Formula (a3), two Ms may be the same as or different from each other.

[0165] Examples of the onium group represented by M in Formula (a2) to Formula (a4) include an ammonium group, an iodonium group, a phosphonium group, a sulfonium group, and the like.

[0166] All of CO₂M in Formula (a2), PO₃M₂ in Formula (a2), and SO₃M in Formula (a4) may have an anion structure from which M is dissociated. The countercation of the anion structure may be A₁⁺ or a cation that can be contained in R¹-L in Formula 1-1.

[0167] Among the groups represented by Formula (a1) to Formula (a4), the group represented by Formula (a1), Formula (a2), or Formula (a4) is preferable.
n₁₁ and n₁₂ in Formula 1-1 are preferably the same as each other, and preferably both represent an integer of 1 to 5, more preferably both represent an integer of 1 to 3, even more preferably both represent 1 or 2, and particularly preferably both represent 2.

[0168] A₁ and A₂ in Formula 1-1 each independently represent an oxygen atom, a sulfur atom, or a nitrogen atom. Among these, a nitrogen atom is preferable.

[0169] A₁ and A₂ in Formula 1-1 are preferably the same atoms.

[0170] Za in Formula 1-1 represents a counterion that neutralizes charge.

[0171] In a case where all of R¹¹ to R¹⁸ and R¹-L are groups having a neutral charge, Za is a monovalent counteranion. Here, R¹¹ to R¹⁸ and R¹-L may have an anion structure or a cation structure. For example, in a case where two or more among R¹¹ to R¹⁸ and R¹-L have an anion structure, Za can also be a countercation.

[0172] In a case where the cyanine dye represented by Formula 1-1 has such a structure that the overall charge of the compound is neutral except for Za, Za is unnecessary.

[0173] In a case where Za is a counteranion, examples thereof include a sulfonate ion, a carboxylate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, a p-toluenesulfonate ion, a perchlorate ion, and the like. Among these, a tetrafluoroborate ion is preferable.

[0174] In a case where Za is a countercation, examples thereof include an alkali metal ion, an alkaline earth metal ion, an ammonium ion, a pyridinium ion, a sulfonium ion, and the like. Among these, a sodium ion, a potassium ion, an ammonium ion, a pyridinium ion, or a sulfonium ion is preferable, and a sodium ion, a potassium ion, or an ammonium ion is more preferable.

[0175] From the viewpoint of improving visibility of exposed portions, the decomposition-type infrared absorber is more preferably a compound represented by Formula 1-2 (that is, a cyanine dye).

[0176] In Formula 1-2, R¹ represents a group that is represented by any of Formula 2 to Formula 4, R¹⁹ to R²² each independently represent a hydrogen atom, a halogen atom, -R^a, -OR^b, -CN, -SR^c, or -NR^dR^e, R²³ and R²⁴ each independently represent a hydrogen atom or -R^a, R^a to R^e each independently represent a hydrocarbon group, R¹⁹ and R²⁰, R²¹ and R²², or R²³ and R²⁴ may be linked to each other to form a monocyclic or polycyclic ring, L represents an oxygen atom, a sulfur atom, or -NR¹⁰-, R¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, R^d1 to R^d4 and W¹ and W² each independently represent an alkyl group which may have a substituent, and Za represents a counterion that neutralizes charge.

[0177] R¹ in Formula 1-2 has the same definition as R¹ in Formula 1-1, and preferred aspects thereof are also the same.

[0178] In Formula 1-2, R¹⁹ to R²² preferably each independently represent a hydrogen atom, a halogen atom, -R^a, -OR^b, or -CN.

[0179] More specifically, R¹⁹ and R²¹ are preferably a hydrogen atom or -R^a.

[0180] Furthermore, R²⁰ and R²² are preferably a hydrogen atom, -R^a, -OR^b, or -CN.

[0181] -R^a represented by R¹⁹ to R²² is preferably an alkyl group or an alkenyl group.

[0182] In a case where all of R¹⁹ to R²² are -R^a, it is preferable that R¹⁹ and R²⁰ and R²¹ and R²² be linked to each other to form a monocyclic or polycyclic ring.

[0183] Examples of the ring formed of R¹⁹ and R²⁰ or R²¹ and R²² linked to each other include a benzene ring, a cyclohexane ring, a cyclopentane ring, and the like.

[0184] R²³ and R²⁴ in Formula 1-2 are preferably linked to each other to form a monocyclic or polycyclic ring.

[0185] The ring formed of R²³ and R²⁴ linked to each other may be a monocyclic or polycyclic ring. Specifically, examples of the ring to be formed include a monocyclic ring such as a cyclopentene ring, a cyclopentadiene ring, a cyclohexene ring, or a cyclohexadiene ring, and a polycyclic ring such as an indene ring or an indole ring.

[0186] R^d1 to R¹⁴ in Formula 1-2 are preferably an unsubstituted alkyl group. Furthermore, all of R^d1 to R^d4 are preferably the same group.

[0187] Examples of the unsubstituted alkyl group include a methyl group, an ethyl group, and the like. Among these, a methyl group is preferable.

[0188] From the viewpoint of improving water solubility of the compound represented by Formula 1-2, W¹ and W² in Formula 1-2 preferably each represent a substituted alkyl group.

[0189] Examples of the substituted alkyl group represented by W¹ and W² include a group represented by any of Formula (a1) to Formula (a4) in Formula 1-1, and preferred aspects thereof are also the same.

[0190] Za represents a counterion that neutralizes charge in the molecule.

[0191] In a case where all of R¹⁹ to R²², R²³ and R²⁴, R^d1 to R^d4, W¹ and W², and R¹-L are groups having a neutral charge, Za is a monovalent counteranion. Here, R¹⁹ to R²², R²³ and R²⁴, R^d1 to R^d4, W¹ and W², and R¹-L may have an anion structure or a cation structure. For example, in a case where two or more among R¹⁹ to R²², R²³ and R²⁴, R^d1 to R^d4, W¹ and W², and R¹-L have an anion structure, Za can be a countercation.

[0192] In a case where the compound represented by Formula 1-2 has such a structure that the overall charge of the compound is neutral except for Za, Za is unnecessary.

[0193] Examples of the case where Za is a counteranion are the same as such examples of Za in Formula 1-1, and preferred aspects thereof are also the same. Furthermore, examples of the case where Za is a countercation are the same as such examples of Za in Formula 1-1, and preferred aspects thereof are also the same.

[0194] From the viewpoint of improving visibility of exposed portions, the cyanine dye as a decomposition-type infrared absorber is even more preferably a compound represented by any of Formula 1-3 to Formula 1-7.

[0195] Particularly, from the viewpoint of improving visibility of exposed portions, the cyanine dye is preferably a compound represented by any of Formula 1-3, Formula 1-5, and Formula 1-6.

[0196] In Formula 1-3 to Formula 1-7, R¹ represents a group that is represented by any of Formula 2 to Formula 4, R¹⁹ to R²² each independently represent a hydrogen atom, a halogen atom, -R^a, -OR^b, -CN, -SR^c, or -NR^dR^e, R²⁵ and R²⁶ each independently represent a hydrogen atom, a halogen atom, or -R^a, R^a to R^e each independently represent a hydrocarbon group, R¹⁹ and R²⁰, R²¹ and R²², or R²⁵ and R²⁶ may be linked to each other to form a monocyclic or polycyclic ring, L represents an oxygen atom, a sulfur atom, or -NR¹⁰-, R¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, R^d1 to R^d4, W¹ and W² each independently represent an alkyl group which may have a substituent, and Za represents a counterion that neutralizes charge.

[0197] R¹, R¹⁹ to R²², R^d1 to R^d4, W¹ and W², and L in Formula 1-3 to Formula 1-7 have the same definitions as R¹, R¹⁹ to R²², R^d1 to R^d4, W¹ and W², and L in Formula 1-2, and preferred aspects thereof are also the same.

[0198] It is preferable that R²⁵ and R²⁶ in Formula 1-7 each independently represent a hydrogen atom or a methyl group.

[0199] Specific examples of the cyanine dye as a decomposition-type infrared absorber will be shown below. However, the present disclosure is not limited thereto.

[0200] Furthermore, as the cyanine dye which is a decomposition-type infrared absorber, the infrared absorbing compounds described in WO2019/219560A can be suitably used.

[0201] One kind of decomposition-type infrared absorber may be used alone, or two or more kinds of decomposition-type infrared absorbers may be used in combination.

[0202] In a case where the outermost layer contains a decomposition-type infrared absorber, the content of the decomposition-type infrared absorber with respect to the total mass of the outermost layer is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, and even more preferably 10% by mass to 30% by mass.

[Other components]

[0203] The outermost layer in the present disclosure may contain known additives, such as an inorganic lamellar compound and a surfactant, in addition to the components described above.

[Method of forming outermost layer]

[0204] The method of forming the outermost layer is not particularly limited. From the viewpoint of improving ozone blocking properties, it is preferable to use the following method.

[0205] That is, it is a method of coating an image-recording layer formed on a support with a coating liquid having a concentration of solid contents of 5% by mass to 30% by mass, and drying the obtained coating film under drying condition 70°C to 200°C and 5 seconds to 30 seconds to form an outermost layer.

[0206] Using this method makes it easy to form an outermost layer in which the decomposition rate of the infrared absorber by exposure to ozone is 50% or less.

[0207] In forming the outermost layer, the concentration of solid contents of the coating liquid is preferably 7.5% by mass to 25% by mass, and more preferably 10% by mass to 20% by mass.

[0208] Furthermore, in forming the outermost layer, the drying conditions of the coating film are preferably 80°C to 170°C and 7.5 seconds to 25 seconds, and more preferably 90°C to 150°C and 10 seconds to 20 seconds.

[0209] The coating amount of the outermost layer (solid content) is preferably 0.01 g/m² to 10 g/m², more preferably 0.02 g/m² to 3 g/m², and particularly preferably 0.1 g/m² to 2 g/m².

[0210] The film thickness of the outermost layer is preferably 0.005 µm to 2 µm, preferably 0.05 µm to 5 µm, and more preferably 0.1 µm to 3 µm.

[0211] In the present disclosure, the film thickness of each layer in the lithographic printing plate precursor is an average film thickness determined by preparing a slice by cutting the lithographic printing plate precursor in a direction perpendicular to the surface of the precursor, and observing the cross section of the slice with a scanning electron microscope (SEM) in a range having a width of 50 µm in the horizontal direction with respect to the surface of the lithographic printing plate.

[Oxygen permeability]

[0212] The outermost layer may have oxygen permeability.

[0213] "The outermost layer has oxygen permeability" means that the ratio of halftone dot area rate determined by the method which will be described later is more than 0.9.

[0214] In a case where the outermost layer has oxygen permeability, that is, in a case where the halftone dot area rate is more than 0.9, it is possible to inhibit streak-like unevenness (so-called swath unevenness) observed due to thickening of halftone dot images in the scanning direction of exposure from occurring in a printed matter. This streak-like unevenness is likely to be affected by the type of platesetter. Therefore, in a case where the outermost layer has oxygen permeability, the outermost layer is applicable to a platesetter being likely to cause streak-like unevenness, which can provide a wider range of choices in selecting the platesetter.

[0215] From the viewpoint of suppressing streak-like unevenness, the ratio of halftone dot area rate is preferably 0.92 or more, more preferably 0.94 or more, even more preferably 0.96 or more, and particularly preferably 0.98 or more.

[0216] For example, the upper limit of the ratio of halftone dot area rate is 1.00.

[0217] Hereinafter, the method of determining the halftone dot area rate and the ratio of halftone dot area rate will be described.

[0218] First, two lithographic printing plate precursors are prepared which are the same as each other except for the presence or absence of the outermost layer (that is, a lithographic printing plate precursor with an outermost layer and a lithographic printing plate precursor without an outermost layer are prepared).

[0219] By using the two lithographic printing plate precursors, the halftone dot area rate is determined by the following method, and from the determined halftone dot area rate, the ratio of halftone dot area rate which is an indicator of oxygen permeability is calculated.

[0220] By using Luxel PLATESETTER T-9800II manufactured by FUJIFILM Corporation that is equipped with an infrared semiconductor laser, each of the prepared two lithographic printing plate precursors is exposed under the conditions of outer drum rotation speed of 220 rpm (revolutions per minute), a laser output of 99.7, 99.6, and 99.5%, resolution of 2,400 dpi (dot per inch, 1 inch = 2.54 cm), and an extinction ratio of 1:14, 1:17, and 1:19. At this time, the exposure image includes a solid image and a 50% halftone dot chart of a 20 µm dot FM screen.

[0221] The obtained lithographic printing plate precursor having undergone exposure is mounted on a plate cylinder of a printer LITHRONE26 manufactured by KOMORI Corporation, without being subjected to a development treatment. The speed of a water supply roller is reduced by 5% for a plate cylinder, and then by using dampening water containing Ecolity-2 (manufactured by FUJIFILM Corporation)/tap water = 2/98 (volume ratio)) and SPACE COLOR FUSION G black ink (manufactured by DIC Graphics Corporation), on-press development is performed by supplying the dampening water and ink according to the standard automatic printing start method of LITHRONE26. Thereafter, printing is performed on 1,000 sheets of TOKUBISHI art paper (manufactured by MITSUBISHI PAPER MILLS LIMITED., ream weight: 76.5 kg) at a printing rate of 10,000 sheets/hour.

[0222] The density of a solid image area (that is, solid density) in the 1,000th printed matter is denoted by DS, the density of a halftone dot area in the same printed matter is denoted by DT, and the halftone dot area rate is calculated by Equation M: Murray-Davies equation. Then, the obtained halftone dot area rate is plugged into Equation OT to calculate the ratio of halftone dot area rate.

[0223] The higher the ratio of halftone dot area rate, the better the oxygen permeability.

<Image-recording layer>

[0224] The lithographic printing plate precursor according to the present disclosure has an image-recording layer between the outermost layer and the support described above.

[0225] The image-recording layer in the present disclosure contains a polymerization initiator, a polymerizable compound, and an infrared absorber.

[0226] The image-recording layer in the present disclosure is a negative tone image-recording layer, and is preferably a water-soluble or water-dispersible negative tone image-recording layer.

[0227] In the image-recording layer of the present disclosure, from the viewpoint of on-press developability, a non-exposed portion of the image-recording layer is preferably removable by at least any of dampening water or printing ink.

[0228] Hereinafter, each of the components to be incorporated into the image-recording layer will be specifically described.

[Polymerization initiator]

[0229] The image-recording layer in the present disclosure contains a polymerization initiator.

[0230] The polymerization initiator preferably includes an electron-accepting polymerization initiator, and more preferably includes an electron-accepting polymerization initiator and an electron-donating polymerization initiator.

[Electron-accepting polymerization initiator]

[0231] It is preferable that the image-recording layer contain an electron-accepting polymerization initiator as a polymerization initiator.

[0232] The electron-accepting polymerization initiator is a compound which accepts an electron by intermolecular electron migration in a case where electrons of an infrared absorber are excited by exposure to infrared, and generates a polymerization initiation species such as radicals.

[0233] The electron-accepting polymerization initiator is a compound that generates a polymerization initiation species such as a radical or a cation by either or both of light energy and heat energy, and can be appropriately selected from known thermal polymerization initiators, compounds having a bond that requires low bond dissociation energy, photopolymerization initiators, and the like.

[0234] The electron-accepting polymerization initiator is preferably a radical polymerization initiator and more preferably an onium salt compound.

[0235] In addition, as the electron-accepting polymerization initiator, an infrared-ray-sensitive polymerization initiator is preferable.

[0236] Among the above electron-accepting polymerization initiators, from the viewpoint of curing properties of the image-recording layer, an oxime ester compound and an onium salt compound are preferable. Particularly, from the viewpoint of printing durability, an iodonium salt compound, a sulfonium salt compound, or an azinium salt compound is preferable, an iodonium salt compound or a sulfonium salt compound is more preferable, and an iodonium salt compound is particularly preferable.

[0237] Specific examples of these compounds will be shown below, but the present disclosure is not limited thereto.

[0238] As the iodonium salt compound, for example, a diaryliodonium salt compound is preferable. Particularly, a diphenyl iodonium salt compound substituted with an electron-donating group such as an alkyl group or an alkoxyl group is more preferable. Furthermore, an asymmetric diphenyl iodonium salt compound is preferable. Specific examples thereof include diphenyliodonium=hexafluorophosphate, 4-methoxyphenyl-4-(2-methylpropyl)phenyliodonium=hexafluorophosphate, 4-(2-methylpropyl)phenyl-p-tolyliodonium=hexafluorophosphate, 4-hexyloxyphenyl-2,4,6-trimethoxyphenyl iodonium=hexafluorophosphate, 4-hexyloxyphenyl-2,4-diethoxyphenyl iodonium=tetrafluoroborate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyl iodonium=1-perfluorobutane sulfonate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium=hexafluorophosphate, and bis(4-t-butylphenyl)iodonium=hexafluorophosphate.

[0239] Examples of counteranions of the iodonium salt compound and the sulfonium salt compound include a sulfonate anion, a carboxylate anion, a tetrafluoroborate anion, a hexafluorophosphate anion, a p-toluene sulfonate anion, a tosylate anion, a sulfonamide anion, and a sulfonimide anion. Among the above, a sulfonamide anion or a sulfonimide anion is preferable, and a sulfonimide anion is more preferable.

[0240] As the sulfonamide anion, an aryl sulfonamide anion is preferable.

[0241] As the sulfonimide anion, a bisaryl sulfonimide anion is preferable.

[0242] Specific examples of the sulfonamide anion and the sulfonimide anion include the compounds described in paragraph "0034" of WO2019/013268A.

[0243] From the viewpoint of developability and UV printing durability of the lithographic printing plate to be obtained, the aforementioned electron-accepting polymerization initiator is preferably a compound represented by any of Formula (II) and Formula (III), and particularly preferably a compound represented by Formula (II).

[0244] In Formulas (II) and (III), X represents a halogen atom, and R³, R⁴, and R⁵ each independently represent a monovalent hydrocarbon group having 1 to 20 carbon atoms.

[0245] In Formula (II), X preferably represents a halogen atom, and R³ preferably represents an aryl group.

[0246] Specific examples of X in Formulas (II) and (III) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, a chlorine atom or a bromine atom is preferable because these have excellent sensitivity, and a bromine atom is particularly preferable.

[0247] R³, R⁴, and R⁵ in Formulas (II) and (III) preferably each independently represent an aryl group. Particularly, from the viewpoint of excellent balance between sensitivity and storage stability, R³, R⁴, and R⁵ preferably each independently represent an aryl group substituted with an amide group.

[0248] Among the above electron-accepting polymerization initiators, a compound represented by Formula (IV) is particularly preferable.

[0249] In Formula (IV), R⁴ and R⁵ each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms, p and q each independently represent an integer of 1 to 5. Here, p + q = 2 to 6.

[0250] Specific examples of the electron-accepting polymerization initiator represented by any of Formula (II) to Formula (IV) include compounds represented by the following formulas. However, the present disclosure is not limited thereto.

[0251] From the viewpoint of improving sensitivity and suppressing the occurrence of plate missing, the lowest unoccupied molecular orbital (LUMO) of the electron-accepting polymerization initiator is preferably -3.00 eV or less, and more preferably -3.02 eV or less.

[0252] The lower limit of the lowest unoccupied molecular orbital (LUMO) of the electron-accepting polymerization initiator is preferably -3.80 eV or more, and more preferably -3.50 eV or more.

[0253] In the present disclosure, the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) which will be described later are calculated by the following methods.

[0254] First, in a case where a compound as a calculation object has counterions that are not a main structure forming HOMO or LUMO, the counterions may be ignored.

[0255] The structural optimization is carried out by DFT (B3LYP/6-31G(d)) using quantum chemical calculation software Gaussian 09.

[0256] The molecular orbital (MO) energy is calculated by DFT (B3LYP/6-31+G(d,p)/CPCM (solvent = methanol)) using the structure obtained by the structural optimization.

[0257] By the following formula, the MO energy Ebare (unit: hartree) obtained by the above MO energy calculation is converted into Escaled (unit: eV) used as the values of HOMO and LUMO in the present disclosure.

[0258] 27.2114 is simply a coefficient for converting hartree into eV, and 0.823168 and -1.07634 are adjustment coefficients. These are determined such that the calculated values of HOMO and LUMO of the compound as a calculation object match the measured values.

[0259] One kind of electron-accepting polymerization initiator may be used alone, or two or more kinds of electron-accepting polymerization initiators may be used in combination.

[0260] The content of the electron-accepting polymerization initiator with respect to the total mass of the image-recording layer is preferably 0.1% by mass to 50% by mass, more preferably 0.5% by mass to 30% by mass, and particularly preferably 0.8% by mass to 20% by mass.

[Electron-donating polymerization initiator (polymerization aid)]

[0261] It is preferable that the image-recording layer in the present disclosure contain an electron-donating polymerization initiator (also called "polymerization aid") as a polymerization initiator.

[0262] The electron-donating polymerization initiator is a compound which donates one electron by intermolecular electron migration to an orbit of an infrared absorber that has lost one electron in a case where electrons of the infrared absorber are excited or perform intramolecular migration by exposure to infrared, and thus generates polymerization initiation species such as radicals.

[0263] The electron-donating polymerization initiator is preferably an electron-donating radical polymerization initiator.

[0264] From the viewpoint of printing durability, the image-recording layer preferably contains a borate compound as an electron-donating polymerization initiator.

[0265] From the viewpoint of printing durability, the borate compound is preferably a tetraaryl borate compound or a monoalkyl triaryl borate compound, and more preferably a tetraaryl borate compound.

[0266] A countercation that the borate compound has is not particularly limited, but is preferably an alkali metal ion or a tetraalkyl ammonium ion and more preferably a sodium ion, a potassium ion, or a tetrabutylammonium ion.

[0267] The countercation that the borate compound has may also be a cationic polymethine colorant described in the present disclosure as an infrared absorber. For example, the aforementioned borate compound may be used as the countercation of the cyanine dye.

[0268] Specifically, preferred examples of the borate compound include sodium tetraphenyl borate.

[0269] Specifically, as the electron-donating polymerization initiator, for example, B-1 to B-9 are preferable. It goes without saying that the present disclosure is not limited thereto. In the following chemical formulas, Ph represents a phenyl group, and Bu represents a n-butyl group.

[0270] From the viewpoint of improving sensitivity and making it difficult for plate missing to occur, the highest occupied molecular orbital (HOMO) of the electron-donating polymerization initiator is preferably -6.00 eV or more, more preferably -5.95 eV or more, and even more preferably -5.93 eV or more.

[0271] The upper limit of the highest occupied molecular orbital (HOMO) of the electron-donating polymerization initiator is preferably -5.00 eV or less, and more preferably -5.40 eV or less.

[0272] Only one kind of electron-donating polymerization initiator may be used alone, or more kinds of electron-donating polymerization initiators may be used in combination.

[0273] From the viewpoint of sensitivity and printing durability, the content of the electron-donating polymerization initiator with respect to the total mass of the image-recording layer is preferably 0.01% by mass to 30% by mass, more preferably 0.05% by mass to 25% by mass, and even more preferably 0.1% by mass to 20% by mass.

[0274] The polymerization initiator may be a compound in the form of conjugate salt of an electron-donating polymerization initiator and an electron-accepting polymerization initiator.

[0275] For example, the polymerization initiator is preferably a compound in the form of a conjugate salt of an anion in an electron-donating polymerization initiator and a cation in an electron-accepting polymerization initiator, and more preferably a compound in the form of a salt composed of a cation having the structure of an electron-accepting polymerization initiator and an anion having the structure of an electron-donating polymerization initiator, as the electron-accepting polymerization initiator and the electron-donating polymerization initiator described above. Specifically, the polymerization initiator is preferably a compound in the form of a conjugate salt of an onium cation and a borate anion, more preferably a compound in the form of a conjugate salt of an iodonium cation or a sulfonium cation and a borate anion, and particularly preferably a compound in the form of a conjugate salt of a diaryliodonium cation or a triarylsulfonium cation and a tetraarylborate anion.

[0276] Preferred aspects of the anion in the electron-donating polymerization initiator and the cation in the electron-accepting polymerization initiator are the same as the preferred aspects of the anion in the aforementioned electron-donating polymerization initiator and the cation in the aforementioned electron-accepting polymerization initiator.

[0277] In a case where the image-recording layer contains an anion as an electron-donating polymerization initiator and a cation as an electron-accepting polymerization initiator (that is, in a case where the image-recording layer contains a compound in the form of a conjugate salt described above), the image-recording layer is regarded as containing an electron-accepting polymerization initiator and an electron-donating polymerization initiator.

[0278] The compound in the form of a conjugate salt of an electron-donating polymerization initiator and an electron-accepting polymerization initiator may be used as an electron-donating polymerization initiator or an electron-accepting polymerization initiator.

[0279] The compound in the form of a conjugate salt of an electron-donating polymerization initiator and an electron-accepting polymerization initiator may be used in combination with the aforementioned electron-donating polymerization initiator or used in combination with the aforementioned electron-accepting polymerization initiator.

[Preferred aspects of infrared absorber and electron-donating polymerization initiator]

[0280] In the image-recording layer of the present disclosure, from the viewpoint of sensitivity improvement and printing durability, HOMO of the infrared absorber - HOMO of the electron-donating polymerization initiator (that is, a value obtained by subtracting HOMO of the electron-donating polymerization initiator from HOMO of the infrared absorber) is preferably 0.70 eV or less, and more preferably 0.70 eV to -0.10 eV

[0281] The negative sign means that HOMO of the electron-donating polymerization initiator is higher than HOMO of the infrared absorber.

[Preferred aspects of electron-accepting polymerization initiator and infrared absorber]

[0282] In the image-recording layer of the present disclosure, from the viewpoint of sensitivity improvement and printing durability, LUMO of the electron-accepting polymerization initiator - LUMO of the infrared absorber (that is, a value obtained by subtracting LUMO of the infrared absorber from LUMO of the electron-accepting polymerization initiator) is preferably 1.00 eV or less, more preferably 0.80 eV or less, and even more preferably 0.70 eV or less. Furthermore, LUMO of the electron-accepting polymerization initiator - LUMO of the infrared absorber is preferably 1.00 eV to -0.10 eV, and more preferably 0.80 eV to 0.30 eV

[0283] The negative sign means that LUMO of the infrared absorber is higher than LUMO of the electron-accepting polymerization initiator.

[Polymerizable compound]

[0284] The image-recording layer in the present disclosure contains a polymerizable compound.

[0285] In the present disclosure, a polymerizable compound refers to a compound having a polymerizable group.

[0286] The polymerizable group is not particularly limited and may be a known polymerizable group. As the polymerizable group, an ethylenically unsaturated group is preferable. The polymerizable group may be a radically polymerizable group or a cationically polymerizable group. The polymerizable group is preferably a radically polymerizable group.

[0287] Examples of the radically polymerizable group include a (meth)acryloyl group, an allyl group, a vinylphenyl group, a vinyl group, and the like. From the viewpoint of reactivity, a (meth)acryloyl group is preferable.

[0288] The molecular weight of the polymerizable compound (weight-average molecular weight in a case where the polymerizable compound has molecular weight distribution) is preferably 50 or more and less than 40,000.

[0289] The polymerizable compound used in the present disclosure may be, for example, a radically polymerizable compound or a cationically polymerizable compound. As the polymerizable compound, an addition polymerizable compound having at least one ethylenically unsaturated bond (ethylenically unsaturated compound) is preferable.

[0290] The ethylenically unsaturated compound is preferably a compound having at least one ethylenically unsaturated bond on a terminal, and more preferably a compound having two or more ethylenically unsaturated bonds on a terminal. The chemical form of the polymerizable compound is, for example, a monomer, a prepolymer which is in other words a dimer, a trimer, or an oligomer, a mixture of these, or the like.

[0291] Particularly, from the viewpoint of UV printing durability, the aforementioned polymerizable compound preferably includes a polymerizable compound having functionalities of 3 or more, more preferably includes a polymerizable compound having functionalities of 7 or more, and even more preferably includes a polymerizable compound having functionalities of 10 or more. Particularly, from the viewpoint of UV printing durability of the lithographic printing plate to be obtained, the aforementioned polymerizable compound preferably includes an ethylenically unsaturated compound having functionalities of 3 or more (preferably having functionalities of 7 or more and more preferably having functionalities of 10 or more), and more preferably includes a (meth)acrylate compound having functionalities of 3 or more (preferably having functionalities of 7 or more and more preferably having functionalities of 10 or more).

[Oligomer]

[0292] As the polymerizable compound to be incorporated into in the image-recording layer, a polymerizable compound which is an oligomer (hereinafter, also simply called "oligomer") is preferable.

[0293] In the present disclosure, an oligomer represents a polymerizable compound which has a molecular weight (weight-average molecular weight in a case where the compound has molecular weight distribution) of 600 or more and 30,000 or less and at least one polymerizable group.

[0294] Preferred examples of the molecular weight of the oligomer include 1,000 or more and 25,000 or less.

[0295] From the viewpoint of excellent chemical resistance and excellent UV printing durability, the molecular weight of the oligomer is preferably 1,000 or more and 5,000 or less.

[0296] Furthermore, from the viewpoint of improving UV printing durability, the number of polymerizable groups in one molecule of the oligomer is preferably 2 or more, more preferably 3 or more, even more preferably 6 or more, and particularly preferably 10 or more.

[0297] The upper limit of the polymerizable groups in the oligomer is not particularly limited. The number of polymerizable groups is preferably 20 or less.

[0298] From the viewpoint of UV printing durability and on-press developability, an oligomer having 7 or more polymerizable groups and a molecular weight of 1,000 or more and 10,000 or less is preferable, and an oligomer having 7 or more and 20 or less polymerizable groups and a molecular weight of 1,000 or more and 5,000 or less is more preferable.

[0299] In a case where the image-recording layer contains an oligomer as a polymerizable compound, the image-recording layer may also contain a polymer component that is likely to be generated in the process of manufacturing the oligomer.

[0300] From the viewpoint of UV printing durability and on-press developability, the oligomer preferably has at least one kind of compound selected from the group consisting of a compound having a urethane bond, a compound having an ester bond, and a compound having an epoxy residue, and preferably has a compound having a urethane bond.

[0301] In the present disclosure, an epoxy residue refers to a structure formed of an epoxy group. For example, the epoxy residue means a structure similar to a structure established by the reaction between an acid group (carboxylic acid group or the like) and an epoxy group.

(Compound having urethane bond)

[0302] As the compound having a urethane bond, which is an example of the oligomer, for example, a compound having at least a group represented by Formula (Ac-1) or Formula (Ac-2) is preferable, and a compound having at least a group represented by Formula (Ac-1) is more preferable.

[0303] In Formula (Ac-1) and Formula (Ac-2), L¹ to L⁴ each independently represent a divalent hydrocarbon group having 2 to 20 carbon atoms, and the portion of the wavy line represents a bonding position with other structures.

[0304] L¹ to L⁴ preferably each independently represent an alkylene group having 2 to 20 carbon atoms, more preferably each independently represent an alkylene group having 2 to 10 carbon atoms, and even more preferably each independently represent an alkylene group having 4 to 8 carbon atoms. The alkylene group may have a branched structure or a ring structure. The alkylene group is preferably a linear alkylene group.

[0305] The portion of the wavy line in Formula (Ac-1) or Formula (Ac-2) is preferably each independently directly bonded to the portion of the wavy line in a group represented by Formula (Ae-1) or Formula (Ae-2).

[0306] In Formula (Ae-1) and Formula (Ae-2), R each independently represent an acryloyloxy group or a methacryloyloxy group, and the portion of the wavy line represents a position bonded to the portion of the wavy line in Formula (Ac-1) and Formula (Ac-2).

[0307] As the compound having a urethane bond, a compound may also be used which is prepared by obtaining polyurethane by a reaction between a polyisocyanate compound and a polyol compound and introducing a polymerizable group into the polyurethane by a polymer reaction.

[0308] For example, the compound having a urethane bond may be obtained by reacting a polyol compound having an acid group with a polyisocyanate compound to obtain a polyurethane oligomer and reacting this polyurethane oligomer with a compound having an epoxy group and a polymerizable group.

(Compound having ester bond)

[0309] The number of polymerizable groups in the compound having an ester bond, which is an example of oligomer, is preferably 3 or more, and more preferably 6 or more.

(Compound having epoxy residue)

[0310] As the compound having an epoxy residue, which is an example of oligomer, a compound containing a hydroxy group is preferable.

[0311] The number of polymerizable groups in the compound having an epoxy residue is preferably 2 to 6, and more preferably 2 or 3.

[0312] The compound having an epoxy residue can be obtained, for example, by reacting a compound having an epoxy group with an acrylic acid.

[0313] Commercially available products as specific examples of the oligomer will be shown below, but the oligomer used in the present disclosure is not limited thereto.

[0314] Examples of commercially available products of the oligomer include UA510H, UA-306H, UA-306I, and UA-306T (KYOEISHA CHEMICAL Co., LTD.), UV-1700B, UV-6300B, and UV7620EA (NIHON GOSEI KAKO Co., Ltd.), U-15HA (SHIN-NAKAMURA CHEMICAL Co., LTD.), EBECRYL450, EBECRYL657, EBECRYL885, EBECRYL800, EBECRYL3416, and EBECRYL860 (DAICEL-ALLNEX LTD.), and the like.

[0315] From the viewpoint of improving chemical resistance and UV printing durability and further suppressing the residues of on-press development, the content of the oligomer with respect to the total mass of polymerizable compounds in the image-recording layer is preferably 30% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass.

[Low-molecular-weight polymerizable compound]

[0316] The polymerizable compound may further include a polymerizable compound other than the oligomer described above.

[0317] From the viewpoint of chemical resistance, the polymerizable compound other than the oligomer is preferably a low-molecular-weight polymerizable compound. The low-molecular-weight polymerizable compound may take a chemical form such as a monomer, a dimer, a trimer, or a mixture of these.

[0318] From the viewpoint of chemical resistance, the low-molecular-weight polymerizable compound is preferably at least a polymerizable compound selected from the group consisting of a polymerizable compound having three or more ethylenically unsaturated groups and a polymerizable compound having an isocyanuric ring structure.

[0319] In the present disclosure, a low-molecular-weight polymerizable compound refers to a polymerizable compound having a molecular weight (weight-average molecular weight in a case where the compound has molecular weight distribution) of 50 or more and less than 600.

[0320] From the viewpoint of excellent chemical resistance, excellent UV printing durability, and excellently suppressing the residues of on-press development, the molecular weight of the low-molecular-weight polymerizable compound is preferably 100 or more and less than 600, more preferably 300 or more and less than 600, and even more preferably 400 or more and less than 600.

[0321] In a case where the polymerizable compound includes a low-molecular-weight polymerizable compound as the polymerizable compound other than an oligomer (total amount in a case where the polymerizable compound includes two or more kinds of low-molecular-weight polymerizable compounds), from the viewpoint of chemical resistance, UV printing durability, and suppression of the residues of on-press development, the ratio of the oligomer to the low-molecular-weight polymerizable compound (oligomer/low-molecular-weight polymerizable compound) is preferably 10/1 to 1/10, more preferably 10/1 to 3/7, and even more preferably 10/1 to 7/3, based on mass.

[0322] Specific examples of the low-molecular-weight polymerizable compound include the compounds described in paragraphs "0082" to "0086" of WO2019/013268A.

[0323] The details of how to use the polymerizable compound, such as the structure of the compound, whether the compound is used alone or used in combination with other compounds, and the amount of the compound to be added, can be randomly set.

[0324] Particularly, from the viewpoint of UV printing durability, the image-recording layer preferably contains two or more kinds of polymerizable compounds.

[0325] The content of the polymerizable compound (total content of polymerizable compounds in a case where the image-recording layer contains two or more kinds of polymerizable compounds) with respect to the total mass of the image-recording layer is preferably 5% by mass to 75% by mass, more preferably 10% by mass to 70% by mass, and even more preferably 15% by mass to 60% by mass.

[Infrared absorber]

[0326] The image-recording layer in the present disclosure contains an infrared absorber.

[0327] The infrared absorber is not particularly limited, and examples thereof include pigments and dyes.

[0328] As the dye that is used as the infrared absorber, it is possible to use commercially available dyes and known dyes described in publications, for example, "Dye Handbooks" (edited by the Society of Synthetic Organic Chemistry, Japan, 1970). Specific examples thereof include dyes such as an azo dye, a metal complex azo dye, a pyrazolone azo dye, a naphthoquinone dye, an anthraquinone dye, a phthalocyanine dye, a carbonium dye, a quinoneimine dye, a methine dye, a cyanine dye, a squarylium colorant, a pyrylium salt, and a metal thiolate complex.

[0329] Among these dyes, for example, a cyanine dye, a squarylium colorant, a pyrylium salt, a nickel thiolate complex, and an indolenine cyanine dye are preferable, and a cyanine dye or an indolenine cyanine dye is more preferable. Among these, a cyanine dye is particularly preferable.

[0330] The aforementioned infrared absorber is preferably a cationic polymethine colorant having an oxygen atom, a nitrogen atom, or a halogen atom at the meso-position. Preferred examples of the cationic polymethine colorant include a cyanine dye, a pyrylium colorant, a thiopyrylium colorant, an azulenium colorant, and the like. From the viewpoint of ease of availability, solubility in a solvent during an introduction reaction, and the like, a cyanine dye is preferable.

[0331] Specific examples of the cyanine dye include the compounds described in paragraphs "0017" to "0019" of JP2001-133969A and the compounds described in paragraphs "0016" to "0021" of JP2002-023360A and paragraphs "0012" to "0037" of JP2002-040638A. As the cyanine dye, for example, the compounds described in paragraphs "0034" to "0041" of JP2002-278057A and paragraphs "0080" to "0086" of JP2008-195018A are preferable, and the compounds described in paragraphs "0035" to "0043" of JP2007-90850A and the compounds described in paragraphs "0105" to "0113" of JP2012-206495A are particularly preferable.

[0332] Furthermore, the compounds described in paragraphs "0008" and "0009" of JP1993-5005A (JP-H05-5005A) and paragraphs "0022" to "0025" of JP2001-222101A can also be preferably used.

[0333] As pigments, the compounds described in paragraphs "0072" and" 0076" of JP2008-195018A are preferable.

[0334] As the aforementioned infrared absorber, an infrared absorber that decomposes by exposure to infrared can also be suitably used.

[0335] As the infrared absorber that decomposes by exposure to infrared, those described in JP2008-544322A, WO2016/027886A, WO2017/141882A, or WO2018/043259A can also be suitably used.

[0336] In addition, as the infrared absorber that decomposes by exposure to infrared, the aforementioned decomposition-type infrared absorber used in the outermost layer may also be used.

[0337] One kind of infrared absorber may be used alone, or two or more kinds of infrared absorbers may be used in combination.

[0338] In addition, as the infrared absorber, a pigment and a dye may be used in combination.

[0339] The content of the infrared absorber with respect to the total mass of the image-recording layer is preferably 0.1% by mass to 10.0% by mass, and more preferably 0.5% by mass to 5.0% by mass.

[Particles]

[0340] From the viewpoint of developability and UV printing durability, it is preferable that the image-recording layer in the present disclosure contain particles. The particles may be inorganic particles or organic particles.

[0341] Particularly, the image-recording layer preferably contains organic particles as particles, and more preferably contains polymer particles as particles.

[0342] That is, it is preferable that the image-recording layer in the present disclosure contain polymer particles.

[0343] Known inorganic particles can be used as inorganic particles, and metal oxide particles such as silica particles and titania particles can be suitably used.

[Polymer particles]

[0344] Examples of the polymer particles include particles containing an addition polymerization-type resin (that is, addition polymerization-type polymer particles), particles containing a polyaddition-type resin (that is, polyaddition-type polymer particles), particles containing a polycondensation-type resin (that is, polycondensation-type polymer particles), and the like. Among these, addition polymerization-type polymer particles or polyaddition-type polymer particles are preferable.

[0345] From the viewpoint of enabling thermal fusion, the polymer particles may also be particles containing a thermoplastic resin (that is, thermoplastic polymer particles).

[0346] The polymer particles may be in the form of microcapsules, a microgel (that is, crosslinked polymer particles), or the like.

[0347] The polymer particles are preferably selected from the group consisting of thermoplastic polymer particles, thermal reactive polymer particles, polymer particles having a polymerizable group, microcapsules encapsulating a hydrophobic compound, and microgel (crosslinked polymer particles). Among these, polymer particles having a polymerizable group are preferable.

[0348] In a particularly preferred embodiment, the polymer particles have at least one ethylenically unsaturated group. The presence of such polymer particles brings about effects of improving the printing durability of an exposed portion and improving the on-press developability of a non-exposed portion.

[0349] As the thermoplastic polymer particles, the thermoplastic polymer particles described in Research Disclosure No. 33303 published in January 1992, JP1997-123387A (JP-H09-123387A), JP1997-131850A (JP-H09-131850A), JP1997-171249A (JP-H09-171249A), JP1997-171250A (JP-H09-171250A), EP931647B, and the like are preferable.

[0350] Specific examples of thermoplastic resins constituting the thermoplastic polymer particles include homopolymers or copolymers of monomers of ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile, vinylcarbazole, acrylates or methacrylates having polyalkylene structures, and the like and mixtures of these.

[0351] From the viewpoint of ink receptivity and UV printing durability, the thermoplastic polymer particles preferably contain a thermoplastic resin that has a constitutional unit formed of an aromatic vinyl compound and a nitrile group-containing constitutional unit.

[0352] The aforementioned aromatic vinyl compound may have a structure composed of an aromatic ring and a vinyl group bonded thereto. Examples of the compound include a styrene compound, a vinylnaphthalene compound, and the like. Among these, a styrene compound is preferable, and styrene is more preferable.

[0353] Examples of the styrene compound include styrene, p-methylstyrene, p-methoxystyrene, β-methylstyrene, p-methyl-β-methylstyrene, α-methylstyrene, p-methoxy-β-methylstyrene, and the like.

[0354] From the viewpoint of ink receptivity, the content of the constitutional unit formed of an aromatic vinyl compound is preferably higher than the content of the nitrile group-containing constitutional unit that will be described later. The content of the constitutional unit formed of an aromatic vinyl compound with respect to the total mass of the thermoplastic resin is more preferably 15% by mass to 85% by mass, and even more preferably 30% by mass to 70% by mass.

[0355] The nitrile group-containing constitutional unit is preferably introduced using a monomer having a nitrile group.

[0356] Examples of the monomer having a nitrile group include an acrylonitrile compound. As the monomer having a nitrile group, for example, (meth)acrylonitrile is suitable.

[0357] As the nitrile group-containing constitutional unit, a constitutional unit formed of (meth)acrylonitrile is preferable.

[0358] From the viewpoint of ink receptivity, the content of the nitrile group-containing constitutional unit is preferably lower than the content of the aforementioned constitutional unit formed of an aromatic vinyl compound. The content of the nitrile group-containing constitutional unit with respect to the total mass of the resin is more preferably 55% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass.

[0359] In a case where the resin contained in the thermoplastic polymer particles has the constitutional unit formed of an aromatic vinyl compound and the nitrile group-containing constitutional unit, the content ratio between the constitutional unit formed of an aromatic vinyl compound and the nitrile group-containing constitutional unit (constitutional unit formed of aromatic vinyl compound:nitrile group-containing constitutional unit) is preferably 5:5 to 9: 1, and more preferably 6:4 to 8:2, based on mass.

[0360] From the viewpoint of UV printing durability and chemical resistance, the resin contained in the thermoplastic polymer particles preferably further has a constitutional unit formed of a N-vinyl heterocyclic compound.

[0361] Examples of the N-vinyl heterocyclic compound include N-vinylpyrrolidone, N-vinylcarbazole, N-vinylpyrrole, N-vinylphenothiazine, N-vinylsuccinic acid imide, N-vinylphthalimide, N-vinylcaprolactam, and N-vinylimidazole. Among these, N-vinylpyrrolidone is preferable.

[0362] The content of the constitutional unit formed of a N-vinyl heterocyclic compound with respect to the total mass of the thermoplastic resin is preferably 5% by mass to 50% by mass, and more preferably 10% by mass to 40% by mass.

[0363] The resin contained in the thermoplastic polymer particles may contain an acidic group-containing constitutional unit. From the viewpoint of on-press developability and ink receptivity, it is preferable that the resin do not contain an acidic group-containing constitutional unit.

[0364] Specifically, in the thermoplastic resin, the content of the acidic group-containing constitutional unit is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The lower limit of the content is not particularly limited, and may be 0% by mass.

[0365] The acid value of the thermoplastic resin is preferably 160 mg KOH/g or less, more preferably 80 mg KOH/g or less, and even more preferably 40 mg KOH/g or less. The lower limit of the acid value is not particularly limited, and may be 0 mg KOH/g.

[0366] In the present disclosure, the acid value is determined by the measurement method based on JIS K 0070-1992.

[0367] From the viewpoint of ink receptivity, the thermoplastic resin contained in the thermoplastic polymer particles may contain a hydrophobic group-containing constitutional unit.

[0368] Examples of the hydrophobic group include an alkyl group, an aryl group, an aralkyl group, and the like.

[0369] As the hydrophobic group-containing constitutional unit, a constitutional unit formed of an alkyl (meth)acrylate compound, an aryl (meth)acrylate compound, or an aralkyl (meth)acrylate compound is preferable, and a constitutional unit formed of an alkyl (meth)acrylate compound is more preferable.

[0370] In the thermoplastic resin contained in the thermoplastic polymer particles, the content of the hydrophobic group-containing constitutional unit with respect to the total mass of the resin is preferably 5% by mass to 50% by mass, and more preferably 10% by mass to 30% by mass.

[0371] From the viewpoint of UV printing durability and on-press developability, the thermoplastic resin contained in the thermoplastic polymer particles preferably has a hydrophilic group.

[0372] The hydrophilic group is not particularly limited as long as it has a hydrophilic structure, and examples thereof include an acid group such as a carboxy group, a hydroxy group, an amino group, a nitrile group, a polyalkylene oxide structure, and the like.

[0373] From the viewpoint of UV printing durability and on-press developability, the hydrophilic group is preferably a group having a polyalkylene oxide structure, a group having a polyester structure, or a sulfonic acid group, more preferably a group having a polyalkylene oxide structure or a sulfonic acid group, and even more preferably a group having a polyalkylene oxide structure.

[0374] From the viewpoint of on-press developability, the polyalkylene oxide structure is preferably a polyethylene oxide structure, a polypropylene oxide structure, or a poly(ethylene oxide/propylene oxide) structure.

[0375] From the viewpoint of on-press developability, among the above hydrophilic groups, groups having a polypropylene oxide structure as a polyalkylene oxide structure are preferable, and groups having a polyethylene oxide structure and a polypropylene oxide structure are more preferable.

[0376] From the viewpoint of on-press developability, the number of alkylene oxide structures in the polyalkylene oxide structure is preferably 2 or more, more preferably 5 or more, even more preferably 5 to 200, and particularly preferably 8 to 150.

[0377] From the viewpoint of on-press developability, as the aforementioned hydrophilic group, a group represented by Formula Z, which will be described later, is preferable.

[0378] Among the hydrophilic groups that the thermoplastic resin has, a group represented by Formula PO is preferable.

[0379] In Formula PO, L^P each independently represent an alkylene group, R^P represents a hydrogen atom or an alkyl group, and n represents an integer of 1 to 100.

[0380] In Formula PO, L^P preferably each independently represent an ethylene group, a 1-methylethylene group, or a 2-methylethylene group, and more preferably each independently represent an ethylene group.

[0381] In Formula PO, R^P is preferably a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, even more preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and particularly preferably a hydrogen atom or a methyl group.

[0382] In Formula PO, n is preferably an integer of 1 to 10, and more preferably an integer of 1 to 4.

[0383] The content of the hydrophilic group-containing constitutional unit with respect to the total mass of the resin is preferably 5% by mass to 60% by mass, and more preferably 10% by mass to 30% by mass.

[0384] The resin contained in the thermoplastic polymer particles may further contain other constitutional units.

[0385] The resin can contain, as those other constitutional units, constitutional units other than the constitutional units described above without particular limitations. Examples thereof include constitutional units formed of an acrylamide compound, a vinyl ether compound, and the like.

[0386] In the thermoplastic resin, the content of those other constitutional units with respect to the total mass of the thermoplastic resin is preferably 5% by mass to 50% by mass, and more preferably 10% by mass to 30% by mass.

[0387] Examples of the thermal reactive polymer particles include polymer particles having a thermal reactive group.

[0388] The thermal reactive resin particles form a hydrophobic region through crosslinking by a thermal reaction and the accompanying change in functional groups.

[0389] The thermal reactive group in the polymer particles having a thermal reactive group may be a functional group that causes any reaction as long as chemical bonds are formed. The thermally reactive group is preferably a polymerizable group. Preferred examples of the polymerizable group include an ethylenically unsaturated group that causes a radical polymerization reaction (for example, an acryloyl group, a methacryloyl group, a vinyl group, an allyl groups, and the like), a cationically polymerizable group (for example, a vinyl group, a vinyloxy group, an epoxy group, an oxetanyl group, and the like), an isocyanato group or a blocked isocyanato group that causes an addition reaction, an epoxy group, a vinyloxy group, an active hydrogen atom-containing functional group that is a reaction partner thereof (for example, an amino group, a hydroxy group, a carboxy group, and the like), a carboxy group that causes a condensation reaction, a hydroxy group or an amino group that is a reaction partner of the carboxy group, an acid anhydride that causes a ring-opening addition reaction, an amino group or a hydroxy group which is a reaction partner of the acid anhydride, and the like.

[0390] The resin having a thermal reactive group may be an addition polymerization-type resin, a polyaddition-type resin, or a polycondensation-type resin or may be a thermoplastic resin.

[0391] As the microcapsules, for example, microcapsules are preferable which encapsulate at least some of the constituent components (preferably a hydrophobic compound) of the image-recording layer as described in JP2001-277740A and JP2001-277742A. In a preferred aspect of the image-recording layer containing microcapsules as polymer particles, the image-recording layer is composed of microcapsules that encapsulate a hydrophobic component (that is, a hydrophobic compound) among the constituent components of the image-recording layer and a hydrophilic component (that is, a hydrophilic compound) that is on the outside of the microcapsules.

[0392] In order to obtain microcapsules containing a constituent component of the image-recording layer, known synthesis methods can be used.

[0393] The microgel (crosslinked polymer particles) can contain some of the constituent components of the image-recording layer, in at least one of the surface or the interior of the microgel. From the viewpoint of sensitivity of the lithographic printing plate precursor to be obtained and printing durability of the lithographic printing plate to be obtained, reactive microgel having a polymerizable group on the surface thereof is particularly preferable.

[0394] In order to obtain microgel containing a constituent component of the image-recording layer, known synthesis methods can be used.

[0395] As the polymer particles, from the viewpoint of printing durability, antifouling properties, and storage stability of the lithographic printing plate to be obtained, polyaddition-type polymer particles are preferable which are obtained by a reaction between a polyvalent isocyanate compound that is an adduct of a polyhydric phenol compound having two or more hydroxy groups in a molecule and isophorone diisocyanate and a compound having active hydrogen.

[0396] As the polyhydric phenol compound, a compound having a plurality of benzene rings having a phenolic hydroxyl group is preferable.

[0397] As the compound having active hydrogen, a polyol compound or a polyamine compound is preferable, a polyol compound is more preferable, and at least one kind of compound selected from the group consisting of propylene glycol, glycerin, and trimethylolpropane is even more preferable.

[0398] As the aforementioned compound having active hydrogen, water may also be used. In a case where water is used, the amine generated by the reaction between an isocyanate group of the aforementioned polyvalent isocyanate compound and water can form a urea bond to form particles.

[0399] Preferred examples of the resin particles obtained by the reaction between a polyvalent isocyanate compound that is an adduct of a polyhydric phenol compound having two or more hydroxy groups in a molecule and isophorone diisocyanate and a compound having active hydrogen include the microgel obtained by the preparation method described in paragraphs "0230" to "0234" of WO2018/043259A.

[0400] As the polymer particles, from the viewpoint of printing durability and solvent resistance of the lithographic printing plate to be obtained, addition polymerization-type polymer particles are preferable which have a hydrophobic main chain and include both i) constitutional unit having a nitrile group directly bonded to the hydrophobic main chain and ii) constitutional unit having a pendant group including a hydrophilic polyalkylene oxide segment.

[0401] Specifically, as such addition polymerization-type polymer particles, the particles described in paragraph "0156" of JP2019-64269A are preferable.

(Group represented by Formula Z)

[0402] It is preferable that the polymer particles in the present disclosure have a group represented by Formula Z as a hydrophilic group.

[0403] Particularly, the polymer particles in the present disclosure are preferably addition polymerization-type polymer particles having a hydrophilic group including a group represented by Formula Z.

        Formula Z:     ^∗-Q-W-Y

[0404] In formula Z, Q represents a divalent linking group, W represents a divalent group having a hydrophilic structure or a divalent group having a hydrophobic structure, and Y represents a monovalent group having a hydrophilic structure or a monovalent group having a hydrophilic structure, either W or Y has a hydrophilic structure, and * represents a bonding site with another structure.

[0405] Furthermore, it is preferable that any of the hydrophilic structures included in Formula Z include a polyalkylene oxide structure.

[0406] Q in Formula Z is preferably a divalent linking group having 1 to 20 carbon atoms, and more preferably a divalent linking group having 1 to 10 carbon atoms.

[0407] Furthermore, Q in Formula Z is preferably an alkylene group, an arylene group, an ester bond, an amide bond, or a group formed by combining two or more of these, and more preferably a phenylene group, an ester bond, or an amide bond.

[0408] The divalent group having a hydrophilic structure represented by W in Formula Z is preferably a group having a polyalkylene oxide structure, and more preferably a polyalkyleneoxy group or a group in which -CH₂CH₂NR^W- is bonded to one terminal of a polyalkyleneoxy group. R^W represents a hydrogen atom or an alkyl group. R^W mentioned hereinbelow also represents a hydrogen atom or an alkyl group.

[0409] The divalent group having a hydrophobic structure represented by W in Formula Z is preferably -R^WA-, -O-R^WA-O-, -R^WN-R^WA-NR^W-, -OC(=O)-R^WA-O-, or -OC(=O)-R^WA-O-. R^WA each independently represents a linear, branched, or cyclic alkylene group having 6 to 120 carbon atoms, a haloalkylene group having 6 to 120 carbon atoms, an arylene group having 6 to 120 carbon atoms, an alkarylene group having 7 to 120 carbon atoms (divalent group formed by removing one hydrogen atom from an alkylaryl group), or an aralkylene group having 7 to 120 carbon atoms.

[0410] The monovalent group having a hydrophilic structure represented by Y in Formula Z is preferably -OH, -C(=O)OH, a polyalkyleneoxy group having a hydrogen atom or an alkyl group on a terminal, or a group in which -CH₂CH₂N(R^W)- is bonded to one terminal of a polyalkyleneoxy group having a hydrogen atom or an alkyl group on the other terminal. Particularly, the monovalent group having a hydrophilic structure is preferably a group having a polyalkylene oxide structure, a polyalkyleneoxy group having a hydrogen atom or an alkyl group on a terminal, or a group in which -CH₂CH₂N(R^W)- is bonded to one terminal of a polyalkyleneoxy group having a hydrogen atom or an alkyl group on the other terminal.

[0411] The monovalent group having a hydrophobic structure represented by Y in Formula Z is preferably a linear, branched, or cyclic alkyl group having 6 to 120 carbon atoms, a haloalkyl group having 6 to 120 carbon atoms, an aryl group having 6 to 120 carbon atoms, an alkaryl group having 7 to 120 carbon atoms (alkylaryl group), an aralkyl group having 7 to 120 carbon atoms, -OR^WB, -C(=O)OR^WB, or -OC(=O)R^WB. R^WB represents an alkyl group having 6 to 20 carbon atoms.

[0412] From the viewpoint of printing durability, receptivity, and on-press developability, in the polymer particles having a group represented by formula Z, W is more preferably a divalent group having a hydrophilic structure, Q is more preferably a phenylene group, an ester bond, or an amide bond, W is more preferably a polyalkyleneoxy group, and Y is more preferably a polyalkyleneoxy group having a hydrogen atom or an alkyl group on a terminal.

[0413] The group represented by Formula Z may function as a dispersible group for improving the dispersibility of the polymer particles.

[0414] From the viewpoint of printing durability and on-press developability, the polymer particles in the present disclosure preferably have a polymerizable group (preferably an ethylenically unsaturated group). Particularly, the polymer particles more preferably have a polymerizable group on the surface thereof. Using the polymer particles having a polymerizable group makes it easy to suppress plate missing (preferably UV plate missing) and improves printing durability (preferably UV printing durability) as well.

[0415] From the viewpoint of printing durability, it is preferable that the polymer particles in the present disclosure be resin particles having a hydrophilic group and a polymerizable group.

[0416] The polymerizable group may be a cationically polymerizable group or a radically polymerizable group. From the viewpoint of reactivity, the polymerizable group is preferably a radically polymerizable group.

[0417] The aforementioned polymerizable group is not particularly limited as long as it is a polymerizable group. From the viewpoint of reactivity, an ethylenically unsaturated group is preferable, a vinylphenyl group (styryl group), a (meth)acryloxy group, or a (meth)acrylamide group is more preferable, and a (meth)acryloxy group is particularly preferable.

[0418] In addition, it is preferable that the resin constituting the polymer particles having a polymerizable group have a polymerizable group-containing constitutional unit.

[0419] The polymerizable group may be introduced into the surface of the polymer particles by a polymer reaction.

[0420] Furthermore, from the viewpoint of printing durability, receptivity, on-press developability, and suppression of the occurrence of development residues during on-press development, the polymer particles preferably contain a polyaddition-type resin having a urea bond, more preferably contain a polyaddition-type resin having a structure obtained by reacting at least an isocyanate compound represented by Formula (Iso) with water, and particularly preferably contain a polyaddition-type resin that has a structure obtained by reacting at least an isocyanate compound represented by Formula (Iso) with water and has a polyethylene oxide structure and a polypropylene oxide structure as polyoxyalkylene structures. Furthermore, the particles containing the polyaddition-type resin having a urea bond are preferably microgel.

[0421] In Formula (Iso), n represents an integer of 0 to 10.

[0422] An example of the reaction between the isocyanate compound represented by Formula (Iso) and water is the reaction shown below. In the following example, a 4,4-isomer in which n = 0 is used.

[0423] As shown below, in a case where the isocyanate compound represented by Formula (Iso) is reacted with water, the isocyanate group is partially hydrolyzed by water and generates an amino group. The generated amino group reacts with the isocyanate group and generates a urea bond, and a dimer is consequently formed. Furthermore, the following reaction is repeated to form a polyaddition-type resin having a urea bond.

[0424] In the following reaction, by adding a compound (compound having active hydrogen) such as an alcohol compound or an amine compound reactive with an isocyanate group, it is possible to introduce the structure of an alcohol compound, an amine compound, or the like to the polyaddition-type resin having a urea bond.

[0425] Preferred examples of the compound having active hydrogen include the aforementioned compound having active hydrogen.

[0426] The polyaddition-type resin having a urea bond preferably has an ethylenically unsaturated group, and more preferably has a group represented by Formula (PETA).

[0427] In Formula (PETA), the portion of the wavy line represents a bonding position with other structures.

(Synthesis of polymer particles)

[0428] The synthesis method of the polymer particles is not particularly limited, and may be a method that makes it possible to synthesize particles with various resins described above. Examples of the synthesis method of the polymer particles include known synthesis methods of polymer particles, such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, a soap-free polymerization method, and a microemulsion polymerization method.

[0429] In addition, for the synthesis of the polymer particles, a known microcapsule synthesis method, a known microgel (crosslinked resin particle) synthesis method, and the like may be used.

(Average particle diameter of particles)

[0430] The average particle diameter of the particles is preferably 0.01 µm to 3.0 µm, more preferably 0.03 µm to 2.0 µm, and even more preferably 0.10 µm to 1.0 µm. In a case where the average particle diameter is in this range, excellent resolution and temporal stability are obtained.

[0431] The average particle diameter of the particles is measured using a light scattering method or by capturing an electron micrograph of the particles, measuring the particle diameter of a total of 5,000 particles in the photograph, and calculating the average thereof. For nonspherical particles, the equivalent circular diameter of the particles in a photograph is adopted.

[0432] Note that unless otherwise specified, the average particle diameter of the particles in the present disclosure means a volume average particle diameter.

[0433] As the particles (preferably polymer particles), only one kind of particles may be used, or two or more kinds of particles may be used in combination.

[0434] From the viewpoint of developability and printing durability, the content of the particles (preferably polymer particles) with respect to the total mass of the image-recording layer is preferably 5% by mass to 90% by mass, more preferably 10% by mass to 90% by mass, even more preferably 20% by mass to 90% by mass, and particularly preferably 50% by mass to 90% by mass.

[Other components]

[0435] The image-recording layer in the present disclosure may contain other components in addition to the components described above.

[0436] Examples of those other components include a binder polymer, a color developing agent, a chain transfer agent, a low-molecular-weight hydrophilic compound, an oil sensitizing agent, other additives, and the like.

[Binder polymer]

[0437] As necessary, the image-recording layer may contain a binder polymer.

[0438] The binder polymer refers to a polymer other than polymer particles, that is, a polymer that is not in the form of particles.

[0439] In addition, the binder polymer excludes an ammonium salt-containing polymer in an oil sensitizing agent and a polymer used as a surfactant.

[0440] As the binder polymer, known binder polymers (for example, a (meth) acrylic resin, a polyvinyl acetal resin, a polyurethane resin, and the like) used for the image-recording layer of a lithographic printing plate precursor can be suitably used.

[0441] As an example, a binder polymer that is used for an on-press development type lithographic printing plate precursor (hereinafter, also called binder polymer for on-press development) will be specifically described.

[0442] As the binder polymer for on-press development, a binder polymer having an alkylene oxide chain is preferable. The binder polymer having an alkylene oxide chain may have a poly(alkylene oxide) moiety in a main chain or side chain. In addition, the binder polymer may be a graft polymer having poly(alkylene oxide) in a side chain or a block copolymer of a block composed of a poly(alkylene oxide)-containing repeating unit and a block composed of an (alkylene oxide)-free repeating unit.

[0443] As a binder polymer having a poly(alkylene oxide) moiety in the main chain, a polyurethane resin is preferable.

[0444] In a case where the binder polymer has a poly(alkylene oxide) moiety in the side chain, examples of polymers as the main chain include a (meth)acrylic resin, a polyvinyl acetal resin, a polyurethane resin, a polyurea resin, a polyimide resin, a polyamide resin, an epoxy resin, a polystyrene resin, a novolac-type phenol resin, a polyester resin, synthetic rubber, and natural rubber. Among these, a (meth)acrylic resin is particularly preferable.

[0445] In addition, as the binder polymer, for example, a polymer compound is also preferable which has a polyfunctional thiol having functionalities of 6 or more and 10 or less as a nucleus and a polymer chain that is bonded to the nucleus by a sulfide bond and has a polymerizable group (hereinafter, this compound will be also called star-shaped polymer compound).

[0446] As the star-shaped polymer compound, for example, the compounds described in JP2012-148555A can be preferably used.

[0447] Examples of the star-shaped polymer compound include the compound described in JP2008-195018A that has a polymerizable group such as an ethylenically unsaturated bond for improving the film hardness of an image area in a main chain or side chain and preferably in a side chain. The polymerizable group of the star-shaped polymer compound forms crosslinks between the molecules of the star-shaped polymer compound, which facilitates curing.

[0448] As the polymerizable group, an ethylenically unsaturated group such as a (meth)acryloyl group, a vinyl group, an allyl group, or a vinyl phenyl group (styryl group), an epoxy group, or the like is preferable, a (meth)acryloyl group, a vinyl group, or a vinyl phenyl group (styryl group) is more preferable from the viewpoint of polymerization reactivity, and a (meth)acryloyl group is particularly preferable. These groups can be introduced into the polymer by a polymer reaction or copolymerization. Specifically, for example, it is possible to use a reaction between a polymer having a carboxy group in a side chain and glycidyl methacrylate or a reaction between a polymer having an epoxy group and an ethylenically unsaturated group-containing carboxylic acid such as methacrylic acid.

[0449] The molecular weight of the binder polymer that is a polystyrene-equivalent weight-average molecular weight (Mw) determined by GPC is preferably 40,000 or more, and more preferably 40,000 to 300,000.

[0450] In a case where the binder polymer does not have a polymerizable group, the weight-average molecular weight (Mw) is preferably 10,000 to 300,000.

[0451] As the binder polymer, as necessary, a hydrophilic polymer such as polyacrylic acid or polyvinyl alcohol described in JP2008-195018A can be used in combination. In addition, a lipophilic polymer and a hydrophilic polymer can be used in combination.

[0452] One kind of binder polymer may be used alone, or two or more kinds of binder polymers may be used in combination.

[0453] The content of the binder polymer to be incorporated into the image-recording layer can be randomly set. The content of the binder polymer with respect to the total mass of the image-recording layer is preferably 1% by mass to 90% by mass, and more preferably 5% by mass to 80% by mass.

[Color developing agent]

[0454] The image-recording layer may contain a color developing agent.

[0455] The color developing agent is preferably an acid color developing agent. Furthermore, the color developing agent preferably includes a leuco compound.

[0456] "Color developing agent" used in the present disclosure means a compound that develops or removes color by a stimulus such as light or acid and thus changes the color of the image-recording layer. Furthermore, "acid color developing agent" means a compound that develops or removes color by being heated in a state of accepting an electron accepting compound (for example, a proton of an acid or the like) and thus changes the color of the image-recording layer.

[0457] The acid color developing agent is particularly preferably a colorless compound which has a partial skeleton such as lactone, lactam, sultone, spiropyran, an ester, or an amide and allows such a partial skeleton to rapidly open the ring or to be cleaved when coming into contact with an electron accepting compound.

[0458] Examples of the acid color developing agent include the compounds described in paragraphs "0184" to "0191" of JP2019-18412A.

[0459] Particularly, from the viewpoint of color developability, the color developing agent is preferably at least one kind of compound selected from the group consisting of a spiropyran compound, a spirooxazine compound, a spirolactone compound, and a spirolactam compound.

[0460] From the viewpoint of visibility, the color of the color developing agent after color development preferably has maximum absorption in a range of 450 nm to 650 nm. The tint of the color developing agent after color development is preferably red, purple, blue, or dark green.

[0461] From the viewpoint of improving visibility of exposed portions, it is preferable to use a leuco colorant as the color developing agent (preferably the acid color developing agent).

[0462] The aforementioned leuco colorant is not particularly limited as long as it has a leuco structure. The leuco colorant preferably has a spiro structure, and more preferably has a spirolactone ring structure.

[0463] From the viewpoint of improving visibility of exposed portions, the leuco colorant preferably has a phthalide structure or a fluoran structure.

[0464] Furthermore, from the viewpoint of improving visibility of exposed portions, the color developing agent (preferably the acid color developing agent) is preferably the aforementioned leuco colorant having a phthalide structure or a fluoran structure, which is a compound represented by represented by any of Formula (Le-1) to Formula (Le-3), and more preferably a compound represented by Formula (Le-2).

[0465] In Formula (Le-1) to Formula (Le-3), ERG each independently represent an electron-donating group, X₁ to X₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, X₅ to X₁₀ each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, Y₁ and Y₂ each independently represent C or N, X₁ does not exist in a case where Y₁ is N, X₄ does not exist in a case where Y₂ is N, Ra₁ represents a hydrogen atom, an alkyl group, or an alkoxy group, and Rb₁ to Rb₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group.

[0466] From the viewpoint of color developability and visibility of exposed portions, the electron-donating group represented by ERG in Formula (Le-1) to Formula (Le-3) is preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkyl monoarylamino group, a monoalkyl monoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoaryl monoheteroarylamino group, an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, more preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkyl monoarylamino group, a monoalkyl monoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoaryl monoheteroarylamino group, an alkoxy group, or an aryloxy group, even more preferably a monoalkyl monoarylamino group, a diarylamino group, a diheteroarylamino group, or a monoaryl monoheteroarylamino group, and particularly preferably a monoalkyl monoarylamino group.

[0467] In addition, from the viewpoint of color developability and visibility of exposed portions, the electron-donating group represented by ERG is preferably a disubstituted amino group having an aryl group that has a substituent at at least one ortho position or a heteroaryl group that has a substituent at at least one ortho position, and more preferably a disubstituted amino group having a substituent at at least one ortho position and a phenyl group having an electron-donating group at the para position. Furthermore, for the same reason as above, the electron-donating group represented by ERG is even more preferably an amino group having a substituent at at least one ortho position and having a phenyl group having an electron-donating group and an aryl group or a heteroaryl group at the para position, and particularly preferably an amino group having a substituent at at least one ortho position and having a phenyl group having an electron-donating group and an aryl group having an electron-donating group or a heteroaryl group having an electron-donating group at the para position.

[0468] In the present disclosure, in a case where a bonding position of an aryl group or a heteroaryl group with other structures is defined as 1-position, the ortho position in the aryl group or heteroaryl group other than a phenyl group is a bonding position (for example, 2-position or the like) adjacent to the 1-position.

[0469] From the viewpoint of color developability and visibility of exposed portions, the electron-donating group that the aforementioned aryl group or heteroaryl group has is preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkyl monoarylamino group, a monoalkyl monoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoaryl monoheteroarylamino group, an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, more preferably an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, and particularly preferably an alkoxy group.

[0470] From the viewpoint of improving visibility of exposed portions, X₁ to X₄ in Formula (Le-1) to Formula (Le-3) preferably each independently represent a hydrogen atom or a chlorine atom, and more preferably each independently represent a hydrogen atom.

[0471] From the viewpoint of improving visibility of exposed portions, X₅ to X₁₀ in Formula (Le-2) or Formula (Le-3) preferably each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkyl monoarylamino group, a monoalkyl monoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoaryl monoheteroarylamino group, a hydroxy group, an alkoxy group, an aryloxy group, a heteroaryloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a heteroaryloxycarbonyl group, or a cyano group, more preferably each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, or an aryloxy group, even more preferably each independently represent a hydrogen atom, a halogen atom, an alkyl group, or an aryl group, and particularly preferably each independently represent a hydrogen atom.

[0472] From the viewpoint of improving visibility of exposed portions, it is preferable that at least one of Y₁ or Y₂ in Formula (Le-1) to Formula (Le-3) be C, and it is more preferable that both of Y₁ and Y₂ be C.

[0473] From the viewpoint of improving visibility of exposed portions, Ra₁ in Formula (Le-3) is preferably an alkyl group or an alkoxy group, more preferably an alkoxy group, and particularly preferably a methoxy group.

[0474] From the viewpoint of improving visibility of exposed portions, Rb₁ to Rb₄ in Formula (Le-1) preferably each independently represent a hydrogen atom or an alkyl group, more preferably each independently represent an alkyl group, and particularly preferably each independently represent a methyl group.

[0475] Furthermore, from the viewpoint of improving visibility of exposed portions, the leuco colorant having a phthalide structure or a fluoran structure is more preferably a compound represented by any of Formula (Le-4) to Formula (Le-6), and even more preferably a compound represented by Formula (Le-5).

[0476] In Formula (Le-4) to Formula (Le-6), ERG each independently represent an electron-donating group, X₁ to X₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, Y₁ and Y₂ each independently represent C or N, X₁ does not exist in a case where Y₁ is N, X₄ does not exist in a case where Y₂ is N, Ra₁ represents a hydrogen atom, an alkyl group, or an alkoxy group, and Rb₁ to Rb₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group.

[0477] ERG, X₁ to X₄, Y₁, Y₂, Ra₁, and Rb₁ to Rb₄ in Formula (Le-4) to Formula (Le-6) have the same definitions as ERG, X₁ to X₄, Y₁, Y₂, Ra₁, and Rb₁ to Rb₄ in Formula (Le-1) to Formula (Le-3) respectively, and preferred aspects thereof are also the same.

[0478] Furthermore, from the viewpoint of improving visibility of exposed portions, the leuco colorant having a phthalide structure or a fluoran structure is more preferably a compound represented by any of Formula (Le-7) to Formula (Le-9), and particularly preferably a compound represented by Formula (Le-8).

[0479] In Formula (Le-7) to Formula (Le-9), X₁ to X₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, Y₁ and Y₂ each independently represent C or N, X₁ does not exist in a case where Y₁ is N, X₄ does not exist in a case where Y₂ is N, Ra₁ to Ra₄ each independently represent a hydrogen atom, an alkyl group, or an alkoxy group, Rb₁ to Rb₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group, and Rc₁ and Rc₂ each independently represent an aryl group or a heteroaryl group.

[0480] X₁ to X₄, Y₁, and Y₂ in Formula (Le-7) to Formula (Le-9) have the same definition as X₁ to X₄, Y₁, and Y₂ in Formula (Le-1) to Formula (Le-3) respectively, and preferred aspects thereof are also the same.

[0481] From the viewpoint of improving visibility of exposed portions,Ra₁ to Ra₄ in Formula (Le-7) or Formula (Le-9) preferably each independently represent an alkyl group or an alkoxy group, more preferably each independently represent an alkoxy group, and particularly preferably each independently represent a methoxy group.

[0482] From the viewpoint of improving visibility of exposed portions, Rb₁ to Rb₄ in Formula (Le-7) to Formula (Le-9) preferably each independently represent a hydrogen atom, an alkyl group, or an aryl group substituted with an alkyl group or alkoxy group, more preferably each independently represent a hydrogen atom or an alkyl group, and particularly preferably each independently represent a hydrogen atom or a methyl group.

[0483] From the viewpoint of improving visibility of exposed portions, Rc₁ and Rc₂ in Formula (Le-8) preferably each independently represent a phenyl group or an alkylphenyl group, and more preferably each independently represent a phenyl group.

[0484] In Formula (Le-8), from the viewpoint of improving visibility of exposed portions, X₁ to X₄ preferably each represent a hydrogen atom, and Y₁ and Y₂ preferably each represent C.

[0485] From the viewpoint of improving visibility of exposed portions, Rb₁ and Rb₂ in Formula (Le-8) preferably each independently represent a hydrogen atom, an alkyl group, or an aryl group substituted with an alkyl group or an alkoxy group, more preferably each independently represent a hydrogen atom or an alkyl group.

[0486] Furthermore, it is also preferable that Rb₁, Rb₂, Rc₁, and Rc₂ in Formula (Le-8) have the following aspects.

[0487] From the viewpoint of color developability and visibility of exposed portions, Rb₁ and Rb₂ in Formula (Le-8) preferably each independently represent an aryl group or a heteroaryl group, more preferably each independently represent an aryl group, even more preferably each independently represent an aryl group having an electron-donating group, and particularly preferably each independently represent a phenyl group having an electron-donating group at the para position.

[0488] From the viewpoint of color developability and visibility of exposed portions, Rc₁ and Rc₂ in Formula (Le-8) preferably each independently represent an aryl group having a substituent at at least one ortho position or a heteroaryl group having a substituent at at least one ortho position, more preferably each independently represent an aryl group having a substituent at at least one ortho position, even more preferably each independently represent a phenyl group having a substituent at at least one ortho position, and particularly preferably each independently represent a phenyl group having a substituent at at least one ortho position and having an electron-donating group at the para position. Examples of the substituent in Rc₁ and Rc₂ include substituents that will be described later.

[0489] In addition, Rc₁ and Rb₁ as well as Rc₂ and Rb₁ in Formula (Le-8) may be each independently bonded at the ortho position to form a ring (for example, a carbazole ring).

[0490] From the viewpoint of color developability and visibility of exposed portions, the electron-donating group in Rb₁, Rb₂, Rc₁, and Rc₂ is preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkyl monoarylamino group, a monoalkyl monoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoaryl monoheteroarylamino group, an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, more preferably an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, and particularly preferably an alkoxy group.

[0491] From the viewpoint of color developability and visibility of exposed portions, the color developing agent (preferably the acid color developing agent) is preferably the aforementioned leuco colorant having a phthalide structure or a fluoran structure, which is a compound represented by Formula (Le-10).

[0492] In Formula (Le-10), Ar₁ each independently represents an aryl group or a heteroaryl group, and Ar₂ each independently represents an aryl group having a substituent at at least one ortho position or a heteroaryl group having a substituent at at least one ortho position.

[0493] Preferred aspects of Ar₁ in Formula (Le-10) are the same as the preferred aspects of Rb₁ and Rb₂ in Formula (Le-8).

[0494] Preferred aspects of Ar₂ in Formula (Le-10) are the same as the preferred aspects of Rc₁ and Rc₂ in Formula (Le-8).

[0495] The alkyl group in Formula (Le-1) to Formula (Le-9) may be linear or branched or may have a ring structure.

[0496] The number of carbon atoms in the alkyl group in Formula (Le-1) to Formula (Le-9) is preferably 1 to 20, more preferably 1 to 8, even more preferably 1 to 4, and particularly preferably 1 or 2.

[0497] The number of carbon atoms in the aryl group in Formula (Le-1) to Formula (Le-10) is preferably 6 to 20, more preferably 6 to 10, and particularly preferably 6 to 8.

[0498] Specific examples of the aryl group in Formula (Le-1) to Formula (Le-10) include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, and the like which may have a substituent.

[0499] Specific examples of the heteroaryl group in Formula (Le-1) to Formula (Le-10) include a furyl group, a pyridyl group, a pyrimidyl group, a pyrazoyl group, a thiophenyl group, and the like which may have a substituent.

[0500] Each of the groups in Formula (Le-1) to Formula (Le-9), such as a monovalent organic group, an alkyl group, an aryl group, a heteroaryl group, a dialkylanilino group, an alkylamino group, and an alkoxy group, may have a substituent.

[0501] Examples of the substituent in Formula (Le-1) to Formula (Le-10) include an alkyl group, an aryl group, a heteroaryl group, a halogen atom, an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkyl monoarylamino group, a monoalkyl monoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoaryl monoheteroarylamino group, a hydroxy group, an alkoxy group, an aryloxy group, a heteroaryloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a heteroaryloxycarbonyl group, a cyano group, and the like. These substituents may be further substituted with these substituents.

[0502] Specific examples of the leuco colorant having a phthalide structure or a fluoran structure that are suitably used include compounds (S-1) to (S-21).

[0503] As the acid color developing agent, commercially available products can also be used. Examples of commercially available products of the acid color developing agent include ETAC, RED500, RED520, CVL, S-205, BLACK305, BLACK400, BLACK100, BLACK500, H-7001, GREEN300, NIRBLACK78, BLUE220, H-3035, BLUE203, ATP, H-1046, and H-2114 (all manufactured by Fukui Yamada Chemical Co., Ltd.), ORANGE-DCF, Vermilion-DCF, PINK-DCF, RED-DCF, BLMB, CVL, GREEN-DCF, and TH-107 (all manufactured by Hodogaya Chemical Co., Ltd.), ODB, ODB-2, ODB-4, ODB-250, ODB-BlackXV, Blue-63, Blue-502, GN-169, GN-2, Green-118, Red-40, and Red-8 (all manufactured by Yamamoto Chemicals, Inc.), crystal violet lactone (manufactured by Tokyo Chemical Industry Co., Ltd.), and the like.

[0504] Among these commercially available products, ETAC, S-205, BLACK305, BLACK400, BLACK100, BLACK500, H-7001, GREEN300, NIRBLACK78, H-3035, ATP, H-1046, H-2114, GREEN-DCF, Blue-63, GN-169, and crystal violet lactone are preferable because these form a film (that is, an image-recording layer) having excellent visible light absorbance.

[0505] As the leuco colorant, from the viewpoint of improving visibility of exposed portions, for example, the following compound can also be suitably used.

[0506] One kind of color developing agent may be used alone, or two or more kinds of color developing agents may be used in combination.

[0507] The content of the color developing agent with respect to the total mass of the image-recording layer is preferably 0.5% by mass to 10% by mass, and more preferably 1% by mass to 5% by mass.

[0508] The image-recording layer may contain components other than the components described above.

[0509] Examples of components other than the components described above include a colorant, a bakeout agent, a polymerization inhibitor, a higher fatty acid derivative, a plasticizer, inorganic fine particles, and a low-molecular-weight hydrophilic compound described in paragraphs "0181" to "0190" of JP2009-255434A, and the like.

[0510] Examples components other than the components described above also include a hydrophilic precursor (fine particles capable of converting the image-recording layer into a hydrophobic image-recording layer in a case where heat is applied thereto), a low-molecular-weight hydrophilic compound, an oil sensitizing agent (for example, a phosphonium compound, a nitrogen-containing low-molecular-weight compound, or an ammonium group-containing polymer), and a chain transfer agent described in paragraphs "0191" to "0217" of JP2012-187907A, and the like.

[Formation of image-recording layer]

[0511] The image-recording layer in the lithographic printing plate precursor according to the present disclosure can be formed, for example, by preparing a coating liquid by dispersing or dissolving the necessary components described above in a known solvent, coating a support with the coating liquid by a known method such as bar coating, and drying the coating liquid, as described in paragraphs "0142" and "0143" of JP2008-195018A.

[0512] As the solvent to be used in the coating liquid, known solvents can be used. Specific examples thereof include water, acetone, methyl ethyl ketone (2-butanone), cyclohexane, ethyl acetate, ethylene dichloride, tetrahydrofuran, toluene, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, acetyl acetone, cyclohexanone, diacetone alcohol, ethylene glycol monomethyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether acetate, 1-methoxy-2-propanol, 3-methoxy-1-propanol, methoxy methoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, 3-methoxypropyl acetate, N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, methyl lactate, ethyl lactate, and the like.

[0513] One kind of solvent may be used alone, or two or more kinds of solvents may be used in combination.

[0514] The concentration of solid contents in the coating liquid is preferably 1% by mass to 50% by mass.

[0515] The coating amount (solid content) of the image-recording layer after coating and drying varies with uses. However, from the viewpoint of obtaining excellent sensitivity and excellent film characteristics of the image-recording layer, the coating amount is preferably 0.3 g/m² to 3.0 g/m².

[0516] The film thickness of the image-recording layer in the lithographic printing plate precursor according to the present disclosure is preferably 0.1 µm to 3.0 µm, and more preferably 0.3 µm to 2.0 µm.

<Support>

[0517] The lithographic printing plate precursor according to the present disclosure has a support.

[0518] The support to be used can be appropriately selected from known supports for a lithographic printing plate precursor.

[0519] As the support, a support having a hydrophilic surface (hereinafter, also called "hydrophilic support") is preferable.

[0520] As the support in the present disclosure, an aluminum plate is preferable which has been roughened using a known method and has undergone an anodization treatment. That is, the support in the present disclosure preferably has an aluminum plate and an anodic oxide film of aluminum disposed on the aluminum plate.

[Preferred aspect of support]

[0521] One of the examples of preferred aspects of the support used in the present disclosure (the aluminum support according to this example is also called "support (1)") is as below.

[0522] That is, the support (1) has an aluminum plate and an anodic oxide film of aluminum disposed on the aluminum plate, the anodic oxide film is at a position closer to a side of the image-recording layer than the aluminum plate and has micropores extending in a depth direction from the surface of the anodic oxide film on the side of the image-recording layer, and the average diameter of the micropores within the surface of the anodic oxide film is more than 10 nm and 100 nm or less.

[0523] The value of brightness L* of surface of anodic oxide film on the image-recording layer side in the L*a*b* color system is preferably 70 to 100.

[0524] Fig. 1 is a schematic cross-sectional view of an embodiment of an aluminum support 12a.

[0525] The aluminum support 12a has a laminated structure in which an aluminum plate 18 and an anodic oxide film 20a of aluminum (hereinafter, also simply called "anodic oxide film 20a") are laminated in this order. The anodic oxide film 20a in the aluminum support 12a is positioned such that the anodic oxide film 20a is closer to the image-recording layer side than the aluminum plate 18. That is, it is preferable that the lithographic printing plate precursor according to the present disclosure have at least an anodic oxide film, an image-recording layer, and an outermost layer in this order on an aluminum plate.

-Anodic oxide film-

[0526] Hereinafter, preferred aspects of the anodic oxide film 20a will be described.

[0527] The anodic oxide film 20a is a film prepared on a surface of the aluminum plate 18 by an anodization treatment. This film has uniformly distributed ultrafine micropores 22a approximately perpendicular to the surface of the film. The micropores 22a extend from a surface of the anodic oxide film 20a on the image-recording layer side (a surface of the anodic oxide film 20a opposite to the aluminum plate 18) along the thickness direction (toward the aluminum plate 18).

[0528] The average diameter (average opening diameter) of the micropores 22a within the surface of the anodic oxide film 20a is preferably more than 10 nm and 100 nm or less. Particularly, from the viewpoint of balance between printing durability, antifouling properties, and image visibility, the average diameter of the micropores 22a is more preferably 15 nm to 60 nm, even more preferably 20 nm to 50 nm, and particularly preferably 25 nm to 40 nm. The internal diameter of the pores may be larger or smaller than the pore diameter within the surface layer.

[0529] In a case where the average diameter is more than 10 nm, printing durability and image visibility are further improved. Furthermore, in a case where the average diameter is 100 nm or less, printing durability is further improved.

[0530] The average diameter of the micropores 22a is determined by observing the surface of the anodic oxide film 20a with a field emission scanning electron microscope (FE-SEM) at 150,000X magnification (N = 4), measuring the size (diameter) of 50 micropores existing in a range of 400 nm × 600 nm in the obtained 4 images, and calculating the arithmetic mean thereof.

[0531] In a case where the shape of the micropores 22a is not circular, the equivalent circular diameter is used. "Equivalent circular diameter" is a diameter determined on an assumption that the opening portion is in the form of a circle having the same projected area as the projected area of the opening portion.

[0532] The depth of the micropores 22a is not particularly limited, but is preferably 10 nm to 3,000 nm, more preferably 50 nm to 2,000 nm, and even more preferably 300 nm to 1,600 nm.

[0533] The depth is a value obtained by taking a photograph (150,000X magnification) of a cross section of the anodic oxide film 20a, measuring the depths of 25 or more micropores 22a, and calculating the average thereof.

[0534] The shape of the micropores 22a is not particularly limited. In Fig. 2, the micropores 22a have a substantially straight tubular shape (substantially cylindrical shape). However, the micropores 22a may have a conical shape that tapers along the depth direction (thickness direction). The shape of the bottom portion of the micropores 22a is not particularly limited, and may be a curved (convex) or flat surface shape.

[0535] In the L*a*b* color system, the value of brightness L* of the surface of the aluminum support 12a on the image-recording layer side (surface of the anodic oxide film 20a on the image-recording layer side) is preferably 70 to 100. Especially, the value of brightness L* is preferably 75 to 100 and more preferably 75 to 90, because printing durability and image visibility are better balanced in this range.

[0536] The brightness L* is measured using a color difference meter Spectro Eye manufactured by X-Rite, Incorporated.

[0537] For example, an aspect is also preferable in which the micropores in the support (1) are each composed of a large diameter portion that extends to a position at a depth of 10 nm to 1,000 nm from the surface of the anodic oxide film and a small diameter portion that is in communication with the bottom portion of the large diameter portion and extends to a position at a depth of 20 nm to 2,000 nm from a communicate position, an average diameter of the large diameter portion within the surface of the anodic oxide film is 15 nm to 100 nm, and an average diameter of the small diameter portion at a communicate position is 13 nm or less (hereinafter, the support according to this aspect will be also called "support (2)").

[0538] Fig. 2 is a schematic cross-sectional view of an embodiment of the aluminum support 12a that is different from what is shown in Fig. 1.

[0539] In Fig. 2, an aluminum support 12b includes an aluminum plate 18 and an anodic oxide film 20b having micropores 22b each composed of a large diameter portion 24 and a small diameter portion 26.

[0540] The micropores 22b in the anodic oxide film 20b are each composed of the large diameter portion 24 that extends to a position at a depth of 10 nm to 1,000 nm (depth D: see

[0541] Fig. 2) from the surface of the anodic oxide film and the small diameter portion 26 that is in communication with the bottom portion of the large diameter portion 24 and further extends from the communicate position to a position at a depth of 20 nm to 2,000 nm.

[0542] The details of the large diameter portion 24 and the small diameter portion 26 are as described in, for example, paragraphs "0107" to "0114" of JP2019-162855A, and the aspects thereof are also applicable to the present disclosure.

[Manufacturing method of aluminum support]

[0543] As the manufacturing method of the aluminum support in the present disclosure, for example, a manufacturing method is preferable in which the following steps are sequentially performed.

·Roughening treatment step: step of performing roughening treatment on aluminum plate

·Anodization treatment step: step of subjecting aluminum plate having undergone roughening treatment to anodization

·Pore widening treatment step: step of bringing aluminum plate having anodic oxide film obtained by anodization treatment step into contact with aqueous acid solution or aqueous alkali solution such that diameter of micropores in anodic oxide film increases

[0544] Hereinafter, the procedure of each step will be specifically described.

(Roughening treatment step)

[0545] The roughening treatment step is a step of performing a roughening treatment including an electrochemical roughening treatment on the surface of the aluminum plate. It is preferable that this step be performed before the anodization treatment step that will be described later. However, in a case where the surface of the aluminum plate already has a preferred surface shape, the roughening treatment step may not be performed.

[0546] The roughening treatment for the aluminum plate can be carried out by the method described in paragraphs "0086" to "0101" of JP2019-162855A.

(Anodization treatment step)

[0547] The procedure of the anodization treatment step is not particularly limited as long as the aforementioned micropores can be obtained. Examples thereof include known methods.

[0548] In the anodization treatment step, an aqueous solution of sulfuric acid, phosphoric acid, oxalic acid, or the like can be used as an electrolytic cell. For example, the concentration of sulfuric acid is 100 g/L to 300 g/L.

[0549] The conditions of the anodization treatment are appropriately set depending on the electrolytic solution used. For example, the liquid temperature is 5°C to 70°C (preferably 10°C to 60°C), the current density is 0.5 A/dm² to 60 A/dm² (preferably 5 A/dm² to 60 A/dm²), the voltage is 1 V to 100 V (preferably 5 V to 50 V), the electrolysis time is 1 second to 100 seconds (preferably 5 seconds to 60 seconds), and the film amount is 0.1 g/m² to 5 g/m² (preferably 0.2 g/m² to 3 g/m²).

(Pore widening treatment)

[0550] The pore widening treatment is a treatment of enlarging the diameter of micropores (pore diameter) present in the anodic oxide film formed by the aforementioned anodization treatment step (pore diameter enlarging treatment).

[0551] The pore widening treatment can be carried out by bringing the aluminum plate obtained by the anodization treatment step into contact with an aqueous acid solution or an aqueous alkali solution. The contact method is not particularly limited, and examples thereof include a dipping method and a spraying method.

<Undercoat layer>

[0552] The lithographic printing plate precursor according to the present disclosure preferably has an undercoat layer (also called interlayer in some cases) between the image-recording layer and the support. The undercoat layer enhances the adhesiveness between the support and the image-recording layer in an exposed portion, and enables the image-recording layer to be easily peeled from the support in a non-exposed portion. Therefore, the undercoat layer inhibits the deterioration of printing durability and contributes to the improvement of developability. Furthermore, in the case of exposure to infrared laser, the undercoat layer functions as a heat insulating layer and thus brings about an effect of preventing sensitivity reduction resulting from the diffusion of heat generated by exposure to the support.

[Polymer]

[0553] Examples of compounds that are used in the undercoat layer include polymers having adsorbent group that can be adsorbed onto the surface of the support and hydrophilic groups. In order to improve adhesiveness to the image-recording layer, polymers having adsorbent groups and hydrophilic groups plus crosslinking groups are preferable. The compounds that are used in the undercoat layer may be low-molecular-weight compounds or polymers. As necessary, as the compounds that are used in the undercoat layer, two or more kinds of compounds may be used by being mixed together.

[0554] In a case where the compound used in the undercoat layer is a polymer, a copolymer of a monomer having an adsorbent group, a monomer having a hydrophilic group, and a monomer having a crosslinking group is preferable.

[0555] As the adsorbent group that can be adsorbed onto the surface of the support, a phenolic hydroxyl group, a carboxy group, -PO₃H₂, -OPO₃H₂, -CONHSO₂-, -SO₂NHSO₂-, and -COCH₂COCH₃ are preferable. As the hydrophilic groups, a sulfo group or salts thereof and salts of a carboxy group are preferable. As the crosslinking groups, an acryloyl group, a methacryloyl group, an acrylamide group, a methacrylamide group, an allyl group, and the like are preferable.

[0556] The polymer may have a crosslinking group introduced by the formation of a salt of a polar substituent of the polymer and a compound that has a substituent having charge opposite to that of the polar substituent and an ethylenically unsaturated bond, or may be further copolymerized with monomers other than the monomers described above and preferably with hydrophilic monomers.

[0557] Specifically, for example, silane coupling agents having addition polymerizable ethylenic double bond reactive groups described in JP1998-282679A (JP-H10-282679A) and phosphorus compounds having ethylenic double bond reactive groups described in JP1990-304441A (JP-H02-304441A) are suitable. The low-molecular-weight compounds or polymer compounds having crosslinking groups (preferably ethylenically unsaturated bonding groups), functional groups that interact with the surface of the support, and hydrophilic groups described in JP2005-238816A, JP2005-125749A, JP2006-239867A, and JP2006-215263A are also preferably used.

[0558] For example, the high-molecular-weight polymers having adsorbent groups that can be adsorbed onto the surface of the support, hydrophilic groups, and crosslinking groups described in JP2005-125749A and JP2006-188038A are more preferable.

[0559] The content of ethylenically unsaturated bonding group in the polymer used in the undercoat layer is preferably 0.1 mmol to 10.0 mmol per gram of the polymer, and more preferably 0.2 mmol to 5.5 mmol per gram of the polymer.

[0560] The weight-average molecular weight (Mw) of the polymer used in the undercoat layer is preferably 5,000 or more, and more preferably 10,000 to 300,000.

[Hydrophilic compound]

[0561] From the viewpoint of developability, it is preferable that the undercoat layer contain a hydrophilic compound.

[0562] The hydrophilic compound is not particularly limited, and known hydrophilic compounds used for the undercoat layer can be used.

[0563] Preferred examples of the hydrophilic compound include phosphonic acids having an amino group such as carboxymethyl cellulose and dextrin, an organic phosphonic acid, an organic phosphoric acid, an organic phosphinic acid, amino acids, a hydrochloride of an amine having a hydroxy group, and the like.

[0564] In addition, examples of preferable hydrophilic compounds include a compound having an amino group or a functional group capable of inhibiting polymerization and a group that interacts with the surface of the support (for example, 1,4-diazabicyclo[2.2.2]octane (DABCO), 2,3,5,6-tetrahydroxy-p-quinone, chloranil, sulfophthalic acid, ethylenediaminetetraacetic acid (EDTA) or a salt thereof, hydroxyethyl ethylenediaminetriacetic acid or a salt thereof, dihydroxyethyl ethylenediaminediacetic acid or a salt thereof, hydroxyethyl iminodiacetic acid or a salt thereof, and the like).

[0565] From the viewpoint of scratch and contamination suppressiveness, it is preferable that the hydrophilic compound include hydroxycarboxylic acid or a salt thereof.

[0566] Furthermore, from the viewpoint of scratch and contamination suppressiveness, it is preferable that the hydrophilic compound, which is preferably hydroxycarboxylic acid or a salt thereof, be contained in a layer on the aluminum support. The layer on the aluminum support is preferably a layer on the side where the image-recording layer is formed or a layer in contact with the aluminum support.

[0567] Preferred examples of the layer on the aluminum support include a layer in contact with the aluminum support, such as the undercoat layer or the image-recording layer. Furthermore, a layer other than the layer in contact with the aluminum support, for example, the outermost layer or the image-recording layer may contain a hydrophilic compound and preferably contains hydroxycarboxylic acid or a salt thereof.

[0568] In the lithographic printing plate precursor according to the present disclosure, from the viewpoint of scratch and contamination suppressiveness, it is preferable that the image-recording layer contain hydroxycarboxylic acid or a salt thereof.

[0569] Moreover, regarding the lithographic printing plate precursor according to the present disclosure, for example, an aspect is also preferable in which the surface of the aluminum support on the image-recording layer side is treated with a composition (for example, an aqueous solution or the like) containing at least hydroxycarboxylic acid or a salt thereof. In a case where the above aspect is adopted, at least some of the hydroxycarboxylic acid or a salt thereof used for treatment can be detected in a state of being contained in the layer on the image-recording layer side (for example, the image-recording layer or the undercoat layer) that is in contact with the aluminum support.

[0570] In a case where the layer on the side of the image-recording layer that is in contact with the aluminum support, such as the undercoat layer, contains hydroxycarboxylic acid or a salt thereof, the surface of the aluminum support on the image-recording layer side can be hydrophilized, and it is easy for the surface of the aluminum support on the image-recording layer side to have a water contact angle of 110° or less measured by an airborne water droplet method, which result in excellent scratch and contamination suppressiveness.

[0571] "Hydroxycarboxylic acid" is the generic term for organic compounds having one or more carboxy groups and one or more hydroxy groups in one molecule. These compounds are also called hydroxy acid, oxy acid, oxycarboxylic acid, or alcoholic acid (see Iwanami Dictionary of Physics and Chemistry, 5th Edition, published by Iwanami Shoten, Publishers. (1998)).

[0572] The hydroxycarboxylic acid or a salt thereof is preferably represented by Formula (HC).

        Formula (HC):     R^HC(OH)_mhc(COOM^HC)_nhc

[0573] In Formula (HC), R^HC represents an (mhc + nhc)-valent organic group, M^HC each independently represent a hydrogen atom, an alkali metal, or an onium, and mhc and nhc each independently represent an integer of 1 or more. In a case where n is 2 or more, Ms may be the same as or different from each other.

[0574] Examples of the (mhc + nhc)-valent organic group represented by R^HC in Formula (HC) include an (mhc + nhc)-valent hydrocarbon group and the like. The hydrocarbon group may have a substituent and/or a linking group.

[0575] Examples of the hydrocarbon group include an (mhc + nhc)-valent group derived from aliphatic hydrocarbon, such as an alkylene group, an alkanetriyl group, an alkanetetrayl group, an alkanepentayl group, an alkenylene group, an alkenetriyl group, an alkenetetrayl group, and alkenepentayl group, an alkynylene group, an alkynetriyl group, alkynetetrayl group, or an alkynepentayl group, an (mhc + nhc)-valent group derived from aromatic hydrocarbon, such as an arylene group, an arenetriyl group, an arenetetrayl group, or an arenepentayl group, and the like. Examples of the substituent include an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group, and the like. Specific examples of the substituent include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a hexadecyl group, an octadecyl group, eicosyl group, isopropyl group, isobutyl group, s-butyl group, t-butyl group, isopentyl group, a neopentyl group, a 1-methylbutyl group, an isohexyl group, a 2-ethylhexyl group, a 2-methylhexyl group, a cyclohexyl group, a cyclopentyl group, a 2-norbornyl group, a methoxymethyl group, a methoxyethoxyethyl group, an allyloxymethyl group, a phenoxymethyl group, an acetyloxymethyl group, a benzoyloxymethyl group, a benzyl group, a phenethyl group, an α-methylbenzyl group, a 1-methyl-1-phenylethyl group, a p-methylbenzyl group, a cinnamyl group, an allyl group, a 1-propenylmethyl group, a 2-butenyl group, a 2-methylallyl group, a 2-methylpropenylmethyl group, a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a phenyl group, a biphenyl group, a naphthyl group, a tolyl group, a xylyl group, a mesityl group, a cumenyl group, a methoxyphenyl group, an ethoxyphenyl group, a phenoxyphenyl group, an acetoxyphenyl group, a benzoyloxyphenyl group, a methoxycarbonylphenyl group, an ethoxycarbonylphenyl group, a phenoxycarbonylphenyl group, and the like. Furthermore, the linking group is composed of at least one atom selected from the group consisting of a hydrogen atom, a carbon atom, an oxygen atom, a nitrogen atom, a sulfur atom, and a halogen atom, and the number of atoms is preferably 1 to 50. Specific examples thereof include an alkylene group, a substituted alkylene group, an arylene group, a substituted arylene group, and the like. The linking group may have a structure in which a plurality of these divalent groups is linked through any of an amide bond, an ether bond, a urethane bond, a urea bond, and an ester bond.

[0576] Examples of the alkali metal represented by M^HC include lithium, sodium, potassium, and the like. Among these, sodium is particularly preferable. Examples of the onium include ammonium, phosphonium, sulfonium, and the like. Among these, ammonium is particularly preferable.

[0577] From the viewpoint of scratch and contamination suppressiveness, M^HC is preferably an alkali metal or an onium, and more preferably an alkali metal.

[0578] The sum of mhc and nhc is preferably 3 or more, more preferably 3 to 8, and even more preferably 4 to 6.

[0579] The molecular weight of the hydroxycarboxylic acid or a salt thereof is preferably 600 or less, more preferably 500 or less, and particularly preferably 300 or less. The molecular weight is preferably 76 or more.

[0580] Specifically, examples of the hydroxycarboxylic acid constituting the hydroxycarboxylic acid or a salt of the hydroxycarboxylic acid include gluconic acid, glycolic acid, lactic acid, tartronic acid, hydroxybutyrate (such as 2-hydroxybutyrate, 3-hydroxybutyrate, or γ-hydroxybutyrate), malic acid, tartaric acid, citramalic acid, citric acid, isocitric acid, leucine acid, mevalonic acid, pantoic acid, ricinoleic acid, ricineraidic acid, cerebronic acid, quinic acid, shikimic acid, a monohydroxybenzoic acid derivative (such as salicylic acid, creosotic acid (homosalicylic acid, hydroxy(methyl) benzoate), vanillic acid, or syringic acid), a dihydroxybenzoic acid derivative (such as pyrocatechuic acid, resorcylic acid, protocatechuic acid, gentisic acid, or orsellinic acid), a trihydroxybenzoic acid derivative (such as gallic acid), a phenyl acetate derivative (such as mandelic acid, benzilic acid, or atrolactic acid), a hydrocinnamic acid derivative (such as melilotic acid, phloretic acid, coumaric acid, umbellic acid, caffeic acid, ferulic acid, sinapic acid, cerebronic acid, or carminic acid), and the like.

[0581] Among these, as the aforementioned hydroxycarboxylic acid or a hydroxycarboxylic acid constituting a salt of the hydroxycarboxylic acid, from the viewpoint of scratch and contamination suppressiveness, a compound having two or more hydroxy groups is preferable, a compound having 3 or more hydroxy groups is more preferable, a compound having 5 or more hydroxy groups is even more preferable, and a compound having 5 to 8 hydroxy groups is particularly preferable.

[0582] Furthermore, as a hydroxycarboxylic acid having one carboxy group and two or more hydroxy groups, gluconic acid or shikimic acid is preferable.

[0583] As hydroxycarboxylic acid having two or more carboxy groups and one hydroxy group, citric acid or malic acid is preferable.

[0584] As hydroxycarboxylic acid having two or more carboxy groups and two or more hydroxy groups, tartaric acid is preferable.

[0585] Among these, gluconic acid is particularly preferable as the aforementioned hydroxycarboxylic acid.

[0586] One kind of hydrophilic compound may be used alone, or two or more kinds of hydrophilic compounds may be used in combination.

[0587] In a case where the undercoat layer contains a hydrophilic compound (preferably hydroxycarboxylic acid or a salt thereof), the content of the hydrophilic compound (preferably hydroxycarboxylic acid or a salt thereof) with respect to the total mass of the undercoat layer is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 40% by mass, and particularly preferably 1.0% by mass to 30% by mass.

[0588] The undercoat layer may contain, in addition to the compounds for an undercoat layer described above, a chelating agent, a secondary or tertiary amine, a polymerization inhibitor, and the like to prevent the contamination caused over time.

[0589] The undercoat layer can be formed by dissolving the aforementioned necessary components in a known solvent to prepare a coating liquid, coating a support with the coating liquid by a known method, and drying the coating liquid.

[0590] The coating amount (solid content) of the undercoat layer is preferably 0.1 mg/m² to 300 mg/m², and more preferably 5 mg/m² to 200 mg/m².

[0591] The lithographic printing plate precursor according to the present disclosure may have other layers in addition to those described above.

[0592] Known layers can be adopted as those other layers without particular limitations. For example, as necessary, a backcoat layer may be provided on a surface of the support that is opposite to the image-recording layer side.

«Manufacturing method of lithographic printing plate precursor»

[0593] The lithographic printing plate precursor according to the present disclosure is preferably manufactured by a manufacturing method including a step of forming an image-recording layer on a support by the aforementioned method and forming an outermost layer on the formed image-recording layer by the following method.

[0594] The step of forming an outermost layer is the aforementioned method of forming an outermost layer, that is, a step of coating an image-recording layer formed on a support with a coating liquid having a concentration of solid contents of 5% by mass to 30% by mass, and drying the obtained coating film under drying condition 70°C to 200°C and 5 seconds to 30 seconds to form an outermost layer.

[0595] Details of the step of forming an outermost layer will not be described again because the step is described above in the section of Method of forming outermost layer.

[0596] With this manufacturing method of a lithographic printing plate precursor, it is easy to obtain a lithographic printing plate precursor in which the decomposition rate of an infrared absorber by exposure to ozone is 50% or less.

<<Method of preparing lithographic printing plate and lithographic printing method>>

[0597] It is possible to prepare a lithographic printing plate by performing image exposure and a development treatment on the lithographic printing plate precursor according to the present disclosure.

[0598] The method of preparing a lithographic printing plate according to the present disclosure preferably includes a step of exposing the lithographic printing plate precursor according to the present disclosure in the shape of an image (hereinafter, this step will be also called "exposure step") and a step of removing the image-recording layer in a non-image area by supplying at least one material selected from the group consisting of a printing ink and dampening water on a printer (hereinafter, this step will be also called "on-press development step").

[0599] The lithographic printing method according to the present disclosure preferably includes a step of exposing the lithographic printing plate precursor according to the present disclosure in the shape of an image (exposure step), a step of removing the image-recording layer in a non-image area on a printer by supplying at least one material selected from the group consisting of a printing ink and dampening water such that a lithographic printing plate is prepared (on-press development step), and a step of performing printing by using the obtained lithographic printing plate (hereinafter, also called "printing step").

[0600] Hereinafter, regarding the method of preparing a lithographic printing plate according to the present disclosure and the lithographic printing method according to the present disclosure, preferred aspects of each step will be described in order. Note that the lithographic printing plate precursor according to the present disclosure can also be developed using a developer.

[0601] Hereinafter, the exposure step and the on-press development step in the method of preparing a lithographic printing plate will be described. The exposure step in the method of preparing a lithographic printing plate according to the present disclosure is the same step as the exposure step in the lithographic printing method according to the present disclosure. Furthermore, the on-press development step in the method of preparing a lithographic printing plate according to the present disclosure is the same step as the on-press development step in the lithographic printing method according to the present disclosure.

<Exposure step>

[0602] The method of preparing a lithographic printing plate according to the present disclosure preferably includes an exposure step of exposing the lithographic printing plate precursor according to the present disclosure in the shape of an image such that an exposed portion and a non-exposed portion are formed. The lithographic printing plate precursor according to the present disclosure is preferably exposed to a laser through a transparent original picture having a linear image, a halftone dot image, or the like or exposed in the shape of an image by laser light scanning according to digital data or the like.

[0603] The wavelength of a light source to be used is preferably 750 nm to 1,400 nm. As the light source having a wavelength of 750 nm to 1,400 nm, a solid-state laser or a semiconductor laser that radiates infrared is suitable. In a case where an infrared laser is used, the output is preferably 100 mW or higher, the exposure time per pixel is preferably 20 microseconds or less, and the amount of irradiation energy is preferably 10 mJ/cm² to 300 mJ/cm². In addition, in order to shorten the exposure time, a multibeam laser device is preferably used. The exposure mechanism may be any one of an in-plane drum method, an external surface drum method, a flat head method, or the like.

[0604] The image exposure can be carried out by a common method using a platesetter or the like. In the case of on-press development, image exposure may be carried out on a printer after the lithographic printing plate precursor is mounted on the printer.

<On-press development step>

[0605] The method of preparing a lithographic printing plate according to the present disclosure preferably includes an on-press development step of removing the image-recording layer in a non-image area by supplying at least one selected from the group consisting of printing ink and dampening water on a printer.

[0606] Hereinafter, the on-press development method will be described.

[On-press development method]

[0607] In the on-press development method, the lithographic printing plate precursor having undergone image exposure is preferably supplied with an oil-based ink and an aqueous component on a printer, such that the image-recording layer in a non-image area is removed and a lithographic printing plate is prepared.

[0608] That is, in a case where the lithographic printing plate precursor is subjected to image exposure and then directly mounted on a printer without being subjected to any development treatment, or in a case where the lithographic printing plate precursor is mounted on a printer, then subjected to image exposure on the printer, and then supplied with an oil-based ink and an aqueous component for printing, at the initial stage in the middle of printing, in a non-image area, a non-cured image-recording layer is removed by either or both of the supplied oil-based ink and the aqueous component by means of dissolution or dispersion, and the hydrophilic surface is exposed in the non-image area. On the other hand, in an exposed portion, the image-recording layer cured by exposure forms an oil-based ink-receiving portion having a lipophilic surface. What is supplied first to the surface of the plate may be any of the oil-based ink or the aqueous component. However, in view of preventing the plate from being contaminated by the components of the image-recording layer from which aqueous components are removed, it is preferable that the oil-based ink be supplied first. In the manner described above, the lithographic printing plate precursor is subjected to on-press development on a printer and used as it is for printing a number of sheets. As the oil-based ink and the aqueous component, ordinary printing ink and ordinary dampening water for lithographic printing are suitably used.

[0609] As the laser used for performing image exposure on the lithographic printing plate precursor according to the present disclosure, a light source having a wavelength of 300 nm to 450 nm or 750 nm to 1,400 nm is preferably used. A light source of 300 nm to 450 nm is preferable for a lithographic printing plate precursor including an image-recording layer containing sensitizing dye having maximum absorption in such a wavelength range. As the light source of 750 nm to 1,400 nm, those described above are preferably used. As the light source of 300 nm to 450 nm, a semiconductor laser is suitable.

<Printing step>

[0610] The lithographic printing method according to the present disclosure includes a printing step of printing a recording medium by supplying a printing ink to the lithographic printing plate.

[0611] The printing ink is not particularly limited, and various known inks can be used as desired. In addition, preferable examples of the printing ink include oil-based ink or ultraviolet-curable ink (UV ink).

[0612] In the printing step, as necessary, dampening water may be supplied.

[0613] Furthermore, the printing step may be successively carried out after the on-press development step without stopping the printer.

[0614] The recording medium is not particularly limited, and known recording media can be used as desired.

[0615] In the method of preparing a lithographic printing plate from the lithographic printing plate precursor according to the present disclosure and in the lithographic printing method according to the present disclosure, as necessary, the entire surface of the lithographic printing plate precursor may be heated as necessary before exposure, in the middle of exposure, or during a period of time from exposure to development. In a case where the lithographic printing plate precursor is heated as above, an image-forming reaction in the image-recording layer is accelerated, which can result in advantages such as improvement of sensitivity and printing durability, stabilization of sensitivity, and the like. Heating before development is preferably carried out under a mild condition of 150°C or lower. In a case where this aspect is adopted, it is possible to prevent problems such as curing of a non-image area. For heating after development, it is preferable to use an extremely severe condition which is preferably in a range of 100°C to 500°C. In a case where this aspect is adopted, a sufficient image-strengthening action is obtained, and it is possible to inhibit problems such as the deterioration of the support or the thermal decomposition of the image area.

Examples

[0616] Hereinafter, the present disclosure will be specifically described based on examples, but the present disclosure is not limited thereto. In the present examples, unless otherwise specified, "%" and "part" mean "% by mass" and "part by mass" respectively. Unless otherwise described, the molecular weight of a polymer compound is a weight-average molecular weight (Mw), and the ratio of repeating constitutional units of a polymer compound is expressed as molar percentage. The weight-average molecular weight (Mw) is a polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC).

<Preparation of support>

(Preparation of support (1))

[0617] An aluminum alloy plate made of a material 1S having a thickness of 0.3 mm was subjected to (A-a) Mechanical roughening treatment (brush grain method) to (A-i) Desmutting treatment in aqueous acidic solution described in paragraphs "0126" to "0134" of JP2012-158022A.

[0618] Then, an anodic oxide film was formed by performing (A-j) First-stage anodization treatment to (A-m) Third-stage anodization treatment described in paragraphs "0135" to "0138" of JP2012-158022A by appropriately adjusting the treatment conditions, and the obtained support was used as a support (1).

[0619] A rinsing treatment was performed between all the treatment steps. After the rinsing treatment, water was drained using a nip roller.

[0620] The details of the obtained support (1) are as below.

[0621] Support (1): value of brightness L* of surface of anodic oxide film having micropores in L*a*b* color system: 83, average diameter of large diameter portion of micropores within surface of oxide film: 35 nm (depth 100 nm), average diameter of small diameter portion of micropores at communicate position: 10 nm (depth 1,000 nm), ratio of depth of large diameter portion to average diameter of large diameter portion: 2.9

(Preparation of support (2))

(a) Alkaline etching treatment

[0622] An aqueous solution of caustic soda having a caustic soda concentration of 26% by mass and an aluminum ion concentration of 6.5% by mass was sprayed onto the aluminum plate at a temperature of 70°C, thereby performing an etching treatment. Then, rinsing was performed by means of spraying. The amount of dissolved aluminum within the surface to be subjected to the electrochemical roughening treatment later was 5 g/m².

(b) Desmutting treatment using aqueous acidic solution (first desmutting treatment)

[0623] Next, a desmutting treatment was performed using an aqueous acidic solution. In the desmutting treatment, a 150 g/L aqueous sulfuric acid solution was used as the aqueous acidic solution. The liquid temperature was 30°C. The desmutting treatment was performed for 3 seconds by spraying the aqueous acidic solution onto the aluminum plate. Then, a rinsing treatment was performed.

(c) Electrochemical roughening treatment

[0624] Next, an electrochemical roughening treatment was performed using alternating current and an electrolytic solution having a hydrochloric acid concentration of 14 g/L, an aluminum ion concentration of 13 g/L, and a sulfuric acid concentration of 3 g/L. The liquid temperature of the electrolytic solution was 30°C. The aluminum ion concentration was adjusted by adding aluminum chloride.

[0625] The waveform of the alternating current was a sine wave in which positive and negative waveforms are symmetrical, the frequency was 50 Hz, the ratio of the anodic reaction time and the cathodic reaction time in one cycle of the alternating current was 1:1, and the current density was 75 A/dm² in terms of the peak current value of the alternating current waveform. In addition, the quantity of electricity was 450 C/dm² which was the total quantity of electricity used for the aluminum plate to have an anodic reaction, and the electrolysis treatment was performed 4 times by conducting electricity of 112.5 C/dm² for 4 seconds at each treatment session. A carbon electrode was used as the counter electrode of the aluminum plate. Then, a rinsing treatment was performed.

(d) Desmutting treatment using aqueous acidic solution

[0626] Next, a desmutting treatment was performed using an aqueous acidic solution. Specifically, the desmutting treatment was performed for 3 seconds by spraying the aqueous acidic solution onto the aluminum plate. In the desmutting treatment, an aqueous solution having a sulfuric acid concentration of 170 g/L and an aluminum ion concentration of 5 g/L was used as aqueous acidic solution. The liquid temperature was 30°C.

(e) Anodization treatment

[0627] By using an anodization device for direct current electrolysis, an anodization treatment was performed in a sulfuric acid solution such that the amount of an oxide film was 3.6 g/m².

[0628] By the above method, a support (2) was prepared.

(Preparation of support (3))

[0629] A Hydro 1052 aluminum alloy strip or web (available from Norsk Hydro ASA, Norway) having a thickness of 0.28 mm was used as an aluminum-containing support.

[0630] Both the pre-etching and post-etching steps were performed in an alkaline solution under known conditions. Roughening (or graining) was performed by electrochemical means in a hydrochloric acid solution at about 23°C, such that a calculated average roughness (Ra) of 0.5 µm was obtained on the plane of the aluminum-containing support. These treatment steps were performed in a continuous process on a typical manufacturing line used for manufacturing a lithographic printing plate precursor.

[0631] Then, the obtained aluminum-containing support having undergone graining and etching was washed with water, dried, and cut into aluminum-containing sheets having undergone graining and etching.

[0632] Each of the sheets was anodized twice. Each of the anodization treatment baths contained about 100 L of an anodization solution. During the first anodization, each sheet was treated for 21.3 seconds under the conditions of an electrolyte concentration of 175 g/L, a temperature of 60°C, and a current density of 5.8 A/dm². During the second anodization, each sheet was treated for 18 seconds under the conditions of an electrolyte concentration of 280 g/L, a temperature of 23°C, and a current density of 10 A/dm². The first anodization process for forming an outer aluminum oxide layer was performed using phosphoric acid as an electrolyte, and the second anodization process for forming an inner aluminum oxide layer was performed using sulfuric acid as an electrolyte.

[0633] By the above method, a support (3) was prepared.

(Preparation of support (4))

[0634] In order to remove the rolling oil on the surface of an aluminum plate (material: JIS A 1050) having a thickness of 0.3 mm, the aluminum plate was subjected to a degreasing treatment at 50°C for 30 seconds by using a 10% by mass aqueous sodium aluminate solution. Then, by using three bundled nylon brushes having a bristle diameter of 0.3 mm and a water suspension of pumice having a median diameter of 25 µm (specific gravity: 1.1 g/cm³), graining was performed on the surface of the aluminum, and then the aluminum plate was thoroughly rinsed with water. The plate was etched by being immersed in a 25% by mass aqueous sodium hydroxide solution at 45°C for 9 seconds, rinsed with water, then further immersed in a 20% by mass aqueous nitric acid solution at 60°C for 20 seconds, and rinsed with water. At this time, the amount of the grained surface etched was about 3 g/m².

[0635] Then, an electrochemical roughening treatment was continuously performed using an alternating current voltage of 60 Hz. At this time, a 1% by mass aqueous nitric acid solution was used as an electrolytic solution (containing 0.5% by mass of aluminum ions), and the liquid temperature was 50°C. By using a light source of alternating current having a trapezoidal rectangular waveform and a carbon electrode as a counter electrode, an electrochemical roughening treatment was performed under the conditions of a time TP taken for the current value to reach the peak from zero of 0.8 msec and the duty ratio of 1:1. As an auxiliary anode, ferrite was used. The current density was 30 A/dm² in terms of the peak value of current, and 5% of the current coming from the power source was allowed to flow into the auxiliary anode. The quantity of electricity during the nitric acid electrolysis was 175 C/dm², which was the quantity of electricity used when the aluminum plate was an anode. Then, rinsing was performed by means of spraying.

[0636] Subsequently, by using a 0.5% by mass aqueous solution of hydrochloric acid (containing 0.5% by mass of aluminum ions) at a liquid temperature of 50°C as an electrolytic solution, an electrochemical roughening treatment was performed by the same method as the nitric acid electrolysis under the condition of a quantity of electricity of 50 C/dm² that was used when the aluminum plate was an anode. Then, the aluminum plate was rinsed with water by spraying.

[0637] Thereafter, by using a 15% by mass sulfuric acid (containing 0.5% by mass of aluminum ions) as an electrolytic solution, a 2.5 g/m² direct current anodic oxide film was provided on the plate at a current density of 15 A/dm², followed by rinsing with water and drying, thereby preparing a support A.

[0638] Subsequently, in order to ensure the hydrophilicity of the non-image area, the support A was treated with silicate at 60°C for 10 seconds by using a 2.5% by mass aqueous solution of No. 3 sodium silicate and then rinsed with water, thereby obtaining a support (4). The amount of Si adhered was 10 mg/m². The centerline average roughness (Ra) of the support (4) measured using a needle having a diameter of 2 µm was 0.51 µm.

<Preparation of coating liquid for undercoat layer>

(Preparation of coating liquid (1) for undercoat layer)

[0639] A coating liquid (1) for an undercoat layer having the following composition was prepared.

·Compound for undercoat layer (the following (P-1), 11% aqueous solution): 0.10502 parts

·Sodium gluconate: 0.07000 parts

·Surfactant (EMALEX 710 (registered trademark), NIHON EMULSION Co., Ltd.): 0.00159 parts

·Preservative (BIOHOPE L, manufactured by K·I Chemical Industry Co., LTD.): 0.00149 parts

·Water: 2.87190 parts

(Preparation of coating liquid (2) for undercoat layer)

[0640] A coating liquid (2) for an undercoat layer having the following composition was prepared.

·Compound for undercoat layer (the above (P-1), 11% aqueous solution): 0.10502 parts

·Hydroxyethyl diiminodiacetic acid: 0.01470 parts

·Sodium ethylenediaminetetraacetate: 0.06575 parts

·Surfactant (EMALEX 710 (registered trademark), NIHON EMULSION Co., Ltd.): 0.00159 parts

·Preservative (BIOHOPE L, manufactured by K·I Chemical Industry Co., LTD.): 0.00149 parts

·Water: 2.86144 parts

(Preparation of coating liquid (3) for undercoat layer)

[0641] A coating liquid (3) for an undercoat layer having the following composition was prepared.

·Compound for undercoat layer (the following (P-2)): 0.18 parts

·Hydroxyethyl iminodiacetic acid: 0.10 parts

·Methanol: 55.24 parts

·Water: 6.15 parts

<Composition of coating liquid for image-recording layer>

(Preparation of coating liquid (1-1) for image-recording layer)

[0642] A mixed solution obtained by mixing together the following components other than a microgel liquid 1 was mixed with the microgel liquid 1 immediately before coating, followed by stirring, thereby preparing a coating liquid (1-1) for an image-recording layer.

·Infrared absorber IR-1 (the following structure, HOMO: -5.35 eV, LUMO: -3.75 eV): 0.02000 parts

·Color developing agent S-1 (the following structure): 0.02500 parts

·Electron-accepting polymerization initiator Int-1 (the following structure, HOMO: -6.70 eV, LUMO: -3.08 eV): 0.11000 parts

·Electron-donating polymerization initiator TPB (the following structure, HOMO: -5.90 eV): 0.02500 parts

·Polymerizable compound M-1 (obtained by the following synthesis method): 0.27500 parts

·Anionic surfactant A-1 (the following structure): 0.00600 parts

·Fluorine-based surfactant W-1 (the following structure): 0.00416 parts

· 2-Butanone: 4.3602 parts

·1-Methoxy-2-propanol: 4.4852 parts

·Methanol: 2.2838 parts

·Microgel liquid 1 (obtained by the following preparation method): 2.3256 parts

(Preparation of coating liquid (1-2) for image-recording layer)

[0643] A coating liquid (1-2) for an image-recording layer was prepared in the same manner as in the preparation of the coating liquid (1-1) for an image-recording layer, except that a color developing agent S-3 (the following structure) was used instead of a color developing agent S-1.

(Preparation of coating liquid (1-3) for image-recording layer)

[0644] A coating liquid (1-3) for an image-recording layer was prepared in the same manner as in the preparation of the coating liquid (1-1) for an image-recording layer, except that a color developing agent S-4 (the following structure) was used instead of a color developing agent S-1.

(Preparation of coating liquid (2-1) for image-recording layer)

[0645] A mixed solution obtained by mixing together the following components other than a microgel liquid 2 was mixed with the microgel liquid 2 immediately before coating, followed by stirring, thereby preparing a coating liquid (2-1) for an image-recording layer.

·Infrared absorber IR-1 (the following structure, HOMO: -5.35 eV, LUMO: -3.75 eV): 0.00600 parts

·Infrared absorber IR-2 (the following structure, HOMO: -5.31 eV, LUMO: -3.78 eV): 0.0200 parts

·Color developing agent S-1 (the following structure): 0.02500 parts

·Electron-accepting polymerization initiator Int-1 (the following structure, HOMO: -6.70 eV, LUMO: -3.08 eV): 0.11000 parts

·Electron-donating polymerization initiator TPB (the following structure, HOMO: -5.90 eV): 0.02500 parts

·Polymerizable compound M-1 (obtained by the following synthesis method): 0.27500 parts

·Anionic surfactant A-1 (the following structure): 0.09000 parts

·Fluorine-based surfactant W-1 (the following structure): 0.00416 parts

· 2-Butanone: 4.9200 parts

·1-Methoxy-2-propanol: 3.1000 parts

·Methanol: 2.7900 parts

·Microgel liquid 2 (obtained by the following preparation method): 2.90700 parts

(Preparation of coating liquid (2-2) for image-recording layer)

[0646] A coating liquid (2-2) for an image-recording layer was prepared in the same manner as in the preparation of the coating liquid (2-1) for an image-recording layer, except that a color developing agent S-3 (the following structure) was used instead of the color developing agent S-1.

(Preparation of coating liquid (2-3) for image-recording layer)

[0647] A coating liquid (2-3) for an image-recording layer was prepared in the same manner as in the preparation of the coating liquid (2-1) for an image-recording layer, except that a color developing agent S-4 (the following structure) was used instead of the color developing agent S-1.

(Preparation of coating liquid (3) for image-recording layer)

[0648] A coating liquid (3) for an image-recording layer was prepared by mixing together the following components.

• Electron-accepting polymerization initiator Int-2 (the following structure, HOMO: -6.96 eV, LUMO: -3.18 eV): 0.060 parts
• Infrared absorber IR-3 (the following structure, HOMO: -5.43 eV, LUMO: -3.95 eV): 0.026 parts
• Electron-donating polymerization initiator TPB (the following structure, HOMO: -5.90 eV): 0.050 parts
• Polymerizable compound M-2 (the following structure): 0.250 parts
• Polymerizable compound M-3 (the following structure): 0.250 parts
• Binder polymer BP-1 (the following structure, S-LEC BX-5 (Z), SEKISUI CHEMICAL CO., LTD.: 0.150 parts
• 1-Methoxy-2-propanol: 4.988 parts
• 2-Butanone: 9.262 parts

(Preparation of coating liquid (4) for image-recording layer)

[0649] A coating liquid (4) for an image-recording layer was prepared by mixing together the following components.

·Electron-accepting polymerization initiator Int-3 (the following structure, HOMO: -7.34 eV, LUMO: -3.26 eV): 0.041 parts

·Infrared absorber IR-4 (the following structure, HOMO: -5.42 eV, LUMO: -3.82 eV): 0.027 parts

·Infrared absorber IR-5 (the following structure, HOMO: -5.43 eV, LUMO: -3.84 eV): 0.015 parts

·Polymerizable compound M-4 (the following structure): 0.100 parts

·Polymerizable compound M-5 (the following structure): 0.096 parts

·Polymerizable compound M-6 (the following structure): 0.096 parts

·Polymer particles PP-1 (particles containing polymer having the following structure, average particle diameter 100 µm): 0.300 parts

·Color developing agent S-2 (the following structure): 0.041 parts

·Hydroxypropyl cellulose: 0.030 parts

·n-Propanol: 5.168 parts

· 2-Butanone: 6.460 parts

·1-Methoxy-2-propanol: 1.615 parts

·Methanol: 2.907 parts

[0650] Details of each component used in each of the coating liquids for an image-recording layer that was described above or will be described later are as follows.

[0651] In BP-1, l is 72 mol%, m is 1 mol%, n is 27 mol%, and the weight-average molecular weight is 130,000.

[0652] In PP-1, n is 40, and the weight-average molecular weight is 90,000.

[0653] Int-3 is a mixture of compounds formed of each of the following two types of iodonium cation structures and the following counteranion (that is, a tetraphenylborate ion).

[Synthesis of polymerizable compound M-1]

[0654] A mixed solution of 4.7 parts by mass of TAKENATE D-160N (polyisocyanate trimethylolpropane adduct, manufactured by Mitsui Chemicals, Inc.), ARONIX M-403 (manufactured by TOAGOSEI CO., LTD.) in an amount yielding the ratio of NCO value of TAKENATE D-160N:hydroxyl number of ARONIX M-403 = 1:1, 0.02 parts by mass of t-butylbenzoquinone, and 11.5 parts by mass of methyl ethyl ketone was heated at 65°C. NEOSTANN U-600 (bismuth-based polycondensation catalyst, manufactured by NITTO KASEI CO., LTD., 0.11 parts by mass) was added to the reaction solution, and the reaction solution was heated at the same temperature for 4 hours. The reaction solution was cooled to room temperature (25°C), and methyl ethyl ketone was added thereto, thereby synthesizing a urethane acrylate solution having a solid content of 50% by mass.

[0655] Then, by using recycling GPC (instrument: LC908-C60, column: JAIGEL-1H-40 and 2H-40 (manufactured by Japan Analytical Industry Co., Ltd.)) and tetrahydrofuran (THF) as an eluent, molecular weight fractionation of the urethane acrylate solution was performed. The weight-average molecular weight of the obtained polymerizable compound M-1 was 20,000.

[Preparation of microgel liquid 1]

-Preparation of polyvalent isocyanate compound-

[0656] Bismuth tris(2-ethylhexanoate) (NEOSTAN U-600, manufactured by NITTO KASEI CO., LTD., 0.043 parts) was added to an ethyl acetate (25.31 g) suspension solution of 17.78 parts (80 molar equivalents) of isophorone diisocyanate and 7.35 parts (20 molar equivalents) of polyhydric phenol compound (1), and the obtained solution was stirred. The reaction temperature was set to 50°C at a point in time when heat release subsided, and the solution was stirred for 3 hours, thereby obtaining an ethyl acetate solution of the polyvalent isocyanate compound (1) (50% by mass).

-Preparation of microgel-

[0657] The following oil-phase components and water-phase components were mixed together and emulsified at 12,000 rpm for 10 minutes by using a homogenizer. The obtained emulsion was stirred at 45°C for 4 hours, a 10% by mass aqueous solution of 5.20 g of 1,8-diazabicyclo[5.4.0]undec-7-ene-octylate (U-CAT SA102, manufactured by San-Apro Ltd.) was added thereto, and the solution was stirred at room temperature for 30 minutes and left to stand at 45°C for 24 hours. Distilled water was added thereto such that the concentration of solid contents was adjusted to 20% by mass, thereby obtaining an aqueous dispersion of a microgel 1 (that is, the microgel liquid 1). The average particle diameter of the microgel 1 measured by a light scattering method was 0.28 µm.

-Oil-phase component-

[0658] 

(Component 1) ethyl acetate: 12.0 parts

(Component 2) an adduct obtained by addition of trimethylolpropane (6 molar equivalents), xylene diisocyanate (18 molar equivalents), and polyoxyethylene having one methylated terminal (1 molar equivalent, the number of repeating oxyethylene units: 90) (50% by mass ethyl acetate solution, manufactured by Mitsui Chemicals, Inc.): 3.76 parts

(Component 3) polyvalent isocyanate compound (1) (as 50% by mass ethyl acetate solution): 15.0 parts

(Component 4) 65% by mass ethyl acetate solution of dipentaerythritol pentaacrylate (SR-399, manufactured by Sartomer Company Inc.): 11.54 parts

(Component 5) 10% ethyl acetate solution of sulfonate type surfactant (PIONIN A-41-C, manufactured by TAKEMOTO OIL & FAT Co., Ltd.): 4.42 parts

-Water-phase component-

[0659] Distilled water: 46.87 parts

[Preparation of microgel liquid 2]

-Preparation of oil-phase component-

[0660] A polyfunctional isocyanate compound (PM-200: manufactured by Wanhua Chemical Group Co., Ltd.: 6.66 g, a 50% by mass ethyl acetate solution of "TAKENATE (registered trademark) D-116N (adduct of trimethylolpropane (TMP), m-xylylene diisocyanate (XDI), and polyethylene glycol monomethyl ether (EO90) (following structure)" manufactured by Mitsui Chemicals, Inc.: 5.46 g, a 65% by mass ethyl acetate solution of dipentaerythritol pentaacrylate (SR-399, manufactured by Sartomer Company Inc.): 11.24 g, ethyl acetate: 14.47 g, and PIONIN (registered trademark) A-41-C manufactured by TAKEMOTO OIL & FAT Co., Ltd.: 0.45 g were mixed together and stirred at room temperature (25°C) for 15 minutes, thereby obtaining an oil-phase component.

-Preparation of water-phase component-

[0661] As a water-phase component, 47.2 g of distilled water was prepared.

-Microcapsule forming step-

[0662] The oil-phase component and the water-phase component were mixed together, and the obtained mixture was emulsified at 12,000 rpm for 16 minutes by using a homogenizer, thereby obtaining an emulsion.

[0663] Distilled water (16.8 g) was added to the obtained emulsion, and the obtained liquid was stirred at room temperature for 10 minutes.

[0664] After stirring, the liquid was heated at 45°C, and stirred for 4 hours in a state of being kept at 45°C such that ethyl acetate was distilled away from the liquid. Then, a 10% by mass aqueous solution of 5.12 g of 1,8-diazabicyclo[5.4.0]undec-7-ene-octylate (U-CAT SA102, manufactured by San-Apro Ltd.) was added thereto, and the solution was stirred at room temperature for 30 minutes and left to stand at 45°C for 24 hours. Distilled water was added thereto such that the concentration of solid contents was adjusted to 20% by mass, thereby obtaining an aqueous dispersion of a microgel 2. The microgel 2 had a volume average particle diameter of 165 nm that was measured using a laser diffraction/scattering-type particle diameter distribution analyzer LA-920 (manufactured by HORIBA, Ltd.).

[0665] The obtained aqueous dispersion of the polymer particles 2 was designated as a microgel liquid 2.

(Preparation of coating liquid (5) for image-recording layer)

[0666] A mixed solution obtained by mixing together the following components other than a microgel liquid 3 was mixed with the microgel liquid 3 immediately before coating, followed by stirring, thereby preparing a coating liquid (5) for an image-recording layer.

·Binder polymer BP-2 (the following structure): 0.240 parts

·Infrared absorber IR-6 (the following structure, HOMO: -5.38 eV, LUMO: -3.70 eV): 0.030 parts

·Polymerization initiator Int-4 (the following structure, HOMO: -6.70 eV, LUMO: -3.08 eV): 0.162 parts

·Polymerizable compound: 0.192 parts

·Tris(acryloyloxyethyl)isocyanurate, NK ESTER A-9300, SHIN-NAKAMURA CHEMICAL CO, LTD.

·Low-molecular-weight hydrophilic compound (tris(2-hydroxyethyl) isocyanurate): 0.062 parts

·Low-molecular-weight hydrophilic compound A-1 (the following structure): 0.050 parts

·Oil sensitizing agent C-1 (the following structure): 0.055 parts

·Oil sensitizing agent (benzyl-dimethyl-octylammonium·PF₆ salt): 0.018 parts

·Oil sensitizing agent C-2 (the following structure, reduced specific viscosity: 44 ml/g): 0.035 parts

·Fluorine-based surfactant W-1 (the above structure): 0.008 parts

·2-Butanone: 1.091 parts

·1-Methoxy-2-propanol: 8.609 parts

·Microgel liquid 3 (obtained by the following preparation method): 5.065 parts

[0667] Details of each component used in the coating liquid (5) for an image-recording layer are as follows.

[Preparation of microgel liquid 3]

[0668] As oil-phase components, 10 g of an adduct of trimethylolpropane and xylene diisocyanate (manufactured by Mitsui Chemicals & SKC Polyurethanes Inc., TAKENATE D-110N), 3.15 g of pentaerythritol triacrylate (manufactured by Nippon Kayaku Co., Ltd., SR444), and 0.1 g of PIONIN A-41C (manufactured by TAKEMOTO OIL & FAT CO., LTD.) were dissolved in 17 g of ethyl acetate. As a water-phase component, 40 g of a 4% by mass aqueous solution of polyvinyl alcohol (PVA-205 manufactured by KURARAY CO., LTD.) was prepared.

[0669] The oil-phase components and water-phase components were mixed together and emulsified at 12,000 rpm for 10 minutes by using a homogenizer. The obtained emulsion was added to 25 g of distilled water, stirred at room temperature for 30 minutes, and then stirred at 50°C for 3 hours. The microgel liquid obtained in this way was diluted with distilled water such that the concentration of solid contents thereof was 15% by mass.

[0670] The average particle diameter of the microgel measured by a light scattering method was 0.2 µm.

[0671] The microgel liquid (2.640 parts) obtained in this way was mixed with 2.425 parts of distilled water, thereby obtaining a microgel liquid 3.

<Preparation of coating liquid for outermost layer>

[0672] The components shown in the following Table 1 were mixed together, thereby obtaining coating liquids (1) to (27) for an outermost layer.

[0673] Details of the various components used in Table 1 will be shown below.

-Water-soluble polymer-

[0674] 

·GOHSENX L-3266: sulfonic acid-modified polyvinyl alcohol having the following structure, GOHSENX (registered trademark) L-3266 manufactured by Mitsubishi Chemical Corporation.

·GOHSENX CKS-50: sulfonic acid-modified polyvinyl alcohol having the following structure, GOHSENX (registered trademark) CKS-50 manufactured by Mitsubishi Chemical Corporation.

·Water-soluble polymer 1: polymer having the following structure

·Mowiol 4-88: polyvinyl alcohol particles having a saponification degree of 88 mol%, Mowiol (registered trademark) 4-88 manufactured by Sigma-Aldrich Inc.

·METOLOSE SM04: methyl cellulose (methoxy group substitution degree 1.8), METOLOSE (registered trademark) SM04 manufactured by Shin-Etsu Chemical Co., Ltd.

·METOLOSE SM15: methyl cellulose (methoxy group substitution degree 1.8, high viscosity), METOLOSE (registered trademark) SM15 manufactured by Shin-Etsu Chemical Co., Ltd.

·METOLOSE 60SH 50: hydroxypropylmethyl cellulose (methoxy group substitution degree 1.9), METOLOSE (registered trademark) 60SH 50 manufactured by Shin-Etsu Chemical Co., Ltd.

·CELLOGEN F 5A: sodium carboxymethyl cellulose, manufactured by DKS Co. Ltd., CELLOGEN (registered trademark) F 5A

·PENON JE-66: modified starch, manufactured by NIPPON STARCH CHEMICAL CO., LTD.

-Hydrophobic polymer-

[0675] 

·FINE SPHERE FS-102: aqueous dispersion of styrene-acrylic resin particles having the following structure, glass transition temperature Tg 103°C, softening point 225°C, FINE SPHERE (registered trademark) FS-102 manufactured by Nipponpaint Industrial Coatings Co., LTD.

·POLYMARON 385: dispersion of styrene-acrylic resin, POLYMARON 385 manufactured by Arakawa Chemical Industries, Ltd.

·AQUAMAT 263: high-density oxidized polyethylene wax dispersion, AQUAMAT (registered trademark) 263 manufactured by BYK.

·TAKESEAL PCeco primer: emulsion of styrene-acrylic resin, manufactured by Takebayashi Chemical Industry Co., Ltd.

·Diofan A50: aqueous polyvinylidene chloride dispersion, Diofan (registered trademark) A50 manufactured by Solvin S.A.

·Diofan A602: polyvinylidene chloride dispersion, Diofan (registered trademark) A602 manufactured by Solvin S.A.

-Other components-

[0676] 

·Microgel liquid 2: microgel liquid 2 described above

·Decomposition-type infrared absorber 1: compound having the following structure

[Examples 1 to 29 and Comparative Examples 1 and 2]

[0677] The lithographic printing plate precursors of Examples 1 to 29 and Comparative Examples 1 and 2 were prepared by the following method.

[0678] The support described in Table 2 was coated with a coating liquid for an undercoat layer described in Table 2 such that the dry coating amount was 20 mg/m², thereby forming an undercoat layer.

[0679] Then, the undercoat layer was bar-coated with the coating liquid for an image-recording layer described in Table 2 such that the dry coating amount was 1.0 g/m², followed by drying in an oven at 120°C for 40 seconds, thereby forming an image-recording layer.

[0680] For the lithographic printing plate precursor having no undercoat layer, the support described in Table 2 was bar-coated with a coating liquid for an image-recording layer described in Table 2 under the same conditions as described above such that the dry coating amount was 1.0 g/m², thereby forming an image-recording layer.

[0681] The obtained image-recording layer was then bar-coated with the coating liquid for an outermost layer described in Table 2 such that the dry coating amount was 0.2 g/m², followed by drying in an oven under the drying conditions described in Table 2, thereby forming an outermost layer.

[0682] By the above method, an on-press development type lithographic printing plate precursor was obtained.

[0683] In the obtained on-press development type lithographic printing plate precursor, the film thickness of the outermost layer was in a range of 0.005 µm to 2 µm.

<Evaluation of lithographic printing plate precursor>

[Decomposition rate of infrared absorber]

[0684] For the obtained lithographic printing plate precursor, the decomposition rate of the infrared absorber in the image-recording layer was determined by the method described above.

[0685] The results are shown in Table 2.

[Evaluation on discoloration caused by exposure to ozone]

[0686] In determining the decomposition rate of the infrared absorber as described above, L*, a*, and b* of the sample not yet being exposed to ozone and L*, a*, and b* of the sample having been exposed to ozone are measured using a colorimeter (eXact from X-Rite, Incorporated.). From the obtained values of L^∗, a^∗, and b^∗, a color difference ΔE was calculated using the CIE 1976 color difference calculation formula. Based on the difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone, the discoloration of the lithographic printing plate precursor caused by exposure to ozone was evaluated according to the following standard. The results are shown in Table 2.

-Evaluation standard-

[0687] 

10: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is less than 0.5.

9: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 0.5 or more and less than 1.0.

8: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 1.0 or more and less than 1.5.

7: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 1.5 or more and less than 2.0.

6: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 2.0 or more and less than 2.5.

5: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 2.5 or more and less than 3.0.

4: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 3.0 or more and less than 3.5.

3: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 3.5 or more and less than 4.0.

2: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 4.0 or more and less than 4.5.

1: The difference between the color difference ΔE before exposure to ozone and the color difference ΔE after exposure to ozone is 4.5 or more.

[Oxygen permeability]

[0688] For the obtained lithographic printing plate precursor, the ratio of halftone dot area rate was calculated by the method described above to check whether or not the lithographic printing plate precursor has oxygen permeability.

[0689] The results are shown in Table 2.

[Evaluation of streak-like unevenness (swath unevenness)]

[0690] In a case of confirming the oxygen permeability, a streak-like unevenness (swath unevenness) was evaluated using the 1000th printed matter printed by the lithographic printing plate obtained from the lithographic printing plate precursor having the outermost layer.

[0691] More specifically, a 50% halftone dot chart portion of the FM screen of the 1000th printed matter was observed, and streak-like unevenness (swath unevenness) was evaluated according to the following standard. The results are shown in Table 2.

-Standard-

[0692] 

5: Swath unevenness cannot be visually confirmed with a 6X loupe.

4: Slight swath unevenness can be visually confirmed with a 6X loupe.

3: Apparent swath unevenness can be visually confirmed with a 6X loupe.

2: Slightly swath unevenness can be visually confirmed.

1: Apparent swath unevenness can be clearly visually confirmed.

[On-press developability]

[0693] By using Magnus 800 Quantum manufactured by Kodak Japan Ltd. that was equipped with an infrared semiconductor laser, the prepared lithographic printing plate precursor was exposed under the conditions of output of 27 W, an outer drum rotation speed of 450 rpm, and a resolution of 2,400 dpi (irradiation energy equivalent to 110 mJ/cm²). The exposure image included a solid image and a 10% halftone dot chart of Amplitude Modulation Screen (AM screen).

[0694] The exposed precursor was mounted on a Kikuban-sized (636 mm × 939 mm) cylinder of a printer SX-74 manufactured by Heidelberger Druckmaschinen AG without being developed. This printer was connected to a 100 L-capacity dampening water circulation tank having a non-woven fabric filter and a temperature control device. A circulation device was filled with 80 L of dampening water containing 2.0% by mass of dampening water S-Z1 (manufactured by FUJIFILM Corporation), and an ultraviolet-curable ink T&K UV OFS K-HS black GE-M (manufactured by T&K TOKA CO., LTD.) was used as printing ink. The dampening water and ink were supplied by a standard automatic printing start method, and then printing was performed 500 sheets of TOKUBISHI art paper (ream weight: 76.5 kg, manufactured by MITSUBISHI PAPER MILLS LIMITED.) at a printing rate of 10,000 sheets/hour.

[0695] During printing, the number of printing papers used until no ink was transferred to a non-image area was measured as the on-press developability. It can be said that the smaller the number of printing papers, the better the on-press developability. The results are shown in Table 2.

[Table 2]

	Support No.	Coating liquid for undercoat layer No.	Coating liquid for image-recording layer No.	Coating liquid for outermost layer No.	Drying conditions of coating liquid for outermost layer		Decomposition rate of infrared absorber	Discoloration caused by exposure to ozone	Ratio of halftone dot area rate	Streak-like unevenness	On-press developability [number of sheets]
					Drying temperature	Drying time
Example 1	(1)	(1)	(1-1)	(1)	120°C	40 see	50%	4	0.94	3	10
Example 2	(1)	(1)	(1-1)	(2)	120°C	30 see	45%	5	0.94	3	10
Example 3	(1)	(1)	(1-1)	(3)	120°C	20 see	40%	6	0.94	3	10
Example 4	(1)	(1)	(1-1)	(4)	120°C	20 see	45%	5	0.92	2	10
Example 5	(1)	(1)	(1-1)	(5)	120°C	20 see	45%	5	0.94	3	10
Example 6	(1)	(1)	(1-1)	(6)	120°C	20 see	45%	5	0.92	2	10
Example 7	(1)	(1)	(1-1)	(7)	120°C	20 see	35%	7	0.96	4	10
Example 8	(1)	(1)	(1-1)	(8)	120°C	20 see	35%	7	0.94	3	10
Example 9	(1)	(1)	(1-1)	(9)	120°C	20 see	35%	7	0.94	3	10
Example 10	(1)	(1)	(1-1)	(10)	120°C	20 see	40%	6	0.94	3	10
Example 11	(1)	(1)	(1-1)	(11)	120°C	20 see	35%	7	0.94	3	10
Example 12	(1)	(1)	(1-1)	(12)	120°C	20 see	35%	7	0.94	3	10
Example 13	(1)	(2)	(2-1)	(13)	120°C	20 see	30%	8	0.98	5	12
Example 14	(1)	(2)	(2-1)	(14)	120°C	20 see	40%	6	0.96	4	12
Example 15	(1)	(2)	(2-1)	(15)	120°C	20 see	30%	8	0.96	4	12
Example 16	(1)	(2)	(2-1)	(16)	120°C	20 see	30%	8	0.96	4	12
Example 17	(1)	(2)	(2-1)	(17)	120°C	20 see	35%	7	0.96	4	12
Example 18	(1)	(2)	(2-1)	(18)	120°C	20 see	35%	7	0.96	4	12
Example 19	(1)	(2)	(2-1)	(19)	120°C	20 see	35%	7	0.96	4	12
Example 20	(1)	(2)	(2-1)	(20)	120°C	20 see	35%	7	0.96	4	12
Example 21	(1)	(2)	(2-1)	(21)	120°C	20 see	20%	9	0.98	5	12
Example 22	(1)	(2)	(2-1)	(22)	120°C	20 see	10%	10	0.98	5	12
Example 23	(2)	-	(3)	(23)	120°C	20 see	20%	9	0.96	4	15
Example 24	(2)	-	(3)	(24)	120°C	20 see	20%	9	0.96	4	15
Example 25	(3)	-	(4)	(25)	120°C	20 see	35%	7	0.96	4	20
Example 26	(1)	(1)	(1-2)	(11)	120°C	20 see	35%	7	0.94	3	10
Example 27	(1)	(1)	(1-3)	(11)	120°C	20 see	35%	7	0.94	3	10
Example 28	(1)	(2)	(2-2)	(13)	120°C	20 see	30%	8	0.98	5	12
Example 29	(1)	(2)	(2-3)	(13)	120°C	20 see	30%	8	0.98	5	12
Comparative Example 1	(4)	(3)	(5)	(26)	120°C	60 see	80%	2	0.90	1	20
Comparative Example 2	(1)		(1-1)	(27)	120°C	20 see	80%	1	0.90	1	10

[0696] As is evident from Table 2, it has been revealed that discoloration caused by exposure to ozone is further suppressed in the lithographic printing plate precursors according to examples than in the lithographic printing plate precursors according to comparative examples.

[0697] In addition, the lithographic printing plate precursor according to examples has an outermost layer having oxygen permeability. It is considered that accordingly, the streak-like unevenness (swath unevenness) may be suppressed.

Explanation of References

[0698] 

18: aluminum plate

12a, 12b: aluminum support

20a, 20b: anodic oxide film

22a, 22b: micropore

24: large diameter portion

26: small diameter portion

[0699] The entirety of the disclosure of Japanese Patent Application No. 2020-095073 filed on May 29, 2020 and the disclosure of Japanese Patent Application No. 2021-002219 filed on January 8, 2021 is incorporated into the present specification by reference. All of documents, patent applications, and technical standards described in the present specification are incorporated into the present specification by reference to approximately the same extent as a case where it is specifically and respectively described that the respective documents, patent applications, and technical standards are incorporated by reference.

Claims

1. An on-press development type lithographic printing plate precursor comprising, in the following order:

a support;

an image-recording layer; and

an outermost layer,

wherein the image-recording layer contains a polymerization initiator, a polymerizable compound, and an infrared absorber, and

a decomposition rate of the infrared absorber after storage for 8 hours in an environment at an ozone concentration of 150 ppb is 50% or less.

2. The on-press development type lithographic printing plate precursor according to claim 1,
wherein a film thickness of the outermost layer is 0.005 µm to 2 µm.

3. The on-press development type lithographic printing plate precursor according to claim 1 or 2,
wherein the outermost layer has oxygen permeability.

4. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 3,
wherein the outermost layer contains a polysaccharide.

5. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 4,
wherein the outermost layer contains a cellulose derivative having a methoxy group substitution degree of 1 to 2.

6. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 5,
wherein the outermost layer further contains a hydrophobic polymer.

7. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 6,
wherein the outermost layer further contains polymer particles.

8. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 7,
wherein the outermost layer further contains a decomposition-type infrared absorber.

9. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 8,
wherein the polymerization initiator includes an electron-donating polymerization initiator and an electron-accepting polymerization initiator.

10. The on-press development type lithographic printing plate precursor according to claim 9,
wherein HOMO of the infrared absorber - HOMO of the electron-donating polymerization initiator is 0.70 eV or less.

11. The on-press development type lithographic printing plate precursor according to claim 9 or 10,
wherein LUMO of the electron-accepting polymerization initiator - LUMO of the infrared absorber is 0.80 eV or less.

12. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 11,
wherein the polymerizable compound includes a polymerizable compound having functionalities of 7 or more.

13. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 12,
wherein the polymerizable compound includes a polymerizable compound having functionalities of 10 or more.

14. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 13,
wherein the image-recording layer further contains polymer particles.

15. The on-press development type lithographic printing plate precursor according to claim 14,

wherein the polymer particles are addition polymerization-type polymer particles having a hydrophilic group, and

the hydrophilic group includes a group represented by Formula Z,

        Formula Z:     ^∗-Q-W-Y

in formula Z, Q represents a divalent linking group, W represents a divalent group having a hydrophilic structure or a divalent group having a hydrophobic structure, Y represents a monovalent group having a hydrophilic structure or a monovalent group having a hydrophobic structure, either W or Y has a hydrophilic structure, and * represents a bonding site with another structure.

16. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 15,
wherein the image-recording layer further contains a color developing agent.

17. The on-press development type lithographic printing plate precursor according to claim 16,

wherein the color developing agent is a compound represented by any of Formula (Le-1) to Formula (Le-3),

in Formula (Le-1) to Formula (Le-3), ERG's each independently represents an electron-donating group, X₁ to X₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, X₅ to X₁₀ each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, Y₁ and Y₂ each independently represent C or N, X₁ does not exist in a case where Y₁ is N, X₄ does not exist in a case where Y₂ is N, Ra₁ represents a hydrogen atom, an alkyl group, or an alkoxy group, and Rb₁ to Rb₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group.

18. The on-press development type lithographic printing plate precursor according to claim 16 or 17,

wherein the color developing agent is a compound represented by Formula (Le-8),

in Formula (Le-8), X₁ to X₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, Y₁ and Y₂ each independently represent C or N, X₁ does not exist in a case where Y₁ is N, X₄ does not exist in a case where Y₂ is N, Rb₁ and Rb₂ each independently represent an alkyl group, an aryl group, or a heteroaryl group, and Rc₁ and Rc₂ each independently represent an aryl group or a heteroaryl group.

19. The on-press development type lithographic printing plate precursor according to claim 18,
wherein Rc₁ and Rc₂ each independently represent a phenyl group that has a substituent at at least one ortho position and an electron-donating group at a para position.

20. The on-press development type lithographic printing plate precursor according to claim 16 or 17,

wherein the color developing agent includes a compound represented by Formula (Le-10),

in Formula (Le-10), Ar₁'s each independently represent an aryl group or a heteroaryl group, and Ar₂'s each independently represent an aryl group having a substituent at at least one ortho position or a heteroaryl group having a substituent at at least one ortho position.

21. The on-press development type lithographic printing plate precursor according to claim 20,
wherein Ar₁'s each independently represent an aryl group having an electron-donating group or a heteroaryl group having an electron-donating group, and Ar₂'s each independently represent a phenyl group having a substituent at at least one ortho position and an electron-donating group at a para position.

22. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 21,

wherein the support has an aluminum plate and an anodic oxide film of aluminum disposed on the aluminum plate,

the anodic oxide film is at a position closer to a side of the image-recording layer than the aluminum plate and has micropores extending in a depth direction from a surface of the anodic oxide film on the side of the image-recording layer,

an average diameter of the micropores within the surface of the anodic oxide film is more than 10 nm and 100 nm or less, and

in an L*a*b* color system, a value of brightness L* of the surface of the anodic oxide film on the side of the image-recording layer is 70 to 100.

23. The on-press development type lithographic printing plate precursor according to claim 22,

wherein the micropores are each composed of a large diameter portion that extends to a position at a depth of 10 nm to 1,000 nm from the surface of the anodic oxide film and a small diameter portion that is in communication with a bottom portion of the large diameter portion and extends to a position at a depth of 20 nm to 2,000 nm from a communicate position,

an average diameter of the large diameter portion within the surface of the anodic oxide film is 15 nm to 100 nm, and

an average diameter of the small diameter portion at the communicate position is 13 nm or less.

24. A method of preparing a lithographic printing plate, comprising:

a step of exposing the on-press development type lithographic printing plate precursor according to any one of claims 1 to 23 in a shape of an image; and

a step of supplying at least one material selected from the group consisting of a printing ink and dampening water on a printer to remove the image-recording layer in a non-image area.

25. A lithographic printing method, comprising:

a step of exposing the on-press development type lithographic printing plate precursor according to any one of claims 1 to 23 in a shape of an image;

a step of supplying at least one material selected from the group consisting of a printing ink and dampening water on a printer to remove the image-recording layer in a non-image area and to prepare a lithographic printing plate; and

a step of performing printing by using the obtained lithographic printing plate.

Drawing