FIELD OF THE INVENTION
[0001] The present invention relates to a method for making a lithographic printing plate
by exposing a heat-sensitive, negative working lithographic printing plate precursor
to infrared light, thereby forming a visible image immediately after the exposure.
BACKGROUND OF THE INVENTION
[0002] Lithographic printing presses use a so-called printing master such as a printing
plate which is mounted on a cylinder of the printing press. The master carries a lithographic
image on its surface and a print is obtained by applying ink to said image and then
transferring the ink from the master onto a receiver material, which is typically
paper. In conventional, so-called "wet" lithographic printing, ink as well as an aqueous
fountain solution (also called dampening liquid) are supplied to the lithographic
image which consists of oleophilic (or hydrophobic, i.e. ink-accepting, water-repelling)
areas as well as hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling)
areas. In so-called driographic printing, the lithographic image consists of ink-accepting
and ink-abhesive (ink-repelling) areas and during driographic printing, only ink is
supplied to the master.
[0003] Printing masters are generally obtained by the image-wise exposure and processing
of an imaging material called plate precursor. In addition to the well-known photosensitive,
so-called pre-sensitized plates, which are suitable for UV contact exposure through
a film mask, also heat-sensitive printing plate precursors have become very popular
in the late 1990s. Such thermal materials offer the advantage of daylight stability
and are especially used in the so-called computer-to-plate method wherein the plate
precursor is directly exposed, i.e. without the use of a film mask. The material is
exposed to heat or to infrared light and the generated heat triggers a (physico-)chemical
process, such as ablation, polymerization, insolubilization by crosslinking of a polymer,
heat-induced solubilization, or by particle coagulation of a thermoplastic polymer
latex.
[0004] Although some of these thermal processes enable plate making without wet processing,
the most popular thermal plates form an image by a heat-induced solubility difference
in an alkaline developer between exposed and non-exposed areas of the coating. The
coating typically comprises a hydrophobic layer of which the rate of dissolution in
the developer is either reduced (negative working) or increased (positive working)
by the image-wise exposure. During processing, the solubility differential leads to
the removal of the non-image (non-printing) areas of the coating, thereby revealing
the hydrophilic support, while the image (printing) areas of the coating remain on
the support.
[0005] Plates comprising an infrared-sensitized photopolymerizable or infrared-sensitized
photocurable coating are typical examples of negative-working thermal plates. Such
plates have been described in e.g. US4997745, US5514521, US5275917, EP-A 611997, US5705309
and EP-A 889363. Infrared-sensitized photopolymer plates which are especially designed
for on-press processing have been described in e.g. EP-A 1315998, US2002/177074, US6576401,
EP-A 1495866, EP-A 1506855 EP-A 1516724, EP-A 1518672 and EP-A 1520694. Such plates
are developed by mounting the exposed precursor on the plate cylinder of a lithographic
printing press and starting a press run : the non-exposed areas of the coating are
removed by the ink and/or fountain that is supplied to the plate.
[0006] It is beneficial that the exposed plate precursor shows a visible image even before
being processed, i.e. a print-out image. This enables the end-user to establish immediately
whether or not the precursor has already been exposed, to inspect the image quality
on the printing plate and to distinguish the different color selections. Photopolymer
plates that produce a print-out image are known in the art, e.g. as disclosed in US
3,359,109, US 3,042,515, US 4,258,123, US 4,139,390, US 5,141,839, US 5,141,842, US
4,232,106, US 4,425,424, US 5,030,548, US 4,598,036, EP 0 434 968, WO 96/35143 and
US 2003/68575. In these materials the print-out image formation is triggered by the
photoinitiating system which also induces the photopolymerization of the image-recording
layer. As a result, the print-out image formation leads to a reduced sensitivity of
the lithographic imaging process.
[0007] In thermal plates a color change can be obtained by the addition of a heat-decomposable
dye which is bleached upon heating. Such materials are disclosed in e.g. DD 213 530,
EP 897 134, EP 0 925 916, WO 96/35143, EP 1 300 241 and EP 1 508 440. Another approach
is followed in EP 0 925 916 and US 2004/134365 wherein IR dyes are disclosed of which
the light absorption changes upon IRradiation. In the latter prior art materials,
the IR dyes exhibit, beside strong absorption in IR wavelength range, also side-absorption
in the visible wavelength range. Due to IR-exposure the IR dye decomposes and a print-out
image is obtained by the reduction of this side-absorption in the visible wavelength
range.
[0008] A problem of these prior art materials is that the print-out image is formed by a
heat-induced reduction of the visible light absorption of the coating or by a switch
from a highly colored to a weakly colored coating. Such bleaching processes produce
print-out images which are characterized by a low contrast between the exposed and
the non-exposed areas. A better contrast can be obtained by forming -rather than bleaching-
a dye upon exposure or by a color switch from one hue to another upon exposure. Only
a few examples of lithographic printing plates using such systems are known in the
prior art. EP-A 1502736 discloses printing plates comprising a dye of which the absorption
maximum shifts by at least 50 nm upon heating. EP-A 1508440 discloses printing plates
comprising an infrared dye as light-to-heat converter and a dye precursor which forms
a visible color upon heating.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a method for making a lithographic
printing plate by means of a heat-sensitive precursor which forms a high contrast
print-out image immediately after exposure to infrared light. The combination of the
following essential features, as defined in claim 1, provide a solution for this object
:
- the support of the plate precursor is an aluminum support with a grained and anodized
surface that appears essentially white, i.e. which has CIE 1976 lightness values L*
higher than 70 and CIE 1976 color coordinates a* and b* each in the range from -4
to +4; these L*, a* and b* color coordinates of the support are referred to hereafter
as L*sup, a*sup and b*sup respectively.
- the visible light absorption of the coating on said support is low, so that the complete
material (i.e. support + coating) has a CIE 1976 lightness value L* which is not less
than 50; this lightness value of the coated support in the non-exposed state is referred
to hereafter as L*nonexp.
- a visible color is formed or changed by the exposure, whereby a print-out image is
formed of which the lightness difference ΔL* is at least 5; ΔL* is defined as the
CIE 1976 lightness value L* at non-exposed areas (i.e. L*nonexp defined above) minus the CIE 1976 lightness value L* at exposed areas, the latter
being referred to hereafter as L*exp.
The combination of a bright, white support, a coating which is essentially colorless
or only slightly colored and a lightness difference of at least 5 between non-exposed
and exposed areas provides a crisp print-out image, which enables convenient quality
control of the image before developing the plate.
[0010] Surprisingly, a smooth support contributes also to a better visible contrast, probably
because it shows a higher light reflection. This additional benefit is defined in
claims 9 and 10.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The CIE 1976 color coordinates L*, a* and b* discussed herein are part of the well-known
CIE (Commission Internationale de l'Eclairage) system of tristimulus color coordinates,
which also includes the additional chroma value C* defined as C* = [(a)
2 + (b)
2]
1/2. The CIE 1976 color system is described in e.g. "Colorimetry, CIE 116-1995: Industrial
Colour Difference Evaluation", or in "Measuring Colour" by R.W.G. Hunt, second edition,
edited in 1992 by Ellis Horwood Limited, England.
[0012] CIE L*-a*-b* values discussed and reported herein have been measured following the
ASTM E308-85 method.
The coating
[0013] The coating on the support may comprise one or more layer(s). Coating a plurality
of layers may be carried out by the simultaneous coating of a plurality of coating
solutions with a multi-layer coating head, using the known coating techniques, or
by the subsequent coating of a plurality of coating solutions using single-layer coating
heads, either with or without intermediate drying (respectively wet-on-dry or wet-on-wet).
[0014] In one of its layer, the coating preferably contains a compound, sometimes referred
to as "sensitizer", which absorbs infrared light and converts the absorbed infrared
light into heat. These infrared absorbers can be used in combination with the color-forming
infrared dyes discussed below. Alternatively, the color-forming infrared dye is the
only infrared absorber in the coating. Since the coating is essentially colorless
or only slightly colored, it is preferred that the infrared dye does not show a substantial
light absorption in the visible wavelength range. For the same reason, the amount
of dyes or pigments that show visible light absorption in the coating is kept low,
so that the material has a CIE 1976 lightness value L*
nonexp which is not less than 50, preferably not less than 60.
[0015] Another parameter that quantifies how a human observer perceives light absorption
is the ISO visual density (as described in ISO document CD 5.1 to 5.4 of 30 January
2002). This parameter is similar to the well-known optical density (absorbance) but
also takes into account that the sensitivity of the human eye is not the same over
the whole visible wavelength range. Preferred plate precursors (support + coating)
for use in the method of the present invention have a visual density in the nonexposed
state of at most 0.6, more preferably at most 0.5.
[0016] The amount of infrared absorbing agent in the coating is preferably between 0.25
and 25.0 % by weight, more preferably between 0.5 and 20.0 % by weight. The infrared
absorbing compound can be present in the image-recording layer and/or an optional
other layer. In the embodiment wherein the infrared absorbing agent is present in
the image-recording layer of the coating, its concentration is preferably at least
6 % by weight, more preferably at least 8 % by weight, relative to the weight of all
the components in the image-recording layer.
[0017] Preferred IR absorbing compounds are organic dyes having an absorption between 750
nm and 1300 nm, preferably between 780 nm and 1200 nm, more preferably between 800
nm and 1100 nm, such as cyanine, merocyanine, indoaniline, oxonol, pyrilium and squarilium
dyes. Examples of suitable IR absorbers may be found in EP 1 359 008, including the
references cited therein. Other suitable sensitizers are disclosed in US 6,410,205,
US 5,049,479, EP 1 079 276, EP 1 369 232, EP 1 369 231, EP 1 341 040, US 2003/0124460,
EP 1 241 002 and EP 1 288 720.
[0018] The coating may also contain one or more additional layer(s) besides the image-recording
layer. Besides the additional layer already discussed above - i.e. an optional light-absorbing
layer comprising one or more compounds that are capable of converting infrared light
into heat - the coating may further comprise for example an adhesion-improving layer
between the image-recording layer and the support. Also compounds may be present which
are capable of interacting with the surface of the support, e.g. the compounds described
in EP-A 1495866, EP-A 1500498 and EP-A 1520694.
[0019] It is also well known to provide a layer on top of the image-recording layer which
protects the photopolymerizable or photocurable composition from atmospheric oxygen.
Suitable composition of such top coats are described in e.g. EP-A 1315998, US2002/177074,
US6576401, EP-A 1495866, EP-A 1506855 EP-A 1516724, EP-A 1518672 and EP-A 1520694.
[0020] Optionally, the coating may further contain additional ingredients. These ingredients
may be present in the image-recording layer or in on optional other layer. For example,
additional binders, polymer particles such as matting agents and spacers, surfactants
such as perfluoro surfactants, fillers such as silicon or titanium dioxide particles,
development inhibitors or development accelerators are well-known components of lithographic
coatings.
The image-recording layer
[0021] Typical infrared-sensitized photopolymerizable or photocurable compositions have
been described in e.g. EP-A 1315998, US2002/177074, US6576401, EP-A 1495866, EP-A
1506855 EP-A 1516724, EP-A 1518672 and EP-A 1520694. The coating thickness of the
image-recording layer is preferably between 0.1 and 4.0 g/m
2, more preferably between 0.4 and 2.0 g/m
2.
[0022] The photopolymerizable composition typically comprises a polymerizable monomer or
oligomer and an initiator capable of hardening said monomer or oligomer and, preferably,
a sensitizer capable of absorbing light used in the image-wise exposure step. In one
embodiment, the composition comprises a polymerizable monomer or oligomer comprising
at least one epoxy or vinyl ether functional group and an initiator which is a Bronsted
acid generator capable of generating a free acid upon exposure, hereinafter also referred
to as "cationic photoinitiator" or "cationic initiator". Suitable polyfunctional epoxy
monomers include, for example, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohex-ane carboxylate,
bis-(3,4 - epoxycyclohexymethyl) adipate, difunctional bisphenol A epichlorohydrin
epoxy resin and multifunctional epichlorohydrinitetraphenylol ethane epoxy resin.
Suitable cationic photoinitiators include, for example, triarylsulfonium hexafluoroantimonate,
triarylsulfonium hexafluorophosphate, diaryliodonium hexafluoroantimonate, and haloalkyl
substituted s-triazine. It is noted that most cationic initiators are also free radical
initiators because, in addition to generating a free acid, they also generate free
radicals during photo or thermal decomposition.
[0023] In another embodiment, the polymerizable monomer or oligomer is an ethylenically
unsaturated compound, having at least one terminal ethylenic group, hereinafter also
referred to as "free-radical polymerizable monomer", and said initiator is a compound
which is capable of generating free radical upon exposure, hereinafter also referred
to as "free radical initiator". Suitable free-radical polymerizable monomers include,
for example, multifunctional (meth)acrylate monomers (such as (meth)acrylate esters
of ethylene glycol, trimethylolpropane, pentaerythritol, ethoxylated ethylene glycol
and ethoxylated trimethylolpropane, multifunctional urethanated (meth)acrylate, and
epoxylated (meth)acrylate), and oligomeric amine diacrylates. The (meth)acrylic monomers
may also have other double bond or epoxide group, in addition to (meth)acrylate group.
The (meth)acrylate monomers may also contain an acidic (such as carboxylic acid) or
basic (such as amine) functionality.
[0024] Suitable free-radical initiators include, for example, the derivatives of acetophenone
(such as 2,2-dimethoxy-2-phenylacetophenone, and 2-methyl-1-[4-(methylthio) phenyl-2-morpholino
propan-1-one); benzophenone; benzil; ketocoumarin (such as 3-benzoyl-7-methoxy coumarin
and 7-methoxy coumarin); xanthone; thioxanthone; benzoin or an alkyl-substituted anthraquinone;
onium salts (such as diaryliodonium hexafluoroantimonate, diaryliodonium triflate,
(4-(2-hydroxytetradecyl-oxy)-phenyl) phenyliodonium hexafluoroantimonate, triarylsulfonium
hexafluorophosphate, triarylsulfonium p-toluenesulfonate, (3-phenylpropan-2-onyl)
triaryl phosphonium hexafluoroantimonate, and N-ethoxy(2-methyl)pyridinium hexafluorophosphate,
and onium salts as described in U.S. Pat.Nos. 5,955,238,6,037,098, and 5,629,354);
borate salts (such as tetrabutylammonium triphenyl(n-butyl)borate, tetraethylammonium
triphenyl(n-butyl)borate, diphenyliodonium tetraphenylborate, and triphenylsulfonium
triphenyl(n-butyl)borate, and borate salts as described in U.S. Pat. Nos. 6,232,038
and 6,218,076,); haloalkyl substituted s-triazines (such as 2,4-bis(trichloromethyl)-6-(p-methoxy-styryl)-s-triazine,
2,4-bis(trichloromethyl)-6-(4-methoxy-naphth-1-yl)-s-triazine, 2,4-bis(trichloromethyl)-6-piperonyl-s-triazine,
and 2,4-bis(trichloromethyl)-6-[(4 -ethoxy-ethylenoxy)-phen-1-yl]-s-triazine, and
s-triazines as described in U.S. Pat. Nos. 5,955,238, 6,037,098, 6,010,824 and 5,629,354);
and titanocene (bis(etha.9-2,4-cyclopentadien-1-yl) bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)
titanium). Onium salts, borate salts, and s-triazines are preferred free radical initiators.
Diaryliodonium salts and triarylsulfonium salts are preferred onium salts. Triarylalkylborate
salts are preferred borate salts. Trichloromethyl substituted s-triazines are preferred
s-triazines.
[0025] In still another embodiment, the polymerizable monomer or oligomer is a combination
of a monomer or oligomer comprising at least one epoxy or vinyl ether functional group
and a polymerizable ethylenically unsaturated compound, having at least one terminal
ethylenic group, and said initiator is a combination of a cationic initiator and a
free-radical initiator. A monomer or oligomer comprising at least one epoxy or vinyl
ether functional group and a polymerizable ethylenically unsaturated compound, having
at least one terminal ethylenic group, can be the same compound wherein the compound
contains both ethylenic group and epoxy or vinyl ether group. Examples of such compounds
include epoxy functional acrylic monomers, such as glycidyl acrylate. The free radical
initiator and the cationic initiator can be the same compound if the compound is capable
of generating both free radical and free acid. Examples of such compounds include
various onium salts such as diaryliodonium hexafluoroantimonate and s-triazines such
as 2,4-bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen-1-yl]-s-triazine which are
capable of generating both free radical and free acid in the presence of a sensitizer.
[0026] The photopolymerizable composition may also comprise a multifunctional monomer. This
monomer contains at least two functional groups selected from an ethylenically unsaturated
group and/or an epoxy or vinyl ether group. Particular multifunctional monomers for
use in the photopolymer composition are disclosed in US 6,410,205 , US 5,049,479 ,
EP 1079276 , EP 1369232 , EP 1369231 EP 1341040 , US 2003/0124460 , EP 1241002 , EP
1288720 and in the reference book including the cited refences : Chemistry & Technology
UV & EB formulation for coatings, inks & paints - Volume 2 - Prepolymers and Reactive
Diluents for UV and EB Curable Formulations by N.S. Allen, M.A. Johnson, P.K.T. Oldring,
M.S. Salim - Edited by P.K.T. Oldring - 1991 - ISBN 0 947798102.
[0027] The photopolymerizable composition may also comprise a co-initiator. Typically, a
co-initiator is used in combination with a free radical initiator and/or cationic
initator. Particular coinitiators for use in the photopolymer composition are disclosed
in US 6,410,205 , US 5,049,479 , EP 1079276 , 1369232 , EP 1369231 EP 1341040 , US
2003/0124460 , EP 1241002 , EP 1288720 and in the reference book including the cited
refences : Chemistry & Technology UV & EB formulation for coatings, inks & paints
- Volume 3 - Photoinitiators for Free Radical and Cationic Polymerisation by K.K.
Dietliker - Edited by P.K.T. Oldring - 1991 - ISBN 0 947798161.
[0028] The photopolymerizable composition may also comprise an inhibitor. Particular inhibitors
for use in the photopolymer composition are disclosed in US 6,410,205 and EP 1288720.
[0029] The photopolymerizable composition may also comprise a binder. The binder can be
selected from a wide series of organic polymers. Compositions of different binders
can also be used. Useful binders include for example chlorinated polyalkylene (in
particular chlorinated polyethylene and chlorinated polypropylene), polymethacrylic
acid alkyl esters or alkenyl esters (in particular polymethyl (meth)acrylate, polyethyl
(meth)acrylate, polybutyl (meth)acrylate, polyisobutyl (meth)acrylate, polyhexyl (meth)acrylate,
poly(2-ethylhexyl) (meth)acrylate and polyalkyl (meth)acrylate copolymers of (meth)
acrylic acid alkyl esters or alkenyl esters with other copolymerizable monomers (in
particular with (met)acrylonitrile, vinyl chloride, vinylidene chloride, styrene and/or
butadiene), polyvinyl chloride (PVC, vinylchloride/(meth)acrylonitrile copolymers,
polyvinylidene chloride (PVDC), vinylidene chloride/(meth)acrylonitrile copolymers,
polyvinyl acetate, polyvinyl alcohol, poly (meth)acrylonitrile, (meth)acrylonitrile/styrene
copolymers, (meth)acrylamide/alkyl (meth)acrylate copolymers, (meth)acrylonitrile/butadiene/styrene
(ABS) terpolymers, polystyrene, poly(α-methylstyrene), polyamides, polyurthanes, polyesters,
methyl cellulose, ethylcellulose, acetyl cellulose, hydroxy-(C
1-C
4-alkyl)cellulose, carboxymethyl cellulose, polyvinyl formal and polyvinyl butyral.
[0030] In order to facilitate on-press processing, preferred binders are hydrophilic such
as binders containing carboxylic groups, in particular copolymers containing monomeric
units of α,β-unsaturated carboxylic acids or monomeric units of α,β-unsaturated dicarboxylic
acids (preferably acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid,
maleic acid or itaconic acid). The term "copolymers" is to be understood in the context
of the present invention as polymers containing units of at least 2 different monomers,
thus also terpolymers and higher mixed polymers. Particular examples of useful copolymers
are those containing units of (meth)acrylic acid and units of alkyl (meth)acrylates,
allyl (meth)acrylates and/or (meth)acrylonitrile as well as copolymers containing
units of crotonic acid and units of alkyl (meth)acrylates and/or (meth)acrylonitrile
and vinylacetic acid/alkyl (meth)acrylate copolymers. Also suitable are copolymers
containing units of maleic anhydride or maleic acid monoalkyl esters. Among these
are, for example, copolymers containing units of maleic anhydride and styrene, unsaturated
ethers or esters or unsaturated aliphatic hydrocarbons and the esterification products
obtained from such copolymers. Further suitable binders are products obtainable from
the conversion of hydroxyl-containing polymers with intramolecular dicarboxylic anhydrides.
Further useful binders are polymers in which groups with acid hydrogen atoms are present,
some or all of which are converted with activated isocyanates. Examples of these polymers
are products obtained by conversion of hydroxyl-containing polymers with aliphatic
or aromatic sulfonyl isocyanates or phosphinic acid isocyanates. Also suitable are
polymers with aliphatic or aromatic hydroxyl groups, for example copolymers containing
units of hydroxyalkyl (meth)acrylates, allyl alcohol, hydroxystyrene or vinyl alcohol,
as well as epoxy resins, provided they carry a sufficient number of free OH groups.
Particular useful binder and particular useful reactive binders are disclosed in EP
1 369 232, EP 1 369 231, EP 1 341 040, US 2003/0124460, EP 1 241 002, EP 1 288 720,
US 6,027,857, US 6,171,735 and US 6,420,089.
[0031] The organic polymers used as binders have a typical mean molecular weight M
w between 600 and 200 000, preferably between 1 000 and 100 000. Preference is further
given to polymers having an acid number between 10 to 250, preferably 20 to 200, or
a hydroxyl number between 50 and 750, preferably between 100 and 500. The amount of
binder(s) generally ranges from 10 to 90 % by weight, preferably 20 to 80 % by weight,
relative to the total weight of the non-volatile components of the composition.
[0032] Various surfactants may be added into the photopolymerizable composition to allow
or enhance the developability of the precursor. Both polymeric and small molecule
surfactants can be used. Nonionic surfactants are preferred. Preferred nonionic surfactants
are polymers and oligomers containing one or more polyether (such as polyethylene
glycol, polypropylene glycol, and copolymer of ethylene glycol and propylene glycol)
segments. Examples of preferred nonionic surfactants are block copolymers of propylene
glycol and ethylene glycol (also called block copolymer of propylene oxide and ethylene
oxide); ethoxylated or propoxylated acrylate oligomers; and polyethoxylated alkylphenols
and polyethoxylated fatty alcohols. The nonionic surfactant is preferably added in
an amount ranging between 0.1 and 30% by weight of the photopolymerizable composition,
more preferably between 0.5 and 20%, and most preferably between 1 and 15%.
The visible print-out image
[0033] The coating is capable of producing a visible print-out image upon exposure to infrared
light. The print-out image is characterized by a contrast between exposed and non-exposed
areas which is quantified by the CIE 1976 lightness difference ΔL*, measured immediately
after exposure, i.e. before the exposed plate precursor is developed, of at least
5. In preferred embodiments of the present invention, ΔL* is preferably at least 8,
more preferably at least 10, and most preferably at least 15.
[0034] Said lightness difference ΔL* is defined as follows :

wherein L*
nonexp is the CIE 1976 lightness value of the material at non-exposed areas and L*
exp is the CIE 1976 lightness value of the material at exposed areas.
[0035] A quantitative measure of the color difference ΔE between the print-out image (exposed
areas) and the background (non-exposed areas) can be calculated by the equation

wherein ΔC*, Δa* and Δb* are the differences between the non-exposed and the exposed
areas, measured immediately after the exposure step, of the CIE 1976 color coordinate
values C*, a* and b* respectively. In a preferred embodiment, the color difference
ΔE between the non-exposed and exposed areas is at least 5, preferably at least 10,
more preferably at least 15 and most preferably at least 18.
[0036] The compounds, which produce the print-out image upon infrared exposure, can be present
in the image-recording layer and/or optionally in (an)other layer(s) of the coating.
The following embodiments of color forming compounds can be used :
1. A dye which undergoes a color change as described in EP-A 1502736.
2. More preferred, a dye precursor as described in EP-A 1508440 can also be used.
3. According to another preferred embodiment, the coating comprises a product DQ which
is obtained by
- the step of coating a solution or dispersion comprising a nucleophilic compound Q
and a dye D selected from the list consisting of di- or tri-arylmethane dyes, cyanine
dyes, styryl dyes and merostyryl dyes; or by
- the steps of coating a solution or dispersion comprising said compound Q and coating
another solution or dispersion comprising said dye D;
wherein D and Q interact to form interaction product DQ, wherein DQ has a lower white
light absorption than D, and wherein said interaction product DQ is capable of at
least partially releasing a dye during the exposure step, thereby forming the visible
print-out image in the coating.
[0037] The interaction between D and Q may be a reaction whereby the compound Q and the
dye D are covalently and/or ionically bound to each other, or whereby D and Q form
a complex and/or one ore more hydrogen bonds. D and Q may be added to the coating
solution of the image-recording layer or to another layer of the coating, e.g. a layer
on top of the coating or an intermediate layer between the support and the image-recording
layer or another intermediate layer between the top layer and the image-recording
layer. D and Q may first be allowed to form the interaction product DQ which is then
added to a coating solution or D and Q may be coated in separate layers and are then
allowed to interact by diffusion between said layers.
[0038] The interaction between D and Q reduces the white light absorption of the dye D.
Said reduction of the white light absorption of D due to the interaction with Q can
be measured by comparing the white light optical density of a coating comprising D
and Q with the white light optical density of the same coating without Q. Upon image-wise
exposure to infrared light, said interaction product DQ at least partially releases
a dye, possibly D, and thereby forms the visible print-out image.
[0039] In a preferred embodiment, the dye D is a di- or tri-arylmethane dye wherein an aryl
group is substituted with an amino group, hereinafter also referred to as a "amino
substituted di- or tri-aryl methane dye". Specific examples of such amino substituted
di- or tri-aryl methane dyes are given in the following list. In this list the dyes
are mentioned in their reduced form (also called "leuco form" or "leuco dye") having
one or two hydrogen atoms, the removal of which together with one or two electrons
produces the dyes D which are suitable in the present invention.
A. AMINOTRIARYLMETHANES
[0040]
bis(4-amino-2-butylphenyl) (p-dimethylaminophenyl)-methane
bis(4-amino-2-chlorophenyl) (p-aminophenyl)methane
bis(4-amino-3-chlorophenyl) (o-chlorophenyl)methane
bis(4-amino-3-chlorophenyl)phenylmethane
bis(4-amino-3,5-diethylphenyl) (o-chlorophenyl)-methane
bis(4-amino-3,5-diethylphenyl) (o-ethoxyphenyl)-methane
bis(4-amino-3,5-diethylphenyl) (P-methoxyphenyl)-methane
bis(4-amino-3,5-diethylphenyl)phenylmethane
bis(4-amino-ethylphenyl) (o-chlorophenyl)methane
bis(p-aminophenyl) (4-amino-m-tolyl)methane
bis(p-aminophenyl) (o-chlorophenyl)methane
bis(p-aminophenyl) (p-chlorophenyl)methane
bis(p-aminophenyl) (2,4-dichlorophenyl)methane
bis(p-aminophenyl) (2,5-dichlorophenyl)methane
bis(p-aminophenyl) (2,6-dichlorophenyl)methane
bis(p-aminophenyl)phenylmethane-9-methylacridine
bis(4-amino-tolyl) (p-chlorophenyl)methane
bis(4-amino-o-tolyl) (2,4-dichlorophenyl)methane
bis(p-anilinophenyl) (4-amino-m-tolyl)methane
bis(4-benzylamino-2-cyanophenyl) (p-aminophenyl)methane
bis(p-benzylethylaminophenyl) (p-chlorophenyl)methane
bis(p-benzylethylaminophenyl) (p-diethylaminophenyl)methane
bis(p-benzylethylaminophenyl) (p-dimethylaminophenyl) methane
bis(4-benzylethylamino-o-tolyl) (p-methoxyphenyl)methane
bis(p-benzylethylaminophenyl)phenylmethane
bis(4-benzylethylamino-o-tolyl) (o-chlorophenyl)methane
bis(4-benzylethylamino-o-tolyl) (p-diethylaminophenyl) methane
bis(4-benzylethylamino-o-tolyl) (4-diethylamino-o-tolyl) methane
bis(4-benzylethylamino-o-tolyl) (p-dimethylaminophenyl) methane
bis[2-chloro-4-(2-diethylaminoethyl)ethylaminophenyl]-(o-chlorophenyl) methane
bis[p-bis(2-cyanoethyl)aminophenyl]phenylmethane
bis[p-(2-cyanoethyl)ethylamino-o-tolyl](p-dimethylaminophenyl)methane
bis[p-(2-cyanoethyl)methylaminophenyl](p-diethylaminophenyl)methane
bis(p-dibutylaminophenyl) [p-(2-cyanoethyl)methylaminophenyl]methane
bis(p-dibutylaminophenyl) (p-diethylaminophenyl)methane
bis(4-diethylamino-2-butoxyphenyl) (p-diethylaminophenyl)methane
bis(4-diethylamino-2-fluorophenyl)-o-tolylmethane
bis(p-diethylaminophenyl) (p-aminophenyl)methane
bis(p-diethylaminophenyl) (4-anilino-1-naphthyl)methane
bis(p-diethylaminophenyl) (m-butoxyphenyl)methane
bis(p-diethylaminophenyl) (o-chlorophenyl)methane
(p-diethylaminophenyl) (p-cyanophenyl)methane
bis(p-diethylaminophenyl) (2,4-dichlorophenyl)methane
bis(p-diethylaminophenyl) (4-diethylamino-1-naphthyl)methane
bis(p-diethylaminophenyl) (p-dimethylaminophenyl)methane
bis(p-diethylaminophenyl) (4-ethylamino-1-naphthyl)methane
bis(p-diethylaminophenyl)-2-naphthylmethane
bis(p-diethylaminophenyl) (p-nitrophenyl)methane
bis(p-diethylaminophenyl)-2-pyridylmethane
bis(p-diethylamino-m-tolyl) (p-diethylaminophenyl)methane
bis(4-diethylamino-o-tolyl) (o-chlorophenyl)methane
bis(4-diethylamino-o-tolyl) (p-diethylaminophenyl)methane
bis(4-diethylamino-o-tolyl) (diphenylaminophenyl)methane
bis(4-diethylamino-o-tolyl)phenylmethane
bis(4-dimethylamino-2-bromophenyl)phenylmethane
bis(p-dimethylaminophenyl) (4-amino-1-naphthyl)methane
bis(p-dimethylaminophenyl) (p-butylaminophenyl)methane
bis(p-dimethylaminophenyl) (p-scc. butylethylaminophenyl)methane
bis(p-dimethylaminophenyl) (p-chlorophenyl)methane
bis(p-dimethylaminophenyl) (p-diethylaminophenyl)methane
bis(p-dimethylaminophenyl) (4-dimethylamino-1-naphthyl) methane
bis(p-dimethylaminophenyl) (6-dimethylamino-m-tolyl) methane
bis(p-dimethylaminophenyl) (4-dimethylamino-o-tolyl) methane
bis(p-dimethylaminophenyl) (4-ethylamino-1-naphthyl) methane
bis(p-dimethylaminophenyl) (p-hexyloxyphenyl)methane
bis(p-dimethylaminophenyl) (p-methoxyphenyl)methane
bis(p-dimethylaminophenyl) (5-methyl-2-pyridyl)methane
bis(4-diethylamino-2-ethoxyphenyl) (4-diethylamino phenyl)methane
bis(p-dimethylaminophenyl)-2-quinolylmethane
bis(p-dimethylaminophenyl)-o-tolylmethane
bis(p-dimethylaminophenyl))1,3,3-trimethyl-2-indolinylidenemethyl)methane
bis(4-dimethylamino-o-tolyl) (p-aminophenyl)methane
bis(4-dimethylamino-o-tolyl) (o-bromophenyl)methane
bis(4-dimethylamino-o-tolyl) (o-cyanophenyl)methane
bis(4-dimethylamino-o-tolyl) (o-fluorophenyl)methane
bis(4-dimethylamino-o-tolyl)-1-naphthylmethane
bis(4-dimethylamino-o-tolyl)phenylmethane
bis(p-ethylaminophenyl) (o-chlorophenyl)methane
bis(4-ethylamino-m-tolyl) (o-methoxyphenyl)methane
bis(4-ethylamino-m-tolyl) (p-methoxyphenyl)methane
bis(4-ethylamino-m-tolyl) (p-dimethylaminophenyl)methane
bis(4-ethylamino-m-tolyl) (p-hydroxyphenyl)methane
bis[4-ethyl(2-hydroxyethyl)amino-m-tolyl](p-diethylaminophenyl)methane
bis[p-(2-hydroxyethyl)aminophenyl](o-chlorophenyl)methane
bis[p-bis(2-hydroxyethyl)aminophenyl](4-diethylamino-o-tolyl)methane
bis[p-(2-methoxyethyl)aminophenyl]phenylmethane
bis(p-methylaminophenyl) (o-hydroxyphenyl)methane
bis(p-propylaminophenyl) (m-bromophenyl)methane
tris(4-amino-o-tolyl)methane
tris(4-anilino-o-tolyl)methane
tris(p-benzylaminophenyl)methane
tris[4-bis(2-cyanoethyl)amino-o-tolyl]methane
tris[p-(2-cyanoethyl)ethylaminophenyl]methane
tris(p-dibutylaminophenyl)methane
tris(p-di-t-butylaminophenyl)methane
tris(p-dimethylaminophenyl)methane
tris(4-diethylamino-2-chlorophenyl)methane
tris(p-diethylaminophenyl)methane
tris(4-diethylamino-o-tolyl)methane
tris(p-dihexylamino-o-tolyl)methane
tris(4-dimethylamino-o-tolyl)methane
tris(p-hexylaminophenyl)methane
tris[p-bis(2-hydroxyethyl)aminophenyl]methane
tris(p-methylaminophenyl)methane
tris(p-dioctadecylaminophenyl)methane
B. AMINOXANTHENES
[0041]
3-amino-6-dimethylamino-2-methyl-9-(o-chlorophenyl)xanthene
3-amino-6-dimethylamino-2-methyl-9-phenylxanthene
3-amino-6-dimethylamino-2-methylxanthene
3,6-bis(diethylamino)-9-(o-chlorophenyl)xanthene
3,6-bis(diethylamino)-9-hexylxanthene
3,6-bis(diethylamino)-9-(o-methoxycarbonylphenyl) xanthene
3,6-bis(diethylamino)-9-methylxanthene
3,6-bis(diethylamino)-9-phenylxanthene
3,6-bis(diethylamino)-9-o-tolyxanthene
3,6-bis(dimethylamino)-9-(o-chlorophenyl)xanthene
3,6-bis(dimethylamino)-9-ethylxanthene
3,6-bis(dimethylamino)-9-(o-methoxycarbonylphenyl) xanthene
3,6-bis(dimethylamino)-9-methylxanthene
C. AMINOTHIOXANTHENES
[0042]
3,6-bis(diethylamino)-9-(o-ethoxycarbonylphenyl) thioxanthene
3,6-bis(dimethylamino)-9-(o-methoxycarbonylphenyl) thioxanthene
3,6-bis(dimethylamino)thioxanthene
3,6-dianilino-9-(o-ethoxycarbonylphenyl)thioxanthene
D. Amino-9,10-dihydroacridines
[0043]
3,6-bis(benzylamino)-9,10-dihydro-9-methylacridine
3,6-bis(diethylamino)-9-hexyl-9,10-dihydroacridine
3,6-bis(diethylamino)-9,10-dihydro-9-methylacridine
3,6-bis(diethylamino)-9,10-dihydro-9-phenylacridine
3,6-diamino-9-hexyl-9,10-dihydroacridine
3,6-diamino-9,10-dihydro-9-methylacridine
3,6-diamino-9,10-dihydro-9-phenylacridine
3,6-bis(dimethylamino)-9-hexyl-9,10-dihydroacridine
3,6-bis(dimethylamino)-9,10-dihydro-9-methylacridine
E. AMINOPHENOXAZINES
[0044]
3,7-bis(diethylamino)phenoxazine
9-dimethylamino-benzo[a]phenoxazine
F. AMINOPHENOTHIAZINES
[0045]
3,7-bis(benzylamino)phenothiazine
G. AMINODIHYDROPHENAZINES
[0046]
3,7-bis(benzylethylamino)-5,10-dihydro-5-phenylphenazine
3,7-bis(diethylamino)-5-hexyl-5,10-dihydrophenazine
3,7-bis(dihexylamino)-5,10-dihydrophenazine
3,7-bis(dimethylamino)-5-(p-chlorophenyl)-5,10-dihydrophenazine
3,7-diamino-5-(o-chlorophenyl)-5,10-dihydrophenazine
3,7-diamino-5,10-dihydrophenazine
3,7-diamino-5,10-dihydro-5-methylphenazine
3,7-diamino-5-hexyl-5,10-dihydrophenazine-3,7-bis(dimethylamino)-5,10-dihydrophenazine
3,7-bis(dimethylamino)-5,10-dihydro-5-phenylphenazine
3,7-bis(dimethylamino)-5,10-dihydro-5-methylphenazine
H. AMINODIPHENYLMETHANES
[0047]
1,4-bis[bis-p(diethylaminophenyl)methyl]piperazine
bis(p-diethylaminophenyl)anilinomethane
bis(p-diethylaminophenyl)-1-benzotriazolylmethane
bis(p-diethylaminophenyl)-2-benzotriazolylmethane
bis(p-diethylaminophenyl) (p-chloroanilino)methane
bis(p-diethylaminophenyl) (2,4-dichloroanilino)methane
bis(p-diethylaminophenyl) (methylamino)methane
bis(p-diethylaminophenyl) (octadecylamino)methane
bis(p-dimethylaminophenyl)aminomethane
bis(p-dimethylaminophenyl)anilinomethane
1,1-bis(dimethylaminophenyl)ethane
1,1-bis(dimethylaminophenyl)heptane
bis(4-methylamino-m-tolyl)aminoethane
I. LEUCO INDAMINES
[0048]
4-amino-4'-dimethylaminodiphenylamine
p-(p-dimethylaminoanilino)phenol
J. AMINOHYDROCINNAMIC ACIDS (CYANOETHANES, LEUCO METHINES)
[0049]
4-amino-µ,µ-dicyanohydrocinnamic acid, methyl ester
4-anilino-µ,µ-dicyanohydrocinnamic acid, methyl ester
4-(p-chloroanilino)-µ,β-dicyanohydrocinnamic acid, methyl ester
µ-cyano-4-dimethylaminohydrocinnamide
µ-cyano-4-dimethylaminohydrocinnamic acid, methyl ester
µ,µ-dicyano-4-diethylaminohydrocinnamic acid, methyl ester
µ,µ-dicyano-4-dimethylaminohydrocinnamide
µ,µ-dicyano-4-dimethylaminohydrocinnamic acid, methyl ester
µ,µ-dicyano-4-dimethylaminohydrocinnamic acid
µ,µ-dicyano-4-dimethylaminohydrocinnamic acid, hexyl ester
µ,µ-dicyano-4-hexylaminohydrocinnamic acid, methyl ester
µ,µ-dicyano-4-methylaminocinnamic acid, methyl ester
p-(2,2-dicyanoethyl)-N,N-dimethylaniline
4-methoxy-4'-(1,2,2-tricyanoethyl)azobenzene
4-(1,2,2-tricyanoethyl)azobenzene
p-(1,2,2-tricyanoethyl)-N,N-dimethylaniline
K. HYDRAZINES
[0050]
1-(p-diethylaminophenyl)-2-(2-pyridyl)hydrazine
1-(p-dimethylaminophenyl)-2-(2-pyridyl)hydrazine
1-(3-methyl-2-benzothiazolyl)-2-(4-hydroxy-1-naphthyl)hydrazine
1-(2-naphthyl)-2-phenylhydrazine
1-p-nitrophenyl-2-phenylhydrazine
1-(1,3,3-trimethyl-2-indolinyl)-2-(3-N-phenylcarbamoyl-4-hydroxy-1-naphthyl )hydrazine
L. LEUCO INDIGOID DYES
M. AMINO-2,3-DIHYDROANTHRAQUINONES
[0051]
1,4-dianilino-2,3-dihydroanthraquinones
1,4-bis(ethylamino)-2,3-dihydroanthraquinone
N. PHENETHYLANILINES
[0052]
N-(2-cyanoethyl)-p-phenethylaniline
N,N-diethyl-p-phenylethylaniline
N,N-dimethyl-p-[2-(1-naphthyl)ethyl]aniline.
[0053] In a highly preferred embodiment, the dye D is an amino substituted di- or tri-arylmethane
dye, having at least one hydrophilic group. Preferred hydrophilic groups are selected
from sulphonic acid group, carboxylic acid group, phosphoric acid group or phosphonic
acid group or salts thereof, such as alkali metal salts or ammonium salt; most preferred
hydrophilic group is sulphonic acid group or salt thereof.
[0054] In another preferred embodiment of the present invention, the dye D is a cationic
dye. Cationic dyes are dyes which carry a positive charge in their molecule. Preferred
cationic dyes are dyes having a positive charge in the chromophore moiety of the molecule.
More preferred cationic dyes are dyes having a positive charge in the chromophore
moiety and having a hydrophilic group in a side chain of the chromophoric moiety.
Examples of cationic dyes are those mentioned by R. Raue in the Ullmann's Encyclopedia
of Industrial Chemistry, edited by Wiley-VCH, volume A5, p. 369-373 (1986).
[0055] The dye D may also be incorporated into a polymer, comprising at least one monomeric
unit having a dye D which is covalently or ionically bound to the monomeric unit by
a linking group. The dye D in such a polymer is preferably an amino substituted di-
or tri-arylmethane dye.
[0056] The nucleophilic compound Q is preferably a compound having one or more electron-rich
sites such as an unshared pair of electrons or ions, the negative end of a polar bond,
or µ-electrons, and this compound is able to donate electrons to, or to share electrons
with dye D. Nucleophilic compounds are usually organic compounds comprising a hetero-atom
such as O, S, N or P. The nucleophilicity of the compound Q is preferably high enough
to form the interaction product DQ, especially when DQ is formed in situ in the coating
at low pH, e.g. pH<7. Upon heating, the interaction product DQ releases at least partially
a dye and this release is less likely when the nucleophilicity is high. So, the nucleophilicity
of Q is preferably sufficiently low to maintain its leaving capability upon heating
(formation of dye); on the other hand, the nucleophilicity of Q is preferably sufficiently
high to be able to from a leuco dye adduct DQ, even at a low pH value (pH<7); as a
result, the compound Q of the present invention exhibits preferably an acceptable
compromise as to its nucleophilicity.
[0061] The nucleophilic compound Q and the dye D may both be present in the same compound,
e.g. a compound wherein Q and D are covalently coupled by a linking group such as
an alkylene group. Another example of such a compound is a polymer comprising at least
one monomeric unit having a nucleophilic group and at least one monomeric unit having
a dye D. The nucleophilic group in this polymer is preferably a thiol group and the
dye D is preferably an amino substituted di-or tri-arylmethane dye.
4. According to a fourth embodiment of the color forming system, the coating comprises
an infrared dye which undergoes a chemical transformation induced by the image-wise
exposure and thereby forms the visible print-out image. Such a dye is referred to
herein as a color-forming infrared dye.
5. A preferred class of such color-forming IR dyes have a structure according to the
following formula :

wherein
+Y
1= is represented by one of the following structures:

and wherein Y
2- is represented by one of the following structures:

and n is 0, 1, 2 or 3;
and each of p and q is 0, 1 or 2;
and R
1 and R
2 are independently an optionally substituted hydrocarbon group, or wherein two of
said R
1, R
2, R
d or R
a groups together comprise the necessary atoms to form a cyclic structure;
characterised in that
at least one of the R
d groups is a group which is transformed by a chemical reaction, induced by the image-wise
exposure to infrared light, into a group which is a stronger electron-donor than said
R
d; or
at least one of the R
a groups is a group which is transformed by achemical reaction, induced by the image-wise
exposure to infrared light, into a group which is a stronger electron-acceptor than
said R
a;
thereby forming the visible print-out image;
and wherein the other R
d and R
a groups are independently represented by a group selected from the list consisting
of a hydrogen atom, a halogen atom, -R
e, -OR
f, -SR
g and -NR
uR
v, wherein R
e, R
f, R
g, R
u and R
v independently are an optionally substituted aliphatic hydrocarbon group or an optionally
substituted (hetero)aryl group.
[0062] The transformation of said R
a and/or R
d group referred to above results in a decrease of the lightness value L* of the coating.
[0063] In a preferred class of such infrared dyes the R
d group, which is transformed by a chemical reaction, is selected from the list consisting
of
-(N=CR17)a -NR3-CO-R4,
-(N=CR17)b -NR5-SO2-R6,
-(N=CR17)c -NR11-SO-R12,
-SO2-NR15R16 and
-S-L-CR7(H)1-d(R8)d -NR9-COOR18,
wherein
a, b, c and d independently are 0 or 1,
-L- is a linking group,
R
17 is a hydrogen atom, an optionally substituted aliphatic hydrocarbon group or an optionally
substituted (hetero)aryl group,
or wherein R
17 and R
3, R
17 and R
5, or R
17 and R
11 together comprise the necessary atoms to form a cyclic structure, preferably a 5-
or 6-membered ring,
R
4 is -OR
10, -NR
13R
14 or -CF
3,
wherein
R
10 is an optionally substituted (hetero)aryl group or an alpha-branched aliphatic hydrocarbon
group, preferably an alpha-branched aliphatic hydrocarbon group, more preferably a
secondary or tertiary aliphatic hydrocarbon group, most preferably a tertiary butyl
group;
R
13 and R
14 independently are a hydrogen atom, an optionally substituted aliphatic hydrocarbon
group or an optionally substituted (hetero)aryl group, or wherein R
13 and R
14 together comprise the necessary atoms to form a cyclic structure, preferably a 5-
or 6-membered ring,
R
3 is a hydrogen atom, an optionally substituted aliphatic hydrocarbon group or an optionally
substituted (hetero)aryl group, or wherein R
3 together with at least one of R
10, R
13 and R
14 comprise the necessary atoms to form a cyclic structure, preferably a 5- or 6-membered
ring,
R
6 is an optionally substituted aliphatic hydrocarbon group or an optionally substituted
(hetero)aryl group, -OR
10, -NR
13R
14 or -CF
3 wherein R
10, R
13 and R
14 have the same meaning as in R
4,
R
5 is a hydrogen atom, an optionally substituted aliphatic hydrocarbon group or an optionally
substituted (hetero)aryl group, or wherein R
5 together with at least one of R
10, R
13 and R
14 comprise the necessary atoms to form a cyclic structure, preferably a 5- or 6-membered
ring,
R
11, R
15 and R
16 are independently a hydrogen atom, an optionally substituted aliphatic hydrocarbon
group or an optionally substituted (hetero)aryl group, or wherein R
15 and R
16 together comprise the necessary atoms to form a cyclic structure, preferably a 5-
or 6-membered ring,
R
12 is an optionally substituted aliphatic hydrocarbon group or an optionally substituted
(hetero)aryl group,
R
7 and R
9 independently are a hydrogen atom or an optionally substituted aliphatic hydrocarbon
group,
R
8 is -COO
- or -COOR
8' wherein R
8' is a hydrogen atom, an alkali metal cation, an ammonium ion or a mono-, di-, tri-
or tetra-alkyl ammonium ion,
R
18 is an optionally substituted (hetero)aryl group or an alpha-branched aliphatic hydrocarbon
group, preferably an alpha-branched aliphatic hydrocarbon group, more preferably a
secondary or tertiary aliphatic hydrocarbon group, most preferably a tertiary butyl
group.
[0064] Preferred classes of such color forming IR-dyes have a structure according to one
of the following formulae II, III or IV:

wherein
Ar
1, Ar
2 and Ar
3 are independently an optionally substituted aromatic hydrocarbon group or an aromatic
hydrocarbon group with an annulated benzene ring which is optionally substituted,
W
1 and W
2 are independently a sulfur atom or a -CM
10M
11 group wherein M
10 and M
11 are independently an optionally substituted aliphatic hydrocarbon group or an optionally
substituted (hetero)aryl group, or wherein M
10 and M
11 together comprise the necessary atoms to form a cyclic structure, preferably a 5-
or 6-membered ring,
M
1 and M
2 are independently an optionally substituted aliphatic hydrocarbon group or wherein
M
1 and M
2 together comprise the necessary atoms to form an optionally substituted cyclic structure,
preferably a 5- or 6-membered ring, more preferably a 5-membered ring, most preferably
a 5-membered ring having a cyclic structure of 5 carbon atoms,
M
3 and M
4 are independently an optionally substituted aliphatic hydrocarbon group,
M
5, M
6, M
7, M
8, M
16 and M are independently a hydrogen atom, a halogen atom or an optionally substituted
aliphatic hydrocarbon group,
W
3 is a sulfur atom or a -CA
3=CA
4- group,
M
12 and M
13 are independently an optionally substituted aliphatic hydrocarbon group or an optionally
substituted (hetero)aryl group, or wherein two of said M , M
13, A
2 or A
4 together comprise the necessary atoms to form at least one cyclic structure, preferably
a 5- or 6-membered ring,
W
4 is a sulfur atom or a -CA
7=CA
8- group,
A
1 to A
8 are independently a hydrogen atom, a halogen atom, an optionally substituted aliphatic
hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein each
of A
1 and A
2, A
3 and A
4, A
5 and A
6, or, A
7 and A
8, together comprise the necessary atoms to form a cyclic structure, preferably a 5-
or 6-membered ring,
M
14 and M
15 are independently an optionally substituted aliphatic hydrocarbon group or an optionally
substituted (hetero)aryl group, or wherein two of said M
14, M
15, A
5 or A
7 together comprise the necessary atoms to form at least one cyclic structure, preferably
a 5- or 6-membered ring, and
M
9 is the R
d group which is transformed by a chemical reaction.
[0065] The color-forming infrared dye can be a neutral, an anionic or a cationic dye depending
on the type of the substituting groups and the number of each of the substituting
groups. In a preferred embodiment, the dye of formula II, III or IV has at least one
anionic or acid group, selected from the list consisting of -CO
2H, - CONHSO
2R
h, -SO
2NHCOR
i, -SO
2NHSO
2R
j, -PO
3H
2, -OPO
3H
2, -OSO
3H or -SO
3H groups or their corresponding salts, wherein R
h, R
i and R
j are independently an aryl or an alkyl group, preferably a methyl group, and wherein
the salts are preferably alkali metal salts or ammonium salts, including mono- or
di- or tri- or tetra-alkyl ammonium salts. These anionic or acid groups may be present
on the aromatic hydrocarbon group or the annulated benzene ring of Ar
1, Ar
2 or Ar
3, or on the aliphatic hydrocarbon group of M
3, M
4 or M
12 to M
15, or on the (hetero)aryl group of M
12 to M
15. Other substituting groups can be selected from a halogen atom, a cyano group, a
sulphone group, a carbonyl group or a carboxylic ester group.
[0066] In another preferred embodiment, each of the aliphatic hydrocarbon groups of M
3, M
4 or M
12 to M
15 is terminally substituted with at least one of these groups, more preferably with
-CO
2H, - CONHSO
2-Me, -SO
2NHCO-Me, -SO
2NHSO
2-Me, -PO
3H
2 or -SO
3H groups or their corresponding salt, wherein Me represents a methyl group.
[0067] According to other preferred embodiments, the color-forming IR-dye has a structure
according to one of the following formulae :

wherein
Q is O, S, -CR
sR
t or -COOR
u wherein R
s, R
t and R
u are independently a hydrogen atom or an alkyl group; and
the other groups have the same meaning as defined in formula II, III and IV.
The support
[0069] The support of the lithographic printing plate precursor used in the method of the
present invention is a grained and anodized aluminum support. In order to produce
a print-out image with a high contrast, it is beneficial to use a support having a
bright, white surface : the aluminum support is characterized by a lightness value
L*
sup not less than 70, more preferably even not less than 75. The a*
sup and b*
sup values of the surface of the aluminum on the other hand are as low as possible :
a*
sup and b*
sup are each in the range between -4 and +4, preferably between -1.5 and +1.5 and more
preferably between -1 and +1. A low surface roughness also contributes to a higher
contrast of the print-out image : a preferred aluminum surface is characterized by
an arithmetical mean roughness Ra, measured according to DIN4768, between 0.1 and
0.7, more preferably between 0.1 and 0.5 and most preferably between 0.15 and 0.40.
[0070] In order to produce such supports, one begins with a lithographic grade aluminum
or aluminum alloy substrate. The aluminum substrates used in the present invention
include those composed of substantially pure aluminum and aluminum alloys. Aluminum
alloys include alloys of aluminum and materials such as silicon, copper, manganese,
magnesium, chromium, zinc, lead, bismuth or nickel.
[0071] As a first step, the substrate is preferably degreased to remove milling oils. Degreasing
is preferably conducted by passing the substrate through an aqueous solution of an
alkali hydroxide, such as sodium hydroxide which is present in the solution at a concentration
of from about 5 to about 50 g/l. The solution is preferably maintained at about 40
to about 100°C. Degreasing may be conducted at from about 1 to about 180 seconds.
Next, the substrate may be rinsed with water and/or chemically etched. This is preferably
done by passing the substrate through a second aqueous solution of an alkali hydroxide,
such as sodium hydroxide which is present in the solution at a concentration of from
about 5 to about 25 g/l. The solution is preferably maintained at about 40 to about
100°C. Chemical etching is typically conducted between about 10 to about 180 seconds.
[0072] The substrate is then preferably electrochemically grained. Electrochemical graining
is preferably done by electrolyzing the substrate in an aqueous solution of nitric
or hydrochloric acid at a concentration of from about 8 g/l to about 20 g/l, preferably
from about 10 g/l to about 16 g/l and most preferably from about 12 to about 15 g/l.
Preferably, if nitric acid is used, aluminum nitrate is also added to the solution
and if hydrochloric acid is used, then aluminum chloride and/or sulfate may be added
to the solution. The aluminum salt is preferably added in an amount of from about
5 to about 100 g/l, more preferably from about 20 to about 80 g/l and most preferably
from about 30 to about 60 g/l. The graining is preferably conducted in either direct
or alternating current, however alternating current is most preferred. Graining is
performed at a charge density of from about 5 to about 100 coulombs/dm
2, preferably from about 40 to about 90 coulombs/dm
2. Graining is done for from about 5 seconds to about 5 minutes.
[0073] The substrate is then preferably rinsed and desmutted, e.g. with an aqueous solution
of sulfuric or phosphoric acid in an amount of 100 to 300 g/l at a temperature for
40 to 100 °C for 2 to 10 seconds and again rinsed with water. Desmutting can also
be carried out with an aqueous alkaline solution, e.g. a solution of an alkali hydroxide,
such as sodium hydroxide which is present in the solution at a concentration of from
about 5 to about 50 g/l. The solution is preferably maintained at about 40 to about
100°C.
[0074] The substrate is then anodized, preferably by electrolytically treating the substrate
in an aqueous solution of sulfuric or phosphoric acid having a concentration of from
about 100 to about 300 g/l at a temperature of from about 40 to about 100°C. Sulfuric
acid is most preferred. Anodizing preferably takes place for about from 5 seconds
to about 5 minutes at a charge density from about 20 to about 100 coulombs/dm
2. The anodization preferably produces an anodic oxide weight of from about 0.1 to
about 5 g/m
2, preferably from 3.0 to 4.5 g/m
2.
[0075] The substrate is then preferably washed with water and post-treated with an aqueous
solutions of a hydrophilizing compound such as alkali silicate, silicic acid, Group
IV-B metal fluorides, the alkali metal salts, polyvinylphosphonic acid, polyvinylmethyl
phosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid,
polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinyl alcohol, and acetals
of polyvinyl alcohols formed by reaction with a sulfonated aliphatic aldehyde. Other
useful hydrophilizing compounds are poly(acrylic acid), the alkali zirconium fluorides,
such as potassium zirconium hexafluoride, or hydrofluozirconic acid. Such hydrophilizing
compounds are used in concentrations of from about 0.01 to about 10% by volume. A
preferred concentration range is from about 0.05 to about 5% and the most preferred
range is from about 0.1 to about 1%.
Exposure and processing
[0076] The printing plate precursor of the present invention is image-wise exposed with
infrared light, preferably near infrared light. The infrared light is preferably converted
into heat by an IR light absorbing compound as discussed above. The image-recording
layer preferably has a low sensitivity towards visible light. Most preferably, the
material can be kept in ambient daylight at an intensity corresponding to normal working
conditions without the need for a safe light environment during at least 4 hours,
more preferably at least 12 hours.
[0077] The printing plate precursors of the present invention can be exposed to infrared
light by means of e.g. LEDs or an infrared laser. Preferably, the light used for the
exposure is a laser emitting near infrared light having a wavelength in the range
from about 700 to about 1500 nm, e.g. a semiconductor laser diode, a Nd:YAG or a Nd:YLF
laser. In a preferred embodiment of the present invention, the energy density of the
infrared light used in the exposure step is 250 mJ/cm
2 or less, more preferably 200 mJ/cm
2 or less and most preferably 150 mJ/cm
2 or less. Preferably an energy density in the range between 70 and 250 mJ/cm
2 is sufficient to induce the color change according to the present invention. In a
more preferred embodiment, said energy density range is between 100 and 200 mJ/cm
2 and most preferably between 100 and 150 mJ/cm
2.
[0078] Due to the heat generated during the exposure step, the photopolymerizable or photocurable
composition is hardened, so as to form a hydrophobic phase which corresponds to the
printing areas of the printing plate. Here, "hardened" means that the coating becomes
insoluble or non-dispersible for the developer and may be achieved through polymerization
and/or crosslinking of the photosensitive coating, optionally followed by a heating
step to enhance or to speed-up the polymerization and/or crosslinking reaction. In
this optionally heating step, hereinafter also referred to as "pre-heat", the exposed
plate precursor is heated before being developed, preferably at a temperature of about
80°C to 150°C and preferably during a dwell time of about 5 seconds to 1 minute.
[0079] In the development step, the non-exposed areas of the image-recording layer are removed,
preferably without essentially removing the exposed areas, i.e. without affecting
the exposed areas to an extent that renders the ink-acceptance of the exposed areas
unacceptable. Depending on the coating composition, the developer may be plain water,
an aqueous solution such as a gum solution, an alkaline developer, a solvent-based
developer, etc.
[0080] The development step may also be carried out on-press, i.e. while the exposed precursor
is mounted on the plate cylinder of a lithographic printing press, by rotating said
plate cylinder while feeding dampening liquid and/or ink to the coating of the precursor.
In a preferred embodiment, only dampening liquid is supplied to the plate during start-up
of the press. After a number of revolutions of the plate cylinder, preferably less
than 50 and most preferably less than 10, also the ink supply is switched on. In an
alternative embodiment, supply of dampening liquid and ink can be started simultaneously
or only ink can be supplied during a number of revolutions before switching on the
supply of dampening liquid.
[0081] The printing plate thus obtained can be used for conventional, so-called wet offset
printing, in which ink and an aqueous dampening liquid is supplied to the plate during
printing. Another suitable printing method uses so-called single-fluid ink without
a dampening liquid. Suitable single-fluid inks have been described in US 4,045,232;
US 4,981,517 and US 6,140,392. In a most preferred embodiment, the single-fluid ink
comprises an ink phase, also called the hydrophobic or oleophilic phase, and a polyol
phase as described in WO 00/32705. The single-fluid ink can also be used for the on-press
development of the exposed precursor. In that embodiment, no dampening liquid is required
in the development step.
EXAMPLES
[0082] Quantities are expressed in terms of pw = parts per weight or wt.% = weight percentage.
L*, a*, b* values were measured following the ASTM E308-85 method, based on illuminant
D65.
EXAMPLE 1
Preparation of aluminum support AS-1 :
[0083] A 0.3 mm thick aluminum foil was degreased by spraying with an aqueous solution containing
26 g/l of NaOH at 65°C for 2 seconds and rinsed with demineralized water for 1.5 seconds.
The foil was then electrochemically grained during 10 seconds using an alternating
current in an aqueous solution containing 15 g/l of HCl, 15 g/l of SO
42- ions and 5 g/l of Al
3+ ions at a temperature of 37°C and a current density of about 100 A/dm
2. The aluminum foil was then desmutted by etching with an aqueous solution containing
5.5 g/l of NaOH at 36°C for 2 seconds and rinsed with demineralized water for 2 seconds.
The foil was subsequently subjected to anodic oxidation during 15 seconds in an aqueous
solution containing 145 g/l of sulfuric acid at a temperature of 50°C and a current
density of 17 A/dm
2, then washed with demineralized water for 11 seconds and post-treated for 3 seconds
by spraying a solution containing 2.2 g/l of polyvinylphosphonic acid at 70°C, rinsed
with demineralized water for 1 seconds and dried at 120°C for 5 seconds.
[0084] The support thus obtained was characterized by a surface roughness Ra of 0.37 µm
and had an anodic weight of 3.0 g/m
2. The L*, a* and b* values of the anodized surface were as follows :

Preparation of the printing plate precursors PPP-33:
[0085] The coating solution defined in Table 1 was prepared and coated on support AS-1.
After drying, the thickness of the layer was 1.5 g/m
2.

[0086] On top of the image-recording layer, the aqueous solution defined in Table 2 was
coated and then dried at 110°C for 2 minutes to obtain a top coat having a dry thickness
of 2.0 g/m
2.

The lightness value L*
nonexp of the complete material PPP-33 (support + image-recording layer + top coat) was
67. Its ISO visual density was 0.43.
Image-wise exposure
[0087] Plate precursor PPP-33, which comprises color-forming IR dye IRD-004 in the top coat,
was exposed with a Creo Trendsetter IR laser (830 nm) at 275 mJ/cm
2. A high-contrast print-out image was observed : the exposed areas were dark blue
as opposed to the pale green background color of the non-exposed areas. ΔL* of the
print-out image was 10.6 and ΔE was 12.3.
EXAMPLES 2 and 3
Preparation of the printing plate precursors PPP-34 and 35:
[0088] Two coating solutions were prepared and coated on separate samples of support AS-1
at a dry thickness of 1.5 g/m
2. The dried image-recording layers had the composition specified in the following
table :

[0089] On top of the image-recording layer, the aqueous solution defined in Table 4 was
coated and then dried at 110°C for 2 minutes to obtain a top coat having a dry thickness
of 2.0 g/m
2.
Table 4 : Composition (g) of the coating solution of the protective top coat
Ingredient |
PPP-34 |
PPP-35 |
partially hydrolyzed polyvinylalcohol (degree of hydrolysis 88 %, viscosity 4 mPa·s
in a solution of 4 wt.% at 20 °C). |
17.03 |
partially hydrolyzed polyvinylalcohol (degree of hydrolysis 88 %, viscosity 8 mPa·s
in a solution of 4 wt.% at 20 °C). |
7.43 |
fully hydrolyzed polyvinylalcohol (degree of hydrolysis 98 %, viscosity 6 mPa·s in
a solution of 4 wt.% at 20 °C). |
14.87 |
Acticide LA1206 (see table 2) |
0.26 |
Metolat FC 355 (see table 2) |
0.38 |
Lutensol A8 (90%) (see table 2) |
0.032 |
Water |
960 |
The lightness value L*nonexp of the complete materials PPP-34 and -35 was 66 and 65 respectively. The ISO visual
density was 0.46 and 0.47 respectively. |
Image-wise exposure
[0090] Plate precursors PPP-34 and 35 were exposed with a Creo Trendsetter IR laser (830
nm) at 275 mJ/cm
2. PPP-34 and PPP-35 showed a high-contrast print-out image : the exposed areas were
dark blue as opposed to the green background color of the non-exposed areas. ΔL* of
the print-out image obtained with PPP-34 and -35 was 9.0 and 14.9 respectively. ΔE
was 11.0 and 15.6 respectively.
EXAMPLES 4 and 5
[0091] In these examples, a color forming system according to embodiment 3, discussed above,
was used wherein a dye D (ingredient L defined below) and a nucleophilic compound
Q (NUC-07 and NUC-08 respectively, defined above) are allowed to form interaction
product DQ. The following ingredients were used in Examples 4 and 5 :
(A) A solution containing 32.8 wt.% of a methyl methacrylate /methacrylic acid-copolymer
(ratio methylmethacrylate /methacrylic acid of 4:1 by weight; acid number: 110 mg
KOH/g) in 2-butanone (viscosity 105 mm2/s at 25°C).
(B) A solution containing 86.8 wt.% of a reaction product from 1 mole of 2,2,4-trimethyl-hexamethylenediisocyanate
and 2 moles of hydroxyethylmethacrylate (viscosity 3.30 mm2/s at 25°C).
(C) Infrared dye IR-1 (see table 1).
(D) S-Triazine
(E) Edaplan LA 411@ (1 wt.% in Dowanol PM@, trade mark of Dow Chemical Company).
(F) 2-Butanone.
(G) Propyleneglycol-monomethylether (Dowanol PM@, trade mark of Dow Chemical Company).
(H) Water
(L) A 7.5 wt.% solution of the following dye in water :

(M) A 1 wt.% solution of the following IR dye in water :

(N) A solution of 3 wt.% of NUC-07 (see above) in water.
(O) A solution of 3 wt.% of NUC-08 (see above) in water.
(P) A 5 wt.% aqueous solution of GLASCOL D15, a polyacrylic acid, commercially available
from ALLIED COLLOIDS.
[0092] A coating solution was prepared by mixing the ingredients as specified in Table 5.
This composition was coated on support AS-1 and was dried at 105 °C . The resulting
thickness of the layer was 1.5 g/m
2.
Table 5 : Composition of the coating solution of the image-recording layer.
Ingredient |
Parts per weight (g) |
(A) |
5.77 |
(B) |
3.14 |
(C) |
0.13 |
(D) |
0.34 |
(E) |
0.57 |
(F) |
16.72 |
(G) |
33.32 |
[0093] On top of the above image-recording layer, the aqueous solution defined in table
6 was coated and then dried at 120°C for 2 minutes to obtain a top coat having a dry
thickness of 0.80 g/m
2.
Table 6 : Composition (g) of the coating solution of the top coat layers OC-01 and
OC-02.
Ingredient |
OC-01 (Example 4) |
OC-02 (Example 5) |
(L) |
3.02 |
3.02 |
(N) |
7.56 |
- |
(O) |
- |
7.56 |
(M) |
22.67 |
22.67 |
(P) |
39.73 |
39.73 |
(H) |
27.02 |
27.02 |
The lightness value L*nonexp of the complete materials with top coat OC-01 and OC-02, i.e. measured on the complete
material (support + image-recording layer + top coat), was 64 and 63 respectively.
The ISO visual density was 0.49 and 0.51 respectively. |
Image-wise exposure
[0094] The plate precursors of Examples 4 and 5 were exposed with a Creo Trendsetter 3244T
(plate setter available from Creo, Burnaby, Canada), operating at 300 mJ/cm
2 and 150 rpm. The ΔL* values of the print-out image were 10.4 and 6.3 respectively.
The ΔE values were 17.4 and 8.1 respectively.
[0095] After development with an aqueous alkaline developer, the above plates of Examples
1-5 were mounted on a press and produced very good prints.