FIELD OF THE INVENTION
[0001] The present invention relates to a positive working lithographic printing plate precursor
that requires aqueous alkaline processing and comprises an infrared absorbing dye
containing a polysiloxane group.
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 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 so-called computer-to-film method
wherein various pre-press steps such as typeface selection, scanning, color separation,
screening, trapping, layout and imposition are accomplished digitally and each color
selection is transferred to graphic arts film using an image-setter. After processing,
the film can be used as a mask for the exposure of an imaging material called plate
precursor and after plate processing, a printing plate is obtained which can be used
as a master.
[0004] A typical printing plate precursor for computer-to-film methods comprise a hydrophilic
support and an image-recording layer of a photosensitive polymer layers which include
UV-sensitive diazo compounds, dichromate-sensitized hydrophilic colloids and a large
variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely
used. Upon image-wise exposure, typically by means of a film mask in a UV contact
frame, the exposed image areas become insoluble and the unexposed areas remain soluble
in an aqueous alkaline developer. The plate is then processed with the developer to
remove the diazonium salt or diazo resin in the unexposed areas. So the exposed areas
define the image areas (printing areas) of the printing master, and such printing
plate precursors are therefore called 'negative-working'. Also positive-working materials,
wherein the exposed areas define the non-printing areas, are known, e.g. plates having
a novolac/naphtoquinone-diazide coating which dissolves in the developer only at exposed
areas.
[0005] In addition to the above photosensitive materials, also heat-sensitive printing plate
precursors are known. Such 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 cross-linking of a
polymer or by particle coagulation of a thermoplastic polymer latex, and solubilization
by the destruction of intermolecular interactions.
[0006] US 5,466,557 describes a positive-working printing plate precursor which is sensitive to both
ultraviolet (UV) and infrared (IR) light but not to visible light, comprising a support
and a coating comprising an oleophilic polymer that is soluble in an aqueous alkaline
developer and a latent Bronsted acid.
[0007] EP-A 864420 describes a positive-working heat-sensitive printing plate precursor comprising a
support, a first layer containing an oleophilic polymer that is soluble in an aqueous
alkaline developer and an IR-sensitive top layer of which the penetrability by or
solubility in the aqueous alkaline developer is changed upon exposure to IR light.
[0008] WO 97/39894 describes a positive-working heat-sensitive printing plate precursor which is sensitive
to IR light but not to UV light comprising a support and an IR-sensitive coating comprising
an oleophilic polymer that is soluble in an aqueous alkaline developer and a dissolution
inhibitor which reduces the solubility of the polymer in the developer.
[0009] WO99/21725 and
WO99/21715 describe a positive-working heat sensitive printing plate precursor of which the
coating comprises a compound which increases the developer resistance thereof. Said
compound is selected from the group of poly(alkylene oxide), siloxanes and esters
or amides of polyhydric alcohols.
[0010] US 5 491 046 describes a method for imaging a positive and/or negative lithographic printing plate
precursor wherein the imaging layer comprises a resole resin, a novolac resin, a latent
Bronsted acid and an IR absorber.
[0011] EP 1 162 078 describes an image formation material comprising a substrate and an image formation
layer on the substrate which contains an infrared absorption dye having at least one
surface orientation group as substituent for the purpose of improving sensitivity
and/or image forming property of the image formation material.
[0012] EP 1 256 444 describes a heat-sensitive lithographic printing plate precursor comprising a coating
comprising in the order given a first layer containing an oleophilic resin soluble
in an aqueous alkaline developer and a second layer capable of preventing penetration
of the developer at unexposed areas, said second layer comprising a water-repellent
compound selected from the group consisting of a polymer comprising siloxane and/or
perfluoroalkyl monomeric units, and a block- or graft-copolymer comprising a poly-
or oligo(alkylene oxide) and a polymer or oligomer comprising siloxane and/ or perfluoroalkyl
monomeric units, and wherein the alkali-solubility of said coating increases on heating
and said coating comprises an infrared light absorbing dye.
[0013] The major problems associated with the prior art materials is (i) the low differentiation
between the development kinetics of exposed and non-exposed areas - i.e. the dissolution
of the exposed coating in the developer is not completely finished before the unexposed
coating also starts dissolving in the developer - and (ii) thermal diffusion of heat
into the substrate resulting in a reduced sensitivity of the printing plate precursor.
This leads to low quality prints showing unsharp edges and toning (ink-acceptance
in exposed areas) and narrow development latitude.
SUMMARY OF THE INVENTION
[0014] It is an object of the present invention to provide a positive-working lithographic
printing plate precursor which shows a high differentiation between exposed and non-exposed
areas and which has a high sensitivity. These objects are realized by the material
in claim 1 and by the specific embodiments in the dependent claims. By providing a
water-repellent compound in the second layer of the coating and by the use of infrared
absorbing dyes comprising specific substituents which increase the compatibility of
the dye with the second layer of the coating the heat created during infrared exposure
is concentrated in the second layer.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The lithographic printing plate precursor of the present invention contains a support
having a hydrophilic surface and a coating provided thereon. The coating comprises
at least two layers, designated herein as first and second layer, the first layer
being closest to the support, i.e. located between the support and the second layer.
The printing plate precursor is positive-working, i.e. after exposure by light and
development the exposed areas of the coating are removed from the support and define
hydrophilic (non-printing) areas, whereas the unexposed coating is not removed from
the support and defines an oleophilic (printing) area. The second layer is believed
to act as a barrier that prevents penetration of the aqueous alkaline developer into
the oleophilic resin of the first layer at unexposed areas. At exposed areas, the
barrier function of the second layer can be reduced due to the exposure and dissolution
of the coating at those areas can be increased upon immersion in an aqueous alkaline
developer. This reduction of the barrier function of the second layer upon exposure
can be tested e.g. by measuring the water uptake, due to swelling of the oleophilic
resin, of an exposed and a non-exposed sample: typically, the exposed sample absorbs
a small amount of water whereas the average water-uptake of non-exposed samples is
within statistical error not different from zero.
[0016] The barrier function of the second layer arises from the presence of a water-repellent
compound. Suitable examples thereof are polymers comprising siloxane and/or perfluoroalkyl
units or block- or graft-copolymers comprising a poly- or oligo(alkylene oxide) block
and a block of poly- or oligosiloxane and/or perfluoroalkyl units. The water-repellent
polymer may be present in an amount of e.g. between 0.5 and 15 mg/m
2, preferably between 0.5 and 10 mg/m
2, more preferably between 0.5 and 5 mg/m
2 and most preferably between 0.5 and 2 mg/m
2. Higher or lower amounts are also suitable, depending on the hydrophobic/oleophobic
character of the compound. When the water-repellent polymer is also ink-repelling,
higher amounts than 15 mg/m
2 can result in poor ink-acceptance of the non-exposed areas. An amount lower than
0.5 mg/m
2 on the other hand may lead to an unsatisfactory development latitude: development
of the exposed areas is not completed before the start of the development of the non-exposed
areas.
[0017] The block comprising the siloxane and/or perfluoroalkyl units may be a linear, branched,
cyclic or complex cross-linked polymer or copolymer. The perfluoroalkyl unit is e.g.
a -(CF
2)- unit. The number of such units may be larger than 10, preferably larger than 20.
The term polysiloxane compound shall include any compound which contains more than
one siloxane group -Si(R,R')-O-, wherein R and R' are optionally substituted alkyl
or aryl groups. Preferred siloxanes are phenylalkylsiloxanes and dialkylsiloxanes,
e.g. phenylmethylsiloxanes and dimethylsiloxanes. The number of siloxane groups -Si(R,R')-O-
in the (co-)polymer is at least 2, preferably at least 10, more preferably at least
20. It may be less than 100, preferably less than 60. The alkylene-oxide block preferably
includes units of the formula -C
nH
2n-O- wherein n is preferably an integer in the range 2 to 5. The moiety - C
nH
2n- may include straight or branched chains. The alkylene-oxide block moiety may also
comprise optional substituents. Preferred embodiments and explicit examples of such
polymers have been disclosed in
WO99/21725. A suitable water-repellent polysiloxane compound is preferably a random or block-copolymer
comprising siloxane and alkyleneoxide groups, suitably comprising about 15 to 25 siloxane
units and 50 to 70 alkyleneoxide groups. Preferred polysiloxanes include a copolymer
of dimethyldichlorosilane, ethylene oxide and propylene oxide. Specific compounds
are the following:

wherein o, p, q, r and s are integers >1.
[0018] In formula I, a poly(alkylene oxide) block consisting of ethylene oxide and propylene
oxide units is grafted to a polysiloxane block. In formula II, long chain alcohols
consisting of ethylene oxide and propylene oxide units are grafted to a trisiloxane
group.
[0019] The second layer may contain the oleophilic resin as well as the water-repellent
compound. However, it is believed that block- or graft-copolymers comprising a poly-
or oligo(alkylene oxide) block and a block of poly- or oligosiloxane and/or perfluoroalkyl
units due to their bifunctional structure, position themselves during coating at the
interface between the coating solution and air and thereby automatically form a separate
layer, corresponding to the second layer of the present invention, even when applied
as an ingredient of the coating solution of the oleophilic layer.
[0020] Alternatively, the water-repellent compound can be applied in a second solution,
coated on top of the first layer. In that embodiment, it may be advantageous to use
a solvent in the second coating solution that is not capable of dissolving in the
ingredients present in the first layer so that a phase of highly concentrated water-repellent
polymer is obtained at the top of the material.
[0021] Whilst the applicants do not wish to be limited by any theoretical explanation of
how their printing plate precursor operates, it is believed that the spreading of
the second layer on the first layer is reduced by the exposure, e.g. by 'thermal dewetting',
i.e. heat-induced decrease of the surface tension of the polysiloxane, to such an
extent that the second layer breaks up, thereby forming an incomplete layer which
can no longer shield the first layer from the developer completely. Rubbing with a
cotton pad also removes a sufficient amount of the polysiloxane to trigger development.
The removal of the polysiloxane by rubbing can be measured e.g. by comparing the ratio
of the siloxane
1H-NMR signals versus the signals of the phenolic resin of a sample before and after
rubbing.
[0022] The oleophilic resin is preferably a polymer that is soluble in an aqueous developer,
more preferably an aqueous alkaline developing solution with a pH between 7.5 and
14. Preferred polymers are phenolic resins e.g. novolac, resoles, polyvinyl phenols
and carboxy substituted polymers. Typical examples of these polymers are described
in
DE-A-4007428,
DE-A-4027301 and
DE-A-4445820.
[0023] The coating comprises an IR dye containing a polysiloxane group, which sensitizes
the material to the IR light used during the exposure. The polysiloxane group can
be linear, branched, cyclic or complex cross-linked. The number of silicium atoms
in the polysiloxane group may be greater than 2, preferably 4 or greater than 4. Preferred
siloxane groups -Si(R,R')-O- are groups wherein R and R' are optionally substituted
alkyl or aryl groups. Preferred siloxane groups are phenylalkylsiloxanes and dialkylsiloxanes,
e.g. phenylmethylsiloxanes and dimethylsiloxanes. The IR dye is preferably a compound
having an absorption maximum in the wavelength range between 750 and 1500 nm, so that
a daylight stable material is obtained which can be handled without the need for darkroom
conditions. Daylight stable material means that no substantial dissolution in the
developer is induced by exposure to visible light.
[0024] The sensitizing dye may be present in the first layer, in the second layer discussed
above or in an optional other layer. It is believed that the high hydrophobicity of
the polysiloxane group comprised in the IR light absorbing dye makes the dye more
compatible with the water-repellent compound and thereby promotes the tendency of
the dye to position itself preferentially in the second layer, i.e. further away from
the support. As a result, the heat generated by the exposure is concentrated in the
second layer and a high sensitivity is observed. The concentration of the IR absorbing
compound in the coating is typically between 0.25 and 10.0 wt %, more preferably between
0.5 and 7.5 wt %.
[0025] Preferred IR absorbing compounds for use in this invention are represented by the
general formula III:

wherein
a and b each independently represent an integer from 0 to 4;
-L1- and -L2- independently represent a divalent linking group such as alkylene, arylene, heteroarylene,
-(CH2)t-O-, -(CH2)t-NH-,-(CH2)t-COO-, -(CH2)t-COO-(CH2)u-, -(CH2)t-OCO-,-(CH2)t-OCO-(CH2)u-,-(CH2)t-CONH- or -(CH2)t-CONH-SO2-, or combinations thereof;
-E1 and -E2 independently represent a neutral, anionic or cationic terminal group selected from
alkyl, -H, -OH, -Cl, -Br,-F, -SiRaRbRc (neutral groups); -SO3- , -SO4-, -PO32-, -PO42-, -COO- (anionic groups); -[NRdReRf]+(cationic group);
Ra, Rb and Rc independently represent an optionally substituted alkyl, alkenyl, aryl or aralkyl
group;
Rd, Re and Rf independently represent a hydrogen atom or an optionally substituted alkyl, alkenyl,
aryl or aralkyl group; -A1- and -A2- independently represent -[Si(RgRh)-O]m-, -CvF2v-, -[(CF2)2-O]w- or an optionally substituted alkyl, alkenyl, aryl or aralkyl group;
Rg and Rh independently represent an optionally substituted alkyl, alkenyl, aryl or aralkyl
group, -[O-Si(RaRb)]q-E1 or -[O-Si(RaRb)]q-E2;
with p1 and p2 is 0 or 1;
with t , u, q and m is 1 or an integer greater than 1;
with v and w is 2 or an integer greater than 2;
-Y1- and -Y2- independently represent one or two non-metallic atoms, which may be substituted,
necessary to complete a 5- or 6-membered heterocyclic ring;
-Z1 and -Z2 each independently represent a hydrogen atom, an alkyl group or -Z1 and -Z2 together represent the necessary atoms to complete a 5- or 6-membered ring;
R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl, alkenyl,
aryl or aralkyl group or a group selected from a halogen atom, -NO2, -O-Ri, -CO-Ri, -CO-O-Ri, -O-CO-Ri, -CO-NRiRj, -NRiRj, -NRi-CO-Rj, -NRi-CO-O-Rj, -NRi-CO-NRjRk, -SRi, -SO-Ri, -SO2-Ri, -SO2-O-Ri, -SO2NRiRj, a perfluoroalkyl group or a polysiloxane group; each of said groups may optionally
comprise a terminal group E defined above as -E1 and -E2 and/or wherein two adjacent groups selected from R1, R2 ,-Y1- and -Y2- together form an optionally substituted 5- or 6- membered ring;
Ri, Rj and Rk independently represent a hydrogen or an optionally substituted alkyl, alkenyl, aryl
or aralkyl group;
R3 represents a substituent selected from a hydrogen, a halogen atom, an alkyl, alkenyl,
aryl or aralkyl group, a perfluoroalkyl group, a polysiloxane group, an amino group,
a thioalkyl group, a thioaryl group, an aryloxy group, an alkoxy group, a barbituric
group or a thiobarbituric group, each of said groups being optionally substituted;
X represents one or more optional counter ions selected from: Cl-, Br-, I-, F-, D-SO3-, D-SO4-, D-PO42-, D-PO32-, D-COO-,D-[NRoRpRq]+, ClO4 or BF4-;
D represents Si(RrRsRt)-[O-Si(RuRv)]n-, [(RrRsRt)SiO]3-Si-, CjF2j+1-, CF3-[(CF2)2-O]i-, an alkyl group, an aryl group or a substituted aryl group;
with n and i are 1 or an integer greater than 1;
with j is 3 or an integer greater than 3;
Ro, Rp, Rq, independently represent a hydrogen atom or an optionally substituted alkyl, alkenyl,
aryl or aralkyl group;
Rr, Rs, Rt, Ru and Rv independently represent an optionally substituted alkyl, alkenyl, aryl or aralkyl
group;
with the proviso that for the general formula III above at least one of the following
substituents is represented by a polysiloxane group: -A1-, -A2-, R1, R2, R or X.
[0026] In the embodiment wherein the IR light absorbing dye carries a negative or positive
electrical charge, a counter ion X with opposite charge is required to neutralize
the compound. The dye can be anionic or cationic as the chromophore and/or polysiloxane
containing substituents on the chromophore and/or other substituents on the chromophore
can have a charge. The unit of charge of the dye is determined by the sum of the positive
and/or negative charges of the substituents on the dye and one or more counter ions
with equal sum of opposite charge is present to neutralize the dye. The unit of charge
of the counter ions can be mono or multiple and/or positive or negative.
[0027] In the embodiment wherein -E
1 and -E
2 represent a neutral terminal group such as alkyl, -H, -OH,-F or -SiR
aR
bR
c (and no other charged groups are present on the IR light absorbing dye), a counter
ion X carrying a negative charge is present to neutralise the positively charged IR
light absorbing dye. If, on the other hand one of the terminal groups is represented
by an anionic group such as-SO
3-, -SO
4-, or -COO (and the other terminal group is represented by a neutral group and no other
charged groups are present on the IR light absorbing dye) no counter ion is required.
One of the terminal groups can be a cationic group such as -[NR
aR
bR
c]
+, than one counter ion carrying two negative charges (e.g. D-PO
42-, D-PO
32-) or two counter ions each carrying one negative charge (e.g. Cl, Br
-, I
-, F
-, D-SO
3-, D-SO
4-, D-COO
-, ClO
4- or BF
4-) are present. Depending on the kind of the terminal groups -E
1 and -E
2 and their unit of charge, none, one or more counter ions are necessary to neutralise
the IR light absorbing dye.
[0028] In the embodiment wherein R
3 represents a substituent carrying a negative charge, e.g. a negatively charged barbituric
group, and no other substituents carrying a positive or negative charge are present
on the IR light absorbing dye, a Zwitterion where the sum of charge of the dye is
zero is obtained and no counter ion is present.
[0029] Negatively charged barbituric group:

wherein R
4 and R
5 independently represent an optionally substituted alkyl, alkenyl, cycloalkyl, aryl
or aralkyl group, a perfluoroalkyl group or a polysiloxane group; each of said groups
may optionally comprise a terminal group E defined above as -E
1 and -E
2. The negatively charged barbituric group is bonded to the heptamethine group by *.
[0031] In the above formulae IV to XIV, P1, P2, a, b, -L
1-, -L
2-, -A
1 -, -A
2-, -E
1, -E
2, R
1, R
2, R
3, -Y
1-, -Y
2-, -Z
1, -Z
2 and X have the same meaning as in formula III above; R
4 and R
5 have the same meaning as defined above, with the proviso that at least one of the
following substituents is represented by a polysiloxane group: -A
1-, -A
2-, R
1, R
2, R
3, R
4, R
5 or X.
[0032] Additional suitable subclasses of IR light absorbing dyes are represented by formulae
wherein two adjacent R
1 groups or two adjacent R
2 groups form an optionally substituted phenyl group, annelated with another phenyl
group of the dye. So any of the formulae III to XIV wherein such phenyl group is present
also represent dyes that are suitable for a precursor of the present invention. Two
preferred embodiments of such dyes are represented by formulae XV and XVI:

wherein
P1, P2, a, b, -L1-, -L2-, -E1 , -E2 , -A1-,-A2-, -Y1-, -Y2 -, -Z1, - Z2, -R3 and X have the same meaning as in formula III above;
c and d are independently 0, 1 or 2;
each R6 to R9 independently represent a group as defined for R1 and R2 above;
with the proviso that at least one of the following substituents is represented by
a polysiloxane group: -A
1-, -A
2-, R
3, R
6 to R
9 or X.
[0033] In formulae IV to XIV two adjacent R
1 groups and/or two adjacent R
2 groups can form an optionally substituted annelated phenyl group and such subclasses
also are part of the present invention.
[0034] Other preferred subclasses of IR light absorbing dyes are represented by formula
III in which the polysiloxane group is covalently linked to the dye and/or comprised
in the counter ion X, if a counter ion X is present. The indices/substituents p
1, p
2, -L
1-, -L
2-, -E
1, -E
2, -A
1-, -A
2-, -Y
1-, -Y
2-, R
1, R
2, R
3, -Z
1, -Z
2 and X have the same meaning as in formula III above.
[0035] Additional preferred subclasses of IR light absorbing dyes are represented by formula
III in which the polysiloxane group is not covalently linked to the dye but comprised
in the counter ion X. The indices/substituents p
1, p
2, -L
1-, -L
2-, -E
1, -E
2, -A
1-, -A
2-, -Y
1-, -Y
2-, R
1, R
2, R
3, -Z
1, -Z
2 and X have the same meaning as in formula III above with the proviso that:
- -A1-, -A2-, R1, R2 and R3 can not represent a polysiloxane group;
- X contains a polysiloxane group.
[0036] Further preferred subclasses of IR light absorbing dyes are represented by the following
formulae XVII and XVIII:

wherein
R10 represents -(CH2)e-Si-[OSi(R11R12R13)]3 or
-(CH2)e-OCO-(CH2)f-[Si(R14R15)-O]g-(CH2)h-CH3;
R4 and R5 have the same meaning as defined above;
R11, R12, R13, R14 and R15 independently represent an optionally substituted alkyl, alkenyl, aryl or aralkyl
group;
e, f, g and h are 1 or an integer greater than 1.
[0039] The first layer may further contain other ingredients such as additional binders
to improve the run length of the plate, colorants, development inhibitors as disclosed
in
WO 97/39894 and
EP-A 823 327 or accelerators such as 3,4,5-trimethoxybenzoic acid. Said colorants are preferably
dyes which during development remain in the coating at non-exposed areas and which
are washed out at exposed areas, thereby producing a visible image. Such indicator
dyes preferably do not sensitize the coating to visible light.
[0040] Suitable development accelerators are described in e.g.
EP-A933682. Such compounds act as dissolution promoters because they are capable of reducing
the dissolution time of the first layer. For example, cyclic acid anhydrides, phenols
or organic acids can be used in order to improve the aqueous developability. Example
of the cyclic acid anhydride include phtalic anhydride, tetrahydrophtalic anhydride,
hexahydrophtalic anhydride, 3,6-endoxy 4-tertrahydrophalic anhydride, tetrachlorophtalic
anhydride, maleic anhydride, chloromaleic anhydride, alpha-phenylmaleic anhydride,
succinic anhydride, alpha-phenylmaleic anhydride, succinic anhydride, and pyromellitic
anhydride, as described in
U.S. Patent No. 4,115,128. Examples of the phenols include bisphenol A, p-nitrophenol, p-ethoxyphenol, 2,4,4'-trihydroxybenzophenone,
2,3,4-trihydroxy-benzophenone, 4-hydroxyphenone, 4,4',4"-trihydroxytriphenylmethane,
and 4,4',3",4"-tetrahydroxy-3,5,3',5'-tetramethyltriphenyl-methane, and the like.
Examples of the organic acids include sulfonic acids, sulfinic acids, alkylsulfuric
acids, phosphonic acids, phosphates, and carboxylic acids, as described in, for example,
JP-A Nos. 60-888,942 and
2-96,755. Specific examples of these organic acids include p-toluenesulfonic acid, dodecylbenzenesylfonic
acid, p-tolenesulfinic acid, ethylsulfuric acid, phenylphosphonic acid, phenylphosphinic
acid, phenyl phosphate, diphenyl phosphate, benzoic acid, isophtalic acid, adipic
acid, p-toluic acid, 3,4-dimethylmethoxybenzoic acid, phtalic acid, terephtalic acid,
4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid,
and ascorbic acid. The amount of the cyclic acid anhydride, phenol, or organic acid
contained in the image forming composition is preferably in the range of 0.05 to 20%
by weight.
[0041] The support has a hydrophilic surface or is provided with a hydrophilic layer. The
support may be a sheet-like material such as a plate or it may be a cylindrical element
such as a sleeve which can be slid around a print cylinder of a printing press. Preferably,
the support is a metal support such as aluminum or stainless steel.
[0042] A particularly preferred lithographic support is an electrochemically grained and
anodized aluminum support. The anodized aluminum support may be treated to improve
the hydrophilic properties of its surface. For example, the aluminum support may be
silicated by treating its surface with a sodium silicate solution at elevated temperature,
e.g. 95°C. Alternatively, a phosphate treatment may be applied which involves treating
the aluminum oxide surface with a phosphate solution that may further contain an inorganic
fluoride. Further, the aluminum oxide surface may be rinsed with a citric acid or
citrate solution. This treatment may be carried out at room temperature or may be
carried out at a slightly elevated temperature of about 30 to 50°C. A further interesting
treatment involves rinsing the aluminum oxide surface with a bicarbonate solution.
Still further, the aluminum oxide surface may be treated with polyvinylphosphonic
acid, polyvinylmethylphosphonic 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. It is further evident that one or more of these post treatments may be carried
out alone or in combination. More detailed descriptions of these treatments are given
in
GB-A- 1 084 070,
DE-A- 4 423 140,
DE-A- 4 417 907,
EP-A- 659 909,
EP-A- 537 633,
DE-A- 4 001 466,
EP-A- 292 801,
EP-A- 291 760 and
US-P- 4 458 005.
[0043] According to another embodiment, the support can also be a flexible support, which
is provided with a hydrophilic layer, hereinafter called 'base layer'. The flexible
support is e.g. paper, plastic film, thin aluminum or a laminate thereof. Preferred
examples of plastic film are polyethylene terephthalate film, polyethylene naphthalate
film, cellulose acetate film, polystyrene film, polycarbonate film, etc. The plastic
film support may be opaque or transparent.
[0044] The base layer is preferably a cross-linked hydrophilic layer obtained from a hydrophilic
binder cross-linked with a hardening agent such as formaldehyde, glyoxal, polyisocyanate
or a hydrolyzed tetra-alkylorthosilicate. The latter is particularly preferred. The
thickness of the hydrophilic base layer may vary in the range of 0.2 to 25 µm and
is preferably 1 to 10 µm.
[0045] The hydrophilic binder for use in the base layer is e.g. a hydrophilic (co)polymer
such as homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide,
methylol methacrylamide, acrylate acid, methacrylate acid, hydroxyethyl acrylate,
hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers. The hydrophilicity
of the (co)polymer or (co)polymer mixture used is preferably the same as or higher
than the hydrophilicity of polyvinyl acetate hydrolyzed to at least an extent of 60%
by weight, preferably 80% by weight.
[0046] The amount of hardening agent, in particular tetraalkyl orthosilicate, is preferably
at least 0.2 parts per part by weight of hydrophilic binder, more preferably between
0.5 and 5 parts by weight, most preferably between 1 parts and 3 parts by weight.
[0047] The hydrophilic base layer may also contain substances that increase the mechanical
strength and the porosity of the layer. For this purpose colloidal silica may be used.
The colloidal silica employed may be in the form of any commercially available water
dispersion of colloidal silica for example having an average particle size up to 40
nm, e.g. 20 nm. In addition inert particles of larger size than the colloidal silica
may be added e.g. silica prepared according to Stöber as described in
J. Colloid and Interface Sci., Vol. 26, 1968, pages 62 to 69 or alumina particles or particles having an average diameter of at least 100 nm which
are particles of titanium dioxide or other heavy metal oxides. By incorporating these
particles the surface of the hydrophilic base layer is given a uniform rough texture
consisting of microscopic hills and valleys, which serve as storage places for water
in background areas.
[0049] It is particularly preferred to use a film support to which an adhesion improving
layer, also called support layer, has been provided. Particularly suitable adhesion
improving layers for use in accordance with the present invention comprise a hydrophilic
binder and colloidal silica as disclosed in
EP-A- 619 524,
EP-A- 620 502 and
EP-A- 619 525. Preferably, the amount of silica in the adhesion improving layer is between 200
mg/m
2 and 750 mg/m
2. Further, the ratio of silica to hydrophilic binder is preferably more than 1 and
the surface area of the colloidal silica is preferably at least 300 m
2/gram, more preferably at least 500 m
2/ gram.
[0050] The printing plate precursor of the present invention can be exposed to light, e.g.
by means of LEDs or a laser head. Preferably, one or more lasers or a laser diode
are used. The light used for the exposure is infrared light having a wavelength in
the range from about 750 to about 1500 nm and preferably a laser such as a semiconductor
laser diode, a Nd:YAG or a Nd:YLF laser is used. The required laser power depends
on the sensitivity of the image-recording layer, the pixel dwell time of the laser
beam, which is determined by the spot diameter (typical value of modern plate-setters
at 1/e
2 of maximum intensity: 10-25 µm), the scan speed and the resolution of the exposure
apparatus (i.e. the number of addressable pixels per unit of linear distance, often
expressed in dots per inch or dpi; typical value: 1000-4000 dpi).
[0051] Two types of laser-exposure apparatuses are commonly used: internal (ITD) and external
drum (XTD) plate-setters. ITD plate-setters for thermal plates are typically characterized
by a very high scan speed up to 1500 m/sec and may require a laser power of several
Watts. The Agfa Galileo T (trademark of Agfa Gevaert N.V.) is a typical example of
a plate-setter using the ITD-technology. XTD plate-setters operate at a lower scan
speed typically from 0.1 m/sec to 20 m/sec and have a typical laser-output-power per
beam from 20 mW up to 500 mW. The Creo Trendsetter plate-setter family (trademark
of Creo) and the Agfa Excalibur plate-setter family (trademark of Agfa Gevaert N.V.)
both make use of the XTD-technology.
[0052] The known plate-setters can be used as an off-press exposure apparatus, which offers
the benefit of reduced press down-time. XTD plate-setter configurations can also be
used for on-press exposure, offering the benefit of immediate registration in a multi-color
press. More technical details of on-press exposure apparatuses are described in e.g.
US 5,174,205 and
US 5,163,368.
[0053] In the development step, the non-exposed areas of the coating are removed by immersion
in an aqueous alkaline developer, which may be combined with mechanical rubbing, e.g.
by a rotating brush. The development step may be followed by a drying step, a rinsing
step, a gumming step, and/or a post-baking step.
[0054] The printing plate thus obtained can be used for conventional, so-called wet offset
printing, in which ink and an aqueous dampening liquid are supplied to the plate.
Another suitable printing method uses so-called single-fluid ink without a dampening
liquid. Single-fluid inks which are suitable for use in the method of the present
invention have been described in
US 4,045,232 and
US 4,981,517. 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.
Examples
SYNTHESIS OF THE IR LIGHT ABSORBING DYES.
Synthesis of IR-1
Product 1 + product 2 → IR-1
[0055]

[0056] 2 mol of product 1 and 1 mol of product 2 are dissolved in 7.5 1 acetonitrile and
stirred at 70°C for 90 minutes. After this period, 17 1 acetonitrile is added and
the reaction mixture is cooled to room temperature. IR-1 is filtered and dried. (Yield
= 46%)
Synthesis of intermediate product 1
Product 3 + product 4 → product 1
[0057]

[0058] 1 mol of product 4, 1.4 mol of product 3 and 1 mol of potassium Iodide are added
to 0.3 1 sulfolane. The reaction mixture is kept for 6 hours at 150°C; subsequently
the mixture is cooled to room temperature and 2 1 methyl-tertiair-butylether is added.
After extraction with 10 1 water, 2 1 butylacetate is added to the organic layer.
The reaction mixture is stirred for 30 minutes and product 1 is filtered and dried.
(yield = 21%)
Synthesis of intermediate product 2
Product 5 + product 6 → product 2
[0059]

[0060] 1 mol of product 5 and 3.5 mol of product 6 are added to 0.3 1 ethylacetate and the
mixture is kept at 65°C for 30 minutes. 0.75 1 methyl-tertiair-butylether and 0.7
1 hexane are added and product 2 is filtered and dried. (yield = 55%)
Synthesis of intermediate product 5
Product 6 + product 7 → product 5
[0061]

[0062] To 1 mol of product 7 in 0.8 1 toluene and 1 mol of acetic acid, 1,13 mol of product
6 is added at room temperature. Subsequently 1,5 1 hexane is added and the reaction
mixture is stirred for 1 hour at room temperature. Product 5 is filtered and dried.
(yield = 79%)
Synthesis of intermediate product 7
Product 8 + cyclopentanon → product 7
[0063]

[0064] 1 mol of product 8, 1.1 mol cyclopentanon, 0.07 mol ammonium acetate and 0.15 1 methanol
are mixed and refluxed for 4.5 hours. After that period, 1 l toluene is added and
methanol and water are separated by distillation. The reaction solution obtained is
used for synthesis of intermediate product 5.
Synthesis of intermediate product 8
Product 9 + product 10 → product 8
[0065]

[0066] 1 mol of product 9, 1 mol of product 10, 2 mol of acetic acid anhydride and 0.15
l acetic acid are reacted at 90 °C for 2.5 hours. Acetic acid is removed by vacuum
distillation and product 8 is obtained.
Synthesis of intermediate product 9
Product 11 + product 12 → product 9
[0067]

[0068] 1 mol of product 11 is dissolved in 0.07 1 toluene and 1 mol of product 12 is added
at 50°C. The solvent is evaporated and product 9 is obtained.
Synthesis of IR-2
Product 13 + product 14 + product 18 → IR-2
[0069]

[0070] 4 mol of product 14 and 2 mol of product 18 are stirred in 10 1 toluene for 10 minutes
at 80 °C. Subsequently, 1 mol of product 13 and 40 l toluene are added. The reaction
mixture is refluxed for 45 minutes. The organic layer is evaporated and the remaining
product is dissolved in a mixture of 5 1 toluene and 5 1 methanol. 40 1 methanol is
added and IR-2 is filtered and dried. (yield = 50%)
Synthesis of intermediate product 13
Product 15 + product 16 → product 13
[0071]

[0072] 1 mol of product 15, 1.1 mol of product 16 and 1.5 mol of potassium acetate are dissolved
in 4 1 methylene chloride and 6 1 methanol. The mixture is stirred for one hour at
room temperature. Product 13 is filtered and dried. (yield = 30%)
Synthesis of intermediate product 15
Product 19 + product 20 → product 15
[0073]

[0074] A mixture of 2 mol of product 19, 1 mol of product 20, 4 1 methanol, 0.5 1 triethyl
amine and 0.4 1 acetic acid anhydride is stirred at 60°C for 2 hours. 200 g NaI and
4 l methyl-tertiair-butylether are added. Product 15 is filtered and dried. (yield
= 25%)
Synthesis of intermediate product 19
[0075] 1 mol of product 3 and 0.1 mol 2-bromoethanol are dissolved in 0,2 1 sulfolane and
are kept at 100°C for 4 hours. Adding 1 l acetone precipitates the product. Product
19 is filtered and dried. (yield = 82%)
Synthesis of intermediate product 16
Product 29 + product 10 → product 16
[0076]

[0077] A mixture of 1 mol of product 29, 0.5 1 toluene, 0.18 1 acetic acid, 1.05 mol of
product 10 and 0.25 1 acetic acid anhydride are kept at 100°C for 2.5 hours. The reaction
mixture is poured into methanol/water and product 16 is filtered and dried. (yield
= 44%)
Synthesis of intermediate product 29
Product 17 + product 18 → product 29
[0078]

[0079] 2 mol of product 17 and 1 mol of product 18 are stirred at 90°C for 30 minutes. The
reaction mixture is poured into methanol/water and product 29 is filtered and dried.
(yield = 28%)
Synthesis of IR-3
Product 14 + product 18 + product 24 → IR-3
[0080]

[0081] 4 mol of product 14, 10 l toluene and 2 mol of product 18 are kept at 80°C for 10
minutes. Subsequently 1 mol of product 24 and 50 l toluene are added and the mixture
is refluxed for 45 minutes. The organic layer is evaporated and 5 1 toluene and 5
1 methanol is added. After addition of 40 1 methanol, IR-3 is filtered and dried.
(yield = 75 %)
Synthesis of intermediate product 24
Product 25 + product 16 → product 24
[0082]

[0083] 8 l methanol, 4 1 methylene chloride, 1 mol of product 25, 1 mol of product 16 and
1.5 mol of potassium acetate are stirred at room temperature for 3 hours. Adding methyl
ethyl ketone precipitates the product. Product 19 is filtered, washed with water and
dried. (yield = 67%)
Synthesis of intermediate product 25
Product 20 + product 26 → product 25
[0084]

[0085] 2 l methanol, 0.25 1 triethylamine, 2 mol of product 26, 1 mol of product 20 and
0.2 1 acetic acid anhydride are stirred at 60°C for 2 hours. Product 25 is filtered
and dried. (yield = 40%)
Synthesis of intermediate product 26
2-bromoethanol + product 27 → product 26
[0086]

[0087] 1 mol of product 27 and 1.1 mol of 2-bromoethanol are dissolved in 2 1 sulfolane
and stirred at 100°C for 4 hours. Adding aceton precipitates the product. Product
26 is filtered and dried. (yield = 85%)
Synthesis of intermediate product 20
[0088] 10 mol of dimethylformamide, 3 mol phosphorylchloride are heated to 65°C. Than 1
mol of cyclopentanon is dropped to this mixture and the mixture is stirred for 1 hour
at 60°C. The reaction mixture is poured into 2 1 water containing 7 mol sodium acetate.
Product 20 is filtered and dried. (yield = 60%)
Synthesis of IR-4
Product 28 + product 18+ product 24 → IR-4
[0089]

[0090] 4 mol of product 28 and 2 mol of product 18 are added to 50 1 toluene and the mixture
is stirred for 10 minutes at 80°C. 1 mol of product 24 and 50 1 toluene are added
and the mixture is refluxed for 45 minutes. The organic layer is evaporated and 500
1 hexane is added. The mixture is filtered and the filtrate is evaporated. IR-4 is
obtained. (yield = 11%)
Synthesis of IR -COMP1
[0091] Product 30 + product 16 → IR -COMP1

[0092] 1 mol of product 30 and 1 mol of product 16 are dissolved in 15 1 methanol and 7
1 methylene chloride. 2 mol potassium acetate is added and the mixture is stirred
for 3 hours at 40°C. After evaporation of methylene chloride, COMP-1 is filtered and
dried. (Yield 46%)
Synthesis of intermediate product 30
Product 31 + product 32 → product 30
[0093]

[0094] 1 mol of product 32 and 2 mol of product 31 are added to 2 1 acetic acid anhydride
and 2.2 mol triethylamine. The mixture is stirred for 2 hours at room temperature.
After stirring 40 l ethyl acetate is added and product 30 is filtered and dried. (Yield
= 30%)
Synthesis of intermediate product 31
Product 27 + n-butyl bromide → product 31
[0095] 1 mol of product 27 and 2 mol n-butyl bromide are stirred in 0.5 1 sulfolane for
four hours at 100°C. Product 31 is filtered, washed with ethyl acetate and dried.
(Yield: 61%)
Synthesis of intermediate product 32
Product 33 + product 34 → product 32
[0096]

[0097] 1 mol of product 33 and 2 mol of product 34 are dissolved in 5 1 acetone and 2 1
water and stirred for one hour at room temperature. Product 32 is filtered and dried.
(Yield = 80%)
Examples 1 and 2
[0098] These examples demonstrate the use of infrared dyes which contain a polysiloxane
group in a coating according to the present invention in which the water repellent-compound
is a polysiloxane containing polymer.
Preparation of the support
[0099] A 0.30 mm thick aluminum foil was degreased by immersing the foil in an aqueous solution
containing 5 g/l of sodium hydroxide at 50°C and rinsed with demineralized water.
The foil was then electrochemically grained using an alternating current in an aqueous
solution containing 4 g/l of hydrochloric acid, 4 g/l of hydroboric acid and 5 g/l
of aluminum ions at a temperature of 35°C and a current density of 1200 A/m
2 to form a surface topography with an average center-line roughness Ra of 0.5 µm.
[0100] After rinsing with demineralized water the aluminum foil was then etched with an
aqueous solution containing 300 g/l of sulfuric acid at 60°C for 180 seconds and rinsed
with demineralized water at 25°C for 30 seconds.
[0101] The foil was subsequently subjected to anodic oxidation in an aqueous solution containing
200 g/l of sulfuric acid at a temperature of 45°C, a voltage of about 10 V and a current
density of 150 A/m
2 for about 300 seconds to form an anodic oxidation film of 3.00 g/m
2 of Al
2O
3 then washed with demineralized water, post-treated with a solution containing polyvinylphosphonic
acid and subsequently with a solution containing aluminum trichloride, rinsed with
demineralized water at 20°C during 120 seconds and dried.
Plate precursor materials
[0102] The solutions in Table 1 below were coated on the above support at a wet coating
thickness of 20 µm and dried for 1 minute at 130°C. The materials were then imaged
on a Creo Trendsetter 3244 (830 nm) using different energy density settings (intensity
at the image plane) in the range from 80 mJ/cm
2 up to 200 mJ/cm
2. The plates were then processed by dipping for 60 seconds in a development tank filled
with DP300 (aqueous alkaline developer commercially available from Agfa) at a temperature
of 25°C. The IR-sensitivity of the different compositions corresponds to the minimum
energy density setting that is required to obtain a 50% reduction of the light absorption
of the coating, measured on the developed plate at the wavelength maximum of the contrast
dye, in areas which have been exposed with a dot area of a 50% screen (@200 lpi).
[0103] The results in Table 1 indicate that the coating which comprises an infrared dye
containing a polysiloxane group provide a higher sensitivity than the comparative
coating in which the corresponding infrared dye does not contain a polysiloxane group.
Table 1
Ingredients (g) |
Ex. 1 (inv.) |
Ex. 2 (comp.) |
Tetrahydrofuran |
25.76 |
25.76 |
Alnovol SPN452* |
6.59 |
6.59 |
Methoxypropanol |
16.98 |
16.98 |
IR-2 |
0.1 |
- |
IR-COMP1 |
- |
0.1 |
Flexo blau 630** |
0.03 |
0.03 |
Tego Glide 410 *** |
0.14 |
0.14 |
Tego Wet 265 **** |
0.05 |
0.05 |
2,3,4-trimethoxybenzoic acid |
0.36 |
0.36 |
IR sensitivity (mJ/cm2) |
120 |
> 200 |
*Alnovol SPN452 is a 40.5% solution in Dowanol PM (commercially available from Clariant)
**Triaryl methane dye commercially available from BASF
***a polymer containing polysiloxane commercially available from Tego Chemie, Essen,
Germany; 10 wt.% solution in methoxypropanol.
****a polymer containing polysiloxane commercially available from Tego Chemie, Essen,
Germany; 10 wt.% solution in methoxypropanol. |
EXAMPLES 3 AND 4
[0104] These examples demonstrate the use of an infrared dye which contains a polysiloxane
group in a coating according to the present invention in which the water repellent-compound
is a perfluoroalkyl containing polymer.
Preparation of the support
[0105] The support was prepared as described in examples 1 and 2.
Plate precursor materials
[0106] The solutions in Table 2 below were coated on the above support at a wet coating
thickness of 20 µm and dries for 1 minute at 130°C. The materials were then imaged
on a Creo Trendsetter 3244 (830 nm) using different energy density settings (intensity
at the image plane) in the range from 80 mJ/cm
2 up to 200 mJ/cm
2. The plates were then processed by dipping for 60 seconds in a development tank filled
with DP300 (aqueous alkaline developer commercially available from Agfa) at a temperature
of 25°C. The IR-sensitivity of the different compositions corresponds to the minimum
energy density setting that is required to obtain a 50% reduction of the light absorption
of the coating, measured on the developed plate at the wavelength maximum of the contrast
dye, in areas which have been exposed with a dot area of a 50% screen (@200 lpi).
[0107] The results in Table 2 indicate that the coating which comprises an infrared dye
containing a polysiloxane group provides a higher sensitivity than the comparative
coating in which the corresponding infrared dye does not contain a polysiloxane group.
Table 2
Ingredients (g) |
Ex. 3 (inv.) |
Ex. 4 (comp.) |
Tetrahydrofuran |
25.76 |
25.76 |
Alnovol SPN452* |
6.59 |
6.59 |
Methoxypropanol |
16.98 |
16.98 |
IR-2 |
0.1 |
- |
IR-COMP1 |
- |
0.1 |
Flexo blau 630** |
0.03 |
0.03 |
Fluorad FC431 *** |
0.14 |
0.14 |
2,3,4-trimethoxybenzoic acid |
0.36 |
0.36 |
IR sensitivity (mJ/cm2) |
100 |
> 200 |
*Alnovol SPN452 is a 40.5% solution in Dowanol PM (commercially available from Clariant)
**Triaryl methane dye commercially available from BASF
***a polymer containing perfluoroalkyl commercially available from 3M; 10 wt.% solution
in methoxypropanol. |
1. A heat-sensitive lithographic printing plate precursor comprising a support having
a hydrophilic surface and a coating provided on the hydrophilic surface, said coating
comprising in the order given a first layer containing an oleophilic resin soluble
in an aqueous alkaline developer and a second layer capable of preventing penetration
of the developer at unexposed areas, said second layer comprising a water-repellent
compound selected from the group consisting of
- a polymer comprising siloxane and/or perfluoroalkyl monomeric units, and
- a block- or graft-copolymer comprising a poly- or oligo(alkylene oxide) and a polymer
or oligomer comprising siloxane and/ or perfluoroalkyl monomeric units, and
wherein the alkali-solubility of said coating increases on heating and said coating
comprises an infrared light absorbing dye
characterised in that the infrared absorbing dye comprises at least one polysiloxane group.
2. A lithographic printing plate precursor according to claim 1 wherein the polysiloxane
group is covalently linked to the infrared light absorbing dye.
3. A lithographic printing plate precursor according to claim 1 wherein the infrared
light absorbing dye carries a charge and the polysiloxane group is comprised in a
counter ion.
4. A lithographic printing plate precursor according to claim 1 wherein at least one
polysiloxane group is covalently linked to the infrared light absorbing dye and at
least one polysiloxane is comprised in a counter ion.
5. A lithographic printing plate precursor according to any of the preceding claims wherein
the infrared light absorbing dye is selected from the group consisting of squarylium,
croconate, merocyanine, cyanine, indolizine, pyrilium and metal dithioline dyes.
6. A lithographic printing plate precursor according to any of the preceding claims wherein
the amount of the water-repellent compound in the coating is between 0.5 and 15 mg/m2.
7. A lithographic printing plate precursor according to any of the preceding claims wherein
the second layer of the coating consists essentially of the water-repellent compound
and the infrared light absorbing dye.
8. A lithographic printing plate precursor according to any of the preceding claims wherein
the infrared light absorbing dye corresponds to the following formula:

wherein
a and b each independently represent an integer from 0 to 4;
-L1- and -L2- independently represent a divalent linking group;
-E1 and -E2 independently represent a neutral, anionic or cationic terminal group selected from
alkyl, -OH, -H, -Cl, -Br, -F,-SiRaRbRc (neutral groups); SO3-, -SO4-, -PO32-, -PO42-, -COO (anionic groups); -[NRdReRf]+(cationic group);
Ra, Rb and Rc independently represent an optionally substituted alkyl, alkenyl, aryl or aralkyl
group;
Rd, Re and Rf independently represent a hydrogen atom or an optionally substituted alkyl, alkenyl,
aryl or aralkyl group;
-A1- and -A2- independently represent -[Si(RgRh)-O]m- , -CvF2v-, -[(CF2)2-O]w- or an optionally substituted alkyl, alkenyl, aryl or aralkyl group;
Rg and Rh independently represent an optionally substituted alkyl, alkenyl, aryl or aralkyl
group, -[O-Si(RaRb)]q-E1 or -[O-Si(RaRb)]q-E2;
with p1 and p2 is 0 or 1;
with t, q and m is 1 or an integer greater than 1;
with v and w is 2 or an integer greater than 2;
-Y1- and -Y2- independently represent one or two non-metallic atoms, which may be substituted,
necessary to complete a 5- or 6-membered heterocyclic ring;
-Z1 and -Z2 each independently represent a hydrogen atom, an alkyl group or -Z and -Z together
represent the necessary atoms to complete a 5- or 6-membered ring;
R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl, alkenyl,
aryl or aralkyl group or a group selected from a halogen atom, -NO2, -O-Ri, -CO-Ri, -CO-O-Ri,-O-CO-Ri, -CO-NRiRj, -NRiRj, -NRi-CO-Rj, -NRi-CO-O-Rj, -NRi-CO-NRjRk, -SRi, -SO-Ri, -SO2-Ri, -SO2-O-Ri, -SO2NRiRj, a perfluoroalkyl group or a polysiloxane group; each of said groups optionally comprise
a terminal group E defined above as -E1 and -E2 and/or wherein two adjacent groups selected from R1, R2 -Y1- and -Y2- together form an optionally substituted 5- or 6- membered ring;
Ri , Rj and Rk independently represent a hydrogen or an optionally substituted alkyl, alkenyl, aryl
or aralkyl group;
R3 represents a substituent selected from a hydrogen, a halogen atom, an alkyl, alkenyl,
aryl or aralkyl group, a perfluoroalkyl group, a polysiloxane group, an amino group,
a thioalkyl group, a thioaryl group, an aryloxy group, an alkoxy group, a barbituric
group or a thiobarbituric group, each of said groups being optionally substituted;
X represents one or more optional counter ions having a total charge opposite to the
dye and wherein X optionally comprises a polysiloxane group;
with the provisio that at least one of the following substituents contains a polysiloxane
group: R
1, R
2, R
3, -A
1-, -A
2- or X.
9. A printing plate precursor according to claim 8 wherein -Z1 and -Z2 together represent -(CH2)2- or -(CH2)3-.
10. A lithographic printing plate precursor according to claims 8 or 9 wherein the IR
light absorbing dye corresponds to the following formulae:

wherein P1, P2, a, b, -L
1 -, -L
2-, -E
1, -E
2 , -A
1-, -A
2, -Y
1-, -Y
2,
-Z1, Z2, R3 and X have the same meaning as defined in claim 8; c and d are independently 0, 1
or 2;
each R6 to R9 independently represent a group as defined for R1 and R2 in claim 8,
with the provisio that at least one of the following substituents contains a polysiloxane
group: R
3, R
6 to R
9, -A
1-, -A
2 or X.
11. A lithographic printing plate precursor according to any of the claims 8 to 10 wherein
the IR light absorbing dye corresponds to the following formulae:

wherein
P1, P2, a, b, -L1-, -L2-, -E1, -E2 , -A1-, -A2, R1, R2,
R3 and X have the same meaning as defined in claim 8;
R4 and R5 independently represent an optionally substituted alkyl, alkenyl, cycloalkyl, aryl
or aralkyl group, a perfluoroalkyl group or a polysiloxane group; each of said groups
optionally comprise a terminal group E defined in claim 8 as -E1 and -E2; with the provisio that at least one of the following substituents contains a polysiloxane
group: R1, R2, R3, R4, R5, 1 2 -A -, -A or X.
12. A lithographic printing plate precursor according to any of the claims 8 to 11 wherein
the IR light absorbing dye corresponds to the following formulae:

wherein
R10 represents -(CH2)e-Si-[OSi(R11R12R13)]3 or -(CH2)e-OCO-(CH2)f-[Si(R14R15)-O]g-(CH2)h-CH3;
R4 and R5 have the same meaning as defined in claim 11;
R11, R12, R13, R14 and R15 independently represent an optionally substituted alkyl, alkenyl, aryl or aralkyl
group;
e, f, g and h is 1 or an integer greater than 1.
13. A lithographic printing plate precursor according to any of the preceding claims wherein
the polysiloxane group has a linear or branched structure.
1. Eine wärmeempfindliche lithografische Druckplattenvorstufe mit einem Träger mit einer
hydrophilen Oberfläche und einer auf die hydrophile Oberfläche angebrachten Beschichtung,
wobei die Beschichtung der Reihe nach eine erste Schicht, die ein oleophiles, in wässrig-alkalischem
Entwickler lösliches Harz enthält, und eine zweite Schicht, die in der Lage ist, Durchdringung
des Entwicklers in unbelichteten Bereichen zu verhindern, umfasst, wobei die zweite
Schicht eine wasserabstoßende Verbindung aus folgender Gruppe enthält :
- einem Polymer mit Siloxanmonomereinheiten und/oder Perfluoralkylmonomereinheiten
und
- einem Blockcopolymer oder Pfropfcopolymer mit einem Poly(alkylenoxid) oder Oligo(alkylenoxid)
und einem Polymer oder Oligomer mit Siloxanmonomereinheiten und/oder Perfluoralkylmonomereinheiten,
und
wobei die Alkalilöslichkeit der Beschichtung durch Erwärmung gesteigert wird und die
Beschichtung einen Infrarot-Farbstoff enthält,
dadurch gekennzeichnet, dass der Infrarot-Farbstoff zumindest eine Polysiloxangruppe enthält.
2. Lithografische Druckplattenvorstufe nach Anspruch 1, dadurch gekennzeichnet, dass die Polysiloxangruppe kovalent an den Infrarot-Farbstoff gebunden ist.
3. Lithografische Druckplattenvorstufe nach Anspruch 1, dadurch gekennzeichnet, dass der Infrarot-Farbstoff geladen ist und die Polysiloxangruppe in einem Gegenion eingebettet
ist.
4. Lithografische Druckplattenvorstufe nach Anspruch 1, dadurch gekennzeichnet, dass zumindest eine Polysiloxangruppe kovalent an den Infrarot-Farbstoff gebunden ist
und zumindest eine Polysiloxangruppe in einem Gegenion eingebettet ist.
5. Lithografische Druckplattenvorstufe nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass der Infrarot-Farbstoff ein Squaryliumfarbstoff, ein Croconatfarbstoff, ein Merocyaninfarbstoff,
ein Cyaninfarbstoff, ein Indolizinfarbstoff, ein Pyriliumfarbstoff oder ein Metalldithiolinfarbstoff
ist.
6. Lithografische Druckplattenvorstufe nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die wasserabstoßende Verbindung in einer Menge zwischen 0,5 und 15 mg/m2 in der Beschichtung verwendet wird.
7. Lithografische Druckplattenvorstufe nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die zweite Schicht der Beschichtung im Wesentlichen aus der wasserabstoßenden Verbindung
und dem Infrarot-Farbstoff zusammengesetzt ist.
8. Lithografische Druckplattenvorstufe nach einem der vorstehenden Ansprüche,
dadurch gekennzeichnet, dass der Infrarot-Farbstoff folgender Formel entspricht :

in der :
a und b unabhängig voneinander eine ganze Zahl zwischen 0 und 4 bedeuten,
-L1- und -L2- unabhängig voneinander eine zweiwertige Verbindungsgruppe bedeuten,
-E1 und -E2 unabhängig voneinander eine neutrale, anionische oder kationische Endgruppe aus der
Gruppe bestehend aus Alkyl, -OH, -H, -Cl, -Br, -F, -SiRaRbRc (neutrale Gruppen), -SO3-, -SO4-, -PO3 2-, -PO42-, -COO- (anionische Gruppen) und -[NRdReRf]+ (kationische Gruppe) bedeuten,
wobei Ra, Rb und Rc unabhängig voneinander eine gegebenenfalls substituierte Alkylgruppe, Alkenylgruppe,
Arylgruppe oder Aralkylgruppe bedeuten und
Rd, Re und Rf unabhängig voneinander ein Wasserstoffatom oder eine gegebenenfalls substituierte
Alkylgruppe, Alkenylgruppe, Arylgruppe oder Aralkylgruppe bedeuten,
-A1- und -A2- unabhängig voneinander -[Si(RgRh)-O]m-, -CvF2v-, -[(CF2)2-O]w- oder eine gegebenenfalls substituierte Alkylgruppe, Alkenylgruppe, Arylgruppe oder
Aralkylgruppe bedeuten,
wobei Rg und Rh unabhängig voneinander eine gegebenenfalls substituierte Alkylgruppe, Alkenylgruppe,
Arylgruppe oder Aralkylgruppe, -[O-Si(RaRb)]q-E1 oder -[O-Si(RaRb)]q-E2 bedeuten,
wobei p1 und p2 0 oder 1 bedeuten,
wobei t, u, q und m 1 oder eine ganze Zahl über 1 bedeuten,
wobei v und w 2 oder eine ganze Zahl über 2 bedeuten,
-Y1- und -Y2- unabhängig voneinander ein oder zwei gegebenenfalls substituierte, zur Vervollständigung
eines 5-gliedrigen oder 6-gliedrigen heterocyclischen Ringes benötigte Nichtmetallatome
bedeuten,
-Z1- und -Z2- unabhängig voneinander ein Wasserstoffatom oder eine Alkylgruppe oder gemeinsam
die zur Vervollständigung eines 5-gliedrigen oder 6-gliedrigen Ringes benötigten Atome
bedeuten, R1 und R2 unabhängig voneinander ein Wasserstoffatom, eine gegebenenfalls substituierte Alkylgruppe,
Alkenylgruppe, Arylgruppe oder Aralkylgruppe oder ein Halogenatom, -NO2, -O-Ri-, -CO-Ri, -CO-O-Ri, -O-CO-Ri, -CO-NRiRj, -NRiRj, -NRi-CO-Rj, -NRi-CO-O-Rj, -NRi-CO-NRjRk, -SRi, -SO-Ri, -SO2-Ri, -SO2-O-Ri, -SO2NRiRj, eine Perfluoralkylgruppe oder eine Polysiloxangruppe bedeuten, wobei jede der besagten
Gruppen gegebenenfalls eine oben als -E1 und -E2 definierte Endgruppe E umfasst und/oder zwei Nachbargruppen aus der Gruppe bestehend
aus R1, R2, -Y1- und -Y2-gemeinsam einen gegebenenfalls substituierten 5-gliedrigen oder 6-gliedrigen Ring
bilden,
wobei Ri, Rj und Rk unabhängig voneinander ein Wasserstoffatom oder eine gegebenenfalls substituierte
Alkylgruppe, Alkenylgruppe, Arylgruppe oder Aralkylgruppe bedeuten, R3 einen Substituenten aus der Gruppe bestehend aus einem Wasserstoffatom, einem Halogenatom
und einer gegebenenfalls substituierten Alkylgruppe, Alkenylgruppe, Arylgruppe, Aralkylgruppe,
Perfluoralkylgruppe, Polysiloxangruppe, Aminogruppe, Thioalkylgruppe, Thioarylgruppe,
Aryloxygruppe, Alkoxygruppe, Barbitursäuregruppe oder Thiobarbitursäuregruppe bedeutet
und
X ein oder mehrere eventuelle Gegenionen mit einer der Gesamtladung des Farbstoffes
entgegengesetzten Gesamtladung bedeutet und X gegebenenfalls eine Polysiloxangruppe
enthält, vorausgesetzt, dass zumindest einer der folgenden Substituenten eine Polysiloxangruppe
enthält : R1, R2, R3, -A1-, -A2- oder X.
9. Druckplattenvorstufe nach Anspruch 8, dadurch gekennzeichnet, dass -Z1 und -Z2 gemeinsam -(CH2)2- oder -(CH2)3- bilden.
10. Lithografische Druckplattenvorstufe nach Anspruch 8 oder 9,
dadurch gekennzeichnet, dass der Infrarot-Farbstoff folgenden Formeln entspricht :

in denen :
p1, p2, a, b, -L1- -L2-, -E1, -E2, -A1- -A2- -Y1-, -Y2-, -Z1, -Z2, -R3 und X die diesen Symbolen in Anspruch 8 zugemessene Bedeutung haben,
c und d unabhängig voneinander 0, 1 oder 2 bedeuten und
R6 bis R9 unabhängig voneinander jeweils eine wie in Anspruch 8 für R1 und R2 definierte Gruppe bedeuten,
unter der Voraussetzung, dass zumindest einer der folgenden Substituenten eine Polysiloxangruppe
enthält : R3, R6 bis R9, -A1-, -A2- oder X.
11. Lithografische Druckplattenvorstufe nach einem der Ansprüche 8 bis 10,
dadurch gekennzeichnet, dass der Infrarot-Farbstoff folgenden Formeln entspricht :

in denen :
p1, p2, a, b, -L1-, -L2-, -E1, -E2, -A1-, -A2-, R1, R2, R3 und X die diesen Symbolen in Anspruch 8 zugemessene Bedeutung haben,
R4 und R5 unabhängig voneinander eine gegebenenfalls substituierte Alkylgruppe, Alkenylgruppe,
Cycloalkylgruppe, Arylgruppe oder Aralkylgruppe oder eine Perfluoralkylgruppe oder
Polysiloxangruppe bedeuten und jede dieser Gruppen gegebenenfalls eine in Anspruch
8 als -E1 und -E2 definierte Endgruppe E enthält,
unter der Voraussetzung, dass zumindest einer der folgenden Substituenten eine Polysiloxangruppe
enthält : R
1, R
2, R
3, R
4, R
5, -A
1-, -A
2- oder X.
12. Lithografische Druckplattenvorstufe nach einem der Ansprüche 8 bis 11,
dadurch gekennzeichnet, dass der Infrarot-Farbstoff folgenden Formeln entspricht :

in denen :
R10 -(CH2)e-Si-[OSi(R11R12R13)]3 oder
-(CH2)e-OCO-(CH2)f-[Si(R14R15)-O]g-(CH2)h-CH3 bedeutet,
R4 und R5 die diesen Resten in Anspruch 11 zugemessene Bedeutung haben,
R11, R12, R13, R14 und R15 unabhängig voneinander eine gegebenenfalls substituierte Alkylgruppe, Alkenylgruppe,
Arylgruppe oder Aralkylgruppe bedeuten und
e, f, g und h 1 oder eine ganze Zahl über 1 bedeuten.
13. Lithografische Druckplattenvorstufe nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die Polysiloxangruppe eine lineare oder verzweigte Struktur aufweist.
1. Un précurseur de plaque d'impression lithographique thermosensible comprenant un support
ayant une surface hydrophile et un revêtement appliqué sur la surface hydrophile,
ledit revêtement contenant dans l'ordre indiqué une première couche contenant une
résine oléophile soluble dans un révélateur alcalin aqueux et une deuxième couche
capable d'empêcher la pénétration du révélateur dans des zones non exposées, ladite
deuxième couche contenant un composé hydrophobe choisi parmi :
- un polymère contenant des unités monomères de siloxane et/ou de perfluoroalkyle
et
- un copolymère séquencé ou greffé composé d'un bloc d'oxyde de polyalkylène ou d'un
bloc d'oxyde d'oligoalkylène et d'un polymère ou oligomère contenant des unités monomères
de siloxane et/ou de perfluoroalkyle,
la solubilité en milieu alcalin du revêtement étant augmentée sous l'effet d'un chauffage
et ledit revêtement contenant un colorant absorbant les rayons infrarouges,
caractérisé en ce que le colorant absorbant les rayons infrarouges contient au moins un groupe polysiloxane.
2. Précurseur de plaque d'impression lithographique selon la revendication 1, caractérisé en ce que le groupe polysiloxane est lié par covalence au colorant absorbant les rayons infrarouges.
3. Précurseur de plaque d'impression lithographique selon la revendication 1, caractérisé en ce que le colorant absorbant les rayons infrarouges porte une charge et que le groupe polysiloxane
est incorporé dans un contre-ion.
4. Précurseur de plaque d'impression lithographique selon la revendication 1, caractérisé en ce qu'au moins un groupe polysiloxane est lié par covalence au colorant absorbant les rayons
infrarouges et qu'au moins un groupe polysiloxane est incorporé dans un contre-ion.
5. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications
précédentes, caractérisé en ce que le colorant absorbant les rayons infrarouges est un colorant de squarylium, un colorant
de croconate, un colorant de mérocyanine, un colorant de cyanine, un colorant d'indolizine,
un colorant de pyrilium ou un colorant métal dithioline.
6. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications
précédentes, caractérisé en ce que la quantité du composé hydrophobe utilisé dans le revêtement est comprise entre 0,5
et 15 mg/m2.
7. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications
précédentes, caractérisé en ce que la deuxième couche du revêtement est composée essentiellement du composé hydrophobe
et du colorant absorbant les rayons infrarouges.
8. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications
précédentes,
caractérisé en ce que le colorant absorbant les rayons infrarouges répond à la formule suivante :

où :
a et b représentent, indépendamment l'un de l'autre, un nombre entier de 0 à 4,
-L1- et -L2- représentent, indépendamment l'un de l'autre, un groupe de liaison bivalent,
-E1 et -E2 représentent, indépendamment l'un de l'autre, un groupe terminal neutre, anionique
ou cationique choisi parmi un groupe alkyle, -OH, -H, -Cl, -Br, -F ou -SiRaRbRc (groupes neutres), un groupe -SO3-, -SO4-, -PO32-, -PO42- ou -COO- (groupes anioniques) et un groupe -[NRdReRf]+ (groupe cationique),
où Ra, Rb et Rc représentent, indépendamment l'un de l'autre, un groupe alkyle, alkényle, aryle ou
aralkyle éventuellement substitué et
où Rd, Re et Rf représentent, indépendamment l'un de l'autre, un atome d'hydrogène ou un groupe alkyle,
alkényle, aryle ou aralkyle éventuellement substitué,
-A1- et -A2- représentent, indépendamment l'un de l'autre, un groupe -[Si(RgRh)-O]m-, un groupe -CvF2v-, un groupe
-[(CF2)2-O]w- ou un groupe alkyle, alkényle, aryle ou aralkyle éventuellement substitué,
où Rg et Rh représentent, indépendamment l'un de l'autre, un groupe alkyle, alkényle, aryle ou
aralkyle éventuellement substitué, un groupe -[O-Si(RaRb)]q-E1 ou un groupe
-[O-Si(RaRb)]q-E2,
où p1 et p2 représentent 0 ou 1,
où t, u, q et m représentent 1 ou un nombre entier supérieur à 1,
où v et w représentent 2 ou un nombre entier supérieur à 2,
-Y1- et -Y2- représentent, indépendamment l'un de l'autre, un ou deux atomes non métalliques
éventuellement substitués, nécessaires pour compléter un noyau hétérocyclique pentagonal
ou hexagonal,
-Z1- et -Z2- représentent, indépendamment l'un de l'autre, un atome d'hydrogène ou un groupe
alkyle ou représentent ensemble les atomes nécessaires pour compléter un noyau pentagonal
ou hexagonal,
R1 et R2 représentent, indépendamment l'un de l'autre, un atome d'hydrogène, un groupe alkyle,
alkényle, aryle ou aralkyle éventuellement substitué, un atome d'halogène, -NO2, -O-Ri, -CO-Ri, -CO-O-Ri, -O-CO-Ri, -CO-NRiRj, -NRiRj, -NRi-CO-Rj, -NRi-CO-O-Rj, -NRi-CO-NRjRk, -SRi, -SO-Ri, -SO2-Ri, -SO2-O-Ri, -SO2NRiRj, un groupe perfluoroalkyle ou un groupe polysiloxane, chacun desdits groupes pouvant
éventuellement contenir un groupe terminal E défini ci-dessus comme -E1 et -E2 et/ou deux groupes adjacents choisis parmi R1, R2, -Y1- et -Y2- formant ensemble un noyau pentagonal ou hexagonal éventuellement substitué,
où Ri, Rj et Rk représentent, indépendamment l'un de l'autre, un atome d'hydrogène ou un groupe alkyle,
alkényle, aryle ou aralkyle éventuellement substitué,
R3 représente un substituant choisi parmi un atome d'hydrogène, un atome d'halogène
et un groupe alkyle, alkényle, aryle, aralkyle, perfluoroalkyle, polysiloxane, amino,
thioalkyle, thioaryle, aryloxy, alkoxy, acide barbiturique ou acide thiobarbiturique
éventuellement substitué,
X représente un ou plusieurs contre-ions éventuels portant une charge totale opposée
à la charge totale du colorant et X contient éventuellement un groupe polysiloxane,
à condition qu'au moins un des substituants suivants contienne un groupe polysiloxane
: R
1, R
2, R
3, -A
1-, -A
2- ou X.
9. Précurseur de plaque d'impression selon la revendication 8, caractérisé en ce que -Z1 et -Z2 forment ensemble un groupe -(CH2)2- ou un groupe -(CH2)3-.
10. Précurseur de plaque d'impression lithographique selon la revendication 8 ou 9,
caractérisé en ce que le colorant absorbant les rayons infrarouges répond aux formules suivantes :

où :
P1, P2, a, b, -L1-, -L2-, -E1, -E2, -A1-, -A2-, -Y1-, -Y2-, -Z1, -Z2, -R3 et X ont la signification définie dans la revendication 8,
c et d représentent, indépendamment l'un de l'autre, 0, 1 ou 2 et
R6 à R9 représentent, indépendamment l'un de l'autre, un groupe tel que défini pour R1 et R2 dans la revendication 8,
à condition qu'au moins un des substituants suivants contienne un groupe polysiloxane
: R
3, R
6 à R
9, -A
1-, -A
2- ou X.
11. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications
8 à 10,
caractérisé en ce que le colorant absorbant les rayons infrarouges répond aux formules suivantes :

où :
p1, p2, a, b, -L1- -L2-, -E1, -E2, -A1-, -A2-, R1, R2, R3 et X ont la signification définie dans la revendication 8 et
R4 et R5 représentent, indépendamment l'un de l'autre, un groupe alkyle, alkényle, cycloalkyle,
aryle ou aralkyle éventuellement substitué ou un groupe perfluoroalkyle ou polysiloxane,
chacun de ces groupes pouvant éventuellement contenir un groupe terminal E défini
comme -E1 et -E2 dans la revendication 8,
à condition qu'au moins un des substituants suivants contienne un groupe polysiloxane
: R
1, R
2, R
3, R
4, R
5, -A
1-, -A
2- ou X.
12. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications
8 à 11,
caractérisé en ce que le colorant absorbant les rayons infrarouges répond aux formules suivantes :

où :
R10 représente un groupe -(CH2)e-Si-[OSi(R11R12R13)]3 ou un groupe (CH2)e-OCO-(CH2)f- [Si(R14R15)-O]g-(CH2)h-CH3,
R4 et R5 ont la signification définie dans la revendication 11, R11, R12 R13, R14 et R15 représentent, indépendamment l'un de l'autre, un groupe alkyle, alkényle, aryle ou
aralkyle éventuellement substitué et
e, f, g et h représentent 1 ou un nombre entier supérieur à 1.
13. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications
précédentes, caractérisé en ce que le groupe polysiloxane présente une structure linéaire ou ramifiée.