Lithographic printing plate precursor

Abstract

Disclosed is a lithographic printing plate precursor comprising a support and a coating layer, said coating layer comprising a photopolymerizable layer comprising a polymerizable compound and a photoinitiator, characterized in that said coating layer comprises a hydrophilic adhesion-promoting copolymer, said copolymer comprising at least one monomeric unit according to Formula I and at least one monomeric unit according to Formula II; and at least one group and / or moiety comprising a phosphorus atom.

Description

TECHNICAL FIELD

[0001] The present invention relates to a novel lithographic printing plate precursor. BACKGROUND

[0002] Lithographic printing typically involves the use of a so-called printing master, for example a printing plate mounted on the cylinder of a rotary 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 consisting of oleophilous (or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as hydrophilous (or oleophobic, i.e. water-accepting, ink-repelling) areas. In so-called driographic printing, the lithographic image consists of ink-accepting areas and ink-repelling areas and during driographic printing only ink is supplied to the master.

[0003] Lithographic printing masters are typically obtained by image-wise exposure and processing of a radiation-sensitive layer on a lithographic support. Imaging and processing turns the so-called lithographic printing plate precursor into a printing plate or master. The radiation-sensitive coating is typically triggered to physically and / or chemically process, such as ablation, polymerization, insolubilization through cross-linking of polymers or through particle coalescence of a thermoplastic polymer latex, solubilization through disruption of intermolecular interactions or increasing the permeability of the resist layer, by image-wise exposure to heat or light, e.g. by a digitally modulated exposure device, such as a laser. Although some plate precursors are capable of producing a lithographic image immediately after exposure, the most popular lithographic printing plate precursors require wet processing because the exposure creates a difference in solubility or in rate of dissolution in a developer between the exposed and the non-exposed areas of the coating. In positive working lithographic printing plate precursors, the exposed areas of the coating dissolve in the developer, while the non-exposed areas remain resistant to the developer. In negative working lithographic printing plate precursors, the non-exposed areas of the coating dissolve in the developer, while the exposed areas remain resistant to the developer. Most lithographic printing plate precursors contain a hydrophobic coating on a hydrophilic support, so that the areas that remain resistant to the developer define the ink-accepting areas of the plate, and thus the printing areas of the plate, while the hydrophilic support is revealed by the dissolution of the coating in the developer in the non-printing areas.

[0004] Photopolymer printing plates rely on a working mechanism whereby a coating layer typically comprising free-radically polymerizable compounds hardens upon exposure. By "hardens" is meant that the coating layer becomes insoluble or non-dispersible in a developer solution and can be achieved by polymerization and / or crosslinking of the photosensitive coating upon exposure to light and / or heat. Photopolymer plate precursors can be sensitized to blue light, green light or red light (i.e. wavelength range between 450-750 nm), to violet light (i.e. wavelength range between 300-450 nm) or to infrared light (i.e. wavelength range between 750-1500 nm). Optionally, the exposure step is followed by a heating step to enhance or accelerate the polymerization and / or crosslinking reaction.

[0005] Typically, a top layer or protective top coating on the imageable layer is required to act as an oxygen barrier to provide the desired sensitivity to the plate. The protective top coating typically comprises a water-soluble or water-swellable polymer, such as polyvinyl alcohol and / or copolymers thereof. In addition to acting as a barrier to oxygen, the protective top coating should preferably be easily removable during processing and be sufficiently transparent to actinic radiation (e.g. 300-450 nm or 450-750 nm or 750-1500 nm).

[0006] The classical workflow for photopolymer printing plates comprises a first exposure step of the photopolymer printing plate precursor in a violet or infrared plate maker, followed by an optional pre-heat step, a wash-off step of the protective top coating, an alkaline development step and a rinsing and gumming step. However, there is a clear move towards a simplified workflow, wherein the pre-heat step and / or the wash-off step are eliminated and wherein the processing and gumming steps are carried out in one single step, or wherein the processing is carried out with a neutral gum followed by gumming in a second step. Alternatively, in-press processing has become very popular, wherein the plate is mounted on the printing press and the coating is developed by interaction with dampening solution and / or ink supplied to the plate during the run of the printing press. During the first run of the printing press, the non-image areas are removed from the support and thereby define the non-printing areas of the plate. These processing methods are environmentally friendly and are highly appreciated by the customers as "chemical element free processing methods". In particular, printing plates designed for in-press processing require a lithographic printing coating that dissolves or disperses sufficiently on the printing press so that a good clean-out (complete removal of the coating at the non-printing areas of the image) is obtained. Furthermore, in addition to the clean-out behavior, the print life of such printing plates should also be optimized. Both the print life and the clean-out performance are determined by the interaction between the coating and the substrate: optimal print life requires sufficient adhesion between the substrate and the coating in the image areas, while good clean-out requires minimal interaction of the coating with the substrate in the non-image areas upon processing. Therefore, maximizing the clean-out performance can result in a reduced image adhesion and thus in a reduced print life.

[0007] Therefore, compounds for improving the adhesion between the photopolymer coating and the support are often added to the printing plate precursors as disclosed in EP 851 299, EP 1 091 251, EP 1 695 822, EP 1 844 946, EP 2 105 797, EP 1 495 866, EP 1 500 498, EP 2 105 797 and EP 1 520 694, to increase the resistance of the exposed areas during the processing steps and to improve the durability of the plate during the printing process.

[0008] However, it remains a challenge to simultaneously achieve (i) an excellent removal of the non-image areas, in particular under non-etching processing conditions, such as processing in the absence of a strong alkaline (pH > 12) solution - i.e. off-press processing with gum solution or on-press processing with dampening solution and ink; (ii) in combination with a high printing durability during the printing. SUMMARY

[0009] It is therefore an object of the present invention to provide a negative-working printing plate precursor which is characterized by both a sufficient removal behavior and a high printing life. It is also important that the precursor exhibits an improved shelf life stability, i.e. an excellent removal without toning when the precursor is stored under critical conditions such as high temperature and high relative humidity before imaging and processing.

[0010] This object is achieved by the printing plate precursor defined in the present invention and the preferred embodiments defined in the dependent claims. The printing plate precursor of the present invention is in particular characterized in that it contains a coating which comprises a hydrophilic copolymer which comprises monomer units according to formula I and formula II and at least one group and / or moiety comprising a phosphorous atom.

[0011]

[0012] wherein

[0013] L represents O or NH;

[0014] n and m independently represent an integer greater than 0;

[0015] R represents hydrogen, optionally substituted linear, branched or cyclic alkyl, optionally substituted aryl, optionally substituted aralkyl or optionally substituted heteroaryl;

[0016] R 1 and R 2 independently represent optionally substituted linear, branched or cyclic alkyl.

[0017] According to the present invention, it was surprisingly found that by including a hydrophilic polymer according to the present invention, the cleaning behavior is greatly improved, whereby the occurrence of chalking on paper printed matter is highly reduced, while the printing life of the plate is substantially not affected.

[0018] Inadequate cleaning means that after processing, the non-image areas are not completely removed from the support, or that the compounds of the non-image areas remaining on the support are too hydrophobic, as a result of which the hydrophilic properties of the surface of the support are reduced. Inadequate cleaning can result in chalking, i.e. an undesirable tendency of the ink receptivity in the non-image areas of the printed matter to increase.

[0019] The development is preferably carried out by treating the precursor with a gum solution, however more preferably by mounting the precursor on a plate cylinder of a lithographic printing press and rotating the plate cylinder while feeding fountain solution and / or ink to the precursor.

[0020] It is another object of the present invention to provide a method for manufacturing a lithographic printing plate comprising the steps of:

[0021] - exposing the printing plate precursor comprising a coating as defined above to heat and / or light radiation in an image, thereby forming a lithographic printing image consisting of image areas and non-image areas, and thereby inducing a color change of the imaged areas;

[0022] - developing the exposed precursor.

[0023] Further features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention. DETAILED DESCRIPTION

[0024] Lithographic printing plate precursor

[0025] The lithographic printing plate precursor according to the present invention is negative working, i.e. after exposure and development, the non-exposed areas of the coating are removed from the support and define hydrophilic (non-printing) areas, while the exposed coating is not removed from the support and defines oleophilic (printing) areas. The hydrophilic areas are defined by the support having a hydrophilic surface or being provided with a hydrophilic layer. The hydrophobic areas are defined by the coating, which hardens upon exposure, optionally followed by a heating step. Areas having hydrophilic properties mean areas having a higher affinity for aqueous solutions than for (oleophilic) inks; areas having hydrophobic properties mean areas having a higher affinity for (oleophilic) inks than for aqueous solutions.

[0026] "Hardening" means that the coating becomes insoluble or non-dispersible in the developing solution and can be achieved by polymerization and / or crosslinking of the photoactive coating, optionally followed by a heating step to enhance or accelerate the polymerization and / or crosslinking reaction. In this optional heating step, hereinafter also referred to as "pre- heating", the plate precursor is preferably heated at a temperature of about 80°C to 150°C and preferably during a residence time of about 5 seconds to 1 minute.

[0027] The coating contains at least one layer comprising a photopolymerizable composition, also referred to as "photopolymerizable layer". On top of the photopolymerizable layer a protective top coating can be provided. The coating can further comprise other layers, such as intermediate layers between the support and the photopolymerizable layer and / or between the optional top layer and the photopolymerizable layer, adhesion-improving layers, hydrophilic layers and / or other layers. The coating thickness of the photopolymerizable layer is preferably in the range of 0.1 to 5.0 g / m 2 , more preferably 0.3 to 3.0 g / m 2 , most preferably 0.4 to 1.5 g / m 2 .

[0028] The printing plate of the present application is characterized in that it can be exposed at low energy density, i.e. below 190 mJ / m 2 ; preferably between 70 and 190 mJ / m 2 ; more preferably between 75 and 150 mJ / m 2 , and most preferably between 80 and 120 mJ / m 2 .

[0029] Photopolymer coating

[0030] Hydrophilic substrate binder polymer

[0031] The lithographic printing plate precursor of the present application comprises a hydrophilic copolymer comprising at least one monomeric unit according to formula I and at least one monomeric unit according to formula II and at least one group and / or moiety comprising at least one phosphorous atom. Said hydrophilic copolymer is also referred to as "hydrophilic substrate binder polymer".

[0032]

[0033]

[0034] wherein

[0035] L represents O or NH;

[0036] n and m independently represent an integer greater than 0; preferably n and m independently represent an integer of 1 to 500, more preferably an integer of 2 to 250, and most preferably an integer of 3 to 100;

[0037] R represents hydrogen, optionally substituted straight-chain, branched or cyclic alkyl, optionally substituted aryl, optionally substituted aralkyl or optionally substituted heteroaryl; preferably R represents optionally substituted straight-chain, branched or cyclic alkyl - such as methyl, ethyl or propyl - or optionally substituted aryl.

[0038] R 1 and R 2 Independently represents an optionally substituted straight-chain, branched, or cyclic alkyl group, preferably R representing an alkyl group, such as methyl, ethyl, n-propyl, or isopropyl.

[0039] In a preferred embodiment, the hydrophilic substrate adhesive polymer comprises at least one monomer unit according to Formula III, at least one monomer unit according to Formula IV, and at least one group and / or portion comprising at least one phosphorus atom.

[0040]

[0041]

[0042] in

[0043] n and m independently represent integers greater than 0; preferably n and m independently represent integers from 1 to 500, more preferably integers from 2 to 250, and most preferably integers from 3 to 100.

[0044] R represents hydrogen, an optionally substituted straight-chain, branched, or cyclic alkyl group, an optionally substituted aryl group, an optionally substituted aralkyl group, or an optionally substituted heteroaryl group; preferably R represents an optionally substituted straight-chain, branched, or cyclic alkyl group—such as methyl, ethyl, or propyl—or an optionally substituted aryl group.

[0045] At least one group and / or portion comprising at least one phosphorus atom may be selected, for example, from phosphonates or phosphonates. These portions may be randomly present in the backbone of the hydrophilic substrate adhesive polymer and / or may exist as end groups in the polymer. A preferred portion comprising at least one phosphorus atom as an end group is preferably represented by formula V:

[0046]

[0047] in

[0048] 'a' represents 0 or 1.

[0049] R4 represents -OH or methyl; and

[0050] * indicates the connection point of the monomer unit of the adhesive polymer to the hydrophilic substrate.

[0051] The preferred portion comprising at least one phosphorus atom randomly present in the main chain of the hydrophilic substrate adhesive polymer is preferably represented by Formula VI:

[0052]

[0053] in

[0054] b and c independently represent 0 or 1, and

[0055] * indicates the connection point of the monomer unit of the adhesive polymer to the hydrophilic substrate.

[0056] In a highly preferred embodiment, the hydrophilic substrate adhesive polymer comprises at least one monomer unit according to Formula I and at least one monomer unit according to Formula VII. More preferably, the hydrophilic substrate adhesive polymer comprises at least one monomer unit according to Formula III and at least one monomer unit according to Formula VII.

[0057]

[0058] in

[0059] R' represents hydrogen, optionally substituted straight-chain, branched or cyclic alkyl, optionally substituted aryl, optionally substituted aralkyl or optionally substituted heteroaryl, more preferably R' represents hydrogen or optionally substituted straight-chain, branched or cyclic alkyl, most preferably R' represents hydrogen;

[0060] o represents an integer between 1 and 100; and

[0061] p and q independently represent integers between 0 and 500, more preferably between 2 and 250, and most preferably between 3 and 100.

[0062] The hydrophilic substrate adhesive polymer can be a random or block copolymer, comprising monomer units of formulas I to IV and VII as defined above. In a later embodiment, the copolymer may comprise an alternating sequence of blocks consisting of monomer units of formula I or III and monomer units of formulas II, IV, or VII. Such blocks may range from small blocks, such as blocks containing fewer than 5 parts, to blocks containing 100 parts or more. The monomer units of formulas I, II, or IV may be all the same or different.

[0063] The hydrophilic substrate adhesive polymer according to the invention can be synthesized, for example, by copolymerization of 2-acrylamide-2-methyl-1-propanesulfonic acid (AMPS) and phosphino carboxylic acid (PCA). Other suitable methods including chain transfer agents such as sodium hypophosphite are described in EP 618 240 and EP 405 818.

[0064] Hydrophilic substrate adhesive polymers can be used at concentrations of 5 to 100 mg / m³. 2The amount present in the coating is more preferably 10 to 50 mg / m³. 2 The amount present is preferably 12 to 25 mg / m³. 2 The quantity exists.

[0065] The weight-average molecular weight (Mw) of the copolymer according to the invention is preferably less than 100,000, more preferably less than 50,000, and most preferably between 1,000 and 20,000. The weight-average molecular weight (Mw) can be determined by size exclusion chromatography.

[0066] Alternatively, other monomer units may be present in the hydrophilic substrate adhesive polymer. These other monomer units may be selected from (meth)acrylic acid, maleic acid, crotonic acid, itaconic acid, vinylbenzoic acid, vinylphenylacetic acid, (meth)acrylate sulfonyl ethyl ester, (meth)acrylate sulfonyl propionyl ester, (meth)acrylate sulfonyl butyl ester, (meth)acrylamido-2-propanesulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, vinylphenol, 4-hydroxystyrene, ethylene oxide, propylene oxide, methyl vinyl ether, vinyl alcohol, hydrolyzed vinyl acetate, and maleic anhydride or maleimide grafted with a polyoxyethylene group having at least two ethylene oxide groups. Amines, N-vinylpyrrolidone, N-vinylcaprolactam, (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, 2-(dimethylamino)ethyl (meth)acrylate, hydroxyethyl (meth)acrylate, quaternized aminoethyl (meth)acrylate, quaternized aminopropyl (meth)acrylamide, and quaternized vinylpyridine, and their salts, and each of these monomers may optionally be substituted. More preferably, the second monomer unit is ethyl methacrylate, styrene sulfonic acid, vinyl alcohol, (meth)acrylic acid, maleic acid, crotonic acid, itaconic acid, (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-vinylpyrrolidone, and ethylene oxide, and their salts, and each of these monomers may optionally be substituted. The most preferred second monomer unit is (meth)acrylic acid, maleic acid, crotonic acid, itaconic acid, vinyl alcohol, and ethylene oxide, as well as their salts, and each of these monomers may optionally be substituted.

[0067] The hydrophilic substrate adhesive polymer according to the invention may be present in the photopolymerizable layer, and / or in an optional top layer, and / or in any other optional layer, such as an intermediate layer, adhesion-improving layer, hydrophilic layer and / or other layer located between the carrier and the photopolymerizable layer.

[0068] Adhesion-promoting compoundsThe lithographic printing plate precursor of the present invention preferably comprises an adhesion-promoting compound; that is, a compound capable of interacting with the carrier. The adhesion-promoting compound preferably comprises an addition-polymerizable olefinic unsaturated bond and functional groups capable of interacting with the carrier. Under "interaction," it can be understood as various types of physical and / or chemical reactions or processes in which a bond is formed between the functional group and the carrier. This bond can be a covalent bond, ionic bond, complex bond, coordinate bond, or hydrogen bridge bond, and can be formed through adsorption processes, chemical reactions, acid-base reactions, complex formation reactions, or reactions of chelating groups or ligands. The adhesion-promoting compound is present in the photopolymerizable layer, and / or in an optional top layer, and / or in any other optional layer, such as an intermediate layer, adhesion-improving layer, hydrophilic layer, and / or other layer located between the carrier and the photopolymerizable layer.

[0069] The adhesion-promoting compound may be selected from at least one low molecular weight compound or polymeric compound described in EP 2 916 171

[0058] , EP 851 299 from page 3, line 22 to page 4, line 1, EP 1 500 498 from page 7, paragraph

[0023] to page 20, paragraph

[0052] , EP 1 495 866 from page 5, paragraph

[0030] to page 11, paragraph

[0049] , EP 1 091 251 from page 3, paragraph

[0014] to page 20, paragraph

[0018] , and EP 1 520 694 from page 6, paragraph

[0023] to page 19, paragraph

[0060] . Preferred compounds are those containing phosphate or phosphonate groups as functional groups capable of adsorbing onto an aluminum support, and containing olefinic double-bond reactive groups capable of addition polymerization. Also preferred are compounds containing a trialkoxysilyl group, hereinafter also referred to as a "trialkoxysilane" group, wherein the alkyl group is preferably methyl or ethyl, or wherein the trialkoxysilyl group is at least partially hydrolyzed to a silanol group as a functional group capable of adsorbing onto a support, particularly silane coupling agents having olefinic double-bond reactive groups capable of addition polymerization.

[0070] The adhesion-promoting compound may be present in the coating in an amount of 1-50 wt%, preferably 3-30 wt%, more preferably 5-20 wt%, comprising the non-volatile components of the coating composition. The adhesion-promoting compound and the hydrophilic substrate adhesive polymer according to the invention are preferably both present in the coating; that is, present in the photopolymerizable layer, and / or in the top layer, and / or in the intermediate layer, adhesion-improving layer, hydrophilic layer, and / or other layers located between the carrier and the photopolymerizable layer.

[0071] Photopolymerizable compounds

[0072] The photopolymerizable layer comprises at least one polymerizable compound, a photoinitiator, and optionally a binder. The coating thickness of the photopolymerizable layer is preferably between 0.2 and 5.0 g / m². 2 More preferably, it is between 0.4-3.0 g / m 2 The optimal range is between 0.6-1.5 g / m³. 2 Within the range between.

[0073] According to a preferred embodiment of the invention, the polymerizable compound is a polymerizable monomer or oligomer comprising at least one terminal olefinically unsaturated group, hereinafter also referred to as a "radically polymerizable monomer". Polymerization involves linking the radically polymerizable monomers together. Suitable radically polymerizable monomers include, for example, polyfunctional (meth)acrylate monomers (e.g., ethylene glycol, trimethylolpropane, pentaerythritol, ethylene glycol, ethoxylated trimethylolpropane (meth)acrylate, urethane (meth)acrylate) and oligomer amine di(meth)acrylate. In addition to the (meth)acrylate group, the (meth)acrylate monomer may also have other olefinically unsaturated groups or epoxy groups. The (meth)acrylate monomer may also contain acidic (e.g., carboxylic acid or phosphoric acid) or basic (e.g., amine) functional groups.

[0074] Suitable free radical polymerizable monomers are disclosed in

[0042] and

[0050] of EP 2 916 171.

[0075] Initiators

[0076] According to the present invention, any radical initiator capable of generating free radicals upon direct exposure or in the presence of a sensitizer is a suitable initiator, also referred to herein as a photoinitiator. Suitable examples of photoinitiators include onium salts, carbon-halogen bond-containing compounds (e.g., [1,3,5]triazines having a trihalomethyl group), organic peroxides, aromatic ketones, thio compounds, azo polymerization initiators, azide compounds, ketoxime esters, hexaaryldiimidazoles, metallocenes, active ester compounds, borates, and quinone diazides. Onium salts, particularly iodonium salts and / or sulfonium salts, are preferred from the viewpoint of storage stability.

[0077] More particularly suitable free radical initiators include, for example, derivatives of acetophenone (e.g., 2,2-dimethoxy-2-phenylacetophenone and 2-methyl-1-[4-(methylthio)phenyl-2-morpholinopropyl-1-one); benzophenone; benzoin; ketocoumarins (e.g., 3-benzoyl-7-methoxycoumarin and 7-methoxycoumarin); xanthones; thioxanthones; benzoin or alkyl-substituted anthraquinones; ononium salts (e.g., diaryliodoonium hexafluoroantimonyate, diaryliodoonium trifluoromethanesulfonate, 4-( 2-Hydroxytetradecyl)-phenyl)phenyliodomonium salts, triarylsulfonium hexafluorophosphate, triarylsulfonium p-toluenesulfonate, (3-phenylprop-2-one)triarylphosphine ononium salts of hexafluoroantimonyate and N-ethoxy(2-methyl)pyridinium ononium salts of hexafluorophosphate, and ononium salts as described in U.S. Patent Nos. 5,955,238, 6,037,098, and 5,629,354; borates (e.g., tetrabutylammonium triphenyl(n-butyl)borate, tetraethylammonium triphenyl(n-butyl)borate, diphenyliodotetraphenylborate). Onion salts, tetraphenylborate diphenyliodoonium salt (wherein the phenyl group of the iodoonium salt is substituted with a group comprising at least six carbon atoms), and triphenyl(n-butyl)borate triphenylsulfonium, and borates as described in U.S. Patent Nos. 6,232,038 and 6,218,076; halogenated alkyl-substituted s-triazines (e.g., 2,4-bis(trichloromethyl)-6-(p-methoxy-styryl)-s-triazine, 2,4-bis(trichloromethyl)-6-(4-methoxy-naphthyl-1-yl)-s-triazine, 2, 4-bis(trichloromethyl)-6-piperyl-s-triazine and 2,4-bis(trichloromethyl)-6-[(4-ethoxy-ethyleneoxy)-phenyl-1-yl]-s-triazine and s-triazine as described in U.S. Patent Nos. 5,955,238, 6,037,098, 6,010,824, and 5,629,354; and diacenetimonite (bis(etha.9-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrolo-1-yl)phenyl)titanium). Preferred radical initiators are ononium salts, borates, and s-triazines. Preferred ononium salts are diaryliodoonium salts and triarylsulfonium salts. Preferred borates are triarylalkylborates. Preferred s-triazines are trichloromethyl-substituted s-triazines. These initiators may have optional substituents and may be used alone or in combination.

[0078] Optionally substituted trihaloalkyl sulfones are particularly preferred initiators, wherein the halogen is independently represented as bromine, chlorine, or iodine, and the sulfone is a compound containing a sulfonyl functional group attached to two carbon atoms. The most preferred initiator is tribromomethylphenyl sulfone. Further details about this initiator can be found in paragraphs

[0029] to

[0040] of patent application WO2019 / 179995.

[0079] The amount of initiator relative to the total dry weight of the components in the photopolymerizable composition is typically in the range of 0.05-30% by weight, preferably 0.1-15% by weight, and most preferably 0.2-10% by weight.

[0080] The photopolymerizable layer may also contain a co-initiator. Typically, the co-initiator is used in combination with a free radical initiator. Suitable co-initiators for photopolymer coatings are disclosed in US 6,410,205, US 5,049,479, EP 1 079 276, EP 1369 232, EP 1 369 231, EP 1 341 040, US 2003 / 0124460, EP 1 241 002, EP 1 288 720 and in the reference book including the cited literature: Chemistry & Technology UV & EB formulation for coatings, inks & paints, Vol. 3, Photoinitiators for Free Radical and Cationic Polymerisation, KK Dietliker, edited by PKT Oldring, 1991, ISBN 0 947798161. As described in EP107 792, specific co-initiators may be present in the photopolymerizable layer to further enhance sensitivity. Preferred co-initiators are disclosed in EP 2 916 171

[0051] .

[0081] Very high sensitivity can be obtained by including a fluorescent whitening agent as a sensitizer in the coating. Suitable examples of fluorescent whitening agents as sensitizers are described on page 24, lines 20 to 39 of WO 2005 / 109103. Useful sensitizers may be selected from the sensitizing dyes 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.

[0082] As described in EP 107 792, specific co-initiators may be present in the photopolymerizable layer to further enhance sensitivity. Preferred co-initiators are sulfur compounds, particularly thiols, such as 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzimidazole, 4-methyl-3-propyl-1,2,4-triazolin-5-thione, 4-methyl-3-n-heptyl-1,2,4-triazolin-5-thione, 4-phenyl-3-n-heptyl-1,2,4-triazolin-5-thione, 4-phenyl-3,5-dimercapto-1 2,4-Triazole, 4-decyl-3,5-dimercapto-1,2,4-triazole, 5-phenyl-2-mercapto-1,3,4-oxadiazole, 5-methylthio-1,3,4-thiadiazolin-2-thione, 5-hexylthio-1,3,4-thiadiazolin-2-thione, mercaptophenyltetraazole, pentaerythritol mercaptopropionate, butyrate-3-mercaptoneopentetrate, pentaerythritol tetra(thioglycolate). Other preferred co-initiators are polythiols disclosed in WO 2006 / 048443 and WO 2006 / 048445. These polythiols can be used in combination with the aforementioned thiols (e.g., 2-mercaptobenzothiazole).

[0083] Binders

[0084] The photopolymerizable layer preferably includes an adhesive. The adhesive can be selected from a wide range of organic polymers. Combinations of different adhesives can also be used. Useful adhesives are described, for example, in paragraph

[0013] of EP 1 043 627, WO2005 / 111727, page 17, line 21 to page 19, line 30, and WO2005 / 029187, page 16, line 26 to page 18, line 11.

[0085] The photopolymerizable layer may include discrete particles, i.e., particulate polymers, comprising homopolymers or copolymers prepared from monomers such as ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, vinylcarbazole, acrylates, or methacrylates or mixtures thereof. Preferably, the discrete particles are particles suspended in the polymerizable composition. The presence of discrete particles tends to promote the developability of unexposed areas. Thermoreactive polymer fine particles include thermoreactive groups, such as olefinically unsaturated groups, cationic polymerizable groups, isocyanate groups, epoxy groups, ethoxy groups, and functional groups having active hydrogen atoms, carboxyl groups, hydroxyl groups, amino groups, or acid anhydrides.

[0086] The average particle size of the polymer particles is preferably from 0.01 mm to 3.0 mm. Particulate polymers in the form of microcapsules, microgels or reactive microgels are suitable, as disclosed in EP 1 132 200, EP 1 724 112 and US 2004 / 106060.

[0087] Specific examples of binders are described in

[0029] ,

[0030] , and

[0031] of US 6,899,994, US 2004 / 0260050, US 2005 / 0003285, US2005 / 0170286, US 2005 / 0123853, and EP 2 916 171. Other suitable binders described in EP 2471 655, EP 2 492 748, and EP 2 660 068 include polyfunctional thiols having 6-10 functional groups as a core (central backbone) and polymer chains linked to said core by sulfur bonds. Furthermore, the imageable layer may optionally contain one or more co-binders. Typical co-binders are water-soluble or water-dispersible polymers, such as cellulose derivatives, polyvinyl alcohol, polyacrylic acid, poly(meth)acrylic acid, polyvinylpyrrolidone, polylactide, polyvinylphosphonic acid, and synthetic copolymers, such as copolymers of alkoxy polyethylene glycol (meth)acrylate. Specific examples of co-binders are described in US2004 / 0260050, US 2005 / 0003285, and US 2005 / 0123853.

[0088] Other ingredients

[0089] The photopolymerizable layer may also contain particles that increase the coating's resistance to manual or mechanical damage. The particles may be inorganic, organic, or fillers, as described, for example, in US 7,108,956. Further details of suitable spacer particles are described in EP 2 916 171

[0053] through

[0056] . The photopolymerizable layer may also contain inhibitors. Specific inhibitors for use in photopolymer coatings are disclosed in US 6,410,205, EP 1 288 720, and EP 1 749 240.

[0090] The photopolymerizable layer may include a leuco dye that forms a colored compound upon exposure to light and / or heat (preferably infrared light), thereby forming the printed image. More information about suitable leuco dyes can be found in

[0069] to

[0085] of unpublished application EP19153178.

[0091] The photopolymerizable layer may further comprise at least one borate compound. The borate compound preferably refers to a compound comprising a borate anion and, preferably a cation, as counterions. The borate anion may be derived from the counterion of a photoinitiator; for example, diphenyliodonium photoinitiator and / or the aforementioned infrared absorbing compound or any other salt (e.g., sodium tetraphenylborate).

[0092] Preferably, the borate anion is a tetrahedral boron anion, and can be represented by the following formula A:

[0093]

[0094] Where R b 1 R b 2 R b 3 and R b 4 Independently, it is an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group, or a heteroaryl group; or, R b 1 R b 2 R b 3 and R b 4 Two or more of the atoms can bond with boron atoms to form a heterocycle, which may include up to seven carbon, nitrogen, oxygen, and / or nitrogen atoms. Preferably, R b 1 R b 2 R b 3 and R b 4 Independently, it is an optionally substituted aryl or heteroaryl group. More preferably, R b 1 R b 2 R b 3 and R b 4 The aryl group is independently substituted. Most preferably, the borate compound includes at least one substituted phenyl group, more preferably at least two substituted phenyl groups, even more preferably at least three substituted phenyl groups, and most preferably four substituted phenyl groups.

[0095] M + It is an alkali metal cation, such as Li + Na + K + Alternatively, substituted ononium ions. Examples of substituted ononium ions include pyridinium, ammonium, iodonium, or sulfonium.

[0096] Examples of pyridinium ions include N-alkyl-3-pyridinium groups, N-benzyl-3-pyridinium groups, N-(alkoxypolyalkyleneoxyalkyl)-3-pyridinium groups, N-alkoxycarbonylmethyl-3-pyridinium groups, N-alkyl-4-pyridinium groups, N-benzyl-4-pyridinium groups, N-(alkoxypolyalkyleneoxyalkyl)-4-pyridinium groups, and N-alkoxycarbonyl groups. The methyl-4-pyridinium group, N-alkyl-3,5-dimethyl-4-pyridinium, N-alkyl-3-pyridinium group or N-alkyl-4-pyridinium, N-methyl-3-pyridinium, N-octyl-3-pyridinium, N-methyl-4-pyridinium, or particularly preferably N-octyl-4-pyridinium, and most preferably N-octyl-3-pyridinium or N-octyl-4-pyridinium group.

[0097] The optionally substituted ononium ion is preferably an ammonium ion represented by formula B:

[0098]

[0099] in

[0100] R n 1 R n 2 and R n 3 Independently, it can be an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl or heteroaryl group, or a halogen atom.

[0101] The optionally substituted ononium ion is most preferably an iodonium ion; more preferably an optionally substituted diphenyliodonium salt. Particularly preferred are diphenyliodonium salts substituted with electron-donating groups (e.g., alkyl or alkoxy) and asymmetric diphenyliodonium salts. The phenyl group of the iodonium ion is preferably substituted with a group comprising at least six carbon atoms.

[0102] Specific examples of borate compounds including iodonium ions include 4-hexyloxyphenyl-2,4-diethoxyphenyliodonium tetrafluoroborate, 4-octyloxyphenylphenyliodonium tetraphenylborate, [4-[(2-hydroxytetradecyl)-oxy]phenyl]phenyliodonium tetraphenylborate, bis(4-tert-butylphenyl)iodonium tetraphenylborate, 4-methylphenyl-4'-hexylphenyliodonium tetraphenylborate, 4-methylphenyl-4'-cyclohexylphenyliodonium tetraphenylborate, bis(tert-butylphenyl)iodonium tetra(pentafluorophenyl)borate, 4-hexylphenyl-phenyliodonium tetraphenylborate, and n-butyltriphenylboronium. 4-Methylphenyl-4'-cyclohexylphenyliodonium salt, 4-cyclohexylphenyl-phenyliodonium salt of tetraphenylboronic acid, 2-5-methyl-4-tert-butylphenyl-4'-methylphenyliodonium salt of tetraphenylboronic acid, 4-methylphenyl-4'-pentylphenyliodonium salt of tetra[3,5-bis(trifluoromethyl)phenyl]boronic acid, 4-methoxyphenyl-4'-cyclohexylphenyliodonium salt of tetra(pentafluorophenyl)boronic acid, 4-methylphenyl-4'-dodecylphenyliodonium salt of tetra(4-fluorophenyl)boronic acid, bis(dodecylphenyl)iodonium salt of tetra(pentafluorophenyl)boronic acid, and bis(4-tert-butylphenyl)iodonium salt of tetra(imidazolyl)boronic acid. Preferred compounds include bis(4-tert-butylphenyl)iodonium tetraphenylboronic acid, 4-methylphenyl-4'-hexylphenyliodonium tetraphenylboronic acid, 2-methyl-4-tert-butylphenyl-4'-methylphenyliodonium tetraphenylboronic acid, and 4-methylphenyl-4'-cyclohexylphenyliodonium tetraphenylboronic acid.

[0103] The borate compound may be present in an amount between 0.05-30% by weight, more preferably between 0.1-25% by weight, and most preferably between 0.5-15% by weight, relative to the components of the photopolymerizable layer.

[0104] Various surfactants can be added to the photopolymerizable layer to allow or enhance the developability of the precursor; particularly with gel solutions. Both polymers and small molecule surfactants, such as nonionic surfactants, are preferred. More details are described in EP 2 916 171

[0059] .

[0105] Top layer

[0106] The coating may include a top layer or a protective top coating, which can act as an oxygen barrier layer. Low molecular weight substances present in the air may degrade or even inhibit image formation, thus necessitating the application of a top layer to the coating. The top layer should preferably be easily removable during development, sufficiently adherent to the photopolymerizable layer or optionally other layer of the coating, and preferably should not inhibit light transmission during exposure. The top layer is preferably provided on top of the photopolymerizable layer.

[0107] The optional top layer may further include an adhesive. A preferred adhesive that can be used for the top layer is polyvinyl alcohol (PVA). PVA preferably has a degree of hydrolysis between 74 mol% and 99 mol%, more preferably between 80-98%. The weight-average molecular weight of PVA can be measured by the viscosity of a 4% by weight aqueous solution at 20°C, as defined in DIN 53 015, and this viscosity value is preferably between 2 and 26, more preferably between 2 and 15, and most preferably between 2 and 10.

[0108] The optional top layer may include a halogenated polymer, preferably a hydrophobic polymer, i.e., insoluble or non-swellable in water at approximately neutral pH. The binder may be used in the top layer in the form of a dispersion; i.e., an emulsion or suspension. The amount of halogenated binder in the top layer may be between 30% by weight and 96% by weight, more preferably between 40% by weight and 90% by weight, and most preferably between 50% by weight and 85% by weight. The halogenated binder preferably comprises between 60% by weight and 95% by weight monomer units derived from vinylidene monomers (e.g., vinylidene fluoride, vinylidene chloride, vinylidene bromide, and / or vinylidene iodide).

[0109] The optional top layer may optionally include other components, such as inorganic or organic acids, matting agents, surfactants such as anionic surfactants, such as sodium alkyl sulfate or sodium alkyl sulfonate; amphoteric surfactants, such as alkylaminocarboxylate and alkylaminodicarboxylate; nonionic surfactants, such as polyoxyethylene alkylphenyl ethers, (co)polymers comprising siloxane and / or perfluoroalkyl units and / or oligomeric (epoxy) units; fillers; (organic) waxes; alkoxylated alkylene diamines, such as those disclosed in EP 1 085 380 (paragraphs

[0021] and

[0022] ); glycerol; inorganic particles; pigments or wetting agents, such as those disclosed in EP 2 916 171. The optional top layer may further include an infrared absorbing compound that is capable of forming a colored compound upon exposure to infrared light and / or heat—thereby forming a printed image. More information about such infrared absorbing dyes can be retrieved in unpublished applications EP 20181812

[0055] to

[0072] .

[0110] The optional top coating thickness can range from 0.10 to 1.75 g / m. 2 More preferably, it is between 0.20-1.30 g / m 2 More preferably, it is between 0.25-1.0 g / m 2 The optimal range is between 0.30 and 0.80 g / m³. 2 Between 0.25 and 1.75 g / m². Preferably, the optional top coating thickness is between 0.25 and 1.75 g / m². 2The range includes polyvinyl alcohols with a degree of hydrolysis between 74 mol% and 99 mol% and a viscosity value between 2 and 26 mPas as defined above.

[0111] Hydrophilic polymers in the protective topcoat can cause a problematic increase in viscosity of printing chemicals (such as dampening solutions and / or developer solutions). Therefore, the coating weight of the hydrophilic polymer and / or the thickness of the protective topcoat should preferably not be too high; for example, above the ranges given above.

[0112] Definitions

[0113] Aliphatic hydrocarbon groups are preferably alkyl, cycloalkyl, alkenyl, cycloalkenyl, or ynyl; suitable groups are described below. Aromatic hydrocarbon groups are preferably hetero(aryl); suitable hetero(aryl) groups (i.e., suitable aryl or heteroaryl) are described below.

[0114] In this document, the term "alkyl" refers to all possible variations in the number of carbon atoms per alkyl group, namely methyl; ethyl; for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl, and tert-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl, and 2-methyl-butyl, etc. Examples of suitable alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, 1-isobutyl, 2-isobutyl and tert-butyl, n-pentyl, n-hexyl, chloromethyl, trichloromethyl, isopropyl, isobutyl, isopentyl, neopentyl, 1-methylbutyl and isopentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl and 2-methyl-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and methylcyclohexyl. Preferably, the alkyl group is a C1-C6 alkyl group.

[0115] Suitable alkenyl groups are preferably C2-C6-alkenyl groups, such as vinyl, n-propenyl, n-butenyl, n-pentenyl, n-hexenyl, isopropenyl, isobutenyl, isopentenyl, neopentenyl, 1-methylbutenyl, isohexenyl, cyclopentenyl, cyclohexenyl and methylcyclohexenyl.

[0116] Suitable alkynyl groups are preferably C2-C6-alkynyl groups; suitable aralkyl groups are preferably phenyl or naphthyl groups comprising one, two, three or more C1-C6-alkyl groups; suitable alkylaryl groups are preferably C1-C6-alkyl groups comprising aryl groups (preferably phenyl or naphthyl groups).

[0117] A cyclic group or cyclic structure includes at least one ring structure and can be a monocyclic or polycyclic group, wherein a polycyclic group refers to one or more rings fused together.

[0118] Suitable examples of aryl groups can be represented by, for example, optionally substituted phenyl, benzyl, tolyl, or o-, m-, or p-xylyl, optionally substituted naphthyl, anthracene, phenanthryl, and / or combinations thereof. The heteroaryl group is preferably a monocyclic or polycyclic aromatic ring containing a carbon atom and one or more heteroatoms in its ring structure, preferably 1-4 heteroatoms independently selected from nitrogen, oxygen, selenium, and sulfur. Preferred examples include optionally substituted furanyl, pyridinyl, pyrimidinyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, thiophene, tetrazolyl, thiazolyl, (1,2,3)triazolyl, (1,2,4)triazolyl, thiadiazolyl, thiophene, and / or combinations thereof.

[0119] A cyclic group or cyclic structure includes at least one ring structure and can be a monocyclic or polycyclic group, wherein a polycyclic group refers to one or more rings fused together.

[0120] Halogens are selected from fluorine, chlorine, bromine or iodine.

[0121] In the context of substituted alkyl groups, the term "substituted" means that the alkyl group can be replaced by atoms other than those normally present in such groups (i.e., carbon and hydrogen). For example, substituted alkyl groups can include halogen atoms or thiol groups. Unsubstituted alkyl groups contain only carbon and hydrogen atoms.

[0122] Optional substituents on alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aralkyl, alkylaryl, aryl, and heteroaryl groups are preferably selected from hydroxyl, -Cl, -Br, -I, -OH, -SH, -CN, -NO2, alkyl (e.g., methyl or ethyl), alkoxy (e.g., methoxy or ethoxy), aryloxy, carboxylic acid or its alkyl ester, sulfonic acid or its alkyl ester, phosphonic acid or its alkyl ester, phosphate or ester (e.g., alkyl ester, such as methyl or ethyl ester), thioalkyl, thioaryl, thioheteroaryl, -SH, thioether (e.g., thioalkyl or thioaryl), ketone, aldehyde, sulfoxide, sulfone, sulfonate, sulfonamide, amino, vinyl, alkenyl, alkynyl, cycloalkyl, alkylaryl, aralkyl, aryl, heteroaryl, or heterocycloalkyl and / or combinations thereof.

[0123] Monomer units are the structural units that make up polymers.

[0124] Support

[0125] The lithographic printing plate used in this invention comprises a carrier having a hydrophilic surface or being provided with a hydrophilic layer. The carrier is preferably a granulated and anodized aluminum carrier known in the art. Suitable carriers are disclosed, for example, in EP 1 843 203 (paragraphs

[0066] to

[0075] ). The surface roughness obtained after the granulation step is generally expressed as an arithmetic mean centerline roughness Ra (ISO 4287 / 1 or DIN 4762) and can vary between 0.05 and 1.5 μm. The aluminum substrate of this invention preferably has an Ra value between 0.1 and 1.4 μm, more preferably between 0.3 and 1.0 μm, and most preferably between 0.4 and 0.9 μm. The lower limit of the Ra value is preferably about 0.1 μm. More details regarding the preferred Ra value of the granulated and anodized aluminum carrier surface are described in EP 1 356 926. By anodizing the aluminum carrier, an Al2O3 layer is formed, and the anode weight (g / m³) is... 2 Al2O3 formed on the aluminum surface (at a concentration of 1-8 g / m³) 2 The variation is within a certain range. The preferred anode weight is ≥2.0 g / m³. 2 More preferably ≥2.5g / m 2 And the optimal value is ≥3.0g / m 2 Granulated and anodized aluminum supports can be subjected to so-called post-anodization treatments, such as treatment with polyvinylphosphonic acid or derivatives thereof, treatment with polyacrylic acid or derivatives thereof, treatment with potassium fluorozirconate or potassium phosphate, treatment with alkali metal silicates, or combinations thereof. Treatment of the support edges, as described, for example, in US 2017 / 320351, may be of interest to prevent printing edges. Alternatively, the support can be treated with adhesion-promoting compounds, such as those described in EP 1 788 434

[0010] and WO 2013 / 182328. However, for precursors optimized for use without a preheating step, it is preferable to use granulated and anodized aluminum supports without any post-anodization treatment.

[0126] In addition to aluminum carriers, plastic carriers, such as polyester carriers, can also be used, which are provided with one or more hydrophilic layers, as disclosed in, for example, EP 1 025 992.

[0127] Exposure step

[0128] Preferably, the printing plate precursor is exposed according to the image using a laser that emits IR light. Preferably, the image exposure step is performed off-machine in a plate-making machine, which is suitable for using a laser, such as a laser diode emitting about 830 nm, an NdYAG laser emitting about 1060 nm, a violet laser emitting about 400 nm, or a gas laser such as an Ar laser, or a digitally modulated UV exposure device (using, for example, a digital mirror device), or an exposure instrument that exposes the precursor according to the image through conventional exposure in contact with a mask. In a preferred embodiment of the invention, the precursor is exposed according to the image using a laser that emits IR light or violet light, more preferably by using a laser that emits IR light.

[0129] Preheating step

[0130] Following the exposure step, the precursor can be preheated in a preheating unit, preferably at a temperature of about 80°C to 150°C, and preferably for a residence time of about 5 seconds to 1 minute. This preheating unit may include a heating element, preferably an IR lamp, a UV lamp, heated air, or heated rollers. Such a preheating step can be used for printing plate precursors containing photopolymerizable compositions to enhance or accelerate polymerization and / or crosslinking reactions.

[0131] Developing step

[0132] Following the exposure step or preheating step (when a preheating step is present), the plate precursor can be processed (developed). A pre-rinsing step can be performed before developing the image precursor, particularly for negative lithographic printing precursors with a protective oxygen barrier or top coating. This pre-rinsing step can be performed in a separate instrument, or manually by rinsing the image precursor with water, or it can be performed in a washing unit integrated into the processor for developing the image precursor. The washing solution is preferably water, more preferably tap water. Further details regarding the washing step are described in

[0026] of EP 1788 434.

[0133] During the developing step, at least partially, the unexposed areas of the image recording layer are removed, while the exposed areas are not substantially removed. The processing solution (also called developer) can be applied to the plate by hand or in automated processing equipment, for example, by rubbing with an immersion pad, by dipping, immersion, coating, spin coating, spraying, or pouring. Processing solution treatment can be combined with mechanical friction (e.g., by a rotating brush). During the developing step, it is preferable to also remove any water-soluble protective layer present. Developing is preferably carried out in an automated processing unit at a temperature between 20-40°C.

[0134] In a highly preferred embodiment, the above-described processing steps are replaced by machining, whereby the imaging precursor is mounted on the printing press and machining is performed by rotating the plate cylinder while simultaneously feeding dampening solution and / or ink to the coating of the precursor to remove unexposed areas from the carrier. In a preferred embodiment, the supply of dampening solution and ink is started simultaneously, or ink may be supplied only during multiple rotations prior to the activation of the dampening solution supply. In an alternative embodiment, dampening solution is supplied only to the plate during the start-up of the printing press, and ink supply is also activated after multiple rotations of the plate cylinder.

[0135] The processing steps can also be performed by combining the above-described embodiments, for example, by combining the development of the processing liquid with in-machine development by applying ink and / or dampening solution.

[0136] Processing liquid

[0137] The processing solution can be an alkaline developer or a solvent-based developer. Suitable alkaline developers are described in US2005 / 0162505. An alkaline developer is an aqueous solution with a pH of at least 11, more typically at least 12, and preferably 12-14. Alkaline developers typically contain alkaline reagents to obtain a high pH value and can be inorganic or organic alkaline reagents. The developer may contain anionic, nonionic, and amphoteric surfactants (up to 3% by weight of the total composition); biocides (antimicrobial and / or antifungal agents), defoamers or chelating agents (e.g., basic gluconates), and thickeners (water-soluble or water-dispersible polyhydroxy compounds, such as glycerol or polyethylene glycol).

[0138] Preferably, the processing solution is an adhesive solution, thereby removing unexposed areas of the photopolymerizable layer from the carrier during the development step and applying adhesive to the plate in a single step. Developing with an adhesive solution has the additional advantage that, due to the remaining adhesive in the unexposed areas of the plate, no additional adhesive application step is required to protect the carrier surface in non-printing areas. As a result, the precursor is processed and coated in a single step, involving a developing instrument simpler than one comprising a developer tank, a rinsing section, and an adhesive application section. The adhesive application section may comprise at least one adhesive application unit or may comprise two or more adhesive application units. These adhesive application units may be configured as a cascaded system, i.e., when a supplemental adhesive solution is added to a second adhesive application unit or when the adhesive solution in the second adhesive application unit is used only once, i.e., when the precursor is developed in the second adhesive application unit using only the initial adhesive solution via a preferred spray or jet technique, the adhesive solution used in the second adhesive application unit and present in the second tank overflows from the second tank to the first tank. Further details regarding such adhesive development are described in EP1 788 444.

[0139] The adhesive solution is typically an aqueous liquid containing one or more surface-protective compounds that protect the lithographic image on the printing plate from contamination, such as from oxidation, fingerprints, grease, oil, or dust, or from damage, such as from scratching during plate handling. Suitable examples of such surface-protective compounds are film-forming hydrophilic polymers or surfactants. The layer retained on the plate after treatment with the adhesive solution preferably contains 0.005-20 g / m³. 2 More preferably, it is between 0.010-10 g / m 2 The optimal value is between 0.020-5 g / m³. 2 The surface protective compound in the adhesive solution. More details about the surface protective compound in the adhesive solution can be found on page 9, line 3 to page 11, line 6 of WO 2007 / 057348. Since the plate precursor is developed and coated in one step, no post-processing of the plate is required.

[0140] The adhesive solution preferably has a pH value between 3 and 11, more preferably between 4 and 10, even more preferably between 5 and 9, and most preferably between 6 and 8. Suitable adhesive solutions are described, for example, in EP 1 342568

[0008] to

[0022] and WO2005 / 111727. The adhesive solution may further comprise inorganic salts, anionic surfactants, wetting agents, chelating compounds, preservative compounds, defoaming compounds and / or ink absorbers and / or combinations thereof. Further details regarding these additional components are described on page 11, line 22 to page 14, line 19 of WO2007 / 057348.

[0141] Drying and baking step

[0142] After the processing steps, the plate can be dried in a drying unit. In a preferred embodiment, the plate is dried by heating it in a drying unit, which may contain at least one heating element selected from IR lamps, UV lamps, heated metal rollers, or heated air. After drying, the plate may optionally be heated in a baking unit. Further details regarding heating in a baking unit can be found on page 44, line 26 to page 45, line 20 of WO 2007 / 057348.

[0143] According to the present invention, a method for manufacturing a negative lithographic printing plate is also provided, the method comprising the steps of: exposing a printing plate precursor according to an image, followed by developing the image-exposed precursor such that unexposed areas dissolve in a developer solution. Development is preferably performed by treating the precursor with a glue solution, however more preferably by mounting the precursor on a plate cylinder of a lithographic printing press and rotating the plate cylinder while feeding dampening solution and / or ink to the precursor. Optionally, after the imaging step, a heating step is performed to enhance or accelerate the polymerization and / or crosslinking reaction. The lithographic printing plate precursor can be prepared by (i) applying a coating as described above onto a carrier and (ii) drying the precursor. Any coating method can be used to apply one or more coating solutions to a hydrophilic surface of the carrier. Multilayer coatings can be applied by continuously coating / drying each layer or by simultaneously coating several coating solutions at once. In the drying step, volatile solvents are removed from the coating until the coating is self-supporting and feels dry to the touch.

[0144] The resulting printing plate can be used in conventional so-called wet offset printing, where ink and aqueous dampening solution are supplied to the plate. Another suitable printing method uses so-called single-fluid inks without dampening solution. Suitable single-fluid inks have been described in US 4,045,232, US 4,981,517, and US 6,140,392. In the most preferred embodiment, the single-fluid ink comprises an ink phase (also called a hydrophobic or oleophilic phase) and a polyol phase, as described in WO 00 / 32705.

[0145] Example

[0146] Example 1

[0147] 1. Preparation of printing plate precursors

[0148] Preparation of aluminum carrier S-01

[0149] A 0.3 mm thick aluminum foil was degreased by spraying it with an aqueous solution containing 26 g / L NaOH at 65 °C for 2 seconds, followed by rinsing with softened water for 1.5 seconds. Then, it was subjected to a temperature of 37 °C and approximately 100 A / dm². 2 At a current density of 15 g / L HCl and 15 g / L SO4, 2- Ions and 5g / l Al 3+ The foil was electrochemically granulated for 10 seconds using alternating current in an aqueous solution containing ions. Then, the aluminum foil was decontaminated by etching for 2 seconds at 36°C with an aqueous solution containing 5.5 g / L NaOH, followed by rinsing with softened water for 2 seconds. Subsequently, it was subjected to etching at 50°C and 17 A / dm³. 2 The foil was anodized for 15 seconds in an aqueous solution containing 145 g / L sulfuric acid at a current density, then washed with softened water for 11 seconds and dried at 120°C for 5 seconds.

[0150] The resulting support is characterized by a surface roughness Ra of 0.35–0.4 μm (measured using an NT1100 interferometer) and an oxide weight of 3.0 g / m². 2 .

[0151] Preparation of printing plates PP-01 to PP-05

[0152] Photopolymerizable layer

[0153] The printing plate precursor was produced by coating the carrier S-01 described above with the components defined in Table 1, dissolved in a mixture of 35 vol% MEK and 65 vol% Dowanol PM (1-methoxy-2-propanol, commercially available from DOWCHEMICAL Company). The coating solution was applied to a wet coating thickness of 30 μm and then dried in a circulating oven at 120°C for 1 minute.

[0154] Table 1: Composition of the photosensitive layer PL-0X

[0155]

[0156] 1) FST 510 is the reaction product of 1 mole of 2,2,4-trimethylhexamethylene diisocyanate and 2 moles of hydroxyethyl methacrylate, and is commercially available from AZ Electronics as an 82% by weight solution in MEK;

[0157] 2) CN 104 is an epoxy acrylate oligomer, commercially available from Arkema;

[0158] 3) Initiator-01 is bis(4-tert-butylphenyl)-iodonium tetraphenylborate, which is commercially available from Hampford Research Inc.

[0159] 4) S2539 is an infrared absorbing dye, commercially available from FEW Chemicals.

[0160]

[0161] 5) Ruco coat EC4811 is a polyether polyurethane, commercially available from Rudolf Chemistry.

[0162] 6) Tegoglide 410 is a surfactant and is commercially available from Evonik Tego Chemie GmbH;

[0163] 7) Sipomer PAM 100 is a phosphonate methacrylate, commercially available from Rhodia;

[0164] 8) HAP is a hydrophilic substrate adhesive polymer according to Table 2;

[0165] 9) Aerosil R972 is hydrophobic vapor-deposited silica, commercially available from Evonik Resource Efficiency GmbH.

[0166] Table 2: Hydrophilic substrate adhesive polymers (HAP)

[0167]

[0168]

[0169] Protective top coating

[0170] On top of the photosensitive layer, an aqueous solution (40 μm) with the composition defined in Table 3 is coated and dried at 110 °C for 2 minutes. Printing precursors PPP-01 to PPP-05 are obtained (Table 4).

[0171] Table 3: Composition of Protective Top Coating OC-01

[0172]

[0173] 1) Mowiol 4-88 is partially hydrolyzed polyvinyl alcohol, commercially available from Kuraray;

[0174] 2) PVDC-1 is Diofan A050 and PVDC-2 is Diofan A602, both of which are polyvinylidene chloride latex and can be purchased from Solvay.

[0175] 3) IR-01 is a thermochromic infrared absorbing dye with the following formula:

[0176]

[0177] 4) Lutensol A8™ is a surfactant that is commercially available from BASF.

[0178] Table 4: Printing Plate Precursors PPP-01 to PPP-05

[0179]

[0180] * Hydrophilic substrate adhesive polymers; see Table 2 above.

[0181] Accelerated aging

[0182] Subsequently, the resulting printing plate precursor was subjected to accelerated aging tests for 3 days in a climate chamber at 50°C and 50% relative humidity.

[0183] Imaging

[0184] Two printing plate precursors, one unaged and one aged, were imaged at 2400 dpi using a High Power Creo 40W TE38 thermal plate setter™ (200 lpi Agfa Balanced Screening (ABS)). This thermal plate setter is commercially available from Kodak and is equipped with an 830 nm IR laser diode with an energy density of 130 mJ / cm². 2 .

[0185] print

[0186] After imaging, the printing plate is mounted on a Heidelberg GTO 52Dalghren printing press. Each printing job begins with a dampening solution of K+ESkinnex 800SPEED IK black ink (trademark of BASF Druckfarben GmbH), 4% by weight Prima FS303SF (trademark of Agfa Graphics), and 8% isopropyl alcohol in water. A compressible blanket is used, and printing is performed on uncoated offset paper.

[0187] Before feeding the paper, the printing press is rotated 10 times using only the dampening system, followed by 5 rotations using only the ink rollers. The first 250 sheets are visually evaluated to assess toning (i.e., ink acceptance) in the non-image areas of the print.

[0188] Results

[0189] Table 5 summarizes the results of the printing tests regarding color mixing behavior.

[0190] Table 5: Color Correction Results

[0191]

[0192]

[0193] (a) Toning is a rating of the number of blemishes in non-image areas of a printed sheet, and includes the following categories:

[0194] A: No color correction was applied before page 25.

[0195] B: No color correction printing between pages 25 and 50.

[0196] C: No color toning printing between pages 50 and 250, and

[0197] D: Enables up to 250 sheets of printing without color correction.

[0198] The results in Table 5 show that the printing plates of the present invention, including hydrophilic adhesion promoters (which include the copolymers of the present invention (PP-02 and PP-03)), showed no color correction for non-aged samples, but slightly more color correction for aged samples. Comparative printing plates (PP-01, PP-04, and PP-05) showed unacceptable color correction after the aging test.

[0199] Example 2

[0200] Preparation of printing plates PP-06 to PP-08

[0201] Photopolymerizable layer

[0202] Photopolymerizable layers PL-06 to PL-08 were produced by coating the carrier S-01 described above with the components defined in Table 6, dissolved in a mixture of 35 vol% MEK and 65 vol% Dowanol PM (1-methoxy-2-propanol, commercially available from DOWCHEMICAL Company). The coating solution was applied to a wet coating thickness of 30 μm and then dried in a circulating oven at 120°C for 1 minute.

[0203] Table 6: Composition of the photopolymerizable layer PL-0X

[0204]

[0205] (1) See Table 1 above;

[0206] (2) JPA 528 is a polyethylene glycol monomethacrylate phosphate ester, which is commercially available from Johoku Chemical Co., Ltd.

[0207] Protective top coating

[0208] On top of the photosensitive layer, an aqueous solution (40 μm wet film) with the composition defined in Table 7 is coated and dried at 110 °C for 2 minutes.

[0209] Table 7: Composition of the protective topcoat

[0210]

[0211]

[0212] (1) See Table 3 above.

[0213] Accelerated aging

[0214] Subsequently, the resulting printing plate precursor was subjected to accelerated aging tests for 3 days in a climate chamber at 50°C and 50% relative humidity.

[0215] Imaging

[0216] Two printing plate precursors, one unaged and one aged, were imaged at 2400 dpi using a High Power Creo 40W TE38 thermal plate setter™ (200 lpi Agfa Balanced Screening (ABS)). This thermal plate setter is commercially available from Kodak and is equipped with an 830 nm IR laser diode with an energy density of 130 mJ / cm². 2 .

[0217] Printing

[0218] After imaging, the printing plate is mounted on a Heidelberg GTO 52Dalghren printing press. Each printing job begins with a dampening solution of K+ESkinnex 800SPEED IK black ink (trademark of BASF Druckfarben GmbH), 4% by weight Prima FS303SF (trademark of Agfa Graphics), and 8% isopropyl alcohol in water. A compressible blanket is used, and printing is performed on uncoated offset paper.

[0219] Before feeding the paper, the printing press is rotated 10 times using only the dampening system, followed by 5 rotations using only the ink rollers. The first 250 sheets are visually evaluated to assess toning (i.e., ink acceptance) in the non-image areas of the print.

[0220] Results

[0221] Table 8 summarizes the results of the printing tests. Up to 40,000 print runs were performed. Toning on each sheet was evaluated every 25 sheets. Table 8 summarizes the toning results.

[0222] Table 8: Color Correction Behavior

[0223]

[0224] (a) See Table 2 above;

[0225] Toning is a rating of the amount of ink accepted in non-image areas of a printed sheet, and includes the following categories:

[0226] A: No color correction was applied before page 25.

[0227] B: No color correction printing between pages 25 and 50.

[0228] C: No color toning printing between pages 50 and 250, and

[0229] D: Enables up to 250 sheets of printing without color correction.

[0230] The results in Table 8 show that the printing plates of the present invention, including the copolymer (HAP 2) in the photosensitive layer, the protective topcoat, or both the photosensitive layer and the protective topcoat, enable rapid, toning-free printing. Printing can be performed up to 40,000 times without significant wear.

Claims

1. Lithographic printing plate precursor comprising on a support a coating layer comprising a photopolymerizable layer, said photopolymerizable layer comprising a polymerizable compound, a photoinitiator and an adhesion promoting compound, characterized in that said coating layer further comprising a hydrophilic substrate adhesive polymer comprising at least one monomeric unit according to formula III, at least one monomeric unit according to formula IV and at least one group and / or moiety comprising a phosphorous atom according to formula V and / or formula VI; formula III wherein n represents an integer greater than 0; formula IV wherein m represents an integer greater than 0; R represents hydrogen; formula V wherein a represents 0; R4represents an OH group; * represents a position of attachment to a monomeric unit of the hydrophilic substrate adhesive polymer; formula VI wherein b and c independently represent 0 or 1 ; * represents a position of attachment to a monomeric unit of the hydrophilic substrate adhesive polymer.

2. Printing plate precursor according to claim 1, wherein the group and / or moiety comprising at least one phosphorous atom is randomly present in the main chain of the hydrophilic substrate adhesive polymer.

3. Printing plate precursor according to claim 1 or 2, wherein the group and / or moiety comprising at least one phosphorous atom is present as end group in the polymer.

4. Printing plate precursor according to claim 1 or 2, wherein the hydrophilic substrate adhesive polymer is a block copolymer comprising an alternating sequence of blocks consisting of monomeric units according to formula III and monomeric units according to formula IV.

5. Printing plate precursor according to claim 1, wherein the hydrophilic substrate adhesive polymer comprises at least one monomeric unit according to formula III and at least one monomeric unit according to formula VII: formula VII wherein R’ represents hydrogen; o represents an integer between 1 and 100; and p and q independently represent an integer between 2 and 250.

6. Printing plate precursor according to claim 1 or 2, wherein the hydrophilic substrate adhesive polymer further comprises monomeric units derived from acrylate, methacrylate, styrene, acrylamide, methacrylamide or maleimide.

7. Printing plate precursor according to claim 1 or 2, wherein the hydrophilic substrate adhesive polymer is present in the coating layer in an amount comprised between 5 and 100 mg / m2.

8. Printing plate precursor according to claim 1 or 2, wherein the weight average molecular weight of the hydrophilic substrate adhesive polymer is below 100 000.

9. Printing plate precursor according to claim 1, wherein the coating layer comprises a top layer on top of the photopolymerizable layer and the hydrophilic substrate adhesive polymer is present in this top layer.

10. Printing plate precursor according to claim 9, wherein the hydrophilic substrate adhesive polymer is present in both the photopolymerizable layer and the top layer.

11. A method of manufacturing a printing plate precursor comprising the steps of - coating on a support (i) a photopolymerizable layer comprising a polymerizable compound, a photoinitiator and an adhesion promoting compound and (ii) a substrate adhesive polymer as defined in any one of claims 1 to 8, and - drying the precursor.

12. A method of manufacturing a printing plate comprising the steps of - exposing the printing plate precursor as defined in any of the preceding claims 1 to 10 to heat and / or IR radiation in an image, thereby forming a lithographic image consisting of image areas and non-image areas, - developing the exposed precursor.

13. The method according to claim 12, wherein the developing of the precursor is by mounting the precursor on a plate cylinder of a lithographic printing press and rotating the plate cylinder while feeding dampening liquid and / or ink to the precursor.

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