Lithographic printing plate precursors

Abstract

A lithographic printing plate precursor comprises a coating on a substrate having a hydrophilic surface or provided with a hydrophilic layer, the coating comprising a photopolymerizable layer comprising a polymerizable compound, a photoinitiator and an adhesion-promoting compound containing at least one thiol group and at least one group capable of adhering to the substrate.

Description

Technical Field

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

[0002] Lithographic printing generally involves the use of a so-called printing master, such as a printing plate mounted on a rotary printing press cylinder. The master carries a lithographic image on its surface, and the printed product is obtained by applying ink to the image and then transferring the ink from the master to a receiving material, generally paper. In conventional lithographic printing, ink and an aqueous fountain solution (also called dampening liquid) are supplied to the lithographic image, which consists of oleophilic (or hydrophobic, i.e., ink-receiving and water-repelling) areas and hydrophilic (or oleophobic, i.e., water-receiving and ink-repelling) areas. In so-called waterless offset printing, the lithographic image consists of ink-receiving and ink-resistant (ink-repelling) areas, and during waterless offset 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 transform the so-called lithographic printing plate precursor into a printing plate or master. The radiation-sensitive coating is image-wise exposed to heat or light, typically with the aid of a digitally modulated exposure device (e.g., a laser), triggering physical and / or chemical processes such as ablation, polymerization, insolubilization by polymer crosslinking or by agglomeration of particles of a thermoplastic polymer latex, solubilization by disrupting intermolecular interactions, or by increasing the permeability of a developer barrier. While some plate precursors are capable of producing a lithographic image immediately after exposure, the most popular lithographic plate precursors require wet processing because exposure creates a solubility difference or dissolution rate difference in the developer between exposed and unexposed areas of the coating. In positive-working lithographic printing plate precursors, the exposed areas of the coating dissolve in the developer, while the unexposed areas remain resistant to the developer. In negative-working lithographic printing plate precursors, the unexposed areas of the coating dissolve in the developer, while the exposed areas remain resistant to the developer. Most lithographic printing plate precursors comprise a hydrophobic coating on a hydrophilic support, such that areas remaining resistant to the developer define the ink receptive, and hence printing, areas of the plate, while the hydrophilic support is revealed in the non-printing areas by dissolution of the coating in the developer.

[0004] Photopolymer printing plates rely on a working mechanism whereby a coating, typically comprising a free radical polymerizable compound, hardens upon exposure. "Hardening" refers to the coating becoming insoluble or non-dispersible in a developer solution and can be achieved by polymerizing and / or crosslinking the photosensitive coating upon exposure to light and / or heat. Photopolymer plate precursors can be sensitive to blue, green, or red light (i.e., wavelengths in the range of 450 to 750 nm), violet light (i.e., wavelengths in the range of 300 to 450 nm), or infrared light (i.e., wavelengths in the range of 750 to 1500 nm). The exposure step can optionally be followed by a heating step to enhance or accelerate the polymerization and / or crosslinking reaction.

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

[0006] The classic workflow for photopolymer printing plates involves first exposing the photopolymer printing plate precursor in a UV or infrared platesetter, followed by an optional preheating step, a washing step for the protective overcoat, an alkaline development step, and a rinsing and gumming step. However, there is significant progress in simplifying the workflow, where the preheating and / or washing steps are eliminated and the processing and gumming steps are performed in a single step, or processing is performed with a neutral gum followed by gumming in a second step. Alternatively, on-press processing has become popular, where the plate is mounted on a printing press and the coating is developed through interaction with fountain solution and / or ink supplied to the plate during a press run. During the first press run, the non-image areas are removed from the support, thereby defining the non-printing area of the plate. These processing methods are environmentally friendly and highly sought after by customers as "chemical-free processing methods."

[0007] In particular, printing plates designed for on-machine processing require lithographic coatings that dissolve or disperse sufficiently on the press to achieve good removal (complete removal of the coating in non-printing areas of the image). Furthermore, in addition to the removal behavior, the press life of such printing plates should also be optimized. Both press life and removal performance are determined by the interaction between the coating and the substrate: optimal press life requires sufficient adhesion between the substrate and the coating in the image area, while good removal requires minimal interaction of the coating with the substrate in the non-image area during processing. Therefore, maximizing removal performance can lead to reduced image adhesion and, therefore, reduced press life.

[0008] Therefore, compounds for improving the adhesion between the photopolymer coating and the support are often added to printing plate precursors, as disclosed in EP 851 299, EP 1 091 251, EP 1 495 866, EP 1 500 498 and EP 1 520 694, in order to increase the resistance of the areas exposed during the processing steps and to improve the durability of the printing plate during the printing process. Typically, these compounds have ethylenically unsaturated bonds and functional groups capable of adsorbing on the surface of the support and may be present in the photopolymerizable layer or in an intermediate layer between the support and the photopolymerizable layer.

[0009] US 2010 / 0248140 discloses a lithographic printing plate precursor comprising an image-recording layer containing an infrared absorber, a radical polymerization initiator, a radical polymerizable monomer, a compound having two or more mercapto-containing groups per molecule, and polymer particles containing polyoxyalkylene segments.

[0010] Although many attempts have been made in the art to provide high performance photopolymer printing plates, there remains a need to improve lithographic properties, such as print durability during printing of such printing plates. Summary of the Invention

[0011] It is therefore an object of the present invention to provide a negative-working printing plate precursor characterized by both adequate removal behavior and high run length. It is also important that the precursor exhibits improved shelf life stability, i.e. excellent removal and no toning when the precursor is stored under harsh conditions, such as high temperature and high relative humidity, prior to imaging and processing.

[0012] This object is achieved by the printing plate precursor defined in the present application and the preferred embodiments defined in the present application. The printing plate precursor of the present invention is particularly characterized in that it contains a coating comprising a compound containing at least one thiol group and at least one group capable of adhering to a substrate.

[0013] The inventors have surprisingly discovered that the compounds used in the present invention, which contain at least one thiol group and at least one group capable of adhering to substrates, exhibit highly improved removal behavior combined with excellent resistance to the imaged areas on the printing press. Insufficient removal means that, after processing, the non-image areas are not completely removed from the support, or that the compounds remaining in the non-image areas of the support are too hydrophobic, resulting in a reduction in the hydrophilic properties of the support surface. Insufficient removal can lead to toning on the printing press, i.e., an undesirable tendency for ink acceptance to increase in the non-image areas of the printed product.

[0014] Compounds used in the present invention that contain at least one thiol group and at least one group capable of adhering to a substrate are also referred to herein as "adhesion-promoting compounds."

[0015] Development is preferably performed by treating the precursor with a gum solution, but 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.

[0016] Another object of the present invention is to provide a method for manufacturing a lithographic printing plate, the method comprising the steps of:

[0017] - exposing the printing plate precursor as defined above comprising the coating to heat and / or light radiation in an image-wise manner, thereby forming a lithographic image consisting of image areas and non-image areas, and thereby inducing a color change in the image areas;

[0018] - developing the exposed precursor.

[0019] Other 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. Specific embodiments of the present invention are also defined in this application. DETAILED DESCRIPTION

[0020] Lithographic printing plate precursors

[0021] The lithographic printing plate precursor according to the 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 provided with a hydrophilic layer. The hydrophobic areas are defined by the coating that hardens upon exposure (optionally followed by a heating step). Areas having hydrophilic properties are those that have a higher affinity for aqueous solutions than for (oleophilic) inks; areas having hydrophobic properties are those that have a higher affinity for (oleophilic) inks than for aqueous solutions.

[0022] "Hardening" means that the coating becomes insoluble or non-dispersible in the developer solution and can be achieved by polymerization and / or crosslinking of the photosensitive 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 "preheating"), the printing plate precursor is preferably heated at a temperature of about 80° C. to 150° C. and preferably during a dwell time of about 5 seconds to 1 minute.

[0023] The coating comprises at least one layer comprising a photopolymerizable composition, also referred to as a "photopolymerizable layer". A protective overcoat layer may be provided on top of the photopolymerizable layer. The coating may further comprise other layers, such as an intermediate layer between the support and the photopolymerizable layer and / or between the optional top layer and the photopolymerizable layer, an adhesion-improving layer, a hydrophilic layer and / or other layers.

[0024] The coating thickness of the photopolymerizable layer is preferably in the range of 0.1 to 5.0 g / m 2 between 0.3 and 3.0 g / m 2 between 0.4 and 1.5 g / m 2 between.

[0025] The printing plate of the present invention is characterized in that it can be exposed at low energy densities, i.e. below 190 mJ / m 2 ; preferably 70 to 190 mJ / m 2 More preferably, between 75 and 150 mJ / m 2 and most preferably between 80 and 120 mJ / m 2 between.

[0026] Photopolymerizable layer

[0027] Adhesion-promoting compounds

[0028] The adhesion promoting compound includes at least one thiol group. The adhesion promoting compound preferably includes at least two thiol groups, more preferably three or four thiol groups. The thiol group of the adhesion promoting compound can react with the monomer containing ethylenically unsaturated double bonds present in the coating (such as acrylate groups). This reaction is called a thiol-ene reaction. The adhesion promoting compound further includes at least one group that can adhere to the substrate, preferably at least two groups that can adhere to the substrate. It is believed that the combination of these two reactions (i.e., the reaction with the monomer containing ethylenically unsaturated double bonds, and adhesion to the substrate) can cause the run length of the printing plate comprising the adhesion promoting compound to be improved.

[0029] The group capable of adhering to the substrate is preferably selected from a phosphate group or a phosphonate group; most preferably a phosphonate group. The adhesion promoter is a compound having at least one, preferably at least two, and most preferably at least three, phosphate groups, and further having at least one, preferably two to four, thiol groups. In a preferred embodiment, the adhesion promoter comprises two or three thiol groups and one or two phosphate groups.

[0030] The adhesion promoting compound is preferably represented by formula I:

[0031]

[0032] in

[0033] m and p independently represent 1, 2 or 3;

[0034] Y represents a z-valent nucleus having 1 to 12 atoms;

[0035] z is the sum of m and p, and z is 2, 3, 4, or 5.

[0036] X represents a phosphate group or a phosphonate group; and

[0037] L1, L2 and L3 each independently represent a linking group.

[0038] Preferably, the linking groups L1, L2 and L3 each independently represent an optionally substituted straight or branched C1-C 12 -alkanediyl, more preferably C2-C 12 -alkanediyl, most preferably C3-C 12 -alkanediyl, preferably interrupted by one or more oxygen atoms and / or one or more carboxyl groups. Optional substituents on the straight-chain or branched alkanediyl are, for example, alkyl groups, such as methyl or ethyl or hydroxyl groups and / or combinations thereof.

[0039] The linking group L3 preferably includes -(O-CH2-CH2) O -, wherein o is an integer greater than 0, preferably an integer from 1 to 30, most preferably an integer from 1 to 15; and the linking group L3 may further include

[0040] –(CH2) x -、-(CH2) x -(C=O)-O-(CH2) y 、-(CH2) x -(C=O)-(CH2) y -CH(CH3)-(CH2) x -(C=O)-, -(CH2) x -CH(CH3)-(C=O)-, -CH2-CH2-CH(CH3)-(C=O)-, -CH2-CH2-CH2-CH(CH3)-(C=O)-, -CH2-(C=O)-CH2-CH2-, -CH2-(C=O)-CH(CH3)-CH2-, -CH2-(C=O)-CH(CH3)-CH2-, -CH2-(C=O)-CH(CH3)-CH2-; and / or combinations thereof, wherein x and y are independently integers greater than 0.

[0041] The linking groups L1 and L2 are preferably each independently selected from -CH2-, -CH2-CH2-, -CH2-CH2-O-CH2-CH2-, -CH2-CH2-O-CH2-CH2-O-CH2-CH2-, -CH2-CH2-(C=O)-O-CH2-, -CH2-CH2-(C=O)-O-CH(CH3)-, -CH2-CH2-(C=O)-O-CH2-CH2-, -CH2-CH2-(C=O)-O-CH2-CH(CH3)-, -CH2-CH2-(C=O)-O-CH2-CH2-, -CH2-CH2-(C=O)-O-CH2-CH(CH3)-, -CH(CH3)-CH2-(C=O)-O-CH2-, -CH(CH3)-CH2-(C=O)-O-CH(CH3)-, -CH(CH3)-CH2-(C=O)-O-CH2-CH2-, -CH2-CH(CH3)-(C=O)-O-CH2-CH(CH3)-, -CH2-CH(CH3)-(C=O)-O-CH2-CH2-, -CH2-CH(CH3)-(C=O)-O-CH2-CH2 -O-CH2-CH2-, -CH2-CH(CH3)-(C=O)-O-CH2-CH2-O-CH2-CH2-O-CH2-CH2-, and -CH2-CH(CH3)-(C=O)-O-CH2-CH2-O-CH2-CH2-O-CH2-CH2-O-CH2-CH2-.

[0042] The z-valent core Y preferably has a small size of not more than 500 g / mol or even less than 300 g / mol and preferably contains no further atoms than C, N, O or H. In a preferred embodiment, the z-valent core Y represents a carbon atom optionally substituted by a methyl or ethyl group, or an isocyanurate group.

[0043] The adhesion promoting compound preferably has a molecular weight of at least 400 g / mol and not more than 5,000 g / mol and is preferably present in an amount of 1 to 15 wt % based on the total weight of the dry coating. More preferably, the adhesion promoting compound is present in an amount of 15 to 200 mg / m 2 More preferably, 20 to 150 mg / m 2 and most preferably 25 to 75 mg / m 2 An amount between 1% and 2% is present in the coating.

[0044] Particularly preferred adhesion-promoting compounds are given below:

[0045]

[0046]

[0047]

[0048]

[0049] wherein n is an integer greater than 0, preferably an integer between 1 and 30, and most preferably an integer between 1 and 15.

[0050] The adhesion promoting compound is preferably synthesized using a multifunctional thiol and a polymerizable compound containing a phosphate group, such as Sipomer from SOLVAY. TM PAM100. Thiol groups can participate in a reaction known as a thiol-ene reaction, which is a reaction between a thiol and an ethylenically unsaturated double bond (such as an acrylate group). Preferred multifunctional thiols contain 2, 3, or 4 thiol groups. The multifunctional thiol is mixed with a polymerizable compound having phosphate and / or phosphonate groups in a specific molar ratio to produce a preferred adhesion-promoting compound having 1 or 2 phosphate groups and 1 to 3 thiol groups.

[0051] The synthesis of adhesion promoting compounds is preferably carried out via a free radical pathway, wherein free radicals are formed under heat or light (UV) stimulation. This process can be carried out in the absence of a catalyst or in the presence of a catalyst that is a free radical generator. Different catalysts can be used depending on the stimulus (heat or light). The reaction can also be carried out via a nucleophilic pathway, wherein a base or nucleophile is used as a catalyst.

[0052] Suitable catalysts for thermal initiation include AIBN, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexanecarbonitrile), t-amyl peroxybenzoate, 4,4'-azobis(4-cyanovaleric acid), benzoyl peroxide, 2,2-bis(t-butylperoxy)butane, 1,1-bis(t-butylperoxy)cyclohexane, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, 2,5 -Bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, bis(1-(tert-butylperoxy)-1-methylethyl)benzene, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butyl hydroperoxide, tert-butyl peracetate, tert-butyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, cumene hydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroyl peroxide, 2,4-pentanedione peroxide, peracetic acid, and potassium persulfate.

[0053] Suitable catalysts for photoinitiation include Norrish Type I and Type II photoinitiators. Type I photoinitiators include hydroxyacetophenones, alkylaminoacetophenones, benzyl ketones and dialkoxyacetophenones, benzoin ethers, phosphine oxides, BCIM and HABI, etc. Type II photoinitiators include optionally substituted benzophenones, thioxanthones, anthraquinones, benzoylformates, and camphorquinone. Blends of photoinitiators can also be used, as well as polymeric photoinitiators.

[0054] Suitable polymerizable compounds containing at least one phosphate group and / or phosphonate group are, for example:

[0055]

[0056] Suitable multifunctional thiols may be selected from the following list:

[0057]

[0058] n represents an integer greater than 0, preferably an integer between 1 and 30, and most preferably an integer between 1 and 15.

[0059]

[0060]

[0061]

[0062]

[0063] Without being limited thereto, specific examples of the adhesion promoting compounds according to the present invention are given below:

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] In the above structure, n represents an integer greater than 0, preferably an integer between 1 and 30, and most preferably an integer between 1 and 15.

[0073] Multifunctional thiols can be synthesized via thiol-ene reactions using excess thiols, which is also described in US 8,513,339. Thiols can also be introduced into molecules by reacting amines with cyclic thiolactones, by reacting amines with 2-iminothiolane (Traut's reagent), by nucleophilic ring opening of ethylene sulfide, by reacting cyclic dithiocarbonates with amines, and the like.

[0074] Polyfunctional thiols having secondary thiol groups are particularly preferred due to their better stability to oxidation.

[0075] The adhesion promoting compound according to the invention may be present in the photopolymerizable layer, and / or in the optional top layer, and / or in any other optional layer; however, the adhesion promoting compound according to the invention is most preferably present in the photopolymerizable layer.

[0076] Photopolymerizable compounds

[0077] The photopolymerizable layer comprises at least one polymerizable compound, a photoinitiator and optionally a binder. The coating thickness of the photopolymerizable layer is preferably in the range of 0.2 to 5.0 g / m 2 between 0.4 and 3.0 g / m 2 between 0.6 and 1.5 g / m 2 The range between.

[0078] According to a preferred embodiment of the present invention, the polymerizable compound is a polymerizable monomer or oligomer containing at least one terminal ethylenically unsaturated group, hereinafter also referred to as a "free radical polymerizable monomer". Polymerization involves linking together free radical polymerizable monomers. Suitable free radical polymerizable monomers include, for example, multifunctional (meth)acrylate monomers (such as (meth)acrylates of ethylene glycol, trimethylolpropane, pentaerythritol, ethylene glycol, ethoxylated trimethylolpropane, urethane (meth)acrylates) and oligoamine di(meth)acrylates. In addition to the (meth)acrylate group, the (meth)acrylate monomer may also have other ethylenically unsaturated groups or epoxide groups. The (meth)acrylate monomer may also contain acidic (such as carboxylic acid or phosphoric acid) or basic (such as amine) functional groups.

[0079] Suitable free radical polymerizable monomers are disclosed in

[0042] and

[0050] of EP 2 916 171 and incorporated herein by reference.

[0080] initiator

[0081] According to the present invention, any free radical initiator capable of generating free radicals upon exposure, either directly 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, compounds containing carbon-halogen bonds (such as [1,3,5] triazines with trihalomethyl groups), organic peroxides, aromatic ketones, thio compounds, azo polymerization initiators, azides, ketoxime esters, hexaarylbisimidazoles, metallocenes, active ester compounds, borate esters (salts), and quinone diazides. Among these, onium salts, especially iodonium and / or sulfonium salts, are preferred in view of storage stability.

[0082] More specific suitable free radical initiators include, for example, derivatives of acetophenone (such as 2,2-dimethoxy-2-phenylacetophenone and 2-methyl-1-[4-(methylthio)phenyl-2-morpholinopropan-1-one); benzophenone; benzil; ketocoumarins (such as 3-benzoyl-7-methoxycoumarin and 7-methoxycoumarin); xanthone; thioxanthone; benzoin or alkyl-substituted anthraquinone; onium salts (such as diaryl iodinium hexafluoroantimonate, diaryl iodinium trifluoromethanesulfonate, (4-(2-hydroxytetradecyloxy)-phenyl)phenyl iodinium hexafluoroantimonate, triarylsulfonium hexafluorophosphate); , triarylsulfonium p-toluenesulfonate, (3-phenylpropan-2-onyl)triarylphosphonium hexafluoroantimonate, and N-ethoxy(2-methyl)pyridinium hexafluorophosphate, as well as onium salts as described in U.S. Patent Nos. 5,955,238, 6,037,098, and 5,629,354); borates (such as tetrabutylammonium triphenyl(n-butyl)borate, tetraethylammonium triphenyl(n-butyl)borate, diphenyliodonium tetraphenylborate, (4-tert-butyl-phenyl)-(4-methoxy-phenyl)iodonium tetraphenylborate, phenyl-(4-tert-butyl-phenyl)iodonium tetraphenylborate, tetraphenyl phenyl-(4-isopropylphenyl-phenyl)iodonium tetraphenylboronate, phenyl-(3-isopropylphenyl-phenyl)iodonium tetraphenylboronate and / or mixtures thereof; diphenyliodonium tetraphenylboronate (wherein the phenyl group of the iodonium salt is substituted with a group comprising at least six carbon atoms) and triphenylsulfonium triphenyl(n-butyl)borate and borates as described in U.S. Patent Nos. 6,232,038 and 6,218,076); haloalkyl-substituted s-triazines (such as 2,4-bis(trichloromethyl)-6-(p-methoxy-phenylphenyl)-s-triazine, 2,4-bis(trichloromethyl)-6-(4

[0014] The preferred free radical initiators include bis(etha.9-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium salts. Onium salts, borates, and s-triazines are preferred free radical initiators. Diaryliodonium salts and triarylsulfonium salts are preferred onium salts. Triarylalkylborates are preferred borates. Trichloromethyl-substituted s-triazines are preferred s-triazines. These initiators may have an optional substituent and may be used alone or in combination.

[0083] Particularly preferred initiators are optionally substituted trihaloalkylsulfones, wherein the halogen independently represents bromine, chlorine, or iodine, and the sulfone is a compound comprising a sulfonyl functional group attached to two carbon atoms. Tribromomethylphenylsulfone is the most preferred initiator. More details about this initiator can be found in patent application WO2019 / 179995, paragraphs

[0029] to

[0040] .

[0084] The amount of initiator is generally in the range of 0.05 to 30 wt%, preferably 0.1 to 15 wt%, most preferably 0.2 to 10 wt%, relative to the total dry weight of the components in the photopolymerizable composition.

[0085] The photopolymerizable layer may further comprise a coinitiator. Typically, the coinitiator is used in combination with a free radical initiator. Suitable coinitiators for photopolymer coatings are disclosed in US 6,410,205, US 5,049,479, EP 1 079 276, EP 1 369 232, EP 1 369 231, EP 1 341 040, US 2003 / 0124460, EP 1 241 002, EP 1 288 720, and in the reference book including the cited literature: Chemistry & Technology UV & EB formulation for coatings, inks & paints – Volume 3 – Photoinitiators for Free Radical and Cationic Polymerisation, KK Dietliker – edited by PKT Oldring – 1991 – ISBN 0 947798161. Specific coinitiators as described in EP 107 792 may be present in the photopolymerizable layer to further increase the sensitivity. Preferred coinitiators are disclosed in EP 2 916 171

[0051] and incorporated herein by reference.

[0086] By including a fluorescent whitening agent as a sensitizer in the coating, very high sensitivity can be achieved. Suitable examples of fluorescent whitening agents as sensitizers are described in WO 2005 / 109103, page 24, lines 20 to page 39. Useful sensitizers can 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.

[0087] Specific coinitiators as described in EP 107 792 may be present in the photopolymerizable layer to further increase the sensitivity. Preferred coinitiators are sulfur compounds, especially 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 ... 2,4-triazole, 4-n-decyl-3,5-dimercapto-1,2,4-triazole, 5-phenyl-2-mercapto-1,3,4-oxadiazole, 5-methylthio-1,3,4-thiadiazoline-2-thione, 5-hexylthio-1,3,4-thiadiazoline-2-thione, mercaptophenyltetrazolyl, pentaerythritol mercaptopropionate, butyric acid-3-mercapto-neopentane tetraester, pentaerythritol tetrakis(thioglycolate). Other preferred coinitiators are polythiols as disclosed in WO 2006 / 048443 and WO 2006 / 048445. These polythiols can be used in combination with the above-mentioned thiols (e.g., 2-mercaptobenzothiazole).

[0088] Adhesives

[0089] The photopolymerizable layer preferably comprises a binder. The binder can be selected from a wide range of organic polymers. Combinations of different binders can also be used. Useful binders are described, for example, in EP 1 043 627, paragraph

[0013] , WO 2005 / 111727, page 17, lines 21 to page 19, line 30, and WO 2005 / 029187, page 16, lines 26 to page 18, line 11.

[0090] The photopolymerizable layer may include discrete particles, i.e., particulate polymers, including homopolymers or copolymers prepared from monomers such as ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, vinyl carbazole, acrylates, or methacrylates, or mixtures thereof. Preferably, the discrete particles are particles suspended in the polymerizable composition. The presence of the discrete particles tends to improve the developability of the unexposed areas.

[0091] The thermoreactive polymer fine particles include thermoreactive groups such as an ethylenically unsaturated group, a cationically polymerizable group, an isocyanate group, an epoxy group, a vinyloxy group, and a functional group having an active hydrogen atom, a carboxyl group, a hydroxyl group, an amino group, or an acid anhydride.

[0092] The average particle size of the polymer fine particles is preferably from 0.01 mm to 3.0 mm. As disclosed in EP 1 132 200, EP 1 724 112 and US 2004 / 106060, particulate polymers in the form of microcapsules, microgels or reactive microgels are suitable.

[0093] Specific examples of binders are described in US 6,899,994, US 2004 / 0260050, US 2005 / 0003285, US 2005 / 0170286, US 2005 / 0123853 and EP 2 916 171 at

[0029] ,

[0030] and

[0031] . Other suitable binders include polyfunctional thiols having 6 to 10 functional groups as a core (central backbone) and polymer chains connected to the core via sulfide bonds, as described in EP 2 471 655, EP 2 492 748 and EP 2 660 068. In addition, the imageable layer may optionally contain one or more co-binders. Typical co-binders are water-soluble or water-dispersible polymers, for example, cellulose derivatives, polyvinyl alcohol, polyacrylic acid poly(meth)acrylic acid, polyvinyl pyrrolidone, polylactic acid, polyvinyl phosphonic acid, synthetic copolymers, such as copolymers of alkoxy polyethylene glycol (meth)acrylates. Specific examples of co-binders are described in US 2004 / 0260050, US 2005 / 0003285 and US 2005 / 0123853.

[0094] Other ingredients

[0095] The photopolymerizable layer may also contain particles that increase the resistance of the coating to manual or mechanical damage. The particles may be inorganic particles, organic particles or fillers, as described, for example, in US 7,108,956. More details of suitable spacer particles are described in EP 2916 171

[0053] to

[0056] and are incorporated herein by reference.

[0096] The photopolymerizable layer may also comprise an inhibitor. Specific inhibitors for photopolymer coatings are disclosed in US 6,410,205, EP 1 288 720 and EP 1 749 240.

[0097] The photopolymerizable layer may comprise a leuco dye which forms a colored compound upon exposure to light and / or heat, preferably infrared light, thereby forming a printed image. More information on suitable leuco dyes can be found in the unpublished application EP19153178

[0069] to

[0085] .

[0098] The photopolymerizable layer may further comprise at least one borate compound. A borate compound preferably refers to a compound comprising a borate anion and preferably a cation as a counterion. The borate anion may be derived from the counterion of a photoinitiator, such as a diphenyl iodonium photoinitiator, and / or the counterion of the aforementioned infrared absorbing compounds or any other salt, such as sodium tetraphenylborate.

[0099] Preferably, the borate anion is a tetrahedral boron anion and can be represented by the following formula A:

[0100]

[0101] where R b 1 、R b 2 、R b 3 and R b 4 are independently optionally substituted aliphatic hydrocarbon, optionally substituted aryl or heteroaryl; or, R b 1 、R b 2 、R b 3 and R b 4 Two or more of may be linked together to form a heterocyclic ring with the boron atom, such a ring may include up to seven carbon, nitrogen, oxygen and / or nitrogen atoms. b 1 、R b 2 、R b 3 and R b 4 R is independently an optionally substituted aryl or heteroaryl. b 1 、R b 2 、R b 3 and R b 4 is independently an optionally substituted aryl.Most preferably, the borate compound comprises at least one optionally substituted phenyl group, more preferably at least two optionally substituted phenyl groups, even more preferably at least three optionally substituted phenyl groups, and most preferably four optionally substituted phenyl groups.

[0102] M + is an alkali metal cation, such as Li + 、Na + , K + or an optionally substituted onium ion. Examples of the optionally substituted onium ion include pyridinium, ammonium, iodonium or sulfonium.

[0103] Examples of the pyridinium ion 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, N-alkoxycarbonylmethyl-3-pyridinium groups, Methyl-4-pyridinium, N-alkyl-3,5-dimethyl-4-pyridinium, N-alkyl-3-pyridinium or N-alkyl-4-pyridinium, particularly preferably N-methyl-3-pyridinium, N-octyl-3-pyridinium, N-methyl-4-pyridinium or N-octyl-4-pyridinium, most preferably N-octyl-3-pyridinium or N-octyl-4-pyridinium.

[0104] The optionally substituted onium ion is preferably an ammonium ion represented by formula B:

[0105]

[0106] in

[0107] R n 1 、R n 2 and R n 3 is independently an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl or heteroaryl group, or a halogen atom.

[0108] The optionally substituted onium 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 groups), and asymmetric diphenyliodonium salts. The phenyl group of the iodonium ion is preferably substituted with a group containing at least six carbon atoms.

[0109] Specific examples of the borate compound including an iodine ion include 4-hexyloxyphenyl-2,4-diethoxyphenyliodine tetrafluoroborate, 4-octyloxyphenylphenyliodine tetraphenylborate, [4-[(2-hydroxytetradecyl)-oxy]phenyl]phenyliodine tetraphenylborate, bis(4-tert-butylphenyl)iodine tetraphenylborate, 4-methylphenyl-4'-hexylphenyliodine tetraphenylborate to 4-methylphenyl-4'-cyclohexylphenyliodine tetraphenylborate, bis(tert-butylphenyl)iodine tetraphenylborate, 4-hexylphenyl-phenyliodine tetraphenylborate, n-butyltriphenyl 4-Methylphenyl-4'-cyclohexylphenyl iodine borate, 4-cyclohexylphenyl-phenyl iodine tetraphenyl borate, 2-5-methyl-4-tert-butylphenyl-4'-methylphenyl iodine tetraphenyl borate, 4-methylphenyl-4'-pentylphenyl iodine tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 4-methoxyphenyl-4'-cyclohexylphenyl iodine tetrakis(pentafluorophenyl)borate, 4-methylphenyl-4'-dodecylphenyl iodine tetrakis(4-fluorophenyl)borate, bis(dodecylphenyl) iodine tetrakis(pentafluorophenyl)borate, and bis(4-tert-butylphenyl) iodine tetrakis(imidazolyl)borate. Preferred compounds include bis(4-tert-butylphenyl)iodinium tetraphenylborate, 4-methylphenyl-4'-hexylphenyliodinium tetraphenylborate, 2-methyl-4-tert-butylphenyl-4'-methylphenyliodinium tetraphenylborate, and 4-methylphenyl-4'-cyclohexylphenyliodinium tetraphenylborate.

[0110] The borate compound may be present in an amount between 0.05 and 30% by weight, more preferably between 0.1 and 25% by weight, and most preferably between 0.5 and 15% by weight relative to the components of the photopolymerizable layer.

[0111] Various surfactants may be added to the photopolymerizable layer to allow or enhance the developability of the precursor, particularly with a gum solution. Both polymeric and small molecule surfactants are preferred, such as nonionic surfactants. Further details are described in EP 2 916 171

[0059] , which is incorporated herein by reference.

[0112] Top floor

[0113] The coating may include a topcoat or protective outer coating, which may serve as an oxygen barrier. Low molecular weight substances present in the air may deteriorate or even inhibit image formation, and therefore a topcoat is applied to the coating. The topcoat should preferably be easily removable during development, adhere well to the photopolymerizable layer or optional other layers of the coating, and should preferably not inhibit light transmission during exposure. The topcoat is preferably provided on top of the photopolymerizable layer.

[0114] The optional top layer may further comprise a binder. A preferred binder for the top layer is polyvinyl alcohol. The degree of hydrolysis of the polyvinyl alcohol is preferably between 74 mol% and 99 mol%, more preferably between 80% and 98%. The weight-average molecular weight of the polyvinyl alcohol can be measured by the viscosity of a 4 wt% aqueous solution at 20°C, as defined in DIN 53 015. This viscosity value is preferably between 2 and 26, more preferably between 2 and 15, and most preferably between 2 and 10.

[0115] The optional top layer may comprise a halogenated polymer, preferably a hydrophobic polymer, i.e., one that is insoluble or non-swellable in water at approximately neutral pH. Such a 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 range from 30% to 96% by weight, more preferably from 40% to 90% by weight, and most preferably from 50% to 85% by weight. The halogenated binder preferably comprises from 60% to 95% by weight of monomer units derived from vinylidene monomers, such as vinylidene fluoride, vinylidene chloride, vinylidene bromide, and / or vinylidene iodide.

[0116] The optional top layer may optionally contain other ingredients, such as inorganic or organic acids; matting agents; surfactants, such as anionic surfactants (e.g. sodium alkyl sulfates or sodium alkyl sulfonates), amphoteric surfactants (e.g. alkylaminocarboxylates and alkylaminodicarboxylates), nonionic surfactants (e.g. polyoxyethylene alkylphenyl ethers, (co)polymers containing siloxane and / or perfluoroalkyl units and / or oligo(alkylene oxide) units); fillers; (organic) waxes; alkoxylated alkylenediamines, such as disclosed in EP 1 085 380 (paragraphs

[0021] and

[0022] ); glycerol; inorganic particles; pigments or wetting agents, such as disclosed in EP 2 916 171 and incorporated herein by reference. The optional top layer may further contain an infrared absorbing compound, which is capable of forming a colored compound upon exposure to infrared light and / or heat—thus forming a printed image. More information on such infrared absorbing dyes can be retrieved in the unpublished application EP 20181812

[0055] to

[0072] .

[0117] The optional top layer may have a coating thickness of 0.10 to 1.75 g / m 2 between 0.20 and 1.3 g / m 2 between 0.25 and 1.0 g / m 2 and most preferably between 0.30 and 0.80 g / m 2 Preferably, the optional top layer has a g / m 2and comprises polyvinyl alcohol having a degree of hydrolysis ranging between 74 mol % and 99 mol % and a viscosity value ranging between 2 and 26 mPas as defined above.

[0118] The hydrophilic polymer in the protective overcoat layer may lead to a problematic increase in the viscosity of the printing chemicals (e.g., fountain solution and / or developer solution). Therefore, the coating weight of the hydrophilic polymer and / or the thickness of the protective overcoat layer should preferably not be too high, e.g., above the ranges given above.

[0119] definition

[0120] The aliphatic hydrocarbon group preferably represents an alkyl, cycloalkyl, alkenyl, cycloalkenyl or alkynyl group; suitable groups thereof are described below. The aromatic hydrocarbon group preferably represents a hetero(aryl) group; suitable hetero(aryl) groups (i.e. suitable aryl or heteroaryl groups) are described below.

[0121] In this document, the term "alkyl" refers to all possible variations for each number of carbon atoms in the alkyl group, i.e., methyl, ethyl; for 3 carbon atoms: n-propyl and isopropyl; for 4 carbon atoms: n-butyl, isobutyl and tert-butyl; for 5 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 isohexyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl and 2-methylbutyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and methylcyclohexyl. Preferably, the alkyl group is a C1 to C6 alkyl group.

[0122] Suitable alkenyl groups are preferably C2 to C6-alkenyl groups, for example ethenyl, n-propenyl, n-butenyl, n-pentenyl, n-hexenyl, isopropenyl, isobutenyl, isopentenyl, neopentenyl, 1-methylbutenyl, isohexenyl, cyclopentenyl, cyclohexenyl and methylcyclohexenyl.

[0123] Suitable alkynyl is preferably C2 to C6-alkynyl, suitable aralkyl is preferably phenyl or naphthyl including one, two, three or more C1 to C6-alkyl groups, suitable alkaryl is preferably C1 to C6-alkyl including aryl, aryl is preferably phenyl or naphthyl.

[0124] The cyclic group or cyclic structure includes at least one ring structure and may be a monocyclic or polycyclic group, where a polycyclic group means one or more rings are fused together.

[0125] The example of suitable aryl can be by for example optionally substituted phenyl, benzyl, tolyl or o-, m- or p-xylyl, optionally substituted naphthyl, anthracenyl, phenanthrenyl and / or its combination representative.Heteroaryl is preferably a monocyclic or polycyclic aromatic ring comprising carbon atoms and one or more heteroatoms in the ring structure, preferably 1 to 4 heteroatoms independently selected from nitrogen, oxygen, selenium and sulphur.Its preferred examples include optionally substituted furyl, pyridyl, pyrimidyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, thienyl (thienyl), tetrazolyl, thiazolyl, (1,2,3) triazolyl, (1,2,4) triazolyl, thiadiazolyl, thienyl (thiofenyl) and / or its combination.

[0126] The cyclic group or cyclic structure includes at least one ring structure and may be a monocyclic or polycyclic group, where a polycyclic group means one or more rings are fused together.

[0127] "Halogen" is selected from fluorine, chlorine, bromine or iodine.

[0128] The term "substituted," for example, in a substituted alkyl group, means that the alkyl group may be substituted with atoms other than the atoms normally present in such a group (i.e., carbon and hydrogen). For example, a substituted alkyl group may include a halogen atom or a thiol group. An unsubstituted alkyl group contains only carbon and hydrogen atoms.

[0129] The optional substituents on the alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aralkyl, alkaryl, aryl and heteroaryl groups are preferably selected from hydroxy, -Cl, -Br, -I, -OH, -SH, -CN, -NO2, alkyl (such as methyl or ethyl), alkoxy (such as methoxy or ethoxy), aryloxy, carboxylic acid groups or alkyl esters thereof, sulfonic acid groups or alkyl esters thereof, phosphonic acid groups or alkyl esters thereof, phosphoric acid groups or esters (such as alkyl esters, for example methyl or ethyl), thioalkyl, thioaryl, thioheteroaryl, -SH, thioether (such as thioalkyl or thioaryl), ketone, aldehyde, sulfoxide, sulfone, sulfonate, sulfonamide, amino, vinyl, alkenyl, alkynyl, cycloalkyl, alkaryl, aralkyl, aryl, heteroaryl or heteroalicyclic groups and / or combinations thereof.

[0130] The term leuco dye refers to a compound that changes from being substantially colorless or light-colored to a colored color, or vice versa, when irradiated with UV light, IR light, and / or heated.

[0131] carrier

[0132] The lithographic printing plate used in the present invention comprises a support having a hydrophilic surface or provided with a hydrophilic layer, also referred to herein as substrate. The support is preferably a grained and anodized aluminum support well known in the art. Suitable supports are disclosed, for example, in EP 1 843 203 (paragraphs

[0066] to

[0075] ). The surface roughness obtained after the graining step is usually expressed as the 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 the present invention preferably has an Ra value between 0.1 μm and 1.4 μm, more preferably between 0.3 μm and 1.0 μm, most preferably between 0.4 μm and 0.9 μm. The lower limit of the Ra value is preferably about 0.1 μm. More details on the preferred Ra values for the surface of the grained and anodized aluminum support are described in EP 1 356 926. By anodizing the aluminum support, an Al2O3 layer is formed, and the anode weight (g / m 2 The Al2O3 formed on the aluminum surface is between 1 and 8 g / m 2 The anode weight is preferably ≥2.0g / m 2 , more preferably ≥2.5g / m 2 , most preferably ≥3.0g / m 2 .

[0133] The granulated and anodized aluminum support may be subjected to a so-called post-anodic treatment, for example, treatment with polyvinylphosphonic acid or a derivative thereof, treatment with polyacrylic acid or a derivative thereof, treatment with potassium fluorozirconate or potassium phosphate, treatment with an alkali metal silicate, or a combination thereof. Treatment of the support edge, as described, for example, in US 2017 / 320351, may be of interest to prevent the appearance of printed edges. Alternatively, the support may be treated with an adhesion-promoting compound, such as those described in

[0010] of EP 1 788 434 and in WO 2013 / 182328. However, for precursors optimized for use without a preheating step, it is preferred to use the granulated and anodized aluminum support without any post-anodic treatment.

[0134] Besides aluminum supports, it is also possible to use plastic supports, for example polyester supports, which are provided with one or more hydrophilic layers, as disclosed, for example, in EP 1 025 992.

[0135] Exposure Steps

[0136] The printing plate precursor is preferably exposed imagewise by means of a laser emitting IR light. The imagewise exposure step is preferably carried out off-machine in a platemaking machine, i.e., an exposure device suitable for imagewise exposure of the precursor with a laser, such as a laser diode emitting at about 830 nm, or an Nd YAG laser emitting at about 1060 nm, or a violet laser emitting at about 400 nm, or a gas laser (e.g., an Ar laser), or using a digitally modulated UV exposure device (using, for example, a digital mirror device), or conventional exposure by contact with a mask. In a preferred embodiment of the invention, the precursor is exposed imagewise by means of a laser emitting IR light or violet light, more preferably by means of a laser emitting IR light.

[0137] Preheating steps

[0138] After the exposure step, the precursor can be preheated in a preheating unit, preferably at a temperature of about 80° C. to 150° C., preferably during a residence time of about 5 seconds to 1 minute. This preheating unit can comprise a heating element, preferably an IR lamp, a UV lamp, heated air or a heated roller. Such a preheating step can be used for printing plate precursors comprising a photopolymerizable composition in order to enhance or accelerate the polymerization and / or crosslinking reaction.

[0139] Development step

[0140] After the exposure step or the preheating step (if present), the printing plate precursor can be processed (developed). Before developing the imaged precursor, a pre-rinsing step can be performed, particularly for negative-working lithographic printing precursors having a protective oxygen barrier or overcoat. This pre-rinsing step can be performed in a separate instrument, or by manually rinsing the imaged precursor with water, or the pre-rinsing step can be performed in a washing unit integrated into the processing machine used to develop the imaged precursor. The washing liquid is preferably water, more preferably tap water. Further details regarding the washing step are described in

[0026] of EP 1 788 434.

[0141] During the development step, the non-exposed areas of the image-recording layer are at least partially removed, while the exposed areas are substantially not removed. The processing liquid (also called developer) is applied to the printing plate, for example by rubbing with an impregnated pad, by dipping, immersing, coating, spin coating, spraying, or pouring onto it. This can be done manually or in an automated processing machine. Treatment with the processing liquid can be combined with mechanical rubbing (for example, by a rotating brush). During the development step, any water-soluble protective layer present is also preferably removed. Development is preferably carried out in an automated processing unit at a temperature between 20 and 40°C.

[0142] In a highly preferred embodiment, the processing steps described above are replaced by on-machine processing, whereby the imaged precursor is mounted on a printing press and processed on-machine by rotating the plate cylinder while feeding fountain solution and / or ink to the precursor coating to remove unexposed areas from the support. In a preferred embodiment, the supply of fountain solution and ink is started simultaneously, or only ink may be supplied during a few revolutions before the fountain solution supply is turned on. In an alternative embodiment, only fountain solution is supplied to the printing plate during startup of the printing press, and the ink supply is also turned on after a few revolutions of the plate cylinder.

[0143] The processing steps can also be performed by combining the above-described embodiments, for example combining development with a processing fluid with on-press development by applying ink and / or fountain solution.

[0144] Processing fluid

[0145] The processing fluid can be an alkaline developer or a solvent-based developer. Suitable alkaline developers are described in US 2005 / 0162505. Alkaline developers are aqueous solutions having a pH of at least 11, more typically at least 12, and preferably between 12 and 14. Alkaline developers typically contain an alkaline agent to achieve a high pH, which can be inorganic or organic. The developer can 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., alkaline gluconates), and thickeners (water-soluble or water-dispersible polyols, such as glycerol or polyethylene glycol).

[0146] The processing liquid is preferably a glue solution, whereby during the development step, the non-exposed areas of the photopolymerizable layer are removed from the support and the printing plate is glued in a single step. Developing with a glue solution has the additional benefit that, due to the residual glue in the non-exposed areas of the printing plate, no additional glueing step is required to protect the support surface in the non-printing areas. As a result, the precursor is processed and glued in a single step, which involves a simpler development apparatus than a development apparatus comprising a developer tank, a rinse section, and a glue section. The glue section may comprise at least one glue unit, or may comprise two or more glue units. These glue units may have a cascade system configuration, i.e., when a glue replenishing solution is added to a second glue unit, or when the glue solution in the second glue unit is used only once, i.e., when the precursor is developed in this second glue unit using only the starting glue solution, preferably by spraying or jetting technology, the glue solution used for the second glue unit and present in the second tank overflows from the second tank to the first tank. More details about such glue development are described in EP1 788 444.

[0147] The gum solution is generally an aqueous liquid containing one or more surface-protective compounds capable of protecting the lithographic image of the printing plate from contamination (e.g., by oxidation, fingerprints, fat, oil, or dust) or damage (e.g., by scratches during handling of the printing plate). Suitable examples of such surface-protective compounds are film-forming hydrophilic polymers or surfactants. The layer remaining on the printing plate after treatment with the gum solution preferably contains from 0.005 to 20 g / m 2 between 0.010 and 10 g / m 2 between 0.020 and 5 g / m 2 Further details on surface-protective compounds in the gum solution can be found in WO 2007 / 057348, page 9, line 3 to page 11, line 6. Since the developed printing plate precursor is developed and gummed in one step, there is no need to after-treat the processed printing plate.

[0148] The glue 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 glue solutions are described, for example, in

[0008] to

[0022] of EP 1 342 568 and WO 2005 / 111727. The glue solution may further comprise an inorganic salt, an anionic surfactant, a wetting agent, a chelating compound, an antiseptic compound, a defoaming compound and / or an ink absorbent and / or a combination thereof. More details about these additional ingredients are described in WO 2007 / 057348, page 11, line 22 to page 14, line 19.

[0149] Drying and baking steps

[0150] After the processing step, the printing plate can be dried in a drying unit. In a preferred embodiment, the printing plate is dried by heating the printing plate in a drying unit, which may comprise at least one heating element selected from IR lamps, UV lamps, heated metal rollers or heated air.

[0151] After drying, the printing plate can optionally be heated in a baking unit. More details about heating in a baking unit can be found in WO 2007 / 057348, page 44, line 26 to page 45, line 20.

[0152] According to the present invention, a method for preparing a negative-working lithographic printing plate is also provided, the method comprising the steps of exposing a printing plate precursor in an image manner and subsequently developing the image-exposed precursor so that the non-exposed areas dissolve in a developer. Development is preferably carried out by treating the precursor with a gum solution, but more preferably by mounting the precursor on a plate cylinder of a lithographic printing press and rotating the plate cylinder while feeding a fountain solution and / or ink to the precursor. Optionally, a heating step is performed after the imaging step to enhance or accelerate polymerization and / or cross-linking reactions. The lithographic printing plate precursor can be prepared by (i) applying the above-mentioned coating on a support, and (ii) drying the precursor. Any coating method can be used to apply one or more coating solutions to the hydrophilic surface of the support. Multilayer coating can be carried out by continuously coating / drying each layer or applying several coating solutions at the same time. In the drying step, the volatile solvent is removed from the coating until the coating is self-supporting and dry to the touch.

[0153] The printing plate thus obtained can be used for conventional so-called wet offset printing, in which ink and an aqueous fountain solution are supplied to the printing plate. Another suitable printing method uses so-called single-fluid inks, without fountain solution. Suitable single-fluid inks are described in US 4,045,232, US 4,981,517 and US 6,140,392. In a most preferred embodiment, the single-fluid ink comprises an ink phase (also called a hydrophobic or oleophilic phase) and a polyol phase, as described in WO 00 / 32705.

[0154] Example

[0155] 1. Materials

[0156] Unless otherwise stated, all materials used in the following examples are readily available from standard sources such as SIGMA-ALDRICH, MERCK, and ACROS ORGANICS.

[0157] The adhesion-promoting compounds according to the invention used in the examples are summarized in Table 1 below.

[0158] Table 1: Adhesion promoting compound of the present invention (APC-0X)

[0159]

[0160]

[0161] 2. Synthesis of Adhesion-Promoting Compounds

[0162] Synthesis of APC-01

[0163] In a 500 mL three-necked flask, 2.067 g of 3,6-dioxa-1,8-octanedithiol was added to 5.453 g of Sipomer TM The mixture was flushed with nitrogen and stirred at room temperature for 15 minutes. The temperature was then raised to 80°C, after which 0.001 g of 2,2'-azobis(2-methylbutyronitrile) was added. The reaction was allowed to proceed at 80°C overnight. Proton NMR analysis showed that the reaction was complete and no more Sipomer was present. TM PAM100 was present. The product was used as is.

[0164] Synthesis of APC-02

[0165] By reacting the precursor X with Sipomer TM PAM100 was reacted at a 1:2 molar ratio to synthesize APC-02 in a similar manner to APC-01.

[0166] Precursor X was prepared as follows:

[0167] A 100 mL flask was charged with 4.98 g of 2,4,6-triallyloxy-1,3,5-triazine. Next, 9.351 g of DL-1,4-dithiothreitol and 0.21 g of BHT were added. The mixture was then heated to 80°C while stirring. 0.037 g of 2,2'-azobis(2-methylbutyronitrile) was added, and the mixture was further stirred at 70°C for 16 hours. The product was used as is.

[0168] Synthesis of APC-03

[0169] APC-03 was synthesized in a similar manner to APC-01 by reacting trimethylolpropane tris(3-mercaptopropionate) with vinylphosphonic acid in a 1:1 molar ratio.

[0170] Synthesis of APC-04

[0171] By making trifunctional thiol CASRN 590678-06-1 (available as Karenz TM MT TPMB obtained from SHOWA DENKO) and Sipomer TM PAM100 was reacted at a 1:2 molar ratio to synthesize APC-04 in a similar manner to APC-01.

[0172] Synthesis of APC-05

[0173] In a 100 mL three-necked flask, 6.185 g of 3,6-dioxa-1,8-octanedithiol was added to a 50 mL MEK solution of 10 g of SIPOMER PAM4000. The mixture was flushed with nitrogen and stirred at room temperature for 15 minutes. 0.65 g of BHT was added. The temperature was then raised to 60°C, after which 0.003 g of 2,2'-azobis(2-methylbutyronitrile) was added. The reaction was allowed to proceed at 75°C overnight. The MEK was then removed under reduced pressure. Proton NMR analysis showed that the reaction was complete and no SIPOMER PAM4000 was present. The product was used as is.

[0174] Synthesis of APC-06

[0175] In a 100 mL three-necked flask, 4.798 g of 3,6-dioxa-1,8-octanedithiol was added to 3,062 g of vinylphosphonic acid. The mixture was flushed with nitrogen and stirred at room temperature for 15 minutes. The temperature was then raised to 80°C, after which 0.001 g of 2,2'-azobis(2-methylbutyronitrile) was added. The reaction was allowed to proceed at 80°C overnight. Proton NMR analysis showed that the reaction was complete and no vinylphosphonic acid was present. The product was used as is.

[0176] Example 1

[0177] Preparation of printing plates PP-01 to PP-08

[0178] Preparation of aluminum support S-01

[0179] The aluminum foil was degreased by spraying it with an aqueous solution containing 26 g / l NaOH at 65°C for 2 seconds and rinsing it with demineralized water for 1.5 seconds. 2 The current density is in the presence of 15g / lHCl, 15g / lSO4 2- ions and 5g / l Al 3+ The foil was electrochemically grained for 10 seconds in an aqueous solution containing 5.5 g / l NaOH at 36°C. The foil was then decontaminated by etching it for 2 seconds with an aqueous solution containing 5.5 g / l NaOH and rinsing with demineralized water for 2 seconds. Subsequently, the foil was electrochemically grained for 10 seconds in an aqueous solution containing 5.5 g / l NaOH at 36°C. The foil was then decontaminated by etching it for 2 seconds with an aqueous solution containing 5.5 g / l NaOH and rinsing with demineralized water for 2 seconds. 2 The foil was anodized during 15 seconds at a current density of 145 g / l of sulfuric acid in an aqueous solution, then washed with demineralized water for 11 seconds and dried at 120° C. for 5 seconds.

[0180] The support thus obtained is characterized by a surface roughness Ra of 0.35-0.4 μm (measured with interferometer NT1100) and a strength of 3.0 g / m 2 The weight of oxides.

[0181] Photopolymerizable layer

[0182] Printing plate precursors PPP-01 to PPP-10 were prepared by coating the above-described support S-01 with the components defined in Table 2, dissolved in a mixture of 34 wt.% MEK, 62 wt.% Dowanol PM (1-methoxy-2-propanol, commercially available from DOWCHEMICAL Company), and 4 wt.% water. The coating solution was applied to a wet coating thickness of 30 μm and then dried in a circulation oven at 120° C. for 1 minute.

[0183] Table 2: Composition of the photosensitive layer

[0184]

[0185]

[0186] 1) FST 510 is the reaction product of 1 mole of 2,2,4-trimethylhexamethylene diisocyanate and 2 moles of hydroxyethyl methacrylate, commercially available from AZ Electronics as an 82 wt% solution in MEK;

[0187] 2) CN 104 is an epoxy acrylate oligomer commercially available from Arkema;

[0188] 3) Initiator-01 is 4-hydroxyphenyl-tribromomethyl sulfone, Initiator-02 is (4-tert-butyl-phenyl)-(4-methoxy-phenyl)-iodonium tetraphenylborate, and Initiator-03 is (4-isopropylphenyl-phenyl)-iodonium tetraphenylborate;

[0189] 4) The infrared absorbing compound is represented by the following structure, wherein the R-group substituent is butyl:

[0190]

[0191] 5) Ruco coat EC4811 is a polyether polyurethane commercially available from Rudolf Chemistry;

[0192] 6) Copolymer of vinyl alcohol, vinyl acetate, vinyl butyral and vinyl acetal was obtained from Sekisui Chemical Co. Ltd.

[0193] 7) Tegoglide 410 is a surfactant commercially available from Evonik Tego Chemie GmbH;

[0194] 8) Dispersion of 15% AEROSIL R972 (commercially available from Degussa) and 5% BYKJET 9152 (commercially available from Altana (BYK CHEMIE GMBH)) in methoxypropanol.

[0195] 9) Disperbyk 162 is commercially available from Altana (BYK Chemie GmbH);

[0196] 10) Sipomer PAM 100 is a phosphonic methacrylate commercially available from Rhodia;

[0197] 11) Copolymer of polyacrylic acid and polyvinylphosphonic acid (70 / 30), commercially available from Rhodia.

[0198] 12) See Table 1;

[0199] Table 3: Adhesion-promoting compounds

[0200]

[0201] Protective outer coating

[0202] On top of the photosensitive layer, an aqueous solution (40 μm) having the composition defined in Table 4 was applied and dried for 2 minutes at 110° C. Printing plate precursors PPP-01 to PPP-10 were obtained (Table 5).

[0203] Table 4: Composition of protective topcoat OC-01

[0204]

[0205] 1) Mowiol 4-88 is a partially hydrolyzed polyvinyl alcohol commercially available from Kuraray;

[0206] 2) polyvinylidene chloride latex, commercially available from Solvay;

[0207] 3) Biocides, commercially available from Bode Chemie GmbH & Co.

[0208] 4) Lutensol A8 is a surfactant commercially available from BASF;

[0209] 5) Viomal is a 20% aqueous dispersion of PV23, commercially available from CLARIANT Benelux NV, with 0.02% biocide;

[0210] 6) IR thermochromic dyes have the following structure:

[0211]

[0212] Table 5: Printing plate precursors PPP-01 to PPP-10

[0213]

[0214] Imaging

[0215] Printing plate precursors PPP-01 to PPP-10 were prepared at 2400 dpi using a high power Creo 40WTE38 thermal platesetter™ (200 lpi Agfa Balanced Screening (ABS)) at 130 mJ / cm 2 Energy density imaging, platesetters are commercially available from Kodak and are equipped with an 830 nm IR laser diode.

[0216] print

[0217] After imaging, printing plate precursors PPP-01 to PPP-10 were mounted on a Heidelberg GTO 52 Dalghren press. Each print run was initiated using K+E Skinnex 800SPEED IK black ink (trademark of BASF Druckfarben GmbH) and 3 wt% Prima FS303 SF (trademark of Agfa Graphics) and 5% isopropyl alcohol in water as a fountain solution. A compressible blanket was used and printing was performed on uncoated offset paper.

[0218] Before the paper is fed, 10 revolutions of printing are performed using only the dampening system, followed by 5 revolutions using only the inking roller. Pages 1 to 250 are visually evaluated to assess image quality.

[0219] Test results

[0220] Image quality

[0221] The printing test results with respect to image quality are summarized in Table 6.

[0222] Table 6: Image quality results

[0223]

[0224]

[0225] *See Table 2;

[0226] **After 250 pages, the image wear was visually assessed as follows:

[0227] A: No image wear,

[0228] B: Some images are worn,

[0229] C: Many images are worn, and

[0230] D: Severe image wear.

[0231] The results in Table 6 show that the image quality of the printing plates of the present invention comprising a thiol-based adhesion promoter is significantly higher than that of the printing plates comprising a comparative adhesion promoter. The image quality differences between the adhesion-promoting compounds are more pronounced at low concentrations: 50 and 25 mg / m 2 Comparative printouts of Sipomer PAM PP-03 and PP-04, including 50mg / m 2 The images of the comparative printing plates PP-10 and PP-11 of Sipomer PAM were completely destroyed, whereas the images of the inventive printing plates PP-07 and PP-08 comprising 50 and 25 mg / m2 of the inventive adhesion promoter, respectively, were not affected.

[0232] Printing durability

[0233] Printing plate precursors PPP-02, PPP-03, PPP-06, and PPP-07 were installed on a Drent Vision printing press. Each print run was initiated using coldest flint Eurostar black CS 40 (a trademark of the Flint Group) and 2.5% by weight of Prima FS404AS (a trademark of Agfa Graphics) and 2.5% isopropyl alcohol in water as a dampening solution. A compressible rubber blanket was used and printing was performed on non-coated offset paper. Approximately 20 print revolutions were performed using both the dampening system and the inking roller before paper was fed. Page runs of 1 to 50,000 were visually evaluated to assess press run length for image strength.

[0234] result

[0235] The results of the printing tests are summarized in Table 7.

[0236] Table 7: Printing run evaluation

[0237]

[0238] *See Table 2;

[0239] **After 50,000 pages, run length was visually evaluated and relatively rated as follows:

[0240] A: Almost no image wear,

[0241] B: Some images are worn,

[0242] C: Many images are worn, and

[0243] D: Severe image wear.

[0244] The results in Table 7 show that the press run of the inventive printing plates PP-06 and PP-07 comprising a thiol-based adhesion promoter is significantly higher than the press run of the comparative printing plates PP-02 and PP-03 comprising a comparative adhesion promoter.

[0245] Example 2

[0246] Preparation of printing plates PP-11 to PP-15

[0247] Photopolymerizable layer

[0248] Photopolymerizable layers PL-11 to PL-15 were produced by coating the above-described support S-01 with the components defined in Table 8, dissolved in a mixture of 34 wt.% MEK, 62 wt.% Dowanol PM (1-methoxy-2-propanol, commercially available from DOWCHEMICAL Company), and 4 wt.% water. The coating solution was applied to a wet coating thickness of 30 μm and then dried in a circulation oven at 120° C. for 1 minute.

[0249] Table 8: Composition of photosensitive layer PL-0X

[0250]

[0251] 1) See Table 2;

[0252] 2) Initiator-02 is (4-methylphenyl)[4-(2-methylpropyl)phenyl]iodonium tetraphenylborate.

[0253] Table 9: Adhesion-promoting compounds

[0254]

[0255]

[0256] *See Table 1

[0257] Protective outer coating

[0258] On top of the photosensitive layer, an aqueous solution (40 μm wet film) having the composition defined in Table 4 above was coated and dried for 2 minutes at 110° C. This gave printing plate precursors PPP-11 to PPP-15 (Table 10).

[0259] Table 10: Printing plate precursors PPP-11 to PPP-15

[0260]

[0261] Imaging

[0262] Printing plate precursors PPP-11 to PPP-15 were prepared at 2400 dpi using a high power Creo 40WTE38 thermal platesetter™ (200 lpi Agfa Balanced Screening (ABS)) at 130 mJ / cm 2 Energy density imaging, platesetters are commercially available from Kodak and are equipped with an 830 nm IR laser diode.

[0263] print

[0264] After imaging, printing plate precursors PPP-11 to PPP-15 were mounted on a Drent Vision printing press. Each print run was initiated using coldest flint Eurostar black CS 40 (a trademark of the Flint Group) and 2.5 wt% Prima FS404AS (a trademark of Agfa Graphics) with 2.5% isopropyl alcohol in water as a dampening solution. A compressible rubber blanket was used and printing was performed on uncoated offset paper. Approximately 20 print revolutions were performed using both the dampening system and the inking roller before paper was fed. Visual evaluation of print runs after 30,000 prints was performed to assess press run length in terms of image strength.

[0265] Printing durability results

[0266] The results of the printing tests are summarized in Table 11.

[0267] Table 11: Run strength evaluation

[0268]

[0269] **After 30,000 pages, run length was visually assessed and rated relative to the following:

[0270] A: Almost no image wear,

[0271] B: Some images are worn,

[0272] C: Many images are worn, and

[0273] D: Severe image wear.

[0274] The results in Table 11 show that the press run of the inventive printing plates PP-12 to PP-15 comprising a thiol-based adhesion promoter is significantly higher than the press run of the comparative printing plate PP-09 comprising a comparative adhesion promoter.

Claims

1. A lithographic printing plate precursor comprising a coating on a substrate having a hydrophilic surface or provided with a hydrophilic layer, the coating comprising a photopolymerizable layer comprising a polymerizable compound, a photoinitiator and an adhesion-promoting compound containing at least one thiol group and at least one group capable of adhering to the substrate, the group capable of adhering to the substrate being selected from a phosphate group or a phosphonate group.

2. A printing plate precursor according to claim 1 wherein the adhesion promoting compound comprises at least two thiol groups.

3. A printing plate precursor according to claim 1 wherein the adhesion promoting compound is represented by formula I: in m and p independently represent 1, 2 or 3; Y represents a z-valent nucleus having 1 to 12 atoms; z is the sum of m and p, and z is 2, 3, 4, or 5; X represents a phosphate group or a phosphonate group; and L1, L2 and L3 each independently represent a linking group.

4. A printing plate precursor according to any one of claims 1 to 3, wherein L3 includes –(O-CH2-CH2) O -, where o is an integer between 1 and 15.

5. A printing plate precursor according to claim 3 wherein the z-valent nucleus represents an optionally substituted carbon atom or an isocyanurate group.

6. A printing plate precursor according to any one of claims 1 to 3 wherein the adhesion promoting compound has a molecular weight of at least 400 g / mol.

7. A printing plate precursor according to any one of claims 1 to 3 wherein the adhesion promoting compound has a weight average molecular weight of not more than 5,000 g / mol.

8. A printing plate precursor according to any one of claims 1 to 3, wherein the adhesion promoting compound is selected from the list comprising: wherein n=1 to 15.

9. A method for producing a printing plate precursor comprising the steps of: - coating the support with (i) a photopolymerizable layer comprising a polymerizable compound and a photoinitiator and an adhesion-promoting compound as defined in any one of claims 1 to 8, and - Drying the precursor.

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

11. A method according to claim 10, wherein the precursor is developed 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.

12. A method according to claim 10, wherein the precursor is developed by applying a gum solution.

Images