Application of hydrophilic thermosensitive polymer in negative lithographic plate precursor, lithographic plate imaging layer composition and precursor

Abstract

The invention provides an application of a hydrophilic thermosensitive polymer in a negative lithographic plate precursor, a lithographic plate imaging layer composition and a lithographic plate precursor, the polymer is obtained by copolymerization of styrene, cyclodextrin or a cyclodextrin substitute, acrylamide or an acrylamide derivative and the like, and the hydrophilic thermosensitive polymer provided by the invention is applied to the negative lithographic plate precursor. And the on-machine developing performance of the plate material is improved, so that the printing plate has good on-machine developing tolerance, and the number of paper passing through the printing plate is greatly reduced.

Description

Technical Field

[0001] The present invention relates to a negative lithographic plate precursor, and particularly to the application of a hydrophilic thermosensitive polymer in a negative lithographic plate precursor, as well as a lithographic plate imaging layer composition and precursor. Background Art

[0002] A lithographic printing plate precursor generally comprises a radiation-sensitive coating coated on a substrate. The radiation-sensitive coating usually includes one or more radiation-sensitive components dispersed in an organic polymer binder. After a part of the coating is exposed to radiation (usually referred to as exposure imaging), the exposed part of the coating becomes more or less developable in a specific liquid (developer) than the unexposed part. When the exposed part or area becomes difficult to develop in the developer and the unexposed part is removed during the developing process, such a printing plate precursor is generally considered a negative precursor (or negative printing plate, negative lithographic plate). After development in a suitable liquid, the imaged area (image part) accepts ink during printing, while the surface exposed on the hydrophilic surface of the substrate repels ink.

[0003] In recent years, from the aspects of global environmental protection and adaptation to digitalization, the industry has emphasized simplifying the manufacturing process of lithographic printing plates, including omitting the pre-development heating step (preheating) and using lithographic printing ink, dampening solution, or both for in-press development (develop on press, abbreviated as DOP) to remove the unnecessary coating material on the lithographic printing plate precursor. It is a method of using an image recording layer that can remove the non-image part of the original lithographic printing plate during the ordinary printing process, and removing the non-image part after exposure on the printing press to obtain a lithographic printing plate. As a specific example of in-press development, for example, a method of using a dampening solution, ink, or a dampening solution and ink to remove the soluble image recording layer of the original lithographic printing plate; a method of mechanically removing the image recording layer by contacting with the printing press rollers and the blanket; and a method of mechanically removing the image recording layer by contacting with the rollers and the blanket after reducing the cohesive strength of the image recording layer or the adhesion strength between the image recording layer and the carrier through the penetration of the dampening solution and ink.

[0004] Technologies for developing in-press developable lithographic printing plate precursors: W02013 / 032780 discloses a lithographic printing plate precursor for in-press development; EP0980754 introduces the technology of achieving hydrophilic-hydrophobic transformation by decarboxylation; W094 / 23954 introduces the hot melt microgel technology; US4004924 introduces a mixture of thermoplastic hydrophobic particles and a hydrophilic binder; EP 2006-5-2406114475.4 introduces a hot melt thermoplastic particle; US 2005-8-3 11 / 196,124 introduces a one-dimensional linear structure hydrophilic binder; US 2006-7-27 11 / 494,235 introduces a lithographic printing plate precursor containing a hydrophilic group and an esterified allyl group, etc.

[0005] At present, there are many technologies for on-press-developed lithographic plate precursors. One of the mainstream technologies is to use an infrared absorber to apply the thermal energy of a laser to a thermal initiator, and the thermal initiator triggers a chemical reaction in the thermosensitive layer to achieve laser imaging. After imaging, the plate is installed on a printing press and developed on-press with dampening solution and ink.

[0006] In the process of continuous technological progress, technicians found that the on-press development process remains the key to process-free lithographic plates. Either the removal rate of the coating in the non-image area during on-press development is slow, or the adaptability to printing presses, dampening solutions, inks, etc. is poor, and the on-press development state is unstable, ultimately resulting in a large number of on-press development blanket sheets, wasting paper and also resulting in low startup efficiency. Summary of the Invention

[0007] To solve the above problems, the present invention provides an application of a hydrophilic thermosensitive polymer in a negative lithographic plate precursor, a lithographic plate imaging layer composition, and a precursor. The hydrophilic thermosensitive polymer provided in this application is applied to a negative lithographic plate precursor, improving the on-press development performance of the plate material, enabling the plate to have good on-press development latitude and significantly reducing the number of blanket sheets.

[0008] The object of the present invention is achieved in the following manner: An application of a hydrophilic thermosensitive polymer in a negative lithographic plate precursor, wherein the polymer is copolymerized from styrene, cyclodextrin or a cyclodextrin substitute, acrylamide or an acrylamide derivative, etc.; the structure of the acrylamide or acrylamide derivative is as follows: R1 is an H atom or a methyl group, and R2 and R3 each independently represent hydrogen, an alkyl group with 1-12 carbon atoms, an alkoxy group with 1-12 carbon atoms, or an aryl group with 6-12 carbon atoms.

[0009] A negative lithographic plate imaging layer composition, comprising a hydrophilic thermosensitive polymer, a polymerizable / crosslinkable component, an infrared absorber, and an initiator, wherein the hydrophilic thermosensitive polymer is copolymerized from styrene, cyclodextrin or a cyclodextrin substitute, acrylamide or an acrylamide derivative, etc.; the structure of the acrylamide or acrylamide derivative is as follows: R1 is an H atom or a methyl group, and R2 and R3 each independently represent hydrogen, an alkyl group with 1-12 carbon atoms, an alkoxy group with 1-12 carbon atoms, or an aryl group with 6-12 carbon atoms.

[0010] The hydrophilic thermosensitive polymer accounts for 10%-60% of the weight of the imageable layer, the polymerizable / crosslinkable component accounts for 10%-70% of the weight of the imageable layer, the infrared absorber accounts for 1%-30% of the weight of the imageable layer, and the initiator accounts for 1%-30% of the weight of the imageable layer.

[0011] The polymerizable / crosslinkable component is composed of at least one of polyfunctional acrylic monomers, polyfunctional polyurethane acrylic monomers or free radical crosslinkable polymers; The infrared light absorber is a cyanine dye that absorbs in the range of 750 - 850 nm; The initiator is selected from one or more of iodonium salts, sulfonium salts, and phosphonium salts; The cyclodextrin is α - cyclodextrin, β - cyclodextrin, γ - cyclodextrin or hydroxypropyl - cyclodextrin. The weight - average molecular weight of the hydrophilic thermosensitive polymer is 2000 - 300000; the glass transition temperature is 30 - 400 °C; the weight percentage content of styrene in the hydrophilic thermosensitive polymer is 20% - 70%; the weight percentage content of cyclodextrin or cyclodextrin derivative in the hydrophilic thermosensitive polymer is 1% - 40%; the weight percentage content of acrylamide or acrylamide derivative in the hydrophilic thermosensitive polymer is 5% - 60%.

[0012] The weight - average molecular weight of the hydrophilic thermosensitive polymer is 10000 - 200000; the glass transition temperature is 40 - 300 °C; the weight percentage content of styrene in the hydrophilic thermosensitive polymer is 30% - 60%; the weight percentage content of cyclodextrin or cyclodextrin derivative in the hydrophilic thermosensitive polymer is 1% - 30%; the weight percentage content of acrylamide or acrylamide derivative in the hydrophilic thermosensitive polymer is 5% - 40%.

[0013] The weight - average molecular weight of the hydrophilic thermosensitive polymer is 30000 - 150000; the glass transition temperature is 60 - 150 °C; the weight percentage content of styrene in the hydrophilic thermosensitive polymer is 40% - 60%; the weight percentage content of cyclodextrin or cyclodextrin derivative in the hydrophilic thermosensitive polymer is 1% - 25%; the weight percentage content of acrylamide or acrylamide derivative in the hydrophilic thermosensitive polymer is 5% - 40%.

[0014] R1 is an H atom or a methyl group, and R2 is an alkyl group with 2 - 8 carbon atoms or an aryl group with 6 - 8 carbon atoms.

[0015] The hydrophilic thermosensitive polymer exists in the form of discrete particles with a particle diameter of 30 nm to 300 nm.

[0016] The preparation method of the hydrophilic thermosensitive polymer adopts the method of random copolymerization. The polymerization initiator contains at least one of benzoyl peroxide, persulfate or azo compounds, and the copolymerization method adopts emulsion polymerization.

[0017] A negative - type lithographic plate precursor comprises a substrate and an imaging layer, and the composition of the imaging layer is the imaging layer composition according to any one of claims 2 - 8.

[0018] The substrate is an aluminum plate base that has been electrolytically roughened and anodized.

[0019] The negative lithographic plate is a treatment-free lithographic plate. After being exposed by infrared laser scanning, it can be directly installed on the printing press for printing without any washing and processing steps, that is, the lithographic plate is a negative in-machine developing type treatment-free plate.

[0020] Compared with the prior art, the present invention provides an application of a hydrophilic thermosensitive polymer in a negative lithographic plate precursor, a lithographic plate imaging layer composition and a precursor. The hydrophilic thermosensitive polymer provided in this application is applied to the negative lithographic plate precursor, which improves the in-machine developing performance of the plate material, enables the printing plate to have good in-machine developing latitude, and significantly reduces the number of blanket-to-blanket impressions. In addition, the storage stability of the printing plate is improved. Specific embodiments

[0021] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the content of the present invention above.

[0022] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the content of the present invention above.

[0023] Prepare the negative lithographic plate precursor of the present invention having the structure and components described below: Imaging layer The lithographic plate imaging layer requires one or more hydrophilic thermosensitive polymers. Specifically, it is a polymer film-forming resin with functional groups. The hydrophilic thermosensitive polymer in the imaging layer of the present invention is a functional film-forming resin. In addition to having film-forming properties to ensure that the imaging layer coating solution forms a film and adheres to the carrier after drying, this polymer resin also has special functions of hydrophilicity and heat sensitivity.

[0024] As the main resin in the imaging layer of the negative lithographic plate, it must first have hydrophilicity. During laser imaging, the uncrosslinked part can be simply pre-cleaned with water or water containing gum, or be cleaned under the action of dampening solution during in-machine printing to expose the hydrophilic substrate. After being crosslinked and imaged under the action of laser heat, the crosslinked part of the hydrophilic resin and the prepolymer forms a three-dimensional network structure, changing the polarity and solubility of the resin from hydrophilic to hydrophobic. The best way to achieve the water solubility of the resin is to directly select vinyl monomers with hydrophilic side groups as the copolymerization units of the resin. Hydrophilic side groups include carboxyl group, hydroxyl group, phosphate group, sulfonic acid group, amino group, amide group, ether group, etc. Hydrophilic thermosensitive polymers often use branched polyethers or amide groups as hydrophilic groups, that is, the hydrophilic thermosensitive polymer contains at least polyether acrylate or acrylamide hydrophilic copolymerization units on the copolymer chain. The polyether acrylate or acrylamide hydrophilic copolymerization units endow the polymer binder with good self-emulsifying properties, enabling the hydrophilic thermosensitive polymer to form nano / micro thermoplastic particles. At the same time, the polyether group and acrylamide have good solvent resistance and can resist the erosion of monomers in UV ink on the imaging layer.

[0025] In addition, as the main resin in the imaging layer of the lithographic plate, the hydrophilic thermosensitive polymer preferably contains heat-sensitive groups, which is helpful for thermosensitive imaging. Such imaging groups can be double bonds that can undergo free radical polymerization or epoxy groups that can undergo cationic polymerization, etc.

[0026] At the same time, as the main resin in the imaging layer of the lithographic plate, the comprehensive properties such as the rigidity and ink affinity of the resin also need to be considered. When the resin is in the form of nano / micro particles as the hydrophilic copolymer of the processless thermosensitive plate, the resin preferably contains thermoplastic structural units, which is beneficial to laser hot melting into a film, such as styrene structural units. As is well known, styrene structural units have good thermoplasticity and a relatively high glass transition temperature. Styrene copolymers as the binder of the processless thermosensitive CTP plate are more easily hot melted in the heated part, the molecules are arranged more closely, and the thermal image part is more firm.

[0027] The morphology of the hydrophilic thermosensitive polymer in the imaging layer can be solid, solution state or emulsion state, etc. It is preferably in the form of discrete particles. During thermosensitive imaging, the laser can heat up the thermoplastic polymer particles in the discrete particle state to cause an aggregation reaction, and the exposed area changes from hydrophilic to hydrophobic and oleophilic. Such discrete particles can have an average particle size of at least 40 nm and at most 400 nm, and are usually evenly distributed in the infrared radiation-sensitive imaging layer.

[0028] The hydrophilic thermosensitive polymer used in the present invention is copolymerized from styrene, cyclodextrin or cyclodextrin derivatives, acrylamide or acrylamide derivatives, etc. The acrylamide or acrylamide derivative has the following structure: R1 is a hydrogen atom or a methyl group, and R2 and R3 each independently represent hydrogen, an alkyl group having 1 to 12 carbon atoms, an alkoxy group, or an aryl group.

[0029] In the hydrophilic thermosensitive polymer, the styrene structural unit has good thermoplasticity and a moderate glass transition temperature. As an adhesive, it has the characteristic of melting when heated, which can firmly bond the patterns in the heat-exposed part to the printing plate base, thereby enhancing the ink affinity of the pattern part. The content of styrene in the water-soluble thermally crosslinked copolymer directly affects the glass transition temperature and thermoplasticity of the polymer. In the present invention, the weight percentage content of the styrene copolymer unit A in the hydrophilic thermosensitive polymer is 20%-70%, further preferably 30%-60%, and more preferably 40%-60%.

[0030] In the hydrophilic thermosensitive polymer of the present invention, the cyclodextrin or cyclodextrin derivative is α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, hydroxypropyl-cyclodextrin, etc.

[0031] α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), and hydroxypropyl-cyclodextrin can be purchased from Zibo Qianhui Biotechnology Co., Ltd.

[0032] Cyclodextrin (abbreviated as CD) is a general term for a series of cyclic oligosaccharides formed by the action of cyclodextrin glucosyltransferase produced by Bacillus on amylose, usually containing 6 to 12 D-pyranose glucose units. Among them, the molecules containing 6, 7, and 8 glucose units, which have been studied more and have important practical significance, are called α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD), respectively.

[0033] The cyclodextrin molecule has a slightly conical hollow cylindrical three-dimensional ring structure. In its cavity structure, the outer upper end (the larger opening end) is composed of secondary hydroxyl groups at C2 and C3, and the lower end (the smaller opening end) is composed of primary hydroxyl groups at C6, having hydrophilicity, while the cavity forms a hydrophobic region due to the shielding effect of C-H bonds.

[0034] The good hydrophilicity of cyclodextrin can effectively increase the solubility and dissolution rate of some substances with poor water solubility in water. When copolymerized in the hydrophilic thermosensitive polymer, it can improve the hydrophilicity and solubility of the thermosensitive polymer. Various organic compounds can be embedded in the hydrophobic cavity of cyclodextrin to form inclusion complexes, which can effectively adsorb infrared absorbers and initiators, avoid the migration of small molecules of infrared dyes and initiators, and improve the storage stability of the printing plate.

[0035] The weight percentage content of cyclodextrin in the hydrophilic thermosensitive polymer is 1%-40%, further preferably 1%-30%, and more preferably 1%-20%.

[0036] The hydrophilic thermosensitive polymer described in the present invention comprises one or more acrylamides or acrylamide derivatives, and R2 and R3 each independently represent hydrogen, an alkyl group or an aryl group having 1 to 12 carbon atoms. Preferably, they are alkyl groups or aryl groups having 2 to 8 carbon atoms, and more preferably alkyl groups or aryl groups having 3 to 6 carbon atoms. The acrylamide or acrylamide derivative includes the following structures but is not limited thereto: N-methylacrylamide, N-methylmethacrylamide, N-isopropylacrylamide, N-octylmethylacrylamide, N-benzenesulfonamidoacrylamide, N-[(4-sulfonamide)phenyl]acrylamide, N-dodecylacrylamide, etc. These acrylamide substituents can be purchased from Merck Life Science Technologies Co., Ltd. and other places.

[0037] Examples of the structures of acrylamide or acrylamide derivatives are as follows, but are not limited thereto: The weight percentage content of acrylamide or acrylamide derivative in the hydrophilic thermosensitive polymer is 5 - 60%, further preferably 5% - 50%, and more preferably 5% - 40%.

[0038] The preparation method of the hydrophilic thermosensitive polymer described in the present invention synthesizes the hydrophilic thermosensitive polymer described in the present invention by a copolymerization method. The copolymerization reaction can be random copolymerization or block copolymerization, and random copolymerization is preferred. The polymerization initiators include peroxides such as di-tert-butyl peroxide and benzoyl peroxide, persulfates such as potassium persulfate and ammonium persulfate, and azo compounds such as azobisisobutyronitrile. The copolymerization method is emulsion polymerization.

[0039] The reaction solvents that can be selected include water, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, methyl ethyl ketone, cyclohexanone, ethyl acetate, butyl acetate, tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, dimethylacetamide, acetone, methyl ethyl ketone, cyclohexane, dichloroethylene, toluene, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, acetylacetone, diacetone alcohol, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol isopropyl ether, ethylene glycol butyl ether acetate, 3-methoxypropanol, methoxymethoxyethanol, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, dimethyl sulfoxide, methyl lactate and ethyl lactate, etc., or a mixture thereof. Preferably, a mixture of alcohol and water is used, and a mixture of n-propanol - water or isopropanol - water is more preferred. The emulsion copolymerization reaction temperature is preferably 40 - 100°C, and most preferably 60 - 90°C.

[0040] To synthesize the hydrophilic thermosensitive polymer of the present invention, a feeding method of dropwise adding partial raw materials is adopted. The particle size of the multi-component copolymer particles can be controlled by changing the reaction system concentration and the dropping time. The diameter of the multi-component copolymer particles becomes smaller with the decrease of the reaction system concentration and the increase of the dropping time. The particle size of the multi-component copolymer particles can be controlled at the nano / micron level by adjusting the reaction system concentration and the dropping time.

[0041] The weight-average molecular weight of the hydrophilic thermosensitive polymer of the present invention is 2,000 - 300,000, preferably 10,000 - 200,000, more preferably 20,000 - 180,000, further preferably 30,000 - 150,000, and still further preferably 40,000 - 100,000. The glass transition temperature is 30 - 400 °C, preferably 30 - 300 °C, more preferably 40 - 220 °C, and further preferably 60 - 150 °C.

[0042] The hydrophilic thermosensitive polymer can exist in the form of fine particles. Such discrete particles can have an average particle size of at least 10 nm and at most and including 1,500 nm, or at least 80 nm and at most and including 600 nm, or can have an average particle size of at least 40 nm and at most including 400 nm, or the particle diameter is 30 nm to 300 nm, and is generally evenly distributed in the imaging layer sensitive to infrared radiation.

[0043] The hydrophilic thermosensitive polymer accounts for 10% - 60% of the solid weight of the imaging layer composition.

[0044] The imaging layer includes polymerizable / crosslinkable components. The polymerizable / crosslinkable components include one or more free-radically polymerizable / crosslinkable compounds, each containing one or more free-radically polymerizable groups that can be initiated to polymerize using free radicals. In some embodiments, the imaging layer sensitive to infrared radiation contains two or more free-radically polymerizable components, and the components have different numbers of free-radically polymerizable groups in each molecule.

[0045] The free-radical polymerizable components in the imaging layer can be monomers or oligomers that can undergo free-radical polymerization or cationic polymerization, etc. Monomers for free-radical polymerization are generally acrylic monomers containing double bonds, and monomers that can undergo cationic polymerization are generally monomers containing epoxy groups. The polymerizable / crosslinkable components in the imaging layer of the present invention are polyfunctional acrylic monomers or polyfunctional polyurethane acrylate monomers. Here, the meaning of polyfunctional refers to that it contains multiple double bonds. Polyfunctional acrylic monomers such as 1,6-hexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, trimethylolpropane triacrylate, hydroxypropyl glycerol triacrylate, polyethylene glycol dimethacrylate, dipentaerythritol hexaacrylate, etc.; polyfunctional polyurethane acrylate monomers are products of the condensation of isocyanates and polyfunctional acrylates, such as products of the condensation of isocyanates with hydroxyethyl acrylate and pentaerythritol triacrylate, etc.; or products of the condensation of isocyanate containing double bonds such as methacryloyloxy isocyanate and polyhydroxy compounds such as pentaerythritol, etc.

[0046] The polymerizable / crosslinkable components account for 10 - 60% of the solid weight of the imaging layer composition, preferably 20 - 50%.

[0047] The imaging layer further includes an initiator that provides free radicals to initiate the polymerization of one or more free-radical polymerizable components when the radiation-sensitive imaging layer is exposed to infrared radiation, selected from onium salts such as sulfonium salts, iodonium salts, etc. Suitable onium salts include sulfonium salts, oxosulfonium salts, sulfoxonium salts, diazonium salts, and halonium salts such as iodonium salts. Specific examples of suitable onium salts are: diphenyliodonium chloride, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, [4-[(2-hydroxy tetradecyl-oxy] phenyl] phenyliodonium hexafluoroantimonate, triphenylsulfonium iodonium tetrafluoroborate, triphenylsulfonium iodonium octyl sulfate, 2-methoxy-4-aminophenyl diazonium hexafluorophosphate, phenoxyphenyl diazonium hexafluoroantimonate, and so on. The initiator is preferably a diaryliodonium salt compound.

[0048] Examples of the initiator structures used in the present invention are as follows, but are not limited thereto: The initiator accounts for 1 - 30% of the solid weight of the imaging layer composition, preferably 3 - 20%.

[0049] Examples of the infrared absorber structures used in the present invention are as follows, but are not limited thereto: The infrared absorber in the imaging layer accounts for 1 - 30% of the solid weight of the imaging layer composition by weight percentage, preferably 1% - 20%, more preferably 1% - 10%.

[0050] In some embodiments, there may be a variety of hydrophilic copolymers. Examples of the secondary hydrophilic copolymers include, but are not limited to, cellulose derivatives such as hydroxypropyl cellulose, carboxymethyl cellulose; and polyvinyl alcohol with various degrees of saponification, etc.

[0051] In addition, the imaging layer may include pigments / dyes and developers known in the art. The pigments / dyes and developers mentioned here are not essential components in the imaging layer. Useful pigments / dyes include, but are not limited to, phthalides and fluoran leuco dyes containing a lactone skeleton having acid dissociation properties, etc.

[0052] The imaging layer may also contain a combination of various materials and the essential components of the present invention. For example, organic or inorganic particles, wetting agents, plasticizers, binders, surfactants, antioxidants, coating aids, anti-stabilizers, and brighteners, etc., can be used in the present invention without affecting its performance, or any other additives commonly used in the lithography field, and the amount is a conventional amount.

[0053] Protective layer In some embodiments, the negative lithographic plate precursor is not disposed on the outermost layer of the imageable layer, but it is possible to design a hydrophilic protective layer (or oxygen barrier layer or overcoat) directly disposed on the imageable layer on the precursor (without an intermediate layer between these two layers). Such precursors can be developed on-press and off-press using any suitable developer described below.

[0054] The protective layer can prevent and hinder the mixing of low-molecular compounds such as oxygen and alkaline substances in the atmosphere into the photosensitive layer, which affects the image formation reaction initiated by exposure in the photosensitive layer. Therefore, the required characteristics of such a protective layer are low penetrability of low-molecular compounds such as oxygen, and it is required to substantially not hinder the transmission of light used in exposure and have good adhesion to the photosensitive layer, and at the same time can be easily removed during on-press development of the plate. In addition, other properties can also be imparted to the protective layer. For example, by adding a colorant (such as a water-soluble dye) used in exposure, this colorant (such as a water-soluble dye) has good light penetrability at 780 - 850 nm and can effectively absorb light outside the range of 780 - 850 nm. Therefore, the plate-making safety of the lithographic plate under white light can be improved without causing a decrease in sensitivity.

[0055] For materials that can be used for the protective layer, for example, it is preferable to use a water-soluble polymer compound with good crystallinity. Specifically, water-soluble polymers such as polyvinyl alcohol, polyvinylpyrrolidone, acidic cellulose, gelatin, gum arabic, and polyacrylic acid are known. Among these substances, when polyvinyl alcohol is used as the main component, it can bring the best basic properties such as oxygen barrier properties and developability removability. As long as the amount of unsubstituted vinyl alcohol units required for oxygen barrier properties and water solubility is present in the polyvinyl alcohol used in the protective layer, a part of it can be substituted with esters, ethers, and acetals. In addition, a part of it can also have other copolymerization components. For specific examples of polyvinyl alcohol, compounds with 71 - 100% hydrolysis and a molecular weight of 300 - 2400 can be cited. Specific examples include: PVA-105, PVA-110, PVA-117, PVA-117H, PVA-120, PVA-124, PVA-124H, PVA-CS, PVA-CST, PVA-HC, PVA-203, PVA-204, PVA-205, PVA-210, etc.

[0056] When the protective layer is present, the dry coating weight of the protective layer is usually 0.1 - 4 g / m 2 , preferably 0.2 - 2.0 g / m 2 . In some embodiments, the dry coating weight is 0.1 - 0.9 g / m 2 , so that the hydrophilic protective layer is relatively thin and can be easily removed during off-line development or in-line development.

[0057] Substrate The substrate support can be any self-supporting material, including polymer films, glass, ceramics, cellulose materials (including paper), metals, or cardboard, or laminates of any of these materials. The thickness of the support can vary. In most applications, the thickness should be sufficient to withstand wear from printing and thin enough to wrap the printed form. Preferably, a polyester carrier prepared from, for example, polyethylene terephthalate or polyethylene naphthalate is used, with a thickness of about 100 to about 310 μm. Another preferred embodiment uses an aluminum plate base with a thickness of about 100 to about 600 μm.

[0058] The aluminum plate base is a high-purity aluminum plate, and its aluminum content is preferably above 99%. Techniques known in the art can be used to process the aluminum carrier, including roughening a certain type by physical (mechanical) graining, electrochemical graining, or chemical graining, and usually then anodizing. The electrolyte used for electrolytic roughening can be an aqueous solution of an acid, a base, or a salt, or an aqueous solution containing an organic solvent. Among them, an aqueous solution of hydrochloric acid, nitric acid, or their salts is preferably used as the electrolyte. Typically, phosphoric acid or sulfuric acid and a conventional procedure are used for anodizing.

[0059] First, place the aluminum plate in an aqueous solution of 1% to 30% sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, etc., and carry out chemical etching at a temperature of 20 to 80 °C for 5 to 250 seconds. Then neutralize it in 10% to 30% nitric acid or sulfuric acid at a temperature of 20 to 70 °C to remove the ash. The aluminum plate thus cleaned is subjected to electrolytic treatment in an electrolytic solution of nitric acid or hydrochloric acid at a temperature of 10 to 60 °C with a rectangular wave, trapezoidal wave, sine wave, etc. with alternating positive and negative polarities at a current density of 5 to 100 A / dm 2 ². Next, the electrolyzed aluminum plate is subjected to anodic oxidation treatment. Anodic oxidation is usually carried out by the sulfuric acid method. The concentration of sulfuric acid used is 5% to 30%, the current density is 1 to 15 A / dm 2 ², the oxidation temperature is 20 to 60 °C, and the oxidation time is 5 to 250 seconds to form an oxide film of 1 to 10 g / m 2 ². The oxide film thus formed usually has relatively high micropores in the oxide film, strong adsorption ability, and is prone to adhering dirt. Therefore, sealing treatment is usually required. Sealing treatment can use various methods, and it is preferably to seal 50% to 80% of the volume of the micropores in the oxide film. The anodized aluminum carrier can be further treated using known post-anodic treatment (PAT) processes to seal the oxide pores and make its surface hydrophilic. Such processes include, for example, treatment in an aqueous solution of the following substances: poly(vinylphosphonic acid) (PVPA), vinylphosphonic acid copolymer, poly[(meth)acrylic acid], or acrylic acid copolymer, a mixture of phosphate and fluoride salts, or sodium silicate.

[0060] The solution used for the sealing treatment of the base of the lithographic plate of the present invention preferably contains an aqueous solution of fluoride ions and phosphates.

[0061] The lithographic plate of the present invention can be prepared by applying an imaging layer to the hydrophilic surface of a lithographic printing substrate by conventional techniques. The imaging layer can be applied by any suitable method such as coating or lamination.

[0062] Typically, the components of the imaging layer are dispersed or dissolved in a suitable coating solvent. Examples include water, water and organic solvents, such as a mixture of methanol, ethanol, isopropanol, and / or acetone. Surfactants, such as fluorinated surfactants or polyethoxylated dimethyl polysiloxane copolymers, or mixtures of surfactants, may be present to assist in the dispersion of other components in the coating solvent. The resulting mixture is coated onto a lithographic substrate by conventional methods such as spin coating, bar coating, gravure coating, die coating, slot coating, or roll coating. After coating, the imageable layer is dried to evaporate the solvent. The imageable layer can be air-dried at room temperature or at an elevated temperature, such as in an oven. Alternatively, the imageable layer can be dried by blowing warm air over the imageable element.

[0063] After the production of the negative lithographic plate precursor of the present invention is completed, it is exposed imagewise by a laser using digital data, giving a relief image opposite to the original plate. As a preferred exposure light source, for example, solid-state lasers and semiconductor lasers that emit infrared rays with a wavelength of 780 - 850 nm are used. The infrared laser for the present invention is preferably a laser capable of outputting 100 mW or more, and the exposure time for each pixel is preferably not longer than 20 microseconds. The radiation energy is preferably 10 - 300 mj / cm 2 。

[0064] After the lithographic plate original of the present invention is exposed imagewise, printing is carried out by supplying printing ink and dampening solution without undergoing a conventional development process. Specifically, the lithographic plate precursor is exposed imagewise with a laser beam, and then the coating in the blank areas is removed on a printing press by supplying printing ink and dampening solution. A printing ink-receptive portion having an ink-receptive surface is formed in the exposed portion of the image recording layer by the exposure-hardened image recording layer. The unhardened image recording layer is wetted and penetrated by the supplied dampening solution and becomes loose, and then is adhered and transferred by the printing ink to the paper and removed, and the hydrophilic surface is exposed at the unexposed portion, preparing a printable lithographic plate. Subsequently, the dampening solution adheres to the exposed hydrophilic surface, and the printing ink adheres to the image recording layer in the exposed portion, starting the printing process.

[0065] During the in-machine development process, the surface of the plate material should usually be pre-wetted with dampening solution for 10 - 60 seconds. The longer the time and the greater the amount of dampening solution, the more beneficial it is for the removal of the coating in the blank areas. Then, the printing ink is transferred to the surface of the lithographic plate precursor through an ink roller, and the coating in the blank areas is peeled off relying on the viscosity of the printing ink. The ink contact time is 10 - 30 seconds. The longer the time, the more beneficial it is for the removal of the coating in the blank areas.

[0066] In some cases, an aqueous rinse solution can be used offline to remove the unexposed areas to develop the imaged precursor, and to provide a protective layer or coating over the entire imaged and developed (rinsed) precursor printing surface. After offline development, printing can be performed by placing the exposed and rinsed lithographic plate on a suitable printing press.

[0067] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention.

[0068] Preparation of the substrate: A1050 rolled aluminum plate with a diameter of 99.5% purity and a thickness of 0.3 mm is etched in a 5% mass fraction aqueous sodium hydroxide solution at 70 °C for 20 seconds. After rinsing with running water, it is immediately neutralized with a 1% mass fraction aqueous nitric acid solution. Then, in a 1% mass fraction aqueous hydrochloric acid solution, it is electrolytically roughened at 40 °C with a sine-wave alternating current at a current density of 40 A / dm 2 for 16 seconds. Then, at 40 °C, it is neutralized with a 5% mass fraction aqueous sodium hydroxide solution for 10 seconds. Washed with water. Finally, at 30 °C, it is anodized with a 20% mass fraction aqueous sulfuric acid solution at a current density of 15 A / dm 2 for 20 seconds. Washed with water. Sealed at 60 °C with an aqueous solution of 200 ppm sodium fluoride and 6% mass fraction sodium dihydrogen phosphate for 20 seconds. Washed with water. Dried. The substrate thus obtained has an average roughness of the center line of 0.40 μm and an oxide film weight of 3.0 g / m 2 .

[0069] Raw materials used in the imaging layer formulation: Hydrophilic thermosensitive polymer L Lucky Huaguang Printing Technology Co., Ltd. Polyurethane acrylate HGPUA-18 Lucky Huaguang Printing Technology Co., Ltd. Sartomer 399 SartomerCo., Inc. Initiator P Lucky Huaguang Printing Technology Co., Ltd. Infrared absorption dye D Lucky Huaguang Printing Technology Co., Ltd. BYK-330 BYK 1-Methoxy-2-propanol Nanjing Oriental Pearl Industry and Trade Co., Ltd. The structure of initiator P is as follows: The structure of infrared absorption dye D is as follows: Synthesis examples of hydrophilic thermosensitive resins (No. L1-L12): The main raw materials can be obtained from the following companies: Styrene St, isopropyl alcohol, methyl ethyl ketone MEK, acrylonitrile, sodium dodecyl sulfate, n-propanol, polyethoxymethacrylate, azobisisobutyronitrile AIBN can be purchased from Nanjing Chemical Reagent Co., Ltd. and other places.

[0070] Acrylamide or acrylamide derivatives N1-N7 can be purchased from Merck Life Science Technology Co., Ltd. and other places; α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), etc. are from Zibo Qianhui Biotechnology Co., Ltd.

[0071] Hydrophilic thermosensitive polymer L1: In a 500 ml four-necked flask equipped with a temperature-controlled heating, mechanical stirring, condensation reflux and nitrogen protection device, add 30 g (30 wt%) of cyclodextrin, 50 g (50 wt%) of acrylamide, 75 g of deionized water, and 250 g of isopropyl alcohol. Heat up to 70 °C and start dropping 20 g (20 wt%) of styrene and 1 g of azobisisobutyronitrile. The dropping time is 120 minutes. Then, after reacting at 70 °C for 8 hours, add 0.51 g of azobisisobutyronitrile and continue reacting for 8 hours, and then cool down to end the reaction. The measured particle size is 70 nm. The reaction stock solution is used directly according to the solid content.

[0072] According to the addition ratios given in Table 1, referring to the synthesis process of hydrophilic thermosensitive polymer L1, adjust the amounts of water, alcohol and dropping time to synthesize hydrophilic thermosensitive polymers L1-L10 with different ratios and particle sizes. The particle sizes are shown in Table 1.

[0073] Comparative examples for synthesizing the hydrophilic thermosensitive polymer of the present invention: Comparative example F of hydrophilic thermosensitive polymer: According to the description in Agfa patent EP 2006-5-24 06114475.4, synthesize Agfa polymer F. The polymer does not contain hydrophilic groups. The polymer structure: Basic operation: In a 1000 ml four-necked flask equipped with a temperature-controlled heating, mechanical stirring, condensation reflux and nitrogen protection device, add 75 g of deionized water, 250 g of isopropyl alcohol, and 5 g of sodium dodecyl sulfate. Drop 60 g (60 wt%) of St (styrene), 40 g (40 wt%) of AN (acrylonitrile), and 0.7 g of AIBN (azobisisobutyronitrile) at 80 °C. The dropping time is 0.5 hour. After reacting for 7.5 hours, add 0.3 g of AIBN (azobisisobutyronitrile) and continue reacting for 12 hours to end.

[0074] Comparative example K of hydrophilic thermosensitive polymer: According to Kodak patent US 2005-8-3 11 / 196, synthesize Kodak polymer K. The polymer contains polyether hydrophilic groups but does not contain epoxy groups. The polymer structure: Basic operation: add 75g of deionized water and 250g of n-propanol to a 1000ml four-necked flask equipped with temperature-controlled heating, mechanical stirring, condensation reflux and nitrogen protection device, and add 20g (20 wt%) of St (styrene), 70g (70 wt%) of AN (acrylonitrile), 10g (10 wt%) of PEGMA (polyethoxymethyl acrylate) and AIBN (azobisisobutyronitrile) dropwise at 80°C for 0.5 hour. After reacting for 7.5 hours, add 0.3g of AIBN (azobisisobutyronitrile) and continue to react for another 12 hours before ending.

[0075] Preparation of Examples 1-14 and Comparative Examples 1-2 Thermal-sensitive Lithographic Plates: Preparation of thermal-sensitive lithographic plates of Examples 1-14 and Comparative Examples 1-2: According to the specific raw materials used for the hydrophilic thermosensitive polymer in Table 2, 0.5 g of surfactant BYK-330 and 90 g of 1-methoxy-2-propanol were added according to the amounts of hydrophilic thermosensitive polymer, polyurethane acrylate HGPUA-18, Sartomer 399, initiator P, and infrared absorbing dye D in Table 2 to prepare an imaging layer coating solution. The imaging layer coating solution was extrusion-coated on the above-mentioned hydrophilized aluminum substrate, and then dried at 100°C for 60 seconds. 15 mg / dm 2 Dry weight of coating.

[0076] Protective layer formula: Polyvinyl alcohol PVA-205 (Japanese Kuraray) 17g Polyvinylpyrrolidone K30 (BASF, Germany) 3g Emulsifier OP-10 (Helm, Germany) 0.45g Deionized water 480g Protective layer coating: The above protective layer was extrusion coated on the imaging layer and then dried at 110°C for 60 seconds to obtain 10 mg / dm 2 Dry weight of coating.

[0077] The lithographic printing plates of Examples 1-14 and Comparative Examples 1-2 were prepared, and the plates obtained in this way were exposed on a Kodak Thermal CTP plate-making machine to determine the appropriate exposure energy. Then, according to the corresponding exposure energy, the exposed plates were directly mounted on a Heidelberg SpeedMaster74 printing press, and the printing press was turned on. The performance is listed in Tables 2 and 3 below.

[0078] Performance test of plate material: Platemaking energy: It is characterized by the laser energy value required for plate imaging. When exposed with this energy, the plate has good contrast and high printing resistance after platemaking. For each sample obtained from the examples and comparative examples, on a Kodak thermal CTP platemaker, with an increment of 5 mJ / cm 2 exposed within the energy range of 80 - 200 mJ / cm 2 . According to the Pantone LIVE color digital workflow, the platemaking energy of the plate for each example or comparative example is determined, and its performance is listed in Table 2 below.

[0079] Number of transfer sheets: It refers to the number of sheets lost from the start of paper feeding until the paper is blank and clean and the ink color is balanced.

[0080] Printing resistance: After determining the platemaking energy of the plate for each example or comparative example according to the platemaking energy test method, on a Kodak thermal CTP platemaker, the sample is exposed and imaged according to the obtained platemaking energy, and then the sample is directly installed on a Heidelberg SpeedMaster74 printing press for printing. The ability of the printing plate to print a qualified number of printed products is the printing resistance.

[0081] Storage shelf life: All the above samples are placed in a standard thermal CTP plate product packaging box and aged in an oven at 50°C for 4 days. According to experience, aging for 1 day is approximately equivalent to natural storage for 3 months, aging for 2 days is approximately equivalent to natural storage for 6 months, aging for 3 days is approximately equivalent to natural storage for 9 months, and aging for 4 days is approximately equivalent to natural storage for 12 months. Samples are taken every day to observe the appearance of the plate, and on a Kodak thermal CTP platemaker, the sample is exposed and imaged according to the corresponding platemaking energy, and then the sample is installed on a Heidelberg SpeedMaster74 printing press for printing test to determine the corresponding storage shelf life of the sample.

[0082] Migration rating: All the above samples are placed in a standard thermal CTP plate product packaging box and forced to age in an oven at 40°C and 80% RH humidity for 5 days. Observe whether the infrared absorption dye migrates to the surface of the plate and compare it with the appearance of the fresh, unaged plate. It is rated on a 5 - point scale, where "5" is the full score, indicating no observed migration; "4" indicates a small amount of observed migration, which can be ignored; "3" indicates some observed crystals, which is barely acceptable; "2" indicates a relatively large amount of observed migration; "1" indicates a large amount of observed migration; "0" indicates severe migration.

[0083] Table 1 Hydrophilic Thermal Sensitive Resin Synthesis Weight Percentage Feedstock and Particle Size Table Table 2 Imaging Layer Feedstock Table for Example and Comparative Example Plates Unit: gram Table 3 Application Performance Table of Plate Material Table 4 Apparent Migration Rating Table of Plate Material The above are only the preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. It should be pointed out that for those skilled in the art and any person familiar with the technical field, without departing from the overall concept of the present invention, equivalent substitutions or changes made according to the technical solution and inventive concept of the present invention, as well as several changes and improvements made, should also be regarded as the protection scope of the present invention.

Claims

1. Application of a hydrophilic thermosensitive polymer in a negative lithographic printing plate precursor, characterized in that: The polymer is obtained by copolymerizing styrene, cyclodextrin or a cyclodextrin derivative, acrylamide or an acrylamide derivative, etc.; the structure of the acrylamide or acrylamide derivative is as follows: R1 is a hydrogen atom or a methyl group, and R2 and R3 each independently represent hydrogen, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

2. An imaging layer composition for an intaglio lithographic plate, characterized in that: It contains a hydrophilic thermosensitive polymer, a polymerizable / crosslinkable component, an infrared absorber, and an initiator. The hydrophilic thermosensitive polymer is obtained by copolymerizing styrene, cyclodextrin or a cyclodextrin derivative, acrylamide or an acrylamide derivative, etc.; the structure of the acrylamide or acrylamide derivative is as follows: R1 is a hydrogen atom or a methyl group, and R2 and R3 each independently represent hydrogen, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

3. The negative lithographic plate imaging layer composition according to claim 2, wherein: The hydrophilic thermosensitive polymer accounts for 10% - 60% of the solid weight of the imaging layer composition, the polymerizable / crosslinkable component accounts for 10% - 60% of the solid weight of the imaging layer composition, the infrared absorber accounts for 1% - 30% of the solid weight of the imaging layer composition, and the initiator accounts for 1% - 30% of the solid weight of the imaging layer composition.

4. The negative lithographic plate imaging layer composition according to claim 2, wherein: The polymerizable / crosslinkable component is composed of at least one of a polyfunctional acrylic monomer, a polyfunctional polyurethane acrylate monomer, or a free-radical crosslinkable polymer; The infrared light absorber is a cyanine dye that absorbs in the range of 750 - 850 nm; The initiator is selected from one or more of iodonium salts, sulfonium salts, and phosphonium salts; The cyclodextrin is α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, or hydroxypropyl-cyclodextrin. The weight-average molecular weight of the hydrophilic thermosensitive polymer is 2,000 - 300,000; the glass transition temperature is 30 - 400 °C; the weight percentage content of styrene in the hydrophilic thermosensitive polymer is 20% - 70%; the weight percentage content of cyclodextrin or a cyclodextrin derivative in the hydrophilic thermosensitive polymer is 1% - 40%; the weight percentage content of acrylamide or an acrylamide derivative in the hydrophilic thermosensitive polymer is 5% - 60%.

5. The negative lithographic plate imaging layer composition according to claim 4, wherein: The weight-average molecular weight of the hydrophilic thermosensitive polymer is 10,000 - 200,000; the glass transition temperature is 40 - 300 °C; the weight percentage content of styrene in the hydrophilic thermosensitive polymer is 30% - 55%; the weight percentage content of cyclodextrin or a cyclodextrin derivative in the hydrophilic thermosensitive polymer is 1% - 30%; the weight percentage content of acrylamide or an acrylamide derivative in the hydrophilic thermosensitive polymer is 5% - 50%.

6. The negative lithographic plate imaging layer composition according to claim 1 or 2, characterized in that: The weight-average molecular weight of the hydrophilic thermosensitive polymer is 30,000 - 150,000; the glass transition temperature is 60 - 150 °C; the weight percentage content of styrene in the hydrophilic thermosensitive polymer is 40% - 55%; the weight percentage content of cyclodextrin or a cyclodextrin derivative in the hydrophilic thermosensitive polymer is 1% - 20%; the weight percentage content of acrylamide or an acrylamide derivative in the hydrophilic thermosensitive polymer is 5% - 40%.

7. The negative lithographic plate imaging layer composition according to claim 1 or 2, characterized in that: R1 is a hydrogen atom or a methyl group, and R2 is an alkyl group having 2 to 8 carbon atoms or an aryl group having 6 to 8 carbon atoms; The hydrophilic thermosensitive polymer exists in the form of discrete particles with a particle diameter of 30 nm to 300 nm.

8. The negative lithographic plate imaging layer composition according to claim 1 or 2, characterized in that: The preparation method of the hydrophilic thermosensitive polymer adopts the method of random copolymerization, and the copolymerization method adopts emulsion polymerization.

9. A negative lithographic printing plate precursor, characterized in that: It comprises a substrate and an imaging layer, and the composition of the imaging layer is the imaging layer composition according to any one of claims 2-8.

10. The negative lithographic printing plate precursor according to claim 9, wherein: The substrate is an aluminum plate base that has been subjected to electrolytic roughening and anodic oxidation treatment.

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