Original photosensitive resin printing plate

Abstract

To provide a photosensitive resin printing original plate which is excellent in adhesion between an IR-sensitive layer and a protective film.SOLUTION: A photosensitive resin printing original plate has a photosensitive resin layer, an IR-sensitive layer and a protective film in this order on a support, wherein surface energy on the side of the IR-sensitive layer of the protective film is 50 mN / m or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a photosensitive resin printing plate precursor. [Background technology]

[0002] Computer to plate (CTP), a digital image formation technology, is becoming increasingly common in the fields of letterpress and flexographic printing. CTP involves creating an image mask using digital data on the infrared-sensitive layer of a photosensitive resin printing plate precursor, then irradiating the photosensitive resin layer with actinic rays through the image mask to partially photo-cure the photosensitive resin layer, thereby forming a relief pattern.

[0003] As a photosensitive resin printing plate precursor suitable for such CTP technology, with the aim of providing a flexographic printing plate precursor that is small and reduces pinholes in the heat-sensitive mask layer through a simple process, a flexographic printing plate precursor has been proposed (see, for example, Patent Document 1), which is composed of at least a support, a photosensitive resin layer, a heat-sensitive mask layer, and a cover film laminated in that order, and is characterized in that the surface of the cover film in contact with the heat-sensitive mask layer has a surface energy of 25.0 to 40.0 mN / m and a surface roughness (Ra) of 0.01 to 0.2 μm, and a protective layer formed from a polymer compound dispersible in a developer is provided between the photosensitive resin layer and the heat-sensitive mask layer. Furthermore, in a photosensitive resin laminate having a mask layer element and a protective layer, aiming to achieve both scratch resistance of the mask layer element and good adhesion between the mask layer element and the protective layer, a photosensitive resin laminate has been proposed which has a photosensitive resin layer, a mask layer element, and a protective layer in this order on a support, in which the mask layer element contains polyvinyl alcohol, an anionic polymer, and an infrared-absorbing substance, and the saponification degree of the polyvinyl alcohol is greater than 90% (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 054225 [Patent Document 2] Patent Publication No. 2021-162667 Summary of the Invention [Problem to be solved by the invention]

[0005] In a photosensitive resin printing plate precursor having an infrared-sensitive layer, if the infrared-sensitive layer is scratched, an unwanted uneven pattern is formed in the photosensitive resin layer. In the techniques disclosed in Patent Documents 1 and 2, a cover film or a protective layer is used to prevent scratches on the infrared-sensitive layer caused by external forces or the inclusion of foreign matter. However, there is a problem in that the protective film is easily peeled off during transportation of the photosensitive resin printing plate precursor.

[0006] In view of the above problems, an object of the present invention is to provide a photosensitive resin printing plate precursor that has excellent adhesion between the infrared-sensitive layer and the protective film. [Means for solving the problem]

[0007] The present invention is a photosensitive resin printing plate precursor having a photosensitive resin layer, an infrared-sensitive layer, and a protective film in this order on a support, wherein the surface energy of the infrared-sensitive layer side of the protective film is 50 mN / m or more. [Effects of the Invention]

[0008] The photosensitive resin printing plate precursor of the present invention has excellent adhesion between the infrared-sensitive layer and the protective film. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail.

[0010] The photosensitive resin printing plate precursor of the present invention (hereinafter sometimes abbreviated as "printing plate precursor") has a photosensitive resin layer, an infrared-sensitive layer, and a protective film, in this order, on a support. The support serves to hold the photosensitive resin layer in the printing plate precursor. The photosensitive resin layer serves to form a relief pattern (relief) corresponding to the image mask when irradiated with actinic rays through the image mask. The infrared-sensitive layer serves to form the image mask by partial decomposition and evaporation (ablation) by infrared rays. The protective film serves to protect the infrared-sensitive layer from external forces before use of the printing plate precursor, such as during transportation, and to prevent scratches on the infrared-sensitive layer due to external forces or the inclusion of foreign matter.

[0011] The printing plate precursor of the present invention may further include other layers as necessary. For example, an easy-adhesion layer may be provided between the support and the photosensitive resin layer, thereby increasing the adhesive strength between the support and the photosensitive resin layer. Furthermore, an intermediate layer may be provided between the photosensitive resin layer and the infrared-sensitive layer, thereby increasing the adhesive strength between the photosensitive resin layer and the infrared-sensitive layer. However, it is preferable that no other layer is provided between the infrared-sensitive layer and the protective film, i.e., the protective film and the infrared-sensitive layer are in contact with each other. Direct contact between the protective film and the infrared-sensitive layer provides high adhesion between the infrared-sensitive layer and the protective film, protecting the infrared-sensitive layer even during transportation, and preventing scratches on the infrared-sensitive layer due to external forces or the inclusion of foreign matter.

[0012] First, the protective film will be described. Examples of the protective film include plastic films made of polyester, polyethylene, polypropylene, etc. Among these, polyester films are preferred because of their excellent heat resistance, solvent resistance, and weather resistance. As the polyester film, polyethylene terephthalate film is preferred.

[0013] The thickness of the protective film is preferably 10 to 150 μm from the viewpoints of handling and flexibility. Here, the thickness of the protective film is the average value obtained by measuring the thickness at three points at 5 cm intervals using a Digimatic thickness gauge.

[0014] The printing plate precursor of the present invention is characterized in that the surface energy of at least the infrared-sensitive layer side of the protective film is 50 mN / m or more. The surface energy of the protective film contributes to the adhesion between adjacent layers, and if the surface energy of the infrared-sensitive layer side is less than 50 mN / m, the adhesion between the infrared-sensitive layer and the protective film decreases. If the surface energy of the infrared-sensitive layer side is 50 mN / m or more, the adhesion between the infrared-sensitive layer and the protective film is improved, and the wettability when the infrared-sensitive layer is applied by wet coating is excellent, thereby suppressing variations in the optical density of the infrared-sensitive layer. The surface energy of the infrared-sensitive layer side is preferably 65 mN / m or more. On the other hand, the surface energy of the infrared-sensitive layer side is preferably 73 mN / m or less. If the surface energy of the infrared-sensitive layer side is 73 mN / m or less, transfer defects of the infrared-sensitive layer during peeling of the protective film are suppressed, and the protective film can be peeled off with good workability. On the other hand, the surface energy of the protective film on the side opposite the infrared-sensitive layer is not specified.

[0015] Examples of protective films having a surface with a surface energy of 50 mN / m or more include antistatic transparent PET film for high-speed printing KSP-AN (product name) manufactured by Higashiyama Film Co., Ltd. and corona-treated #125 PET manufactured by Toyo Shinko Co., Ltd.

[0016] The surface energy of the protective film can be measured in accordance with the Wet Tension Test Method for Plastic Films and Sheets described in JIS K6768 (1999). More specifically, it is measured by the following method. Wet tension test mixtures of 22.6, 27.3, 30.0-48.0 (in 3.0 mN / m increments), 52.0, 56.0, 60.0, 63.0, 67.0, 70.0, and 73.0 mN / m, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., are used. A 2-mL drop of the test mixture, starting with the lowest surface tension, is dispensed onto the surface of the infrared-sensitive layer side of the protective film, and quickly spread using a cotton swab. The state of the liquid film is observed. If the surface is wet, the next highest surface tension test mixture is used and observed in the same manner. The surface tension of the test mixture when the liquid repels and the liquid film breaks is taken as the surface energy of the protective film.

[0017] The surface roughness (Ra) of the protective film on the infrared-sensitive layer side is preferably 0.01 to 0.20 μm. By setting the Ra of the protective film on the infrared-sensitive layer side to 0.01 μm or more, the protective film can be easily transported in the printing plate precursor manufacturing process. On the other hand, by setting the Ra of the protective film on the infrared-sensitive layer side to 0.20 μm or less, variations in the optical density of the infrared-sensitive layer can be further reduced.

[0018] Plastic films having various Ra values ​​are commercially available, and one having a desired Ra value can be selected and used from among them.

[0019] The Ra of the surface of the protective film can be measured non-contact using a laser microscope. More specifically, it is measured by the following method. Using a laser microscope (VK-X250) manufactured by Keyence Corporation, the surface of the protective film is observed under magnification at a lens magnification of 20x. Three straight lines, each 300 μm long, are drawn randomly on the observation surface, and the average value of the line roughness on the three straight lines is calculated and used as the line roughness of the protective film surface.

[0020] Next, the infrared-sensitive layer will be described. The infrared-sensitive layer has the following functions: (1) efficiently absorbs infrared laser light, and the heat generated evaporates or ablates part or all of the layer, creating a difference in optical density between the laser-irradiated and unirradiated areas, i.e., a decrease in the optical density of the irradiated areas, and (2) practically blocks ultraviolet light. Note that, in this context, "practically blocking ultraviolet light" refers to an optical density of the infrared-sensitive layer of 2.0 or higher, and more preferably 2.5 or higher. Optical density is generally represented by D and is defined by the following formula: D=log10(100 / T)=log10(I0 / I) Here, T is the transmittance (unit: %), I0 is the incident light intensity when measuring the transmittance, and I is the transmitted light intensity.

[0021] The optical density in the present invention refers to a value calculated from the measured value of the transmitted light intensity at a constant incident light intensity. The optical density can be measured using an orthochromatic filter with a Macbeth Transmission Densitometer "TR-927" (manufactured by Kollmorgen Instruments Corp.).

[0022] The infrared-sensitive layer preferably contains an infrared-absorbing substance and polyvinyl alcohol.

[0023] The infrared absorbing material is preferably a material that has absorption characteristics in the wavelength range of 750 nm to 20,000 nm, and examples thereof include black pigments such as carbon black, carbon graphite, and cyanine black; inorganic pigments such as manganese oxide, iron oxide, chromium oxide, and copper chromite; and dyes such as phthalocyanine, substituted phthalocyanine derivatives, cyanine dyes, merocyanine dyes, polymethine dyes, and metal thiolate dyes. Two or more of these may be contained. Among these, carbon black is preferred from the viewpoints of ablation efficiency and ultraviolet absorption performance.

[0024] The carbon black preferably has an anionic group. By having the anionic group, the dispersibility of the carbon black can be improved without using a dispersant. As the anionic group, a sulfo group or a carboxyl group is preferred. The sulfo group has a large dissociation constant in water and is highly effective in suppressing the aggregation of carbon black in the infrared-sensitive layer composition dispersion liquid described below. On the other hand, the carboxyl group suppresses the aggregation of carbon black due to solvent shock, which is likely to occur when an organic solvent such as a lower alcohol is added to the infrared-sensitive layer composition dispersion liquid described below, and can suppress coating defects in the infrared-sensitive layer.

[0025] Carbon black having a carboxyl group as an anionic group preferably also has a lactone group. Carboxyl groups have a low dissociation constant in water and are easily affected by the functional groups of other components and pH, so carbon black having a carboxyl group tends to aggregate easily. However, the inclusion of a lactone group, which is hydrophilic but not ionic, acts as a steric hindrance to electrostatic interactions with other components, thereby suppressing aggregation. Therefore, carbon black having a carboxyl group and a lactone group can improve dispersibility in the infrared-sensitive layer. Therefore, when combined with the protective film having high surface energy and excellent wettability, variations in the optical density of the infrared-sensitive layer can be further suppressed.

[0026] The content of the infrared-absorbing material in the infrared-sensitive layer is preferably 20% by mass or more, more preferably 50% by mass or more, of the total solid content from the viewpoint of improving ablation efficiency, while the content of the infrared-absorbing material in the infrared-sensitive layer is preferably 90% by mass or less, more preferably 80% by mass or less, of the total solid content from the viewpoint of further improving scratch resistance of the infrared-sensitive layer.

[0027] By including polyvinyl alcohol in the infrared-sensitive layer, it is possible to improve the dispersibility of the infrared-absorbing substance and the film-forming properties of the infrared-sensitive layer. Furthermore, when an intermediate layer described below is included, it is possible to improve the adhesion to the intermediate layer.

[0028] The saponification degree of the polyvinyl alcohol contained in the infrared-sensitive layer is preferably 60 mol% or more. By increasing the saponification degree of the polyvinyl alcohol to 60 mol% or more, the solubility in a developer primarily composed of water can be improved, allowing the photosensitive resin layer and the infrared-sensitive layer to be developed together using a developer primarily composed of water. Furthermore, migration of compounds containing ethylenic double bonds, which are generally low-molecular-weight components with high fat solubility, contained in the photosensitive resin layer to the infrared-sensitive layer can be suppressed, thereby suppressing cohesive failure of the infrared-sensitive layer and improving adhesion between the photosensitive resin layer and the infrared-sensitive layer. The saponification degree of the polyvinyl alcohol is more preferably 80 mol% or more. On the other hand, the saponification degree of the polyvinyl alcohol in the infrared-sensitive layer is preferably 97 mol% or less, which can further improve adhesion between the infrared-sensitive layer and the protective film. The saponification degree of the polyvinyl alcohol is more preferably 90 mol% or less.

[0029] The average degree of polymerization of the polyvinyl alcohol contained in the infrared-sensitive layer is preferably 1,000 or more. By making the average degree of polymerization of the polyvinyl alcohol 1,000 or more, the coating strength of the infrared-sensitive layer can be improved, the scratch resistance of the infrared-sensitive layer can be improved, and variations in optical density can be suppressed. Furthermore, peeling defects that tend to occur particularly when peeling a protective film having high surface energy as described above can be suppressed, and the protective film can be peeled with good workability. The average degree of polymerization is more preferably 1,500 or more. On the other hand, by making the average degree of polymerization 3,500 or less, the infrared-sensitive layer can be easily formed. Variations in optical density can be suppressed. The average degree of polymerization is more preferably 2,500 or less.

[0030] Here, the saponification degree and polymerization degree of polyvinyl alcohol are values ​​measured according to JIS K 6726-1994 (Testing method for polyvinyl alcohol). When the infrared-sensitive layer contains two or more types of polyvinyl alcohol, the saponification degree and polymerization degree refer to the total of the two or more types of polyvinyl alcohol.

[0031] The content of polyvinyl alcohol in the infrared-sensitive layer is preferably 10% by mass or more, more preferably 20% by mass or more, of the total solid content in order to more easily form the infrared-sensitive layer, while the content of polyvinyl alcohol in the infrared-sensitive layer is preferably 80% by mass or less, more preferably 50% by mass or less, of the total solid content in order to improve ablation efficiency.

[0032] The infrared-sensitive layer of the present invention may also contain an ultraviolet-absorbing substance that blocks ultraviolet rays. The ultraviolet-absorbing substance is preferably a substance that has absorption characteristics in the wavelength range of 300 to 400 nm, such as a benzotriazole-based compound, a triazine-based compound, or a benzophenone-based compound. Two or more of these may also be contained.

[0033] The infrared-sensitive layer may contain other polymers, fillers, surfactants, coating aids, etc., to the extent that the effects of the present invention are not impaired. Examples of other polymers include polyacrylic acid, polyester, polyamide, and derivatives thereof. Two or more of these may be contained.

[0034] The intermediate layer preferably contains polyvinyl alcohol with a saponification degree of 60 to 100 mol %. By setting the saponification degree of polyvinyl alcohol to 60 mol % or more, the solubility in a developer containing water as the main component can be improved. When the infrared-sensitive layer is removable with a developer containing water as the main component, the photosensitive resin layer, intermediate layer, and infrared-sensitive layer can be developed together with a developer containing water as the main component. The saponification degree is preferably 65 mol % or more. On the other hand, the saponification degree of polyvinyl alcohol in the intermediate layer is preferably 97 mol % or less, which can improve adhesion to the photosensitive resin layer. Here, the saponification degree of polyvinyl alcohol can be measured in the same manner as the saponification degree of polyvinyl alcohol contained in the infrared-sensitive layer. Furthermore, when the intermediate layer contains two or more types of polyvinyl alcohol, the saponification degree refers to the saponification degree of the two or more types of polyvinyl alcohol as a whole.

[0035] The thickness of the intermediate layer is preferably 0.1 to 3 μm. By making the thickness of the intermediate layer 0.1 μm or more, the scratch resistance of the infrared-sensitive layer can be further improved. On the other hand, by making the thickness of the intermediate layer 3 μm or less, a deep relief of the recessed image can be formed, and the reproducibility of cut-out character images and the like can be improved. The thickness of the intermediate layer is more preferably 2 μm or less.

[0036] Next, the photosensitive resin layer will be described. The photosensitive resin layer preferably contains at least a binder resin, a compound having an ethylenic double bond, and a photopolymerization initiator. When the photosensitive resin layer is irradiated with light such as ultraviolet light in an imagewise manner, free radicals are generated from the photopolymerization initiator in the photosensitive resin layer in the exposed areas. The generated free radicals induce radical polymerization between compounds having an ethylenic double bond, and a crosslinked structure can form a relief for obtaining the desired printed image. When the binder resin has an ethylenic double bond, radical polymerization also occurs between the binder resin and the compound having an ethylenic double bond. This further promotes photocuring and improves the image reproducibility of the printing plate.

[0037] Examples of binder resins include styrene-butadiene copolymers, polybutadiene latex, styrene-butadiene copolymer latex, acrylonitrile-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, polyurethane, cellulose derivatives, polyester, polyacrylic acid derivatives, polyvinyl acetate, polyvinyl alcohol, polyvinylpyrrolidone, and polyamide. Two or more of these may be used. From the viewpoints of film-forming properties, water-developability, and adhesion to the intermediate layer or infrared-sensitive layer, polyvinyl alcohol is preferred.

[0038] The saponification degree of the polyvinyl alcohol is preferably 60 to 95 mol%. By setting the saponification degree of the polyvinyl alcohol in the photosensitive resin layer to 60 mol% or more, the solubility in a developer containing water as the main component can be improved. In particular, when the infrared-sensitive layer is removable with a developer containing water as the main component, the photosensitive resin layer and the infrared-sensitive layer can be developed together with a developer containing water as the main component. On the other hand, by setting the saponification degree of the polyvinyl alcohol in the photosensitive resin layer to 95 mol% or less, the compatibility with other components in the photosensitive resin layer can be improved and the migration of low-molecular-weight components to other layers can be suppressed. Here, the saponification degree of the polyvinyl alcohol can be measured in the same manner as the saponification degree of the polyvinyl alcohol contained in the infrared-sensitive layer. Furthermore, when the photosensitive layer contains two or more types of polyvinyl alcohol, the saponification degree refers to the saponification degree of the two or more types of polyvinyl alcohol as a whole.

[0039] The weight-average molecular weight of polyvinyl alcohol is preferably 10,000 or more and 200,000 or less. Here, the weight-average molecular weight can be determined by GPC measurement. More specifically, it can be measured using a gel permeation chromatograph-multiangle light scattering photometer manufactured by Wyatt Technology under conditions of a column temperature of 40°C and a flow rate of 0.7 mL / min, using polyethylene oxide and polyethylene glycol as standard samples.

[0040] The polyvinyl alcohol in the photosensitive resin layer preferably has an ethylenic double bond in the side chain. Examples of the group having an ethylenic double bond include a vinyl group, an acryloyl group, and a methacryloyl group. Two or more of these groups may be used.

[0041] Examples of methods for introducing ethylenic double bonds into polyvinyl alcohol include (1) a method in which the hydroxyl groups of polyvinyl alcohol are reacted with an acid anhydride, and a reactive group such as a carboxyl group is introduced into the polymer side chain starting from the hydroxyl group of the polyvinyl alcohol, and an unsaturated epoxy compound is reacted with the reactive group; and (2) a method in which a copolymer of vinyl acetate and an unsaturated carboxylic acid, an unsaturated carboxylate salt, and / or an unsaturated carboxylic acid ester is partially saponified, and the carboxyl groups of this polymer are reacted with an unsaturated epoxy compound.

[0042] The ethylenic double bond equivalent of polyvinyl alcohol is preferably 1,000 g / eq or more and 19,000 g / eq or less. By setting the ethylenic double bond equivalent to 1,000 g / eq or more, the hardness of the relief surface of the printing plate can be moderately suppressed, further improving printing reproducibility. On the other hand, by setting the ethylenic double bond equivalent to 19,000 g / eq or less, photocuring of the printing surface can be sufficiently promoted, improving image reproducibility and printing durability. Here, when the structure of polyvinyl alcohol is known, the ethylenic double bond equivalent can be calculated by dividing the theoretical weight per mole by the number of ethylenic double bonds contained in one molecule of polyvinyl alcohol. In addition, 1 The number of moles of ethylenic double bonds in polyvinyl alcohol is analyzed by H-NMR, and the ethylenic double bond equivalent can be calculated by dividing the weight of the sample used in the analysis by the number of moles of the detected ethylenic double bonds.

[0043] The content of polyvinyl alcohol in the photosensitive resin layer is preferably 30 to 85% by mass.

[0044] The photosensitive resin layer may contain, in addition to the polyvinyl alcohol, a binder resin having a hydrophilic group that is highly compatible with polyvinyl alcohol, or a binder resin whose polymer main chain is water-swellable or water-soluble. Examples of hydrophilic groups include carboxyl groups, amino groups, hydroxyl groups, phosphate groups, sulfonic acid groups, and salts thereof. Examples of polymers having hydrophilic groups include carboxylated styrene-butadiene latex, polymers of aliphatic conjugated dienes having carboxyl groups, emulsion polymers of ethylenically unsaturated compounds having phosphate groups and / or carboxyl groups, and sulfonic acid group-containing polyurethanes. Examples of polymers whose polymer main chain itself is water-swellable or water-soluble include vinyl alcohol-sodium acrylate copolymers, vinyl alcohol-sodium methacrylate copolymers, polyvinylpyrrolidone, polyether-containing polyamides, tertiary nitrogen atom-containing polyamides, polyethers, cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, starch, starch-sodium polyacrylate grafted products, saponified starch-polyacrylonitrile grafted products, cellulose-polyacrylic acid grafted products, partially crosslinked sodium polyacrylate, polyethylene glycol, polyethylene glycol derivatives, etc. Among these, tertiary nitrogen atom-containing polyamides are preferred in terms of their high physical strength, ability to further improve printing durability, and balance between strength and solubility in solvents.

[0045] The compound having an ethylenic double bond refers to a compound having an ethylenic double bond and a molecular weight of less than 10,000. The molecular weight of the compound having an ethylenic double bond is preferably 2,000 or less.

[0046] Examples of compounds having an ethylenic double bond include (meth)acrylates described in International Publication No. 2017 / 038970, glycerol di(meth)acrylate, (meth)acrylic acid adducts of propylene glycol diglycidyl ether, and tetrahydrofurfuryl (meth)acrylate. Two or more of these may be contained. Here, (meth)acrylate is a general term for acrylate and methacrylate, and (meth)acrylic acid is a general term for acrylic acid and methacrylic acid.

[0047] The content of the compound having an ethylenic double bond in the photosensitive resin layer is preferably 10 to 60% by weight.

[0048] As the photopolymerization initiator, one having the function of generating radicals by self-decomposition or hydrogen abstraction upon light absorption is preferably used. Examples thereof include benzoin alkyl ethers, benzophenones, anthraquinones, benzils, acetophenones, and diacetyls. Two or more of these may be contained.

[0049] The content of the photopolymerization initiator in the photosensitive resin layer is preferably 0.1 to 10% by mass.

[0050] The photosensitive resin layer may contain, as necessary, a compatibilizing aid, an ink repellent, a polymerization inhibitor, a dye, a pigment, a surfactant, an antifoaming agent, an ultraviolet absorber, a fragrance, and the like.

[0051] The inclusion of a miscible aid in the photosensitive resin layer can improve the compatibility of the components constituting the photosensitive resin layer, suppress the bleed-out of low-molecular-weight components, and improve the flexibility of the photosensitive resin layer. Examples of miscible aids include polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, and derivatives thereof. The content of the miscible aid in the photosensitive resin layer is preferably 30% by mass or less.

[0052] By including an ink repellent agent in the photosensitive resin layer, it is possible to prevent ink from penetrating into the recesses of the relief during printing, thereby improving reproducibility. Examples of ink repellent agents include silicone compounds and fluorine-containing compounds. The content of the ink repellent agent in the photosensitive resin layer is preferably 5% by mass or less.

[0053] By including a polymerization inhibitor in the photosensitive resin layer, thermal stability can be improved. Examples of polymerization inhibitors include phenols, hydroquinones, catechols, and hydroxyamine derivatives. One or more of these may be included. The content of the polymerization inhibitor in the photosensitive resin layer is preferably 0.001 to 5% by mass.

[0054] Next, the support will be described. Examples of the support include a plastic sheet made of polyester or the like, a synthetic rubber sheet made of styrene-butadiene rubber or the like, and a metal plate made of steel, stainless steel, aluminum or the like. From the viewpoints of handleability and flexibility, the thickness of the support is preferably in the range of 100 to 350 μm.

[0055] The support is preferably subjected to an easy-adhesion treatment, which can improve adhesion to the relief or floor layer. Examples of easy-adhesion treatment methods include mechanical treatments such as sandblasting, physical treatments such as corona discharge, and chemical treatments such as coating. Among these, from the viewpoint of adhesion, it is preferable to provide an easy-adhesion layer by coating.

[0056] Next, the method for producing a printing plate precursor of the present invention will be described using an example in which a photosensitive resin layer, an intermediate layer, an infrared-sensitive layer and a protective film are provided on a support.

[0057] For example, polyvinyl alcohol, a compound having an ethylenic double bond, and other additives are dissolved in a solvent with heating to obtain a photosensitive resin composition solution, such as a water / alcohol mixed solvent.

[0058] A photosensitive resin composition solution is cast onto a support having an easy-adhesion layer, if necessary, and dried to form a photosensitive resin layer. Next, a protective film having an intermediate layer and an infrared-sensitive layer formed thereon is adhered to the photosensitive resin layer to obtain a photosensitive resin printing plate precursor. For example, a protective film having an intermediate layer and an infrared-sensitive layer formed thereon can be produced by coating an infrared-sensitive layer composition dispersion containing the above-mentioned infrared-sensitive layer components onto the protective film, drying it, and then coating an intermediate layer composition solution containing the above-mentioned intermediate layer components, and drying it.

[0059] A method for producing a printing plate using the printing plate precursor of the present invention will now be described. The method preferably includes an exposure step of partially photocuring the photosensitive resin layer of the printing plate precursor, and a development step of removing the uncured portions of the photosensitive resin layer with a liquid containing water.

[0060] In the exposure step, the photosensitive resin printing plate precursor from which the protective film has been peeled off is attached to a digital imager equipped with an infrared laser such as a fiber laser, and the infrared-sensitive layer is decomposed and ablated (ablated) to form an image mask. Then, ultraviolet light having a wavelength of 300 to 400 nm is irradiated through the image mask formed from the infrared-sensitive layer to photocure the exposed areas of the photosensitive resin layer. Examples of exposure light sources include high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, carbon arc lamps, chemical lamps, and UV-LED lamps.

[0061] In the developing step, it is preferable to remove the photosensitive resin layer in the unexposed areas with a liquid containing water. Examples of the developing device include a spray type developing device and a brush type washing machine.

[0062] Furthermore, if necessary, a post-exposure step of irradiating with ultraviolet light may be carried out after development. The post-exposure step can make the relief stronger by reaction of the compound having an unreacted ethylenic double bond.

[0063] The photosensitive resin printing plate precursor of the present invention and the printing plate obtained using the same can be used for letterpress printing using a label printing rotary press or an intermittent rotary press, dry offset printing, flexographic printing, etc. Among these, it is more preferably used for letterpress printing and dry offset printing. [Example]

[0064] The present invention will be described in detail below with reference to examples.

[0065] <Synthesis of polymer for photosensitive resin layer> (Synthesis Example 1) Partially saponified polyvinyl alcohol "GOHSENOL" (registered trademark) KL-05 (Mitsubishi Chemical Corporation) (average degree of polymerization: 500, degree of saponification: 80 mol%, Mw: 38,000) was swollen in acetone, and 4.2 parts by mass of succinic anhydride was added to 100 parts by mass of "GOHSENOL" KL-05. The mixture was stirred at 60°C for 6 hours to add carboxyl groups to the molecular chains. The polymer was washed with acetone to remove unreacted succinic anhydride and then dried. 100 parts by mass of this polymer was dissolved in 200 parts by mass of a 30 / 70 (weight ratio) ethanol / water mixed solvent at 80°C. 6 parts by mass of glycidyl methacrylate was added to the solution to introduce ethylenic double bonds into the partially saponified polyvinyl alcohol, yielding a solution of Polymer A. The resulting Polymer A had an ethylenic double bond equivalent of 5,611 g / eq and a weight-average molecular weight of 40,000. The weight-average molecular weight was measured using a gel permeation chromatograph-multiangle light scattering photometer manufactured by Wyatt Technology under the conditions of a column temperature of 40°C and a flow rate of 0.7 mL / min, using polyethylene oxide and polyethylene glycol as standard samples. The ethylenic double bond equivalent was measured by dissolving 30 mg of polymer A in 1 mL of a heavy water / heavy methanol mixed solvent containing sodium 3-(trimethylsilyl)propionate-2,2,3,3d4 as an internal standard. 1 H-NMR measurement was carried out to measure the number of moles of ethylenic double bonds, and the amount of polymer A in the sample used for analysis was divided by the number of moles of the detected ethylenic double bonds to calculate the molecular weight.

[0066] (Synthesis Example 2) 20 parts by mass of ε-caprolactam, 80 parts by mass of nylon salt of N-(2-aminoethyl)piperazine and adipic acid, and 100 parts by mass of water were placed in a stainless steel autoclave, and after the air inside was replaced with nitrogen gas, the autoclave was heated at 180°C for 1 hour, and then the water was removed to obtain a water-soluble polyamide resin having tertiary amino groups (Polymer B). The weight-average molecular weight of the obtained Polymer B, measured in the same manner as in Synthesis Example 1, was 72,000.

[0067] <Preparation of a support having an easy-adhesion layer> A mixture of 260 parts by weight of "Vylon" (registered trademark) 31SS (a toluene solution of unsaturated polyester resin, manufactured by Toyobo Co., Ltd.) and 2 parts by weight of PS-8A (benzoin ethyl ether, manufactured by Wako Pure Chemical Industries, Ltd.) was heated at 70°C for 2 hours, cooled to 30°C, and 7 parts by weight of ethylene glycol diglycidyl ether dimethacrylate was added and mixed for 2 hours. 25 parts by weight of "Coronate" (registered trademark) 3015E (an ethyl acetate solution of polyisocyanate resin, manufactured by Tosoh Corporation) and 14 parts by weight of EC-1368 (an industrial adhesive, manufactured by Sumitomo 3M Limited) were then added and mixed to obtain a coating solution for an easy-adhesion layer.

[0068] The coating liquid for the easy-adhesion layer obtained by the above-mentioned method was applied to a 250 μm-thick "Lumilar" (registered trademark) T60 (polyester film, manufactured by Toray Industries, Inc.) using a bar coater so that the thickness after drying would be 30 μm, and the coating liquid was heated in an oven at 180°C for 3 minutes to remove the solvent, thereby obtaining a support having an easy-adhesion layer.

[0069] <Preparation of Photosensitive Resin Layer Composition Solution> Into a three-neck flask equipped with a stirring spatula and a condenser, 45 parts by mass of Polymer A obtained in Synthesis Example 1 and 5 parts by mass of Polymer B obtained in Synthesis Example 2 were added, and a mixed solvent of 50 parts by mass of "Solmix" (registered trademark) H-11 (alcohol mixture, manufactured by Nippon Alcohol Co., Ltd.) and 50 parts by mass of water was added, and the mixture was heated at 90°C for 2 hours with stirring to dissolve the polymers. After the resulting mixture was cooled to 70°C, 5 parts by weight of 2-hydroxy-3-phenoxypropyl acrylate, 15 parts by weight of glycerol dimethacrylate, 15 parts by weight of polyalkylene glycol (PEG200) diacrylate, 1.3 parts by weight of 2,2-dimethoxy-1,1-diphenylethan-1-one, 10 parts by weight of pentaerythritol polyoxyethylene ether, 0.2 parts by weight of N-(ammoniumoxy)-N-nitrosophenylamine, and 0.02 parts by weight of 2,4-di-tert-butyl-6-(5-chloro-2H-1,2,3-benzotriazol-2-yl)phenol were added and stirred for 30 minutes to obtain a photosensitive resin layer composition solution.

[0070] <Preparation of Infrared-Sensing Layer Composition Dispersion> To 5 parts by weight of the polyvinyl alcohol shown in Table 1, 95 parts by weight of a 10 / 90 ethanol / water mixed solvent was added, and the mixture was heated and dissolved at 75°C for 2 hours to prepare a 5% by weight aqueous solution. 50 parts by weight of the resulting 5% by weight aqueous solution of polyvinyl alcohol, 30 parts by weight of a 10% by weight aqueous dispersion of carbon black obtained by further diluting a carbon black aqueous dispersion (Bonjet Black CW-1, manufactured by Orient Chemical Industry Co., Ltd.) with water, and 20 parts by weight of "Solmix" (registered trademark) H-11 (an alcohol mixture, manufactured by Nippon Alcohol Co., Ltd.) were mixed at room temperature to obtain dispersions of infrared-sensitive layer compositions 1 to 6. The dispersibility of the carbon black in the dispersions of infrared-sensitive layer compositions 1 to 6 was good, and no aggregates larger than 2 μm were confirmed using a grind gauge. The degree of saponification and degree of polymerization of the polyvinyl alcohol were measured according to JIS K 6726-1994 (Testing Methods for Polyvinyl Alcohol).

[0071] [Table 1]

[0072] <Preparation of Intermediate Layer Composition Solution> 54 parts by mass of ethanol and 36 parts by mass of pure water were added to 10 parts by mass of polyvinyl alcohol (JP-18 (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., saponification degree 88%, average polymerization degree 1,800)), and the mixture was heated and dissolved at 75°C for 2 hours to obtain an intermediate layer composition solution.

[0073] The evaluation methods used in the examples and comparative examples are as follows.

[0074] <Surface energy of protective film> The surface energy of the protective film was measured in accordance with the wetting tension test method for plastic films and sheets described in JIS K6768 (1999). Specifically, using Fujifilm Wako Pure Chemical Industries, Ltd.'s wetting tension test mixtures of 22.6, 27.3, 30.0-48.0 (in 3.0 mN / m increments), 52.0, 56.0, 60.0, 63.0, 67.0, 70.0, and 73.0, one drop of the test mixture, starting with the lowest surface tension, was dispensed onto the infrared-sensitive layer side of the protective film used in each Example and Comparative Example. The liquid film was then quickly spread using a cotton swab, and the state of the liquid film was observed. If the surface was wet, the next highest surface tension test mixture was used and similar observations were made. The surface tension value of the test mixture when the liquid repelled and the liquid film broke was taken as the surface energy of the protective film.

[0075] <Protection film thickness> For the protective films used in each example and comparative example, the thickness was measured at three points spaced 5 cm apart using a Digimatic Thickness Gauge (ID-C112 manufactured by Mitutoyo Corporation), and the average value was calculated to determine the thickness of the protective film.

[0076] <Protection film line roughness> The surface of the protective film used in each example and comparative example was observed under magnification of 20x using a laser microscope (VK-X250) manufactured by Keyence Corporation. Three straight lines, each 300 μm long, were drawn randomly on the observation surface, and the average value of the line roughness on the three straight lines was calculated and used as the line roughness of the protective film surface.

[0077] <Variations in optical density of the infrared-sensitive layer> The protective film / infrared-sensitive layer laminate obtained in each example and comparative example was cut to A4 size (297 mm long x 210 mm wide). The protective film / infrared-sensitive layer laminate was divided into 30 grids (each grid was approximately 50 mm long x 40 mm wide), and the optical density of each grid was measured using a Macbeth transmission densitometer "TR-927." The standard deviation (σ) was calculated for the optical densities of the 30 grids obtained, and the variation in optical density was evaluated.

[0078] <Protective film adhesion> The printing plate precursors obtained in each Example and Comparative Example were cut into strips measuring 25 cm long x 5 cm wide. Approximately 3 cm of the protective film on the short side of the strip-shaped printing plate precursor was peeled off, and the plate was then fixed to the measurement table of a tensile tester (Shimadzu Corporation: Autograph AGS-X). The protective film was peeled off at a speed of 200 mm / min at an angle of 180°, and the peel resistance value was measured. This value was divided by the sample width of 5 cm to obtain the peel force. A peel force of 20 mN / cm or more was considered to have excellent adhesion.

[0079] [Example 1] A photosensitive resin layer composition solution was cast onto the easy-adhesion layer of the support having the easy-adhesion layer obtained by the above-mentioned method, and dried for 2 hours at 60° C. to form a photosensitive resin layer with a thickness of 650 μm. The thickness of the photosensitive resin layer was adjusted by placing a spacer of a predetermined thickness on the support having the easy-adhesion layer and scraping off the protruding portion of the photosensitive resin layer composition solution with a horizontal metal ruler.

[0080] Next, the dispersion of infrared-sensitive layer composition 1 obtained by the above-mentioned method was applied using a bar coater to a 100 μm-thick PET film KSP-AN (manufactured by Higashiyama Film Co., Ltd.) serving as a protective film, and the coating was dried for 30 seconds in a hot air oven at 120°C to form an infrared-sensitive layer, thereby obtaining a protective film / infrared-sensitive layer laminate. The thickness of the infrared-sensitive layer was adjusted so that the optical density (transmission mode of a Macbeth transmission densitometer "TR-927" (manufactured by Kollmorgen Instruments Corp.)) using an orthochromatic filter with the value of the protective film set to zero was 3.0.

[0081] The intermediate layer composition solution obtained by the above-mentioned method was applied to the obtained protective film / infrared-sensitive layer laminate using a bar coater so that the thickness after drying would be 0.2 μm, and then dried for 30 seconds in a hot air oven at 120°C to form an intermediate layer, thereby obtaining a protective film / infrared-sensitive layer / intermediate layer laminate. A mixed solvent of 50 parts by mass of water and 50 parts by mass of ethanol was applied to the photosensitive resin layer formed by the above-mentioned method, and the intermediate layer / infrared-sensitive layer / protective film laminate was laminated so that the intermediate layer side was on top of the photosensitive resin layer, thereby obtaining printing plate precursor 1. The results of evaluation using the above-mentioned methods are shown in Table 2.

[0082] [Examples 2 to 6] A printing plate precursor was obtained in the same manner as in Example 1, except that the infrared-sensitive layer composition was changed to one shown in Table 1. The evaluation results are shown in Table 2.

[0083] [Example 7] A printing plate precursor was obtained in the same manner as in Example 1, except that the protective film was changed to a 125 μm thick PET film #125 PET corona-treated product (manufactured by Toyo Shinko Co., Ltd.). The evaluation results are shown in Table 2.

[0084] [Comparative Examples 1 to 7] A printing plate precursor was obtained in the same manner as in Example 1, except that the protective film was changed to one shown in Table 3. The evaluation results are shown in Table 3.

[0085] [Table 2]

[0086] Table 3

Claims

1. A photosensitive resin printing plate precursor having a photosensitive resin layer, an infrared-sensitive layer, and a protective film in this order on a support, wherein the surface energy of the protective film on the infrared-sensitive layer side is 50 mN / m or more.

2. 2. The photosensitive resin printing plate precursor according to claim 1, wherein the protective film is a polyester film.

3. 3. The photosensitive resin layer printing plate precursor according to claim 1, wherein the protective film has a surface having a line roughness Ra of 0.01 to 0.20 μm on the infrared-sensitive layer side.

4. 4. The photosensitive resin printing plate precursor according to claim 1, wherein the infrared-sensitive layer contains polyvinyl alcohol having a saponification degree of 60 to 100 mol %.

5. 5. The photosensitive resin printing plate precursor according to claim 1, wherein the infrared-sensitive layer contains polyvinyl alcohol having a degree of polymerization of 1,000 to 3,500.

6. 6. The photosensitive resin printing plate precursor according to claim 1, wherein the infrared-sensitive layer contains carbon black having a carboxyl group and / or a sulfo group.

7. 7. The photosensitive resin printing plate precursor according to claim 6, wherein the carbon black has a carboxyl group and a lactone group.

8. The photosensitive resin printing plate precursor according to any one of claims 1 to 7, wherein the protective film and the infrared-sensitive layer are in contact with each other.

9. 9. The photosensitive resin printing plate precursor according to claim 1, wherein the photosensitive resin layer contains polyvinyl alcohol and / or polyamide.

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