Photosensitive resin composition for flexographic printing plate and flexographic printing plate produced using the same

Abstract

To provide a photosensitive resin composition for a flexographic printing plate, allowing accurate reproduction of a microcell pattern on the surface of a flexographic printing plate even in the absence of an oxygen barrier layer and without special apparatus or additional steps, while exhibiting excellent reproducibility of isolated dots, and a flexographic printing plate produced using the same.SOLUTION: A photosensitive resin composition for flexographic printing plates comprises (A) a conjugated diene polymer, (B) a photopolymerizable unsaturated compound, (C) a photopolymerization initiator, and (D) an oxygen inhibition suppressant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a photosensitive resin composition for a flexographic printing plate precursor and a flexographic printing plate precursor obtained using the same. [Background technology]

[0002] Flexographic printing is a printing method in which ink is applied to the raised areas of a printing plate and then pressed against the substrate, transferring the ink from the plate to the substrate. The printing plates used in flexographic printing are relatively flexible and can conform to various shapes, allowing for printing on a wide range of substrates. Substrates include packaging film, label paper, beverage cartons, paper containers, envelopes, and cardboard. Flexographic printing is primarily used on substrates with rough surfaces. Flexographic printing is also environmentally friendly, as it can use water-based or alcohol-based inks with low VOC emissions. These advantages, such as substrate adaptability and environmental friendliness, are driving a shift from gravure and offset printing to flexographic printing.

[0003] On the other hand, flexographic printing has the problem that ink adhesion in solid areas is inferior to gravure printing when the printing substrate is film. One method for improving ink adhesion in solid areas in flexographic printing is to increase the physical pressure between the printing plate and the substrate. However, the pressure can deform the fine dot areas, impairing the printability of the fine dots.

[0004] Another method for improving ink coverage in solid areas of flexographic printing is to create microcells on the surface of the solid areas of the printing plate. Microcells are specific micro-convex and concave patterns formed on the surface of the solid areas of the printing plate. By creating microcells on the surface, the ink can be given appropriate mobility when the printing plate and the printing substrate are pressed together, improving the uniformity of ink distribution in the solid areas.

[0005] A flexographic printing plate precursor, which is a precursor material for obtaining a printing plate for flexographic printing, usually has a structure in which a photosensitive resin layer and an infrared ablation layer are laminated on a support. The photosensitive resin composition that forms the photosensitive resin layer generally contains a polymer compound such as an elastomer, a photopolymerizable unsaturated compound, and a photopolymerization initiator as essential components, and may also contain additives such as a stabilizer and a plasticizer, as necessary.

[0006] However, the photosensitive resin layer of a flexographic printing plate precursor may be inhibited by polymerization due to oxygen. In such cases, the crosslinking reaction in the photosensitive resin layer does not proceed sufficiently during exposure, and the surface of the photosensitive resin layer is washed out during the development process, resulting in the problem that the microcell pattern cannot be faithfully reproduced on the surface of the flexographic printing plate.

[0007] To address the above-mentioned problem and to faithfully reproduce the microcell pattern, a method has been proposed in which an oxygen barrier layer is provided between the photosensitive resin layer and the infrared ablation layer of the flexographic printing plate to suppress oxygen polymerization inhibition (see Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. WO2021 / 039263 [Non-patent literature]

[0009] [Non-Patent Document 1] Journal of the Japanese Society of Printing Science, Vol. 43, No. 4 (2006), pp. 261-271 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the flexographic printing plate precursor of Patent Document 1 has good microcell pattern reproducibility and excellent ink adhesion in solid areas, but it requires the provision of an oxygen barrier layer. Recently, wrinkles can occur in the oxygen barrier layer at low temperatures and low humidity, and there has been a demand for flexographic printing plate precursors that do not have an oxygen barrier layer. When an oxygen barrier layer is not provided, if a large amount of photopolymerization initiator is used, oxygen inhibition is suppressed to some extent, but there is a problem in that independent point reproducibility cannot be obtained.

[0011] The present invention was made in view of the current state of the prior art. That is, an object of the present invention is to provide a photosensitive resin composition for a flexographic printing plate precursor that can faithfully reproduce a microcell pattern on the surface of a flexographic printing plate without providing an oxygen barrier layer or requiring any special equipment or additional steps, and that has excellent reproducibility of isolated points, and a flexographic printing plate precursor using the same. [Means for solving the problem]

[0012] That is, the present invention comprises the following configurations. Item 1. A photosensitive resin composition for a flexographic printing original plate, comprising (A) a conjugated diene polymer, (B) a photopolymerizable unsaturated compound, (C) a photopolymerization initiator, and (D) an oxygen inhibition suppressor. Item 2. The photosensitive resin composition for a flexographic printing original plate according to Item 1, wherein the (D) oxygen inhibition suppressor has at least two prenyl groups in the molecule. Item 3. The photosensitive resin composition for a flexographic printing original plate according to Item 1 or 2, wherein the (D) oxygen inhibition suppressor is a compound having a molecular structure in which the prenyl groups are bonded to each other via ether bonds. Item 4. The photosensitive resin composition for flexographic printing original plates according to any one of Items 1 to 3, wherein the (D) oxygen inhibition suppressor is a compound having one or more hydroxyl groups in the molecule. Item 5. The photosensitive resin composition for flexographic printing original plates according to any one of Items 1 to 4, wherein the (D) oxygen inhibition suppressor is contained in an amount of 0.3 to 8 mass % in the photosensitive resin composition. Item 6. The photosensitive resin composition for a flexographic printing original plate according to any one of Items 1 to 5, wherein the (C) photopolymerization initiator is at least one selected from the group consisting of benzoin alkyl ethers, benzophenones, anthraquinones, benzils, and acetophenones, and is contained in an amount of 0.5 to 9% by mass in the photosensitive resin composition. Item 7. The photosensitive resin composition for a flexographic printing original plate according to any one of Items 1 to 6, wherein the (B) photopolymerizable unsaturated compound includes a photopolymerizable unsaturated compound having a number-average molecular weight of 100 or more and 600 or less, and a photopolymerizable unsaturated compound having a number-average molecular weight of more than 600 and 20,000 or less. Item 8. The photosensitive resin composition for a flexographic printing plate precursor according to any one of Items 1 to 7, which has water-developability. Item 9. A flexographic printing original plate comprising a photosensitive resin layer made of the photosensitive resin composition according to any one of items 1 to 8, and at least a support, the photosensitive resin layer, and an infrared ablation layer laminated in this order. Item 10. A method for producing a flexographic printing plate, which is obtained by exposing and developing the flexographic printing plate precursor according to Item 9, and which has microcells in solid areas. [Effects of the Invention]

[0013] According to the present invention, since oxygen polymerization inhibition can be suppressed without providing an oxygen barrier layer or without any special equipment or additional process, a microcell pattern can be faithfully reproduced on the surface of a flexographic printing plate. As a result, it is possible to provide a photosensitive resin composition for a flexographic printing plate precursor that exhibits good ink adhesion in solid areas of a printing substrate and excellent reproducibility of isolated points, and a flexographic printing plate precursor using the same. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below.

[0015] <Photosensitive resin composition> The photosensitive resin composition for a flexographic printing plate precursor according to this embodiment is a composition for forming a photosensitive resin layer in a flexographic printing plate precursor, which serves as a precursor material for obtaining a printing plate for flexographic printing.

[0016] The photosensitive resin composition for a flexographic printing plate precursor of the present invention contains (A) a conjugated diene polymer, (B) a photopolymerizable unsaturated compound, (C) a photopolymerization initiator, and (D) an oxygen inhibition suppressor.

[0017] <(A) Conjugated Diene Polymer> The present invention contains (A) a conjugated diene polymer. (A) Conjugated diene polymer is obtained by polymerizing a conjugated diene. Specific examples include polymers obtained by polymerizing a conjugated diene hydrocarbon, and copolymers obtained by copolymerizing a conjugated diene hydrocarbon with a monoolefin-based unsaturated compound. Examples include butadiene polymers, isoprene polymers, chloroprene polymers, styrene-butadiene copolymers, styrene-butadiene-styrene copolymers, styrene-isoprene copolymers, styrene-isoprene-styrene copolymers, styrene-chloroprene copolymers, acrylonitrile-butadiene copolymers, acrylonitrile-isoprene copolymers, methyl methacrylate-butadiene copolymers, methyl methacrylate-isoprene copolymers, acrylonitrile-butadiene-styrene copolymers, and acrylonitrile-isoprene-styrene copolymers. These polymers may be copolymerized with hydrophilic groups such as carboxyl groups, sulfonic acid groups, or polyalkylene glycols. Component (A) may be used alone or in combination.

[0018] From the viewpoints of the properties required for a flexographic printing plate, i.e., the impact resilience, strength-elongation properties, and hardness of the printing plate surface, and the properties required for a flexographic printing plate precursor, i.e., dimensional stability in the unexposed state, water-developability, etc., the conjugated diene polymer (A) is preferably a latex. Specifically, it preferably contains one or more latexes selected from the group consisting of butadiene latex, acrylonitrile-butadiene latex, styrene-butadiene latex, and isoprene latex, and it is more preferable from the viewpoint of water-developability to contain both butadiene latex and acrylonitrile-butadiene latex.

[0019] The conjugated diene polymer (A) is preferably intramolecularly crosslinked, and may be modified with (meth)acrylic, carboxy, silicone, fluorine, or the like, if desired.

[0020] The conjugated diene polymer (A) is preferably a water-dispersed latex because it provides superior water-developability and the effects of the present invention. The conjugated diene polymer (A) is preferably a polymer obtained by removing water from a water-dispersed latex. When a water-dispersed latex is used, it may be added as a water-dispersed latex as is, or may be added as a solid resin after drying to remove water. Many different synthetic and natural water-dispersed latexes are commercially available, so an appropriate one can be selected from these. Hereinafter, "being able to faithfully reproduce a microcell pattern on the surface of a flexographic printing plate and / or having excellent reproducibility of independent points" is also referred to as "having superior effects, etc., of the present invention."

[0021] The content of component (A) in the photosensitive resin composition of the present invention is preferably 10 to 80% by mass, more preferably 20 to 75% by mass. When the amount of component (A) is within this range, the effects of the present invention are more excellent, and a good balance between the strength and developability of the flexographic printing plate can be achieved.

[0022] <(B) Photopolymerizable unsaturated compound> The present invention contains (B) a photopolymerizable unsaturated compound. (B) The photopolymerizable unsaturated compound usually has one or more photopolymerizable unsaturated groups. In the present invention, the photopolymerizable unsaturated group refers to an unsaturated group that can undergo radical polymerization by light.

[0023] The photopolymerizable unsaturated group is preferably at least one selected from the group consisting of a (meth)acryloyl group and a (meth)acryloyloxy group.

[0024] As the (B) photopolymerizable unsaturated compound, any known compound used in a flexographic printing plate precursor can be used, but it is preferable to use a photopolymerizable unsaturated compound having a number average molecular weight of 100 or more and 600 or less.

[0025] Examples of photopolymerizable unsaturated compounds having a number average molecular weight of 100 to 600 include linear, branched, and cyclic monofunctional monomers such as hexyl (meth)acrylate, nonane (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, 2-butylpropanediol (meth)acrylate, hydroxyethyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxyethyl phthalate, (meth)acrylic acid dimer, ECH-modified allyl acrylate, benzyl acrylate, caprolactone (meth)acrylate, dicyclopentenyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and cyclohexyl (meth)acrylate. Also, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, dodecanediol di(meth)acrylate, 2-butyl-2-ethylpropane di(meth)acrylate, neopentyl glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, ECH-modified phthalic acid di(meth)acrylate, dicyclopentadiene di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate and linear, branched, and cyclic polyfunctional compounds such as glycerol tri(meth)acrylate, 5-hydroxy-1,3-adamantyl di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ECH-modified glycerol tri(meth)acrylate, trimethylolpropane benzoate (meth)acrylate, EO(PO)-modified trimethylolpropane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. These compounds may be used alone, or two or more may be used in combination to improve the physical properties of the desired flexographic printing plate.

[0026] From the viewpoint of achieving the effects of the present invention, the photopolymerizable unsaturated compound having a number average molecular weight of 100 or more and 600 or less preferably has one, two, three, or four photopolymerizable unsaturated groups, more preferably has two, three, or four photopolymerizable unsaturated groups, more preferably has two or three photopolymerizable unsaturated groups, and even more preferably has three photopolymerizable unsaturated groups.

[0027] The (B) photopolymerizable unsaturated compound preferably includes a photopolymerizable unsaturated compound having a number-average molecular weight of more than 600 and not more than 20,000, in addition to a photopolymerizable unsaturated compound having a number-average molecular weight of 100 to 600. Here, the photopolymerizable unsaturated compound having a number-average molecular weight of 100 to 600 is crosslinked and cured by a photopolymerization initiator to form a dense crosslinked network, while the photopolymerizable unsaturated compound having a number-average molecular weight of more than 600 and not more than 20,000 is crosslinked and cured by a photopolymerization initiator to form a loose crosslinked network. By combining these, it is possible to more faithfully reproduce the microcell pattern on the surface of the flexographic printing plate and achieve better reproducibility of isolated points.

[0028] Examples of photopolymerizable unsaturated compounds having a number average molecular weight of more than 600 and not more than 20,000 include polymers in which photopolymerizable unsaturated groups are bonded to the terminals and / or side chains of conjugated diene polymers, and urethane (meth)acrylates. Examples of conjugated diene polymers include butadiene polymers, isoprene polymers, chloroprene polymers, styrene-chloroprene copolymers, acrylonitrile-butadiene copolymers, acrylonitrile-isoprene copolymers, methyl methacrylate-isoprene copolymers, acrylonitrile-isoprene copolymers, methyl methacrylate-isoprene copolymers, methyl methacrylate-chloroprene copolymers, methyl acrylate-butadiene copolymers, methyl acrylate-isoprene copolymers, methyl acrylate-chloroprene copolymers, methyl acrylate-chloroprene copolymers, acrylonitrile-butadiene-styrene copolymers, and acrylonitrile-chloroprene-styrene copolymers. Among these, butadiene polymers, isoprene polymers, and acrylonitrile-butadiene copolymers are preferred in terms of rubber elasticity and photocurability, and butadiene polymers and isoprene polymers are particularly preferred. These compounds may be used alone or in combination of two or more to improve the physical properties of the desired flexographic printing plate.

[0029] The photopolymerizable unsaturated compound having a number-average molecular weight of more than 600 and not more than 20,000 preferably has a number-average molecular weight of 1,000 or more and 15,000 or less, more preferably 1,500 or more and 10,000 or less, and even more preferably 2,000 or more and 6,000 or less, from the viewpoints of being able to more faithfully reproduce a microcell pattern on the surface of a flexographic printing plate and achieving even better reproducibility of independent points.

[0030] From the viewpoint of achieving the effects of the present invention, the photopolymerizable unsaturated group-containing compound having a number average molecular weight of more than 600 and not more than 20,000 preferably has one, two, three, or four photopolymerizable unsaturated groups, more preferably one, two, or three photopolymerizable unsaturated groups, even more preferably two or three photopolymerizable unsaturated groups, and even more preferably two photopolymerizable unsaturated groups. Furthermore, it is preferable that the photopolymerizable unsaturated group is present at a terminal, and more preferably at both terminals.

[0031] The content of component (B) in the photosensitive resin composition of the present invention is preferably 5 to 50% by mass, more preferably 8 to 35% by mass, and even more preferably 15 to 30% by mass. Within this range, the microcell pattern can be more faithfully reproduced on the surface of the flexographic printing plate, and the reproducibility of isolated points can be further improved. A good balance can also be achieved between the toughness of the printing plate and the hardness as a printing plate.

[0032] The content of the photopolymerizable unsaturated compound having an average molecular weight of 100 or more and 600 or less in the photosensitive resin composition of the present invention is preferably 2 to 20 mass %, more preferably 5 to 16 mass %, and even more preferably 7 to 13 mass %, from the viewpoints of being able to more faithfully reproduce a microcell pattern on the surface of a flexographic printing plate and achieving more excellent reproducibility of independent points.

[0033] The content of the photopolymerizable unsaturated compound having a number average molecular weight of more than 600 and not more than 20,000 in the photosensitive resin composition of the present invention is preferably 3 to 30 mass%, more preferably 10 to 25 mass%, and even more preferably 15 to 23 mass%, for reasons such as better effects of the present invention.

[0034] In the photosensitive resin composition of the present invention, the ratio of the content of the photopolymerizable unsaturated compound having a number-average molecular weight of 100 or more and 600 or less to the content of the photopolymerizable unsaturated compound having a number-average molecular weight of more than 600 and 20,000 or less is preferably 2.0 or less, more preferably 1.0 or less, and even more preferably 0.7 or less, in terms of mass ratio, from the viewpoints of being able to more faithfully reproduce a microcell pattern on the surface of a flexographic printing plate and achieving even better reproducibility of independent points. There is no particular lower limit to this ratio, but it is preferably 0.1 or more, more preferably 0.2 or more.

[0035] The number average molecular weight of the (B) photopolymerizable unsaturated compound can be measured by gel permeation chromatography (GPC). Measurement of the number average molecular weight by gel permeation chromatography (GPC) can be performed, for example, under the following conditions. GPC device: HLC-8320GPC (Tosoh Corporation) Column: TSKGel Super HM-H × 2 + TSKGel Super H2000 (Tosoh Corporation) Mobile phase: chloroform Flow rate: 0.6ml / min Concentration: 0.1% Column temperature: 40℃ Detector: RI, UV 254 nm Conversion: Polystyrene

[0036] <(C) Photopolymerization initiator> The present invention contains (C) a photopolymerization initiator. The photopolymerization initiator (C) is not particularly limited as long as it can polymerize a polymerizable carbon-carbon unsaturated group by light. Among these, those that have the function of generating radicals by self-decomposition or hydrogen abstraction upon light absorption are preferably used. Examples of such photopolymerization initiators include benzoin alkyl ethers, benzophenones, anthraquinones, benzils, acetophenones, and diacetyls. Specific examples include benzophenone, chlorobenzophenone, benzoin, acetophenone, benzil, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzil dimethyl ketal, benzil diethyl ketal, benzil diisopropyl ketal, anthraquinone, 2-ethylanthraquinone, 2-methylanthraquinone, 2-allylanthraquinone, 2-chloroanthraquinone, thioxanthone, 2-chlorothioxanthone, and 1-hydroxycyclohexan-1-yl phenyl ketone. From the viewpoint of efficiently utilizing the light energy of exposure and exposure by a germicidal lamp, of being able to more faithfully reproduce a microcell pattern on the surface of a flexographic printing plate, and of achieving even better reproducibility of independent points, the photopolymerization initiator preferably contains at least one selected from the group consisting of benzoin alkyl ethers, benzophenones, anthraquinones, benzils, and acetophenones. Of these, it is more preferable to use a benzyl alkyl ketal-based or benzophenone-based photopolymerization initiator, and these two types may be used in combination.

[0037] In one embodiment, the content of component (C) in the photosensitive resin composition is preferably 0.5 to 9 mass%, more preferably 3 to 7 mass%, for reasons of better effects of the present invention, etc. Furthermore, within the above content range, the curing reaction proceeds efficiently from the surface to the depth of the photosensitive resin composition, resulting in even better reproducibility of isolated points.

[0038] <(D) Oxygen Inhibitor> The present invention contains (D) an oxygen inhibition inhibitor. By including (D) an oxygen inhibition inhibitor, the photosensitive resin composition of the present invention exhibits high performance in suppressing oxygen polymerization inhibition during exposure, allowing faithful reproduction of a microcell pattern on the surface of the flexographic printing plate without providing an oxygen barrier layer, and excellent reproducibility of isolated points.

[0039] (D) The oxygen inhibition suppressor preferably has at least two or more prenyl groups in one molecule. Examples of prenyl groups include dimethylallyl, geranyl, farnesyl, geranylgeranyl, geranylfarnesyl, and hexaprenyl groups. The prenyl group preferably has a dimethylallyl or geranyl group, and more preferably has a dimethylallyl group.

[0040] In one embodiment, the oxygen inhibition suppressor (D) preferably has at least two or more prenyl groups in the molecule, from the viewpoint of further achieving the effects of the present invention. It is more preferable that the molecule has 2, 3, 4, 5, 6, 7, or 8 prenyl groups, even more preferably 2, 3, 4, 5, or 6 prenyl groups, even more preferably 2, 3, or 4 prenyl groups, and even more preferably 2 or 3 prenyl groups. It is particularly preferable that the molecule has 2 prenyl groups.

[0041] In one embodiment, the (D) oxygen inhibition suppressor preferably has prenyl groups at both ends of the compound, from the viewpoint of further exhibiting the effects of the present invention.

[0042] In one embodiment, the oxygen inhibition suppressor (D) is preferably a compound having a molecular structure in which prenyl groups are bonded to each other via ether bonds, in order to further enhance the effects of the present invention.

[0043] In one embodiment, the oxygen inhibition suppressor (D) is preferably a compound having at least two prenyl groups and one or more hydroxyl groups in the molecule, for reasons such as better effects of the present invention.

[0044] In one embodiment, the oxygen inhibition suppressor (D) is preferably a compound having prenyl groups at both ends, a molecular structure in which the prenyl groups are bonded by ether bonds, and a hydroxyl group within the molecule, from the viewpoint of further achieving the effects of the present invention.

[0045] In one embodiment, the (D) oxygen inhibition suppressor has Formula 1: R 1 -OXOR 2 formula 1 (In formula 1, R 1 , R 2 each independently represents a prenyl group. X represents a linear or branched alkylene group having 1 to 15 carbon atoms which may have a hydroxyl group, a (meth)acryloyl group, a styryloxy group, or an alkenyloxy group. It is preferable that the compound is a compound represented by the following formula:

[0046] In the above formula 1, X preferably represents a linear or branched alkylene group having 1 to 10 carbon atoms which may have a hydroxyl group, a (meth)acryloyl group, a styryloxy group, or an alkenyloxy group.

[0047] In the above formula 1, X more preferably represents a linear or branched alkylene group having 1 to 6 carbon atoms which may have a hydroxyl group, a (meth)acryloyl group, a styryloxy group, or an alkenyloxy group.

[0048] In the above formula 1, X more preferably represents a hydroxyl group or a linear or branched alkylene group having 1 to 6 carbon atoms which may have a (meth)acryloyl group.

[0049] Examples of such compounds include 1,3-bis(3-methyl-2-butenoxy)-2-hydroxypropane and 1,3-bis(3-methyl-2-butenoxy)-2-methacryloyloxypropane.

[0050] In the above formula 1, X more preferably represents a linear or branched alkylene group having 1 to 6 carbon atoms and a hydroxyl group. An example of such a compound is 1,3-bis(3-methyl-2-butenoxy)-2-hydroxypropane.

[0051] The content of component (D) in the photosensitive resin composition of the present invention is preferably 0.3 to 8 mass %, more preferably 0.5 to 5 mass %, and even more preferably 1 to 3 mass %. When the content is within the above range, component (D) is less likely to bleed out onto the photosensitive layer surface, which is preferable.

[0052] <Other ingredients> In addition to the above components (A) to (D), the photosensitive resin composition of the present invention may contain other components, such as a plasticizer, an ultraviolet absorber, a thermal polymerization inhibitor (stabilizer), a hydrophilic compound, a surface tension modifier, a thermoplastic resin elastomer, a solid rubber, a dye, a pigment, an antifoaming agent, or an anti-aggregation agent, as appropriate, for the purpose of improving various properties, provided that the effects of the present invention are not impaired.

[0053] The plasticizer imparts flexibility to the photosensitive resin layer and is preferably liquid. Examples of plasticizers include liquid rubber, oil, polyester, and phosphoric acid compounds. Examples of liquid rubber include liquid compounds having a conjugated diene structure, or compounds to which hydroxyl groups, carboxyl groups, or sulfonic acid groups have been added. Examples of oils include paraffin, naphthene, and aromatics. Examples of polyesters include adipic acid polyesters. Examples of phosphoric acid compounds include phosphoric acid esters. Among these, liquid polybutadiene and liquid polybutadiene to which hydroxyl groups or carboxyl groups have been added are preferred from the viewpoint of compatibility with the (A) conjugated diene polymer. In the case of carboxyl groups, metal salts may be used. The content of the plasticizer in the photosensitive resin composition of the present invention is preferably up to 40% by mass.

[0054] The ultraviolet absorber broadens the allowable exposure time range of the photosensitive resin layer. Examples of ultraviolet absorbers include benzophenone-based, salicylate-based, benzotriazole-based, acrylonitrile-based, metal complex salt-based, hindered amine-based, anthraquinone-based, azo-based, coumarin-based, and furan-based compounds. Among these, benzotriazole-based compounds are preferred from the viewpoint of exposure latitude. The amount of ultraviolet absorber in the photosensitive resin composition of the present invention is up to 0.1% by mass.Specific examples of the benzotriazole-based ultraviolet absorber include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, and 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol]. ], 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, 2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol, 2-(5-chloro-2-benzotriazolyl)-6-tert-butyl-p-cresol, 2-(2'-hydroxy-5'-tert-butylphenyl)-2H-benzotriazole, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-(2H-benzotriazo 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(2H-benzotriazol-2-yl)-p-cresol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2- Examples thereof include benzotriazol-2-yl-4,6-di-tert-butylphenol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-butylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, and 2-(2H-benzotriazol-2-yl)-4-methyl-6-(3,4,5,6-tetrahydrophthalimidylmethyl)phenol.

[0055] The thermal polymerization inhibitor (stabilizer) enhances the thermal stability and storage stability of the photosensitive resin composition during production, and examples thereof include phenols, hydroquinones, and catechols. Examples include quinones such as hydroquinone, benzoquinone, and naphthoquinone, alkyl- and aryl-substituted hydroquinones, p-methoxyphenol, p-butylpyrocatechol, pyrogallol, β-naphthol, 2,6-di-t-butyl-4-methylphenol, t-butylcresols such as 2,6-di-t-butyl-p-cresol, phenothiazine, pyridine, nitrobenzene, nitro compounds such as dinitrobenzene and nitrosonaphthol, and hydroxylamine derivatives. Specific examples of hydroxylamine derivatives include cupferron derivatives such as N-nitrosophenylhydroxylamine aluminum salt and N-nitrosophenylhydroxylamine ammonium salt, cupferron analogues such as N-benzoylphenylhydroxylamine, benzohydroxamic acid, and 3-hydroxyl-1,3-diphenyltriazine, as well as N,N-diethylhydroxylamine and N-(t-butyl)hydroxylamine hydrochloride. The content of the thermal polymerization inhibitor (stabilizer) in the photosensitive resin composition of the present invention is preferably up to 5% by mass.

[0056] The hydrophilic compound improves water-developability, and is a compound having a hydrophilic group in the molecule, such as carboxylic acid, carboxylate, sulfonic acid, sulfonate, hydroxyl group, amino group, phosphate group, ethylene oxide, or propylene oxide, and is itself water-soluble or water-dispersible. The hydrophilic compound may be a low-molecular-weight compound, an oligomer, or a polymer compound. Specific examples of the hydrophilic compound include polyhydric alcohols, polycarboxylic acids, ester compounds of polycarboxylic acids, acrylic polymers, polyalkylene glycol-modified polymers, urethane polymers, polyamide polymers, and polyester polymers. Surfactants may also be used.

[0057] The surface tension modifier adjusts the surface tension of the flexographic printing plate, and by adjusting the surface tension of the flexographic printing plate, it is possible to adjust the ink transferability and ink clogging on the flexographic printing plate. Examples of the surface tension modifier include paraffin oil, long-chain alkyl compounds, surfactants, fatty acid amides, silicone oil, modified silicone oil, fluorine compounds, and modified fluorine compounds, and among these, modified silicone oil having an amino group or an aromatic ring is preferred. The surface tension modifier may contain a photopolymerizable group in the molecule.

[0058] <Flexographic printing plate> In one embodiment, the flexographic printing plate precursor preferably uses a photosensitive resin layer containing the photosensitive resin composition of the present invention and has a structure in which at least a support, a photosensitive resin layer, and an infrared ablation layer are laminated in this order. Methods for producing a photosensitive resin layer from the photosensitive resin composition of the present invention include melt molding, as well as any known method, such as hot pressing, casting, melt extrusion, or solution casting. The molded photosensitive resin layer is laminated on a support. The photosensitive resin layer may be laminated on the support via an adhesive layer. Conventional supports such as steel, aluminum, glass, and plastic films such as polyester films can be used as the support, and films with a thickness in the range of 50 to 500 μm are generally used. A flexographic printing plate precursor can be produced by laminating a cover film with an infrared ablation layer on the side of the photosensitive resin layer opposite the support. Plastic films such as polyester films with a thickness of 50 to 200 μm are generally used as the cover film. An oxygen barrier layer can also be provided between the infrared ablation layer and the photosensitive resin layer.

[0059] The oxygen barrier layer can be combined with a known oxygen barrier layer. The flexographic printing plate precursor of the present invention may or may not have an oxygen barrier layer. The photosensitive resin composition of the present invention can faithfully reproduce a microcell pattern on the surface of a flexographic printing plate without the need for special equipment or additional processes, even without the oxygen barrier layer. From the viewpoint of ensuring the depth of the microcells, it is preferable not to provide an oxygen barrier layer. When an oxygen barrier layer is provided, examples of the binder polymer in the oxygen barrier layer include polyvinyl alcohol, partially saponified vinyl acetate, alkyl cellulose, cellulose-based polymers, and polyamides. These polymers are not limited to being used alone, and two or more polymers can also be used in combination. Preferred binder polymers in terms of oxygen barrier properties are polyvinyl alcohol, partially saponified vinyl acetate, and polyamides. Examples of partially saponified vinyl acetate include partially saponified vinyl acetate with a saponification rate of 60 to 98 mol%. Examples of polyamides include polyamide resins containing a basic nitrogen atom in the molecule and polyamide resins containing an alkylene glycol structural unit in the molecule. An oxygen barrier layer containing a polyamide resin containing a basic nitrogen atom in the molecule and a polyamide resin containing an alkylene glycol structural unit in the molecule (Patent No. 7243076) is preferred.

[0060] <Flexographic printing plate> In one embodiment, the flexographic printing plate is obtained by exposing and developing a flexographic printing master plate, and has microcells in the solid areas.

[0061] In one embodiment, a method for producing a flexographic printing plate from a flexographic printing precursor involves, for example, back-exposing the photosensitive resin layer from the support side, then peeling off the top cover film to leave an infrared ablation layer on the photosensitive resin layer, drawing an image on the infrared ablation layer using an imaging device, and then irradiating the entire surface with actinic rays from above. This results in only the exposed areas curing and insolubilizing them. Actinic rays can be emitted from sources such as high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, chemical lamps, and LEDs, typically with wavelengths centered around 300 to 450 nm. Next, the unexposed areas are removed with an appropriate solvent or water containing a surfactant, followed by post-exposure and further exposure using a germicidal lamp to obtain a flexographic printing plate with a clear image area. The developing device preferably includes a spray-type developing device, a brush-type developing device, or the like.

[0062] A widely used method for forming microcells on the solid surface of a flexographic printing plate involves imaging a microcell pattern onto the solid portion of the infrared ablation layer of the flexographic printing plate master, and then reproducing the pattern on the flexographic printing plate through exposure and development processes. A typical example is microcell screening manufactured by ESKO-Graphic (see Non-Patent Document 1). Microcell screening includes the MC type, which introduces rectangular cells, the GROOVY type, which introduces diagonal cells, and the single pixel screen, which introduces specially shaped cells.

[0063] A method for forming microcells on the surface of a solid portion of a flexographic printing plate involves, for example, selecting a suitable microcell pattern from the various microcell patterns available on a CDI (Esco Graphics), applying the microcell pattern to an image on a computer, and then using that image to draw on the infrared ablation layer using an imaging device to form the microcells.

[0064] The infrared ablation layer used in the flexographic printing plate precursor can be combined with a known infrared ablation layer. The infrared ablation layer is preferably water-developable. Specific examples of the infrared ablation layer include an infrared ablation layer combining a polar group-containing polyamide and a butyral resin (Japanese Patent No. 4200510), an infrared ablation layer containing a polyamide resin containing a basic nitrogen atom in the molecule and a polyamide resin containing an alkylene glycol structural unit in the molecule (Japanese Patent No. 6414375), an infrared ablation layer containing a polymer having the same structure as the polymer in the photosensitive resin layer and an acrylic resin (Japanese Patent No. 5710961), an infrared ablation layer containing a polymer having an acidic group with an acid value of 10 to 400 mgKOH / g (Japanese Patent No. 6810251), and an infrared ablation layer containing an anionic polymer and a polymer having an ester bond in the side chain and a degree of saponification of 0% to 90%. [Example]

[0065] The effects of the flexographic printing plate precursor using the photosensitive resin composition of the present invention will be shown by the following examples, but the present invention is not limited thereto. The numerical values ​​showing the composition ratios in the tables mean the parts by mass of the solid components after volatilizing the solvent.

[0066] The evaluations in the examples were carried out by the following methods. (1) Uniformity of microcells on the flexographic printing plate (MC uniformity) The surface of the solid portion of a flexographic printing plate prepared from the flexographic printing original plate described below was magnified 500 times using a Keyence digital microscope (VHX5000) and judged according to the following criteria: The judgment was made at a point where the top diameter of the microcell was 15 μm using a WSI (Eskographics) microcell pattern. ⊚: Microcells are faithfully and clearly reproduced on the surface of the solid area of ​​the printing plate. ○: Microcells are reproduced on the surface of the solid area of ​​the printing plate. △: Microcells are only partially reproduced on the surface of the solid area of ​​the printing plate. ×: Microcells are not reproduced on the surface of the solid area of ​​the printing plate.

[0067] (2) Microcell depth on flexographic printing plate (MC depth) The depth (μm) from the top of the microcell to the recess of the same flexographic printing plate as above was measured using a Keyence laser microscope (VK-X3000) at a lens magnification of 50. The measurement was performed on a WSI (Eskographics) microcell pattern where the top diameter of the microcell was 15 μm.

[0068] (3) Ink application in solid areas Flexographic printing plates prepared from the flexographic printing master plates described below were printed onto substrates using a flexographic printing press FPR302 (manufactured by MCK Corporation) and a 900 LPI anilox roll, and the ink coverage of the solid areas of the substrate was evaluated. UV ink (product name: FLEXOCURE CYAN (manufactured by Flint)) was used. Polypropylene film (product name: P4256, manufactured by Toyobo) was used as the substrate. The printing speed was 50 m / min. The printing indentation depth was defined as zero at the point where the flexographic printing plate made contact with the substrate, and 90 μm from there. The ink coverage (ink uniformity) of the solid areas printed with the microcell pattern was measured using a Keyence digital microscope (VHX5000) and expressed as a percentage. The higher the coverage, the more uniform the ink is applied, meaning better ink coverage. The evaluation criteria for ink coverage of solid areas are shown below. ◎: Concealment rate is 97% or more, 100% or less ○: Concealment rate is 94% or more, but less than 97% △: Concealment rate is 90% or more, but less than 94% ×: Concealment rate is less than 90%

[0069] (4) Reproducibility of independent points The reproducibility of the smallest independent point on a flexographic printing plate prepared from the flexographic printing original plate described below was measured. Independent points of 50 μm minimum and 300 μm maximum were evaluated in 50 μm increments. Of these, if the smallest independent point that could be reproduced was 100 μm or less, it was judged as ○; if the smallest independent point that could be reproduced was between 100 μm and 200 μm, it was judged as △; and if the smallest independent point that could be reproduced was greater than 200 μm, it was judged as ×. The smaller the smallest independent point that could be reproduced, the better the reproducibility of the independent points.

[0070] Example 1 Preparation of photosensitive resin composition (A) A butadiene latex (Nipol LX111NF, non-volatile content 55%, manufactured by Zeon Corporation) as a conjugated diene polymer was placed in a container so that the solid content was 55 parts by mass, and a carboxy-modified acrylonitrile-butadiene latex (Nipol SX1503, non-volatile content 42%, manufactured by Nippon Zeon Co., Ltd.) was added to a container so that the solid content was 10 parts by weight, followed by (B) 20 parts by weight of oligobutadiene acrylate having acryloyloxy groups at both ends as a photopolymerizable unsaturated compound (BAC-45, manufactured by Osaka Organic Chemical Co., Ltd., number average molecular weight: 4100), 10 parts by weight of trimethylolpropane trimethacrylate (Light Ester TMP, molecular weight: 338, manufactured by Kyoeisha Chemical Co., Ltd.), (C) 1 part by weight of photopolymerization initiator (Irgacure 651: benzyl dimethyl ketal), (D) 1 part by weight of oxygen inhibition inhibitor (DPNG: 1,3-bis(3-methyl-2-butenoxy)-2-hydroxypropane, manufactured by Kuraray Co., Ltd.), and 8 parts by weight of butadiene oligomer (LBR-352, manufactured by Kuraray Co., Ltd.) as a plasticizer. The mixture was mixed into the container to prepare a dope. The dope was placed in a pressure kneader, and tetrahydrofuran and water were removed under reduced pressure at 80° C. to obtain a photosensitive resin composition.

[0071] Preparation of film laminate (I) with infrared ablation layer Carbon black dispersion (AMBK-8, manufactured by Orient Chemical Industries Co., Ltd.), copolymer polyamide (PA223, manufactured by Toyobo MC Co., Ltd.), propylene glycol, and methanol were mixed in a mass ratio of 45 / 5 / 5 / 45 to obtain an infrared ablation layer coating solution. After a release treatment was applied to both sides of a polyester film (E5000, manufactured by Toyobo Co., Ltd., 100 μm thick), the infrared ablation layer coating solution was applied using a bar coater to a dried coating thickness of 2 μm. The film was then dried at 120°C for 5 minutes to obtain a film laminate (I). The optical density (OD value) was 2.3. The optical density was measured using a black-and-white transmission densitometer DM-520 (manufactured by Dainippon Screen Mfg. Co., Ltd.).

[0072] Flexographic printing plate making Next, the photosensitive resin composition was placed on the adhesive side of a support made of a polyester film (Toyobo Co., Ltd., E5000, 100 μm thick) coated with a copolymer polyester adhesive to a thickness of 25 μm. This photosensitive resin layer was placed on the infrared ablation layer side of the film laminate (I) prepared above, and the resulting laminate was laminated at 100°C using a heat press to obtain a flexographic printing plate precursor consisting of a PET support, adhesive layer, photosensitive resin layer, infrared ablation layer, and cover film laminated in that order. The total plate thickness was 1.14 mm.

[0073] Preparation of flexographic printing plates from flexographic printing masters The printing plate was exposed to light from the backside of the PET support for 10 seconds. The cover film was then peeled off. This plate was wrapped around an Esko Graphics CDI4530, and an image was drawn on the infrared ablation layer at a resolution of 4000 dpi. The image used was a test chart with solid areas without a microcell pattern and solid areas with a WSI (Eskographics) microcell pattern applied, with independent points measuring a minimum of 50 μm and a maximum of 300 μm in 50 μm increments. The main exposure was performed using an LED built into the CDI4530 at an illuminance of 22 mW / cm. 2The plate was then removed from the CDI and developed for 8 minutes in a developing machine manufactured by A&V Corporation (Stuck System, developer: 1% laundry soap solution, 40°C), and water droplets on the plate surface were removed with a water-blowing stick. It was then dried for 10 minutes in a dryer at 60°C. Subsequently, post-exposure was carried out for 7 minutes, and finally, it was irradiated with a germicidal lamp for 5 minutes to obtain a flexographic printing plate. Back exposure and post-exposure were carried out using a Philips TL-K 40W / 10R lamp (peak wavelength 370 nm, illuminance at 350 nm: 10 mW / cm 2 ) and the germicidal lamp was a Panasonic germicidal lamp GL-40 (peak wavelength 250 nm, illuminance at 250 nm is 4.5 mW / cm 2 The resulting flexographic printing plate had a relief depth of 0.6 mm.

[0074] (Examples 2 to 3, 5 to 11), (Comparative Examples 2, 3, 4) A photosensitive resin composition, a flexographic printing original plate, and a flexographic printing plate were prepared in the same manner as in Example 1, except that the composition of each component in the photosensitive resin composition constituting the photosensitive resin layer was changed as shown in Table 1.

[0075] Example 4 A photosensitive resin composition, a flexographic printing original plate, and a flexographic printing plate were prepared in the same manner as in Example 1, except that the composition of each component in the photosensitive resin composition constituting the photosensitive resin layer was changed as shown in Table 1. A synthesis example of the oxygen inhibition suppressor (D) (1,3-bis(3-methyl-2-butenoxy)-2-methacryloyloxypropane) used is shown below. (D) Synthesis method of oxygen inhibition suppressor (1,3-bis(3-methyl-2-butenoxy)-2-methacryloyloxypropane) A reaction vessel equipped with a stirrer, thermometer, and dropping funnel was charged with 16.1 g (0.392 mol) of acetonitrile, 11.43 g (0.050 mol) of 1,3-bis(3-methyl-2-butenoxy)-2-hydroxypropane, and 8.41 g (0.083 mol) of triethylamine under an air stream. The internal temperature was maintained below 15°C, and 6.30 g (0.060 mol) of methacrylic acid chloride (containing 2200 ppm of p-methoxyphenol as a polymerization inhibitor) was added dropwise with stirring. After the addition was complete, the temperature was raised to 25°C and the reaction was continued for 1.5 hours at 25°C with stirring. Then, 7.07 g of ion-exchanged water and 61 mg of p-dimethylaminopyridine were added to the reaction mixture, and the reaction was continued for 2 hours at 25°C. The end point was confirmed by the decomposition of the by-product methacrylic anhydride, and the mixture was extracted three times with ethyl acetate. The organic layer was washed with a 2% by mass aqueous solution of hydrochloric acid, a 3% by mass aqueous solution of sodium bicarbonate, and saturated saline, and then dried over sodium sulfate. The resulting organic layer was purified by distillation to obtain 1,3-bis(3-methyl-2-butenoxy)-2-methacryloyloxypropane.

[0076] (Comparative Examples 1 and 5) Preparation of photosensitive resin composition Photosensitive resin compositions were obtained in the same manner as in Example 1, except that the composition of each component in the photosensitive resin composition constituting the photosensitive resin layer was changed as shown in Table 1. Preparation of film laminate with oxygen barrier layer (II) Polyvinyl acetate (KH20, manufactured by Mitsubishi Chemical Corporation) with a saponification degree of 80% and a plasticizer (glycerin) were mixed in a mass ratio of 70 / 30 to obtain an oxygen barrier layer coating solution. The oxygen barrier layer coating solution was applied to a film laminate (I) obtained in the same manner as in Example 1 using a bar coater so that the coating thickness after drying would be 2.0 μm, and the mixture was dried at 120°C for 5 minutes to obtain a film laminate (II).

[0077] Flexographic printing plate making The prepared photosensitive resin composition was placed on the adhesive side of a support, which had been coated with a copolymer polyester adhesive to a thickness of 25 μm on a polyester film (Toyobo Co., Ltd., E5000, thickness 100 μm). This photosensitive resin layer side was superimposed on the oxygen barrier layer side of the film laminate (II) prepared above. A photosensitive resin composition, flexographic printing plate, and flexographic printing plate were prepared in the same manner as in Example 1, except that lamination was performed at 100°C using a heat press to obtain a flexographic printing plate precursor having a polyester support, adhesive layer, photosensitive resin layer, oxygen barrier layer, infrared ablation layer, and cover film laminated in this order. The total plate thickness was 1.14 mm.

[0078] [Table 1]

[0079] As can be seen from the evaluation results in Table 1, in Examples 1 to 11, even when no oxygen barrier layer was used, the uniformity and depth of the microcells on the flexographic printing plate were good, the reproducibility of the microcell pattern was good, and the ink coverage of solid areas was also good. Furthermore, the reproducibility of isolated points was also good. All of Examples 1 to 11, which met the requirements of the present invention, demonstrated sufficient ink coverage of solid areas and reproducibility of isolated points.

[0080] In contrast, in Comparative Example 1, which did not contain an oxygen inhibition inhibitor, the amount of photopolymerization initiator was small even when an oxygen barrier layer was provided, resulting in poor reproducibility of the microcell pattern on the flexographic printing plate and poor ink adhesion in solid areas. Comparative Example 2, which did not contain an oxygen barrier layer and did not contain an oxygen inhibition inhibitor, was significantly poor in all aspects, including reproducibility of the microcell pattern on the flexographic printing plate, ink adhesion in solid areas, and reproducibility of isolated points. Comparative Example 3, which contained a larger amount of photopolymerization initiator than Comparative Example 2 but did not contain an oxygen inhibition inhibitor, was poor in reproducibility of the microcell pattern and ink adhesion in solid areas. In Comparative Example 4, which did not use a barrier layer, oxygen inhibition was suppressed by using a large amount of photopolymerization initiator, and reproducibility of the microcell pattern was achieved, but ink adhesion in solid areas was poor and reproducibility of isolated points was poor, possibly due to the flexographic printing plate hardness being too high in the solid areas. In Comparative Example 5, when a barrier layer was provided, reproducibility of the microcell pattern could be obtained by using a certain amount of photopolymerization initiator even without containing an oxygen inhibition suppressor, but it was necessary to provide a barrier layer.

Claims

1. A photosensitive resin composition for a flexographic printing original plate, comprising (A) a conjugated diene polymer, (B) a photopolymerizable unsaturated compound, (C) a photopolymerization initiator, and (D) an oxygen inhibition suppressor.

2. 2. The photosensitive resin composition for a flexographic printing plate precursor according to claim 1, wherein the oxygen inhibition suppressor (D) has at least two prenyl groups in the molecule.

3. 2. The photosensitive resin composition for a flexographic printing original plate according to claim 1, wherein the (D) oxygen inhibition suppressor is a compound having a molecular structure in which the prenyl groups are bonded to each other via ether bonds.

4. 2. The photosensitive resin composition for a flexographic printing plate precursor according to claim 1, wherein the oxygen inhibition suppressor (D) is a compound having one or more hydroxyl groups in the molecule.

5. 2. The photosensitive resin composition for a flexographic printing original plate according to claim 1, wherein the (D) oxygen inhibition suppressor is contained in an amount of 0.3 to 8% by mass in the photosensitive resin composition.

6. 2. The photosensitive resin composition for a flexographic printing original plate according to claim 1, wherein the (C) photopolymerization initiator is at least one selected from the group consisting of benzoin alkyl ethers, benzophenones, anthraquinones, benzils, and acetophenones, and is contained in an amount of 0.5 to 9% by mass in the photosensitive resin composition.

7. 2. The photosensitive resin composition for a flexographic printing original plate according to claim 1, wherein the (B) photopolymerizable unsaturated compound comprises a photopolymerizable unsaturated compound having a number average molecular weight of 100 or more and 600 or less, and a photopolymerizable unsaturated compound having a number average molecular weight of more than 600 and 20,000 or less.

8. The photosensitive resin composition for a flexographic printing plate precursor according to claim 1, which has water-developability.

9. A flexographic printing original plate comprising a photosensitive resin layer containing the photosensitive resin composition according to any one of claims 1 to 8, and at least a support, the photosensitive resin layer, and an infrared ablation layer laminated in this order.

10. A method for producing a flexographic printing plate, which is obtained by exposing and developing the flexographic printing plate precursor according to claim 9, and which has microcells in solid areas.

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