Photosensitive resin composition for frekiso printing originals

Abstract

The present invention provides a photosensitive resin composition for flexographic printing plates that enables the reproduction of fine images with short-term UV irradiation, without the need to prepare a low-oxygen environment, install an oxygen barrier layer, or increase the amount of UV irradiation. [Solution] A photosensitive resin composition comprising at least (a) a polymer obtained by polymerizing a conjugated diene, (b) an ethylenically unsaturated compound, and (c) a photopolymerization initiator, wherein the photosensitive resin composition contains 5 to 50% by mass of (b) the ethylenically unsaturated compound, and (b) contains 10% by mass or more of an ethylenically unsaturated compound having a heterocyclic structure including an ether linkage.

Description

[Technical Field]

[0001] The present invention relates to a photosensitive resin composition for flexographic printing plates that can reproduce fine images with short-duration ultraviolet irradiation, and to a flexographic printing plate using the same. [Background technology]

[0002] Typically, flexographic printing plates have a structure in which a photosensitive resin layer is provided on a support. The photosensitive resin composition that forms the photosensitive resin layer generally contains polymer compounds such as elastomers, ethylenically unsaturated compounds, and photopolymerization initiators as essential components, and optionally contains additives such as stabilizers, plasticizers, ultraviolet absorbers, and dyes.

[0003] In recent years, flexographic printing plates have been required to reproduce finer images than before. While increasing the amount of ultraviolet irradiation has been considered to achieve this, it has resulted in poor production efficiency due to the longer exposure time. Furthermore, it is known that the photosensitive resin layer of flexographic printing plates suffers from polymerization failure due to oxygen, leading to reduced image reproducibility. To address this, solutions have been proposed, such as printing plates with a barrier layer on the photosensitive resin layer (see Patent Document 1) and printing plate manufacturing methods that involve irradiating the plate with ultraviolet light in a low-oxygen environment (see Patent Document 2). The solution in Patent Document 1 reduces oxygen penetration into the photosensitive resin layer due to the barrier layer, but it presents problems such as the need for special laminate design to control interlayer adhesion and the problem of thickening due to increased sensitivity of the photosensitive resin layer surface caused by oxygen blockage. The solution in Patent Document 2 presents problems such as a complicated process and increased manufacturing costs due to the introduction of equipment to maintain low oxygen concentrations. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 7-506201 [Patent Document 2] Patent No. 6219954 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] This invention was conceived in view of the current state of the prior art, and its purpose is to provide a photosensitive resin composition for flexographic printing plates with excellent photopolymerization properties, which can achieve fine image reproduction with short-term ultraviolet irradiation without the need to prepare a low-oxygen environment, provide an oxygen barrier layer, or increase the amount of ultraviolet irradiation, and a flexographic printing plate using the same. [Means for solving the problem]

[0006] As a result of diligent research to achieve the above objective, the inventors of the present invention have discovered that by using a certain amount or more of an ethylenically unsaturated compound having a heterocyclic structure containing an ether bond as the ethylenically unsaturated compound used in the photosensitive resin composition for flexographic printing plates, it is possible to provide a flexographic printing plate that enables fine image reproduction with short-term ultraviolet irradiation, thus completing the present invention.

[0007] In other words, the present invention consists of the following configurations (1) to (6). (1) A photosensitive resin composition comprising at least (a) a polymer obtained by polymerizing a conjugated diene, (b) an ethylenically unsaturated compound, and (c) a photopolymerization initiator, wherein the photosensitive resin composition contains 5 to 50% by mass of (b) the ethylenically unsaturated compound, and (b) contains 10% by mass or more of an ethylenically unsaturated compound having a heterocyclic structure including an ether linkage, for use as a photosensitive resin composition for flexographic printing plates. (2) The photosensitive resin composition for flexographic printing plates according to (1), characterized in that the ethylenically unsaturated compound having a heterocyclic structure including an ether bond is one or more compounds selected from the group consisting of ethylenically unsaturated compounds having a furan skeleton, ethylenically unsaturated compounds having a tetrahydrofuran skeleton, and ethylenically unsaturated compounds having a pyrone skeleton. (3) The photosensitive resin composition for flexographic printing plates according to (2), characterized in that the ethylenically unsaturated compound having a furan skeleton is one or more (meth)acrylates selected from the group consisting of frandelol di(meth)acrylate, frandelcarboxylic acid di(meth)acrylate, frandel methanol di(meth)acrylate, furan monomethanol(meth)acrylate, furancarboxylic acid diepoxy(meth)acrylate, frandelol diepoxy(meth)acrylate, and frandel methanol monoepoxy(meth)acrylate. (4) The photosensitive resin composition for flexographic printing plates according to (2), characterized in that the ethylenically unsaturated compound having a tetrahydrofuran skeleton is one or more (meth)acrylates selected from the group consisting of tetrahydrofranmethanol di(meth)acrylate, tetrahydrofuran monomethanol mono(meth)acrylate, tetrahydrofranmethanol diepoxy(meth)acrylate, tetrahydrofrancarcinol di(meth)acrylate, tetrahydrofrancarcinol mono(meth)acrylate, tetrahydrofurancarcinol monoepoxy(meth)acrylate, tetrahydrofrancarcinol diepoxy(meth)acrylate, and tetrahydrofranmol diepoxy(meth)acrylate. (5) The photosensitive resin composition for flexographic printing plates according to (2), characterized in that the ethylenically unsaturated compound having a pyrone skeleton is one or more (meth)acrylates selected from the group consisting of 4-pyrone-2,6-dicarboxylic acid di(meth)acrylate, 4-pyrone-2,6-dicarboxylic acid diexope(meth)acrylate, 4-pyrone-2,6-dicarboxylic acid mono(meth)acrylate, 4-pyrone-2,6-dicarboxylic acid monoepoxy(meth)acrylate, γ-pyrone-2-carboxylic acid mono(meth)acrylate, and γ-pyrone-2,6-dicarboxylic acid di(meth)acrylate. (6) A flexographic printing plate using the photosensitive resin composition for flexographic printing plates described in any one of items (1) to (5). [Effects of the Invention]

[0008] According to the present invention, compared to conventional photosensitive resin compositions for flexographic printing plates that were susceptible to the effects of oxygen, it is possible to achieve fine image reproduction with short-term UV irradiation without preparing a low-oxygen environment, providing an oxygen barrier layer, or increasing the amount of UV irradiation, and to provide a flexographic printing plate with excellent photopolymerization properties. Furthermore, the ethylenically unsaturated compound in the photosensitive resin composition of the present invention uses a heterocyclic compound derived from biomass, which can contribute to solving the problem of depletion of fossil resources. [Modes for carrying out the invention]

[0009] The photosensitive resin composition for flexographic printing plates of the present invention contains (a) a polymer obtained by polymerizing a conjugated diene, (b) an ethylenically unsaturated compound, and (c) a photopolymerization initiator as essential components, and is characterized in that (b) the ethylenically unsaturated compound contains a certain amount or more of an ethylenically unsaturated compound having a heterocyclic structure including an ether linkage. Furthermore, a flexographic printing plate using the photosensitive resin composition for flexographic printing plates of the present invention can provide a flexographic printing plate capable of reproducing fine images with short-time ultraviolet irradiation. The flexographic printing plate of the present invention may also be a CTP flexographic printing plate in which a thermal mask layer is provided on a photosensitive resin layer provided on a support, and the effects of the present invention can be obtained in the same way as when a thermal mask layer is not provided.

[0010] (a) The polymer obtained by polymerizing a conjugated diene used in the photosensitive resin composition for flexographic printing plates of the present invention can be a conventionally known synthetic polymer compound used in printing plates. Specifically, examples include polymers obtained by polymerizing conjugated diene hydrocarbons, or copolymers obtained by copolymerizing a conjugated diene hydrocarbon with a monoolefin 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. Among these, butadiene polymers are preferably used from the viewpoint of characteristics as flexographic printing plates, namely the rebound elasticity of the plate surface, the strength of the stretchable material, the hardness of the resin plate, the morphological stability when unexposed, and availability. These polymers may be used individually or in combination of two or more. The amount of component (a) used in the photosensitive resin composition for flexographic printing plates of the present invention is preferably in the range of 40 to 70% by mass. More preferably it is 45 to 65% by weight. If the amount used is less than the above percentage, the printing plate may not obtain sufficient physical properties, and if it exceeds the above percentage, the photocurability may deteriorate and the image reproducibility may decrease.

[0011] The (b) ethylenically unsaturated compound used in the photosensitive resin composition for flexographic printing plates of the present invention is characterized by containing a certain amount or more of an ethylenically unsaturated compound having a heterocyclic structure including an ether bond. Because the ethylenically unsaturated compound having a heterocyclic structure including an ether bond has an ether bond (COC), the carbon atoms adjacent to the oxygen atom in this ether bond react with the oxygen dissolved in the composition, thereby suppressing polymerization impairment caused by this dissolved oxygen. In particular, the present invention is characterized by introducing the ether bond into the ethylenically unsaturated compound not as a linear polyether or a branched polyether, but as a "heterocyclic structure". Due to its heterocyclic structure, the ethylenically unsaturated compounds are less likely to aggregate due to steric hindrance, and are easily finely dispersed in the polymer obtained by polymerizing (a) conjugated diene, the main component of the composition. This allows the aforementioned effect of suppressing polymerization hindrance by dissolved oxygen due to ether bonds to be uniformly and sufficiently exerted throughout the composition. Furthermore, photocrosslinking by the ethylenically unsaturated compounds proceeds efficiently, so fine image reproduction can be improved with short-term UV irradiation without the need to prepare a low-oxygen environment, provide an oxygen barrier layer, or increase the amount of UV irradiation. Moreover, due to its heterocyclic structure, even if the carbon atom adjacent to the oxygen atom in the ether bond reacts with dissolved oxygen in the composition and the ether bond is cleaved, the cyclic structure remains stable, and the photopolymerization property, which is the original function of the ethylenically unsaturated compounds, is not impaired. In contrast, in the case of linear or branched polyethers, the ethylenically unsaturated compounds cannot be finely dispersed and instead aggregate and localize within the composition. As a result, the polymerization inhibition effect of dissolved oxygen by ether bonding cannot be uniformly and sufficiently exerted throughout the composition, and photocrosslinking by the ethylenically unsaturated compounds does not proceed efficiently. Consequently, it is thought that the exposure time by ultraviolet irradiation cannot be shortened.Furthermore, in the case of linear or branched polyethers, when carbon atoms adjacent to oxygen atoms in the ether bond react with dissolved oxygen in the composition, side reactions such as molecular cleavage occur during the cleavage of the ether bond, which is thought to reduce the photopolymerization properties that are the original function of ethylenically unsaturated compounds.

[0012] In the present invention, the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond may contain nitrogen atoms or sulfur atoms in addition to the oxygen atom contained in the ether bond, to the extent that they do not affect the ethylenicity. Furthermore, the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond preferably contains a polyfunctional ethylenically unsaturated compound having two or more ethylenic groups in the molecule, but it may also contain a monofunctional ethylenically unsaturated compound.

[0013] Examples of ethylenically unsaturated compounds having a heterocyclic structure containing an ether bond include one or more compounds selected from the group consisting of ethylenically unsaturated compounds having one or more oxygen atoms in addition to carbon atoms in the heterocyclic structure, preferably having a furan skeleton, ethylenically unsaturated compounds having a tetrahydrofuran skeleton, and ethylenically unsaturated compounds having a pyrone skeleton. In these compounds, the substituent on the carbon adjacent to the oxygen atom in the ether bond is a hydrogen atom, so they readily react with oxygen.

[0014] Ethylene-unsaturated compounds having a heterocyclic structure containing an ether bond include (meth)acrylates in which an ethylenically unsaturated group is introduced to the heterocyclic structure via an ester bond, or epoxy (meth)acrylates in which an ethylenically unsaturated group is introduced via an epoxy ester bond. Epoxy (meth)acrylates are adducts of epoxy compounds with acrylic acid or methacrylic acid. They can be purchased commercially or synthesized by known methods. Known synthesis methods include, for example, the method for producing alkanediol monoglycidyl ether (meth)acrylate described in WO13 / 168586. Furthermore, (meth)acrylates in which an ethylenically unsaturated group is introduced via an ester bond are obtained by esterifying the hydroxyl group in the heterocyclic structure with acrylic acid or methacrylic acid. They can be purchased commercially or synthesized by known methods. Known synthesis methods include the method for producing hydroxyalkyl (meth)acrylate described in Japanese Patent No. 4116113.

[0015] Examples of ethylenically unsaturated compounds having a furan skeleton include one or more (meth)acrylates selected from the group consisting of frandelol di(meth)acrylate, frandelcarboxylic acid di(meth)acrylate, frandel methanol di(meth)acrylate, furan monomethanol(meth)acrylate, furancarboxylic acid (meth)acrylate, frandelcarboxylic acid diepoxy(meth)acrylate, frandelol diepoxy(meth)acrylate, and frandel methanol monoepoxy(meth)acrylate. Specifically, examples include 2,5-frangimethanol di(meth)acrylate, 3,4-frangimethanol di(meth)acrylate, di(meth)acryloyloxyethyl-2,5-frangic acid, di(meth)acryloyloxypropyl-2,5-frangic acid, (meth)acryloyloxyethyl-2-furanic acid (meth)acrylate, 2,5-frangimol diepoxy(meth)acrylate, 3,4-frangimethanol diepoxy(meth)acrylate, 2,5-frangic acid monoepoxy(meth)acrylate, 2,5-frangic acid diepoxy(meth)acrylate, and 2-furanic acid epoxy(meth)acrylate. Particularly preferred are 2,5-frangimethanol diacrylate and furan-2-methanol methacrylate. The ethylenically unsaturated compound can be purchased commercially or produced by known manufacturing methods.

[0016] Examples of the ethylenically unsaturated compound having a tetrahydrofuran skeleton include one or more (meth)acrylates selected from the group consisting of tetrahydrofranmethanol di(meth)acrylate, tetrahydrofuran monomethanol mono(meth)acrylate, tetrahydrofranmethanol diepoxy(meth)acrylate, tetrahydrofrancarcinol di(meth)acrylate, tetrahydrofrancarcinol mono(meth)acrylate, tetrahydrofurancarcinol monoepoxy(meth)acrylate, tetrahydrofrancarcinol diepoxy(meth)acrylate, tetrahydrofurancarcinol diepoxy(meth)acrylate, and tetrahydrofranmol diepoxy(meth)acrylate. Specifically, examples include tetrahydro-2,5-franze methanol di(meth)acrylate, tetrahydro-2,5-franze carboxylic acid di(meth)acrylate, tetrahydro-2-furanmethanol mono(meth)acrylate, tetrahydro-2,5-franze carboxylic acid mono(meth)acrylate, tetrahydro-2,5-franze methanol diepoxy(meth)acrylate, tetrahydro-2,5-franze carboxylic acid diepoxy(meth)acrylate, tetrahydro-2,5-franze methanol diepoxy(meth)acrylate, tetrahydro-2-furanmethanol epoxy(meth)acrylate, tetrahydro-3-furanmethanol epoxy(meth)acrylate, and tetrahydro-2,5-franze methanol diepoxy(meth)acrylate. Particularly preferred are tetrahydro-2,5-franze methanol diacrylate and tetrahydro-2-furanmethanol methacrylate. The ethylenically unsaturated compounds having a tetrahydrofuran skeleton may be purchased commercially or produced by known manufacturing methods.

[0017] The ethylenically unsaturated compound having the pyrone skeleton is an ethylenically unsaturated compound containing two oxygen atoms in the heterocyclic structure. Examples of the ethylenically unsaturated compound having the pyrone skeleton include one or more (meth)acrylates selected from the group consisting of di(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid, diepoxy(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid, mono(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid, monoepoxy(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid, monoepoxy(meth)acrylate of γ-pyrone-2-carboxylic acid, mono(meth)acrylate of γ-pyrone-2-carboxylic acid, and di(meth)acrylate of γ-pyrone-2,6-dicarboxylic acid. Preferably, it is di(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid. The ethylenically unsaturated compound having the pyrone skeleton may be purchased as a commercial product or can be produced by a known production method.

[0018] When the ethylenically unsaturated compound having the heterocyclic structure containing the above ether bond uses a compound having a heterocyclic structure with an active hydroxyl group as a raw material, an ethylenically unsaturated group may be introduced after adding an alkylene oxide to the active hydrogen atom. As the alkylene oxide to be added, ethylene oxide or propylene oxide is preferable, and ethylene oxide addition is preferable from the viewpoint of water solubility.

[0019] The ethylenically unsaturated compound having the heterocyclic structure containing an ether bond may be produced by a known production method or may be purchased as a commercial product. In the case of (meth)acrylate, it may be produced by changing the raw materials according to the examples of the method of producing by an esterification reaction of a diol and acrylic acid or methacrylic acid (Japanese Patent Laid-Open No. 11-236353 etc.). It can also be synthesized by an esterification reaction of a dicarboxylic acid and hydroxyethyl acrylate or hydroxyethyl methacrylate. Further, when using a dicarboxylic acid containing an oxygen atom in the heterocyclic structure, a dicarboxylic acid diester compound may be used as the raw material.

[0020] When the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond is an epoxy (meth) acrylate, it can be produced by a known method. First, an epoxy compound in which an epoxy group is introduced into the hydroxyl group of a heterocyclic compound having a hydroxyl group is produced, and the epoxy compound may be reacted with methacrylic acid or acrylic acid. For example, the examples of JP-A-11-343331 disclose a method for producing a polyfunctional epoxy acrylate by reacting an epoxy compound with acrylic acid. The production of the epoxy compound can be carried out by a known production method, and it may be produced according to the production methods of bisphenol A and epoxy resins synthesized using epichlorohydrin as a raw material.

[0021] The photosensitive resin composition for a flexographic printing original plate of the present invention contains (b) an ethylenically unsaturated compound in an amount of 5 to 50% by mass of the photosensitive resin composition, preferably 15 to 50% by mass. Further, the content of the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond in the (b) ethylenically unsaturated compound of the photosensitive resin composition for a relief printing original plate of the present invention is 10% by mass or more based on all the ethylenically unsaturated compounds. It is preferably 30% by mass or more, more preferably 50% by mass or more, and may be 100% by mass. When the content of the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond in the (b) ethylenically unsaturated compound is within the above range or more, the effect of fine image reproduction becomes high, and the effect tends to be further enhanced as the content increases.

[0022] (b) As for the ethylenically unsaturated compound, as long as it contains a certain amount or more of an ethylenically unsaturated compound having a heterocyclic structure containing an ether linkage, it may also contain ethylenically unsaturated compounds other than ethylenically unsaturated compounds having a heterocyclic structure containing an ether linkage, as long as it does not significantly reduce the effects of the present invention. Examples of ethylenically unsaturated compounds other than ethylenically unsaturated compounds having a heterocyclic structure containing an ether linkage include photopolymerizable oligomers that are (meth)acrylate compounds with a number average molecular weight of 700 to 20000 and form a loose crosslinking network. An example of such a photopolymerizable oligomer is BAC-45 manufactured by Osaka Organic Chemical Industry Co., Ltd.

[0023] Furthermore, as ethylenically unsaturated compounds other than those having a heterocyclic structure containing an ether bond that can be used in the photosensitive resin composition of the present invention, examples include compounds containing one or more photopolymerizable unsaturated groups in their molecule. Known compounds can be used as such.

[0024] Specifically, examples of compounds containing one photopolymerizable unsaturated group in the molecule include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, N,N′-dimethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, (meth)acrylamide, N-methylol (meth)acrylamide, N-methylol (meth)acrylamide-n-butyl ether, diacetacrylamide, N-tert-butyl (meth)acrylamide, ring-opening addition reaction products of glycidyl (meth)acrylate and monoalcohols, and compounds having one unsaturated bond such as 2-acrylamido-2-methylpropanesulfonic acid.

[0025] Compounds containing two or more photopolymerizable unsaturated groups in the molecule include ethylene glycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolethane di(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, and tetramethylolmethane di(meth)acrylate. Methylolmethane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, tri(meth)acryloyloxyethyl phosphate, triesters of tris(2-hydroxyethyl)isocyanuric acid and (meth)acrylic acid, ring-opening addition reaction products of polyglycidyl ethers of polyhydric alcohols and (meth)acrylic acid, for example, reaction products of (poly)ethylene glycol diglycidyl ether and (meth)acrylic acid, reaction products of (poly)propylene glycol diglycidyl ether and (meth)acrylic acid, 1,Reaction products of 6-hexamethylene glycol diglycidyl ether and (meth)acrylic acid, reaction products of glycerin diglycidyl ether and (meth)acrylic acid, reaction products of trimethylolethane triglycidyl ether and (meth)acrylic acid, reaction products of trimethylolpropane triglycidyl ether and (meth)acrylic acid, reaction products of isophthalate diglycidyl ether and (meth)acrylic acid, reaction products of isoprene oligomer dicarboxylic acid diglycidyl ether and (meth)acrylic acid, and others. The ring-opening addition reaction products of active hydrogen compounds and glycidyl (meth)acrylate, for example, the reaction products of (poly)ethylene glycol and glycidyl (meth)acrylate, the reaction products of (poly)propylene glycol and glycidyl (meth)acrylate, the reaction products of glycerin and glycidyl (meth)acrylate, the reaction products of 2-hydroxyethyl (meth)acrylate and glycidyl (meth)acrylate, the reaction products of trimethylolethane and glycidyl (meth)acrylate, and trimethylolpropane and glycidyl Reaction products with (meth)acrylate, reaction products of (meth)acrylic acid and glycidyl (meth)acrylate, reaction products of aliphatic polycarboxylic acid and glycidyl (meth)acrylate, reaction products of aromatic polycarboxylic acid and glycidyl (meth)acrylate, compounds having two or more unsaturated groups obtained by reaction of a compound having a primary or secondary amino group with glycidyl (meth)acrylate, N,N′-methylenebis(meth)acrylamide, N,N′-ethylenebis(meth)acrylamide, N,N′-prop Lenbis(meth)acrylamide, N,N′-hexamethylenebis(meth)acrylamide, N,N′-m-phenylenebis(meth)acrylamide, N,N′-m-xylylenebis(meth)acrylamide, di(meth)acrylamide-N-methyl ether, 1,3-bis[(meth)acryloylaminomethyl]urea and its derivatives, 1,3-[bis(meth)acryloylaminomethyl]-1,3-dimethylurea and its derivatives, 1,3-[bis(meth)acryloylaminomethyl]ethyleneurea and its derivatives, 1,Examples include compounds having two or more unsaturated bonds, such as 3-[bis(meth)acryloylaminomethyl]trimethyleneurea and its derivatives, triacryl formal, tri(meth)acrylate of tris(2-hydroxyethyl)isocyanuric acid, and 1,3-diglycidyl,5-methyl,5-ethylhydantoin.

[0026] Next, (c) photopolymerization initiators will be described. (c) Photopolymerization initiators are not particularly limited as long as they can polymerize polymerizable carbon-carbon unsaturated groups by light. In particular, 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, benzyls, acetophenones, and diacetyls. For example, benzophenone, chlorobenzophenone, benzoin, acetophenone, benzyl, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzyl dimethyl ketal, benzyl diethyl ketal, benzyl diisopropyl ketal, anthraquinone, 2-ethylanthraquinone, 2-methylanthraquinone, 2-allylanthraquinone, 2-chloroanthraquinone, thioxanthone, 2-chlorothioxanthone, and 1-hydroxycyclohexane-1-ylphenyl ketone. (c) The photopolymerization initiator may be a compound consisting of two types, a benzyl alkyl ketal and a benzophenone, in order to make efficient use of the light energy from post-exposure and exposure with a germicidal lamp. The content of component (c) in the photosensitive resin composition of the present invention is preferably 0.1 to 10% by mass, and more preferably 1 to 10% by mass. If the amount is less than or greater than the above range, the effects of the present invention are difficult to obtain.

[0027] In addition to the essential components (a), (b), and (c) above, the photosensitive resin composition for flexographic printing plates of the present invention may appropriately contain other optional components such as plasticizers, hydrophilic compounds, ultraviolet absorbers, thermal polymerization inhibitors (stabilizers), surface tension modifiers, thermoplastic resin elastomers, solid rubber, dyes, pigments, defoamers, and anti-coagulation agents, to the extent that they do not impede the effects of the present invention, for the purpose of improving various properties.

[0028] Plasticizers impart flexibility to the photosensitive resin layer, and examples of plasticizers include liquid rubber, oil, polyester, and phosphate compounds. Examples of liquid rubber include liquid compounds having a conjugated diene structure, or those to which hydroxyl groups, carboxyl groups, or sulfonic acid groups have been added. Examples of oils include paraffin, naphthenes, and aromas. Examples of polyesters include adipic acid-based polyesters. Examples of phosphate compounds include phosphate 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 polymers obtained by polymerizing conjugated dienes. In the case of carboxyl groups, metal salts may also be used. The amount of plasticizer blended in the photosensitive resin composition of the present invention is a maximum of 40% by mass.

[0029] Hydrophilic compounds are used in the case of water-developable flexographic printing plates. Hydrophilic compounds improve water development and are compounds that have hydrophilic groups in their molecules, such as carboxylic acids, carboxylates, sulfonic acids, sulfonates, hydroxyl groups, amino groups, phosphate groups, ethylene oxide, and propylene oxide, and are either water-soluble or water-dispersible. Hydrophilic compounds may be low-molecular-weight compounds, oligomers, or high-molecular-weight compounds. Hydrophilic compounds may also be compounds that have the same function as plasticizers, such as liquid polybutadiene. Specific examples of hydrophilic compounds include polyhydric alcohols, polyhydric carboxylic acids, ester compounds of polyhydric carboxylic acids, acrylic polymers, polyalkylene glycol-modified polymers, urethane polymers, polyamide polymers, polyester polymers, and polymers obtained by polymerizing conjugated dienes. Surfactants can also be used. These polymers may be urethane polymers with chain extensions by urea bonds and / or urethane bonds, or conjugated diene polymers into which acrylic copolymers modified with acrylic monomers have been introduced. Among these, urethane polymers having carboxylates and liquid polybutadienes having hydroxyl groups or carboxylates in their molecules are preferred from the viewpoint of developability in aqueous developers, and these polymers may also contain ethylenically unsaturated groups in their molecules from the viewpoint of water resistance. The hydrophilic compound content in the photosensitive resin composition of the present invention is preferably a maximum of 15% by mass.

[0030] The flexographic printing plate of the present invention has a structure in which a photosensitive resin layer, made using a photosensitive resin plate composition containing the above-mentioned components, is provided on a support. In addition to melt molding, the photosensitive resin layer can be formed by any known method such as hot pressing, casting, melt extrusion, or solution casting, and this formed photosensitive resin layer can be laminated onto the support via an adhesive layer. As the support, a material that is flexible but has excellent dimensional stability is preferred, and for example, metal supports such as steel, aluminum, copper, and nickel, or thermoplastic resin supports such as polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyethylene furanoate, or polycarbonate film can be used. Among these, polyethylene terephthalate film, which has excellent dimensional stability and sufficiently high viscoelasticity, is particularly preferred. The thickness of the support is preferably 50 to 350 μm, more preferably 100 to 250 μm, considering mechanical properties, shape stabilization, and handling during printing plate making. Furthermore, if necessary, an adhesive layer may be provided between the support and the photosensitive resin layer obtained from the photosensitive resin composition to improve their adhesion.

[0031] The flexographic printing plate may have a thermal mask layer provided on a photosensitive resin layer, and can be combined with known thermal mask layers. The thermal mask layer is preferably water-developable. Specific examples of thermal mask layers include a thermal mask layer combining a polar group-containing polyamide and a butyral resin (Patent No. 4200510), a thermal mask layer containing a polyamide resin containing a basic nitrogen atom in the molecule and a polyamide resin containing alkylene glycol structural units in the molecule (Patent No. 6414375), a thermal mask layer containing a polymer having the same structure as the polymer in the photosensitive resin layer and an acrylic resin (Patent No. 5710961), a thermal mask layer containing a polymer having acidic groups with an acid value of 10 to 400 mgKOH / g (Patent No. 6810251), and a thermal mask layer containing an anionic polymer and a polymer with ester bonds in its side chains and a degree of saponification of 0 mol% to 90 mol%.

[0032] The flexographic printing plate of the present invention may have an intermediate layer between the heat-sensitive mask layer and the photosensitive resin layer to improve adhesion. Examples of film-forming binder polymers used in the intermediate layer include partially saponified vinyl acetate with a saponification rate of 60 to 90 mol% and polyamides having hydrophilic groups. In addition, known additives such as ultraviolet absorbers, surfactants, plasticizers, and latex resins may be incorporated into the intermediate layer.

[0033] The flexographic printing plate of the present invention is exposed by irradiating an active light from above a mask image drawn on a thermal mask layer using an infrared laser device placed on a photosensitive resin layer, or a normal negative film placed on a photosensitive resin layer. As a result, only the exposed areas harden and become insoluble. Preferably, the active light source is a high-pressure mercury lamp, ultra-high-pressure mercury lamp, metal halide lamp, xenon lamp, chemical lamp, or LED lamp, with a wavelength mainly of 300 to 450 nm. Next, the unexposed areas are dissolved or swollen and softened with water to which a suitable solvent or surfactant is added, and then scraped off with a brush to obtain a printing plate with a clear image. For this purpose, it is preferable to use a spray-type developing device or a brush-type developing device. [Examples]

[0034] The effects of a printing plate using the photosensitive resin composition for flexographic printing plates of the present invention are shown in the following examples, but the present invention is not limited to these examples. In the examples, "parts" means parts by mass, and the numerical values ​​indicating the composition ratio in the table also mean parts by mass. Furthermore, the evaluation of the characteristic values ​​in the examples was carried out by the following method.

[0035] UV irradiation dose required to reproduce a 175-line 1% halftone dot The printing plate was exposed to backlighting from the polyester support side for 10 seconds to achieve a relief depth of 0.6 mm. The cover film was then removed. Next, a 175-line 1% halftone evaluation mask image was used to evaluate the minimum UV irradiation dose that the 175-line 1% halftone on this printing plate could reproduce. The minimum UV irradiation dose reproduced by the 175-line 1% halftone was 200 mJ / cm². 2A printing plate was produced by exposing it with an increasing ultraviolet irradiation dose at intervals. The ultraviolet exposure was carried out at a distance of 5 cm from the surface of the photosensitive resin using a chemical lamp adjusted to an illuminance of 10 W / m 2 . The integrated ultraviolet light quantity can be obtained by exposing it to ultraviolet light up to the desired integrated light quantity using a commercially available ultraviolet integrated light quantity meter. Specifically, the ultraviolet integrated light quantity in the range of 2000 - 5000 mj / cm 2 was increased at an interval of 200 mj / cm 2 and irradiated with ultraviolet light. Then, it was developed for 8 minutes using a developing machine (Stuck System, 1% soapy water solution, 40 °C) manufactured by A&V Co., Ltd., and the water droplets on the plate surface were removed with a water squeegee. Then, it was 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. The image reproducibility of 175 lines 1% dot was judged visually using a 10x magnifying glass. The ultraviolet irradiation dose is represented by the integrated ultraviolet light quantity (mj / cm 2 ), and the minimum ultraviolet irradiation dose capable of reproducing 175 lines 1% dot was taken as the minimum ultraviolet irradiation dose. A commercially available integrated light quantity meter can be used for the integrated ultraviolet light quantity. Examples of the ultraviolet integrated light quantity meter include UIT-250 (manufactured by Ushio Denki Co., Ltd.: 365 nm). Also, the integrated ultraviolet light quantity can be calculated by ultraviolet illuminance (unit: mW / cm 2 ) × irradiation time (unit: seconds). For example, when exposed for 180 seconds at an ultraviolet illuminance of 5 mW / cm 2 , the integrated ultraviolet light quantity (integrated light quantity unit: mj / cm 2 ) is represented by 900 mj / cm 2 .

[0036] (Example 1) Synthesis of polyurethane polymers containing carboxylate salts (hydrophilic polymer A) A solution was prepared by dissolving 58.0 parts by mass of polytetramethylene glycol with a molecular weight of 850 (G-850, manufactured by Hodogaya Chemical Co., Ltd.), 124.0 parts by mass of dimethylolpropionic acid (manufactured by Kanto Chemical Co., Ltd.), 238.0 parts by mass of hexamethylene diisocyanate (manufactured by Tosoh Corporation), and 10.0 parts of n-butyltin dilaurate in 700.0 parts by mass of tetrahydrofuran. This solution was placed in a 2-liter flask equipped with a stirrer, and the flask was heated to 65°C while stirring, and the reaction was continued for 4 hours. Further, 52.0 parts by mass of hydroxyethyl methacrylate was added, and the reaction was continued for 2 hours while heating at 65°C. In a separate container, 368.0 parts by mass of terminal amino group-containing acrylonitrile butadiene oligomer (Hycar ATBN 1300×16, manufactured by Hunston) in 540.0 parts of tetrahydrofuran. This solution was then added to the 2-liter flask at room temperature while stirring, and the reaction was carried out. The obtained polymer solution was dried under reduced pressure to remove tetrahydrofuran and obtain polyurethane polymer A having a carboxylate salt. 100 parts by mass of the obtained polyurethane polymer A was dissolved in 200 parts by mass of tetrahydrofuran, and aqueous solutions containing predetermined amounts of lithium hydroxide hydrate and magnesium acetate tetrahydrate were added and stirred. After neutralization, 1.0 part by mass of benzoin methyl ether was added and stirring continued to obtain a polymer solution. The obtained polymer solution was dried under reduced pressure to remove tetrahydrofuran and water and obtain polyurethane polymer (hydrophilic polymer A) having a carboxylate salt.

[0037] Manufacturing of a film laminate (I) with an adhesive layer A copolymer polyester adhesive was coated onto a polyethylene terephthalate film (Toyobo Co., Ltd., E5000, 125 μm thick) to a thickness of 20 μm, thereby obtaining a film laminate (I) with an adhesive layer on the polyethylene terephthalate film.

[0038] Manufacturing of a film laminate (II) with a thermal mask layer A thermal mask layer coating solution was obtained by mixing carbon black dispersion (manufactured by Orient Chemical Industry Co., Ltd., AMBK-8), copolymer polyamide (PA223, manufactured by Toyobo Co., Ltd.), propylene glycol, and methanol in a mass ratio of 45 / 5 / 5 / 45. After applying a release treatment to both sides of a polyethylene terephthalate film (Toyobo Co., Ltd., E5000, thickness 125 μm), the thermal mask layer coating solution was applied using a bar coater so that the thickness of the coating film after drying was 2 μm, and the film was dried at 120°C for 5 minutes to obtain a film laminate (II) with a thermal mask layer.

[0039] Preparation of photosensitive resin composition (a) As a polymer obtained by polymerizing conjugated dienes, 44 parts by mass of butadiene latex (Nipol LX111NF, non-volatile content 55%, manufactured by Nippon Zeon Co., Ltd.) and 9 parts by mass of acrylonitrile-butadiene latex (Nipol SX1503), (b) As an ethylenically unsaturated compound, 26 parts by mass of 2,5-franjmethanol diacrylate as an ethylenically unsaturated compound having a heterocyclic structure including an ether linkage, and 3 parts by mass of BAC-45 (manufactured by Osaka Organic Chemical Industry Co., Ltd., a photopolymerizable oligomer that is a (meth)acrylate compound with a number average molecular weight of 700 to 20000 that forms a loose crosslinking network) as another ethylenically unsaturated compound, (c) 5 parts by mass of benzyldimethyl ketal as a photopolymerization initiator, and as other components, 8 parts by mass of butadiene oligomer (manufactured by Nippon Soda Co., Ltd., B2000, plasticizer), synthesized hydrophilic polymer A A dope was prepared by mixing 5 parts by mass of the ethylenically unsaturated compound, 0.1 parts by mass of the heat stabilizer (4-methoxyphenol), and 0.01 parts by mass of the ultraviolet absorber (tinuvin 326) in a container. The dope was placed in a pressurized kneader, and the solvent was removed under reduced pressure at 80°C to obtain a photosensitive resin composition. The content (%) of the ethylenically unsaturated compound having a heterocyclic structure containing an ether linkage was 89.7% by mass.

[0040] Preparation of flexographic printing plates The above-mentioned photosensitive resin composition was placed on a film laminate (I) having an adhesive layer, and a film laminate (II) having a heat-sensitive mask layer was placed on top of it. Lamination was performed at 100°C using a heat press to obtain a flexographic printing plate consisting of a PET support, an adhesive layer, a photosensitive resin layer, a heat-sensitive mask layer, and a cover film. The total thickness of the plate was 1.14 mm.

[0041] After storing the obtained flexographic printing plates for more than 7 days, the minimum amount of ultraviolet irradiation required to reproduce a 175-line 1% halftone was evaluated. The results are shown in Table 1.

[0042] (Examples 2-15, Comparative Examples 1-5) Except for changing the composition of the photosensitive resin layer (photosensitive resin composition) in the flexographic printing plate as shown in Table 1, the photosensitive resin compositions, flexographic printing plates, and flexographic printing plates of Examples 2 to 15 and Comparative Examples 1 to 5 were prepared in the same manner as in Example 1, and the minimum amount of ultraviolet irradiation required to reproduce a 175-line 1% halftone was evaluated. The results are shown in Table 1.

[0043] [Table 1]

[0044] The details of how to obtain each of the (b) ethylenically unsaturated compounds in Table 1 are as follows: 2,5-Franzil methanol diacrylate: 2,5-Franzil methanol diacrylate was produced by the esterification reaction of a diol with acrylic acid or methacrylic acid. Specifically, the same procedure as in Example 1 of Japanese Patent Publication No. 11-236353 was followed, except that 2-methyl-1,4-butanediol was replaced with 2,5-franzilol (commercial product) and methyl acrylate was used instead of methyl methacrylate, to obtain 2,5-franzil methanol diacrylate. Furan-2-methanol methacrylate: Manufactured by Tokyo Chemical Industry Co., Ltd. Tetrahydro-2,5-flange methanol diacrylate: Tetrahydro-2,5-flange methanol diacrylate was obtained using tetrahydro-2,5-flange methanol (commercial product) in the same manner as the synthesis of 2,5-flange methanol diacrylate. Tetrahydro-2-furanmethanol methacrylate: Tetrahydro-2-furanmethanol methacrylate was obtained using tetrahydrofuran-2-methanol (commercial product) in the same manner as the synthesis of 2,5-franzemethanol diglycyl ether diacrylate. Note that 2,5-franzemethanol diglycyl ether diacrylate can be obtained by replacing the polyhydric alcohol with 2,5-franzemethanol according to Example 4 of Japanese Patent No. 3644761 to produce 2,5-franzemethanol diglycyl ether to which an epoxy group has been introduced, and then reacting the obtained 2,5-franzemethanol diglycyl ether with acrylic acid according to Japanese Patent Application Publication No. 2024-5441. 4-pyrone-2,6-dicarboxylic acid di(meth)acrylate: Using chelidonic acid (4-pyrone-2,6-dicarboxylic acid) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. as a raw material, 4-pyrone-2,6-dicarboxylic acid di(meth)acrylate was obtained in the same manner as the synthesis method for 2,5-franjmethanol diacrylate. Tricyclodecanediol diacrylate: Manufactured by Shin-Nakamura Chemical Co., Ltd., DCP Isobornyl acrylate: Manufactured by Osaka Organic Chemical Industry Co., Ltd. Trimethylolpropane triacrylate: Manufactured by Kyoeisha Chemical Co., Ltd., Light Ester TMP Lauryl methacrylate: Manufactured by Kyoeisha Chemical Co., Ltd., Light Ester L Triethylene glycol dimethacrylate: Manufactured by Shin-Nakamura Chemical Co., Ltd., 3G BAC-45: Manufactured by Osaka Organic Chemical Industry Co., Ltd.

[0045] As can be seen from Table 1, in Examples 1 to 15, the minimum UV irradiation required to reproduce a 175-line 1% halftone dot decreased by more than 23% compared to Comparative Example 1, demonstrating the effect of including an ethylenically unsaturated compound having a heterocyclic structure containing an ether bond. In particular, increasing the proportion of the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond in the ethylenically unsaturated compound tends to increase this effect. On the other hand, in Comparative Examples 1 to 3, where only conventional ethylenically unsaturated compounds without ether bonds were used instead of the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond, the minimum UV irradiation required to reproduce a 175-line 1% halftone dot was high. Furthermore, in Comparative Example 4, which uses an ethylenically unsaturated compound having a heterocyclic structure containing an ether bond but has a low content, the minimum UV irradiation required to reproduce a 175-line 1% halftone dot decreased compared to Comparative Example 1, but the reduction effect was only 10.0%, which is extremely small. Furthermore, in Comparative Example 5, which used an ethylenically unsaturated compound containing an ether linkage but lacking a heterocyclic structure (triethylene glycol dimethacrylate) instead of an ethylenically unsaturated compound having a heterocyclic structure containing an ether linkage, the minimum amount of ultraviolet irradiation required to reproduce a 175-line 1% halftone dot increased compared to Comparative Example 1. This is thought to be because, since triethylene glycol dimethacrylate is a linear polyether, the ethylenically unsaturated compounds could not be finely dispersed and instead aggregated and localized in the composition. As a result, the polymerization inhibition suppression effect of dissolved oxygen by the ether linkage could not be uniformly and sufficiently exerted throughout the composition, and photocrosslinking by the ethylenically unsaturated compounds did not proceed efficiently. In addition, it is thought that because the ethylenically unsaturated compounds were not finely dispersed, ultraviolet light was scattered, making it difficult for ultraviolet light to reach the bottom of the photosensitive resin layer. In addition to 175-line 1% halftone dot reproducibility, performance evaluations of independent dots and development time were also performed, but no significant differences were observed between Examples 1-15 and Comparative Example 1. [Industrial applicability]

[0046] According to the present invention, a photosensitive resin composition for flexographic printing plates and a flexographic printing plate using the same can be provided, which enables the reproduction of fine images with 175 lines and 1% halftone dots with short-term ultraviolet irradiation, without the need to prepare a low-oxygen concentration environment, provide an oxygen barrier layer, or increase the amount of ultraviolet irradiation. Therefore, the present invention is extremely useful in the industry, which seeks flexographic printing plates that can form fine images in a short time.

Claims

1. A photosensitive resin composition for flexographic printing plates, comprising at least (a) a polymer obtained by polymerizing a conjugated diene, (b) an ethylenically unsaturated compound, and (c) a photopolymerization initiator, wherein the photosensitive resin composition contains 5 to 50% by mass of (b) the ethylenically unsaturated compound, and (b) contains 10% by mass or more of an ethylenically unsaturated compound having a heterocyclic structure including an ether linkage.

2. The photosensitive resin composition for flexographic printing plates according to claim 1, characterized in that the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond is one or more compounds selected from the group consisting of ethylenically unsaturated compounds having a furan skeleton, ethylenically unsaturated compounds having a tetrahydrofuran skeleton, and ethylenically unsaturated compounds having a pyrone skeleton.

3. The photosensitive resin composition for flexographic printing plates according to claim 2, characterized in that the ethylenically unsaturated compound having a furan skeleton is one or more (meth)acrylates selected from the group consisting of frandelol di(meth)acrylate, frandelcarboxylic acid di(meth)acrylate, frandel methanol di(meth)acrylate, furan monomethanol(meth)acrylate, furancarboxylic acid (meth)acrylate, frandelcarboxylic acid diepoxy(meth)acrylate, frandelol diepoxy(meth)acrylate, and frandel methanol monoepoxy(meth)acrylate.

4. The photosensitive resin composition for flexographic printing plates according to claim 2, characterized in that the ethylenically unsaturated compound having a tetrahydrofuran skeleton is one or more (meth)acrylates selected from the group consisting of tetrahydrofranmethyl di(meth)acrylate, tetrahydrofuran monomethanol mono(meth)acrylate, tetrahydrofranmethyl diepoxy(meth)acrylate, tetrahydrofrancarboxylic acid di(meth)acrylate, tetrahydrofrancarboxylic acid mono(meth)acrylate, tetrahydrofurancarboxylic acid monoepoxy(meth)acrylate, tetrahydrofrancarboxylic acid diepoxy(meth)acrylate, tetrahydrofuran monomethanol monoepoxy(meth)acrylate, and tetrahydrofranitol diepoxy(meth)acrylate.

5. The photosensitive resin composition for flexographic printing plates according to claim 2, characterized in that the ethylenically unsaturated compound having a pyrone skeleton is one or more (meth)acrylates selected from the group consisting of 4-pyron-2,6-dicarboxylic acid di(meth)acrylate, 4-pyron-2,6-dicarboxylic acid diexope(meth)acrylate, 4-pyron-2,6-dicarboxylic acid mono(meth)acrylate, 4-pyron-2,6-dicarboxylic acid monoepoxy(meth)acrylate, γ-pyron-2-carboxylic acid monoepoxy(meth)acrylate, γ-pyron-2-carboxylic acid mono(meth)acrylate, and γ-pyron-2,6-dicarboxylic acid di(meth)acrylate.

6. A flexographic printing plate using the photosensitive resin composition for flexographic printing plates described in any one of claims 1 to 5.

Images