Photosensitive resin composition for printing plates

Abstract

The present invention provides a photopolymerizable photosensitive resin composition for letterpress printing plates that enables fine image reproduction with short exposure times, without increasing the amount of ultraviolet irradiation or improving the ultraviolet transmittance of the photosensitive resin layer. [Solution] A photosensitive resin composition for letterpress printing plates, comprising at least a water-soluble or water-dispersible polyamide, an ethylenically unsaturated compound, and a photopolymerization initiator, wherein the photosensitive resin composition contains 5 to 50% by mass of the ethylenically unsaturated compound, and the ethylenically unsaturated compound 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 relief printing original plates capable of reproducing fine images by short-time exposure, and a relief printing original plate using the same.

Background Art

[0002] The photosensitive resin composition used for relief printing original plates generally contains a soluble polymer compound, an ethylenically unsaturated compound, and a photopolymerization initiator as essential components, and additives such as a stabilizer and a plasticizer are blended as necessary.

[0003] In recent years, there has been a demand for reproducing finer images than before for relief printing original plates. A method of increasing the ultraviolet irradiation amount has been studied for reproducing fine images, but there has been a problem that the production efficiency is poor because the exposure time becomes long.

[0004] As another method, a relief printing original plate has been proposed in which the image reproducibility is improved by improving the ultraviolet transmittance of the photosensitive resin layer as in Patent Document 1. This method is characterized by improving the ultraviolet transmittance of the photosensitive resin layer by using a specific photopolymerization initiator, and enables improvement of the image reproducibility by improving the curability at the bottom of the photosensitive resin layer. However, although a certain degree of improvement effect was seen in the above printing original plate, sufficient improvement of the image reproducibility was not obtained.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] 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 letterpress printing plates with excellent photopolymerization properties, which enables the reproduction of fine images with short exposure times without increasing the amount of ultraviolet irradiation or improving the ultraviolet transmittance of the photosensitive resin layer, and a letterpress printing plate using the same. [Means for solving the problem]

[0007] 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 letterpress printing plates, it becomes possible to reproduce fine images with short exposure times, thus completing the present invention.

[0008] In other words, the present invention consists of the following configurations (1) to (6). (1) A photosensitive resin composition for letterpress printing plates, comprising at least a water-soluble or water-dispersible polyamide, an ethylenically unsaturated compound, and a photopolymerization initiator, wherein the photosensitive resin composition contains 5 to 50% by mass of the ethylenically unsaturated compound, and the ethylenically unsaturated compound 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 letterpress 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 letterpress 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 (meth)acrylate, frandelcarboxylic acid diepoxy(meth)acrylate, frandelol diepoxy(meth)acrylate, and frandel methanol monoepoxy(meth)acrylate. (4) The photosensitive resin composition for letterpress 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 letterpress 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 diepoxy(meth)acrylate, 4-pyrone-2,6-dicarboxylic acid mono(meth)acrylate, 4-pyrone-2,6-dicarboxylic acid monopoxy(meth)acrylate, γ-pyrone-2-carboxylic acid mono(meth)acrylate, and γ-pyrone-2,6-dicarboxylic acid di(meth)acrylate. (6) A relief printing plate using the photosensitive resin composition for relief printing plates described in any one of items (1) to (5). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a photosensitive resin composition for letterpress printing plates that enables the reproduction of fine images such as 175-line 1% halftones with short exposure times, without increasing the amount of ultraviolet irradiation or improving the ultraviolet transmittance of the photosensitive resin layer, and a letterpress printing plate using the same. Furthermore, since the ethylenically unsaturated compound in the photosensitive resin composition of the present invention can be a heterocyclic compound derived from biomass, it can also contribute to solving the depletion problem of fossil resources. [Modes for carrying out the invention]

[0010] The photosensitive resin composition for letterpress printing plates of the present invention contains at least a water-soluble or water-dispersible polyamide, an ethylenically unsaturated compound, and a photopolymerization initiator as essential components, and is characterized in that the ethylenically unsaturated compound contains a certain amount or more of an ethylenically unsaturated compound having a heterocyclic structure including an ether linkage. Furthermore, using the photosensitive resin composition for letterpress printing plates of the present invention, it is possible to provide a letterpress printing plate capable of reproducing fine images with short exposure times. The letterpress printing plate of the present invention may also be a CTP letterpress 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.

[0011] The water-soluble or water-dispersible polyamide used in the photosensitive resin composition for letterpress printing plates of the present invention refers to a polyamide that has the property of dissolving or dispersing in water. For example, when a polymer (resin) formed into a film is immersed in water at room temperature to 40°C and rubbed with a brush or the like, the polymer (resin) either dissolves completely or partially, or swells and disperses in water, causing the film to lose weight or disintegrate.

[0012] Examples of water-soluble or water-dispersible polyamides include polyetheramides (e.g., Japanese Patent Publication No. 55-79437), polyether esteramides (e.g., Japanese Patent Publication No. 58-117537), tertiary nitrogen-containing polyamides (e.g., Japanese Patent Publication No. 50-7605), ammonium salt type tertiary nitrogen atom-containing polyamides (e.g., Japanese Patent Publication No. 53-36555), tertiary nitrogen-containing polyamides containing alicyclic structural units (e.g., Japanese Patent No. 6226255), and addition polymers of amide compounds having one or more amide bonds and organic diisocyanate compounds (e.g., Japanese Patent Publication No. 58-140737). Among these, tertiary nitrogen atom-containing polyamides and ammonium salt type tertiary nitrogen atom-containing polyamides are preferred, and tertiary nitrogen-containing polyamides containing alicyclic structural units are particularly preferred.

[0013] The amount of polyamide used in the photosensitive resin composition for letterpress printing plates of the present invention is preferably 45 to 65% by mass of the photosensitive resin composition. More preferably, it is 48 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.

[0014] The ethylenically unsaturated compound used in the photosensitive resin composition for letterpress printing plates of the present invention is characterized by containing a certain amount or more of an ethylenically unsaturated compound having a heterocyclic structure containing an ether bond. Because the ethylenically unsaturated compound having a heterocyclic structure containing 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 hindrance 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". Having a cyclic structure called a "heterocyclic structure" makes it less likely for the ethylenically unsaturated compounds to aggregate due to steric hindrance, and it is easier to finely disperse them in the polyamide, which is the main component of the composition. Not only can the polymerization hindrance suppression effect of dissolved oxygen by the ether bond be uniformly and sufficiently exhibited throughout the composition, but photocrosslinking by the ethylenically unsaturated compound also proceeds efficiently, so fine image reproduction can be improved with short exposure times without increasing the amount of ultraviolet irradiation or improving the ultraviolet transmittance of the photosensitive resin layer. Furthermore, due to its "heterocyclic structure," even if the carbon atoms adjacent to the oxygen atom in the ether bond react with dissolved oxygen in the composition and the ether bond cleaves, the cyclic structure remains stable, and the photopolymerization property, which is the original function of ethylenically unsaturated compounds, is not impaired. In contrast, in the case of linear polyethers and branched polyethers, the ethylenically unsaturated compounds cannot be finely dispersed and instead aggregate and localize in the composition. As a result, the aforementioned effect of suppressing polymerization impairment by dissolved oxygen through the ether bond cannot be uniformly and sufficiently exerted throughout the composition, and photocrosslinking by the ethylenically unsaturated compounds does not proceed efficiently, making it impossible to shorten the exposure time. Moreover, in the case of linear polyethers and branched polyethers, when the carbon atoms adjacent to the oxygen atom in the ether bond react with dissolved oxygen in the composition and the ether bond cleaves, side reactions such as molecular scalding also occur, which is thought to reduce the photopolymerization property, the original function of ethylenically unsaturated compounds.

[0015] 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.

[0016] 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.

[0017] 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 monoepoxy (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.

[0018] Examples of the ethylenically unsaturated compound having the furan skeleton include one or more (meth)acrylates selected from the group consisting of furandiol di(meth)acrylate, furandicarboxylic acid di(meth)acrylate, furandimethanol di(meth)acrylate, furanmonomethanol (meth)acrylate, furancarboxylic acid (meth)acrylate, furandicarboxylic acid diepoxy (meth)acrylate, furandiol diepoxy (meth)acrylate, and furandimethanol monoepoxy (meth)acrylate. Specifically, 2,5-furandimethanol di(meth)acrylate, 3,4-furandimethanol di(meth)acrylate, di(meth)acryloyloxyethyl-2,5-furandicarboxylic acid, di(meth)acryloyloxypropyl-2,5-furandicarboxylic acid, (meth)acryloyloxyethyl-2-furancarboxylic acid (meth)acrylate, 2,5-furandiol diepoxy (meth)acrylate, 3,4-furandimethanol diepoxy (meth)acrylate, 2,5-furandicarboxylic acid monoepoxy (meth)acrylate, 2,5-furandicarboxylic acid diepoxy (meth)acrylate, 2-furancarboxylic acid epoxy (meth)acrylate, etc. are mentioned. Particularly preferred are 2,5-furandimethanol diepoxy (meth)acrylate, 2,5-furandimethanol di(meth)acrylate, and 2,5-furandicarboxylic acid diepoxy (meth)acrylate. As the ethylenically unsaturated compound having the furan skeleton, a commercially available product may be purchased, or it may be produced by a known production method.

[0019] Examples of the ethylenically unsaturated compound having the tetrahydrofuran skeleton include tetrahydrofurandimethanol di(meth)acrylate, tetrahydrofuranmonomethanol mono(meth)acrylate, tetrahydrofurandimethanol diepoxy (meth)acrylate, tetrahydrofurandicarboxylic acid di(meth)acrylate, tetrahydrofurandicarboxylic acid mono(meth)acrylate, tetrahydrofurancarboxylic acid monoepoxy (meth)acrylate, tetrahydrofurandicarboxylic acid diepoxy (meth)acrylate, Examples include one or more (meth)acrylates selected from the group consisting of tetrahydrofuran monomethanol monoepoxy(meth)acrylate and tetrahydroflangol diepoxy(meth)acrylate. Specifically, examples include tetrahydro-2,5-flangethanol di(meth)acrylate, tetrahydro-2,5-flangcarboxylic acid di(meth)acrylate, tetrahydro-2-furanmethanol mono(meth)acrylate, tetrahydro-2,5-flangcarboxylic acid mono(meth)acrylate, tetrahydro-2,5-flangethanol diepoxy(meth)acrylate, tetrahydro-2,5-flangcarboxylic acid diepoxy(meth)acrylate, tetrahydro-2,5-flangethanol diepoxy(meth)acrylate, tetrahydro-2-furanmethanol epoxy(meth)acrylate, tetrahydro-3-furanmethanol epoxy(meth)acrylate, and tetrahydro-2,5-flangethanol diepoxy(meth)acrylate. Particularly preferred are tetrahydro-2,5-franze methanol di(meth)acrylate, tetrahydro-2,5-franze methanol diepoxy(meth)acrylate, tetrahydro-2,5-franze carboxylic acid diepoxy(meth)acrylate, and tetrahydro-2-furanmethanol mono(meth)acrylate. The ethylenically unsaturated compounds having a tetrahydrofuran skeleton may be purchased commercially or produced by known manufacturing methods.

[0020] 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 at least 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. Particularly preferred are di(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid, diepoxy(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid, and monoepoxy(meth)acrylate of 4-pyrone-2,6-dicarboxylic acid. As the ethylenically unsaturated compound having the pyrone skeleton, a commercially available product may be purchased, or it may be produced by a known production method.

[0021] When the ethylenically unsaturated compound having the heterocyclic structure containing the above ether bond uses a compound having a heterocyclic structure having 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 preferred, and addition of ethylene oxide is preferred in terms of water solubility.

[0022] Ethylene-unsaturated compounds having a heterocyclic structure containing an ether linkage may be produced by known manufacturing methods or purchased commercially. In the case of (meth)acrylates, they may be produced by changing the raw materials according to the examples of the method of production by esterification reaction of a diol with acrylic acid or methacrylic acid (e.g., Japanese Patent Publication No. 11-236353). They can also be synthesized by esterification reaction of a dicarboxylic acid with hydroxyethyl acrylate or hydroxyethyl methacrylate. Furthermore, when using a dicarboxylic acid containing an oxygen atom in its heterocyclic structure, a dicarboxylic acid diester compound may be used as a raw material.

[0023] When the ethylenically unsaturated compound having a heterocyclic structure containing an ether linkage is an epoxy (meth)acrylate, it can be produced using known methods. First, an epoxy compound is produced by introducing an epoxy group to the hydroxyl group of a heterocyclic compound having a hydroxyl group, and then the epoxy compound is reacted with methacrylic acid or acrylic acid. For example, the examples in Japanese Patent Publication No. 11-343331 disclose a method for producing a polyfunctional epoxy acrylate by reacting an epoxy compound with acrylic acid. The epoxy compound can be produced using known production methods, such as those used to produce bisphenol A or epoxy resins synthesized using epichlorohydrin as a raw material.

[0024] The photosensitive resin composition for letterpress printing plates of the present invention contains 5 to 50% by mass of an ethylenically unsaturated compound, preferably 15 to 50% by mass. Furthermore, the content of the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond in the ethylenically unsaturated compound of the photosensitive resin composition for letterpress printing plates of the present invention is 10% by mass or more relative to the total ethylenically unsaturated compound. Preferably it is 30% by mass or more, more preferably 50% by mass or more, and may even be 100% by mass. If the content of the ethylenically unsaturated compound having a heterocyclic structure containing an ether bond in the ethylenically unsaturated compound is above the above range, the effect of reproducing fine images is enhanced, and as the content increases, the effect tends to increase even further.

[0025] As long as the ethylenically unsaturated compound contains a certain amount or more of an ethylenically unsaturated compound having a heterocyclic structure including an ether bond, it may also contain ethylenically unsaturated compounds other than ethylenically unsaturated compounds having a heterocyclic structure including an ether bond, as long as the effects of the present invention are not significantly reduced.

[0026] Other ethylenically unsaturated compounds that can be used in the photosensitive resin composition of the present invention, besides the ethylenically unsaturated compounds having a heterocyclic structure containing an ether bond as described above, include compounds that contain one or more photopolymerizable unsaturated groups in their molecule. Known compounds can be used for this purpose.

[0027] 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.

[0028] 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.

[0029] Conventionally known photopolymerization initiators can be used in the photosensitive resin composition for letterpress printing plates of the present invention. Specifically, examples include benzophenones, benzoins, acetophenones, benzyls, benzoin alkyl ethers, benzyl alkyl ketals, anthraquinones, and thioxanthones. Specific examples include benzophenone, benzoin, acetophenone, benzoin methyl ether, benzoin ethyl ether, benzyl dimethyl ketal, anthraquinone, 2-chloroanthraquinone, thioxanthone, and 2-chlorothioxanthone. The amount of photopolymerization initiator used in the photosensitive resin composition for letterpress printing plates of the present invention is preferably 0.05 to 5% by weight of the photosensitive resin composition. If the amount of photopolymerization initiator used is less than the above range, photopolymerization may be insufficient, and if it exceeds the above range, fine image formation may not be possible.

[0030] In addition to the essential components mentioned above, the photosensitive resin composition for letterpress printing plates of the present invention may appropriately contain optional components such as plasticizers, ultraviolet absorbers, thermal polymerization inhibitors (stabilizers), hydrophilic compounds, surface tension modifiers, dyes, and pigments, to the extent that they do not impede the effects of the present invention, for the purpose of improving various properties.

[0031] Thermal polymerization inhibitors are added to prevent unintended thermal polymerization due to heating during the preparation, manufacture, or molding of photosensitive resin compositions, or to prevent dark reactions during storage of the composition. Examples of thermal polymerization inhibitors include hydroquinones such as hydroquinone, mono-tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone, and hydroquinone monomethyl ether; benzoquinones such as benzoquinone and 2,5-diphenyl-p-benzoquinone; phenols; catechols such as catechol and p-tert-butylcatechol; aromatic amine compounds; bicric acids; phenothiazines; α-naphthoquinones; anthraquinones; nitro compounds; and sulfur compounds. The amount of thermal polymerization inhibitor used is preferably 0.001 to 2% by weight of the photosensitive resin composition, and particularly preferably 0.005 to 1% by weight. Two or more of these compounds may be used in combination.

[0032] The photosensitive resin composition of the present invention can be molded in the desired laminate configuration by any known method, such as melt molding, hot pressing, casting, melt extrusion, or solution casting, to obtain a relief printing plate with a photosensitive resin layer.

[0033] Printing plates for letterpress printing can be manufactured by laminating sheet-shaped molded products (unexposed resin) onto a support, with or without the use of a known adhesive. When supplying laminates formed by laminating sheet-shaped molded products (unexposed resin) onto a support, it is preferable to further laminate a protective film in contact with the sheet-shaped molded products (unexposed resin). The protective film can be made of film-like plastic, for example, a polyester film with a thickness of 125 μm is used.

[0034] The support used in the letterpress printing plate of the present invention is preferably made of a flexible material with excellent dimensional stability. 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 300 μm, considering mechanical properties, shape stabilization, and handling during plate making. If necessary, an adhesive layer may be provided between the support and the photosensitive resin layer obtained from the photosensitive resin composition to improve adhesion between them.

[0035] The printing plate for relief printing of the present invention may have a multilayer structure of two or more photosensitive resin layers. A multilayer structure is a structure in which the photosensitive resin layer has an upper layer provided on top of at least a lower layer provided on the support side, and an intermediate layer may be provided between the upper and lower layers. The upper layer is a functional resin layer having a different function from the lower layer, and by providing the upper layer, the photocurability of the surface of the photosensitive resin layer, the surface hardness of the printing plate, the surface characteristics of the printing plate, and the print resistance can be adjusted. The functional photosensitive resin layer used for the upper layer is preferably a photosensitive resin layer with a thickness of 1 to 30 μm. Known functional photosensitive resin layers can be used as the functional photosensitive resin layer used for the upper layer. Examples include a printing plate with a sharpened shoulder shape at the top of the relief (Japanese Patent Publication No. 6-313966), a printing plate with increased resin hardness in the upper layer (Japanese Patent No. 1386812), a printing plate in which the ethylenically double bond equivalent in the polymer in the upper layer is greater than in the lower layer (International Publication No. 2022 / 054427), and a printing plate in which the ratio of photoinitiator in the upper layer is increased (International Publication No. 2023 / 277053). The upper layer may also contain an ethylenically unsaturated compound having a heterocyclic structure including an ether bond.

[0036] The letterpress printing plate of the present invention may have a thermal mask layer provided on a photosensitive resin layer, and can be combined with known thermal mask layers. Examples include a thermal mask layer combining a polar group-containing polyamide and a butyral resin (Japanese Patent No. 4247725), and a thermal mask layer containing polyvinyl alcohol with a saponification degree of 60 to 100 mol% (Japanese Patent Publication No. 2023-64817).

[0037] The letterpress printing plate of the present invention may have a non-photosensitive intermediate layer on top of the photosensitive resin layer. When a thermal mask layer is provided, the intermediate layer can improve adhesion between the photosensitive resin layer and the thermal mask layer. When a thermal mask layer is not provided, the intermediate layer has an anti-sticking function on the surface of the photosensitive resin layer, improving peeling from the protective film and adhesion to the negative film. The intermediate layer contains a film-forming binder polymer, such as partially saponified vinyl acetate or celluloses like methylcellulose. The intermediate layer may also contain known additives such as UV absorbers, surfactants, and plasticizers. These polymers are not limited to a single type; two or more polymers can be used in combination.

[0038] The relief printing plate obtained from the photosensitive resin composition of the present invention is produced by exposing a 175-line 1% halftone mask image made from a thermal mask layer provided on the photosensitive resin layer, or a 175-line 1% halftone negative film that is in close contact with the photosensitive resin layer, by irradiating it with active light from above, and insolubilizing only the exposed areas through which the active light has passed. The active light is usually produced using a light source such as a high-pressure mercury lamp, ultra-high-pressure mercury lamp, metal halide lamp, xenon lamp, chemical lamp, or LED lamp with a wavelength centered on 300 to 450 nm. On the other hand, in the case of CTP printing plates, the thermal mask layer is irradiated with an IR laser in an image-like manner to form a mask (with the same function as a negative film) on the photosensitive resin layer. After writing the image information to the thermal mask layer, the entire photosensitive printing plate is irradiated with active light through the mask, and a plate is produced in which only the exposed areas through which the active light has passed have been insolubilized.

[0039] Next, the unexposed areas are dissolved and removed using a suitable solvent, particularly neutral water in this invention. However, the unexposed areas can also be dissolved and removed using a development method such as a spray-type or brush-type developer. After that, the printing plate from which the unexposed areas have been dissolved and removed undergoes a dewatering, drying, and post-exposure process to obtain the final printing plate. [Examples]

[0040] The effects of printing plates using the photosensitive resin composition 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.

[0041] UV irradiation dose required to reproduce a 175-line 1% halftone dot First, a 175-line 1% halftone mask image was prepared from a negative film or thermal mask layer. Using a letterpress printing plate with a total thickness of 0.95 mm, the minimum UV irradiation dose required to reproduce the 175-line 1% halftone was evaluated. UV irradiation dose was expressed as integrated UV light and measured using a commercially available integrated light meter UIT-250 (manufactured by Ushio Inc.: 365 nm). UV exposure was measured at an illuminance of 2.5 mW / cm². 2 The photosensitive resin surface was exposed using a chemical lamp adjusted to the specified intensity from a distance of 5 cm above the surface. The cumulative ultraviolet light intensity was adjusted to the desired amount by changing the exposure time. Specifically, the cumulative ultraviolet light intensity was 700 to 1500 mJ / cm². 2 The range is 50 mJ / cm 2 Ultraviolet light was irradiated at intervals of [specified interval]. Next, the image was developed with 25°C tap water using a brush-type washer (120 μmφ nylon brush, JW-A2-PD model manufactured by JDELK SEIKI Co., Ltd.) to obtain a relief image. After further drying with hot air at 60°C for 10 minutes, the image was exposed to a high-pressure mercury lamp for 30 seconds to obtain a printing plate. The image reproducibility of a 175-line 1% halftone dot was judged visually using a 10x magnifying glass. Note that the amount of ultraviolet irradiation was measured by the integrated ultraviolet light (unit: mJ / cm²). 2The UV integrated light quantity is expressed as UV irradiance (unit: mW / cm²), and the UV irradiation amount that reproduced a 175-line 1% halftone dot was defined as the minimum UV irradiation amount. A commercially available UV integrated light meter may be used to calculate the UV integrated light quantity. An example of a UV integrated light meter is the UIT-250 (manufactured by Ushio Inc.: 365nm). The UV integrated light quantity is expressed as UV irradiance (unit: mW / cm²). 2 It can be calculated by multiplying the UV irradiance by the irradiation time (in seconds). For example, UV irradiance of 5 mW / cm². 2 When exposed to ultraviolet light for 180 seconds using this method, the integrated ultraviolet light dose is 900 mJ / cm². 2 It is represented as follows.

[0042] (Example 1) Synthesis of tertiary nitrogen atom-containing polyamides 52 parts by mass of ε-caprolactam, 38 parts by mass of N,N,-di(γ-aminopropyl)piperazine adipate, 10 parts by mass of 3-bisaminomethylcyclohexane adipate, and 100 parts by mass of water were placed in an autoclave, purged with nitrogen, sealed, and gradually heated. The internal pressure was 10 kg / m³. 3 From the point where the pressure reached a certain level, water was distilled off until it could no longer be maintained, and the pressure was returned to atmospheric pressure after about 2 hours. The reaction was then carried out at atmospheric pressure for 1 hour. The maximum polymerization reaction temperature was 255°C. This yielded a tertiary nitrogen atom-containing polyamide with a melting point of 137°C and a specific viscosity of 1.94. Preparation of photosensitive resin composition 52.5 parts by mass of the obtained tertiary nitrogen atom-containing polyamide was added to a mixture of 62 parts by mass of methanol and 10 parts by mass of water, and the mixture was heated to 65°C to dissolve it. Then, 6.5 parts by mass of N-butylbenzenesulfonamide, 5.0 parts by mass of lactic acid as a quaternizing agent, and 0.1 parts by mass of hydroquinone monomethyl ether were added, and the mixture was stirred and dissolved for a further 30 minutes to ammonium chloride the polyamide and make it water-soluble. Subsequently, 2.5 parts by mass of glycidyl methacrylate (GMA) was added to introduce photopolymerizable groups into the polyamide, 1.0 part by mass of benzyldimethyl ketal as a photopolymerization initiator, 40 parts by mass of frangimethanol diglycyl acrylate as an ethylenically unsaturated compound having a heterocyclic structure containing an ether linkage, and 6.5 parts by mass of N-butylbenzenesulfonamide as a plasticizer, and the mixture was stirred and dissolved for 30 minutes. Next, the temperature was gradually increased to distill off methanol and water, and the mixture was concentrated until the temperature in the vessel reached 110°C. At this stage, a fluid, viscous, photosensitive resin composition was obtained.

[0043] Preparation of printing plates Next, a support having an adhesive layer was prepared. The support having an adhesive layer was obtained by coating a 250 μm thick polyester film with an adhesive composition containing an ultraviolet absorber to a thickness of 20 μm. Using the obtained support, the above photosensitive resin composition was cast onto the adhesive layer surface of the support, and a 125 μm thick polyester film coated with a 2 μm thick film of polyvinyl alcohol (KH-20, manufactured by Mitsubishi Chemical Corporation) with a saponification degree of 80 mol% was placed in contact with the photosensitive resin composition. Using a laminator, a sheet-like photosensitive resin laminate with a total thickness of 1080 μm was obtained. The obtained photosensitive resin laminate is a photosensitive resin relief printing plate with an intermediate layer between the protective film and the photosensitive resin layer.

[0044] After storing the obtained letterpress 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.

[0045] (Examples 2-12, Comparative Examples 1-5) Except for changing the composition of the photosensitive resin layer (photosensitive resin composition) in the letterpress printing plate as shown in Table 1, the photosensitive resin compositions and letterpress printing plates of Examples 2 to 12 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.

[0046] (Example 13) Synthesis of polyetheramides A polyetheramide was obtained by melt polycondensation of 25 parts by weight of ε-caprolactam, 15 parts by weight of a nylon salt of hexamethylenediamine and adipic acid, and 60 parts by weight of a nylon salt of diaminopolyethylene glycol with an average molecular weight of 1,000. A photosensitive resin composition and a letterpress printing plate were prepared in the same manner as in Example 1, except that the polyamide of Example 1 was replaced with the obtained polyetheramide, and the minimum amount of ultraviolet irradiation required to reproduce a 175-line 1% halftone was evaluated. The results are shown in Table 1.

[0047] [Table 1]

[0048] The details of how to obtain each of the ethylenically unsaturated compounds listed in Table 1 are as follows. 2,5-Frangimethanol Diglycyl Ether Diacrylate: According to Example 4 of Japanese Patent No. 3644761, the polyhydric alcohol was replaced with 2,5-frangimethanol to produce 2,5-frangimethanol diglycyl ether with an epoxy group introduced. Using the obtained 2,5-frangimethanol diglycyl ether, it was reacted with acrylic acid according to Japanese Patent Application Publication No. 2024-5441 to obtain 2,5-frangimethanol diglycyl ether diacrylate. 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. 2,5-Franzicarboxylic acid diepoxyacrylate: 2,5-Franzicarboxylic acid diepoxyacrylate was synthesized according to the examples in International Publication No. 2018 / 087868. Specifically, the same procedure as in Example 1 of this publication was followed, except that allyl glycidyl ether, which is an epoxy compound, was replaced with glycidyl acrylate, to obtain 2,5-Franzicarboxylic acid diepoxyacrylate. 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-franmethanol diglycyl ether diacrylate. 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 1,4-Cyclohexanedimethanol monoacrylate: Manufactured by Mitsubishi Chemical Corporation, CHDMMA 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

[0049] As can be seen from Table 1, in Examples 1 to 13, the minimum UV irradiation dose required to reproduce a 175-line 1% halftone dot was reduced 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 enhance this effect. In Example 13, a polyetheramide containing an ether bond was used as the polyamide. However, in the case of polyetheramide, the crystalline structure formed by the amide bond surrounds the polyether, causing layer separation and localization of the polyether. Therefore, it is considered that the ether bond in the polyetheramide can hardly contribute to suppressing polymerization interference from dissolved oxygen. On the other hand, in Comparative Examples 1 to 3, where only conventional ethylenically unsaturated compounds without ether bonds were used instead of an ethylenically unsaturated compound having a heterocyclic structure containing an ether bond, the minimum UV irradiation dose required to reproduce a 175-line 1% halftone dot was high. Furthermore, although an ethylenically unsaturated compound having a heterocyclic structure containing an ether bond was used, in Comparative Example 4, which had a low content of the compound, the minimum amount of UV irradiation required to reproduce a 175-line 1% halftone dot decreased compared to Comparative Example 1, but the reduction effect was only 3.8%, which was extremely small. In addition, in Comparative Example 5, which used an ethylenically unsaturated compound containing an ether bond but without a heterocyclic structure (triethylene glycol dimethacrylate) instead of an ethylenically unsaturated compound having a heterocyclic structure containing an ether bond, the minimum amount of UV 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, preventing the polymerization inhibition effect of dissolved oxygen by the ether bond from being uniformly and sufficiently exerted throughout the composition, and thus preventing efficient photocrosslinking by the ethylenically unsaturated compound. In addition, it is thought that because the ethylenically unsaturated compounds were not finely dispersed, UV light was scattered, making it difficult for UV light to reach the bottom of the photosensitive resin layer.In addition to the 175-line 1% halftone dot reproducibility, we also evaluated the performance of independent points and development time, but no significant differences were observed between Examples 1-13 and Comparative Example 1. [Industrial applicability]

[0050] According to the present invention, a photosensitive resin composition for letterpress printing plates, and a letterpress printing plate using the same, can be provided, which enables the reproduction of 175-line 1% halftone dots with short exposure time without increasing the amount of ultraviolet irradiation or improving the ultraviolet transmittance of the photosensitive resin layer. Therefore, the present invention is extremely useful in the industry, which seeks water-developable letterpress printing plates that can form fine images with short exposure time.

Claims

1. A photosensitive resin composition for letterpress printing plates, comprising at least a water-soluble or water-dispersible polyamide, an ethylenically unsaturated compound, and a photopolymerization initiator, wherein the photosensitive resin composition contains 5 to 50% by mass of the ethylenically unsaturated compound, and the ethylenically unsaturated compound 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 letterpress printing plates according to claim 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 letterpress 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 letterpress 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 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 monoepoxy(meth)acrylate.

5. The photosensitive resin composition for letterpress 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-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 monoepoxy(meth)acrylate, and γ-pyrone-2,6-dicarboxylic acid di(meth)acrylate.

6. A letterpress printing plate using the photosensitive resin composition for letterpress printing plates according to any one of claims 1 to 5.

Images