Photosensitive resin composition and flexographic printing original plate

Abstract

The present invention addresses the problem of providing a photosensitive resin composition which enables printing having good solid-concealing properties with respect to cardboard, while maintaining cleaning performance as a water-developing plate, and which exhibits excellent long-term storage properties and resistance to design chipping due to impact. The means to solve the problem of the present invention is a photosensitive resin composition containing (A) a thermoplastic elastomer, (B) hydrophilic polymer particles, (C) a photopolymerizable monomer, (D) a photopolymerization initiator, (E) a low-polarity plasticizer, and (F) a high-polarity plasticizer, wherein the low-polarity plasticizer (E) is an organic compound that has, as its constituent atoms, only carbon atoms and hydrogen atoms, and the high-polarity plasticizer (F) is an organic compound that has, as its constituent atoms, carbon atoms and hydrogen atoms, as well as atoms other than carbon atoms and hydrogen atoms.

Description

Photosensitive resin composition and flexographic printing plate

[0001] This invention relates to a photosensitive resin composition for flexographic printing plates and a flexographic printing plate. Furthermore, this invention relates to a method for manufacturing a flexographic printing plate using the flexographic printing plate of the present invention.

[0002] Flexographic printing is a type of relief printing that uses flexible materials such as rubber or synthetic resin for the printing plate, giving it the advantage of being applicable to a wide variety of substrates.

[0003] A flexographic printing plate is manufactured, for example, as follows: First, ultraviolet light is irradiated over the entire surface of a photosensitive resin composition layer via a substrate made of a film such as PET resin, forming a uniform cured layer by back exposure. Next, relief exposure is performed by selectively irradiating the photosensitive resin composition layer with ultraviolet light using an arbitrary negative pattern, and the exposed areas of the photosensitive resin composition layer are photocured. Subsequently, the unexposed areas (i.e., areas that have not been photocured) in the photosensitive resin composition layer are dissolved or swollen with a developer solution and removed by applying external force such as a brush, thereby forming the desired relief image and obtaining a flexographic printing plate.

[0004] In recent years, there has been a growing demand to reduce the use of organic solvents from the perspective of improving the working environment and protecting the global environment. As a result, the use of water-based developers (water-based developers) to remove uncured portions in the manufacturing process of flexographic printing plates has expanded, leading to an increase in the use of water-developable plates that form relief images.

[0005] For example, Patent Documents 1 to 3 propose photosensitive resin compositions using water-dispersible polymer particles. These photosensitive resin compositions have the advantage of being developable with aqueous developers, and therefore have excellent washing speed and stability over time.

[0006] Japanese Patent No. 6193019, International Publication No. 2021 / 192536, International Publication No. 2020 / 039975

[0007] Flexographic printing uses a variety of substrates, including plastic packaging such as packaging films, as well as paper packaging such as cardboard boxes and corrugated cardboard. Among these, the demand for corrugated cardboard is increasing globally due to the expansion of online retail.

[0008] However, printing on corrugated cardboard with uneven surfaces presents a challenge: the ink transfer is poorer compared to other substrates due to the uneven shape of the printed surface.

[0009] Patent Document 1 uses water-dispersible latex as polymer particles, but when fine particles like latex are dispersed in a resin composition, the hardness of the resin composition increases due to the filler effect, which presents a problem as it reduces the printability on corrugated cardboard. Generally, methods used to reduce the hardness of a resin composition include lowering the ratio of added polymer or adding plasticizer components. However, lowering the ratio of polymer presents a problem as it reduces resistance to design chipping due to impact. Also, as described in Patent Documents 2 and 3, adding plasticizer components presents a problem as the plasticizer components bleed out during long-term storage.

[0010] As described above, conventional water-dispersible polymer particle-based water-developable photosensitive resin compositions have significant challenges in achieving high corrugated cardboard printing performance, particularly in reducing hardness while maintaining plate properties, and especially in reducing resistance to design chipping due to impact and preventing bleed-out during long-term storage. A composition with a sufficient balance between plate hardness and physical properties has yet to be achieved, and further improvements are needed.

[0011] Therefore, the object of the present invention is to provide a photosensitive resin composition that maintains the washing performance as a water-developable plate, enables printing with good opacity to corrugated cardboard, and has excellent resistance to design chipping due to impact and long-term storage properties.

[0012] In order to solve the problems of the prior art described above, the present inventors conducted extensive research on photosensitive resin compositions and, as a result, discovered that the above-mentioned problems can be solved by using a photosensitive resin composition containing two plasticizers with different polarities, thus completing the present invention.

[0013] That is, the present invention is as follows. [1] A photosensitive resin composition containing (A) a thermoplastic elastomer, (B) hydrophilic polymer particles, (C) a photopolymerizable monomer, (D) a photoinitiator, (E) a low-polarity plasticizer, and (F) a high-polarity plasticizer, wherein the low-polarity plasticizer (E) is an organic compound composed of only carbon atoms and hydrogen atoms as constituent atoms, and the high-polarity plasticizer (F) is an organic compound composed of atoms other than carbon atoms and hydrogen atoms in addition to carbon atoms and hydrogen atoms as constituent atoms. [2] The photosensitive resin composition according to [1] above, wherein the molecular weight of the low-polarity plasticizer (E) is less than 1500, and the molecular weight of the high-polarity plasticizer (F) is less than 1500. [3] The photosensitive resin composition according to [1] or [2] above, wherein the molecular weight of the low-polarity plasticizer (E) is less than 500. [4] The photosensitive resin composition according to any one of [1] to [3] above, wherein the molecular weight of the high-polarity plasticizer (F) is less than 500. [5] The distance Δδa of the HSP polarity term calculated by the following formula (1) based on the Hansen solubility parameter value (HSP value) of the low-polarity plasticizer (E) and the Hansen solubility parameter value (HSP value) of the thermoplastic elastomer (A) Ｅ , Ａ , Ａ , Ｅ , ０．５ , Ｅ , Ａ is 0 or more and 4 or less, and the photosensitive resin composition according to any one of [1] to [4] above. Δδa Ｅ－Ａ = |δa Ｅ - δa Ａ | = |(δp Ｅ ２ + δh Ｅ ２ ) ０．５ - (δp Ａ ２ + δh Ａ ２ ) ０．５ |... Formula (1) δa Ｅ : δa of the low-polarity plasticizer (E) δa <​​​​​​​​δh of thermoplastic elastomer (A) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction [6] The distance Δδa of the HSP polarity term is calculated by the following formula (2) using the Hansen solubility parameter value (HSP value) of the highly polar plasticizer (F) and the Hansen solubility parameter value (HSP value) of the hydrophilic polymer particles (B). Ｆ－Ｂ A photosensitive resin composition according to any of the above [1] to [5], wherein the value is 0 or more and 4 or less. Δδa Ｆ－Ｂ = |δa Ｆ -δa Ｂ | = | (δp) Ｆ ２ +δh Ｆ ２ ) ０．５ -(δp) Ｂ ２ +δh Ｂ ２ ) ０．５ |...Formula (2) δa Ｆ δa of the highly polar plasticizer (F) Ｂ : δa δp of hydrophilic polymer particles (B) Ｆ δp δh of high polarity plasticizer (F) Ｆ δh δp of high polarity plasticizer (F) Ｂ : δp δh of hydrophilic polymer particles (B) Ｂ δh of hydrophilic polymer particles (B) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction [7] The distance Δδa of the HSP polarity term is calculated by the following formula (3) using the Hansen solubility parameter value (HSP value) of the highly polar plasticizer (F) and the Hansen solubility parameter value (HSP value) of the thermoplastic elastomer (A). Ｆ－Ａ A photosensitive resin composition according to any of the above [1] to [6], wherein the value is 2 or more and 20 or less. Δδa Ｆ－Ａ = |δa Ｆ -δa Ａ | = | (δp) Ｆ ２ +δh Ｆ ２ ) ０．５ -(δp)Ａ ２ +δh Ａ ２ ) ０．５ |...Formula (3) δa Ｆ δa of the highly polar plasticizer (F) Ａ δa δp of thermoplastic elastomer (A) Ｆ δp δh of high polarity plasticizer (F) Ｆ δh δp of high polarity plasticizer (F) Ａ δp δh of thermoplastic elastomer (A) Ａ δh of thermoplastic elastomer (A) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction [8] The distance Δδa of the HSP polarity term calculated by the following formula (4) using the Hansen solubility parameter value (HSP value) of the low-polarity plasticizer (E) and the Hansen solubility parameter value (HSP value) of the hydrophilic polymer particles (B) Ｅ－Ｂ A photosensitive resin composition according to any of the above [1] to [7], wherein the value is 2 or more and 20 or less. Δδa Ｅ－Ｂ = |δa Ｅ -δa Ｂ | = | (δp) Ｅ ２ +δh Ｅ ２ ) ０．５ -(δp) Ｂ ２ +δh Ｂ ２ ) ０．５ |...Formula (4) δa Ｅ δa of low-polarity plasticizer (E) δa Ｂ : δa δp of hydrophilic polymer particles (B) Ｅ δp δh of low-polarity plasticizer (E) Ｅ δh δp of low polarity plasticizer (E) Ｂ : δp δh of hydrophilic polymer particles (B) Ｂ δh of hydrophilic polymer particles (B) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: parameter due to HSP in intermolecular polar interaction [9] Content P of low polarity plasticizer (E) Ｅ(mass %) and the content ratio P of the high-polarity plasticizer (F) Ｆ (mass %) ratio (P Ｅ / P Ｆ ) is 0.05 or more and 7 or less, and the photosensitive resin composition according to any one of [1] to [8] above.

[10] Content ratio P of the thermoplastic elastomer (A) Ａ (mass %) and the content ratio P of the hydrophilic polymer particles (B) Ｂ (mass %) ratio (P Ａ / P Ｂ ) and the content ratio P of the low-polarity plasticizer (E) Ｅ (mass %) and the content ratio P of the high-polarity plasticizer (F) Ｆ (mass %) ratio (P Ｅ / P Ｆ ) in the relationship, (P Ａ / P Ｂ ) / (P Ｅ / P ＦA photosensitive resin composition according to any one of [1] to [9] above, wherein the ratio of (1) to (9) is 0.1 or more and 10 or less.

[11] A photosensitive resin composition according to any one of [1] to

[10] above, wherein the hydrophilic polymer particles (B) are particles comprising a copolymer containing a constituent unit derived from 1,3-butadiene and a constituent unit derived from styrene as constituent units of the polymer.

[12] A photosensitive resin composition according to any one of [1] to

[11] above, wherein the thermoplastic elastomer (A) is a copolymer containing a constituent unit derived from 1,3-butadiene and a constituent unit derived from styrene as constituent units of the polymer.

[13] A photosensitive resin composition according to any one of [1] to

[12] above, wherein the highly polar plasticizer (F) is an organic compound having one or more ester structures in one molecule.

[14] The photosensitive resin composition according to any one of [1] to

[13] above, wherein the highly polar plasticizer (F) is an organic compound having one or more carboxylic acid ester structures in one molecule.

[15] A flexographic printing plate in which at least a support, a photosensitive resin composition layer, and an infrared ablation layer are laminated in this order, and the photosensitive resin composition layer comprises (A) a thermoplastic elastomer, (B) hydrophilic polymer particles, (C) a photopolymerizable monomer, (D) a photopolymerization initiator, (E) a low-polarity plasticizer, and (F) a highly polarity plasticizer, wherein the low-polarity plasticizer (E) is an organic compound having only carbon atoms and hydrogen atoms as constituent atoms, and the highly polarity plasticizer (F) is an organic compound having carbon atoms and hydrogen atoms in addition to atoms other than carbon atoms and hydrogen atoms as constituent atoms.

[16] A method for manufacturing a flexographic printing plate, comprising: laser ablation of the infrared ablation layer of the flexographic printing plate described in

[15] above to form a negative pattern; exposure of the photosensitive resin composition layer; and removal of the unexposed portion of the photosensitive resin composition layer.

[0014] According to the present invention, it is possible to provide a photosensitive resin composition that maintains the washing performance as a water-developable plate, enables printing with good opacity to corrugated cardboard, and has excellent resistance to design chipping due to impact and long-term storage properties.

[0015] A schematic front view of a flexographic printing plate used to evaluate the chip resistance of printing plates is shown. A schematic side view illustrating the method for evaluating the chip resistance of printing plates is also shown.

[0016] A description in detail will be given of an embodiment for carrying out the present invention (hereinafter simply referred to as "this embodiment"). This embodiment is illustrative for explaining the present invention and is not intended to limit the present invention to the following content. The present invention can be implemented by modifying it as appropriate within the scope of its gist.

[0017] This embodiment provides a photosensitive resin composition comprising (A) a thermoplastic elastomer, (B) hydrophilic polymer particles, (C) a photopolymerizable monomer, (D) a photopolymerization initiator, (E) a low-polarity plasticizer, and (F) a high-polarity plasticizer. In this embodiment, the low-polarity plasticizer (E) is an organic compound whose constituent atoms consist only of carbon atoms and hydrogen atoms. In this embodiment, the high-polarity plasticizer (F) is an organic compound whose constituent atoms consist of carbon atoms and hydrogen atoms, as well as atoms other than carbon atoms and hydrogen atoms.

[0018] The inclusion of these components makes it possible to provide a photosensitive resin composition that maintains the cleaning performance as a water-developable plate, enables printing with good opacity on corrugated cardboard, and offers excellent resistance to design chipping due to impact and long-term storage.

[0019] Furthermore, the photosensitive resin composition of this embodiment may further contain (G) liquid rubber and other optional components such as dyes, pigments, viscosity modifiers, defoamers, ultraviolet absorbers, fragrances, anti-coagulants, and surfactants.

[0020] The following describes each component of the photosensitive resin composition layer.

[0021] (Thermoplastic Elastomer (A)) The photosensitive resin composition of this embodiment includes thermoplastic elastomer (A). A thermoplastic elastomer is a polymer compound that exhibits rubber-like elasticity at room temperature (25°C) and can be molded by melting or softening upon heating. This may include block copolymers containing hard segments and soft segments in the polymer chain, or polymer compounds having a physical crosslinking structure such as hydrogen bonding. The thermoplastic elastomer (A) is not particularly limited as long as it is used in the technical field of flexographic printing plates, but from the viewpoint of being more suitable as a raw material for a photosensitive resin composition for flexographic printing plates, for example, a copolymer having constituent units derived from monovinyl-substituted aromatic hydrocarbons and constituent units derived from conjugated diene compounds as polymer constituent units is preferred, and it is preferable that the polymer molecule does not have a chemical crosslinking structure (e.g., a crosslinking structure by covalent bonding). Such copolymers may further have constituent units derived from other monomers. By using thermoplastic elastomer (A), the opacity of flexographic printing plates manufactured using the flexographic printing plate of this embodiment tends to be further improved in corrugated cardboard printing.

[0022] The monovinyl-substituted aromatic hydrocarbons constituting the thermoplastic elastomer (A) are not limited to, but include, for example, styrene, t-butylstyrene, 1,1-diphenylethylene, N,N-dimethyl-p-aminoethylstyrene, N,N-diethyl-p-aminoethylstyrene, vinylpyridine, p-methylstyrene, p-methoxystyrene, tertiary butylstyrene, α-methylstyrene, and 1,1-diphenylethylene. These may be used individually or in combination of two or more. Among these, styrene is preferred as the monovinyl-substituted aromatic hydrocarbon from the viewpoint of being able to mold the photosensitive resin composition layer more smoothly at relatively low temperatures.

[0023] The conjugated diene compound constituting the thermoplastic elastomer (A) is not limited to, but examples include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, chloroprene, etc. These may be used individually or in combination of two or more. Among these, 1,3-butadiene is preferred as the conjugated diene compound from the viewpoint of further improving the impact resistance and chipping resistance of the flexographic printing plate manufactured using the flexographic printing plate of this embodiment.

[0024] The thermoplastic elastomer (A) is preferably a copolymer containing constituent units derived from 1,3-butadiene and constituent units derived from styrene as polymer constituent units, and a styrene-butadiene copolymer is particularly preferred. It is preferable that these polymers do not have chemical crosslinking structures (e.g., crosslinking structures by covalent bonds) within the polymer molecule.

[0025] The number-average molecular weight (Mn) of the thermoplastic elastomer (A) is preferably 50,000 to 300,000, more preferably 50,000 to 250,000, and even more preferably 80,000 to 250,000, from the viewpoint of further improving viscosity at room temperature. The number-average molecular weight can be measured by gel permeation chromatography (GPC) and is expressed as polystyrene-equivalent molecular weight.

[0026] The thermoplastic elastomer (A) is preferably a block copolymer having a polymer block composed of structural units derived from a monovinyl-substituted aromatic hydrocarbon and a polymer block composed of structural units derived from a conjugated diene compound. More preferably, as the structural unit derived from a monovinyl-substituted aromatic hydrocarbon, it is a polymer block composed of structural units derived from styrene, and as the structural unit derived from a conjugated diene compound, it is a polymer block composed of structural units derived from 1,3-butadiene. Particularly preferably, it is a styrene-butadiene block copolymer. When the thermoplastic elastomer (A) is a block copolymer having a polymer block composed of structural units derived from a monovinyl-substituted aromatic hydrocarbon and a polymer block composed of structural units derived from a conjugated diene compound, the thermoplastic elastomer (A) includes, for example, a linear block copolymer represented by the following general formula group (I) and / or a linear block copolymer or a radial block copolymer represented by the following general formula group (II).

[0027] General formula group (I): (A - B) ｎ , A - (B - A) ｎ , A - (B - A) ｎ - B, B - (A - B) ｎ

[0028] General formula group (II): [(A - B) ｋ ｍ - X, [(A - B) ｋ - A] ｍ - X, [(B - A) ｋ ｍ - X, [(B - A) ｋ - B] ｍ - X

[0029] In general formula groups (I) and (II), A represents a polymer block consisting of constituent units derived from monovinyl-substituted aromatic hydrocarbons. B represents a polymer block consisting of constituent units derived from conjugated diene compounds. X represents a residue of a coupling agent selected from the group consisting of silicon tetrachloride, tin tetrachloride, epoxidized soybean oil, polyhalogenated hydrocarbon compounds, carboxylic acid ester compounds, polyvinyl compounds, bisphenol-type epoxy compounds, alkoxysilane compounds, halogenated silane compounds, and ester compounds, or a residue of a polymerization initiator such as a polyfunctional organolithium compound. In general formula groups (I) and (II), n, k, and m each independently represent an integer of 1 or more, for example, an integer from 1 to 5.

[0030] The content of constituent units derived from conjugated diene compounds and constituent units derived from monovinyl-substituted aromatic hydrocarbons in thermoplastic elastomer (A) is measured in a nuclear magnetic resonance apparatus ( １ It can be measured using H-NMR. Specifically, １ For the 1H-NMR measurement, the JNM-LA400 (manufactured by JEOL, trade name) was used, with deuterated chloroform (CDCl) as the solvent. ３ Using this method, the sample concentration is set to 50 mg / mL, the observation frequency to 400 MHz, TMS (tetramethylsilane) is used as the chemical shift reference, the pulse delay is set to 2.904 seconds, the number of scans to 64, the pulse width to 45°, and the measurement temperature to 25°C, allowing for measurement.

[0031] In the thermoplastic elastomer (A), the copolymerization ratio (mass ratio) of monovinyl-substituted aromatic hydrocarbon and conjugated diene compound is preferably in the range of 10 / 90 to 90 / 10, more preferably in the range of 15 / 85 to 85 / 15, even more preferably in the range of 20 / 80 to 60 / 40, and particularly preferably in the range of 20 / 80 to 50 / 50, from the viewpoint of further improving the print resistance of flexographic printing plates manufactured using the photosensitive resin structure for flexographic printing plates of this embodiment.

[0032] When the copolymerization ratio (mass ratio) of monovinyl-substituted aromatic hydrocarbons to conjugated diene compounds is 10 / 90 or higher, a more appropriate hardness can be obtained in the photosensitive resin composition layer, and more appropriate printing can be performed at normal printing pressure. Furthermore, when the copolymerization ratio (mass ratio) of monovinyl-substituted aromatic hydrocarbons to conjugated diene compounds is 90 / 10 or lower, a more appropriate hardness can be obtained in the photosensitive resin composition layer, and the ink can be transferred more favorably to the printing target during the printing process.

[0033] Thermoplastic elastomer (A) may have other functional groups introduced into it as needed, may be chemically modified such as by hydrogenation, or may be copolymerized with other components.

[0034] Increasing the content of thermoplastic elastomer (A) in the photosensitive resin composition tends to improve the impact chipping resistance of flexographic printing plates manufactured using the flexographic printing plates of this embodiment. On the other hand, decreasing the content of thermoplastic elastomer (A) in the photosensitive resin composition reduces the hardness of the flexographic printing plate, thus improving the opacity when printing on corrugated cardboard.

[0035] The content of thermoplastic elastomer (A) in the photosensitive resin composition is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less, from the viewpoint of achieving both better impact resistance and solid opacity in flexographic printing plates, when the total amount of the photosensitive resin composition is 100% by mass.

[0036] (Hydrophilic polymer particles (B)) The photosensitive resin composition of this embodiment contains hydrophilic polymer particles (B). Hydrophilic polymer particles (B) are, for example, polymer particles having a crosslinking structure within the polymer molecule. Such polymer particles are not particularly limited, but examples include those obtained by preparing a water-dispersible latex in which polymer particles are dispersed as a dispersed phase in water by emulsion polymerization, and then removing water from the resulting water-dispersible latex.

[0037] The hydrophilic polymer particles (B) disperse in water when immersed, thus improving the development speed when developing with aqueous developers. Furthermore, because they act as fillers within the photosensitive resin composition, they can suppress design chipping caused by impact.

[0038] The content of hydrophilic polymer particles (B) in the photosensitive resin composition is preferably relatively high from the viewpoint of further improving the development speed with aqueous developer. Specifically, the content of hydrophilic polymer particles (B) in the photosensitive resin composition is preferably 3% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more, when the total amount of the photosensitive resin composition is 100% by mass. On the other hand, the content of hydrophilic polymer particles (B) in the photosensitive resin composition is preferably low from the viewpoint of reducing the hardness of the flexographic printing plate and further improving the opacity of corrugated cardboard. Specifically, when the total amount of the photosensitive resin composition is 100% by mass, the content is preferably 35% by mass or less, more preferably 33% by mass or less, and particularly preferably 30% by mass or less.

[0039] The monomers used in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited as long as they have polymerizable double bonds, but examples include monobasic acid monomers, polybasic acid monomers, conjugated diene compounds, aromatic vinyl compounds, (meth)acrylic acid esters, monomers having hydroxyl groups, unsaturated dibasic acid alkyl esters, maleic anhydride, vinyl cyanide compounds, (meth)acrylamide and its derivatives, vinyl esters, vinyl ethers, vinyl halides, basic monomers having amino groups, vinylpyridine, olefins, silicon-containing α,β-ethylenically unsaturated monomers, allyl compounds, etc. Furthermore, the monomers constituting the polymer contained in the hydrophilic polymer particles (B) may also contain reactive emulsifiers used in emulsion polymerization described later. Among these monomers, it is preferable that they consist of aromatic vinyl compounds, conjugated diene compounds, and (meth)acrylic acid esters. By including aromatic vinyl compounds, the elastic modulus can be increased by forming physical crosslinking points in the polymer particles, thereby suppressing design defects due to impact. The inclusion of a conjugated diene compound enhances compatibility with the aforementioned thermoplastic elastomer (A). Furthermore, the reaction of the conjugated diene compound with the photopolymerizable compound in the photosensitive resin composition via unsaturated bonds increases the elastic modulus, thereby suppressing design chipping due to impact. The inclusion of a (meth)acrylic acid ester facilitates adjustment of the moldability of the polymer particles.

[0040] The aromatic vinyl compounds used as monomers in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited, but examples include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, vinyltoluene, vinylxylene, bromostyrene, vinylbenzyl chloride, p-t-butylstyrene, chlorostyrene, alkylstyrene, divinylbenzene, trivinylbenzene, and the like. Among the above aromatic vinyl compounds, styrene is particularly preferred from the viewpoint of further improving compatibility with the thermoplastic elastomer (A).

[0041] The content of constituent units derived from aromatic vinyl compounds in the polymer contained in the hydrophilic polymer particles (B) is preferably high from the viewpoint of increasing the elastic modulus and further suppressing design defects due to impact. Preferably, it is 12% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, relative to the total amount of polymer contained in the hydrophilic polymer particles (B). On the other hand, a lower content is preferable from the viewpoint of further increasing flexibility. Preferably, it is 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, relative to the total amount of polymer contained in the hydrophilic polymer particles (B).

[0042] The conjugated diene compound used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2-methyl-1,3-butadiene, 1,3-pentadiene, chloroprene, 2-chloro-1,3-butadiene, and cyclopentadiene. Among the above aromatic vinyl compounds, 1,3-butadiene is particularly preferred from the viewpoint of further improving compatibility with the thermoplastic elastomer (A).

[0043] The content of structural units derived from conjugated diene compounds in the polymer contained in the hydrophilic polymer particles (B) is preferably higher from the viewpoint of further enhancing flexibility, and preferably lower from the viewpoint of further suppressing design defects due to impact. Considering these balances, the content is preferably 25% by mass or more and 60% by mass or less, more preferably 30% by mass or more and 55% by mass or less, relative to the total amount of hydrophilic polymer particles (B).

[0044] The (meth)acrylic acid ester used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate. Acrylate, octadecyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, 2-ethyl-hexyl (meth)acrylate, glycidyl (meth)acrylate, ethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,5-pentanediol di(meth)acrylate Neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, aryl(meth)acrylate (T) Acrylate, Bis(4-Acryloxypolyethoxyphenyl)propane, Methoxypolyethylene glycol (meth)acrylate, β-(meth)acryloyloxyethyl hydrogen phthalate, β-(meth)acryloyloxyethyl hydrogen succinate, 3-Chloro-2-hydroxypropyl (meth)acrylate, Stearyl (meth)acrylate, Phenoxyethyl (meth)acrylate, Phenoxypolyethylene glycol (meth)acrylate, 2-Hydroxy-1,3-di(meth)acryloxypropane, 2,Examples include 2-bis[4-((meth)acryloxyethoxy)phenyl]propane, 2,2-bis[4-((meth)acryloxy-diethoxy)phenyl]propane, 2,2-bis[4-((meth)acryloxy-polyethoxy)phenyl]propane, isobornyl (meth)acrylate, etc.

[0045] The molecular weight of the (meth)acrylic acid ester used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is preferably 100 to 1000, and more preferably 150 to 500, from the viewpoint of improving moldability. On the other hand, the number average molecular weight of the (meth)acrylic acid ester is preferably small from the viewpoint of compatibility and reactivity in the mixed solution during emulsion polymerization. It is preferably 1000 or less, more preferably 500 or less, even more preferably 400 or less, and particularly preferably 300 or less.

[0046] In the polymerization of the polymer contained in the hydrophilic polymer particles (B), the (meth)acrylic acid ester used as a monomer is preferably composed of a chain-like hydrocarbon in the ester portion, from the viewpoint of improving moldability. It may have a linear or branched structure.

[0047] The content of constituent units derived from (meth)acrylic acid ester in the polymer contained in the hydrophilic polymer particles (B) is preferably 10% by mass or more and 45% by mass or less, more preferably 15% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 36% by mass or less, based on the total amount of hydrophilic polymer particles (B).

[0048] The monomer units constituting the polymer contained in the hydrophilic polymer particles (B) preferably include, with respect to 100 parts by mass of conjugated diene compound, 40 to 120 parts by mass of aromatic vinyl compound and 25 to 140 parts by mass of (meth)acrylic acid ester. This allows for a good balance between impact-induced design defects and flexibility. From the viewpoint of easier and more balanced design, the amount of constituent units derived from aromatic vinyl compound is preferably 40 to 160 parts by mass, and more preferably 80 to 160 parts by mass. Furthermore, the amount of constituent units derived from (meth)acrylic acid is preferably 25 to 140 parts by mass, more preferably 60 to 135 parts by mass, and particularly preferably 65 to 130 parts by mass.

[0049] The monobasic acid monomer used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include monomers having one carboxyl group in the molecule, such as acrylic acid, methacrylic acid, crotonic acid, vinylbenzoic acid, and cinnamic acid; and monomers having one sulfonic acid group in the molecule, such as styrene sulfonic acid.

[0050] The content of constituent units derived from monobasic acid monomers in the polymer contained in the hydrophilic polymer particles (B) is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 20% by mass or less, even more preferably 3% by mass or more and 15% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less, based on the total amount of hydrophilic polymer particles (B).

[0051] The polybasic acid monomers used as monomers in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited, but examples include monomers having two or more carboxyl groups in the molecule, such as itaconic acid, fumaric acid, maleic acid, citraconic acid, and muconic acid; monomers having an acid anhydride group; and other monomers having a polybasic acid group of a phosphate group.

[0052] The monomers having hydroxyl groups used as monomers in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited, but examples include ethylene-based monocarboxylate alkyl ester monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 1-hydroxypropyl acrylate, 1-hydroxypropyl methacrylate, and hydroxycyclohexyl (meth)acrylate.

[0053] The unsaturated dibasic acid alkyl ester used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include alkyl crotonic acid esters, alkyl itaconic acid esters, alkyl fumarate esters, and alkyl maleate esters.

[0054] The vinyl cyanide compound used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include acrylonitrile and methacrylonitrile.

[0055] The (meth)acrylamide and its derivatives used as monomers in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited, but examples include (meth)acrylamide, N-methylol(meth)acrylamide, N-alkoxy(meth)acrylamide, and the like.

[0056] The vinyl esters used as monomers in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited, but examples include vinyl acetate, vinyl butyrate, vinyl stearate, vinyl laurate, vinyl myristate, vinyl propionate, and vinyl versatate.

[0057] The vinyl ethers used as monomers in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited, but examples include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, amyl vinyl ether, hexyl vinyl ether, and the like.

[0058] The vinyl halides used as monomers in the polymerization of the polymer contained in the hydrophilic polymer particles (B) are not particularly limited, but examples include vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, and vinylidene fluoride.

[0059] The basic monomer having an amino group used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate.

[0060] The olefin used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include ethylene.

[0061] The silicon-containing α,β-ethylenically unsaturated monomer used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include vinyltrichlorosilane and vinyltriethoxysilane.

[0062] The allyl compound used as a monomer in the polymerization of the polymer contained in the hydrophilic polymer particles (B) is not particularly limited, but examples include allyl esters and diallyl phthalates.

[0063] In addition, compounds having three or more double bonds, such as triallyl isocyanurate, can also be used as monomers for polymerization of the polymer contained in the hydrophilic polymer particles (B).

[0064] These monomers may be used individually or in mixtures of two or more. In particular, from the viewpoint of further improving the development speed in aqueous developers, it is preferable to include monomers having acidic groups, such as monobasic acid monomers and polybasic acid monomers (hereinafter also simply referred to as "acidic monomers"), and monomers having hydrophobic groups, such as conjugated diene compounds, aromatic vinyl compounds, and (meth)acrylic acid esters (hereinafter also simply referred to as "hydrophobic monomers"). Note that the conjugated diene compounds, aromatic vinyl compounds, and (meth)acrylic acid esters that fall under the above hydrophobic monomer category have hydrocarbon groups, and those having hydrophilic groups such as hydroxyl groups are excluded from the hydrophobic monomer category, even if they are (meth)acrylic acid esters.

[0065] The content of constituent units derived from acidic monomers in the polymer contained in the hydrophilic polymer particles (B) is preferably 1% to 30% by mass, more preferably 2% to 20% by mass, even more preferably 3% to 15% by mass, and even more preferably 5% to 10% by mass, relative to the total amount of polymer contained in the hydrophilic polymer particles (B). A content of constituent units derived from acidic monomers of 1% by mass or more tends to further improve water-based developing performance. Furthermore, a content of 30% by mass or less prevents an increase in the swelling amount of the water-based ink in the photosensitive resin composition, thereby stabilizing quality during long-run printing.

[0066] The content of constituent units derived from monomers having hydrophobic groups in the polymer contained in the hydrophilic polymer particles (B) is preferably 70% to 99% by mass, more preferably 80% to 98% by mass, even more preferably 85% to 97% by mass, and even more preferably 90% to 95% by mass. Having such a composition in the polymer contained in the hydrophilic polymer particles (B) further improves the rubber elasticity of the photosensitive resin composition, enabling printing with good opacity on corrugated cardboard.

[0067] The hydrophilic polymer particles (B) are preferably particles containing polymers that include structural units derived from conjugated diene compounds as polymer structural units, more preferably particles containing polymers that include structural units derived from 1,3-butadiene, and even more preferably particles containing copolymers that include structural units derived from both 1,3-butadiene and styrene as polymer structural units. These polymers preferably have crosslinked structures within the polymer molecule.

[0068] Specific examples of polymers contained in hydrophilic polymer particles (B) are not particularly limited, but include, for example, polymers having a butadiene skeleton such as polybutadiene, acrylonitrile-butadiene copolymer, styrene-butadiene copolymer, and (meth)acrylate-butadiene copolymer; polymers having an isoprene skeleton such as polyisoprene and polychloroprene; polymers obtained by further polymerizing the above-mentioned polymers having a butadiene skeleton or isoprene skeleton with monomers having carboxyl groups and / or hydroxyl groups; polymers obtained by further polymerizing the above-mentioned polymers having a butadiene skeleton or isoprene skeleton with (meth)acrylic acid esters; polymers obtained by further polymerizing the above-mentioned polymers having a butadiene skeleton or isoprene skeleton with (meth)acrylic acid esters and monomers having carboxyl groups and / or hydroxyl groups; polyurethane, vinylpyridine polymer, butyl polymer, thiocol polymer, acrylate polymer, and natural rubber. Among these, styrene-butadiene copolymer is preferred, and it is more preferred that it is derived from styrene-butadiene latex in which styrene-butadiene copolymer particles are dispersed in water as a dispersed phase.

[0069] In this context, a monomer having a carboxyl group refers to the monobasic acid monomer and / or polybasic acid monomer described above.

[0070] Among these, polymers having a butadiene skeleton, polymers having an isoprene skeleton, and polymers obtained by further polymerizing the above-mentioned polymers having a butadiene skeleton or isoprene skeleton with an aromatic vinyl compound and / or (meth)acrylic acid ester and / or monomers having carboxyl groups and / or hydroxyl groups are preferred, and polymers obtained by further polymerizing the butadiene skeleton with an aromatic vinyl compound and / or (meth)acrylic acid ester and / or monomers having carboxyl groups and / or hydroxyl groups are more preferred. The hydrophilic polymer particles (B) may be used alone or in combination of two or more types. It is preferable that these polymers have a crosslinking structure within the polymer molecule.

[0071] The average particle size of the hydrophilic polymer particles (B) is preferably 500 nm or less, and more preferably 100 nm or less. An average particle size of 500 nm or less tends to further improve the water-based developability of the flexographic printing plate. On the other hand, from the viewpoint of the kneadability of the photosensitive resin composition during kneading, the average particle size of the hydrophilic polymer particles (B) is preferably 10 nm or more, and more preferably 30 nm or more. Here, the average particle size is the volume-average particle size based on the volume of the particles, and means the particle size corresponding to the cumulative frequency of 50% in the volume-based particle size distribution, and can be measured, for example, by the laser diffraction / scattering method based on Mie scattering theory.

[0072] Furthermore, the toluene gel fraction of the hydrophilic polymer particles (B) is preferably 60% to 99%. When the toluene gel fraction is 60% or more, design defects due to impact can be suppressed. When the toluene gel fraction is 99% or less, the miscibility between the hydrophilic polymer particles (B) and the thermoplastic elastomer (A) tends to be good.

[0073] Here, the toluene gel fraction is defined as follows:

[0074] A 30% by mass dispersion of hydrophilic polymer particles (B) is dropped onto a Teflon® sheet in appropriate amounts and dried at 130°C for 30 minutes. 0.5 g of the hydrophilic polymer particles (B) is then taken and immersed in 30 mL of toluene at 25°C. After shaking for 3 hours using a shaker, the mixture is filtered through a 320 SUS mesh to obtain the impermeable portion. The mass fraction (%) obtained by dividing the mass of the impermeable portion after drying at 130°C for 1 hour by 0.5 g is called the toluene gel fraction.

[0075] The Hansen solubility parameter (HSP) can be used as an indicator for selecting hydrophilic polymer particles (B). The HSP value (Hansen solubility parameter) (hereinafter sometimes referred to as "HSP value") is important for achieving good water-developability. The Hansen solubility parameter (HSP value) is a value used to predict the solubility of a substance, published by Charles M. Hansen in 1967, and is a parameter based on the idea that "two substances with similar intermolecular interactions readily dissolve in each other." The HSP value consists of the following three parameters (unit: MPa) ０．５ It is composed of the following: δd: HSP parameter due to intermolecular dispersion forces δp: HSP parameter due to intermolecular dipole interactions δh: HSP parameter due to intermolecular hydrogen bonding

[0076] These three parameters can be considered as coordinates in three-dimensional space (Hansen space), and when the HSP values ​​of two substances are placed in Hansen space, the closer the distance between the two points, the easier they are to dissolve in each other. As explained in the March 2010 issue of Chemical Industry (Chemical Industry Co., Ltd.), Hansen solubility parameter values ​​(HSP values) of various substances can be obtained by using the PC software "HSPiP" (Hansen Solubility Parameters in Practice) provided at hansen-solubility.com. In the photosensitive resin composition of this embodiment, the Hansen solubility parameters obtained using the PC software "HSPiP" are used.

[0077] In the photosensitive resin composition of this embodiment, the δa of the hydrophilic polymer particles (B), calculated by the following formula (5), is preferably 5 or more, more preferably 7 or more, and even more preferably 9 or more. δa = (δp ２ +δh ２ ) ０．５ ...Equation (5) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction

[0078] (Method for producing hydrophilic polymer particles (B)) The method for producing hydrophilic polymer particles (B) is not particularly limited, but it is preferable that the polymer is synthesized by emulsion polymerization, for example. An emulsion polymerization method for hydrophilic polymer particles (B) is to pre-charge a predetermined amount of water, emulsifier, and other additives into a reaction system adjusted to a polymerization temperature, and then add polymerization initiators, monomers, emulsifiers, modifiers, etc. to this system in batch or continuous operation. Alternatively, a predetermined amount of seed latex, polymerization initiator, monomer, and other modifiers may be pre-charged into the emulsion polymerization reaction system.

[0079] Furthermore, by devising methods for adding monomers, emulsifiers, other additives, and modifiers to the reaction system, it is possible to change the layer structure of the synthesized polymer particles stepwise. In this case, representative physical properties of each layer structure include hydrophilicity, glass transition temperature, molecular weight, and crosslinking density. Also, the number of layers in this layer structure is not particularly limited.

[0080] The following describes each component other than the monomers mentioned above.

[0081] The emulsifier (surfactant) used during emulsion polymerization for the production of hydrophilic polymer particles (B) is not particularly limited, but examples include reactive emulsifiers and / or non-reactive emulsifiers. Among these, the use of a reactive emulsifier is preferred.

[0082] For the production of hydrophilic polymer particles (B), a reactive emulsifier is preferred that contains a radically polymerizable double bond, a hydrophilic functional group, and a hydrophobic group in its molecular structure, and has emulsifying, dispersing, and wetting functions similar to general emulsifiers. Among these, an emulsifier (surfactant) is preferred in which, when 0.1 parts by mass or more of the reactive emulsifier is used per 100 parts by mass of the total monomers other than the reactive emulsifier, the average particle size of the resulting polymer particles is 5 nm to 500 nm.

[0083] The hydrophilic functional groups possessed by a reactive emulsifier for the production of hydrophilic polymer particles (B) are not particularly limited, but include, for example, anionic groups such as sulfate groups, nitrate groups, phosphoric acid groups, boric acid groups, and carboxyl groups; cationic groups such as amino groups; polyoxyalkylene chain structures such as polyoxyethylene, polyoxymethylene, and polyoxypropylene; or hydroxyl groups. Depending on the type of hydrophilic functional group, reactive emulsifiers can be classified as anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, or amphoteric emulsifiers.

[0084] The hydrophobic group of the reactive emulsifier for producing hydrophilic polymer particles (B) is not particularly limited, but examples include alkyl groups and phenyl groups. The radical polymerizable double bond of the reactive emulsifier is not particularly limited, but examples include vinyl groups, acryloyl groups, or methacryloyl groups. Furthermore, the molecular structure may contain multiple types of radical polymerizable double bonds, hydrophilic functional groups, and hydrophobic groups.

[0085] For the production of hydrophilic polymer particles (B), commercially available surfactants can be used as reactive emulsifiers. Commercially available anionic surfactants are not limited to those listed above, but examples include Adekaria Soap SE (manufactured by ADEKA Corporation), Aqualon HS, BC, and KH (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Latemul S (manufactured by Kao Corporation), Antox MS (manufactured by Nippon Emulsifier Co., Ltd.), Adekaria Soap SDX and PP (manufactured by ADEKA Corporation), Hytenol A (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Eleminol RS (manufactured by Sanyo Chemical Industries, Ltd.), and Spinomer (manufactured by Toyo Soda Industries Co., Ltd.). Commercially available nonionic surfactants are not limited to those listed above, but examples include Aqualon RN and Neugen N (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and Adekaria Soap NE (manufactured by ADEKA Corporation). These may be used individually or in combination of two or more.

[0086] In the production of hydrophilic polymer particles (B), the amount of reactive emulsifier used is preferably 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of hydrophilic polymer particles (B) calculated from the amount of raw materials used. When the amount of reactive emulsifier used is 1 part by mass or more, the image reproducibility of the resulting flexographic printing plate tends to improve. Furthermore, when the amount of reactive emulsifier used is 20 parts by mass or less, the impact resistance and design chipping resistance of the resulting flexographic printing plate tend to improve.

[0087] The nonreactive emulsifier for the production of hydrophilic polymer particles (B) is not particularly limited, but examples include anionic surfactants such as fatty acid soaps, rosinate soaps, sulfonates, sulfates, phosphate esters, polyphosphate esters, and salicodynes; cationic surfactants such as nitrile oil derivatives, oil derivatives, fatty acid derivatives, and α-olefin derivatives; and nonionic surfactants such as alcohol ethoxylates, alkylphenol ethoxylates, propoxylates, aliphatic alkanolamides, alkyl polyglycosides, polyoxyethylene sorbitan fatty acid esters, and oxyethylene oxypropylene block copolymers. These may be used individually or in combination of two or more.

[0088] The sulfonates used for producing hydrophilic polymer particles (B) are not particularly limited, but examples include alkyl sulfonates, alkyl sulfates, alkyl sulfosuccinates, polyoxyethylene alkyl sulfates, sulfonated oils and fats, alkyl diphenyl ether disulfonates, α-olefin sulfonates, alkyl glyceryl ether sulfonates, N-acylmethyl taurates, etc. Examples of non-reactive emulsifiers other than those mentioned above are not particularly limited, but examples include those listed in the "Surfactant Handbook" (Takahashi, Nanba, Koike, Kobayashi: Engineering Books, 1972).

[0089] In the production of hydrophilic polymer particles (B), the amount of non-reactive emulsifier used is preferably less than 1 part by mass per 100 parts by mass of hydrophilic polymer particles (B) calculated from the amount of raw materials used. By using less than 1 part by mass of non-reactive emulsifier, the resulting flexographic printing plate has an appropriate water swelling rate, preventing a decrease in abrasion resistance when ink is applied and a decrease in image reproducibility after moisture absorption.

[0090] The polymerization initiator for the production of hydrophilic polymer particles (B) is not particularly limited, but examples include radical polymerization initiators. The radical polymerization initiator is not particularly limited, but examples include those that initiate addition polymerization of monomers by radical decomposition in the presence of heat or a reducing substance, and both inorganic and organic initiators can be used. The radical polymerization initiator is not particularly limited, but examples include water-soluble or oil-soluble peroxodisulfates, peroxides, azobis compounds, etc. Specifically, examples include potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2-azobisbutyronitrile, cumene hydroperoxide, etc. Furthermore, the above radical polymerization initiators are described in the Polymer Handbook (3rd edition), J. Brandrup and E. H. Compounds described in Immergut, published by John Willy & Sons (1989), can also be used. Furthermore, so-called redox polymerization can be employed, using reducing agents such as sodium acidic sulfite, ascorbic acid or its salts, erythorbic acid or its salts, and rongalit as polymerization initiators. Among these, peroxodisulfate is preferred as a polymerization initiator.

[0091] The amount of polymerization initiator used in the production of hydrophilic polymer particles (B) is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.2% by mass or more and 3.0% by mass or less, relative to the total amount of monomers used in the polymerization of hydrophilic polymer particles (B). When the amount of polymerization initiator used is 0.1% by mass or more, high stability can be obtained during the synthesis of hydrophilic polymer particles (B). Furthermore, when the amount of polymerization initiator used is 5.0% by mass or less, the amount of moisture absorbed by the photosensitive resin composition can be suppressed to a range that is practically acceptable.

[0092] In the polymerization process of hydrophilic polymer particles (B), known chain transfer agents can be used. Chain transfer agents containing sulfur elements are preferably used as chain transfer agents for the production of hydrophilic polymer particles (B). Chain transfer agents containing sulfur elements are not particularly limited, but examples include alkanethiols such as t-dodecyl mercaptan and n-dodecyl mercaptan; thioalkyl alcohols such as mercaptoethanol and mercaptopropanol; thioalkyl carboxylic acids such as thioglycolic acid and thiopropionic acid; alkyl thiocarboxylic acid esters such as octyl thioglycolate and octyl thiopropionate; and sulfides such as dimethyl sulfide and diethyl sulfide.

[0093] In addition, other chain transfer agents besides those mentioned above can also be used. Other chain transfer agents are not particularly limited, but examples include halogenated hydrocarbons such as terpinolene, dipentene, t-terpinene, and carbon tetrachloride. Among these chain transfer agents, alkanethiols are preferred because they exhibit a high chain transfer rate and a good balance of physical properties in the resulting polymer. These chain transfer agents may be used individually or in combination of two or more.

[0094] In the production of hydrophilic polymer particles (B), the chain transfer agent is either mixed with the monomer and supplied to the reaction system, or added alone in a predetermined amount at a predetermined time. The amount of these chain transfer agents used is preferably 0.1% by mass or more and 10% by mass or less, relative to the total amount of monomers used in the polymerization of hydrophilic polymer particles (B). By setting it to 0.1% by mass or more, good processability is achieved when mixing with the photosensitive resin composition, and by setting it to 10% by mass or less, the number average molecular weight of the hydrophilic polymer particles (B) can be made practically sufficient.

[0095] Polymerization inhibitors can be used as needed during the polymerization of hydrophilic polymer particles (B). Polymerization inhibitors are compounds that reduce the radical polymerization rate when added to an emulsion polymerization system. More specifically, polymerization inhibitors include polymerization rate retarders, polymerization inhibitors, chain transfer agents with low radical restart reactivity, and monomers with low radical restart reactivity. Polymerization inhibitors are generally used to adjust the polymerization reaction rate and the properties of latex. These polymerization inhibitors are added to the reaction system in batch or continuous operations. When polymerization inhibitors are used, the strength and print resistance of the latex coating are improved. Although the details of the reaction mechanism are unknown, polymerization inhibitors are thought to be closely involved in the stereostructure of the polymer, and it is presumed that this is how they are effective in adjusting the properties of the latex coating.

[0096] The polymerization reaction inhibitors for the production of hydrophilic polymer particles (B) are not particularly limited, but examples include quinones such as o-, m-, or p-benzoquinone; nitro compounds such as nitrobenzene, o-, m-, or p-dinitrobenzene; amines such as diphenylamine; catechol derivatives such as tertiary butylcatechol; 1,1-disubstituted vinyl compounds such as 1,1-diphenylethylene or α-methylstyrene, 2,4-diphenyl-4-methyl-1-pentene; and 1,2-disubstituted vinyl compounds such as 2,4-diphenyl-4-methyl-2-pentene, cyclohexene, etc. Other compounds that can be used as polymerization inhibitors or polymerization blockers include those described in "Polymer Handbook 3rd Ed. (J. Brandup, E.H. Immergut: John Wiley & Sons, 1989)" and "Revised Chemistry of Polymer Synthesis (Otsu: Kagaku Dojin, 1979)". Among these, 2,4-diphenyl-4-methyl-1-pentene (α-methylstyrene dimer) is particularly preferred from the viewpoint of further improving reactivity. These polymerization inhibitors may be used individually or in mixtures of two or more. The amount of these polymerization inhibitors used is preferably 10% by mass or less relative to the total amount of monomers used in the polymerization of hydrophilic polymer particles (B). By setting the amount to 10% by mass or less, a practically sufficient polymerization rate tends to be obtained.

[0097] During the production of hydrophilic polymer particles (B), various polymerization regulators such as pH adjusters and chelating agents may be added as needed.

[0098] The pH adjusting agent for producing hydrophilic polymer particles (B) is not particularly limited, but examples include sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium bicarbonate, sodium carbonate, and disodium hydrogen phosphate.

[0099] The chelating agent for producing hydrophilic polymer particles (B) is not particularly limited, but examples include sodium ethylenediaminetetraacetate.

[0100] Other additives for the production of hydrophilic polymer particles (B) may include alkali-sensitive latex, viscosity reducers such as hexametaphosphate, water-soluble polymers such as polyvinyl alcohol and carboxymethylcellulose, thickeners, various antioxidants, UV absorbers, preservatives, bactericides, defoamers, dispersants such as sodium polyacrylate, water-resistant agents, metal oxides such as zinc oxide, crosslinking agents such as epoxy compounds, isocyanate compounds, lubricants, and water-retaining agents. The method of adding these additives is not particularly limited, and they can be added during or after the synthesis of hydrophilic polymer particles (B).

[0101] When hydrophilic polymer particles (B) are produced by emulsion polymerization, the polymerization temperature is usually between 60°C and 120°C. Alternatively, polymerization may be carried out at a lower temperature using methods such as redox polymerization. Furthermore, as an oxidation-reduction catalyst, a metal catalyst, not particularly limited, may be used, such as divalent iron ions, trivalent iron ions, or copper ions.

[0102] (Photopolymerizable monomer (C)) The photosensitive resin composition of this embodiment contains a photopolymerizable monomer (C). The photopolymerizable monomer (C) is a compound having a radically polymerizable unsaturated double bond and is not particularly limited as long as it is used in the art of flexographic printing plates.

[0103] The photopolymerizable monomer (C) is not limited to, but examples include olefins such as ethylene, propylene, vinyltoluene, styrene, and divinylbenzene; acetylenes; (meth)acrylic acid and / or its derivatives; haloolefins; unsaturated nitriles such as acrylonitrile; derivatives of acrylamide and methacrylamide; unsaturated dicarboxylic acids and their derivatives such as maleic anhydride, maleic acid, and fumaric acid; vinyl acetates; N-vinylpyrrolidone; N-vinylcarbazole; and N-substituted maleimide compounds. In particular, (meth)acrylic acid and / or its derivatives are preferred from the viewpoint of variety. The aforementioned derivatives are not limited to the following, but include, for example, alicyclic compounds having cycloalkyl groups, bicycloalkyl groups, cycloalkenyl groups, bicycloalkenyl groups, etc.; aromatic compounds having benzyl groups, phenyl groups, phenoxy groups, or naphthalene skeletons, anthracene skeletons, biphenyl skeletons, phenanthrene skeletons, fluorene skeletons, etc.; compounds having alkyl groups, halogenated alkyl groups, alkoxyalkyl groups, hydroxyalkyl groups, aminoalkyl groups, glycidyl groups, etc.; ester compounds with alkylene glycols, polyoxyalkylene glycols, polyalkylene glycols, and polyhydric alcohols such as trimethylolpropane; and compounds having a polysiloxane structure such as polydimethylsiloxane and polydiethylsiloxane. Furthermore, heteroaromatic compounds containing elements such as nitrogen and sulfur may also be used.

[0104] Examples of (meth)acrylic acid and / or its derivatives include, but are not limited to, diacrylates and dimethacrylates of alkanediols such as hexanediol and nonanediol; diacrylates and dimethacrylates of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, and butylene glycol; trimethylolpropane tri(meth)acrylate; dimethylol tricyclodecane di(meth)acrylate; isobolonyl(meth)acrylate; phenoxypolyethylene glycol(meth)acrylate; pentaerythritol tetra(meth)acrylate, etc. These may be used individually or in combination of two or more types.

[0105] The content of photopolymerizable monomer (C) in the photosensitive resin composition is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 4% by mass or more, when the total amount of the photosensitive resin composition is 100% by mass, from the viewpoint of further improving photocrosslinkability. Furthermore, from the viewpoint of obtaining a more suitable hardness for the flexographic printing plate, it is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 16% by mass or less. In particular, it is preferable to contain 1 to 20% by mass of diacrylate monomer.

[0106] (Photopolymerization initiator (D)) The photosensitive resin composition of this embodiment contains a photopolymerization initiator (D). The photopolymerization initiator (D) refers to a compound that absorbs light energy and generates radicals. Various known photopolymerization initiators (D) can be used, but various organic carbonyl compounds, particularly aromatic carbonyl compounds, are preferred. The photopolymerization initiator (D) is not limited to the following, but examples include thioxanthones such as benzophenone, 4,4-bis(diethylamino)benzophenone, t-butylanthraquinone, 2-ethylanthraquinone, 2,4-diethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone; diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethane-1-one (also known as benzyldimethylketal), 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2 Examples include acetophenones such as benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone; benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; acylphosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; methylbenzoyl formate; 1,7-bisacridinylheptane; and 9-phenylacridine. These may be used individually or in combination of two or more types.

[0107] The content of the photopolymerization initiator (D) in the photosensitive resin composition is preferably 1.0% to 5.0% by mass, more preferably 1.2% to 4.5% by mass, and even more preferably 1.5% to 4.0% by mass, when the total amount of the photosensitive resin composition is 100.0% by mass, from the viewpoint of further suppressing the decrease in the ability to form fine dots and characters in the photosensitive resin composition layer and further suppressing the decrease in the transmittance of active light such as ultraviolet light.

[0108] (Low-polarity plasticizer (E)) The photosensitive resin composition of this embodiment contains a low-polarity plasticizer (E). The low-polarity plasticizer (E) is a component that does not fall under the category of a photopolymerizable monomer (C). The low-polarity plasticizer (E) is an organic compound whose constituent atoms consist only of carbon atoms and hydrogen atoms. The low-polarity plasticizer (E) may have the effect of plasticizing the material when added to a polymer material. It is preferable that the low-polarity plasticizer (E) is a compound that does not have polymerizable unsaturated carbon-carbon bonds.

[0109] A "polymerizable unsaturated carbon-carbon bond" refers to a double or triple bond that, when subjected to addition chain polymerization conditions commonly used by those skilled in the art (e.g., free radicals, anions, cations, or similar initiating systems; application of light or heat; presence of a suitable solvent, catalyst, or initiator), can cleave and initiate chain growth, resulting in an increase in average molecular weight or the formation of crosslinks. Specific examples of polymerizable unsaturated carbon-carbon bonds include unsaturated carbon-carbon bonds in vinyl groups (e.g., vinyl groups of styrene monomers, vinyl groups derived from fumaric acid, vinyl groups derived from itaconic acid), allyl groups, (meth)acryloyl groups, vinyl ether compounds, vinyl ester compounds, conjugated diene compounds (e.g., butadiene, isoprene), maleimide compounds, and unsaturated carbon-carbon bonds in strained olefins such as norbornene.

[0110] The low-polarity plasticizer (E) may have non-polymerizable unsaturated carbon-carbon bonds. A "non-polymerizable unsaturated carbon-carbon bond" refers to an unsaturated bond that does not substantially contribute to the chain growth under addition chain polymerization conditions commonly used by those skilled in the art. Typical examples include aromatic carbon-carbon bonds of aromatic rings (benzene, naphthalene, etc.). Non-polymerizable unsaturated carbon-carbon bonds, under these conditions, are mainly capable of undergoing substitution or addition reactions but do not readily transition to chain addition polymerization, and do not result in a significant increase in average molecular weight or gel fraction.

[0111] In this specification, the distinction between "polymerizable" and "non-polymerizable" is based on the behavior in addition chain polymerization (radical, anionic, cation), and polymerization by different mechanisms such as condensation polymerization (e.g., step growth via carbonyl or isocyanate) or oxidative coupling is excluded from this definition. Unless otherwise specified, "polymerizable" or "polymerizable" as used herein means that the unsaturated bond can be cleaved and chain growth can occur through addition chain polymerization.

[0112] The low-polarity plasticizer (E) is not particularly limited as long as it is used in the technical field of flexographic printing plates, and examples include saturated chain hydrocarbons, non-polymerizable unsaturated chain hydrocarbons, saturated cyclic hydrocarbons, non-polymerizable unsaturated cyclic hydrocarbons, and aromatic hydrocarbons.

[0113] The low-polarity plasticizer (E) is preferably an organic compound having a linear saturated hydrocarbon structure with four or more carbon atoms. Known low-polarity plasticizers can be used as the low-polarity plasticizer (E). Specific examples of the low-polarity plasticizer (E) are not limited to, but include, for example, long-chain hydrocarbons such as octane, nonane, and decane; long-chain alkylbenzenes such as butylbenzene, amylbenzene, nonylbenzene, decylbenzene, and hexadecylbenzene; hydrocarbon oils such as paraffin oil, naphthenic oil, and aromatic oil; and hydrocarbon waxes such as microcrystalline wax and Fischertrops wax. These may be used individually or in combination of two or more.

[0114] The molecular weight of the low-polarity plasticizer (E) is not particularly limited, but from the viewpoint of plasticizing the flexographic printing plate and lowering its hardness to further improve the opacity in corrugated cardboard printing, it is preferably less than 1500, more preferably less than 1000, even more preferably less than 750, and particularly preferably less than 500. On the other hand, the lower limit is preferably 100 or more, more preferably 200 or more, and even more preferably 300 or more.

[0115] The chemical structure of the low-polarity plasticizer (E) is not particularly limited and may include linear or cyclic structures. In particular, compounds that do not contain unsaturated bonds are preferred from the viewpoint of further improving long-term stability, and paraffin oil or naphthenic oil is even more preferred from the viewpoint of further improving the kneadability of the photosensitive resin.

[0116] The content of the low-polarity plasticizer (E) in the photosensitive resin composition is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of softening the hardness of the flexographic printing plate and further improving the opacity during corrugated cardboard printing, when the total amount of the photosensitive resin composition is considered as 100% by mass. Furthermore, from the viewpoint of further suppressing design defects on the flexographic printing plate, it is preferably 20% by mass or less, and more preferably 15% by mass or less.

[0117] In the photosensitive resin composition of this embodiment, the Hansen solubility parameter (HSP) can be used as an indicator of the compatibility between the combination of thermoplastic elastomer (A) and low-polarity plasticizer (E), and between the combination of hydrophilic polymer particles (B) and low-polarity plasticizer (E). In order to improve the compatibility between thermoplastic elastomer (A) and low-polarity plasticizer (E), and between hydrophilic polymer particles (B) and low-polarity plasticizer (E), the distance in HSP values ​​between the thermoplastic elastomer (A) and low-polarity plasticizer (E), and between hydrophilic polymer particles (B) and low-polarity plasticizer (E) is important.

[0118] In the photosensitive resin composition of this embodiment, the distance Δδa of the HSP polarity term is calculated by the following formula (1) using the Hansen solubility parameter value (HSP value) of the low-polarity plasticizer (E) and the Hansen solubility parameter value (HSP value) of the thermoplastic elastomer (A).Ｅ－Ａ However, it is preferably 0 to 4, more preferably 0 to 3, and even more preferably 0 to 2. Δδa Ｅ－Ａ = |δa Ｅ -δa Ａ | = | (δp) Ｅ ２ +δh Ｅ ２ ) ０．５ -(δp) Ａ ２ +δh Ａ ２ ) ０．５ | ...Formula (1) δa Ｅ δa of low-polarity plasticizer (E) δa Ａ δa δp of thermoplastic elastomer (A) Ｅ δp δh of low-polarity plasticizer (E) Ｅ δh δp of low polarity plasticizer (E) Ａ δp δh of thermoplastic elastomer (A) Ａ δh of thermoplastic elastomer (A) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction

[0119] Δδa of thermoplastic elastomer (A) and low-polarity plasticizer (E) Ｅ－Ａ Because the range is as described above, the plasticizer can be better miscible with the thermoplastic elastomer (A) phase, and the amount of plasticizer necessary to reduce the hardness to a level that improves corrugated cardboard printability while preventing plasticizer bleed-out can be added. Although the technical mechanism is not fully understood, the inventors speculate that by using Δδa, which takes into account the effects of intermolecular dipole interactions and intermolecular hydrogen bonding, as an indicator, it is possible to quantify the intermolecular interactions that correlate with the good miscibility between the plasticizer and the high molecular weight component.

[0120] In the photosensitive resin composition of this embodiment, the distance Δδa of the HSP polarity term is calculated by the following formula (4) using the Hansen solubility parameter value (HSP value) of the low-polarity plasticizer (E) and the Hansen solubility parameter value (HSP value) of the hydrophilic polymer particles (B). Ｅ－ＢHowever, it is preferably 2 to 20, more preferably 3 to 20, and even more preferably 4 to 20. Δδa Ｅ－Ｂ = |δa Ｅ -δa Ｂ | = | (δp) Ｅ ２ +δh Ｅ ２ ) ０．５ -(δp) Ｂ ２ +δh Ｂ ２ ) ０．５ |...Formula (4) δa Ｅ δa of low-polarity plasticizer (E) δa Ｂ : δa δp of hydrophilic polymer particles (B) Ｅ δp δh of low-polarity plasticizer (E) Ｅ δh δp of low polarity plasticizer (E) Ｂ : δp δh of hydrophilic polymer particles (B) Ｂ δh of hydrophilic polymer particles (B) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: parameter due to HSP in intermolecular polar interaction

[0121] Δδa of hydrophilic polymer particles (B) and low-polarity plasticizer (E) Ｅ－Ｂ The inventors speculate that the larger size makes it more difficult for the low-polarity plasticizer (E) to penetrate the hydrophilic polymer particles (B), and thus prevents competition for compatibility between the hydrophilic polymer particles (B) and the high-polarity plasticizer (F), thereby better preventing plasticizer bleed-out.

[0122] (High Polarity Plasticizer (F)) The photosensitive resin composition of this embodiment contains a high polarity plasticizer (F). The high polarity plasticizer (F) is a component that does not fall under the category of a photopolymerizable monomer (C). The high polarity plasticizer (F) is an organic compound whose constituent atoms include atoms other than carbon atoms and hydrogen atoms in addition to carbon atoms and hydrogen atoms. The high polarity plasticizer (F) can be a highly polar component that has the effect of plasticizing the material when added to a polymer material. Examples of atoms other than carbon atoms and hydrogen atoms that the high polarity plasticizer (F) may have include heteroatoms such as oxygen atoms, nitrogen atoms, sulfur atoms, and phosphorus atoms. The high polarity plasticizer (F) is a compound having hydrophilic groups such as carboxyl groups, amino groups, hydroxyl groups, phosphate groups, and sulfonic acid groups, or polar groups in which the hydrophilic hydrogen atoms of these groups are substituted with hydrocarbons. It is preferable that the high polarity plasticizer (F) is a compound that does not have polymerizable unsaturated carbon-carbon bonds.

[0123] The molecular weight of the highly polar plasticizer (F) is not particularly limited, but from the viewpoint of plasticizing the flexographic printing plate, lowering its hardness, and further improving the opacity in corrugated cardboard printing, it is preferably less than 1500, more preferably less than 1000, even more preferably less than 750, and particularly preferably less than 500. On the other hand, it is preferably 100 or more, more preferably 200 or more, and even more preferably 300 or more.

[0124] The highly polar plasticizer (F) is not limited, but from the viewpoint of further improving the long-term stability of the compound, it is preferable that it be an organic compound having one or more ester structures (e.g., one, two, three, or four) in one molecule and an organic compound having one or more ether structures (e.g., one, two, three, or four) in one molecule. From the viewpoint of more effectively plasticizing flexographic printing plates and improving corrugated cardboard printability, it is more preferable that it be an organic compound having one or more ester structures (e.g., one, two, three, or four) in one molecule, and even more preferable that it be an organic compound having one or more carboxylic acid ester structures (e.g., one, two, three, or four) in one molecule. An ether structure is a structure in which one oxygen atom is bonded between two carbon atoms that do not have an oxo group (=O). An ester structure is a structure in which a heteroatom (excluding oxygen atoms) or carbon atom having one or more oxo groups (=O) and optionally one or more hydroxyl groups (-OH) is bonded to one or more different carbon atoms via oxygen or sulfur atoms, and optionally directly bonded to one or more different carbon atoms. An example of an ester structure is a carboxylic acid ester structure (CO ２ ), carboxylic acid thioester structure (COS), carbonate ester structure (OCO ２ ) Carbon-containing ester structures such as; sulfinic acid ester structures (SO ２ ), sulfonic acid ester structure (SO ３ ), sulfate ester structure (OSO ３ ) Sulfur-containing ester structures such as; phosphinic acid ester structures (PO ２ ), phosphonic acid ester structure (PO ３ ), phosphate ester structure (OPO ３ Phosphorus-containing ester structures such as (ONO); nitrate ester structures (ONO) ２ Examples include nitrogen-containing ester structures such as those shown above.

[0125] Specific examples of organic compounds having one or more ester structures in a single molecule are not particularly limited, but include, for example, alkyl esters of monocarboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, and benzoic acid; mono or di-alkyl esters of dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, tartaric acid, adipic acid, glutamic acid, sebacic acid, and phthalic acid; mono, di, or tri-alkyl esters of tricarboxylic acids such as trimellitic acid, citric acid, and acetylcitric acid; and mono, di, or tri-alkyl esters of phosphoric acid. Examples of alkyl moieties in the alkyl esters of these organic compounds include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl (n-pentyl), isopentyl (3-methylbutyl), neopentyl (2,2-dimethylpropyl), hexyl (n-hexyl), 2-methylpentyl, 3-methylpentyl, heptyl (n-heptyl), 2-methylhexyl, 3-methylhexyl, octyl (n-octyl), 2-ethylhexyl, 3-ethylhexyl, nonyl (n-nonyl), decyl (n-decyl), undecyl (n-undecyl), dodecyl (n-dodecyl), tridecyl (n-tridecyl), tetradecyl (n-tetradecyl), and pentadecyl (n-pentadecyl). When multiple alkyl moieties exist in these organic compounds, these alkyl moieties may be the same or different within the same molecule. These organic compounds may be used individually or in combination of two or more.

[0126] Specific examples of organic compounds having one or more ether structures in a single molecule are not particularly limited, but include, for example, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, diethylene glycol dialkyl ether, diethylene glycol monoalkyl ether, triethylene glycol dialkyl ether, triethylene glycol dialkyl ether, polyethylene glycol, etc. Examples of alkyl moieties in the alkyl ethers of these organic compounds include methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl. When multiple alkyl moieties exist in these organic compounds, these alkyl moieties may be the same or different within the same molecule. These organic compounds may be used individually or in combination of two or more.

[0127] The content of the highly polar plasticizer (F) in the photosensitive resin composition is preferably 1% by mass or more, and more preferably 2% by mass or more, from the viewpoint of softening the hardness of the flexographic printing plate and further improving the opacity during corrugated cardboard printing, when the total amount of the photosensitive resin composition is considered to be 100% by mass. Furthermore, from the viewpoint of further suppressing design defects on the flexographic printing plate, it is preferably 20% by mass or less, and more preferably 15% by mass or less.

[0128] In the photosensitive resin composition of this embodiment, the Hansen solubility parameter (HSP) can be used as an indicator of the compatibility between the combination of thermoplastic elastomer (A) and high-polarity plasticizer (F), and the combination of hydrophilic polymer particles (B) and high-polarity plasticizer (F). In order to improve the compatibility between thermoplastic elastomer (A) and high-polarity plasticizer (F), and between hydrophilic polymer particles (B) and high-polarity plasticizer (F), the distance in HSP values ​​between the thermoplastic elastomer (A) and high-polarity plasticizer (F), and between hydrophilic polymer particles (B) and high-polarity plasticizer (F) is important.

[0129] In the photosensitive resin composition of this embodiment, the distance Δδa of the HSP polarity term is calculated by the following formula (2) based on the Hansen solubility parameter value (HSP value) of the highly polar plasticizer (F) and the Hansen solubility parameter value (HSP value) of the hydrophilic polymer particles (B). Ｆ－ＢPreferably, it is 0 to 4, more preferably 0 to 3, and even more preferably 0 to 2. Δδa Ｆ－Ｂ = |δa Ｆ -δa Ｂ | = | (δp) Ｆ ２ +δh Ｆ ２ ) ０．５ -(δp) Ｂ ２ +δh Ｂ ２ ) ０．５ |...Formula (2) δa Ｆ δa of the highly polar plasticizer (F) Ｂ : δa δp of hydrophilic polymer particles (B) Ｆ δp δh of high polarity plasticizer (F) Ｆ δh δp of high polarity plasticizer (F) Ｂ : δp δh of hydrophilic polymer particles (B) Ｂ δh of hydrophilic polymer particles (B) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction

[0130] Δδa of hydrophilic polymer particles (B) and highly polar plasticizer (F) Ｆ－Ｂ Because the range is as described above, the plasticizer can better miscible with the hydrophilic polymer particle (B) phase, and the amount of plasticizer necessary to reduce the hardness to a level that improves corrugated cardboard printability while preventing plasticizer bleed-out can be added. Although the technical mechanism is not fully understood, the inventors speculate that by using Δδa, which takes into account the effects of intermolecular dipole interactions and intermolecular hydrogen bonding, as an indicator, it is possible to quantify the intermolecular interactions that correlate with the miscibility of the plasticizer and high molecular weight components.

[0131] In the photosensitive resin composition of this embodiment, the distance Δδa of the HSP polarity term is calculated by the following formula (3) using the Hansen solubility parameter value (HSP value) of the high-polarity plasticizer (F) and the Hansen solubility parameter value (HSP value) of the thermoplastic elastomer (A). Ｆ－ＡPreferably, it is 2 to 20, more preferably 3 to 20, and even more preferably 4 to 20. Δδa Ｆ－Ａ = |δa Ｆ -δa Ａ | = | (δp) Ｆ ２ +δh Ｆ ２ ) ０．５ -(δp) Ａ ２ +δh Ａ ２ ) ０．５ |...Formula (3) δa Ｆ δa of the highly polar plasticizer (F) Ａ δa δp of thermoplastic elastomer (A) Ｆ δp δh of high polarity plasticizer (F) Ｆ δh δp of high polarity plasticizer (F) Ａ δp δh of thermoplastic elastomer (A) Ａ δh of thermoplastic elastomer (A) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction

[0132] The inventors speculate that the large Δδa between the highly polar plasticizer (F) and the thermoplastic elastomer (A) makes it difficult for the highly polar plasticizer (F) to penetrate the thermoplastic elastomer (A), thus preventing competition for compatibility between the thermoplastic elastomer (A) and the low-polarity plasticizer (E), and thus further preventing plasticizer bleed-out.

[0133] (Content ratio of low-polarity plasticizer E and high-polarity plasticizer F) Content P of low-polarity plasticizer (E) in the photosensitive resin composition Ｅ (mass%) and the content P of the highly polar plasticizer (F) Ｆ (mass%) ratio (P Ｅ / P Ｆ The plasticizers are not particularly limited, but from the viewpoint of plasticizing each phase of the thermoplastic elastomer (A) and hydrophilic polymer particles (B) to the necessary extent and preventing bleed-out, it is preferable that the ratio is not biased towards either a low-polarity plasticizer (E) or a high-polarity plasticizer (F). Content P of low-polarity plasticizer (E) Ｅ(mass%) and the content P of the highly polar plasticizer (F) Ｆ (mass%) ratio (P Ｅ / P Ｆ The ratio is preferably 0.05 or more and 7 or less, more preferably 0.1 or more and 3 or less, and even more preferably 0.5 or more and 1.8 or less.

[0134] (Relationship between the content ratio of thermoplastic elastomer (A) and hydrophilic polymer particles (B), and the content ratio of low-polarity plasticizer (E) and high-polarity plasticizer (F)) Content P of thermoplastic elastomer (A) in the photosensitive resin composition Ａ (mass%) and the content P of hydrophilic polymer particles (B) Ｂ (mass%) ratio (P Ａ / P Ｂ ) and the content P of low-polarity plasticizer (E) Ｅ (mass%) and the content P of the highly polar plasticizer (F) Ｆ (mass%) ratio (P Ｅ / P Ｆ In relation to (P), from the perspective of enhancing the plasticizing effect and preventing bleed-out Ａ / P Ｂ ) and (P Ｅ / P Ｆ ) is preferably of the same degree. (P Ａ / P Ｂ ) / (P Ｅ / P Ｆ ) is not particularly limited, but is preferably 0.1 or more and 10 or less, and more preferably 0.5 or more and 2 or less. (P Ａ / P Ｂ ) / (P Ｅ / P Ｆ ) is close to 1, that is, P Ａ / P Ｂ and P Ｅ / P Ｆ The inventors speculate that the close ratio of these two components allows the plasticizer to be uniformly distributed between the thermoplastic elastomer (A) and hydrophilic polymer particle (B) phases, thereby enhancing the plasticizing effect and better preventing bleed-out.

[0135] (Liquid Rubber (G)) The photosensitive resin composition of this embodiment may contain liquid rubber (G). By including liquid rubber (G) in the photosensitive resin composition, the kneadability can be further improved. Herein, in this specification, "liquid" in "liquid rubber" means a property that is easily fluid and deformable and can solidify into the deformed shape upon cooling, and is a term that corresponds to an elastomer that deforms instantaneously in response to an external force when that external force is applied, and recovers to its original shape in a short time when that external force is removed.

[0136] The liquid rubber (G) is not limited to, but is a polymer compound obtained by polymerization of ethylenic monomers, and includes, for example, liquid 1,2 (or 1,4)-polybutadiene, 1,2 (or 1,4)-polyisoprene, liquid acrylonitrile-butadiene copolymer, liquid styrene-butadiene copolymer, liquid acrylic polymer, and modified main chains or end products thereof, all having a number average molecular weight of 1,000 to 50,000. The liquid rubber may contain polymerizable unsaturated carbon-carbon bonds in its molecular chain. The liquid rubber may be used alone or in combination of two or more types. The weight-average molecular weight can be measured by gel permeation chromatography (GPC) and expressed as polystyrene-equivalent molecular weight.

[0137] In particular, when using a styrene-butadiene-styrene copolymer as the thermoplastic elastomer (A) described above, liquid dienes such as liquid 1,2 (or 1,4)-polybutadiene and 1,2 (or 1,4)-polyisoprene are preferred as the liquid rubber, from the viewpoint of further improving the miscibility with the styrene-butadiene-styrene copolymer. A liquid diene is a compound having a liquid carbon-carbon double bond, and is a copolymer in which the diene component is 50% by mass or more.

[0138] The 1,2 (or 1,4)-polybutadiene of the liquid rubber (G) is not particularly limited, but examples include B1000, B2000, B3000 (manufactured by Nippon Soda), LBR-352, LBR-305, LBR-300 (manufactured by Kuraray), POLYVEST110, 130 (manufactured by EVONIK), Ricon152, Ricon153, Ricon156 (manufactured by Sartomer), etc. The liquid 1,2 (or 1,4)-polyisoprene is not particularly limited, but examples include LIR-30, LIR-50 (manufactured by Kuraray), etc. The main chain or end-modified liquid rubber products are not particularly limited, but examples include G-1000, G-2000, G-3000 (manufactured by Nippon Soda), R-15HT, R-45HT (manufactured by Idemitsu Kosan), and CBB3098 (manufactured by Soken Chemical).

[0139] The number-average molecular weight of the liquid rubber (G) is not particularly limited as long as it is liquid at 20°C, but from the viewpoint of further improving the handling of flexographic printing plates, it is preferably 1,000 to 50,000, more preferably 2,000 to 40,000, and even more preferably 3,000 to 30,000. The number-average molecular weight can be measured by gel permeation chromatography (GPC) and is expressed as polystyrene-equivalent molecular weight.

[0140] The content of liquid rubber (G) in the photosensitive resin composition is preferably higher from the viewpoint of improving kneadability, and preferably lower from the viewpoint of improving print durability. When the total amount of the photosensitive resin composition is 100% by mass, the content is preferably 10% to 50% by mass, more preferably 15% to 45% by mass, and even more preferably 20% to 40% by mass.

[0141] (Other optional components) The photosensitive resin composition of this embodiment may contain other optional components other than (A) thermoplastic elastomer, (B) hydrophilic polymer particles, (C) photopolymerizable monomer, (D) photopolymerization initiator, (E) low polarity plasticizer, (F) high polarity plasticizer, and (G) liquid rubber.

[0142] Other optional ingredients include, for example, polymerization inhibitors, dyes, pigments, viscosity modifiers, defoamers, UV absorbers, fragrances, anti-coagulation agents, and surfactants.

[0143] (Method for manufacturing a flexographic printing plate) The flexographic printing plate of this embodiment is laminated in the following order: at least a support, a photosensitive resin composition layer, and an infrared ablation layer. The photosensitive resin composition layer contains (A) a thermoplastic elastomer, (B) hydrophilic polymer particles, (C) a photopolymerizable monomer, (D) a photopolymerization initiator, (E) a low-polarity plasticizer, and (F) a high-polarity plasticizer. It may also contain (G) liquid rubber and other optional components.

[0144] A method for manufacturing a printing plate according to this embodiment will now be described. First, the above-mentioned components are prepared and mixed to produce a photosensitive resin composition. Next, the obtained photosensitive resin composition is formed into layers to obtain a photosensitive resin composition layer. Specifically, one method is to mix the components of the photosensitive resin composition using an extruder or kneader, and then form a photosensitive resin composition layer of the desired thickness by hot press molding, calendering, or extrusion molding. To maintain the accuracy of the obtained photosensitive resin composition layer as a flexographic printing plate, a support such as polyester is laminated on the side opposite to the relief surface. Furthermore, an infrared ablation layer, which can be removed by an infrared laser, is laminated on the relief surface of the obtained photosensitive resin composition layer. In addition, a film (cover sheet) may be provided on the side of the infrared ablation layer opposite to the photosensitive resin composition layer. The support and the infrared ablation layer can be adhered to the photosensitive resin composition layer by roll lamination after sheet molding. Alternatively, a photosensitive resin composition layer with good accuracy can be obtained by heat pressing after lamination.

[0145] (Method for manufacturing a flexographic printing plate) The method for manufacturing a flexographic printing plate according to this embodiment includes: a step of laser ablation of the infrared ablation layer of the flexographic printing plate according to this embodiment to form a negative pattern (hereinafter referred to as the "pattern formation step"), a step of exposing the photosensitive resin composition layer (hereinafter referred to as the "exposure step"), and a step of removing the unexposed portion of the photosensitive resin composition layer (hereinafter referred to as the "development step").

[0146] In the pattern formation process, first, exposure is performed through the support of the flexographic printing plate to photocur the photosensitive resin composition layer, thereby forming a thin, uniform cured layer (back exposure). If a film (cover sheet) is laminated to the infrared ablation layer of the flexographic printing plate, the film (cover sheet) is first peeled off. Then, the infrared ablation layer is irradiated with infrared light in a pattern to perform laser ablation and form a negative pattern as a mask on the photosensitive resin composition layer. Suitable infrared lasers include, for example, ND / YAG lasers (e.g., 1064 nm) or diode lasers (e.g., 830 nm). In this infrared laser ablation technology, suitable laser systems are commercially available, and for example, the diode laser system CDI Spark (ESKO GRAP HICS) can be used. This laser system includes a rotating cylindrical drum for holding the flexographic printing plate, an IR laser irradiation device, and a layout computer, and image information is transmitted directly from the layout computer to the laser device.

[0147] After forming a negative pattern on the infrared ablation layer, the photosensitive resin composition layer is exposed by irradiating the entire surface with ultraviolet light as an exposure step. The irradiation unit used for this is the same unit used for ultraviolet irradiation from the support side. The light source used to photo-cure the photosensitive resin composition layer is not limited to the following, but examples include high-pressure mercury lamps, ultraviolet fluorescent lamps, carbon arc lamps, xenon lamps, and sunlight.

[0148] After full exposure, a developing process is performed to wash away the unexposed portions of the photosensitive resin composition layer and remove them. Conventional methods known as the developing method can be applied. Specifically, although not particularly limited, the unexposed portions can be removed by washing them with a solvent for solvent development or a developer for water development, or by bringing the unexposed portions, heated to 40°C to 200°C, into contact with a predetermined absorbent layer and removing the absorbent layer. Among these, from the viewpoint of environmental harmony, it is preferable to use a water-based developer.

[0149] The solvent-based developer used to develop the unexposed areas is not particularly limited, but examples include esters such as heptyl acetate and 3-methoxybutyl acetate; hydrocarbons such as petroleum fractions, toluene, and decalin; and mixtures of chlorinated organic solvents such as tetrachloroethylene with alcohols such as propanol, butanol, and pentanol. The unexposed areas are washed out by spraying from a nozzle or by brushing with a brush.

[0150] For developing the unexposed areas with water, the aqueous developer can be water itself, an alkaline aqueous solution, or a neutral detergent. While there are no particular limitations on such aqueous developers, for example, a solution containing water, nonionic or anionic surfactants, pH adjusters, and cleaning accelerators can be used.

[0151] Examples of surfactants include anionic surfactants, amphoteric surfactants, and nonionic surfactants. These may be used individually or in combination of two or more types.

[0152] Anionic surfactants are not particularly limited, but examples include sulfate esters, higher alcohol sulfates, higher alkyl ether sulfates, sulfated olefins, alkylbenzene sulfons, α-olefin sulfons, phosphate esters, and dithiophosphate esters.

[0153] The amphoteric surfactant is not particularly limited, but examples include amino acid-type amphoteric surfactants and betaine-type amphoteric surfactants.

[0154] Nonionic surfactants are not particularly limited, but examples include polyethylene glycol-type surfactants such as higher alcohol ethylene oxide adducts, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid ester ethylene oxide adducts, higher alkylamine ethylene oxide adducts, fatty acid amide ethylene oxide adducts, and polypropylene glycol ethylene oxide adducts, as well as polyhydric alcohol-type surfactants such as glycerol fatty acid esters, pentaerythritol fatty acid esters, sorbitol and sorbitan fatty acid esters, alkyl esters of polyhydric alcohols, and fatty acid amides of alkanolamines. In addition, the alkaline aqueous solution contains a pH adjuster.

[0155] The pH adjusting agent can be either an organic or inorganic material, but one that can adjust the pH to 9 or higher is preferred. The pH adjusting agent is not particularly limited, but examples include sodium hydroxide, sodium carbonate, potassium carbonate, sodium silicate, sodium metasilicate, and sodium succinate.

[0156] Development can also be performed by heat. In thermal development, no solvent is used; instead, the photosensitive resin composition layer and the intermediate layer are brought into contact with an absorbent material after image exposure and heated at 40°C to 200°C to remove unexposed areas. Examples of absorbent layers for thermal development include nonwoven fabrics, paper materials, textile fabrics, open-cell foams, and porous materials. Among these, preferred absorbent layers are nonwoven fabrics made of nylon, polyester, polypropylene, and polyethylene, as well as combinations of these nonwoven fabrics. Particularly preferred absorbent layers are continuous nonwoven webs of nylon or polyester.

[0157] If necessary, the printing plate may be dried to prevent swelling or whitening caused by the developing solution. While not limited to these methods, examples include drying by heat, air drying with an air knife, or absorbing the developing solution with a nonwoven fabric and removing it. For drying by heat, one method is to leave the plate in an oven heated to 40°C to 60°C for 10 to 120 minutes.

[0158] Subsequently, the flexographic printing plate is manufactured by post-exposure treatment as needed. Post-exposure treatment includes irradiating the surface with light with a wavelength of 300 nm or less. If necessary, light with a wavelength longer than 300 nm may also be used.

[0159] (Corrugated cardboard) The flexographic printing plates manufactured from the flexographic printing plates of this embodiment are suitable as printing plates for corrugated cardboard. Corrugated cardboard is not particularly limited as long as it is made by laminating paper to one or both sides of a corrugated paper base. From differences in structure, corrugated cardboard can be classified into single-sided corrugated cardboard, in which a corrugated core paper base is laminated to a single liner; double-sided corrugated cardboard, in which a liner is laminated to the corrugations of single-sided corrugated cardboard; double-double-sided corrugated cardboard, in which the corrugations of single-sided corrugated cardboard are laminated to one side of double-sided corrugated cardboard; and triple-double-sided corrugated cardboard, in which the corrugations of single-sided corrugated cardboard are laminated to one side of double-double-sided corrugated cardboard. It is further classified into A-flute, B-flute, C-flute, E-flute, F-flute, G-flute, etc., depending on the number of layers and the height of the layers. For corrugated cardboard used for outer packaging, the mass of the core (flute) is specified from the viewpoint of strength, and a core of 80 to 160 g is used, but 160 g is preferred from the viewpoint of strength. In direct printing on corrugated cardboard, the pressure applied during printing is relatively lower at the lamination point between the corrugated sheet liner and the core paper compared to the pressure applied to the non-lamination point. This results in a phenomenon called uneven density in the printed material (corrugated cardboard), also known as a washboard effect. The flexographic printing plate obtained from the flexographic printing plate of this embodiment can effectively reduce such unevenness in corrugated cardboard printing.

[0160] The effects of the present invention are demonstrated by the following examples, but the present invention is not limited to these. In the examples, "parts" refers to parts by mass.

[0161] [Calculation of Hansen Solubility Parameter Values ​​(HSP Values)] The Hansen solubility parameter values ​​(HSP values) for each component used in the examples were calculated using the PC software "HSPiP" (Hansen Solubility Parameters in Practice) provided at hansen-solubility.com.

[0162] To calculate the HSP value of the flexographic printing plate material, the following solvents were used: 1,1,2,2-tetrabromoethane, nitrobenzene, chlorobenzene, benzyl alcohol, N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, cis-decahydronaphthalene, formamide, ethylene glycol, tetrahydrofuran, propylene glycol, dibutyl sebacete, 1-butanol, 2-ethylhexanol, n-butyl acetate, ethanol, acetone, propionitrile, hexane, methanol, lauryl methacrylate, and tetraethyl orthosilicate. 5g of each solvent was placed in a 20mL vial, and 5g of the flexographic printing plate material was mixed in. After 24 hours, the presence of undissolved material was checked, and materials without undissolved material were considered to be in a dissolved state. Next, the HSP value was calculated by inputting the above results, namely whether or not the substance dissolved in each solvent, into the Sphere program, which is the main program of the PC software "HSPiP," and performing calculations within the software.

[0163] In calculating the HSP values ​​of the water-dispersed latex particles, the same solvents as in the above measurement were used. 10 g of each solvent was placed in a 20 mL vial, 1 g of the dried water-dispersed latex particles was mixed in, and the mixture was gently shaken by hand. After standing for 24 hours, swelling was checked, and those whose volume had increased compared to the initial volume were considered swollen. Subsequently, the above results, i.e., whether swelling occurred or not for each solvent, were input into the Sphere program, the main program of the PC software "HSPiP," and the HSP values ​​were calculated using the software. Table 1 shows the HSP values ​​(δd, δp, δh, and δa) of each component from the analysis results.

[0164]

[0165] [Method for measuring number-average molecular weight (Mn) by gel permeation column chromatography (GPC)] 1. Sample preparation: 10 g of tetrahydrofuran was added to 0.5 g of the substance to be measured and left to stand for 2 hours under sonication to dissolve. Subsequently, the mixture was filtered through a polytetrafluoroethylene membrane filter (pore size 3 μm, manufactured by ADVANTEC), and the filtrate was used as the measurement sample.

[0166] 2. Apparatus and Measurement Conditions GPC measurement of emulsion compounds was performed using the following apparatus and measurement conditions. In the event that the obtained GPC chart is bimodal, in this embodiment, the one with the larger number-average molecular weight is applied. Apparatus: Tosoh HLC-8220 GPC Column: Four of the following columns were connected in series for separation. Tosoh TSKgel GMH XL Tosoh TSKgel GMH XL Tosoh TSKgel GMH XLL Tosoh TSKgel GMH XLL Column temperature: 40°C Solvent: Tetrahydrofuran Flow rate: 1 mL / min Detector: RI Calibration curve: Standard polystyrene

[0167] The results of the number-average molecular weight (Mn) measurements by the gel permeation column chromatography (GPC) described above are shown in the list of materials used in Table 1.

[0168] [Manufacturing Example 1: Synthesis of Hydrophilic Polymer Particles] In a pressure-resistant reaction vessel equipped with a stirring device and a temperature control jacket, 125 parts by mass of water and 2 parts by mass of the ammonium salt of (α-sulfo(1-nonylphenoxy)methyl-2-(2-propenyloxy)ethoxy-poly(oxy-1,2-ethanediyl) "Adekaria Soap SE1025" (manufactured by ADEKA Corporation) as a reactive emulsifier were initially charged, the internal temperature was raised to 80°C, and 10 parts by mass of styrene, 50 parts by mass of butadiene, 32 parts by mass of butyl acrylate, and methamphetamine were added. An oily mixture consisting of a monomer mixture of 5 parts by mass of lylic acid and 2 parts by mass of acrylic acid, and 2 parts by mass of t-dodecyl mercaptan, was added at a constant flow rate over 5 and 6 hours, respectively. This mixture consisted of 20 parts by mass of water, 1.2 parts by mass of sodium peroxodisulfate, 0.2 parts by mass of sodium hydroxide, and 2 parts by mass of ammonium salt of (α-sulfo(1-nonylphenoxy)methyl-2-(2-propenyloxy)ethoxy-poly(oxy-1,2-ethanediyl)).

[0169] Next, the temperature was maintained at 80°C for 1 hour to complete the polymerization reaction. After that, the mixture was cooled, sodium hydroxide was added to adjust the pH to 7, and unreacted monomers were removed by steam stripping. The mixture was then filtered through a 200-mesh wire mesh, and finally, the solid content of the filtrate was adjusted to 40% by mass to obtain an aqueous dispersion containing hydrophilic polymer particles.

[0170] [Production Example 2: Preparation of Hydrophilic Polymer Particle Mixture] To 110 parts by mass of the aqueous dispersion containing hydrophilic polymer particles 1 obtained in Production Example 1, 20 parts by mass of liquid polybutadiene [LBR352: manufactured by Kuraray] were mixed and dried under reduced pressure at 80°C to obtain a hydrophilic polymer particle-containing mixture 1.

[0171] To 110 parts by mass of an aqueous dispersion containing commercially available hydrophilic polymer particles (LX111NF: polybutadiene latex, manufactured by Nippon Zeon Co., Ltd.), 20 parts by mass of liquid polybutadiene [LBR352: manufactured by Kuraray] were mixed and dried under reduced pressure at 80°C to obtain a hydrophilic polymer particle-containing mixture 2.

[0172] [Manufacturing Example 2: Fabrication of Base Film (Support)] As a solution for the adhesive layer to be coated onto the support (base film), 48 parts by mass of D1116AT (manufactured by Kraton, trade name), a block copolymer of styrene and 1,3-butadiene, 14 parts by mass of liquid rubber LBR305 (manufactured by Kuraray, trade name), 27 parts by mass of paraffin oil (average number of carbon atoms 33, number average molecular weight 470, density at 15°C 0.868), 2 parts by mass of 1,9-nonanediol diacrylate, 4.8 parts by mass of 1,6-hexanediol diacrylate, 1.7 parts by mass of AMD-5700 (manufactured by Kyoeisha Chemical Co., Ltd., trade name), 1.5 parts by mass of 2,2-dimethoxyphenylacetophenone, 0.5 parts by mass of dibutylhydroxyethylene, and 0.3 parts by mass of bis(3,5-di-tert-butyl-4-hydroxybenzyl) sulfide were dissolved in a 1:1 solvent of toluene and methyl ethyl ketone to obtain a solution with a solid content of 26%.

[0173] Subsequently, using a knife coater, a coating of 22.0 g / m² was applied to one side of a 188 μm thick polyester film. ２ The film was applied in this manner and dried at 80°C for 1 minute to obtain a support (base film) having an adhesive layer.

[0174] [Manufacturing Example 3: Preparation of a film having an infrared ablation layer] 65% by mass of Asaflex 810 (manufactured by Asahi Kasei Corporation, trade name), a block copolymer of styrene and 1,3-butadiene, and 35% by mass of carbon black as an infrared-sensitive substance were kneaded in a kneader and cut into pellets. 90 parts by mass of these pellets and 10 parts by mass of 1,6-hexanediol adipate were dissolved in a mixed solvent prepared in a mass ratio of ethyl acetate / butyl acetate / propylene glycol monomethyl ether acetate = 50 / 30 / 20 using ultrasound to prepare a homogeneous solution with a solid content of 12% by mass.

[0175] Next, this solution is applied to a polyester film that will form a cover sheet with a thickness of 100 μm, with a coating amount of 4-5 g / m² after drying. ２The material was applied using a knife coater and dried at 80°C for 1 minute to obtain a film having an ultraviolet shielding layer (infrared ablation layer) that can be removed by infrared light. The optical density of this film having an infrared ablation layer was measured using DM-500 (manufactured by Dainippon Screen Mfg. Ltd., product name) and was found to be 3 to 4.

[0176] [Manufacturing Example 4: Preparation of Flexographic Printing Plates] The components listed in Tables 2 to 6 were mixed using a pressure kneader at 140°C for 45 minutes to obtain the photosensitive resin compositions described in Examples 1 to 31 and Comparative Examples 1 to 10. The parts by mass of the "hydrophilic polymer particle-containing mixture" listed in Tables 2 to 6 are based on the solid content mass of the hydrophilic polymer particles.

[0177] Next, the photosensitive resin composition was fed into an extrusion molding machine and extruded from a T-type die. One side of the photosensitive resin composition was bonded to the side with the adhesive layer of the base film (support) obtained in Manufacturing Example 2. A release film (Mitsubishi Chemical Corporation, Diafoil MRV100) was then bonded to the side of the photosensitive resin composition layer opposite to the support lamination side to obtain a laminate of the support and the photosensitive resin composition layer.

[0178] (Manufacturing of flexographic printing plates for Examples 1-31 and Comparative Examples 1-10) The release film of the laminate of the support and the photosensitive resin composition layer was peeled off, and the cover sheet having the infrared ablation layer obtained in Manufacturing Example 3 was laminated so that the infrared ablation layer was in contact with the photosensitive resin composition layer to obtain a flexographic printing plate.

[0179] [Manufacturing Example 5: Manufacturing of Flexographic Printing Plates] (Manufacturing of flexographic printing plates for Examples 1-31 and Comparative Examples 1-10) The flexographic printing plate was exposed from the side of the support (PET coated with adhesive) using an ultraviolet exposure machine "AFP-1216" (manufactured by Asahi Kasei Corporation, product name) so that the pattern height (RD) after curing was approximately 1.5 mm.

[0180] Next, the cover sheet of the infrared ablation layer was peeled off, and using a CDI Spark 4260 (manufactured by ESKO GRAPHIC, product name), a solid image of 10 cm x 25 cm and an image pattern including a 1.5 cm x 1 cm diamond relief pattern were drawn onto the infrared ablation layer. Then, the infrared ablation layer was exposed to 6000 mJ in an atmospheric atmosphere using an AFP-1216 exposure machine.

[0181] After exposure, an aqueous solution (aqueous developer) of 1% polyoxyalkylene alkyl ether (Newcol 2308: manufactured by Nippon Emulsifier Co., Ltd.) and 1% potassium carbonate was prepared, and the solution was washed (developed) at 40°C using a JOW-A3-P washing machine manufactured by JDELSEIKI to remove unexposed areas. After drying at 50°C for 10 minutes, the surface was re-exposed with an ultraviolet germicidal lamp and an ultraviolet chemical lamp to remove surface tackiness, and a flexographic printing plate was obtained.

[0182] (Printability of corrugated cardboard) A printing test was conducted using a flexographic printing press (manufactured by Umetani Seisakusho Co., Ltd.) with a flexographic printing plate of 2.84 mm thickness obtained.

[0183] A carrier sheet (manufactured by Sogo Seihan Co., Ltd.) was attached to the support and deposition layer side of the flexographic printing plate, and R / bak (manufactured by Rogers Corporation) was attached as a cushion sheet in that order. FK-Fm DF260 (manufactured by Sakata Inx Co., Ltd.) was used as the black aqueous ink, and B-flute corrugated cardboard and a 250 lpi anilox roll were used as the substrate. The solid areas of the printed material were visually observed after 7 shots at a printing speed of 150 sheets / minute.

[0184] The degree of smudging in solid areas of printed materials was ranked according to the following evaluation criteria: <Evaluation Criteria> A: Smudging area less than 0.05% AB: Smudging area less than 0.08% AC: Smudging area less than 0.1% B: Smudging area 0.1% or more but less than 0.4% C: Smudging area 0.4% or more but less than 0.8% D: Smudging area 0.8% or more but less than 1.2% E: Smudging area 1.2% or more

[0185] (Crack Resistance) As shown in the schematic front view of the flexographic printing plate in Figure 1, a diamond-shaped relief pattern 10 with dimensions of 1.5 cm vertically and 1 cm horizontally was formed on the flexographic printing plate 1. Next, as shown in the schematic side view of the crack resistance test state in Figure 2, double-sided tape was attached to the slanted surface of the blade 2, and the blade 2 was dropped from a height of 60 cm while sliding vertically along the guide (blade weight 2 kg, drop distance 60 cm). The percentage of the chipped area of ​​the flexographic printing plate when it came into contact with the relief pattern 10 was visually checked, and the crack resistance of the flexographic printing plate was evaluated according to the following evaluation criteria. <Evaluation Criteria> A: Chip area less than 1% B: Chip area 1% or more but less than 5% C: Chip area 5% or more but less than 10% D: Chip area 10% or more but less than 20% E: Chip area 20% or more

[0186] (Bleed-out characteristics) A 2.84 mm thick printing plate was cut to 15 cm x 20 cm, sandwiched between cardboard, and left to stand at 5°C for 7 days. The amount of oil seepage was then visually evaluated. If there was no oil seepage onto the cardboard, it was ranked as A. As the degree of seepage worsened, it was ranked as B, C, D, E according to the evaluation criteria below. <Evaluation criteria> A: No oil seepage B: Oil seepage area of ​​1 mm ２ Less than C: Oil seepage area is 1 mm ２ 5mm or more ２ Less than D: Oil seepage area is 5 mm ２ 10mm or more ２ Less than E: Oil seepage area is 10 mm ２ That's all.

[0187] Tables 2 to 6 below summarize the mixing amounts of each component used in the preparation of the photosensitive resin compositions of Examples 1 to 31 and Comparative Examples 1 to 10, along with the values ​​of Δδa and the evaluation results of each test. The value of Δδa was calculated using the following formula (I): Δδa = |δa| １ -δa ２ | = | (δp) １ ２ +δh １ ２ ) ０．５ -(δp) ２ ２ +δh ２ ２) ０．５ |...Formula (I) δa １ δa of low-polarity plasticizer (E) or high-polarity plasticizer (F) ２ δa δp of thermoplastic elastomer (A) or hydrophilic polymer particles (B) １ δp δh of low-polarity plasticizer (E) or high-polarity plasticizer (F) １ δh δp of low-polarity plasticizer (E) or high-polarity plasticizer (F) ２ δp δh of thermoplastic elastomer (A) or hydrophilic polymer particles (B) ２ δh of thermoplastic elastomer (A) or hydrophilic polymer particles (B) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction

[0188]

[0189]

[0190]

[0191]

[0192]

[0193] (Ingredients) The following ingredients were used as listed in Tables 1 to 5.

[0194] <Thermoplastic Elastomers (A)> TR2827: Styrene-butadiene block copolymer, number average molecular weight: 100,000, monovinyl-substituted aromatic hydrocarbons / conjugated dienes: 24 / 76, manufactured by JSR Corporation D1101: Styrene-butadiene block copolymer, number average molecular weight: 160,000, monovinyl-substituted aromatic hydrocarbons / conjugated dienes: 31 / 69, manufactured by Kraton Corporation T412: Styrene-butadiene block copolymer, number average molecular weight: 240,000, monovinyl-substituted aromatic hydrocarbons / conjugated dienes: 22 / 78, manufactured by Asahi Kasei Corporation

[0195] <Photopolymerizable monomers (C)> 1.6HX: 1,6-Hexanediol dimethacrylate, manufactured by Kyoeisha Chemical Co., Ltd. 1.6HX-A: 1,6-Hexanediol diacrylate, manufactured by Kyoeisha Chemical Co., Ltd. Dioctyl fumarate: manufactured by Tokyo Chemical Industry Co., Ltd.

[0196] <Photopolymerization Initiator (D)> Irg651: Benzyldimethyl ketal, manufactured by BASF Japan

[0197] <Low-polarity plasticizers (E)> P350: Liquid paraffin, manufactured by Matsumura Petroleum Co., Ltd. R1010: Naphthenic oil, manufactured by Eastman Company P70: Naphthenic oil, manufactured by Arakawa Chemical Industries, Ltd. Amylbenzene: manufactured by Tokyo Chemical Industries, Ltd. Nonylbenzene: manufactured by Tokyo Chemical Industries, Ltd. C105 / H105: Fischer-Tropsch hard wax, manufactured by Sazol Inc. Hi-Mic-1090: Microcrystalline wax, manufactured by Nippon Seiro Co., Ltd.

[0198] <High-Polar Plasticizers (F)> Dimethyl succinate: Manufactured by Tokyo Chemical Industry Co., Ltd. Dimethyl sebacate: Manufactured by Tokyo Chemical Industry Co., Ltd. Tributyl phosphate: Manufactured by Tokyo Chemical Industry Co., Ltd. Tributyl trimellitate: Manufactured by Tokyo Chemical Industry Co., Ltd. Tris(2-ethylhexyl) trimellitate: Manufactured by Tokyo Chemical Industry Co., Ltd. 4,5-Epoxycyclohexane-1,2-dicarboxylic acid di2-ethylhexyl: Manufactured by Tokyo Chemical Industry Co., Ltd. Tributyl acetylcitrate: Manufactured by Tokyo Chemical Industry Co., Ltd. Dodecanediol: Manufactured by Tokyo Chemical Industry Co., Ltd. Di-n-butyl phthalate: Manufactured by Tokyo Chemical Industry Co., Ltd. Glycol benzoate ester: Manufactured by Tokyo Chemical Industry Co., Ltd. Dibutyl sebacate: Manufactured by Tokyo Chemical Industry Co., Ltd. PEG-1000: Polyethylene glycol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. PEG-1500: Polyethylene glycol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Diethylene glycol dibutyl ether: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0199] <Liquid Rubber (G)> LBR-305: Liquid polybutadiene, manufactured by Kuraray Co., Ltd. P130: Liquid polybutadiene, manufactured by Nippon Zeon Co., Ltd. CBB3098: Liquid polybutadiene, manufactured by Soken Chemical Co., Ltd.

[0200] <Stabilizers> BHT: 2,6-di-tert-butyl-p-cresol, manufactured by Tokyo Chemical Industry Co., Ltd. Sandant 103: bis(3,5-di-tert-butyl-4-hydroxybenzyl) sulfide, manufactured by Sanshin Chemical Industry Co., Ltd.

[0201] The present invention has industrial applicability as a flexographic printing plate for obtaining printed materials.

[0202] This application claims priority to Japanese Patent Application No. 2024-225718, filed on 20 December 2024, the entire contents of said application being deemed to be part of the disclosure of this application and incorporated herein by reference.

[0203] 1 Flexographic printing plate 2 Blades 10 Relief patterns

Claims

1. A photosensitive resin composition comprising (A) a thermoplastic elastomer, (B) hydrophilic polymer particles, (C) a photopolymerizable monomer, (D) a photopolymerization initiator, (E) a low-polarity plasticizer, and (F) a high-polarity plasticizer, wherein the low-polarity plasticizer (E) is an organic compound whose constituent atoms consist only of carbon atoms and hydrogen atoms, and the high-polarity plasticizer (F) is an organic compound whose constituent atoms consist of carbon atoms and hydrogen atoms in addition to atoms other than carbon atoms and hydrogen atoms.

2. The photosensitive resin composition according to claim 1, wherein the molecular weight of the low-polarity plasticizer (E) is less than 1500, and the molecular weight of the high-polarity plasticizer (F) is less than 1500.

3. The photosensitive resin composition according to claim 1, wherein the molecular weight of the low-polarity plasticizer (E) is less than 500.

4. The photosensitive resin composition according to claim 1, wherein the molecular weight of the highly polar plasticizer (F) is less than 500.

5. The distance Δδa of the HSP polarity term calculated by the following formula (1) based on the Hansen solubility parameter value (HSP value) of the low-polarity plasticizer (E) and the Hansen solubility parameter value (HSP value) of the thermoplastic elastomer (A) Ｅ－Ａ is 0 or more and 4 or less, and the photosensitive resin composition according to claim 1. Δδa Ｅ－Ａ = |δa Ｅ −δa Ａ | = |(δp Ｅ ２ +δh Ｅ ２ )([[]] ０．５ ０．５ −(δp Ａ ２ +δh Ａ ２ )[[]] ０．５ ０．５ | ・・・Formula (1) δa Ｅ : δa of the low-polarity plasticizer (E) δa Ａ : δa of the thermoplastic elastomer (A) δp Ｅ : δp of the low-polarity plasticizer (E) δh Ｅ : δh of the low-polarity plasticizer (E) δp Ａ : δp of the thermoplastic elastomer (A) δh Ａ : δh of the thermoplastic elastomer (A) δp: HSP parameter due to dipole-dipole interaction between molecules δh: HSP parameter due to hydrogen bonding between molecules δa: HSP parameter due to polar interaction between molecules 6. The distance Δδa of the HSP polarity term is calculated using the following formula (2) based on the Hansen solubility parameter value (HSP value) of the highly polar plasticizer (F) and the Hansen solubility parameter value (HSP value) of the hydrophilic polymer particles (B). Ｆ－Ｂ The photosensitive resin composition according to claim 1, wherein the Δδa is between 0 and 4. Ｆ－Ｂ = |δa Ｆ -δa Ｂ | = | (δp) Ｆ ２ +δh Ｆ ２ ) ０．５ -(δp) Ｂ ２ +δh Ｂ ２ ) ０．５ | ...Formula (2) δa Ｆ δa of the highly polar plasticizer (F) Ｂ : δa δp of hydrophilic polymer particles (B) Ｆ δp δh of high polarity plasticizer (F) Ｆ δh δp of high polarity plasticizer (F) Ｂ : δp δh of hydrophilic polymer particles (B) Ｂ δh of hydrophilic polymer particles (B) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction 7. The distance Δδa of the HSP polarity term is calculated using the following formula (3) based on the Hansen solubility parameter value (HSP value) of the highly polar plasticizer (F) and the Hansen solubility parameter value (HSP value) of the thermoplastic elastomer (A). Ｆ－Ａ The photosensitive resin composition according to claim 1, wherein the value is 2 or more and 20 or less. Δδa Ｆ－Ａ = |δa Ｆ -δa Ａ | = | (δp) Ｆ ２ +δh Ｆ ２ ) ０．５ -(δp) Ａ ２ +δh Ａ ２ ) ０．５ | ...Formula (3) δa Ｆ δa of the highly polar plasticizer (F) Ａ δa δp of thermoplastic elastomer (A) Ｆ δp δh of high polarity plasticizer (F) Ｆ δh δp of high polarity plasticizer (F) Ａ δp δh of thermoplastic elastomer (A) Ａ δh of thermoplastic elastomer (A) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: HSP parameter due to intermolecular polar interaction 8. The distance Δδa of the HSP polarity term is calculated using the following formula (4) based on the Hansen solubility parameter value (HSP value) of the low-polarity plasticizer (E) and the Hansen solubility parameter value (HSP value) of the hydrophilic polymer particles (B). Ｅ－Ｂ The photosensitive resin composition according to claim 1, wherein the value is 2 or more and 20 or less. Δδa Ｅ－Ｂ = |δa Ｅ -δa Ｂ | = | (δp) Ｅ ２ +δh Ｅ ２ ) ０．５ -(δp) Ｂ ２ +δh Ｂ ２ ) ０．５ |...Formula (4) δa Ｅ δa of low-polarity plasticizer (E) δa Ｂ : δa δp of hydrophilic polymer particles (B) Ｅ δp δh of low-polarity plasticizer (E) Ｅ δh δp of low polarity plasticizer (E) Ｂ : δp δh of hydrophilic polymer particles (B) Ｂ δh of hydrophilic polymer particles (B) δp: HSP parameter due to intermolecular dipole interaction δh: HSP parameter due to intermolecular hydrogen bonding δa: parameter due to HSP in intermolecular polar interaction 9. Content P of low-polarity plasticizer (E) Ｅ (mass%) and the content P of the highly polar plasticizer (F) Ｆ (mass%) ratio (P Ｅ / P Ｆ The photosensitive resin composition according to claim 1, wherein the ratio is 0.05 or more and 7 or less.

10. Content percentage P of the thermoplastic elastomer (A) Ａ (% by mass) and the content percentage P Ｂ (% by mass) of the hydrophilic polymer particles (B) ratio (P Ａ / P Ｂ ), and the content percentage P Ｅ (% by mass) of the low-polarity plasticizer (E) and the content percentage P Ｆ (% by mass) of the high-polarity plasticizer (F) ratio (P Ｅ / P Ｆ ), in the relationship where (P Ａ / P Ｂ ) / (P Ｅ / P Ｆ ) is 0.1 or more and 10 or less, the photosensitive resin composition according to claim 1.

11. The photosensitive resin composition according to claim 1, wherein the hydrophilic polymer particles (B) are particles comprising a copolymer containing a polymer constituent unit derived from 1,3-butadiene and a constituent unit derived from styrene.

12. The photosensitive resin composition according to claim 1, wherein the thermoplastic elastomer (A) is a copolymer containing a polymer constituent unit derived from 1,3-butadiene and a constituent unit derived from styrene.

13. The photosensitive resin composition according to claim 1, wherein the highly polar plasticizer (F) is an organic compound having one or more ester structures in one molecule.

14. The photosensitive resin composition according to claim 1, wherein the highly polar plasticizer (F) is an organic compound having one or more carboxylic acid ester structures in one molecule.

15. A flexographic printing plate comprising, at least, a support, a photosensitive resin composition layer, and an infrared ablation layer laminated in this order, wherein the photosensitive resin composition layer comprises (A) a thermoplastic elastomer, (B) hydrophilic polymer particles, (C) a photopolymerizable monomer, (D) a photopolymerization initiator, (E) a low-polarity plasticizer, and (F) a high-polarity plasticizer, wherein the low-polarity plasticizer (E) is an organic compound composed only of carbon atoms and hydrogen atoms, and the high-polarity plasticizer (F) is an organic compound composed of carbon atoms and hydrogen atoms in addition to atoms other than carbon atoms and hydrogen atoms.

16. A method for manufacturing a flexographic printing plate, comprising the steps of: laser ablation of the infrared ablation layer of the flexographic printing plate according to claim 15 to form a negative pattern; exposure of the photosensitive resin composition layer; and removal of the unexposed portion of the photosensitive resin composition layer.

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