Flexographic printing plate master and method for manufacturing flexographic printing plates

Abstract

The present invention addresses the problem of providing an original plate for a flexographic printing plate that ensures good reproducibility of microcells and good durability of independent dots when made into a flexographic printing plate, and a method for producing a flexographic printing plate using the original plate. The original plate for a flexographic printing plate according to the present invention has an infrared ablation layer, a photosensitive resin layer, and a support in this order, wherein the content of a photopolymerization initiator contained in a surface layer region up to 100 μm from the surface of the photosensitive resin layer in contact with the infrared ablation layer in the thickness direction is larger than the content of the photopolymerization initiator contained in the remaining region present on the side of the support relative to the surface layer region of the photosensitive resin layer.

Description

Technical Field

[0001] The present invention relates to a flexographic printing plate original and a method for manufacturing a flexographic printing plate using the same.

Background Art

[0002] The original of a flexographic printing plate generally has a photosensitive resin layer (photosensitive layer) made of a photosensitive resin composition on a support made of a polyester film or the like. The flexographic printing plate is plate - made by exposing a predetermined image on the surface of the photosensitive resin layer of this original and then removing the resin in the unexposed portions.

[0003] In a so - called analog - type flexographic printing plate original, a negative film on which a predetermined image is already formed is placed on the photosensitive resin layer, and a predetermined image is exposed on the surface of the photosensitive resin layer through this negative film. On the other hand, in a LAM (Laser ablation mask) - type flexographic printing plate original, an infrared ablation layer is provided in advance on the photosensitive resin layer. After using an infrared laser to directly draw digitized negative image information on the infrared ablation layer to produce a desired negative pattern, a predetermined image is exposed on the surface of the photosensitive resin layer through this negative pattern.

[0004] As such a LAM - type flexographic printing plate original, for example, Patent Document 1 describes a flexographic printing plate original in which a support, a photosensitive resin layer, and an infrared ablation layer containing a binder polymer and an infrared absorbing substance are laminated.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present inventors have attempted to form a fine uneven pattern (hereinafter also abbreviated as "microcells") on the surface of the image portion of a flexographic printing plate, with respect to a known flexographic printing plate master described in Patent Document 1 and the like, from the viewpoint of improving the ink transferability when it is made into a flexographic printing plate. The inventors have revealed that when microcells are formed on the surface of the image area of ​​a flexographic printing plate, chipping or breakage occurs in independent image areas (hereinafter also abbreviated as "independent dots") with a diameter of approximately 100 to 1000 μm.

[0007] Therefore, the object of the present invention is to provide a flexographic printing plate master that exhibits good reproducibility of microcells and good durability of independent dots when made into a flexographic printing plate, and a method for manufacturing a flexographic printing plate using the same. [Means for solving the problem]

[0008] As a result of diligent research to achieve the above objectives, the inventors of the present invention have found that, in a flexographic printing plate having an infrared ablation layer, a photosensitive resin layer, and a support in that order, if the content of the photopolymerization initiator in the surface region of the photosensitive resin layer is greater than the content of the photopolymerization initiator in the remaining region, the reproducibility of microcells and the durability of independent dots are improved when it is made into a flexographic printing plate, thus completing the present invention. In other words, the inventors have found that the above problem can be solved by the following configuration.

[0009] [1] A flexographic printing plate having an infrared ablation layer, a photosensitive resin layer, and a support in this order, A flexographic printing plate master in which the content of photopolymerization initiator in the surface region of the photosensitive resin layer, from the surface in contact with the infrared ablation layer up to 100 μm in the thickness direction, is greater than the content of photopolymerization initiator in the remaining region located on the support side of the photosensitive resin layer. Here, the content of the photopolymerization initiator in the surface region and the remaining region refers to the molar amount relative to the total mass of the solids in the photosensitive resin layer in each region. [2] The flexographic printing plate according to [1], wherein the photopolymerization initiator content in the surface region is 220 to 400 μmol / g and the photopolymerization initiator content in the remaining region is 60 to 200 μmol / g. [3] A method for manufacturing a flexographic printing plate having a non-image portion and an image portion, A mask formation step is performed to form an image on the infrared ablation layer of the flexographic printing plate described in [1] or [2] and to form a mask, Following the mask formation process, an exposure process is performed in which the photosensitive resin layer of the flexographic printing plate is exposed to the image through the mask. A method for manufacturing a flexographic printing plate, comprising an exposure step followed by a developing step in which the plate is developed using a developing solution to form non-image areas and image areas. [4] The method for manufacturing a flexographic printing plate according to [3], wherein the developer is an aqueous developer. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a flexographic printing plate master that exhibits good reproducibility of microcells and good durability of independent dots when made into a flexographic printing plate, and a method for manufacturing a flexographic printing plate using the same. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a flexographic printing plate according to the present invention. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below. The following description of the constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range indicated using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. Furthermore, in this specification, each component may be represented by a single substance or by a combination of two or more substances. When two or more substances are used in combination for each component, the content of that component refers to the total content of the combined substances, unless otherwise specified.

[0013] [Flexographic printing plate original] The flexographic printing plate of the present invention is a flexographic printing plate having an infrared ablation layer, a photosensitive resin layer, and a support in that order. Furthermore, the flexographic printing plate of the present invention is a flexographic printing plate in which the content of photopolymerization initiator contained in the surface region of the photosensitive resin layer up to 100 μm in the thickness direction from the surface on the side in contact with the infrared ablation layer is greater than the content of photopolymerization initiator contained in the remaining region located on the support side of the surface region of the photosensitive resin layer. Here, the content of the photopolymerization initiator in the surface region and the remaining region refers to the molar amount relative to the total mass of the solids in the photosensitive resin layer in each region.

[0014] Figure 1 is a schematic cross-sectional view showing an example of a flexographic printing plate according to the present invention. The flexographic printing plate master 10 shown in Figure 1 has, in this order, an infrared ablation layer 1, a photosensitive resin layer 2 (reference numeral 2a: surface region, reference numeral 2b: remaining region), and a support 3. Furthermore, the flexographic printing plate master of the present invention may have a cover sheet 4, as shown in Figure 1.

[0015] In the present invention, as described above, if the amount of photopolymerization initiator contained in the surface region of the photosensitive resin layer is greater than the amount of photopolymerization initiator contained in the remaining region, the reproducibility of microcells will be good when made into a flexographic printing plate, and the durability of independent dots will also be good. Although this is not entirely clear, the inventors speculate the following: First, in the prior art, when forming microcells on the surface of the image portion of a flexographic printing plate, from the viewpoint of suppressing polymerization inhibition by oxygen, it is necessary to sufficiently advance the curing reaction during exposure by increasing the content of the photoinitiator contained in the photosensitive resin layer. Therefore, in the prior art, it is considered that the reason for the poor durability of the independent small dots is that the ultraviolet rays irradiated during exposure do not reach the inside of the photosensitive resin layer, causing poor curing. Therefore, in the present invention, by making the content of the photoinitiator contained in the surface layer region of the photosensitive resin layer affected by polymerization inhibition by oxygen higher than the content of the photoinitiator contained in the remaining region that is less affected by polymerization inhibition by oxygen, while suppressing the strong absorption of the ultraviolet rays irradiated during exposure in the surface layer region of the photosensitive resin layer, the curing reaction in the remaining region of the photosensitive resin layer can also proceed sufficiently. Therefore, it is considered that the reproducibility of the microcells and the durability of the independent small dots can be achieved simultaneously. Hereinafter, each layer structure of the original flexographic printing plate of the present invention will be described in detail.

[0016] 〔Infrared ablation layer〕 The infrared ablation layer of the original flexographic printing plate of the present invention is a portion that serves as a mask covering the surface of the photosensitive resin layer. In addition, the infrared ablation layer is a portion that can be removed by an infrared laser and a portion that masks the remaining portion so that the ultraviolet light is shielded (absorbed) and the photosensitive resin layer below is not irradiated with ultraviolet light. Such an infrared ablation layer can be formed using a resin composition containing a binder polymer and an infrared absorbing substance.

[0017] <Binder polymer> Examples of the binder polymer contained in the resin composition include polymer components corresponding to rubber components and resin components.

[0018] (Rubber component) The rubber component is not particularly limited as long as it is a rubber that does not hinder adhesion with the photosensitive resin layer. Examples of rubbers include butadiene rubber (BR), acrylonitrile butadiene rubber (NBR), acrylic rubber, epichlorohydrin rubber, urethane rubber, isoprene rubber (IR), styrene isoprene rubber (SIR), styrene butadiene rubber (SBR), ethylene-propylene copolymer, and chlorinated polyethylene. These may be used individually or in combination of two or more types.

[0019] (Resin components) The resin component is not particularly limited as long as it is a resin that does not impede adhesion to the photosensitive resin layer. Examples of resins include (meth)acrylic resin, polystyrene resin, polyester resin, polyamide resin, polysulfone resin, polyethersulfone resin, polyimide resin, acrylic resin, acetal resin, epoxy resin, and polycarbonate resin. These may be used individually or in combination of two or more types. Note that "(meth)acrylic" is a notation meaning acrylic or methacrylic, and "(meth)acryloyl," which will be discussed later, is a notation meaning acryloyl or methacryloyl.

[0020] Of these, the polymer component corresponding to the rubber component is preferably butadiene rubber (BR), acrylonitrile butadiene rubber (NBR), or styrene butadiene rubber (SBR), with acrylonitrile butadiene rubber (NBR) being more preferable. Furthermore, the polymer component equivalent to the resin component is preferably acrylic resin or methacrylic resin.

[0021] <Infrared absorbing material> The infrared absorbing material contained in the resin composition is not particularly limited, as long as it is a material capable of absorbing infrared rays and converting them into heat. Examples of infrared absorbing materials include, for example, black pigments (e.g., carbon black, aniline black, cyanine black, etc.), green pigments (e.g., phthalocyanine, naphthalocyanine, etc.), rhodamine dyes, naphthoquinone dyes, polymethine dyes, diimonium salts, azoimonium dyes, chalcogen dyes, carbon graphite, iron powder, diamine metal complexes, dithiol metal complexes, phenolthiol metal complexes, mercaptophenol metal complexes, arylaluminum metal salts, water-containing inorganic compounds, copper sulfate, metal oxides (e.g., cobalt oxide, tungsten oxide, etc.), and metal powders (e.g., bismuth, tin, tellurium, aluminum, etc.). Of these, carbon black and carbon graphite are preferred from the viewpoint of having ultraviolet absorption capabilities.

[0022] The infrared ablation layer may contain various additives in addition to the binder polymer and infrared absorbing material described above. Examples of such additives include surfactants, plasticizers, UV absorbers, mold release agents, dyes, pigments, defoamers, and fragrances.

[0023] The method for producing the infrared ablation layer is not particularly limited, but examples include preparing a resin composition containing the above-mentioned components and applying it to a photosensitive resin layer.

[0024] The thickness of the infrared ablation layer is preferably 0.1 to 6 μm, and more preferably 0.5 to 3 μm.

[0025] [Photosensitive resin layer] The photosensitive resin layer of the flexographic printing plate master of the present invention can be formed using a conventionally known photosensitive resin composition, except by adjusting the content of the photopolymerization initiator.

[0026] In the present invention, it is preferable that the content of the photopolymerization initiator in the surface region be 220 to 400 μmol / g, and the content of the photopolymerization initiator in the remaining region be 60 to 200 μmol / g, because this results in better reproducibility of microcells and better durability of independent dots when used as a flexographic printing plate. Here, the content of the photopolymerization initiator in the surface region and the remaining region can be measured by the method shown below. First, using a microtome, the cross-section of the photosensitive resin layer of the flexographic printing plate is cut, separating it into two parts: a surface region extending 100 μm in thickness from the surface in contact with the infrared ablation layer, and the remaining region located on the support side of the surface region. After dissolving the entire volume of each separated region's sample in tetrahydrofuran (THF), diluting it to a concentration of 1 mg / 1 mL, the photoinitiator content in each region, i.e., the molar amount [μmol / g] relative to the total mass of the solid content of the photosensitive resin layer in each region, is calculated using liquid chromatography.

[0027] In the present invention, it is preferable that the photosensitive resin layer contains, in addition to a photopolymerization initiator, water-dispersible particles, a binder, a monomer, and a polymerization inhibitor.

[0028] <Water dispersible particles> While there are no particular limitations on the water-dispersible particles, polymers are preferred because they result in better reproducibility of microcells and better durability of independent dots when used in flexographic printing plates. Hereinafter, "better reproducibility of microcells and better durability of independent dots when used in flexographic printing plates" will also be referred to as "superior effects of the present invention." Specific examples of the above polymers include diene polymers (e.g., polybutadiene, natural rubber, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer, polychloroprene, polyisoprene), polyurethane, vinylpyridine polymer, butyl polymer, thiocol polymer, acrylate polymer, and polymers obtained by copolymerizing these polymers with other components such as acrylic acid and methacrylic acid. These may be used individually or in combination of two or more. The above polymer is preferably a polymer obtained by polymerizing at least one monomer selected from the group consisting of isoprene, butadiene, styrene, butyl, ethylene, propylene, acrylic acid esters, and methacrylic acid esters, and is more preferably polybutadiene, for the reason that it has superior water-based ink resistance. The above polymer is preferably one that does not have reactive functional groups (e.g., (meth)acryloyloxy groups) at either end.

[0029] The polymer described above is preferably a polymer obtained by removing water from a water-dispersed latex, for reasons that it provides superior effects of the present invention. Specific examples of the water-dispersed latex include the water-dispersed latex of the polymer described above.

[0030] The content of water-dispersible particles is preferably 5 to 80% by mass, more preferably 10 to 60% by mass, and even more preferably 20 to 45% by mass, relative to the total mass of the solid content of the photosensitive resin layer, for reasons that the effects of the present invention are superior.

[0031] <Binder> The binder is not particularly limited and can be, for example, a thermoplastic polymer. The thermoplastic polymers mentioned above are not particularly limited as long as they are polymers exhibiting thermoplasticity. Specific examples include polystyrene resins, polyester resins, polyamide resins, polysulfone resins, polyethersulfone resins, polyimide resins, acrylic resins, acetal resins, epoxy resins, polycarbonate resins, rubber, and thermoplastic elastomers. These may be used individually or in combination of two or more. Of these, rubber and thermoplastic elastomers are preferred, rubber is more preferred, and diene rubber is even more preferred, because they facilitate the formation of flexible and pliable films.

[0032] As for the rubber mentioned above, non-flowable rubber is preferred in order to ensure the elasticity of the flexographic sheet. Specifically, examples include butadiene rubber (BR), nitrile rubber (NBR), acrylic rubber, epichlorohydrin rubber, urethane rubber, isoprene rubber, styrene-isoprene rubber, styrene-butadiene rubber (SBR), ethylene-propylene copolymer, and chlorinated polyethylene. These may be used individually or in combination of two or more. Of these, at least one rubber selected from the group consisting of butadiene rubber (BR), styrene-butadiene rubber (SBR), and nitrile rubber (NBR) is preferred for better water-developability, drying properties, and image reproducibility. Furthermore, butadiene rubber and styrene-butadiene rubber are more preferred from the viewpoint of water-based ink resistance.

[0033] Examples of the above-mentioned thermoplastic elastomers include PB (polybutadiene-based thermoplastic elastomer), polyisoprene-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, and acrylic-based thermoplastic elastomer. Specifically, examples include SB (polystyrene-polybutadiene), SBS (polystyrene-polybutadiene-polystyrene), SIS (polystyrene-polyisoprene-polystyrene), SEBS (polystyrene-polyethylene / polybutylene-polystyrene), ABS (acrylonitrile butadiene styrene copolymer), ACM (acrylic acid ester rubber), ACS (acrylonitrile chlorinated polyethylene styrene copolymer), acrylonitrile styrene copolymer, syndiotactic 1,2-polybutadiene, and polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate. Of these, PB, SBS, and SIS are particularly preferred from the viewpoint of better water developability, as well as drying properties and image reproducibility.

[0034] The binder content is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 7 to 30% by mass, based on the total mass of solids in the photosensitive resin layer.

[0035] <Monomer> While the monomers are not particularly limited, a combination of monofunctional and difunctional monomers is preferred for reasons that the effects of the present invention are superior.

[0036] (Monofunctional monomer) The above monofunctional monomer is preferably a compound having one ethylenically unsaturated group, for reasons that the effects of the present invention are superior. Examples of ethylenically unsaturated groups include radical polymerizable groups such as acryloyl groups, methacryloyl groups, vinyl groups, styryl groups, and allyl groups. Among these, acryloyl groups, methacryloyl groups, and C(O)OCH=CH2 are preferred, with acryloyl groups and methacryloyl groups being more preferred.

[0037] Examples of compounds having one ethylenically unsaturated group include, N-vinyl compounds such as N-vinylformamide; (meth)acrylamide compounds such as (meth)acrylamide, N-methylol(meth)acrylamide, diacetone(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, (meth)acryloylmorpholine, and (meth)acrylamide; 2-Hydroxyethyl (meth)acrylate, Butoxyethyl (meth)acrylate, Carbitol (meth)acrylate, Cyclohexyl (meth)acrylate, Tetrahydrofurfuryl (meth)acrylate, Benzyl (meth)acrylate, Tridecyl (meth)acrylate, 2-Phenoxyethyl (meth)acrylate, Glycidyl (meth)acrylate, Isobornyl (meth)acrylate, Dicyclopentenyl (meth)acrylate, Dicyclopentenyloxyethyl (meth)acrylate, Dicyclopentanyl (meth)acrylate, 2-Hydroxy-3-Phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl phthalate, Methoxy-polyethylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl phthalate (meth)acrylate compounds such as 2-hydroxyethylphthalic acid, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethoxylated phenyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, nonylphenol EO adduct (meth)acrylate, phenoxy-polyethylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, lactone-modified (meth)acrylate, stearyl (meth)acrylate, isoamyl (meth)acrylate, isomiristyl (meth)acrylate, isostearyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, and others; Methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, n-octadecyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, cyclohexylmethyl vinyl ether, 4-methylcyclohexylmethyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether Monovinyl ether compounds such as ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl ether, tetrahydrofryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloroethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxypolyethylene glycol vinyl ether, cyclohexanedimethanol monovinyl ether, isopropenyl ether-O-propylene carbonate, etc. These are some examples. Note that EO stands for ethylene oxide.

[0038] The monofunctional monomer content is preferably 0.1 to 30% by mass, and more preferably 1 to 10% by mass, relative to the total mass of the solids in the photosensitive resin layer, for reasons that the effects of the present invention are superior.

[0039] (2-functional monomer) The above-mentioned bifunctional monomer is preferably a compound having two ethylenically unsaturated groups, for reasons that the effects of the present invention are superior. Specific examples of the above-mentioned ethylenically unsaturated groups are as described above.

[0040] Examples of compounds having two ethylenically unsaturated groups include, Glycol di(meth)acrylate compounds such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetrapropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, and propoxylated neopentyl glycol di(meth)acrylate; Divinyl ether compounds such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, and cyclohexanedimethanol divinyl ether; Bisphenol A diglycidyl ether (meth)acrylate adducts, modified bisphenol A di(meth)acrylates, bisphenol A PO adduct di(meth)acrylates, bisphenol A EO adduct di(meth)acrylates, and other bisphenol A di(meth)acrylate compounds; These are some examples. Note that PO represents propylene oxide and EO represents ethylene oxide.

[0041] The content of the bifunctional monomer is preferably 0.1 to 30% by mass relative to the total mass of the solid content of the photosensitive resin layer, for reasons that the effects of the present invention are superior.

[0042] <Photopolymerization initiator> The photopolymerization initiator contained in the photosensitive resin layer is not particularly limited, but examples of photopolymerization initiators include alkylphenones, acetophenones, benzoin ethers, benzophenones, thioxanthones, anthraquinones, benzyls, and biacetyls. More specifically, examples include benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, methyl-o-benzoylbenzoate, and 1-hydroxycyclohexylphenyl ketone.

[0043] From the viewpoint of sensitivity and other factors, the content of the photopolymerization initiator is preferably 0.3 to 15% by mass, and more preferably 0.5 to 10% by mass, relative to the total mass of the solids in the photosensitive resin layer.

[0044] <Polymerization inhibitor> The photosensitive resin layer preferably contains a polymerization inhibitor (stabilizer) for reasons that the effects of the present invention are superior. Examples of polymerization inhibitors include phenols, hydroquinones, and catechols.

[0045] The polymerization inhibitor content is preferably 0.01 to 5% by mass, and more preferably 0.01 to 0.5% by mass, relative to the total mass of solids in the photosensitive resin layer, because this results in better dispersibility of the developing residue of the flexographic printing plate after storage over time.

[0046] <Telechelic polymer> The photosensitive resin layer preferably contains a telechelic polymer for reasons that the effects of the present invention are superior. In this specification, "telechelic polymer" refers to a polymer having reactive functional groups at both ends.

[0047] (Main chain) The polymers that make up the main chain of the telechelic polymer are not particularly limited, but examples include thermoplastic polymers. The above-mentioned thermoplastic polymer is not particularly limited as long as it is a polymer exhibiting thermoplasticity. Specific examples include polystyrene resin, polyester resin, polyamide resin, polysulfone resin, polyethersulfone resin, polyimide resin, acrylic resin, acetal resin, epoxy resin, polycarbonate resin, rubber, and thermoplastic elastomers. Of these, rubber and thermoplastic elastomers are preferred, rubber is more preferred, and diene rubber is even more preferred, because they facilitate the formation of more flexible and pliable films.

[0048] Specifically, examples of the above-mentioned rubbers include butadiene rubber (BR), nitrile rubber (NBR), acrylic rubber, epichlorohydrin rubber, urethane rubber, isoprene rubber, styrene-isoprene rubber, styrene-butadiene rubber (SBR), ethylene-propylene copolymer, and chlorinated polyethylene. These may be used individually or in combination of two or more. Of these, at least one rubber selected from the group consisting of butadiene rubber (BR), styrene-butadiene rubber (SBR), and nitrile rubber (NBR) is preferred, with butadiene rubber and styrene-butadiene rubber being more preferred, due to their superior water-developability, drying properties, and image reproducibility.

[0049] Examples of the above-mentioned thermoplastic elastomers include PB (polybutadiene-based thermoplastic elastomer), polyisoprene-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, and acrylic-based thermoplastic elastomer. Specifically, examples include SB (polystyrene-polybutadiene), SBS (polystyrene-polybutadiene-polystyrene), SIS (polystyrene-polyisoprene-polystyrene), SEBS (polystyrene-polyethylene / polybutylene-polystyrene), ABS (acrylonitrile butadiene styrene copolymer), ACM (acrylic acid ester rubber), ACS (acrylonitrile chlorinated polyethylene styrene copolymer), acrylonitrile styrene copolymer, syndiotactic 1,2-polybutadiene, and polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate. Of these, PB, SBS, and SIS are particularly preferred from the viewpoint of better water developability, as well as drying properties and image reproducibility.

[0050] (end) Telechelic polymers have reactive functional groups at both ends. The above-mentioned reactive functional group is not particularly limited, but it is preferably an ethylenically unsaturated group because it provides superior effects of the present invention. The above ethylenically unsaturated group is preferably a vinyl group (CH2=CH-), an allyl group (CH2=CH-CH2-), a (meth)acryloyl group, or a (meth)acryloyl group, and more preferably a (meth)acryloyloxy group, for reasons that the effects of the present invention are superior.

[0051] Telechelic polymers may have reactive functional groups at both ends of the polymer constituting the main chain via divalent linking groups. The above-mentioned divalent linking groups are not particularly limited, but examples include linear, branched, or cyclic divalent aliphatic hydrocarbon groups (e.g., alkylene groups such as methylene, ethylene, and propylene groups), divalent aromatic hydrocarbon groups (e.g., phenylene group), -O-, -S-, -SO2-, -NRL-, -CO-, -NH-, -COO-, -CONRL-, -O-CO-O-, -SO3-, -NHCOO-, -SO2NRL-, -NH-CO-NH-, or groups formed by combining two or more of these (e.g., alkylene oxy groups, alkylene oxycarbonyl groups, alkylene carbonyl oxy groups, etc.). Here, RL represents a hydrogen atom or an alkyl group (preferably having 1 to 10 carbon atoms).

[0052] (molecular weight) The weight-average molecular weight (Mw) of the telechelic polymer is preferably 6,000 or more, more preferably 7,000 or more, even more preferably 8,000 or more, and particularly preferably 9,000 or more, for reasons that the effects of the present invention are superior. There is no particular upper limit to the Mw of the telechelic polymer, but it is preferably 500,000 or less, and more preferably 100,000 or less, for reasons that the effects of the present invention are superior. Here, the weight-average molecular weight is measured by gel permeation chromatography (GPC) and converted to standard polystyrene. Specifically, for example, the GPC uses HLC-8220GPC (manufactured by Tosoh Corporation), with three columns (TSKgeL Super HZM-H, TSKgeL SuperHZ4000, TSKgeL SuperHZ2000, manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) and THF (tetrahydrofuran) as the eluent. The conditions are a sample concentration of 0.35 mass%, a flow rate of 0.35 mL / min, a sample injection volume of 10 μL, and a measurement temperature of 40°C, and the measurement is performed using an IR detector. Furthermore, the calibration curve will be prepared using eight samples from Tosoh Corporation's "Standard Samples TSK standard, polystyrene": "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0053] (HSP value) The HSP (Hansen solubility parameter) value of the telechelic polymer is not particularly limited, but it is preferably 8 to 12, more preferably 8.5 to 11, and even more preferably 8.5 to 10.5, for reasons that the effects of the present invention are superior.

[0054] (Content) The telechelic polymer content is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, even more preferably 7 to 30% by mass, and particularly preferably 10 to 20% by mass, based on the total mass of the solid content of the photosensitive resin layer, for reasons that the effects of the present invention are superior.

[0055] <Plasticizer> The photosensitive resin layer preferably contains a plasticizer because it improves flexibility.

[0056] Examples of plasticizers include liquid rubber, oil, polyester, and phosphate compounds. Examples of liquid rubber include, for instance, liquid polybutadiene, liquid polyisoprene, or modified versions thereof with maleic acid or epoxy groups. Examples of oils include paraffin, naphthenes, and aromatic oils. Examples of polyesters include, for instance, adipic acid-based polyesters. Examples of phosphate compounds include, for instance, phosphate esters.

[0057] The plasticizer content is preferably 0.1 to 40% by mass, and more preferably 5 to 30% by mass, relative to the total mass of solids in the photosensitive resin layer, in order to further improve flexibility.

[0058] <Surfactants> From the viewpoint of further improving water-developability, the photosensitive resin layer preferably contains a surfactant. Examples of surfactants include cationic surfactants, anionic surfactants, and nonionic surfactants. Among these, anionic surfactants are preferred because they offer superior effects compared to those of the present invention.

[0059] Examples of anionic surfactants include, for instance, Aliphatic carboxylates such as sodium laurate and sodium oleate; Higher alcohol sulfates such as sodium lauryl sulfate, sodium cetyl sulfate, and sodium oleyl sulfate; Polyoxyethylene alkyl ether sulfate salts such as sodium polyoxyethylene lauryl ether sulfate; Polyoxyethylene alkyl allyl ether sulfate salts such as sodium polyoxyethylene octylphenyl ether sulfate and sodium polyoxyethylene nonylphenyl ether sulfate; Alkyl sulfonates such as alkyldiphenyl ether disulfonates, sodium dodecyl sulfonate, and sodium dialkyl sulfosuccinate; Alkylallyl sulfonates such as alkyl disulfonates, sodium dodecylbenzenesulfonate, sodium dibutylnaphthalenesulfonate, and sodium triisopropylnaphthalenesulfonate; Higher alcohol phosphate salts such as sodium lauryl phosphate monoester disodium and sodium lauryl phosphate diester sodium; Polyoxyethylene alkyl ether phosphate salts such as polyoxyethylene lauryl ether phosphate monoester disodium and polyoxyethylene lauryl ether phosphate diester sodium; These are some examples. These may be used individually or in combination of two or more.

[0060] Of these, sulfonic acid-based surfactants such as alkyl sulfonates and alkyl allyl sulfonates are preferred because they offer even better water-developability.

[0061] From the viewpoint of developability and drying properties after development, the surfactant content is preferably 0.1 to 20% by mass, and more preferably 1 to 10% by mass, relative to the total mass of solids in the photosensitive resin layer.

[0062] <Other additives> The photosensitive resin layer may be further enriched with additives such as ultraviolet absorbers, dyes, pigments, defoamers, and fragrances, to the extent that they do not impede the effects of the present invention, for the purpose of improving various properties.

[0063] <Method for fabricating a photosensitive resin layer> The method for producing the photosensitive resin layer is not particularly limited, but examples include preparing a resin composition containing the above-mentioned components and applying it to a support as described later. In the present invention, it is preferable that the photosensitive resin layer is composed of multiple layers, from the viewpoint of making it easy to adjust the content of the photopolymerization initiator in the surface region of the photosensitive resin layer to be greater than the content of the photopolymerization initiator in the remaining region. Examples include a method of forming a photosensitive resin layer (a second photosensitive resin layer with a small amount of photopolymerization initiator) by coating a resin composition onto a support, and then forming a photosensitive resin layer (a first photosensitive resin layer with a large amount of photopolymerization initiator) by coating another resin composition onto the second photosensitive resin layer; a method of forming the first photosensitive resin layer and the second photosensitive resin layer using a calender roll or the like, and then bonding them together with a press or the like.

[0064] The thickness of the photosensitive resin layer is preferably 0.01 to 10 mm, and more preferably 0.2 to 6 mm. Furthermore, if the photosensitive resin layer is composed of multiple layers, the film thickness of the photosensitive resin layer including the surface region (first photosensitive resin layer) is preferably 0.1 to 0.4 mm, and the film thickness of the photosensitive resin layer including the surface region (second photosensitive resin layer) is preferably 0.5 to 5 mm.

[0065] [Support] The material used for the support of the flexographic printing plate master of the present invention is not particularly limited, but materials with high dimensional stability are preferably used. Examples include metals such as steel, stainless steel, and aluminum; polyester (e.g., PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEN (polyethylene naphthalate)), PI (polyimide), polyamide, LCP (liquid crystal polymer), and PAN (polyacrylonitrile); plastic resins such as polyvinyl chloride; synthetic rubbers such as styrene-butadiene rubber; glass fiber-reinforced plastic resins (such as epoxy resins and phenolic resins); cloth, paper, and the like. The support material is preferably a polymer film or cloth, and more preferably a polymer film, from the viewpoint of dimensional stability and availability. The form of the support material is determined by whether the polymer layer is in the form of a sheet or a sleeve.

[0066] As for the fabric, natural fibers such as cotton, linen, silk, and wool, and synthetic fibers such as acetate, vinylon, vinylidene, polyvinyl chloride, acrylic, polypropylene, polyethylene, polyurethane, fluorine-based filaments, polyclar, rayon, nylon, polyamide, and polyester can be used to create woven fabrics, knitted fabrics, and nonwoven fabrics, as well as plain weaves and twill weaves. Examples of polymer films include films made from various polymers such as polyester (e.g., PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEN (polyethylene naphthalate)), PI (polyimide), polyamide, LCP (liquid crystal polymer), PAN (polyacrylonitrile); plastic resins such as polyvinyl chloride; synthetic rubbers such as styrene-butadiene rubber; and glass fiber-reinforced plastic resins (such as epoxy resins and phenolic resins). Among these, polyester films are preferred from the viewpoint of dimensional stability and other factors. Examples of the above-mentioned polyester films include PET film, PBT film, and PEN film, but from the viewpoint of dimensional stability and other factors, PET (polyethylene terephthalate) film is preferred.

[0067] The thickness of the support film is not particularly limited, but from the viewpoint of dimensional stability and handling, it is preferably 5 to 3000 μm, more preferably 50 to 2000 μm, and even more preferably 100 to 1000 μm.

[0068] [Cover sheet] The flexographic printing plate of the present invention may have a cover sheet, as shown in Figure 1. Such cover sheets are not particularly limited, but are preferably transparent polymer films, and may be single layers or laminated with two or more layers. Here, "transparent" as used in this invention means that the transmittance of visible light is 60% or more, preferably 80% or more, and particularly preferably 90% or more. Examples of polymer film materials include cellulose polymers; acrylic polymers having acrylic acid ester polymers such as polymethyl methacrylate and lactone ring-containing polymers; thermoplastic norbornene polymers; polycarbonate polymers; polyester polymers such as polyethylene terephthalate, polyethylene naphthalate, and fluoropolyester polymers; styrene polymers such as polystyrene and acrylonitrile-styrene copolymer (AS resin); polyolefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, and polybutadiene; vinyl chloride polymers; amide polymers such as nylon and aromatic polyamides; imide polymers; sulfone polymers; polyethersulfone polymers; polyetheretherketone polymers; polyphenylene sulfide polymers; vinylidene chloride polymers; vinyl alcohol polymers; vinyl butyral polymers; arylate polymers; polyoxymethylene polymers; epoxy polymers; or polymers which are mixtures of these polymers.

[0069] Furthermore, the surface of the cover sheet (the surface on which the infrared ablation layer is formed) may be treated with a release agent to suppress adhesion of the infrared ablation layer and improve the peelability of the cover sheet. Such release agents include methods such as applying a release agent to the surface of the cover sheet to form a release layer. Examples of release agents include silicone-based release agents and alkyl-based release agents.

[0070] The film thickness of the cover sheet is preferably 25 to 250 μm.

[0071] [Method for manufacturing flexographic printing plates] The present invention relates to a method for manufacturing a flexographic printing plate, which has a non-image portion and an image portion. A mask formation step is to form an image on the infrared ablation layer of the flexographic printing plate master of the present invention described above, and to form a mask, Following the mask formation step described above, an exposure step is performed in which the photosensitive resin layer of the flexographic printing plate master of the present invention described above is exposed in an image-like manner through the mask described above. The process includes a developing step, which follows the exposure step, in which the image is developed using a developing solution to form non-image areas and image areas.

[0072] [Mask Forming Process] The mask formation process described above is a process of forming an image on an infrared ablation layer to form a mask to be used in the exposure process described later. In this process, when an infrared laser is irradiated onto the infrared ablation layer, heat is generated due to the action of the infrared-absorbing material, and this heat causes the infrared ablation layer to be removed, or laser-melted. Therefore, by selectively laser-melting the infrared ablation layer based on image data, an image mask capable of forming a latent image in the photosensitive resin layer can be obtained.

[0073] Infrared laser irradiation uses lasers with an oscillation wavelength in the range of 750 nm to 3000 nm. Examples of such lasers include solid-state lasers such as ruby ​​lasers, alexandrite lasers, perovskite lasers, Nd-YAG lasers, and emerald glass lasers; semiconductor lasers such as InGaAsP, InGaAs, and GaAsAl; and dye lasers such as rhodamine dyes. Furthermore, fiber lasers, which amplify these light sources using fibers, can also be used. Of these, it is preferable to use an exposure light source with an oscillation wavelength of 900 to 1200 nm, and more preferably a fiber laser, because this results in higher sensitivity of the infrared ablation layer.

[0074] [Exposure process] The above exposure step is a step of exposing the photosensitive resin layer in the shape of an image through the mask obtained in the above mask formation step, and by irradiating the photosensitive resin layer with ultraviolet light in the shape of an image, crosslinking and / or polymerization can be induced in the areas irradiated with ultraviolet light, thereby curing the layer.

[0075] [Development process] The above development process involves developing the image using a developing solution to form non-image areas and image areas.

[0076] The developer used in the above development process is not particularly limited, and conventionally known developers can be used. However, from the viewpoint of reducing environmental impact, it is preferable to use a developer containing 50% by mass or more of water (hereinafter also referred to as "aqueous developer"). The developer may be an aqueous solution or a suspension (for example, an aqueous dispersion). Furthermore, the water content in the aqueous developer is preferably 80 to 99.99% by mass, and more preferably 90 to 99.9% by mass, relative to the total mass of the aqueous developer.

[0077] [Rinsing process] The present invention preferably includes a rinsing step after the development step, in which the surfaces of the non-image area and the image area formed in the development step are rinsed with water.

[0078] Rinsing methods in the above rinsing process include washing with tap water, spraying with high-pressure water, and using a batch-type or transport-type brush-type washing machine known as a flexographic printing plate developing machine to mainly brush the non-image and image areas in the presence of water. [Examples]

[0079] The present invention will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below.

[0080] [Example 1] [Preparation of the first photosensitive resin layer] 63.6 parts by mass of water-dispersible latex (Nipol LX111NF, manufactured by Nippon Zeon Co., Ltd., water-dispersible latex of polybutadiene, solids content 55%), 11 parts by mass of telechelic polymer (BAC-45, manufactured by Osaka Organic Chemical Industry Co., Ltd.) (polybutadiene with acryloyloxy groups at both ends, Mw=10,000), and 9 parts by mass of 1,9-nonanediol dimethacrylate (NK ester NOD-N, manufactured by Shin Nakamura Chemical Industry Co., Ltd.) were mixed, and the water was evaporated in a dryer heated to 60°C for 3 hours to obtain a mixture containing water-dispersible particles. This mixture, along with 23 parts by mass of butadiene rubber (Asahi Kasei Corporation, NF35R), 15 parts by mass of plasticizer (Idemitsu Kosan Co., Ltd., Diana Process Oil PW-32), and 4 parts by mass of surfactant (NOF Co., Ltd., Rapisol A-90, 90% effective content), were kneaded for 45 minutes in a kneader set to 110°C. Then, 0.2 parts by mass of a thermal polymerization inhibitor and 8.1 parts by mass of a photopolymerization initiator (Tokyo Chemical Industry Co., Ltd., benzyldimethylketal) were added to the kneader and kneaded for 5 minutes to obtain the first photosensitive resin composition. Next, the first photosensitive resin composition obtained above was formed into a sheet using a calender roll. The first photosensitive resin composition was pre-kneaded for 10 minutes with the warm-up roll set to 50°C. The material wound around the roll was cut midway, pulled out in sheet form, and then wound into a roll. After that, the kneaded material was set between the first and second rolls of the calender roll and rolled. The temperatures of each roll of the calender roll were set as follows: first roll temperature 30°C, second roll temperature 40°C, third roll temperature 50°C, and fourth roll temperature 60°C. The spacing between the rolls was 1.0 mm between the first and second rolls, 0.4 mm between the second and third rolls, and 0.2 mm between the third and fourth rolls. The conveying speed was 1 m / min. After passing through the fourth roll, the first photosensitive resin layer was obtained.

[0081] [Preparation of the second photosensitive resin layer] 63.6 parts by mass of water-dispersible latex (Nipol LX111NF, manufactured by Nippon Zeon Co., Ltd., water-dispersible latex of polybutadiene, solids content 55%), 11 parts by mass of telechelic polymer (BAC-45, manufactured by Osaka Organic Chemical Industry Co., Ltd.) (polybutadiene with acryloyloxy groups at both ends, Mw=10,000), and 9 parts by mass of 1,9-nonanediol dimethacrylate (NK ester NOD-N, manufactured by Shin Nakamura Chemical Industry Co., Ltd.) were mixed, and the water was evaporated in a dryer heated to 60°C for 3 hours to obtain a mixture containing water-dispersible particles. This mixture, along with 23 parts by mass of butadiene rubber (Asahi Kasei Corporation, NF35R), 15 parts by mass of plasticizer (Idemitsu Kosan Co., Ltd., Diana Process Oil PW-32), and 4 parts by mass of surfactant (NOF Co., Ltd., Rapisol A-90, 90% effective content) were kneaded for 45 minutes in a kneader set to 110°C. Then, 0.2 parts by mass of a thermal polymerization inhibitor and 4.5 parts by mass of a photopolymerization initiator (Tokyo Chemical Industry Co., Ltd., benzyldimethyl ketal) were added to the kneader and kneaded for 5 minutes to obtain a second photosensitive resin composition. Next, the second photosensitive resin composition obtained above was formed into a sheet using a calender roll. The second photosensitive resin composition was pre-kneaded for 10 minutes with the warm-up roll set to 50°C. The material wound around the roll was cut midway, pulled out in sheet form, and then wound into a roll. After that, the kneaded material was set between the first and second rolls of the calender roll and rolled. The temperatures of each roll of the calender roll were set as follows: first roll temperature 30°C, second roll temperature 40°C, third roll temperature 50°C, and fourth roll temperature 60°C. The spacing between the rolls was 2.0 mm between the first and second rolls, 1.5 mm between the second and third rolls, and 1.1 mm between the third and fourth rolls. The conveying speed was 1 m / min. After passing through the fourth roll, the second photosensitive resin layer was obtained.

[0082] [Fabrication of laminates for infrared ablation layers] 50 parts by mass of acrylic resin (Hyperl M5000, manufactured by Negami Kogyo Co., Ltd.), 50 parts by mass of elastomer (NBR, Nipol DN101, manufactured by Nippon Zeon Co., Ltd.), and 100 parts by mass of carbon black (MA8, manufactured by Mitsubishi Chemical Corporation) as an IR absorber were mixed with 600 parts by mass of methyl isobutyl ketone. The mixture was mixed by stirring with a feather, and the resulting mixture was dispersed in a paint shaker. Further methyl isobutyl ketone was added until the solid content reached 15% by mass, thereby obtaining a polymer / carbon black dispersion (coating liquid for infrared ablation layer). Next, a coating solution for the infrared ablation layer was applied to one side of a 75 μm thick silica-containing PET film (Toyobo Ester Film U4, manufactured by Toyobo Co., Ltd.), which served as the cover sheet, using a bar coater to achieve a dry thickness of 1.0 μm. This was then dried in an oven set to 140°C for 1 minute to produce a laminate for the infrared ablation layer, consisting of the cover sheet and the infrared ablation layer.

[0083] [Preparation of flexographic printing plates] An adhesive layer was formed on the substrate by applying adhesive to one side of a 125 μm thick PET film (support). Next, a first photosensitive resin layer and a second photosensitive resin layer were laminated between the adhesive layer and the infrared ablation layer of the infrared ablation layer laminate prepared as described above, with the first photosensitive resin layer positioned on the infrared ablation layer side. The plates were then pressed in a press heated to 80°C so that the total thickness of the photosensitive resin layers was 1.14 mm, thereby producing a flexographic printing plate master having the support, adhesive layer, photosensitive resin layer, infrared ablation layer, and cover sheet in this order. Note that the thicknesses of the first and second photosensitive resin layers shown in Table 1 below are the thicknesses before the above pressing. The photopolymerization initiator content in the surface and residual regions of the photosensitive resin layer was measured for the obtained flexographic printing plates using the method described above. The results are shown in Table 1 below.

[0084] [Preparation of flexographic printing plates] The resulting flexographic printing plates were used to produce printing plates using the following equipment. Specifically, the obtained flexographic printing plates were subjected to back exposure by exposing them to the back surface with 80W of energy for 18 seconds using the following ultraviolet exposure machine. Next, imaging was performed by ablating the infrared ablation layer using the following imaging machine, and the main exposure was performed by exposing the surface (the back side of the back surface) with 80W for 180 seconds. Next, the film was developed for 12 minutes using the following wash machine and wash solution. Next, the material was dried using 60°C hot air until all moisture was removed. Next, a flexographic printing plate was prepared by exposing the photosensitive resin layer to light for 720 seconds (post-exposure) using the following ultraviolet exposure apparatus. <Imaging device> ·CDI Spark 4835 Inline (manufactured by ESKO) <Explorer> • UV exposure machine Concept 302 ECDLF (product name) (manufactured by Glunz & Jensen) <Washing machine> • C-Touch2530 Water Wash Plate Processor (manufactured by GS Trading) <Wash-off solution> • Aqueous solution of Finish Power & Pure Powder SP (manufactured by Reckitt Benckiser Japan) (concentration: 0.5% by mass)

[0085] [Examples 2-3 and Comparative Examples 1-3] A flexographic printing plate was prepared in the same procedure as in Example 1, except that the content of the photopolymerization initiator and the thickness of the photosensitive resin layer were changed to the values ​​shown in Table 1 below. Comparative Examples 1 and 2 are examples in which only the second photosensitive resin layer is provided, without the first photosensitive resin layer. Next, using the prepared flexographic printing plate, a flexographic printing plate was prepared following the same procedure as in Example 1, except that the exposure time was changed to the time shown in Table 1 below.

[0086] [evaluation] [Microcell reproducibility] The microcell (MC) reproducibility of the obtained flexographic printing plates was evaluated using the following method. First, the surface of the solid image area of ​​the flexographic printing plate was confocally measured at 0.1 μm height intervals using a hybrid laser microscope OPTELICS® HYBRID (manufactured by Lasertec Corporation) with a 50x Apo objective lens (high numerical aperture (high NA)) to obtain 3D data. The evaluation range was defined as a region of 300 μm vertically and 300 μm horizontally. From the 3D data observed above, we observed more than 100 convex parts and determined how many were reproduced without any defects. Next, the image reproduction percentage was calculated using the following formula. Image reproduction percentage = (Number of convex parts reproduced without defects) / (Number of evaluated parts) × 100 The evaluation was conducted according to the following criteria. The results are shown in Table 1 below. To obtain printed materials with higher solid color density, the image reproduction of microcells is preferably C to A, more preferably B to A, and even more preferably A. If the image reproduction is less than 80%, the ink transfer to the printed material will be uneven, resulting in poor solid color density. <Evaluation Criteria> A: Image reproduction accuracy of 98% or higher B: Image reproduction accuracy is between 90% and 98%. C: Image reproduction is between 80% and 90%. D: Image reproduction is less than 80%

[0087] [Durability of independent points] The obtained flexographic printing plates were tested using a continuous load scratch strength tester (HEIDON TYPE:18) under conditions of a 500g load and a reciprocating speed of 100mm / min. A cotton cloth was used as the abrasive material, and the image area was rubbed four times. Ten independent dots with a diameter of 500μm, which were identified before the abrasion test, were evaluated after the abrasion test to see if any chipping or breakage had occurred in the independent dots according to the following criteria. From the standpoint of handling, practically speaking, C to A is preferable, B to A is more preferable, and A is even more preferable. <Evaluation Criteria> A: None of the 10 independent dots are missing or broken. B: One of the 10 independent dots is missing or broken. C: Two of the ten independent dots are missing or broken. D: Three or more of the ten independent dots are missing or broken.

[0088] [Table 1]

[0089] From the results shown in Table 1 above, it was found that when the amount of photopolymerization initiator in the surface region of the photosensitive resin layer and the amount of photopolymerization initiator in the remaining region are the same, a high content results in poor durability of independent dots (Comparative Example 1), and a low content results in poor reproducibility of microcells when made into a flexographic printing plate (Comparative Example 2). Furthermore, it was found that when the amount of photopolymerization initiator in the surface region of the photosensitive resin layer is less than the amount of photopolymerization initiator in the remaining region, both the reproducibility of microcells and the durability of independent dots are inferior when made into a flexographic printing plate (Comparative Example 3).

[0090] In contrast, it was found that when the amount of photopolymerization initiator contained in the photosensitive resin layer is greater than the amount of photopolymerization initiator contained in the remaining region, the reproducibility of microcells is good when made into a flexographic printing plate, and the durability of independent dots is also good (Examples 1-3). Furthermore, a comparison of Examples 1 to 3 revealed that when the photopolymerization initiator content in the surface region is 220 to 400 μmol / g, and the photopolymerization initiator content in the remaining region is 60 to 200 μmol / g, the reproducibility of microcells and the durability of independent dots are improved when the material is made into a flexographic printing plate. [Explanation of Symbols]

[0091] 1. Infrared ablation layer 2 Photosensitive resin layer 2a Surface area 2b remaining area 3 Support 4 Cover Sheets 10 Flexographic printing plates

Claims

1. A flexographic printing plate master having an infrared ablation layer, a photosensitive resin layer, and a support in this order, The amount of photopolymerization initiator contained in the surface region of the photosensitive resin layer from the surface in contact with the infrared ablation layer up to 100 μm in the thickness direction is greater than the amount of photopolymerization initiator contained in the remaining region of the photosensitive resin layer that is located on the support side rather than the surface region. A flexographic printing plate master in which the photopolymerization initiator content in the surface region is 220 to 400 μmol / g, and the photopolymerization initiator content in the remaining region is 60 to 200 μmol / g. Here, the content of the photopolymerization initiator in the surface region and the remaining region refers to the molar amount relative to the total mass of the solids in the photosensitive resin layer in each region.

2. The flexographic printing plate according to Claim 1, wherein the content of the photopolymerization initiator contained in the surface region is 300 to 400 μmol / g.

3. The flexographic printing plate according to claim 1 or 2, wherein the photopolymerization initiator is alkylphenones, acetophenones, benzoin ethers, benzophenones, thioxanthones, anthraquinones, benzyls, or biacetyls.

4. The flexographic printing plate according to claim 3, wherein the photopolymerization initiator is benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, methyl-o-benzoylbenzoate, or 1-hydroxycyclohexylphenyl ketone.

5. A method for manufacturing a flexographic printing plate having a non-image portion and an image portion, A mask forming step in which an image is formed on the infrared ablation layer of the flexographic printing plate according to claim 1 or 2, and a mask is formed, Following the mask formation step, an exposure step is performed in which the photosensitive resin layer of the flexographic printing plate is exposed to the image through the mask. A method for manufacturing a flexographic printing plate, comprising the above exposure step followed by a developing step in which the plate is developed using a developing solution to form a non-image portion and an image portion.

6. The method for manufacturing a flexographic printing plate according to claim 5, wherein the developing solution is an aqueous developing solution.

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