Flexographic printing plate precursor for UV varnish printing and method for producing flexographic printing plate for UV varnish printing using same

Abstract

To provide a flexographic printing original plate for UV varnish printing capable of obtaining a flexographic printing plate for UV varnish printing which suppresses swelling of a relief during UV varnish printing and enables stable thick coating of UV ink.SOLUTION: The flexographic printing plate precursor for UV varnish printing has a photosensitive resin layer containing polyvinyl alcohol and / or its derivative (A), a compound (B) having an ethylenic double bond, and a photopolymerization initiator (C) on a substrate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flexographic printing plate precursor for UV varnish printing, a method for producing a flexographic printing plate for UV varnish printing using the same, and a method for producing a printed matter. [Background technology]

[0002] UV varnishes that photocure by ultraviolet irradiation are commonly applied to the surfaces of various substrates such as film and paper, or to decorations such as pictures, patterns, and letters applied to the surface of such substrates, in order to impart design properties such as high gloss or matte finish, as well as mechanical strength. UV varnish application requires a thick layer of UV varnish, so flexographic printing using an anilox roll with a large cell capacity is preferably used.

[0003] As a flexographic printing plate precursor suitable for UV varnish printing, for example, a photosensitive resin precursor for flexographic printing has been disclosed (see, for example, Patent Document 1), which comprises a photosensitive resin layer composed of a water-developable photosensitive resin composition for flexographic printing containing at least (a) polyamide and / or polyamide block copolymer, (b) a crosslinking agent having one or more unsaturated groups, (c) a photopolymerization initiator, and a specific amount of (d) a fatty acid ester having two or more hydroxyl groups and 11 to 23 carbon atoms in the molecule, a support, and an adhesive layer for adhering them together. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 159199 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, UV varnish application requires a thick coating of UV varnish, and therefore a large amount of UV varnish is supplied to flexographic printing plates for UV varnish printing. Flexographic printing plates made from the flexographic printing photosensitive resin original plate described in Patent Document 1 have a relief that is prone to swelling due to the monomers in the UV varnish, which tends to make the indentation pressure between the relief and the printing substrate unstable. Furthermore, if the relief on the flexographic printing plate swells and the gap between the relief and the anilox roll that supplies UV varnish to the flexographic printing plate narrows, the amount of UV varnish supplied to the flexographic printing plate decreases. This has led to the problem of difficulty in consistently applying a thick layer of UV varnish. Adjusting the indentation pressure during printing reduces workability, so there is a demand for flexographic printing plates that can more stably apply thick UV ink.

[0006] In view of the above-mentioned problems of the conventional technology, the present invention aims to provide a flexographic printing plate precursor for UV varnish printing that can suppress swelling of the relief during UV varnish printing and can obtain a flexographic printing plate for UV varnish printing that can stably apply a thick layer of UV ink. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention mainly comprises the following components. (1) A flexographic printing plate precursor for UV varnish printing, having a photosensitive resin layer on a substrate, the photosensitive resin layer containing polyvinyl alcohol and / or its derivative (A), a compound having an ethylenic double bond (B), and a photopolymerization initiator (C). (2) The flexographic printing plate precursor for UV varnish printing according to (1), wherein the substrate is a metal substrate. (3) The flexographic printing plate precursor for UV varnish printing according to (2), wherein the metal substrate is a steel plate. (4) The flexographic printing plate precursor for UV varnish printing according to (2) or (3), wherein the metal substrate has a Rockwell hardness HR30TSm of 40 to 80 and a yield point Yp of 200 MPa to 1.0 GPa. (5) The printing plate precursor for UV varnish printing according to any one of (1) to (4), wherein the polyvinyl alcohol and / or its derivative (A) contains a polyvinyl alcohol derivative having an ethylenic double bond in a side chain. (6) The flexographic printing plate precursor for UV varnish printing according to any one of (1) to (5), wherein the compound (B) having an ethylenic double bond is a compound (b) having a polyethylene glycol skeleton, only one ethylenically unsaturated bond in the molecule, and a weight-average molecular weight of 400 to 800, in an amount of 20 to 70 mass % relative to 100 mass % of the component (B). (7) A method for producing a flexographic printing plate for UV varnish printing, comprising an exposure step of irradiating the photosensitive resin layer of the flexographic printing plate precursor for UV varnish printing described in any one of (1) to (6) with ultraviolet light to photocure the exposed portions of the photosensitive resin layer, and a development step of removing the uncured portions of the photosensitive resin layer with a developer containing water as the main component. (8) A method for producing a printed matter, comprising the steps of transferring UV varnish to a substrate using a flexographic printing plate for UV varnish printing obtained by the method described in (7), and irradiating the transferred UV varnish with ultraviolet light. [Effects of the Invention]

[0008] The UV varnish flexographic printing plate precursor of the present invention can provide a flexographic printing plate for UV printing that can suppress swelling of the relief during UV varnish printing and allows stable thick application of UV varnish. DETAILED DESCRIPTION OF THE INVENTION

[0009] The flexographic printing plate precursor for UV varnish printing of the present invention (hereinafter sometimes abbreviated as "printing plate precursor") has a photosensitive resin layer on a substrate, the photosensitive resin layer containing polyvinyl alcohol and / or its derivative (A), a compound having an ethylenic double bond (B), and a photopolymerization initiator (C). The presence of the photosensitive resin layer makes it possible to form a desired relief on the substrate, for example, by imagewise irradiation with ultraviolet light. The substrate may have two or more photosensitive resin layers. The substrate functions to support the photosensitive resin layer and the relief. Furthermore, if necessary, a cover film or a heat-sensitive mask layer may be provided on the photosensitive resin layer. Having a cover film on the photosensitive resin layer protects the surface of the photosensitive resin layer and prevents adhesion of foreign matter, etc. The photosensitive resin layer and the cover film may be in direct contact with each other, or one or more anti-adhesion layers may be provided between the photosensitive resin layer and the cover film.

[0010] The printing plate precursor of the present invention is used for UV varnish printing. UV varnish refers to a varnish that hardens under ultraviolet light. By printing on the surface of various substrates such as film and paper, or on decorations such as pictures, patterns, and letters applied to the surface of such substrates, the UV varnish imparts abrasion resistance, scratch resistance, solvent resistance, and chemical resistance to the surface, protecting the underlying substrate and decoration, and imparting design features such as high gloss or matte finish. It also imparts blocking resistance (non-adhesion) and slip properties, improving the workability of subsequent processes. Furthermore, because UV varnishes are hardened by ultraviolet light, they can be printed at high speeds. UV varnishes typically contain, for example, a photopolymerization initiator and a compound having an ethylenic double bond, and further contain additives to impart desired functions.

[0011] Examples of substrates for the printing plate precursor of the present invention include plastic sheets made of polyester or the like, synthetic rubber sheets made of styrene-butadiene rubber or the like, and metal plates made of steel, stainless steel, aluminum, or the like. As described above, an anilox roll with a large cell capacity is preferably used for UV varnish application in flexographic printing. In order to evenly supply UV varnish from an anilox roll with a large cell capacity to the flexographic printing plate, the flexographic printing plate must be attached to the flexographic printing unit without distortion. For this reason, it is preferable to use a plate cylinder that is fixed by the action of a magnet, i.e., a magnetic plate cylinder, in the flexographic printing unit. Therefore, a metal substrate is preferred as the substrate for the printing plate precursor of the present invention because of its excellent dimensional stability, and a steel plate is even more preferred from the viewpoint of attachment to a magnetic plate cylinder.

[0012] The metal substrate is preferably made of a material with a saturation magnetization of 0.3 tesla or more, so that it can be firmly fixed to the magnetic printing drum. The saturation magnetization is determined from a magnetization curve measured using the method described in JIS C 2501:2019. From the perspective of commercial use, the saturation magnetization is preferably 10 tesla or less. Preferred materials with a saturation magnetization of 0.3 tesla or more include iron (2.2 tesla), cobalt (1.8 tesla), nickel (0.6 tesla), and alloys and oxides thereof. Among these, iron, iron oxide, and iron alloys are more preferred due to their toughness.

[0013] The Rockwell hardness HR30TSm of the metal substrate is preferably 40 or more, more preferably 45 or more, and even more preferably 60 or more, from the viewpoint of preventing the metal substrate from breaking or being dented when removed from a paramagnetic magnetic plate cylinder. On the other hand, from the viewpoint of commercial use, the Rockwell hardness HR30TSm of the metal substrate is preferably 80 or less, more preferably 75 or less. The Rockwell hardness HR30TSm can be measured by the method described in JIS Z 2245:2016. The Rockwell hardness HR30TSm can generally be increased by increasing the temperature and number of hot rolling steps, the number of cold rolling steps, or the amount of carbon added during the production of the metal substrate.

[0014] The yield point Yp of the metal substrate is preferably 200 MPa or more, more preferably 220 MPa or more, from the viewpoint of preventing pin holes in the flexographic printing plate, which correspond to the positions of the pins on the magnetic plate cylinder, from widening due to the rotational force of the plate cylinder during printing, causing the printing plate to shift position. On the other hand, from the viewpoint of commercial use, the yield point Yp of the metal substrate is preferably 1.0 GPa or less, more preferably 700 MPa or less. The yield point Yp can be measured by the method described in JIS Z 2241:2011. The yield point Yp can generally be increased by increasing the number of hot rolling or cold rolling steps during the production of the metal substrate or by aging at high temperatures.

[0015] The thickness of the substrate is preferably 0.1 to 0.5 mm, more preferably 0.15 to 0.3 mm, from the viewpoints of ease of attachment to the plate cylinder, strength, weight, and the like.

[0016] The photosensitive resin layer of the printing plate precursor of the present invention contains at least polyvinyl alcohol and / or a derivative thereof (A) (hereinafter sometimes abbreviated as "component (A)"), a compound having an ethylenic double bond (B) (hereinafter sometimes abbreviated as "component (B)"), and a photopolymerization initiator (C) (hereinafter sometimes abbreviated as "component (C)"). When the photosensitive resin layer is irradiated with light, free radicals are generated from component (C) in the photosensitive resin layer. The generated free radicals undergo radical polymerization with component (B), and a crosslinked structure can form a relief with excellent image reproducibility for obtaining a desired printed image. Furthermore, component (A) acts as a matrix for the photosensitive resin layer and the relief, imparting structural strength to them and improving image reproducibility.

[0017] In the present invention, the term "polyvinyl alcohol" as used in the component (A) refers collectively to (i) polyvinyl alcohol with a saponification degree of 100% and consisting of vinyl alcohol structural units, and partially saponified polyvinyl alcohols containing (i) vinyl alcohol structural units and (ii) vinyl acetate structural units. Polyvinyl alcohol derivatives refer to those in which functional groups have been introduced into the main chain and / or side chain, or those containing additional structural units. The inclusion of such component (A) can suppress swelling of the relief of a flexographic printing plate obtained from the printing plate precursor of the present invention due to UV varnish. This stabilizes the indentation pressure between the relief and the substrate, and also maintains a constant gap between the relief and the anilox roll, allowing for stable thick application of UV varnish. Among these, polyvinyl alcohol derivatives having an ethylenic double bond in the side chain are preferred.

[0018] The polyvinyl alcohol derivative preferably has (i) a vinyl alcohol structural unit, (ii) a vinyl acetate structural unit, and (iii) a structural unit represented by the following general formula (1) and / or a structural unit represented by the following general formula (2). (iii) The structural unit represented by the following general formula (1) and / or the structural unit represented by the following general formula (2) contains an ethylenic double bond, which allows for sufficient curing to the bottom even when the photosensitive resin layer is thick, thereby further improving image reproducibility. When a flexographic printing plate is obtained from a flexographic printing plate precursor having a thick photosensitive resin layer, a micro-relief is typically formed by performing overall exposure (back exposure) from the substrate side to form a floor layer below the relief, and then performing imagewise exposure from the photosensitive resin layer side to form an imagewise relief on the floor layer. In the present invention, when a metal substrate is used as the substrate, it is difficult to form a floor layer by back exposure. Therefore, by selecting a polyvinyl alcohol derivative having (iii) a structural unit represented by the following general formula (1) and / or a structural unit represented by the following general formula (2), the effect of improving image reproducibility is more pronounced.

[0019] [ka]

[0020] In general formulas (1) to (2), R 1 represents a divalent organic group having an alkylene group and / or a cyclic structure, and R 2 represents a hydrogen atom or a methyl group. 1 The bulky cyclic structure of the side chain of component (A) ensures spaces between the highly crystalline components (A), further reducing crystallinity, thereby imparting appropriate flexibility and elasticity to the relief of the flexographic printing plate.

[0021] Examples of the divalent organic group having an alkylene group include -C p H 2p COO-C q H 2q -OCO-, -COO-C p H 2p -OCO-, -C p H 2p -OCO-, etc. Here, p and q each independently represent a natural number.

[0022] Examples of cyclic structures include residues derived from alicyclic hydrocarbons, heterocyclic compounds, aromatic hydrocarbons, and heteroaromatic compounds. Examples of alicyclic hydrocarbons include cyclohexane, cyclopentane, cyclobutane, cyclopropane, cyclopentadiene, decalin, adamantane, and camphor. Examples of heterocyclic compounds include 2-pyrrolidine, tetrahydrofuran, tetrahydrothiophene, pyran, thiopyran, pyrazole, imidazole, piperidine, and morpholine. Examples of aromatic hydrocarbons or heteroaromatic compounds include phenyl, benzyl, pyridine, naphthylene, pyrrole, furan, thiophene, pyrazole, benzimidazole, indole, isoquinoline, purine derivatives, pyrimidine, oxazole, and thiazole. Two or more of these may be present. These may also have a substituent, and examples of the substituent include a halogen group, a hydroxy group, a mercapto group, an ether group, an amino group, a carboxylic acid group, an ester group, a urethane group, an aldehyde group, a nitro group, a CF3 group, and a cyano group. These residues may be monovalent or divalent or higher depending on the bonding position. Examples of cyclohexane residues include a cyclohexyl group and a cyclohexylene group. Among these, residues of alicyclic hydrocarbons are preferred, as they can reduce the SP value of component (A) to improve compatibility within the photosensitive resin layer and suppress bleed-out. Among alicyclic hydrocarbons, cyclohexane is more preferred.

[0023] Examples of the divalent organic group having a cyclic structure include -C p H 2p COO-XC q H 2q -OOC-, -X-COO-C p H 2p -OOC-, -XC p H 2p -OOC-, etc. Here, X represents the above-mentioned divalent group having a cyclic structure, and p and q each independently represent a natural number.

[0024] R in general formulas (1) and (2) 2 represents a hydrogen atom or a methyl group. 2 When a hydrogen atom is selected as the group, the photocrosslinking reaction rate is faster than when a methyl group is selected, and therefore the sensitivity of the photosensitive resin layer can be improved. A hydrogen atom or a methyl group can be appropriately selected depending on the desired sensitivity.

[0025] In component (A), the content of (i) vinyl alcohol structural units is preferably 55 to 85 mol % relative to the total of (i) to (iii). By ensuring that the content of (i) is 55 mol % or more, the developability in a developer primarily containing water can be further improved. On the other hand, by ensuring that the content of (i) is 85 mol % or less, the compatibility with component (B) can be further improved. Furthermore, the water absorption of component (A) can be suppressed, and changes in relief thickness can be further suppressed even in high-humidity environments. Furthermore, the content of (ii) vinyl acetate units is preferably 10 to 40 mol % relative to the total of (i) to (iii). By keeping the content of (ii) within this range, the water absorption of component (A) can be suppressed, and changes in relief thickness can be further suppressed even in high-humidity environments. Furthermore, the total content of (iii) structural units represented by general formula (1) and structural units represented by general formula (2) is preferably 0.1 to 10 mol % relative to the total of (i) to (iii). By setting the content of (iii) to 0.1% or more, image reproducibility can be further improved. The content of (iii) is preferably 0.5% or more. On the other hand, by setting the content of (iii) to 10 mol % or less, developability in a developer containing water as the main component can be improved.

[0026] The weight-average molecular weight of component (A) is preferably 10,000 or more from the viewpoint of improving the printing durability of the printing plate. On the other hand, the weight-average molecular weight of component (A) is preferably 200,000 or less, more preferably 100,000 or less, from the viewpoint of processability of the photosensitive resin layer and suppressing an increase in the viscosity of the developer during development. The weight-average molecular weight of component (A) can be determined by GPC measurement. In the present invention, the weight-average molecular weight is measured using a gel permeation chromatograph-multiangle light scattering photometer manufactured by Wyatt Technology under conditions of a column temperature of 40°C and a flow rate of 0.7 mL / min.

[0027] Examples of methods for producing the polyvinyl alcohol derivative of component (A), in the case of a polyvinyl alcohol derivative having the structural units (i) to (iii) described above, include: (1) a method in which a partially saponified polyvinyl alcohol is reacted with an acid anhydride, and a reactive group such as a carboxyl group is introduced into the polymer side chain starting from the hydroxyl group of the partially saponified polyvinyl alcohol, and the reactive group is then reacted with an unsaturated epoxy compound; (2) a method in which a copolymer of vinyl acetate with an unsaturated carboxylic acid, an unsaturated carboxylate salt, and / or an unsaturated carboxylic acid ester is partially saponified, and the carboxyl group of this polymer is reacted with an unsaturated epoxy compound; and (3) a method in which a hydroxyl group of the partially saponified polyvinyl alcohol is reacted with a carboxylic acid compound having an ethylenic double bond starting from the hydroxyl group of the partially saponified polyvinyl alcohol.

[0028] The content of component (A) in the photosensitive resin layer is preferably 25% by mass or more of the solid content, which can improve printing durability. On the other hand, the content of component (A) in the photosensitive resin layer is preferably 70% by mass or less of the solid content, which can improve the flexibility of the photosensitive resin layer. When two or more types of component (A) are contained, the content of component (A) refers to the total content thereof.

[0029] In the present invention, the component (B) refers to a compound having an ethylenic double bond and a molecular weight of less than 10,000. The molecular weight of the component (B) is preferably 2,000 or less.

[0030] Examples of component (B) include (meth)acrylates described in International Publication No. 2017 / 038970, glycerol di(meth)acrylate, (meth)acrylic acid adducts of propylene glycol diglycidyl ether, and tetrahydrofurfuryl (meth)acrylate. Two or more of these may be contained. Here, (meth)acrylate is a general term for acrylate and methacrylate, and (meth)acrylic acid is a general term for acrylic acid and methacrylic acid.

[0031] In the printing plate precursor of the present invention, from the viewpoint of imparting appropriate flexibility and elasticity to the relief while further improving image reproducibility, component (B) preferably contains a compound (b) having a polyethylene glycol skeleton, only one ethylenically unsaturated bond in the molecule, and a weight-average molecular weight of 400 to 800. Here, the polyethylene glycol skeleton refers to a polymer skeleton of ethylene glycol tetramer or higher. When the ethylenically unsaturated compound has a polyethylene glycol skeleton, the elasticity of the relief can be improved. Furthermore, by adjusting the weight-average molecular weight to 400 or more, the flexibility of the relief can be improved, particularly the flexibility during printing. On the other hand, by adjusting the weight-average molecular weight to 800 or less, the double bond concentration of the photosensitive resin layer can be appropriately increased, thereby further improving image reproducibility. Furthermore, by having only one ethylenically unsaturated bond in the molecule, the crosslinking density of the relief can be appropriately suppressed, improving flexibility and thereby improving the flexibility of the relief during printing.

[0032] Examples of the compound (b) having a polyethylene glycol skeleton, only one ethylenically unsaturated bond in the molecule, and a weight-average molecular weight of 400 to 800 include alkoxypolyethylene glycol (meth)acrylates such as polyethylene glycol mono(meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and ethoxypolyethylene glycol (meth)acrylate, and the like, whose molecular weight falls within the above range.

[0033] The content of component (B) in the photosensitive resin layer is preferably 20 to 65 parts by mass per 100 parts by mass of component (A). By including 20 parts by mass or more of component (B), the image reproducibility of the printing plate can be further improved. On the other hand, by including 65 parts by mass or less of component (B), the flexibility of the photosensitive resin layer can be further improved, and the flexibility of the relief during printing can be further improved.

[0034] The content of component (b) is preferably 20 to 70% by mass relative to 100% by mass of component (B). By including 20% ​​or more by mass of component (b), the elasticity of the relief and flexibility during printing can be further improved. On the other hand, by including 70% or less by mass of component (b), chipping of the relief during the development process can be suppressed, and image reproducibility can be further improved.

[0035] As component (C), a compound having the function of generating radicals by self-decomposition or hydrogen abstraction upon light absorption is preferably used. Examples include benzoin alkyl ethers, benzophenones, anthraquinones, benzils, acetophenones, and diacetyls. Two or more of these compounds may be used. In the present invention, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexan-1-yl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxymethylpropanone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and 2-benzyl-2-(dimethylamino)-4'-morpholinopropylphenone are preferably used.

[0036] The content of the component (C) in the photosensitive resin layer is preferably 0.1 to 20 parts by mass per 100 parts by mass of the component (A).

[0037] The photosensitive resin layer may contain, in addition to the components (A) to (C), binder polymers, compatibilizers, polymerization inhibitors, dyes, pigments, surfactants, antifoaming agents, ultraviolet absorbers, fragrances, and the like, as needed.

[0038] By including a compatibility aid in the photosensitive resin layer, the compatibility of the components constituting the photosensitive resin layer can be improved, the bleeding out of free components can be further suppressed, and the flexibility of the photosensitive resin layer can be improved. Examples of the compatibility aid include polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, and derivatives thereof. The content of the compatibility aid in the photosensitive resin layer is preferably 50% by mass or less.

[0039] By including a polymerization inhibitor in the photosensitive resin layer, thermal stability can be improved. Examples of polymerization inhibitors include phenols, hydroquinones, catechols, and hydroxyamine derivatives. One or more of these may be included. The content of the polymerization inhibitor in the photosensitive resin layer is preferably 0.001 to 5% by mass.

[0040] The thickness of the photosensitive resin layer is preferably 500 μm or more, which ensures the height of the relief of the printing plate and prevents the so-called bottoming out phenomenon, in which ink adheres to the support surface during printing. The thickness of the photosensitive resin layer is more preferably 800 μm or more. On the other hand, the thickness of the photosensitive resin layer is preferably 2.0 mm or less, which improves printing reproducibility.

[0041] Examples of the cover film include plastic sheets made of polyester, polyethylene, polypropylene, etc. The thickness of the cover film is preferably 10 to 150 μm from the viewpoints of ease of handling and flexibility. The surface of the cover film may be roughened to improve adhesion to the original film. Examples of methods for roughening the surface include sandblasting, chemical etching, and coating with a coating agent containing matting particles.

[0042] Furthermore, when the printing plate precursor of the present invention is used in a so-called CTP platemaking method in which laser irradiation is performed based on image data controlled by a digital device, an image mask is formed in situ from mask layer elements, and then exposed and developed, the printing plate precursor may further have a heat-sensitive mask layer. The heat-sensitive mask layer preferably effectively blocks ultraviolet light, absorbs infrared laser light during imaging, and is instantly sublimated or ablated in part or in whole by the heat generated. This creates a difference in optical density between the laser-irradiated and unirradiated areas, allowing the printing plate precursor to function similarly to conventional original film. When the photosensitive resin printing plate precursor has a heat-sensitive mask layer, an adhesion adjustment layer may be present between the photosensitive resin layer and the heat-sensitive mask layer, and a peel-assist layer may be present between the heat-sensitive mask layer and the cover film.

[0043] Examples of the heat-sensitive mask layer, adhesion adjusting layer, and peeling auxiliary layer include those described in WO 2017 / 038970.

[0044] Next, a method for producing a printing plate precursor will be described using an example in which a photosensitive resin layer and a cover film are formed on a substrate.

[0045] For example, components (A) to (C) and other additives as needed are added to a solvent, and the mixture is heated and dissolved with stirring to obtain a photosensitive resin composition solution for the photosensitive resin layer. Examples of the solvent include a water / alcohol mixed solvent.

[0046] A photosensitive resin composition solution is cast onto a substrate having an optional easy-adhesion layer, and dried to form a photosensitive resin layer. A cover film, optionally coated with an anti-tack layer, is then adhered to the photosensitive resin layer to obtain a printing plate precursor.

[0047] Next, a method for producing a printing plate for UV varnish printing (hereinafter sometimes abbreviated as "printing plate") of the present invention will be described. The method for producing a printing plate of the present invention includes at least an exposure step in which the photosensitive resin layer of the printing plate precursor of the present invention is irradiated with ultraviolet light to photocure the exposed areas of the photosensitive resin layer, and a development step in which the uncured areas of the photosensitive resin layer are removed with a developer containing water as the main component.

[0048] In the exposure step, a negative or positive master film is adhered to the photosensitive resin layer after peeling off the cover film, if any, and then irradiated with ultraviolet light having a wavelength of 300 to 400 nm to photocure the exposed portion of the photosensitive resin layer. For ultraviolet irradiation, it is preferable to use, for example, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a xenon lamp, a carbon arc lamp, a chemical lamp, or a UV-LED lamp.

[0049] In the development step, it is preferable to dissolve the unexposed areas using a spray-type developing device or a brush-type washing machine. The developer may be water and / or an organic solvent, and preferably contains water as the main component.

[0050] Furthermore, if necessary, a post-exposure step of irradiating with ultraviolet light may be carried out after development, which makes it possible to further strengthen the relief by reacting unreacted component (B).

[0051] A printing plate produced using the printing plate precursor of the present invention can be suitably used for UV varnish printing.

[0052] Next, a method for producing a printed matter of the present invention will be described. The method for producing a printed matter of the present invention includes a step of transferring UV varnish to a substrate using a flexographic printing plate obtained by the above-mentioned production method, and a step of irradiating the transferred UV varnish with ultraviolet light. In the step of transferring UV varnish to a substrate, the flexographic printing plate is mounted in a flexographic printing unit equipped with a magnetic plate cylinder, and the flexographic printing plate is rotated by 10 to 25 cm. 3 / m 2It is preferable to use an anilox roll having a cell capacity of 1000 ppm or more, to supply UV varnish from the anilox roll to the flexographic printing plate, and to transfer the UV varnish to the printing material.

[0053] UV varnishes generally contain, for example, a photopolymerization initiator and a compound having an ethylenic double bond, and further contain additives for imparting desired functions. [Example]

[0054] The present invention will be specifically illustrated below with reference to examples, but the present invention is not limited to these. Evaluation methods used in the examples and comparative examples are described below.

[0055] (1) Swelling of the relief The cover film was peeled off from the 210 mm × 297 mm flexographic printing plate precursor obtained in each Example and Comparative Example, and the plate was mounted on the rotating cylindrical drum of a digital imager CDI Spark2530 (manufactured by Esco Graphics Co., Ltd.) with the substrate side facing inward. 2 The plate was then exposed to UV-LED light at 22 W for 360 seconds through the formed image mask. The plate was then developed with water at 40°C using a brush-type developing device FTP-640 2D (manufactured by Fujifilm Graphic Solutions Co., Ltd.) at a conveying speed of 220 mm / min, dried at 70°C, and post-exposed to obtain a flexographic printing plate.

[0056] The thickness of the resulting flexographic printing plate with a 100 mm x 100 mm relief was measured at 10 points using a thickness gauge 547-401A (Mitutoyo Corporation) and then immersed in UV flexographic varnish FV-2 (T&K Toka Corporation) at 40°C for 24 hours. The UV varnish was then wiped off the immersed flexographic printing plate with a cloth, and the thickness was measured again. The relief thickness was calculated by subtracting the substrate thickness from the thickness before and after immersion, and the relief swelling was evaluated from the ratio of the relief thickness after immersion to the relief thickness before immersion (after immersion / before immersion). A thickness ratio greater than 1.000 indicates that the relief has swelled due to the UV varnish, making it difficult to apply a thick layer of UV ink stably.

[0057] (2) Image reproducibility The cover film was peeled off from the 210 mm × 297 mm flexographic printing plate precursor obtained in each Example and Comparative Example, and the plate was mounted on the rotating cylindrical drum of a digital imager CDI Spark2530 (manufactured by Esco Graphics Co., Ltd.) with the substrate side facing inward. 2 The thermal mask layer was ablated by irradiating it with a fiber laser under the above conditions, forming five circular dot masks of varying sizes from 50 μm to 300 μm in 10 μm increments, and the resulting image mask was then exposed to UV-LED at 22 W for 360 seconds. The plate was then developed with water at 40°C using a brush-type developing device FTP-640 2D (manufactured by Fujifilm Graphic Solutions Co., Ltd.) at a transport speed of 220 mm / min, dried at 70°C, and post-exposed to obtain a flexographic printing plate.

[0058] The circular reliefs of each size were observed on the obtained flexographic printing plate using a 10x magnifying glass, and the image reproducibility was evaluated based on the size of the smallest relief formed. However, a relief was deemed to have been formed when four or more dots out of five locations of each size remained uncollapsed. The formation of smaller dots is considered to indicate superior image reproducibility.

[0059] (3) Magnetic plate body attachment A magnetic printing cylinder (MMC8-ENOC MODULAR Magnetic Cylinder, manufactured by TDWight, Inc., maximum magnetic force measured with a gauss meter: 0.14 tesla, diameter: 125 mm, circumference: 394 mm, cylinder length: 178 mm) was prepared for mounting the printing cylinder.

[0060] The cover film was peeled off from the 150 mm × 297 mm flexographic printing plate precursor obtained in each Example and Comparative Example, and the plate was mounted on the rotating cylindrical drum of a digital imager CDI Spark2530 (manufactured by Esco Graphics Co., Ltd.) with the substrate side facing inward. 2 The plate was then exposed to UV-LED light at 22 W for 360 seconds through the formed image mask. The plate was then developed with water at 40°C at a conveying speed of 220 mm / min using a brush-type developing device FTP-640 2D (manufactured by Fujifilm Graphic Solutions Co., Ltd.), dried at 70°C, and post-exposed to obtain a flexographic printing plate.

[0061] The obtained flexographic printing plate was attached to a magnetic plate cylinder and then removed 10 times, and the magnetic plate cylinder attachment property was evaluated based on the number of times when the substrate broke. The higher the number of times, the better the magnetic plate cylinder attachment property.

[0062] Next, the methods for producing the materials used in the examples and comparative examples will be described.

[0063] <Preparation of a substrate having an easy-adhesion layer> A mixture of 260 parts by weight of "Vylon" (registered trademark) 31SS (a toluene solution of unsaturated polyester resin, manufactured by Toyobo Co., Ltd.) and 2 parts by weight of PS-8A (benzoin ethyl ether, manufactured by Wako Pure Chemical Industries, Ltd.) was heated at 70°C for 2 hours, then cooled to 30°C. 7 parts by weight of ethylene glycol diglycidyl ether dimethacrylate was added and mixed for 2 hours. 25 parts by weight of "Coronate" (registered trademark) 3015E (an ethyl acetate solution of polyisocyanate resin, manufactured by Tosoh Corporation) and 14 parts by weight of EC-1368 (an industrial adhesive, manufactured by Sumitomo 3M Limited) were then added and mixed to obtain Coating Solution 1 for the easy-adhesion layer.

[0064] Next, 50 parts by mass of "GOHSENOL" (registered trademark) KH-17 (polyvinyl alcohol with a saponification degree of 78.5 to 81.5 mol%, manufactured by Mitsubishi Chemical Corporation) was mixed in a mixed solvent of 200 parts by mass of "SOLMIX" (registered trademark) H-11 (alcohol mixture, manufactured by Nippon Alcohol Co., Ltd.) and 200 parts by mass of water at 70°C for 2 hours, and then 1.5 parts by mass of "BLEMMER" (registered trademark) G (glycidyl methacrylate, manufactured by NOF Corporation) was added and mixed for 1 hour. To this was further added 3 parts by mass of a copolymer (dimethylaminoethyl methacrylate) / (2-hydroxyethyl methacrylate) with a mass ratio of 2 / 1 (manufactured by Kyoeisha Chemical Co., Ltd.), 5 parts by mass of "Irgacure" (registered trademark) 651 (benzyl methyl ketal, manufactured by Ciba-Geigy Co., Ltd.), 21 parts by mass of Epoxy Ester 70PA (acrylic acid adduct of propylene glycol diglycidyl ether, manufactured by Kyoeisha Chemical Co., Ltd.), and 20 parts by mass of ethylene glycol diglycidyl ether dimethacrylate, and mixed for 90 minutes.After cooling to 50°C, 0.1 parts by mass of "Megafac" (registered trademark) F-556 (manufactured by DIC Corporation) was added and mixed for 30 minutes to obtain coating liquid 2 for the easy-adhesion layer.

[0065] The adhesive layer coating solution 1 was applied to chrome-plated steel substrates 1 and 2 (250 μm thick) using a bar coater to a dry thickness of 40 μm, and the substrate was heated in an oven at 180° C. for 3 minutes to remove the solvent. The adhesive layer coating solution 2 was then applied thereon using a bar coater to a dry thickness of 30 μm, and the substrate was heated in an oven at 160° C. for 3 minutes to obtain substrates 1 and 2 having adhesive layers. (Steel substrate 1) SPTFS D T-2.5CA R1 (manufactured by Nippon Steel Corporation), Rockwell hardness HR30TSm: 55, yield point Yp: 270MPa (Steel substrate 2) SPTFS D T-5CA R1 (manufactured by Nippon Steel Corporation), Rockwell hardness HR30TSm: 65, yield point Yp: 450MPa.

[0066] <Preparation of intermediate layer / heat-sensitive mask layer / cover film laminate> 40 parts by mass of polyvinyl alcohol JL-18E (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., degree of saponification: 84 mol%, average degree of polymerization: 1,800) was mixed in a mixed solvent of 100 parts by mass of "Solmix" (registered trademark) H-11 (alcohol mixture, manufactured by Nippon Alcohol Co., Ltd.) and 300 parts by mass of water at 70°C for 2 hours and then cooled to 20°C to obtain a polyvinyl alcohol solution. 20 parts by mass of modified carbon black aqueous dispersion BONJET BLACK CW-1 (manufactured by Orient Chemical Industries Co., Ltd.) was added to 50 parts by mass of the obtained polyvinyl alcohol solution to obtain a composition solution for a heat-sensitive mask layer.

[0067] The heat-sensitive mask layer composition solution obtained by the above-described method was applied to a 100 μm-thick polyester film, "Lumirror" (registered trademark) S10 (manufactured by Toray Industries, Inc.), which served as a cover film, using a bar coater. The solution was then dried at 100°C for 30 seconds to form a heat-sensitive mask layer, resulting in a heat-sensitive mask layer / cover film laminate. The thickness of the heat-sensitive mask layer was adjusted so that the optical density (transmission mode of a Macbeth transmission densitometer "TR-927" (manufactured by Kollmorgen Instruments Corp.)) using an orthochromatic filter with the cover film value set to zero was 3.0.

[0068] Next, a solution for the intermediate layer composition was prepared by dissolving 5 masses of polyvinyl alcohol JL-05E (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., saponification degree: 80 mol%, average polymerization degree: 500) in a mixed solvent of 45 mass parts of water, 20 mass parts of methanol, 20 mass parts of n-propanol, and 10 mass parts of n-butanol at 70°C. The solution was applied to the heat-sensitive mask layer of the heat-sensitive mask layer / cover film laminate using a bar coater so that the film thickness after drying would be 0.1 μm. The solution was then dried at 120°C for 30 seconds to form an intermediate layer, and a laminate consisting of the intermediate layer / heat-sensitive mask layer / cover film was obtained.

[0069] [Example 1] Partially saponified polyvinyl alcohol "GOHSENOL" NK-05R (Mitsubishi Chemical Corporation) (average degree of polymerization: 500, degree of saponification: 72 mol%) was swollen in acetone, and 4.2 parts by mass of succinic anhydride was added to 100 parts by mass of "GOHSENOL" NK-05R. The mixture was stirred at 60°C for 6 hours to add carboxyl groups to the molecular chains of the partially saponified polyvinyl alcohol. The polymer was washed with acetone to remove unreacted succinic anhydride and then dried. 100 parts by mass of this polymer was dissolved in 200 parts by mass of a 30 / 70 ethanol / water mixed solvent at 80°C. 8.3 parts by mass of glycidyl methacrylate was added to the solution to introduce ethylenic double bonds into the partially saponified polyvinyl alcohol, yielding polyvinyl alcohol derivative A-1, component (A). A-1 had a vinyl alcohol structural unit, a vinyl acetate structural unit, and a structural unit represented by the following structural formula (3), and had a weight-average molecular weight of 44,500.

[0070] [ka]

[0071] Next, 100 parts by mass of a 50 / 50 (mass ratio) ethanol / water mixed solvent was placed in a three-necked flask equipped with a stirring spatula and a condenser, and the obtained A-1 was added in the amount shown in Table 1 and dissolved by heating at 90°C for 2 hours. The obtained mixture was cooled to 70°C, and then the other components shown in Table 1 were added and stirred for 30 minutes to obtain photosensitive resin composition solution 1.

[0072] The photosensitive resin composition solution 1 obtained as described above was cast onto the adhesive layer side of the substrate 1 having the adhesive layer, and dried at 60° C. for 2.5 hours to form a photosensitive resin layer. At this time, the thickness of the plate after drying (substrate having the adhesive layer + photosensitive resin layer) was adjusted to 1.18 mm.

[0073] A mixed solvent of water / ethanol = 50 / 50 (mass ratio) was applied onto the photosensitive resin layer thus obtained, and the intermediate layer side of an intermediate layer / heat-sensitive mask layer / cover film laminate was pressure-bonded to the surface to obtain flexographic printing plate precursor 1. The evaluation results of the obtained flexographic printing plate precursor 1 are shown in Table 1.

[0074] [Example 2] A flexographic printing plate precursor 2 was obtained in the same manner as in Example 1, except that the substrate 2 having an easy-adhesion layer was used instead of the substrate 1 having an easy-adhesion layer. The evaluation results are shown in Table 1.

[0075] [Examples 3 to 4] Photosensitive resin printing plate precursors 3 and 4 were obtained in the same manner as in Example 2, except that the type and amount of component (B) was changed as shown in Table 1. The evaluation results are shown in Table 1.

[0076] [Example 5] Partially saponified polyvinyl alcohol "GOHSENOL" NK-05R (Mitsubishi Chemical Corporation) (average degree of polymerization: 500, degree of saponification: 72 mol%) was swollen in acetone, and 4.2 parts by mass of succinic anhydride was added to 100 parts by mass of "GOHSENOL" NK-05R. The mixture was stirred at 60°C for 6 hours to add carboxyl groups to the molecular chains of the partially saponified polyvinyl alcohol. The polymer was washed with acetone to remove unreacted succinic anhydride and then dried. 100 parts by mass of this polymer was dissolved in 200 parts by mass of a mixed solvent of ethanol / water = 30 / 70 (mass ratio) at 80°C. 8.3 parts by mass of the epoxy compound "CYCLOMER" (registered trademark) M100 (Daicel Corporation) was added to the solution to introduce a cyclic structure and ethylenic double bonds into the partially saponified polyvinyl alcohol, yielding polyvinyl alcohol derivative A-2, component (A). A-2 had a vinyl alcohol structural unit, a vinyl acetate structural unit, and a structural unit represented by the following structural formula (4), and had a weight average molecular weight of 45,500.

[0077] [ka]

[0078] Photosensitive resin printing plate precursor 4 was obtained in the same manner as in Example 2, except that polyvinyl alcohol derivative A-2 was used instead of polyvinyl alcohol derivative A-1. The evaluation results are shown in Table 1.

[0079] [Example 6] Photosensitive resin printing plate precursor 5 was obtained in the same manner as in Example 2, except that partially saponified polyvinyl alcohol "GOHSENOL" NK-05R (average polymerization degree: 500, saponification degree: 72 mol%) manufactured by Mitsubishi Chemical Corporation was used instead of polyvinyl alcohol derivative A-1. The evaluation results are shown in Table 1.

[0080] [Comparative Example 1] 50 parts by weight of ε-caprolactam, 56 parts by weight of N,N'-bis(γ-aminopropyl)piperazine adipate, 6.3 parts by weight of 1,3-bisaminomethylcyclohexane adipate, and 10 parts by weight of water were placed in a reactor, thoroughly purged with nitrogen, and then sealed and gradually heated. Once the internal pressure reached 0.98 MPa, the water in the reactor was gradually distilled off, and the pressure was returned to normal over one hour. The reaction was then continued at normal pressure for another 1.0 hour. The maximum polymerization temperature was 220°C. A transparent, pale yellow, alcohol-soluble oligomer with a specific viscosity of 1.5, essentially terminated by primary amino groups at both ends and linked in a block amide bond, had a number-average molecular weight of approximately 3,000, and was obtained. After dissolving 46 parts by weight of this oligomer in 200 parts by weight of methanol, 9 parts by weight of an organic diisocyanate compound having isocyanate groups at essentially both ends, obtained by reacting 1,000 parts by weight of polypropylene glycol (weight average molecular weight: 1,000) with 369 parts by weight of hexamethylene diisocyanate, was gradually added with stirring. The reaction between the two was completed at 65°C in approximately 15 minutes. The solution was placed in a Teflon®-coated Petri dish, and the methanol was evaporated off. The mixture was then dried under reduced pressure to obtain a polyamide block copolymer. This polyamide block copolymer had a specific viscosity of 2.0 and contained 82% by weight of block components consisting of structural units composed of amide bonds. In addition to the amide bonds, it also contained urea and urethane bonds.

[0081] 55 parts by weight of the above polyamide block copolymer was dissolved in 100 parts by weight of methanol at 65°C. 9 parts by weight of N-ethyltoluenesulfonic acid amide, 0.001 parts by weight of 1,4-naphthoquinone, and 0.1 parts by weight of hydroquinone monomethyl ether were added as plasticizers and stirred for 30 minutes. Subsequently, 2 parts by weight of glycerol monobehenate, 5 parts by weight of lactic acid, 18 parts by weight of water, 1 part by weight of benzyl dimethyl ketal as a photopolymerization initiator, and 28 parts by weight of propylene glycol diglycidyl ether acrylic acid adduct as a photopolymerizable unsaturated compound were added and stirred for 30 minutes. The temperature was then gradually increased to distill off methanol and water, and the mixture was concentrated until the temperature inside the kettle reached 110°C. At this stage, a fluid, viscous photosensitive resin composition solution was obtained.

[0082] The photosensitive resin composition solution obtained as described above was cast onto the adhesive layer side of the substrate 2 having the adhesive layer, and dried at 60° C. for 2.5 hours to form a photosensitive resin layer. At this time, the thickness of the plate after drying (substrate having the adhesive layer + photosensitive resin layer) was adjusted to 1.18 mm.

[0083] A mixed solvent of water / ethanol = 50 / 50 (weight ratio) was applied onto the photosensitive resin layer thus obtained, and the intermediate layer side of the intermediate layer / heat-sensitive mask layer / cover film laminate was pressure-bonded to the surface to obtain flexographic printing plate precursor 6. The evaluation results of the obtained flexographic printing plate precursor 6 are shown in Table 1.

[0084] [Table 1]

[0085] The contents of component (B) in Table 1 are as follows: "Blenmer" (registered trademark) AE400: NOF Corporation, polyethylene glycol monoacrylate (Mw: approximately 510) Epoxy ester 70PA: Kyoeisha Chemical Co., Ltd., acrylic acid adduct of propylene glycol diglycidyl ether "Blenmer" (registered trademark) GMR: glycerol dimethacrylate, manufactured by NOF Corporation

Claims

1. A flexographic printing plate precursor for UV varnish printing, comprising a substrate and a photosensitive resin layer comprising (A) polyvinyl alcohol and / or a derivative thereof, (B) a compound having an ethylenic double bond, and (C) a photopolymerization initiator.

2. The flexographic printing plate precursor for UV varnish printing according to claim 1 , wherein the substrate is a metal substrate.

3. The flexographic printing plate precursor for UV varnish printing according to claim 2 , wherein the metal substrate is a steel plate.

4. 3. The flexographic printing plate precursor for UV varnish printing according to claim 2, wherein the metal substrate has a Rockwell hardness HR30TSm of 40 to 80 and a yield point Yp of 200 MPa to 1.0 GPa.

5. The printing plate precursor for UV varnish printing according to claim 1 or 2, wherein the polyvinyl alcohol and / or its derivative (A) contains a polyvinyl alcohol derivative having an ethylenic double bond in a side chain.

6. 3. The flexographic printing plate precursor for UV varnish printing according to claim 1 or 2, wherein the compound (B) having an ethylenic double bond is a compound (b) having a polyethylene glycol skeleton, only one ethylenically unsaturated bond in the molecule, and a weight-average molecular weight of 400 to 800, in an amount of 20 to 70% by mass relative to 100% by mass of component (B).

7. A method for producing a flexographic printing plate for UV varnish printing, comprising: an exposure step of irradiating the photosensitive resin layer of the flexographic printing plate precursor for UV varnish printing according to claim 1 or 2 with ultraviolet light to photo-cure the exposed areas of the photosensitive resin layer; and a development step of removing the uncured areas of the photosensitive resin layer with a developer mainly composed of water.

8. A method for producing a printed matter, comprising the steps of transferring UV varnish to a substrate using a flexographic printing plate for UV varnish printing obtained by the method of claim 7, and irradiating the transferred UV varnish with ultraviolet light.

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