JP2020023634A - Composition for aqueous ink - Google Patents

Abstract

To provide a novel composition for an aqueous ink that is excellent in water resistance of a coated product.SOLUTION: The composition for an aqueous ink contains (A) a modified polyvinyl alcohol containing a constitutional unit represented by the following formula (1) in the range of 0.1 to 5.0 mol%, water, a photopolymerization initiator and a coloring material. [In formula (1), Rrepresents a hydrogen atom, a methyl group, a carboxyl group or a carboxymethyl group.]SELECTED DRAWING: None

Description

  The present invention relates to an aqueous ink composition that can be cured by high energy rays.

  The ink includes a solvent-based ink using an organic solvent as a dispersion medium, a solventless ink using a photocurable monomer as a dispersion medium, and an aqueous ink using water as a dispersion medium. Since the solvent-based ink contains a large amount of an organic solvent, it has a problem in terms of environmental measures and safety. Further, in the solventless ink, the photocurable monomer used is often highly toxic, and similarly has a problem in terms of safety. On the other hand, the water-based ink uses water as a dispersion medium, and thus is excellent in terms of environmental friendliness and safety.

  In recent years, many studies have been made on a system for curing by irradiating a high energy beam such as an electron beam or an ultraviolet ray after ink transfer. In such a system, an ink composition using polyvinyl alcohol having a photocurable group introduced therein based on polyvinyl alcohol having excellent dispersibility of a coloring material such as a dye or a pigment has been studied.

  For example, Patent Literatures 1 and 2 illustrate aqueous ink compositions containing a modified polyvinyl alcohol having a bulky structure having a (meth) acrylate group in a side chain. It is exemplified that these aqueous ink compositions are cured by ultraviolet rays after transfer, so that when a printing paper is immersed in water, the printing does not blur and shows water resistance.

JP 2007-185906 A JP 2008-45047 A

  However, printing on a retort food packaging material or the like may require higher water resistance, and the aqueous ink composition described in the above patent document still has a problem in terms of water resistance after curing. . Therefore, an object of the present invention is to provide a novel aqueous ink composition having excellent water resistance of a cured product after curing.

  The present inventors have conducted intensive studies and found that the unit structure of the side chain having high energy ray reactivity has a specific structure with a small bulk, so that even after a small amount of modification, the coated product after curing has excellent water resistance. The inventors have found that the composition can be a composition, and have found that the above-mentioned problems can be solved by the present composition.

According to the present invention, the above problems are
[1] Modified polyvinyl alcohol (A) containing a structural unit represented by the following formula (1) (hereinafter sometimes referred to as “structural unit (1)”) in an amount of 0.1 to 5.0 mol%. (Hereinafter sometimes referred to as “modified polyvinyl alcohol (A)”), a water-based ink composition containing water, a photopolymerization initiator, and a coloring material;
[In the formula (1), R ¹ represents a hydrogen atom, a methyl group, a carboxyl group or a carboxymethyl group]
[2] The aqueous ink composition of [1], wherein R ¹ is a methyl group;
Is solved by providing.

  The water-based ink composition of the present invention has excellent water resistance of a coated product after irradiation with high energy rays.

  The aqueous ink composition of the present invention contains a modified polyvinyl alcohol (A) containing a structural unit represented by the following formula (1) in a range of 0.1 to 5.0 mol%.

[In the formula (1), R ¹ represents a hydrogen atom, a methyl group, a carboxyl group or a carboxymethyl group]

  Since the olefin present in the structural unit (1) can be cross-linked by a high energy beam, the modified polyvinyl alcohol (A) can be made water-resistant and generate a gel by cross-linking. Further, the olefin is an α, β-unsaturated type and therefore has high reactivity and is easily crosslinked by high energy rays.

In the formula (1), R ¹ represents a hydrogen atom, a methyl group, a carboxyl group or a carboxymethyl group. When the compound has a carboxyl group or a carboxymethyl group, R ¹ is preferably hydrogen or a methyl group because the dispersibility of the coloring material is excellent, but the bulkier side chain structure is more excellent in curability by crosslinking. . Further, from the viewpoint of storage stability of the aqueous ink composition, R ¹ is preferably a methyl group.

  The content of the structural unit (1) in the modified polyvinyl alcohol (A) is 0.1 mol% to 5.0 mol% based on all the structural units of the modified polyvinyl alcohol (A). When the content of the structural unit (1) is equal to or more than the above lower limit, a crosslinking effect by a high-energy ray easily occurs, and is preferably 0.2 mol% or more, more preferably 0.4 mol% or more. When the content of the structural unit (1) is equal to or less than the upper limit, deterioration of water solubility due to self-crosslinking of the structural units (1) is easily suppressed, preferably 4 mol% or less, more preferably 2 mol%. % Or less. The modified polyvinyl alcohol (A) may have one or more structural units (1). When it has two or more types of structural units (1), the total content of these two or more types of structural units (1) is preferably in the above range. In addition, in this invention, a "structural unit" means the repeating unit which comprises a polymer. For example, a vinyl alcohol unit described below and a vinyl ester unit described below are also constituent units.

  In the modified polyvinyl alcohol (A), the content of the vinyl alcohol unit with respect to all the structural units is not particularly limited, but is preferably, for example, 60 to 95 mol%. When the content of the vinyl alcohol unit is less than 60 mol%, the water solubility of the modified polyvinyl alcohol (A) is deteriorated. On the other hand, when the content of the vinyl alcohol unit is more than 95% by mole, water solubility is deteriorated, so that a long-time dissolution treatment is required at a high temperature for dissolution, and gelation due to thermal crosslinking is easily induced. Further, when the content of the vinyl alcohol unit is more than 95 mol%, the dispersibility of the coloring material is also reduced. The content of the vinyl alcohol unit is preferably at least 65 mol%, more preferably at least 68 mol%, further preferably at least 72 mol%, preferably at most 90 mol%, more preferably at most 88 mol%.

  The vinyl alcohol unit can be derived from the vinyl ester unit by hydrolysis or alcoholysis. Therefore, the vinyl ester unit may remain in the modified polyvinyl alcohol (A) depending on the conditions when converting the vinyl ester unit to the vinyl alcohol unit. Therefore, the modified polyvinyl alcohol (A) may include a vinyl ester unit other than the structural unit (1).

  Examples of the vinyl ester of the vinyl ester unit include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, and palmitate. Examples thereof include vinyl acid, vinyl stearate, vinyl oleate, and vinyl benzoate. Of these, vinyl acetate is preferable from an industrial viewpoint.

  The modified polyvinyl alcohol (A) may further contain a structural unit other than the structural unit (1), the vinyl alcohol unit and the vinyl ester unit as long as the effects of the present invention can be obtained. The constituent unit is derived from, for example, an unsaturated monomer copolymerizable with the vinyl ester and convertible into the constituent unit (1), an ethylenically unsaturated monomer copolymerizable with the vinyl ester, and the like. It is a structural unit to perform. Ethylenically unsaturated monomers include, for example, α-olefins such as ethylene, propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate; Acrylates such as i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacrylic acid Metac such as octadecyl Acrylates; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (for example, quaternary salts); Methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (for example, quaternary salts); methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether; i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, Vinyl ethers such as 1,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; halogenation such as vinylidene chloride and vinylidene fluoride Vinylidenes; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid and salts or esters thereof; vinyltrimethoxysilane And vinylsilyl compounds; isopropenyl acetate and the like.

  There are no particular restrictions on the arrangement order of the structural unit (1), the vinyl alcohol unit, and any other structural units in the modified polyvinyl alcohol (A). The modified polyvinyl alcohol (A) is a random copolymer or a block copolymer. Or an alternating copolymer.

  The viscosity average degree of polymerization of the modified polyvinyl alcohol (A) measured according to JIS K6726 is not particularly limited, and is preferably 100 or more, more preferably 200 or more, further preferably 300 or more, and preferably 3,000 or less. , More preferably 2,500 or less, further preferably 2,000 or less. When the viscosity average degree of polymerization is equal to or higher than the lower limit, the water resistance of the cured product after curing tends to be excellent. When the viscosity-average degree of polymerization is less than the above upper limit, water solubility is excellent, so that high-temperature and long-time treatment is not required at the time of preparing an aqueous solution, and gelation due to thermal crosslinking is hardly induced.

  The method for producing the modified polyvinyl alcohol (A) is not particularly limited. For example, (i) a method of reacting polyvinyl alcohol with an unsaturated carboxylic acid or a derivative thereof; (ii) transesterification of polyvinyl alcohol with an unsaturated carboxylic acid ester (Iii) a method of reacting polyvinyl alcohol with an unsaturated carboxylic acid chloride. Among them, method (i) or method (ii) is preferably used from the viewpoint of excellent reactivity and simplifying the process.

  When the modified polyvinyl alcohol (A) is produced by the method (i), a method in which the vinyl alcohol unit of the polyvinyl alcohol and the unsaturated carboxylic acid are dehydrated and condensed by mixing the polyvinyl alcohol and the unsaturated carboxylic acid is preferable. It is adopted as an embodiment. Examples of the unsaturated carboxylic acid include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid and salts thereof; unsaturated dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid and salts thereof; And unsaturated carboxylic anhydrides such as acid, itaconic anhydride and citraconic anhydride. These can be used alone or in combination of two or more.

When the modified polyvinyl alcohol (A) is produced by the method (ii), polyvinyl alcohol, an acrylate or methacrylate represented by the following formula (2) (hereinafter, may be referred to as an ester (2)), As a preferred embodiment, a method of performing a transesterification reaction between the vinyl alcohol unit of the polyvinyl alcohol and the ester (2) by mixing an ester exchange reaction catalyst with the vinyl alcohol unit is employed. Examples of the saturated hydrocarbon group having 1 to 5 carbon atoms represented by R ² include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a t-butyl group and the like. The alcohol represented by R ² OH (R ² has the same meaning as in the following formula (2)) is eliminated by the transesterification reaction. By removing the alcohol outside the reaction system, polyvinyl alcohol and the ester (2) Reaction is promoted. From this viewpoint, the alcohol is preferably a low-boiling compound, and R ² preferably has 1 to 3 carbon atoms, more preferably 1, that is, R ² is preferably a methyl group.

[In the formula (2), R ¹ is as defined above, and R ² represents a saturated hydrocarbon group having 1 to 5 carbon atoms. ]

  When the modified polyvinyl alcohol (A) is produced by the method (ii), a transesterification catalyst may coexist. The ester exchange reaction catalyst is not particularly limited, and examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; organic carboxylic acids such as acetic acid, propionic acid, phthalic acid, and benzoic acid; methylsulfonic acid, benzenesulfonic acid, and p-acid. Organic sulfonic acids such as toluenesulfonic acid and trifluoromethanesulfonic acid; Organic phosphoric acids such as diethyl phosphate and phenyl phosphate; Alkali metal or alkaline earth metal hydroxide such as sodium hydroxide, potassium hydroxide and magnesium hydroxide Substances; alkali metal or alkaline earth metal carbonates and hydrogen carbonates such as sodium hydrogen carbonate, potassium carbonate and calcium hydrogen carbonate; alkali metals such as trilithium phosphate, potassium dihydrogen phosphate, sodium pyrophosphate and calcium metaphosphate Or alkaline earth metal phosphates and Hydrogen phosphate; borate of alkali metal or alkaline earth metal such as potassium metaborate, sodium tetraborate, magnesium orthoborate; alkali metal or alkaline earth such as sodium acetate, potassium acetate, sodium benzoate, magnesium acetate Alkali metal or alkaline earth metal alkoxide compounds or phenoxide compounds such as lithium ethoxide, sodium methoxide, potassium methoxide, magnesium methoxide and sodium phenoxide; alkali metal or alkaline earth such as calcium oxide Metal oxides; ammonia; ammonium hydroxide, tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, ammonium carbonate, hydrogen carbonate Ammonium salts such as monium, tetramethyl ammonium methyl carbonate, tetramethyl ammonium ethyl carbonate, methyl triethyl ammonium methyl carbonate, methyl tri n-butyl ammonium methyl carbonate, methyl tri n-octyl ammonium methyl carbonate; tetraphenyl phosphonium hydroxide, tetramethyl hydroxide Phosphonium salts such as phosphonium, tetramethylphosphonium methyl carbonate, methyltri-n-butylphosphonium ethyl carbonate, methyltri-n-octylphosphonium methyl carbonate; primary amines such as n-butylamine, benzylamine, aniline and ethylenediamine; diethylamine, methylethylamine, pyrrolidine, Secondary A such as N-methyltoluidine Min; triethylamine, tri-n-butylamine, N-methyl-N-ethylaniline, 1,4-diazabicyclo [2.2.2] octane, 1,8-diazabicyclo [5.4.0] -7-undecene, etc. Tertiary amines; nitrogen-containing aromatic heterocyclic compounds such as pyridine, picoline, quinoline, imidazole, pyrimidine, N, N-dimethylaminopyridine; cadmium compounds such as cadmium chloride, cadmium oxide, and cadmium acetate; tin chloride, oxide Tin compounds such as tin, tin acetate, tin octoate, tributyltin, acetylacetone tin (IV) chloride; lead compounds such as lead chloride, lead oxide, lead carbonate, and lead tetraacetate; aluminum chloride, aluminum oxide, and aluminum acetate , Aluminum compounds such as aluminum alkoxide; zinc chloride, zinc bromide, Zinc iodide, zinc oxide, zinc acetate, zinc trifluoroacetate, zinc stearate, zinc nitrate, zinc carbonate, zinc sulfate, zinc acetylacetonate (II), zinc trifluoromethanesulfonate (II), zinc 2-tetrafluoroborate And zinc compounds such as oxo [hexa (trifluoroacetato)] tetrazinc; bismuth compounds such as bismuth chloride, bismuth oxide and bismuth acetate; iron chloride, iron oxide, iron acetate, iron acetylacetone (III), N, Iron compounds such as N'-bis (salicylidene) ethylenediamineiron (II); cobalt compounds such as cobalt chloride, cobalt oxide, cobalt acetate, cobalt stearate, acetylacetonate cobalt (II); copper chloride, copper bromide, iodine Copper-based such as copper oxide, copper oxide, copper acetate, copper acetylacetone (II) Chromium compounds such as chromium chloride, chromium oxide, chromium acetate, chromium acetylacetonate (III); molybdenum compounds such as molybdenum chloride, molybdenum oxide, molybdenum acetate, and acetylacetone molybdenum (VI) dioxide; manganese chloride, manganese oxide; Manganese compounds such as manganese acetate and acetylacetone manganese (II); titanium compounds such as titanium chloride, titanium oxide, titanium acetate, alkoxytitanium, titanium lactate, and acetylacetone titanium (VI) oxide; zirconium chloride, zirconium oxide, zirconium acetate; Zirconium compounds such as acetylacetone zirconium (IV); Hafnium compounds such as hafnium chloride, hafnium oxide, and hafnium (IV) trifluoromethanesulfonate; Lanthanum compounds such as tan, lanthanum oxide, lanthanum acetate, lanthanum nitrate, lanthanum alkoxide, lanthanum (III) acetylacetone, and lanthanum (III) trifluoromethanesulfonate; germanium compounds such as germanium chloride and germanium oxide; enzymes such as lipase; Etc. are preferably used. Among them, from the viewpoint of reactivity and the hue of the resulting modified polyvinyl alcohol (A), inorganic acids, organic carboxylic acids, organic sulfonic acids, organic phosphoric acids, hydroxides of alkali metals or alkaline earth metals, alkali metals or alkalis Earth metal carbonates and bicarbonates, alkali metal or alkaline earth metal phosphates and hydrogen phosphates, alkali metal or alkaline earth metal carboxylates, alkali metal or alkaline earth metal alkoxide compounds Or phenoxide compounds, ammonium salts, phosphonium salts, aluminum compounds, zinc compounds, bismuth compounds, titanium compounds, zirconium compounds, lanthanum compounds are more preferable, and inorganic acids, organic carboxylic acids, organic sulfonic acids, and alkali metals Or hydroxylation of alkaline earth metals , Alkali metal or alkaline earth metal carbonates and bicarbonates, alkali metal or alkaline earth metal carboxylate, alkali metal or alkaline earth metal alkoxide compounds, ammonium salts, zinc compounds, titanium compounds, Zirconium compounds and lanthanum compounds are more preferred, and alkali metal or alkaline earth metal carboxylates, ammonium salts, and zinc compounds are most preferred.

  The amount of the transesterification catalyst used is not particularly limited, but is preferably at least 0.01 part by mass, more preferably at least 0.1 part by mass, and preferably at most 30 parts by mass, based on 100 parts by mass of polyvinyl alcohol. Preferably it is 15 parts by mass or less. When the amount of the ester exchange reaction catalyst is at least the above lower limit, the reaction rate tends to be excellent, and when it is at most the above upper limit, the catalyst residue is easily removed, and the hue and heat stability of the resulting modified polyvinyl alcohol (A) are obtained. Properties tend to be excellent. The amount of the ester (2) is not particularly limited, but is preferably at least 0.1 part by mass, more preferably at least 5 parts by mass, and preferably at most 1,000 parts by mass, based on 100 parts by mass of polyvinyl alcohol. Preferably it is 500 parts by mass or less. If the amount of the ester (2) is greater than or equal to the lower limit, the reaction rate tends to be excellent. If the amount is less than or equal to the upper limit, the ester (2) remaining after the reaction is easily removed.

As the reaction method for producing the modified polyvinyl alcohol (A) by transesterification of the method (ii), in particular, the polyvinyl alcohol and the ester (2), a polyvinyl alcohol, an ester (2) and a transesterification catalyst are used. A method in which the ester (2) and the transesterification catalyst are mixed and reacted with the molten polyvinyl alcohol; the ester (2) and the transesterification catalyst are dissolved, and the polyvinyl alcohol is dissolved. A method in which the reaction is carried out in a slurry state in a solvent which is not used; a method in which the reaction is carried out in a solution state in which polyvinyl alcohol, ester (2) and the transesterification catalyst are all dissolved uniformly. Any of these methods can be appropriately selected in consideration of the reactivity and the isolation of the modified polyvinyl alcohol (A). The reaction temperature in the transesterification is not particularly limited, but is preferably equal to or higher than the boiling point of the alcohol from the viewpoint of removing the alcohol eliminated from the ester (2) to the outside of the reaction system. From such a viewpoint, 20 to 200 ° C is preferable, 30 to 180 ° C is more preferable, 40 to 170 ° C is further preferable, and 50 to 150 ° C is most preferable. In order to lower the boiling point of the alcohol desorbed from the ester (2), the pressure in the reaction system may be reduced. In this case, the pressure in the system is preferably from 5 kPa to 99 kPa, more preferably from 8 kPa to 97 kPa, and still more preferably from 10 kPa to 97 kPa. It is 95 kPa.
The solvent that can be used is not particularly limited, but includes, for example, water; alcohols such as methanol, ethanol, propanol, and butanol; aliphatic or alicyclic hydrocarbons such as n-hexane, n-pentane, and cyclohexane; benzene, toluene, and the like. Aromatic or aromatic halides such as chloroform, chlorobenzene and dichlorobenzene; nitriles such as acetonitrile and benzonitrile; diethyl ether, diphenyl ether, anisole, 1,2-dimethoxyethane, 1,4- Ethers such as dioxane; ketones such as acetone, methyl isopropyl ketone and methyl isobutyl ketone; esters such as ethyl acetate and ethyl propionate; N-alkyl lactams such as N-methyl-2-pyrrolidone; Methylformamide, N, N- dimethylacetamide, etc. of N, N-dialkylamides; sulfoxides such as dimethyl sulfoxide; sulfolane such as sulfolane; and the like. Above all, aprotic polar solvents such as nitriles, ethers, ketones, esters, N-alkyllactams, N, N-dialkylamides, sulfoxides, sulfolanes, and the like are preferable, and N-alkyllactams, , N-Dialkylamides and sulfoxides are more preferred.

  In the composition for an aqueous ink of the present invention, a photopolymerization initiator is used for curing by high-energy radiation curing. Although the type of the photopolymerization initiator is not particularly limited, for example, benzophenone such as benzophenone, hydroxybenzophenone, bis-N, N-dimethylaminobenzophenone, bis-N, N-diethylaminobenzophenone, and 4-methoxy-4'-dimethylaminobenzophenone , Thioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, chlorothioxanthone, isopropoxychlorothioxanthone, 2- (2-hydroxy-3-N, N, N-trimethylaminopropoxy) -3,4-dimethylthioxanthone hydrochloride Thioxanthones, ethylanthraquinone, benzanthraquinone, aminoanthraquinone, chloroanthraquinone, anthraquinone-2-sulfonate, anthraquinone-2,6-disulfonate Benzoin ethers such as anthraquinones, acetophenones, benzoin methyl ether, benzoin ethyl ether and benzoin phenyl ether, 2,4,6-trihalomethyl triazines, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-4 ′-( 2-hydroxyethoxy) -2-methylpropiophenone, (2- (o-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di (m-methoxyphenyl) ) Imidazole dimer, 2- (o-fluorophenyl) -4,5-diphenylimidazole dimer, 2- (o-methoxyphenyl) -4,5-diphenylimidazole dimer, 2- (p-methoxy) Phenyl) -4,5-diphenylimidazole dimer, 2- ( , 4-Dimethoxyphenyl) -4,5-diphenylimidazole dimer, 2,4,5-triarylimidazole dimer, benzyldimethyl ketal, 2-benzyl-2-dimethylamino-1- (4- Morpholinophenyl) -butan-1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-1-propanone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one , 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, phenanthrenequinone, 9,10-phenanthrenequinone, methylbenzoin, ethylbenzoin and the like Acridine derivatives such as benzoins, 9-phenylacridine, 1,7-bis (9,9′-acridinyl) heptane; Bisacylphosphine oxides and mixtures thereof can be mentioned. These can be used alone or in combination of two or more. Although the amount of the photopolymerization initiator is not particularly limited, it is usually preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the modified polyvinyl alcohol (A).

  The coloring material used in the aqueous ink composition of the present invention is not particularly limited, and various pigments and dyes can be used. In the case of the dye, a known dye having a skeleton structure such as an azo type, an anthraquinone type, a dioxazine type, and a fluoran type can be used. On the other hand, when durability is required, a pigment is preferably used. Any pigment can be used regardless of organic or inorganic. For example, in the case of inorganic pigments, oxides, hydroxides, sulfides, ferrocyanides, chromates, carbonates, silicates, phosphates, carbon black, metal powders and the like can be mentioned. In the case of organic pigments, nitrosos, dyed lakes, azo lakes, insoluble azos, monoazos, disazos, condensed azos, benzimidazolones, phthalocyanines, anthraquinones, perylenes, quinacridones, dioxazine , Isoindolines, azomethines and pyrrolopyrroles. Although the amount of the coloring material is not particularly limited, it is usually preferably 0.1 to 10 parts by mass based on 100 parts by mass of the aqueous ink composition.

The aqueous ink composition of the present invention contains water. The type of water is not particularly limited, and pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water, or ultrapure water can be used. Further, if necessary, a water-soluble organic solvent may be further blended, and specific examples thereof include methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, sec-butanol, tert-butanol, iso-butanol, n-pentanol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol, glycerin, trimethylol Polyhydric alcohols such as ethane and trimethylolpropane, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether Alkyl ethers of polyhydric alcohols such as diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, urea, 2-pyrrolidone, and N-methyl-2. -Pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. These may be used alone or in combination of two or more. The amount of the water-soluble organic solvent is not particularly limited, but is preferably 0.1 to 50 parts by mass based on 100 parts by mass of the aqueous ink composition.

The high energy ray used for curing the aqueous ink composition of the present invention is not particularly limited, and examples thereof include an electron beam, an ultraviolet ray, and an X-ray. Among them, an ultraviolet ray is preferable. In the case of ultraviolet rays, it is desirable to use a high-pressure mercury lamp, such as an ultrahigh-pressure mercury lamp, a high-pressure mercury lamp, a carbon arc, a mercury lamp that induces and emits light at a high frequency, or a high-pressure mercury lamp containing more long-wavelength light, such as a mercury lamp lamp containing a metal halide. The irradiation intensity is not particularly limited, but is preferably from 100 to 10,000 mW / cm ² .

  The aqueous ink composition of the present invention is an oxidizing agent, an antioxidant, a reducing agent, an enzyme, a bactericide, an antifoaming agent, an abrasive, an antifungal agent, as long as the effects of the present invention are not impaired. It may further include a viscosity modifier, a conductive agent, an ultraviolet absorber and a chelating agent, a disperse dye, an oil-soluble dye, and the like.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In Examples and Comparative Examples, “%” and “parts” represent “% by mass” and “parts by mass”, respectively, unless otherwise specified.

[Calculation of Content of Structural Unit (1) and Vinyl Alcohol Unit in Modified Polyvinyl Alcohol (A)]
Using a nuclear magnetic resonance apparatus “LAMBDA 500” manufactured by JEOL Ltd., ¹ H-NMR of the modified polyvinyl alcohol obtained in Examples or Comparative Examples was measured at room temperature in deuterated dimethyl sulfoxide, and olefin protons The content of the structural unit (1) was calculated from the integrated value of the peak (5.0 to 7.5 ppm) of the vinyl alcohol, and the peak (3.1 to 4.0 ppm) derived from the main chain methine proton of the vinyl alcohol structure was converted to vinyl alcohol. The unit content was calculated.

[Evaluation of water resistance of aqueous ink composition]
The aqueous ink composition obtained in the following Examples or Comparative Examples was applied on a polyethylene terephthalate substrate using a bar coater (gap: 0.2 mm) to obtain a coating. This coating was irradiated with ultraviolet light at an intensity of 4500 mJ / cm ² to obtain a cured product of the aqueous ink composition. A part of this was cut out together with the polyethylene terephthalate substrate, and the weight was measured [W1]. The cut piece was immersed in ion-exchanged water at room temperature and allowed to stand for 24 hours. The small piece was taken out, lightly wiped off the surface, and the weight after water absorption was measured [W2]. This was dried with a vacuum dryer at 80 ° C. for 1 hour and weighed again [W3]. The dissolution rate and the degree of swelling were calculated according to the following equations.

Elution rate [%] = ([W1] − [W3]) / [W1] × 100
Swelling magnification [times] = [W2] / [W1]

[Synthesis Example 1]
315 parts by mass of dimethyl sulfoxide, 585 parts by mass of methyl methacrylate, 1.1 parts by mass of phenothiazine, and 1.5 parts by mass of sodium acetate were charged into a reactor equipped with a stirrer, a reflux tube, and an addition port, and the mixture was stirred at room temperature and marketed. Of polyvinyl alcohol (PVA 22-88 manufactured by Kuraray Co., Ltd.) was added, the temperature was increased to 100 ° C. with stirring, and the mixture was reacted in a slurry state for 3 hours. Thereafter, the reaction mixture was cooled to room temperature, the content was filtered to collect a reaction product, washed with methanol, and then dried at 40 ° C. and 1.3 Pa for 20 hours to obtain a modified polyvinyl alcohol (A-1). .

[Synthesis Example 2]
315 parts by mass of dimethyl sulfoxide, 585 parts by mass of methyl methacrylate, 1.1 parts by mass of phenothiazine, and 1.5 parts by mass of sodium acetate were charged into a reactor equipped with a stirrer, a reflux tube, and an addition port, and the mixture was stirred at room temperature and commercially available Of polyvinyl alcohol (PVA 5-88 manufactured by Kuraray Co., Ltd.) was added, the temperature was increased to 100 ° C. while stirring, and the mixture was reacted in a slurry state for 1.5 hours. Thereafter, the reaction mixture was cooled to room temperature, the content was filtered, the reaction product was recovered, washed with methanol, and then dried at 40 ° C. and 1.3 Pa for 20 hours to obtain a modified polyvinyl alcohol (A-2). .

[Synthesis Example 3]
180 parts by mass of dimethyl sulfoxide, 720 parts by mass of methyl acrylate, 1.1 parts by mass of phenothiazine, and 1.1 parts by mass of sodium acetate were charged into a reactor equipped with a stirrer, a reflux tube, and an addition port, and the mixture was stirred at room temperature and commercially available. Of polyvinyl alcohol (PVA 5-74, manufactured by Kuraray Co., Ltd.) was added, the temperature was raised to 80 ° C. with stirring, and the mixture was reacted in a slurry state for 1 hour. Thereafter, the mixture was cooled to room temperature, the content was filtered to collect a reaction product, washed with methanol, and then dried at 40 ° C. and 1.3 Pa for 20 hours to obtain a modified polyvinyl alcohol (A-3). .

[Synthesis Example 4]
9 parts by mass of itaconic acid and 0.2 parts by mass of propyl gallate were dissolved in 100 parts by mass of methanol. 100 parts by mass of a commercially available polyvinyl alcohol resin (PVA 28-98, manufactured by Kuraray Co., Ltd.) was added thereto, and the mixture was allowed to stand at room temperature for 3 hours, and then methanol was distilled off under reduced pressure. Thereafter, the obtained particles were heat-treated at 120 ° C. for 4 hours to obtain a modified polyvinyl alcohol (A-4).

[Synthesis Example 5]
A reactor equipped with a stirrer, a reflux tube, and an addition port was charged with 100 parts by mass of commercially available polyvinyl alcohol (PVA 22-88 manufactured by Kuraray Co., Ltd.) and 400 parts by mass of dimethyl sulfoxide to prepare a solution having a concentration of 20% by mass. Here, 65 parts by mass of methyl 3,3-dimethylpentenoate and 0.4 parts by mass of tetramethylammonium methyl carbonate were added, the temperature was raised to 100 ° C. under a nitrogen stream, and the mixture was reacted in a slurry state for 5 hours. Thereafter, the mixture was cooled to room temperature, the solution was dropped into methanol to collect a reaction product, washed with methanol, and then dried at 40 ° C. and 1.3 Pa for 20 hours to obtain a modified polyvinyl alcohol (A ′). .

[Examples 1 to 4 and Comparative Examples 1 and 2]
7.28 parts by mass of the modified polyvinyl alcohol obtained in the above-mentioned synthesis example (unmodified polyvinyl alcohol (Kuraray Co., Ltd., PVA 28-98) was used in Comparative Example 1), and polyethylene glycol diacrylate (new 1.36 parts by mass of A-400 manufactured by Nakamura Chemical Industry Co., Ltd., 0.49 parts by mass of 4-acryloylmorpholine (manufactured by Tokyo Chemical Industry Co., Ltd.), and carbon black (MA100 manufactured by Mitsubishi Chemical Corporation) as a coloring material. 23 parts by mass, 0.74 parts by mass of 2-hydroxy-4 '-(2-hydroxyethoxy) -2-methylpropiophenone (manufactured by Tokyo Chemical Industry Co., Ltd.) as a photopolymerization initiator, and 88.9 parts by mass of ion-exchanged water Were mixed to obtain an aqueous ink composition. Table 1 shows the evaluation results.

  As is clear from Examples 1 to 4, the composition for aqueous ink of the present invention can be cured by, for example, ultraviolet rays, and the cured product has water resistance. For this reason, there is no fear of bleeding or outflow of ink due to contact with water after printing. Therefore, the aqueous ink composition of the present invention can be used as a photocurable aqueous ink.

  When unmodified polyvinyl alcohol is used as in Comparative Example 1, the aqueous ink composition does not cure even after irradiation with ultraviolet light, and does not exhibit water resistance. As in Comparative Example 2, when a modified polyvinyl alcohol having a structure different from the structure specified in the present application is used, the aqueous ink composition does not cure even after irradiation with ultraviolet light, and does not exhibit water resistance.

Claims (2)

An aqueous ink composition comprising a modified polyvinyl alcohol (A) containing a structural unit represented by the following formula (1) in a range of 0.1 to 5.0 mol%, water, a photopolymerization initiator, and a coloring material.

[In the formula (1), R ¹ represents a hydrogen atom, a methyl group, a carboxyl group or a carboxymethyl group] The aqueous ink composition according to claim 1, wherein R ¹ is a methyl group.