Binder for aqueous pigment ink, and aqueous pigment ink composition

Abstract

To provide a binder for an aqueous pigment ink, and an aqueous pigment ink composition, which exhibit excellent adhesion strength at an interface between a substrate and an ink layer and excellent peeling strength within the ink layer.SOLUTION: A binder for an aqueous pigment ink contains a polyolefin emulsion and a synthetic emulsion excluding the polyolefin emulsion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a binder for a water-based pigment ink and a water-based pigment ink composition. [Background technology]

[0002] In recent years, plastic films have come to be used in various fields as packaging materials. Printing on such plastic films is carried out by gravure printing, flexographic printing, inkjet printing, etc. For example, printing inks for plastic films are required to have excellent printability, adhesion, blocking resistance, gloss, etc. on a wide variety of films.

[0003] Traditionally, solvent-based pigment inks using organic solvents as dispersion media or UV-curable inks have been primarily used for printing on low- or non-absorbent substrates. This is because organic solvents penetrate low- or non-absorbent substrates, swelling the surface and immobilizing the pigment within the substrate. They also form a strong resin coating on the substrate after printing, improving bleed and abrasion resistance. However, these conventional inks have issues, such as environmental impacts due to the large amount of organic solvents that disperse into the atmosphere as they dry, and potential safety concerns due to the radical initiators and monomers used in UV-curable inks. For this reason, efforts are currently underway to develop water-based pigment inks that are less harmful to the working environment and the natural environment.

[0004] Patent Document 1 discloses an inkjet ink that contains an aqueous medium and resin particles containing a pigment and a resin dispersed in the aqueous medium, and that has excellent fixability and intermittent ejection properties on non-permeable recording media. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-047783 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inkjet ink described in Patent Document 1 cited above is insufficient in terms of the interfacial adhesive strength between the substrate and the ink layer, and the intralayer peel strength of the ink layer.

[0007] An object of the present invention is to provide a binder for a water-based pigment ink and a water-based pigment ink composition that are excellent in interfacial adhesive strength between a substrate and an ink layer and in intralayer peel strength of the ink layer. [Means for solving the problem]

[0008] The present invention provides the following: [1] A binder for water-based pigment inks containing a polyolefin emulsion and a synthetic emulsion (excluding the polyolefin emulsion).

[0009] [2] The binder for water-based pigment inks according to [1], wherein the polyolefin emulsion contains at least one emulsion selected from the group consisting of polyethylene emulsions and polypropylene emulsions.

[0010] [3] The binder for water-based pigment inks according to [1] or [2], wherein the melting point of the polyolefin emulsion is 90°C or lower.

[0011] [4] The binder for water-based pigment ink according to any one of [1] to [3], wherein the synthetic emulsion contains at least one emulsion selected from the group consisting of a conjugated diene-based latex, a styrene-based emulsion, a (meth)acrylic acid ester-based emulsion, a urethane-based emulsion, and an ethylene vinyl acetate-based emulsion.

[0012] [5] The binder for water-based pigment ink according to any one of [1] to [4], wherein the synthetic emulsion contains at least one selected from the group consisting of a conjugated diene-based latex and a styrene-based emulsion.

[0013] [6] The binder for water-based pigment ink according to any one of [1] to [5], wherein the glass transition temperature of the synthetic emulsion is −40 to 130° C.

[0014] [7] The binder for aqueous pigment inks according to any one of [1] to [6], wherein the proportion of the solid content of the polyolefin emulsion relative to the total amount of the solid content of the polyolefin emulsion and the synthetic emulsion is 20 to 80 mass %, and the proportion of the solid content of the synthetic emulsion is 20 to 80 mass %.

[0015] [8] The binder for water-based pigment ink according to any one of [1] to [7], which is for inkjet printing.

[0016] [9] The binder for water-based pigment ink according to any one of [1] to [8], which is for printing on a non-absorbent substrate.

[0017]

[10] A water-based pigment ink composition comprising the binder for water-based pigment ink according to any one of [1] to [9] and a pigment. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a binder for a water-based pigment ink and a water-based pigment ink composition that are excellent in interfacial adhesive strength between a substrate and an ink layer and in intralayer peel strength of the ink layer. DETAILED DESCRIPTION OF THE INVENTION

[0019] The binder for the water-based pigment ink of this embodiment contains a polyolefin emulsion and a synthetic emulsion (excluding polyolefin emulsion).

[0020] Examples of polyolefin emulsions include polyethylene emulsion, polypropylene emulsion, polybutene emulsion, polyhexene emulsion, and modified emulsions thereof, and one or more of these can be used. Among them, at least one emulsion selected from the group consisting of polyethylene emulsion and polypropylene emulsion is preferred, and polypropylene emulsion is more preferred, because it provides a better balance between the interfacial adhesive strength between the substrate and the ink layer and the intralayer peel strength of the ink layer, particularly the interfacial adhesive strength between the non-permeable substrate or resin substrate and the ink layer.

[0021] As the polyolefin emulsion, commercially available products can also be used, such as SUMIFITT (registered trademark) (manufactured by Sumitomo Chemical Co., Ltd.), ARROWBASE (registered trademark) (manufactured by Unitika Ltd.), ZAIKXEN (registered trademark) (manufactured by Sumitomo Seika Chemicals Co., Ltd.), CHEMIPEARL (registered trademark) (manufactured by Mitsui Chemicals, Inc.), LIOFLEX (registered trademark) (manufactured by Artience), and MGP series (manufactured by Maruyoshi Chemical Co., Ltd.).

[0022] The melting point of the polyolefin emulsion is preferably 90°C or lower. By setting the melting point within the above range, the balance between the interfacial adhesive strength between the substrate and the ink layer and the intralayer peel strength of the ink layer can be improved, particularly the interfacial adhesive strength in the low drying temperature range. The melting point of the polyolefin emulsion can be measured by the method described in the Examples below. When there are two or more melting points, it is preferable that all of the melting points are 90°C or lower. The melting point of the polyolefin emulsion is more preferably 20 to 80°C, and even more preferably 40 to 70°C, in order to improve the balance between the interfacial adhesive strength between the substrate and the ink layer and the intralayer peel strength of the ink layer, particularly the interfacial adhesive strength in the low drying temperature range.

[0023] The average particle size of the polyolefin emulsion is preferably 50 to 300 nm, more preferably 70 to 250 nm, and even more preferably 80 to 200 nm. By adjusting the particle size to within the above range, the intralayer peel strength of the ink layer can be further improved. The average particle size of the polyolefin emulsion can be measured by dynamic light scattering using a photon correlation method in accordance with JIS Z8826.

[0024] The polyolefin emulsion may contain additives such as preservatives, antioxidants, pH adjusters, crosslinking agents, viscosity adjusters, surfactants, etc. The types and amounts of these additives can be adjusted appropriately.

[0025] The synthetic emulsion is a synthetic emulsion other than the above-mentioned polyolefin emulsion, and examples thereof include conjugated diene-based latex, styrene-based emulsion, (meth)acrylic acid ester-based emulsion, vinyl acetate-based emulsion, urethane-based emulsion, vinyl chloride-based emulsion, polyethylene terephthalate emulsion, ethylene vinyl acetate-based emulsion, vinylidene chloride-based emulsion, and polyvinyl alcohol-based emulsion, and these can be used alone or in combination of two or more. Among these, it is preferable to contain at least one selected from the group consisting of conjugated diene-based latex, styrene-based emulsion, (meth)acrylic acid ester-based emulsion, urethane-based emulsion, and ethylene vinyl acetate-based emulsion, because this provides a better balance between the interfacial adhesive strength between the substrate and the ink layer and the intralayer peel strength of the ink layer, and it is even more preferable to contain at least one selected from the group consisting of conjugated diene-based latex and styrene-based emulsion, because this provides a better balance between the interfacial adhesive strength between the substrate and the ink layer, the intralayer peel strength of the ink layer, and the color development properties of the ink layer.

[0026] Examples of conjugated diene latexes include styrene-butadiene latexes, acrylonitrile-butadiene latexes, methyl methacrylate-butadiene latexes, styrene-butadiene-vinylpyridine latexes, butadiene latexes, and natural rubber latexes, and these can be used alone or in combination.

[0027] The conjugated diene-based latex may be a polymer of an aliphatic conjugated diene-based monomer and, if necessary, other copolymerizable monomers.

[0028] Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene, substituted and side-chain conjugated hexadienes, etc., and these can be used alone or in combination of two or more. From the viewpoints of industrial ease of production, availability, and cost, 1,3-butadiene is particularly preferred.

[0029] Other copolymerizable monomers include alkenyl aromatic monomers, vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, ethylenically unsaturated carboxylic acid monomers, unsaturated monomers containing a hydroxyalkyl group, and unsaturated carboxylic acid amide monomers, and these can be used alone or in combination of two or more.

[0030] Examples of alkenyl aromatic monomers include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyltoluene, divinylbenzene, etc., which can be used alone or in combination of two or more. From the viewpoints of industrial ease of production, availability, and cost, styrene is particularly preferred.

[0031] Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, etc., which can be used alone or in combination of two or more. From the viewpoints of industrial ease of production, availability, and cost, it is particularly preferred to use acrylonitrile or methacrylonitrile.

[0032] Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate, and these can be used alone or in combination of two or more. Methyl methacrylate is particularly preferred from the viewpoints of industrial ease of production, availability, and cost.

[0033] Examples of the ethylenically unsaturated carboxylic acid monomer include monobasic acids or dibasic acids (anhydrides) such as itaconic acid, acrylic acid, methacrylic acid, crotonic acid, maleic acid, and fumaric acid, and these can be used alone or in combination of two or more.

[0034] Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di-(ethylene glycol) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis(2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate, and these can be used alone or in combination of two or more.

[0035] Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, and N,N-dimethylacrylamide, and these can be used alone or in combination of two or more.

[0036] In addition to the above monomers, any of the monomers used in ordinary emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, and vinylidene chloride, can also be used.

[0037] The content of the aliphatic conjugated diene monomer unit in the polymer is preferably 10 to 70% by mass, more preferably 20 to 50% by mass, and even more preferably 25 to 40% by mass. By setting the content within this range, the blocking resistance and intralayer peel strength of the ink layer can be further improved.

[0038] The content of other copolymerizable monomer units in the polymer is preferably 30 to 90% by mass, more preferably 50 to 80% by mass, and even more preferably 60 to 75% by mass.

[0039] The content of the alkenyl aromatic monomer unit in the polymer is preferably 10 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 50 to 65% by mass. By setting the content within the above range, the flexibility of the ink layer can be improved.

[0040] The content of the vinyl cyanide monomer unit in the polymer is preferably 1 to 40% by mass, more preferably 2 to 30% by mass, and even more preferably 3 to 20% by mass. By keeping it within this range, the solvent resistance of the ink layer can be further improved.

[0041] The content of the unsaturated carboxylic acid alkyl ester monomer unit in the polymer is preferably 0.1 to 70% by mass, more preferably 0.5 to 50% by mass, and even more preferably 1 to 10% by mass. By setting the content within the above range, the flexibility of the ink layer can be improved.

[0042] The content of the ethylenically unsaturated carboxylic acid monomer unit in the polymer is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass. By keeping it within this range, the particle stability of the synthetic emulsion in the aqueous pigment ink composition can be further improved.

[0043] The content of the hydroxyalkyl group-containing unsaturated monomer unit in the polymer is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and even more preferably 0.5 to 3% by mass. By keeping it within this range, the particle stability of the synthetic emulsion in the aqueous pigment ink composition can be further improved.

[0044] The content of the unsaturated carboxylic acid amide monomer unit in the polymer is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, and even more preferably 0.3 to 3% by mass. By keeping it within this range, the particle stability of the synthetic emulsion in the aqueous pigment ink composition can be further improved.

[0045] Examples of the conjugated diene latex include a polymer of an aliphatic conjugated diene monomer (preferably 10 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 30 to 70% by mass), an alkenyl aromatic monomer (preferably 20 to 80% by mass, more preferably 25 to 75% by mass, and even more preferably 30 to 70% by mass), and other copolymerizable monomers (preferably 60% by mass or less, more preferably 10 to 50% by mass, and even more preferably 15 to 40% by mass), an aliphatic conjugated diene monomer (preferably 10 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 30 to 70% by mass), a vinyl cyanide monomer (preferably 10 to 50% by mass, more preferably 15 to 4 ... or 20 to 45% by mass, and more preferably 30 to 40% by mass), and other copolymerizable monomers (preferably 25% by mass or less, more preferably 5 to 20% by mass, and even more preferably 10 to 15% by mass); and polymers of aliphatic conjugated diene monomers (preferably 10 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 30 to 70% by mass), unsaturated carboxylic acid alkyl ester monomers (preferably 20 to 80% by mass, more preferably 25 to 75% by mass, and even more preferably 30 to 70% by mass), and other copolymerizable monomers (preferably 40% by mass or less, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass).

[0046] The styrene emulsion may contain a polymer of an alkenyl aromatic monomer and, if necessary, other copolymerizable monomers. The other copolymerizable monomers may be the above-mentioned monomers other than the alkenyl aromatic monomer, and one or more of these may be used.

[0047] The content of alkenyl aromatic monomer units in the polymer is preferably 60 to 100% by mass, more preferably 70 to 95% by mass, and even more preferably 80 to 90% by mass. By setting it within the above range, blocking resistance can be further improved.

[0048] The content of other copolymerizable monomer units in the polymer is preferably 0 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass.

[0049] The content of the aliphatic conjugated diene monomer unit in the polymer is preferably less than 25% by mass, more preferably less than 20% by mass, and even more preferably less than 10% by mass.

[0050] The content of the vinyl cyanide monomer unit in the polymer is preferably 1 to 45% by mass, more preferably 3 to 30% by mass, and even more preferably 5 to 15% by mass. By keeping it within the above range, the solvent resistance of the ink layer can be further improved.

[0051] The content of the ethylenically unsaturated carboxylic acid monomer unit in the polymer is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass. By keeping it within this range, the particle stability of the synthetic emulsion in the aqueous pigment ink composition can be further improved.

[0052] The (meth)acrylic acid ester emulsion may include a polymer of an unsaturated carboxylic acid alkyl ester monomer and, if necessary, other copolymerizable monomers. The other copolymerizable monomers may include the above-mentioned monomers other than the unsaturated carboxylic acid alkyl ester monomer, and one or more of them may be used.

[0053] The content of the unsaturated carboxylic acid alkyl ester monomer unit in the polymer is preferably 15 to 90 mass %, more preferably 20 to 85 mass %, and even more preferably 25 to 80 mass %.

[0054] The content of other copolymerizable monomer units in the polymer is preferably from 10 to 85% by mass, more preferably from 15 to 80% by mass, and even more preferably from 20 to 75% by mass.

[0055] The content of the aliphatic conjugated diene monomer unit in the polymer is preferably less than 25% by mass, more preferably less than 20% by mass, and even more preferably less than 10% by mass.

[0056] The content of alkenyl aromatic monomer units in the polymer is preferably less than 80% by mass, more preferably less than 70% by mass, and even more preferably less than 60% by mass.

[0057] The urethane emulsion may be a polymer having a urethane bond formed by the reaction of an isocyanate group with a hydroxyl group, and may also have, in addition to the urethane bond, a urea bond formed by the reaction of an isocyanate group with an amino group or water, an amide bond formed by the reaction of an isocyanate group with a carboxyl group, an allophanate group formed by the reaction of an isocyanate group with a urethane bond, or a biuret group formed by the reaction of an isocyanate group with a urea bond.

[0058] Urethane emulsions are obtained, for example, by the reaction of polyisocyanate and polyol, and in addition to the polyol, compounds containing active hydrogen other than the polyol (such as polyamines) may be added. Furthermore, to improve water dispersibility, polyols having hydrophilic groups can be used. Examples of such hydrophilic groups include carboxyl groups or their salts, sulfonic acid groups or their salts, and groups having a polyoxyethylene skeleton.

[0059] Urethane emulsions include self-emulsifying or forced-emulsifying water dispersions.

[0060] The self-emulsifying aqueous dispersion can be obtained, for example, by a method of dispersing the polyurethane having the above-mentioned hydrophilic group introduced therein in water (the polymer may be polymerized with an organic solvent such as acetone, and the organic solvent may be removed after the dispersion in water), or by a method of dispersing the isocyanate prepolymer having the above-mentioned hydrophilic group introduced therein in water and extending the chains with a chain extender.

[0061] A forced emulsification type aqueous dispersion can be obtained, for example, by dispersing a polyurethane solution (a solution of solution-polymerized polyurethane or a solution of solvent-free synthesized polyurethane in an organic solvent) in water and then removing the organic solvent.

[0062] Examples of the polyisocyanate include aromatic polyisocyanates, araliphatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates.

[0063] Aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate / 2,6-tolylene diisocyanate mixture, m-xylylene diisocyanate, p-xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate / 4,4'-diphenylmethane diisocyanate mixture, and 4,4'-diphenyl ether. Examples of diisocyanate include 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, and 3,3'-dimethoxydiphenyl-4,4'-diisocyanate.

[0064] Examples of the aromatic aliphatic polyisocyanate include 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene or a mixture thereof, and ω,ω'-diisocyanato-1,4-diethylbenzene.

[0065] Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, and trioxyethylene diisocyanate.

[0066] Examples of the alicyclic polyisocyanate include isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate.

[0067] Examples of the polyol include polyester polyol, polyether polyol, polycarbonate polyol, and polyolefin polyol.

[0068] Examples of polyester polyols include dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, succinic acid, tartaric acid, oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, glutaconic acid, azelaic acid, sebacic acid, 1,4-cyclohexyldicarboxylic acid, α-hydromuconic acid, β-hydromuconic acid, α-butyl-α-ethylglutaric acid, α,β-diethylsuccinic acid, maleic acid, and fumaric acid, and anhydrides thereof; and polyester polyols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol. and one or more of the following polyols: 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 3,3-dimethylolheptane, diethylene glycol, dipropylene glycol, neopentyl glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, glycerin, trimethylolpropane, diol dimer acid, ethylene oxide or propylene oxide adduct of bisphenol A, bis(β-hydroxyethyl)benzene, and xylylene glycol.

[0069] Examples of polyether polyols include polyether polyols obtained by addition polymerization of alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, etc., using as an initiator a compound having two active hydrogen groups, such as a low molecular weight polyol or a low molecular weight polyamine such as ethylene diamine, propylene diamine, toluene diamine, metaphenylenediamine, diphenylmethane diamine, xylylene diamine, etc. Further examples of polyether polyols include polyether polyols obtained by ring-opening polymerization of cyclic ether monomers such as alkyl glycidyl ethers such as methyl glycidyl ether, aryl glycidyl ethers such as phenyl glycidyl ether, and tetrahydrofuran.

[0070] Examples of polycarbonate polyols include those obtained by a dealcoholization reaction or a dephenolation reaction between one or more low-molecular-weight polyols and one or more carbonates such as dialkyl carbonates (e.g., dimethyl carbonate, diethyl carbonate), alkylene carbonates (e.g., ethylene carbonate, propylene carbonate), diphenyl carbonate, dinaphthyl carbonate, dianthryl carbonate, diphenanthryl carbonate, and diindanyl carbonate.

[0071] Examples of polyolefin polyols include hydroxyl-terminated polybutadiene and its hydrogenated products, and hydroxyl-containing chlorinated polyolefins.

[0072] The ethylene vinyl acetate emulsion may contain a polymer of ethylene, vinyl acetate, and, if necessary, other copolymerizable monomers. The other copolymerizable monomers may be the above-mentioned monomers other than ethylene and vinyl acetate, and one or more of these may be used.

[0073] The synthetic emulsion can be obtained, for example, by emulsion polymerization of the monomer components that constitute the polymer. In addition to the monomer components, the emulsion polymerization reaction system can contain an emulsifier (surfactant), a polymerization initiator, and, if necessary, a chain transfer agent, a reducing agent, etc. The method for adding the various components is not particularly limited, and any of a lump-sum addition method, a divided addition method, a continuous addition method, and a power feed method can be used. Alternatively, batch polymerization, semi-batch polymerization, seed polymerization, etc. can be used.

[0074] Examples of emulsifiers (surfactants) include anionic surfactants such as sulfate salts of higher alcohols, alkylbenzenesulfonates, alkyldiphenyletherdisulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, formalin condensates of naphthalenesulfonic acid, and sulfate salts of nonionic surfactants, and nonionic surfactants such as alkyl esters, alkylphenyl ethers, and alkyl ethers of polyethylene glycols. These can be used alone or in combination of two or more.

[0075] Examples of chain transfer agents include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan; xanthogen compounds such as dimethyl xanthogen disulfide and diisopropyl xanthogen disulfide; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide; 2,6-di-t-butyl-4-methylphenol, sulfur compounds, and the like. Examples of suitable chain transfer agents include phenolic compounds such as ethyleneated phenol; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, and carbon tetrabromide; vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, and α-benzyloxyacrylamide; and chain transfer agents such as triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, terpinolene, and α-methylstyrene dimer. These can be used alone or in combination of two or more. The amount of chain transfer agent can be adjusted appropriately taking into account the combination with other additives, etc.

[0076] Furthermore, for the purpose of controlling the molecular weight and crosslinking structure of the polymer, hydrocarbon compounds such as saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, and cycloheptane; unsaturated hydrocarbons such as pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, and 1-methylcyclohexene; and aromatic hydrocarbons such as benzene, toluene, and xylene can be blended. These can be used alone or in combination of two or more. Of these, cyclohexene and toluene are preferably used.

[0077] Furthermore, if necessary, the reaction system may contain additives such as electrolytes, oxygen scavengers, chelating agents, dispersants, antifoaming agents, antioxidants, preservatives, antibacterial agents, flame retardants, ultraviolet absorbers, etc. These additives may be used in appropriate amounts and of appropriate types.

[0078] The glass transition temperature of the synthetic emulsion is preferably -40 to 130°C. A glass transition temperature of -40°C or higher provides a better balance between the interfacial adhesive strength between the substrate and the ink layer, the intralayer peel strength of the ink layer, and the blocking resistance of the ink layer. A glass transition temperature of 130°C or lower provides a better balance between the interfacial adhesive strength between the substrate and the ink layer, the intralayer peel strength of the ink layer, runnability, and flexibility of the ink layer. The glass transition temperature of the synthetic emulsion can be measured by the method described in the Examples below. From the viewpoint of a better balance between the interfacial adhesive strength between the substrate and the ink layer, the intralayer peel strength of the ink layer, and the blocking resistance of the ink layer, the glass transition temperature is more preferably -20°C or higher, even more preferably -10°C or higher, and particularly preferably 0°C or higher. From the viewpoint of achieving a better balance between the interfacial adhesive strength between the substrate and the ink layer, the intralayer peel strength of the ink layer, runnability, and flexibility of the ink layer, the glass transition temperature is more preferably 120° C. or less, even more preferably 115° C. or less, and particularly preferably 105° C. or less. The glass transition temperature of the synthetic emulsion can be adjusted as appropriate by the type, amount, and addition method of the monomer used during polymerization of the synthetic emulsion.

[0079] The average particle size of the synthetic emulsion is preferably 50 to 300 nm, more preferably 70 to 250 nm, and even more preferably 80 to 200 nm. By adjusting the size within the above range, the intralayer peel strength of the ink layer can be further improved. The average particle size of the synthetic emulsion can be appropriately adjusted by the emulsifier concentration, etc. The average particle size of the synthetic emulsion can be measured by dynamic light scattering using a photon correlation method in accordance with JIS Z8826.

[0080] The synthetic emulsion may contain additives such as dispersants, preservatives, antioxidants, printability improvers, surfactants, pH adjusters, crosslinking agents, viscosity adjusters, etc. The types and amounts of these additives may be appropriately selected and used.

[0081] The proportion of the solid content of the polyolefin emulsion relative to the total solid content of the polyolefin emulsion and synthetic emulsion in the binder for aqueous pigment inks is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass, and the proportion of the solid content of the synthetic emulsion is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass. By setting the proportion within the above ranges, it is possible to further improve the balance between the interfacial adhesive strength between the substrate and the ink layer and the intralayer peel strength of the ink layer.

[0082] The binder for the water-based pigment ink may be mixed with other binders, etc., as needed. Furthermore, additives such as preservatives, antioxidants, printability improvers, surfactants, etc. may be blended as needed. These additives may be used in appropriate amounts and of appropriate types. Furthermore, an aqueous medium or an organic solvent may be added.

[0083] Examples of aqueous media include distilled water, ion-exchanged water, tap water, and industrial water.

[0084] Examples of the organic solvent include glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin, and dimethyl sulfoxide.

[0085] Examples of glycol compounds include ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0086] Examples of glycol ether compounds include diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, and propylene glycol monomethyl ether.

[0087] Lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0088] Nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0089] The acetate compound includes diethylene glycol monoethyl ether acetate.

[0090] The total content of the solids of the polyolefin emulsion and synthetic emulsion in the binder for aqueous pigment inks may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of solids of the binder for aqueous pigment inks.

[0091] To prepare a binder for an aqueous pigment ink, for example, a polyolefin emulsion and a synthetic emulsion may be mixed at room temperature (23°C). During mixing, other binders, additives, aqueous media, organic solvents, etc. may be added as needed.

[0092] The binder for water-based pigment inks according to this embodiment has an excellent balance between the interfacial adhesive strength between the substrate and the ink layer and the intralayer peel strength of the ink layer, and is therefore useful in various printing methods such as inkjet printing, offset printing, stencil printing, gravure printing, flexographic printing, etc. In particular, the binder is suitable for inkjet printing because it has excellent interfacial adhesive strength between the substrate and the ink layer and excellent intralayer peel strength of the ink layer in the low drying temperature range required for inkjet printing.

[0093] The binder for water-based pigment inks according to this embodiment has an excellent balance between the interfacial adhesive strength between the substrate and the ink layer and the intralayer peel strength of the ink layer, and is therefore useful for printing on a variety of substrates, including substrates made of plastics such as soft vinyl chloride, hard vinyl chloride, polystyrene, expanded polystyrene, PMMA, polypropylene, polyethylene, polyester, PET, polycarbonate, mixtures thereof, or modified products thereof, paper substrates such as fine paper, art paper, coated paper, cast-coated paper, and corrugated cardboard, substrates made of metals such as stainless steel and aluminum, and glass substrates. In particular, the binder for water-based pigment inks according to this embodiment has an excellent interfacial adhesive strength between the substrate and the ink layer, and is therefore suitable for printing on non-absorbent substrates, and is particularly suitable for printing on polyvinyl chloride substrates, polyethylene substrates, and polypropylene substrates.

[0094] The water-based pigment ink composition of this embodiment contains a water-based pigment ink binder and a pigment.

[0095] The pigment is not particularly limited, and examples thereof include organic pigments and inorganic pigments used in conventional aqueous ink compositions. These may be used alone or in combination of two or more. The dispersion stability of the pigment can be improved by using a dispersant or dispersion aid (pigment derivative).

[0096] Examples of organic pigments include insoluble azo pigments, soluble azo pigments, dye derivatives, phthalocyanine organic pigments, quinacridone organic pigments, perylene organic pigments, perinone organic pigments, azomethine organic pigments, anthraquinone organic pigments (anthrone organic pigments), xanthene organic pigments, diketopyrrolopyrrole organic pigments, dioxazine organic pigments, nickel azo pigments, isoindolinone organic pigments, pyranthrone organic pigments, thioindigo organic pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments, isoindoline organic pigments, quinacridone solid solution pigments, and organic solid solution pigments such as perylene solid solution pigments. Other pigments include lake pigments and carbon black.

[0097] Examples of organic pigments by Color Index (CI) number include CI Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 117, 120, 125, 128, 129, 130, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185, 213, 214, CI Pigment Red 5, 7, 9, 12, 48, 48:2, 48:3, 49, 52, 53, 57, 57:1, 97, 112, 122, 123, 146, 149, 150, 168, 177, 180, 184, 185, 192, 202, 206, 208, 209, 213, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 269, 291, CI Pigment Orange 16, 36, 43, 51, 55, 59, 61, 64, 71, 73, CI Pigment Violet 19, 23, 29, 30, 37, 40, 50, CI Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 16, 22, 60, 64, CI Pigment Green 7, 36, 58, 59, 62, 63, CI Pigment Brown 23, 25, 26, CI Pigment Black 7, etc.

[0098] Examples of inorganic pigments include titanium oxide, barium sulfate, calcium carbonate, zinc oxide, barium carbonate, silica, talc, clay, synthetic mica, alumina, zinc oxide, lead sulfate, yellow lead, zinc yellow, red iron oxide (red iron (III) oxide), cadmium red, ultramarine, iron blue, chromium oxide green, cobalt green, umber, titanium black, synthetic iron black, and inorganic solid solution pigments.

[0099] The aqueous pigment ink composition preferably contains 50 to 200 parts by weight (solids content) of the binder for aqueous pigment inks per 100 parts by weight (solids content), more preferably 75 to 175 parts by weight, and even more preferably 100 to 150 parts by weight. By keeping the content within the above range, the viscosity of the aqueous pigment ink composition can be made more favorable.

[0100] The aqueous pigment ink composition may contain additives such as water-soluble binders (e.g., polyvinyl alcohol, starch, carboxymethyl cellulose), dispersants, and antifoaming agents, as needed. These additives may be used in appropriate amounts and of appropriate types. An aqueous medium or an organic solvent may also be added.

[0101] The total content of the solids of the pigment and the binder for the aqueous pigment ink in the aqueous pigment ink composition may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of solids of the aqueous pigment ink composition.

[0102] The aqueous pigment ink composition can be prepared, for example, by mixing the pigment and binder at room temperature (23°C). During mixing, water-soluble binders, additives, aqueous media, organic solvents, etc. can be added as needed. [Example]

[0103] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples. Furthermore, unless otherwise specified, % and parts are based on mass.

[0104] <Measurement of the melting point of polyolefin emulsion> The polyolefin emulsion was cast onto a glass plate and allowed to stand at 23°C for 12 hours. The dried product was placed in an aluminum pan and set in a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). The melting temperature was determined in accordance with JIS K 7121-1987 and used as the melting point.

[0105] <Polyolefin emulsion> A-1: Polypropylene emulsion Melting point: 56°C A-2: Polypropylene emulsion Melting point: 72°C A-3: Polypropylene emulsion Melting point: 30℃, 135℃ A-4: Polyethylene emulsion Melting point: 76℃

[0106] <Measurement of glass transition temperature of synthetic emulsion> The synthetic emulsion was cast onto a glass plate and allowed to stand at 23°C for 12 hours. The dried product was then placed in an aluminum pan and placed in a differential scanning calorimeter (DSC7020, Hitachi High-Tech Science Corporation). After cooling the apparatus to -100°C, the temperature was increased at a heating rate of 10°C / min to obtain a DSC curve. A differential curve of the resulting DSC curve was then obtained. The glass transition temperature was determined by reading the onset of endothermic heat and the maximum inflection point of the phase change on the DSC curve, drawing tangents to each point, and calculating the intersection point of the tangents. If there are multiple endothermic onset points, the onset of endothermic heat and the maximum inflection point of the phase change on the DSC curve were read at each peak whose peak height ratio to the largest peak height on the DSC differential curve was 70% or greater, and the intersection point of the tangents to each point was calculated. The average of these was used as the glass transition temperature. The peak height refers to the length of the perpendicular line drawn from the peak top of the DSC differential curve to the line connecting the onset and end points of endothermic heat on the DSC differential curve. Table 1 shows the glass transition temperatures of the synthetic emulsions B-1 to B-12.

[0107] <Synthetic emulsion> The polymerization water and first-stage polymerization components shown in Table 1 were charged all at once into a pressure-resistant polymerization reactor equipped with a stirrer, the temperature was raised to the polymerization temperature shown in Table 1, and the second-stage polymerization components shown in Table 1 were continuously added for 8 hours. After the addition of the second-stage polymerization components was completed, the temperature was raised to the aging temperature shown in Table 1, and polymerization was continued until the polymerization conversion exceeded 98%. Next, the pH was adjusted to 7 using sodium hydroxide, and steam distillation was performed to remove unreacted monomers and other low-boiling compounds, yielding synthetic emulsions B-1, 3, 4, 5, 6, 8, and 12.

[0108] The polymerization water and first-stage polymerization components shown in Table 1 were charged all at once into a pressure-resistant polymerization reactor equipped with a stirrer, and the temperature was raised to the polymerization temperature shown in Table 1. The second-stage polymerization components shown in Table 1 were then added continuously for 0.5 hours. The polymerization reaction was then carried out for 1 hour. While maintaining the reaction temperature, the third-stage polymerization components shown in Table 1 were added continuously for 3 hours. The polymerization reaction was then carried out for another hour, and the fourth-stage components shown in Table 1 were added continuously for 5 hours. After the addition of the fourth-stage polymerization components was completed, the polymerization was continued while maintaining the temperature, and was terminated when the polymerization conversion rate exceeded 98%. The pH was then adjusted to 7 using sodium hydroxide, and steam distillation was carried out to remove unreacted monomers and other low-boiling compounds, yielding Synthetic Emulsion B-2.

[0109] The polymerization water and first-stage polymerization components shown in Table 1 were charged all at once into a pressure-resistant polymerization reactor equipped with a stirrer, the temperature was raised to the polymerization temperature shown in Table 1, and the second-stage polymerization components shown in Table 1 were continuously added for 1 hour. The polymerization reaction was then carried out for 1 hour. While maintaining the reaction temperature, the third-stage polymerization components shown in Table 1 were continuously added for 6 hours. After the addition of the third-stage polymerization components was completed, the polymerization was continued while maintaining the temperature, and was terminated when the polymerization conversion rate exceeded 98%. The pH was then adjusted to 7 using sodium hydroxide, and steam distillation was carried out to remove unreacted monomers and other low-boiling compounds, yielding Synthetic Emulsion B-7.

[0110] The polymerization water and first-stage polymerization components shown in Table 1 were charged all at once into a pressure-resistant polymerization reactor equipped with a stirrer, and the temperature was raised to the polymerization temperature shown in Table 1. The second-stage polymerization components shown in Table 1 were then added continuously for 1.5 hours. The polymerization reaction was then allowed to proceed for 1.5 hours. While maintaining the reaction temperature, the third-stage polymerization components shown in Table 1 were added continuously for 4.5 hours. The polymerization reaction was then allowed to proceed for another 1.5 hours, and the fourth-stage components shown in Table 1 were added continuously for 2 hours. After the addition of the fourth-stage polymerization components was completed, the polymerization was continued while maintaining the temperature, and terminated when the polymerization conversion rate exceeded 98%. The pH was then adjusted to 7 using potassium hydroxide, and steam distillation was performed to remove unreacted monomers and other low-boiling compounds, yielding Synthetic Emulsion B-9.

[0111] The polymerization water and first-stage polymerization components shown in Table 1 were charged all at once into a pressure-resistant polymerization reactor equipped with a stirrer, and the temperature was raised to the polymerization temperature shown in Table 1 to carry out the polymerization reaction. The polymerization was terminated when the polymerization conversion rate exceeded 98%. Next, the pH was adjusted to 7 using potassium hydroxide, and steam distillation was carried out to remove unreacted monomers and other low-boiling compounds, yielding Synthetic Emulsion B-10.

[0112] The polymerization water and first-stage polymerization components shown in Table 1 were charged all at once into a pressure-resistant polymerization reactor equipped with a stirrer, and the temperature was raised to the polymerization temperature shown in Table 1. The second-stage polymerization components shown in Table 1 were then added continuously for 6 hours. The polymerization reaction was then carried out for 1 hour. While maintaining the reaction temperature, the third-stage polymerization components shown in Table 1 were added continuously for 2.5 hours. After the addition of the third-stage polymerization components was completed, the temperature was raised to the aging temperature shown in Table 1, and the polymerization was terminated when the polymerization conversion rate exceeded 98%. The pH was then adjusted to 7 using potassium hydroxide, and steam distillation was carried out to remove unreacted monomers and other low-boiling compounds, yielding Synthetic Emulsion B-11.

[0113] [Table 1]

[0114] B-13: (Meth)acrylic ester emulsion, glass transition temperature: 1°C B-14: (Meth)acrylic ester emulsion, glass transition temperature: -14°C B-15: Urethane emulsion Glass transition temperature: -40°C B-16: Vinyl acetate emulsion Glass transition temperature: 20°C

[0115] <Preparation of binder for water-based pigment ink> The polyolefin emulsion and synthetic emulsion were mixed according to the formulations shown in Tables 2 and 3, and the solid content was adjusted to 40% by mass using water to obtain binders for water-based pigment inks of Examples 1 to 25 and Comparative Examples 1 to 7.

[0116] [Table 2]

[0117] [Table 3]

[0118] <Preparation of Water-Based Pigment Ink Composition> 50% by mass of Pollux Black and 50% by mass of a binder for water-based pigment ink (solid content) were mixed, and the solid content was adjusted to 3% by mass and the pH to 8 to 10 using water and sodium hydroxide to obtain a water-based pigment ink composition.

[0119] <Evaluation of interfacial adhesive strength> The water-based pigment ink composition was applied to the base film using a wire bar at a rate of 3.5 g / m 2 After coating, the ink was immediately dried in an oven at 130°C for 5 minutes. After drying, the ink was cut into 1.5 cm wide strips with the long side perpendicular to the flow direction, and the strips were arranged on a paperboard with the coated side facing up at 0.1 cm intervals. The top and bottom of the strips were fixed to the paperboard with cellophane tape to prepare evaluation samples. A polypropylene (PP) film (product name: PP Gloss Clear, manufactured by Sheedom Co., Ltd.) was used as the base film. Visual inspection of the ink layer confirmed that the color development of the ink layer in Example 19 was inferior to that of the other examples.

[0120] A 1.5 cm wide double-sided tape (product name: Nice Tack Super Strong Type, manufactured by Nichiban Co., Ltd.) was pressed onto the coated surface of the evaluation sample, and then instantly peeled off while maintaining the vertical position. After peeling off the double-sided tape, the coated surface of the sample was visually observed, and the state in which the ink layer remained completely on the substrate was scored as 5.0, indicating the best interfacial adhesive strength, and this was used as the upper limit. The state in which the ink layer was completely removed from the substrate was scored as 1.0, indicating the worst interfacial adhesive strength, and this was used as the lower limit. All samples from the examples and comparative examples were compared with the upper and lower limit criteria and quantified in 0.1 increments. The obtained results were evaluated according to the following criteria. The results are shown in Tables 2 and 3. A: 5.0 ~ 4.1 B: 4.0 ~ 3.1 C: 3.0 ~ 2.1 D: 2.0 ~ 1.0

[0121] <Evaluation of intralayer peel strength> A 1.8 cm wide cellophane tape (product name: Cellotape (registered trademark), manufactured by Nichiban Co., Ltd.) was pressed onto the coated surface of the evaluation sample described above, and then slowly peeled off while maintaining a perpendicular orientation to prevent peeling at the interface with the substrate. After peeling off the cellophane tape, the amount of ink pigment remaining on the adhesive surface of the cellophane tape was visually observed. A state in which no pigment was found on the adhesive surface of the cellophane tape was evaluated as 5.0, indicating the best intralayer peel strength, and this was used as the upper limit. Furthermore, a state in which light could not be transmitted due to the amount of ink pigment remaining on the adhesive surface was evaluated as 1.0, indicating the worst intralayer peel strength, and this was used as the lower limit. All samples in the examples and comparative examples were compared with the upper and lower limit criteria and quantified to the nearest 0.1. The obtained results were evaluated according to the following criteria. The results are shown in Tables 2 and 3. A: 5.0 ~ 4.1 B: 4.0 ~ 3.1 C: 3.0 ~ 2.1 D: 2.0 ~ 1.0

[0122] <Evaluation of blocking resistance> The coated surface of the evaluation sample was overlaid with the same PP film as the base film. Heat sealing was performed using a TP-701-C heat seal tester manufactured by Tester Sangyo Co., Ltd., with a heat seal width of 10 mm, a sealing temperature of 150°C, a sealing pressure of 0.1 MPa, and 1 second. The PP film was then instantly peeled off while maintaining the sample perpendicular to the surface. After peeling off the PP film, the coated surface of the sample was visually observed. The state in which the ink layer remained completely on the substrate was scored as 5.0, indicating the best blocking resistance, and this was used as the upper limit. The state in which the ink layer was completely removed from the substrate was scored as 1.0, indicating the worst blocking resistance, and this was used as the lower limit. All samples from the examples and comparative examples were compared with the upper and lower limit criteria and quantified in 0.1 increments. The results were evaluated according to the following criteria. The results are shown in Tables 2 and 3. A: 5.0 ~ 4.1 B: 4.0 ~ 3.1 C: 3.0 ~ 2.1 D: 2.0 ~ 1.0

[0123] <Evaluation of operability> The interfacial adhesive strength and intralayer peel strength were determined using the same methods as those for preparing the aqueous pigment ink composition, evaluating the interfacial adhesive strength, and evaluating the intralayer peel strength described above, except that the aqueous pigment ink binders of Examples 5, 6, and 8 were prepared for evaluation by drying in an oven at 130°C for 1 minute. The results are shown in Table 4 for Examples 26 to 28, respectively. Compared to the case where the drying time was 5 minutes, the smaller the changes in interfacial adhesive strength and intralayer peel strength, the fewer the restrictions on the drying conditions for the aqueous pigment ink composition, and the better the operability tends to be.

[0124] [Table 4]

Claims

1. A binder for water-based pigment inks, comprising a polyolefin emulsion and a synthetic emulsion (excluding the polyolefin emulsion).

2. 2. The binder for water-based pigment ink according to claim 1, wherein the polyolefin emulsion contains at least one emulsion selected from the group consisting of a polyethylene emulsion and a polypropylene emulsion.

3. 2. The binder for water-based pigment ink according to claim 1, wherein the melting point of the polyolefin emulsion is 90° C. or lower.

4. 2. The binder for water-based pigment ink according to claim 1, wherein the synthetic emulsion contains at least one emulsion selected from the group consisting of a conjugated diene-based latex, a styrene-based emulsion, a (meth)acrylic acid ester-based emulsion, a urethane-based emulsion, and an ethylene vinyl acetate-based emulsion.

5. 2. The binder for water-based pigment ink according to claim 1, wherein the synthetic emulsion contains at least one selected from the group consisting of a conjugated diene-based latex and a styrene-based emulsion.

6. 2. The binder for water-based pigment ink according to claim 1, wherein the synthetic emulsion has a glass transition temperature of -40 to 130°C.

7. 2. The binder for aqueous pigment inks according to claim 1, wherein a ratio of the solid content of the polyolefin emulsion to the total amount of the solid content of the polyolefin emulsion and the synthetic emulsion is 20 to 80 mass %, and a ratio of the solid content of the synthetic emulsion is 20 to 80 mass %.

8. 2. The binder for a water-based pigment ink according to claim 1, which is for inkjet printing.

9. 2. The binder for water-based pigment ink according to claim 1, which is for printing on a non-absorbent substrate.

10. A water-based pigment ink composition comprising the binder for water-based pigment inks according to any one of claims 1 to 9 and a pigment.

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