Binder for aqueous inkjet ink, aqueous inkjet ink, and printed layer

Abstract

The present invention provides: a binder for aqueous inkjet inks that contains a composite resin (A) and an aqueous medium (B), the binder being characterized in that the composite resin (A) forms core-shell particles each having a shell portion that contains a polyurethane (a1) having an acid group and a core portion that contains an acrylic polymer (a2); an aqueous inkjet ink containing the binder for aqueous inkjet inks; and a printed layer. This binder for aqueous inkjet inks has excellent rub fastness in printed materials on plain paper, coated paper, film, and the like, and excellent wash fastness on fabrics, and thus can be optimally used in printing on various recording media.

Description

[Technical Field]

[0001] The present invention relates to a binder for an aqueous inkjet ink, an aqueous inkjet ink, and a printed layer. [Background technology]

[0002] Inkjet (IJ) recording devices use a printing method in which small droplets of ink composition are propelled onto a recording medium such as paper to print. With the growing demand for on-demand printing, the use of IJ printers has rapidly expanded in recent years for industrial wide-format applications, textile applications, flexible packaging applications, and more.

[0003] As an inkjet ink for use in the inkjet recording device, for example, one containing a polycarbonate-based urethane resin with a breaking elongation of 300% or more has been proposed (see Patent Document 1). However, this ink has the problem of insufficient scratch resistance and wash resistance of printed matter, which have recently been highly demanded. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6119919 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a binder for aqueous inkjet inks that can produce printed matter that is excellent in abrasion resistance and washability. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that a binder for an aqueous inkjet ink containing a specific composite resin and an aqueous medium can solve the above-mentioned problems, and have completed the present invention.

[0007] That is, the present invention relates to a binder for aqueous inkjet inks, which comprises a composite resin (A) and an aqueous medium (B), wherein the composite resin (A) forms core-shell particles having a shell portion containing a polyurethane (a1) having an acid group and a core portion containing an acrylic polymer (a2). [Effects of the Invention]

[0008] The binder for aqueous inkjet inks of the present invention is excellent in abrasion resistance of printed materials such as plain paper, coated paper, and film, and in washing resistance of fabrics, and therefore can be suitably used for printing on various recording media. DETAILED DESCRIPTION OF THE INVENTION

[0009] The binder for aqueous inkjet ink of the present invention is a binder for aqueous inkjet ink containing a composite resin (A) and an aqueous medium (B), in which the composite resin (A) forms core-shell particles having a shell portion containing a polyurethane (a1) having an acid group and a core portion containing an acrylic polymer (a2) having a hydroxyl group.

[0010] The core-shell particles of the composite resin (A) have a morphology in which the polyurethane (a1) entraps and coats a part or all of the acrylic polymer (a2) inside, and are dispersed in the aqueous medium (B).

[0011] The polyurethane (a1) constituting the shell portion of the composite resin (A) is obtained by a reaction between a polyol and a polyisocyanate, and the acid group contained in the polyurethane (a1) can be easily introduced into the polyurethane (a1) by using a polyol having an acid group as one of the components constituting the polyol.

[0012] The polyol having an acid group includes a diol having a carboxyl group or a sulfonic acid group, and preferably includes a diol having a carboxyl group. Examples of the diol having a carboxyl group include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvaleric acid. Among these, 2,2-dimethylolpropionic acid is preferred. Polyester polyols having a carboxyl group obtained by reacting the polyol having a carboxyl group with various polycarboxylic acids can also be used. Examples of the polycarboxylic acid include aliphatic polycarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; alicyclic polycarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and cyclohexanetricarboxylic acid; aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and acid anhydrides thereof. These polyols can be used alone or in combination of two or more.

[0013] Examples of the polyol having a sulfonic acid group include polyester polyols obtained by reacting dicarboxylic acids such as 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfophthalic acid, and 5[4-sulfophenoxy]isophthalic acid or salts thereof with the low-molecular-weight polyols listed above as examples usable for producing polyester polyols having an aromatic structure. These polyols can be used alone or in combination of two or more.

[0014] Examples of other polyols that can be used in combination with the polyol having an acid group include polyether polyols, polyester polyols, and polycarbonate polyols.

[0015] Examples of the polyether polyol include those obtained by addition polymerization of alkylene oxide using one or more compounds having two or more active hydrogen atoms as an initiator.

[0016] Examples of the initiator include ethylene glycol, diethylene glycol, triethylene glycol, trimethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, glycerin, trimethylolethane, trimethylolpropane, sorbitol, sucrose, aconite sugar, trimellitic acid, hemimellitic acid, phosphoric acid, ethylenediamine, diethylenetriamine, triisopropanolamine, pyrogallol, dihydroxybenzoic acid, hydroxyphthalic acid, and 1,2,3-propanetrithiol.

[0017] Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, and tetrahydrofuran.

[0018] Examples of the polyester polyol include aliphatic polyester polyols and aromatic polyester polyols obtained by an esterification reaction between a low-molecular-weight polyol and a polycarboxylic acid, polyesters obtained by a ring-opening polymerization reaction of a cyclic ester compound such as ε-caprolactone, and copolymer polyesters thereof.

[0019] Examples of the low molecular weight polyol used in the production of the polyester polyol include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 2-methyl-1,3-prop ... and neopentyl glycol. Examples of the polyol include aliphatic polyols having a molecular weight of 50 to 300, such as butyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, glycerin, trimethylolpropane, ditrimethylolpropane, trimethylolpropane, and pentaerythritol; polyols having an alicyclic structure, such as cyclohexanedimethanol and hydrogenated bisphenol A; and polyols having an aromatic structure, such as bisphenol A and bisphenol F.

[0020] Examples of the polycarboxylic acid include aliphatic polycarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; alicyclic polycarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and cyclohexanetricarboxylic acid; aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and anhydrides or esters thereof.

[0021] As the polycarbonate polyol, for example, one obtained by reacting a carbonate ester with a polyol, or one obtained by reacting phosgene with bisphenol A or the like can be used.

[0022] As the carbonate ester, methyl carbonate, dimethyl carbonate, ethyl carbonate, diethyl carbonate, cyclocarbonate, diphenyl carbonate, etc. can be used.

[0023] Examples of polyols that can react with the carbonate ester include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,5-hexanediol, 2,5-hexanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, and 2-methyl-1,3-hexanediol. Examples of the polymerizable monomer that can be used include relatively low molecular weight dihydroxy compounds such as hexanediol, 2-methyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethylpropanediol, 2-methyl-1,8-octanediol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydroquinone, resorcinol, bisphenol-A, bisphenol-F, and 4,4'-biphenol; polyether polyols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; and polyester polyols such as polyhexamethylene adipate, polyhexamethylene succinate, and polycaprolactone.

[0024] The amount of the polyol having an acid group used is preferably 3 to 50% by mass based on the total amount of polyols used in producing the polyurethane (a1).

[0025] Examples of the polyisocyanate include aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate; and diisocyanates having an aliphatic or alicyclic structure such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate. Diisocyanates having an aliphatic cyclic structure are preferred because they further improve abrasion resistance and washing resistance. These polyisocyanates can be used alone or in combination of two or more.

[0026] The molar ratio (NCO / OH) of the isocyanate group (NCO) contained in the polyisocyanate to the hydroxyl group (OH) contained in the polyol is preferably 0.9 to 2.

[0027] The polyurethane (a1) may be one having a higher molecular weight obtained by using a chain extender such as polyamine.

[0028] Examples of the polyamine include diamines such as ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-4,4'-dicyclohexylmethanediamine, and 1,4-cyclohexanediamine; diamines having one primary amino group and one secondary amino group such as N-hydroxymethylaminoethylamine, N-hydroxyethylaminoethylamine, N-hydroxypropylaminopropylamine, N-ethylaminoethylamine, and N-methylaminopropylamine; Examples of suitable polyamines include amines; polyamines such as diethylenetriamine, dipropylenetriamine, and triethylenetetramine; hydrazine compounds such as hydrazine, N,N'-dimethylhydrazine, and 1,6-hexamethylenebishydrazine; dihydrazide compounds such as succinic acid dihydrazide, adipic acid dihydrazide, glutaric acid dihydrazide, sebacic acid dihydrazide, and isophthalic acid dihydrazide; and semicarbazide compounds such as β-semicarbazide propionic acid hydrazide, 3-semicarbazide-propyl-carbazate, and semicarbazide-3-semicarbazidemethyl-3,5,5-trimethylcyclohexane. These polyamines can be used alone or in combination of two or more.

[0029] The polyamine is preferably used in such a manner that the equivalent ratio of the amino group of the polyamine to the isocyanate group of the urethane prepolymer is 0.8 to 1.

[0030] The chain extension reaction is preferably carried out by producing an aqueous dispersion of polyurethane and then mixing the aqueous dispersion with the chain extender such as polyamine.

[0031] The acid value of the polyurethane (a1) is preferably from 10 to 70, more preferably from 15 to 65, since this further improves the balance of water dispersibility, abrasion resistance, and washing resistance.

[0032] The acid value of the polyurethane (a1) in the present invention is a value obtained by calculation from the raw material composition.

[0033] The weight average molecular weight of the polyurethane (a1) is preferably from 10,000 to 500,000, more preferably from 10,000 to 300,000, in order to further improve the balance of water dispersibility, abrasion resistance, and washing resistance.

[0034] In the present invention, unless otherwise specified, the weight average molecular weight and number average molecular weight are values ​​measured by gel permeation chromatography (GPC) using polystyrene as a standard sample.

[0035] The acid groups of the polyurethane (a1) are preferably neutralized with a basic compound, since this further improves the water dispersibility of the composite resin (A).

[0036] Examples of the basic compound include alkylamines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, and tripropylamine; alkanolamines such as monoethanolamine, diethanolamine, monoisopropanolamine, diisopropanolamine, N-methylethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, 2-amino-2-methylpropanol, 2-(dimethylamino)-2-methylpropanol, and N-methyldiethanolamine; organic amines such as polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; and metal hydroxides such as ammonia (water), sodium hydroxide, potassium hydroxide, and lithium hydroxide. Metal hydroxides are preferred, and potassium hydroxide is more preferred, as they further improve abrasion resistance and washing resistance. These basic compounds can be used alone or in combination of two or more.

[0037] The acrylic polymer (a2) constituting the core of the composite resin (A) is obtained by a polymerization reaction of a (meth)acrylic monomer and, if necessary, other unsaturated monomers.

[0038] Examples of the (meth)acrylic monomer include alkyl (meth)acrylates having 4 to 10 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, neopentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, cyclopentyl (meth)acrylate, and cyclohexyl (meth)acrylate; alkyl (meth)acrylates having 11 to 22 carbon atoms, such as octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and hexadecyl (meth)acrylate; allyl (meth)acrylates such as phenyl (meth)acrylate; Aralkyl (meth)acrylates having 10 to 20 carbon atoms, such as benzyl (meth)acrylate and phenethyl (meth)acrylate; allyloxyalkyl (meth)acrylates such as phenoxyethyl (meth)acrylate; hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxy-n-butyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-n-butyl (meth)acrylate, 3-hydroxy-n-butyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, N-(2-hydroxyethyl) (meth)acrylamide, glycerin mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, and lactone-modified (meth)acrylates having a terminal hydroxyl group; Nitrogen atom-containing (meth)acrylates such as; Polyoxyethylene group-containing (meth)acrylates such as polyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol polypropylene glycol copolymer (meth)acrylate, methoxypolyethylene glycol polypropylene glycol copolymer (meth)acrylate, polyethylene glycol polytetramethylene glycol copolymer (meth)acrylate, and methoxypolyethylene glycol polytetramethylene glycol copolymer (meth)acrylate; nitrogen atom-containing (meth)acrylic monomers such as (meth)acrylonitrile, (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxyethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylamide, N-(meth)acryloylmorpholine, N-(meth)acryloylpyrrolidine, N-vinylformamide, N-vinylpyrrolidone, N-vinylimidazole, N-vinylcarbazole, N-vinylquinoline, and N-vinylpiperidine; These (meth)acrylic monomers can be used alone or in combination of two or more.

[0039] Examples of the other unsaturated monomers include alkyl crotonates such as methyl crotonate and ethyl crotonate; unsaturated dicarboxylic acid alkyl esters such as dimethyl maleate, dibutyl maleate, dimethyl fumarate, dibutyl fumarate, dimethyl itaconate, and dibutyl itaconate; Aromatic vinyl monomers such as styrene, p-tert-butylstyrene, α-methylstyrene, vinyltoluene, vinylpyridine, chlorostyrene, and chloromethylstyrene; Nitrogen atom-containing monomers such as crotononitrile, N-vinylformamide, N-vinylpyrrolidone, N-vinylimidazole, N-vinylcarbazole, N-vinylquinoline, and N-vinylpiperidine; Halogenated olefins such as vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinyl chloride, and vinylidene chloride; α-olefins such as ethylene, propylene, isobutylene, and 1-butene; vinyl carboxylic acid vinyl esters such as vinyl acetate, vinyl propionate, vinyl pivalate, vinyl versatate, vinyl benzoate, and vinyl neodecanoate; Alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether; cycloalkyl vinyl ethers such as cyclohexyl vinyl ether; Carbonyl group-containing monomers such as acrolein and methyl vinyl ketone; fluoroalkyl group-containing monomers such as perfluorocyclohexyl (meth)acrylate, di-perfluorocyclohexyl fumarate, and N-isopropylfluorooctanesulfonamidoethyl (meth)acrylate; unsaturated dicarboxylic acid anhydrides such as maleic anhydride, citraconic anhydride, mesaconic anhydride, itaconic anhydride, and tetrahydrophthalic anhydride; cyclic ether-containing monomers such as glycidyl (meth)acrylate, allyl glycidyl ether, and tetrahydrofurfuryl (meth)acrylate; Silyl group-containing monomers such as vinyltrichlorosilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, and γ-(meth)acryloxypropyltrimethoxysilane; hydroxy group-containing monomers such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and 2-hydroxyethyl allyl ether; vinyl group-containing sulfonic acid compounds and their salts, such as vinyl sulfonic acid, 3-acryloxypropane-1-sulfonic acid, 3-acryloxyoctyloxybenzenesulfonic acid, 3-acryloxybenzenediazosulfonic acid, 3-acryloxyazobenzene-4'-sulfonic acid, 2-acryloylamino-2-methylpropane-1-sulfonic acid, 2-acryloylamido-2-methylpropanesulfonic acid, and acrylonitrile-tert-butylsulfonic acid; These monomers can be used alone or in combination of two or more.

[0040] In the present invention, the term "(meth)acrylic monomer" refers to either or both of an acrylic monomer and a methacrylic monomer, and the term "(meth)acrylate" refers to either or both of an acrylate and a methacrylate.

[0041] The monomer raw material for the acrylic polymer (a2) preferably contains an alkyl(meth)acrylate having 4 to 10 carbon atoms, since this further improves the abrasion resistance and washing resistance. The amount of the alkyl(meth)acrylate having 4 to 10 carbon atoms in the monomer raw material is more preferably 10 to 100 mass%, further preferably 40 to 100 mass%, and particularly preferably 50 to 100 mass%.

[0042] The glass transition temperature of the acrylic polymer (a2) is preferably from −30 to 110° C., more preferably from 0 to 110° C., and even more preferably from 20 to 110° C., since this further improves the abrasion resistance and washing resistance.

[0043] In the present invention, the glass transition temperature is FOX formula: 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... (Tg: glass transition temperature to be determined, W1: weight fraction of component 1, Tg1: glass transition temperature of homopolymer of component 1) The glass transition temperature of the homopolymer of each component is determined by calculation according to the following formula: The values ​​used are those listed in the "Adhesive Technology Handbook" published by Nikkan Kogyo Shimbun or the "Polymer Handbook" published by Wiley-Interscience.

[0044] When polymerizing the acrylic polymer (a2), it is preferable to use a polymerization initiator. Examples of the polymerization initiator include azo compounds such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 4,4'-azobis(4-cyano)valeric acid, and 2,2'-azobis(2-amidinopropane) dihydrochloride; benzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxypivalate, tert-butyl peroxybenzoate, tert-butylperoxy-2-ethylhexanoate, and di-tert-butyl peroxybenzoate. Examples of peroxides that can be used include organic peroxides such as ethyl peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, decanoyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxybenzoate, cumene hydroperoxide, and paramenthane hydroperoxide; and inorganic peroxides such as hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate.

[0045] The amount of the polymerization initiator is preferably 0.005 to 5 parts by mass, more preferably 0.01 to 1 part by mass, and even more preferably 0.02 to 0.2 parts by mass, relative to 100 parts by mass of the total of the monomer raw materials for the acrylic polymer (a2).

[0046] The mass ratio (a1 / a2) of the polyurethane (a1) to the acrylic polymer (a2) is preferably from 95 / 5 to 50 / 50, more preferably from 90 / 10 to 65 / 35, since this further improves the abrasion resistance and washing resistance.

[0047] The aqueous medium (B) may be water, a water-miscible organic solvent, or a mixture thereof. Examples of the water-miscible organic solvent include alcohol solvents such as methanol, ethanol, n-propanol, isopropyl alcohol, 1,2-propylene glycol, and 1,3-butylene glycol; ketone solvents such as acetone and methyl ethyl ketone; glycol ether solvents such as ethylene glycol-n-butyl ether, diethylene glycol-n-butyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol dimethyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, dipropylene glycol dimethyl ether, dipropylene glycol-n-butyl ether, and tripropylene glycol methyl ether; lactam solvents such as N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone; and amide solvents such as N,N-dimethylformamide, among which ketone solvents are preferred.

[0048] In consideration of safety and reducing the burden on the environment, the aqueous medium (B) is preferably water alone or a mixture of water and a water-miscible organic solvent, more preferably water alone. The water content in the aqueous medium (B) is preferably 50% by mass or more, more preferably 70% by mass or more.

[0049] The content of the aqueous medium (B) in the binder for aqueous inkjet ink is preferably 30 to 80 mass %, more preferably 50 to 70 mass %.

[0050] The binder for an aqueous inkjet ink of the present invention may further contain, as an additive (C), a crosslinker, a plasticizer, an antistatic agent, a wax, a surfactant, a light stabilizer, a flow modifier, a dye, a leveling agent, a rheology control agent, an ultraviolet absorber, an antioxidant, a photocatalytic compound, a preservative, a viscosity modifier, a pH adjuster, a chelating agent, or the like.

[0051] The content of the additive (C) is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, based on 100 parts by mass of the composite resin (A).

[0052] The composite resin (A) is obtained by polymerizing the monomer raw materials of the acrylic polymer (a2) in the presence of the polyurethane (a1).

[0053] The binder for aqueous inkjet inks of the present invention can be obtained, for example, by neutralizing some or all of the acid groups of the polyurethane (a1) with a basic compound and dispersing the resulting neutralized product in an aqueous medium (B) to produce an aqueous dispersion of the polyurethane (a1) in step (I), followed by adding a (meth)acrylic monomer and, if necessary, other unsaturated monomers to the resulting aqueous dispersion of polyurethane (a1) and conducting radical polymerization in step (II). During this process, the hydrophobic monomers are incorporated into the polyurethane (a1) particles, resulting in the formation of core-shell particles having a shell containing the polyurethane (a1) and a core containing the acrylic polymer (a2). The radical polymerization may be carried out in the presence of the additive (C), if necessary, or may be added after the polymerization reaction.

[0054] The aqueous inkjet ink of the present invention contains the above-described binder for an aqueous inkjet ink and a colorant, and may further contain an organic solvent, a surface conditioner, a pigment dispersant, a drying inhibitor, a penetrating agent, a surfactant, etc.

[0055] The colorant may be a dye or a pigment, and preferably contains a pigment.

[0056] As the pigment, for example, compounds classified as pigments in the Color Index (published by The Society of Dyers and Colourists) can be used, and examples thereof include inorganic pigments and organic pigments.

[0057] Examples of the inorganic pigment include iron oxide; carbon black (carbon black produced by a contact method, a furnace method, a thermal method, etc.); and titanium oxide.

[0058] Examples of the carbon black include #2300, #2200B, #990, #900, #960, #980, #33, #40, #45, #45L, #52, HCF88, MA7, MA8, MA100, and the like (all manufactured by Mitsubishi Chemical Corporation); Raven series (5750, 5250, 5000, 3500, 1255, 700, and the like) (all manufactured by Columbia Chemical); Regal series (400R, 330R, 660R, and the like), Mogul series (L, 700, and the like), Monarch series (800, 880, 900, 1000, 10, 1300, 1400, and the like) (all manufactured by Cabot Corporation); Color Examples include the Black series (FW1, FW2, FW2V, FW18, FW200, S150, S160, S1), the Printex series (35, U, V, 1400U, etc.), the Special Black series (6, 5, 4, 4A, etc.), and the NIPEX series (150, 160, 170, 180, 95, 90, 85, 80, 75, etc.) (all manufactured by Orion Engineered Carbons Co., Ltd.).

[0059] The organic pigments can be used alone or in combination of two or more kinds, and examples thereof, based on their chemical structure, include azo pigments such as azo lake pigments, insoluble azo pigments, condensed azo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindoline pigments, and quinophthalone pigments; dye chelates such as basic dye chelates and acid dye chelates; nitro pigments; nitroso pigments; and aniline black.

[0060] Specific examples of the organic pigment include: Yellow pigments such as CI Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 174, 180, 185; Magenta pigments such as CI Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 112, 122, 123, 146, 150, 168, 176, 184, 185, 202, 209, 213, 269, 282; Cyan pigments such as CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 60, 63, 66; Orange pigments such as CI Pigment Orange 5, 13, 16, 17, 34, 36, 43, 51, 64, 71; Violet pigments such as CI Pigment Violet 1, 3, 5:1, 16, 19, 23, 38; Green pigments such as CI Pigment Green 1, 4, 7, 8, 10, 17, 18, 36; Examples of red pigments include CI Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:3, 48:4, 49:1, 52:2, 53:1, 57:1, 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101, 104, 105, 106, 108, 112, 114, 122, 123, 146, 149, 150, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, and 264.

[0061] From the viewpoint of dispersibility, the primary particle size of the pigment is preferably 25 μm or less, more preferably 10 μm or less, and even more preferably 1 μm or less, and from the viewpoint of stability, it may be, for example, 10 μm or more, or 30 nm or more. The primary particle size can be measured by a transmission electron microscope (TEM).

[0062] The volume average particle size of the pigment is preferably 1 μm or less, more preferably 250 nm or less, and even more preferably 200 nm or less from the viewpoint of dispersibility, and may be, for example, 10 nm or more, 50 nm or more from the viewpoint of stability. The volume average particle size of the pigment can be measured by laser diffraction.

[0063] The content of the pigment in the colorant is preferably 80% by mass or more, more preferably 9% by mass or more, and even more preferably 95% by mass or more, with the upper limit being 100% by mass.

[0064] The content of the colorant in the solid content of the inkjet ink composition is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less.

[0065] The pigment dispersant is a compound having a hydrophilic portion and a hydrophobic portion, and has the effect of improving the dispersibility of the pigment in an aqueous medium. Examples of the pigment dispersant include styrene-acrylic acid copolymers such as a styrene-(meth)acrylic acid copolymer, a styrene-(meth)acrylic acid ester-(meth)acrylic acid copolymer, and a (meth)acrylic acid ester-(meth)acrylic acid copolymer. When the styrene-acrylic acid copolymer is used, a basic compound such as potassium hydroxide may also be present in the aqueous pigment dispersion.

[0066] The content of the pigment dispersant is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, relative to 100 parts by mass of the colorant, and is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 50 parts by mass or less.

[0067] The organic solvent is preferably a hydrophilic organic solvent (an organic solvent that is miscible with water at 25°C), and specific examples thereof include ketone solvents such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; alcohol solvents such as methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, 2-butanol, pentyl alcohol, and 2-methoxyethanol; ether solvents such as tetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane; amide solvents such as dimethylformamide and N-methylpyrrolidone; glycol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, and polypropylene glycol; butanediol, pentanediol, and the like. Examples of suitable solvents include diol solvents such as diol, hexanediol, and diols of the same group as these; glycol ester solvents such as propylene glycol laurate; glycol ether solvents such as diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and triethylene glycol monoethyl ether; sulfolane; lactone solvents such as γ-butyrolactone; lactam solvents such as N-methylpyrrolidone, N-(2-hydroxyethyl)pyrrolidone, and 2-pyrrolidone; nitrile solvents such as acetonitrile; glycerin; glycerin derivatives such as glycerin to which a polyoxyalkylene has been added; and mixed solvents of one or more of these.

[0068] From the viewpoint of dispersibility and storage stability, the amount of the organic solvent is preferably 1 to 300 parts by mass, and more preferably 4 to 200 parts by mass, relative to 100 parts by mass of the pigment.

[0069] The aqueous inkjet ink can be produced by first mixing and dispersing the colorant, the pigment dispersant, the organic solvent, the aqueous medium, and a basic compound used as needed to prepare a colorant dispersion, and then further mixing in the resin composition and additives such as a drying inhibitor, a penetrating agent, a surfactant, etc. When preparing the colorant dispersion, examples of the mixing and dispersion method include a wet dispersion method and a kneading dispersion method, and the wet dispersion method is preferred.

[0070] The drying inhibitor is preferably miscible with the aqueous medium and effective in preventing clogging of the inkjet printer head. Examples include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol mono-n-butyl ether, polyethylene glycols with a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, mesoerythritol, and pentaerythritol. Among these, glycerin and triethylene glycol are preferred as the drying inhibitor because they are highly safe and can provide excellent effects on the drying properties and ejection performance of the ink. The content of the drying inhibitor in the aqueous inkjet ink is preferably 3 to 50% by mass.

[0071] Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol, and glycol monoethers of alkyl alcohols such as ethylene glycol hexyl ether, diethylene glycol butyl ether, and propylene glycol propyl ether. The content of the penetrant in the aqueous inkjet ink is preferably 0.01 to 10% by mass, from the viewpoints of improving the ink penetration into the recording medium and adjusting the ink dot diameter on the recording medium.

[0072] Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. From the viewpoint of adjusting ink properties such as surface tension, anionic surfactants and nonionic surfactants are preferred.

[0073] Examples of anionic surfactants include alkylbenzenesulfonates, alkylphenylsulfonates, alkylnaphthalenesulfonates, higher fatty acid salts, sulfate ester salts of higher fatty acid esters, sulfonates of higher fatty acid esters, sulfate ester salts and sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, and the like. Specific examples of these that are preferred include dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, and dibutylphenylphenol disulfonate.

[0074] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkylolamides, alkylalkanolamides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers. Of these, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid alkylolamides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers are preferred.

[0075] Other surfactants that may be used include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers; and biosurfactants such as spiculisporic acid, rhamnolipid, and lysolecithin.

[0076] From the viewpoint of effectively preventing bleeding of printed images, the content of the surfactant in the aqueous inkjet ink is preferably 0.001 to 2% by mass, more preferably 0.001 to 1.5% by mass, and even more preferably 0.01 to 1% by mass.

[0077] The water-based inkjet recording ink can be used for printing on various recording media, including absorbent recording media such as copy paper (PPC paper) commonly used in copiers, recording media having an ink-absorbing layer, non-absorbent recording media that do not absorb ink, poorly absorbent recording media with low ink absorbency, fabrics, films, etc.

[0078] The binder for aqueous inkjet inks of the present invention is useful for printing on various recording media because it has excellent storage stability and ejection properties, as well as excellent abrasion resistance and washing resistance of printed matter. [Example]

[0079] The present invention will be described in more detail below with reference to specific examples. The weight average molecular weight and average particle size were measured under the following measurement conditions.

[0080] [GPC measurement conditions] Measurement equipment: High-speed GPC equipment (Tosoh Corporation "HLC-8220GPC") Column: The following columns manufactured by Tosoh Corporation were connected in series and used. "TSKgel G5000" (7.8mm I.D. x 30cm) x 1 "TSKgel G4000" (7.8mm I.D. x 30cm) x 1 "TSKgel G3000" (7.8mm I.D. x 30cm) x 1 "TSKgel G2000" (7.8mmI.D. x 30cm) x 1 Detector: RI (differential refractometer) Column temperature: 40℃ Eluent: tetrahydrofuran (THF) Flow rate: 1.0mL / min Injection volume: 100 μL (sample concentration 4 mg / mL in tetrahydrofuran solution) Standard sample: A calibration curve was prepared using the following monodisperse polystyrene.

[0081] (monodisperse polystyrene) Tosoh Corporation's "TSKgel Standard Polystyrene A-500" Tosoh Corporation's "TSKgel Standard Polystyrene A-1000" Tosoh Corporation's "TSKgel Standard Polystyrene A-2500" Tosoh Corporation's "TSKgel Standard Polystyrene A-5000" "TSKgel Standard Polystyrene F-1" manufactured by Tosoh Corporation Tosoh Corporation's "TSKgel Standard Polystyrene F-2" Tosoh Corporation's "TSKgel Standard Polystyrene F-4" Tosoh Corporation's "TSKgel Standard Polystyrene F-10" Tosoh Corporation's "TSKgel Standard Polystyrene F-20" Tosoh Corporation's "TSKgel Standard Polystyrene F-40" Tosoh Corporation's "TSKgel Standard Polystyrene F-80" Tosoh Corporation's "TSKgel Standard Polystyrene F-128" Tosoh Corporation's "TSKgel Standard Polystyrene F-288" Tosoh Corporation's "TSKgel Standard Polystyrene F-550"

[0082] [Particle size measurement conditions] The binder for the aqueous inkjet ink was diluted with water to prepare a diluted dispersion with a concentration of 0.1% by mass. This diluted dispersion was then used to measure the particle size using a particle size measuring device (Microtrac Wave II manufactured by Microtrac Bell Co., Ltd.: calculated using dynamic light scattering), and the 50% median diameter was taken as the average particle size.

[0083] (Synthesis Example 1: Synthesis of Acrylic Macromer (1)) A four-neck flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube was charged with 700 parts by mass of methyl ethyl ketone, and then 291 parts by mass of methyl methacrylate, 8.7 parts by mass of 3-mercapto-1,2-propanediol, and 0.15 parts by mass of 2,2'-azobis(2-methylpropionitrile) were fed into the reaction vessel and reacted to obtain acrylic macromer (1), a vinyl polymer having two hydroxyl groups at one end and a number average molecular weight of 3,000.

[0084] (Production Example 1: Production of Polyurethane (a1-1) Having Acid Groups) A four-neck flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet tube was charged with 50.9 parts by mass of PTMG1k (PTMG1000 manufactured by Mitsubishi Chemical Corporation; polytetramethylene ether glycol with a number-average molecular weight of 1000) and 12.6 parts by mass of 2,2-dimethylolpropionic acid (DMPA) and thoroughly stirred. Next, 31.5 parts by mass of isophorone diisocyanate (IPDI) and 0.01 parts by mass of dibutyltin dilaurate as a catalyst were added, and the mixture was reacted at 75°C for 4 hours. After the reaction, methyl ethyl ketone (MEK) was added to adjust the solids concentration to 60% by mass, and the mixture was stirred for 30 minutes and cooled to below 40°C to obtain a urethane prepolymer solution. 5.0 parts by mass of potassium hydroxide was added to the resulting urethane prepolymer solution to neutralize the acid groups. Ion-exchanged water was then added under vigorous stirring to adjust the solids concentration to 18%, emulsifying the polyurethane. After the reaction was completed, MEK was removed by distillation under reduced pressure to obtain an aqueous dispersion of polyurethane (a1-1) having acid groups, which had a nonvolatile content of 30% by mass.

[0085] (Production Example 2: Production of Polyurethane (a1-2) Having Acid Groups) An aqueous dispersion of polyurethane (a1-2) having acid groups was obtained in the same manner as in Production Example 1, except that the raw material composition was changed to that shown in Table 1. The nonvolatile content of this aqueous dispersion was 30 mass %.

[0086] (Production Example 3: Production of Polyurethane (a1-3) Having Acid Groups) A urethane prepolymer solution having acid groups was obtained in the same manner as in Production Example 1, except that the raw material composition was changed to that shown in Table 1. 1.9 parts by mass of potassium hydroxide was added to the obtained urethane prepolymer solution to neutralize the acid groups. Next, ion-exchanged water was added under vigorous stirring to a solids concentration of 18%, and 2.7 parts by mass of ethylenediamine was added dropwise to carry out an elongation reaction. After completion of the reaction, MEK was distilled off under reduced pressure to obtain an aqueous dispersion of polyurethane (a1-3) having acid groups. The nonvolatile content of this aqueous dispersion was 30% by mass.

[0087] (Production Example 4: Production of Polyurethane (a1-4) Having Acid Groups) An aqueous dispersion of polyurethane (a1-4) having an acid group was obtained in the same manner as in Production Example 3, except that the raw material composition was changed to that shown in Table 1. The nonvolatile content of this aqueous dispersion was 30 mass %.

[0088] (Production Example 5: Production of Polyurethane (a1-5) Having Acid Groups) An aqueous dispersion of polyurethane (a1-5) having an acid group was obtained in the same manner as in Production Example 1, except that the raw material composition was changed to that shown in Table 1. The nonvolatile content of this aqueous dispersion was 30 mass %.

[0089] (Production Example 6: Production of Polyurethane (a1-6) Having Acid Groups) An aqueous dispersion of polyurethane (a1-6) having an acid group was obtained in the same manner as in Production Example 1, except that the raw material composition was changed to that shown in Table 1. The nonvolatile content of this aqueous dispersion was 30 mass %.

[0090] Table 1 shows the formulations of the polyurethanes (a1-1) to (a1-6) having acid groups obtained above.

[0091] [Table 1]

[0092] The abbreviations in Table 1 are as follows: PTMG1k: Mitsubishi Chemical's "PTMG1000"; polytetramethylene ether glycol with a number average molecular weight of 1000 Excenol 2020: AGC "Excenol 2020"; polypropylene glycol with a number average molecular weight of 2000 UH-100: Ube Industries "ETERNACOLL UH-100"; crystalline polycarbonate diol with a number average molecular weight of 1000 UH-200: Ube Industries "ETERNACOLL UH-200"; a crystalline polycarbonate diol with a number average molecular weight of 2000 G3450J: Asahi Kasei "DURANOL G3450J"; number average molecular weight 800

[0093] (Example 1: Production of binder (1) for aqueous inkjet ink) 233.4 parts by weight of the aqueous dispersion of the acid group-containing polyurethane (a1-1) obtained in Production Example 1 was mixed with 236.6 parts by weight of ion-exchanged water, and 15 parts by weight of methyl methacrylate and 15 parts by weight of 2-hydroxyethyl (meth)acrylate were reacted with 0.01 parts by weight of ammonium persulfate (APS) under conditions of monomer batch emulsion polymerization (reaction temperature: 80°C). The mixture was then concentrated to remove unreacted monomer and adjusted to a water content of 20% by weight to obtain a water-based inkjet ink binder (1) as an aqueous dispersion of the composite resin. The mass ratio (a1 / a2) was 70 / 30, and the glass transition temperature of the acrylic polymer was 78°C. The particle size distribution of the composite resin showed a single peak, confirming the formation of core-shell particles. The average particle diameter was 24 nm.

[0094] (Examples 2 to 6: Production of binders (2) to (6) for aqueous inkjet inks) Aqueous inkjet ink binders (2) to (6) were obtained as aqueous dispersions of composite resins in the same manner as in Example 1, except that the aqueous dispersion of acid group-containing polyurethane (a1-1) used in Example 1 was replaced with aqueous dispersions of acid group-containing polyurethanes (a1-2) to (a1-6). The mass ratio (a1 / a2) was 70 / 30 in all cases. Furthermore, the particle size distribution of the composite resins showed a single peak, confirming the formation of core-shell particles. The average particle diameters were 83 nm for aqueous inkjet ink binder (2), 44 nm for aqueous inkjet ink binder (3), 45 nm for aqueous inkjet ink binder (4), 111 nm for aqueous inkjet ink binder (5), and 123 nm for aqueous inkjet ink binder (6).

[0095] (Example 7: Production of binder (7) for aqueous inkjet ink) 233.4 parts by weight of the aqueous dispersion of the acid group-containing polyurethane (a1-2) obtained in Production Example 1 was mixed with 236.6 parts by weight of ion-exchanged water, and the mixture was reacted with 30 parts by weight of methyl methacrylate and 0.01 parts by weight of ammonium persulfate (APS) under conditions of monomer batch emulsion polymerization (reaction temperature: 80°C). The mixture was then concentrated to remove unreacted monomer and adjusted to a water content of 20% by weight. This resulted in an aqueous dispersion of the composite resin, aqueous inkjet ink binder (7). The mass ratio (a1 / a2) was 70 / 30. The glass transition temperature of the acrylic polymer was 105°C. The particle size distribution of the composite resin showed a single peak, confirming the formation of core-shell particles. The average particle diameter was 115 nm.

[0096] (Example 8: Production of binder (8) for aqueous inkjet ink) 233.4 parts by weight of the aqueous dispersion of the acid group-containing polyurethane (a1-2) obtained in Production Example 1 was mixed with 236.6 parts by weight of ion-exchanged water, and 20 parts by weight of ethyl acrylate and 10 parts by weight of styrene were reacted with 0.01 part by weight of ammonium persulfate (APS) under conditions of monomer batch emulsion polymerization (reaction temperature: 80°C). The mixture was then concentrated to remove unreacted monomer and adjusted to a water content of 20% by weight. This resulted in an aqueous dispersion of the composite resin, aqueous inkjet ink binder (8). The mass ratio (a1 / a2) was 70 / 30. The glass transition temperature of the acrylic polymer was 9°C. The particle size distribution of the composite resin showed a single peak, confirming the formation of core-shell particles. The average particle diameter was 121 nm.

[0097] (Comparative Example 1: Binder for Water-Based Inkjet Ink (R1)) The aqueous dispersion of the polyurethane (a1-1) having an acid group obtained in Production Example 1 was used as a binder (R1) for aqueous inkjet inks.

[0098] [Production of pigment dispersion] 50 parts by mass of CI Pigment Red 122 ("FASTOGEN Super Magenta RY" manufactured by DIC Corporation), CI Pigment Blue 15:3 (SBG-SD manufactured by DIC Corporation), and 10 parts by mass of styrene-acrylic acid copolymer (weight average molecular weight 11,000, acid value 180 mgKOH / g) were added in that order to a 0.5 L jacketed tank of a mini planetary mixer (Aikosha mini-PLM Co., Ltd.), and the mixture was stirred for 10 minutes at a rotation speed of 80 rpm and an orbital speed of 25 rpm while the temperature of the jacketed tank was heated to 80°C. Next, with the temperature of the jacketed tank maintained at 80°C, 5.3 parts by mass of a 34% by mass aqueous potassium hydroxide solution and 30 parts by mass of triethylene glycol were added to the composition, and the mixture was kneaded for 60 minutes at a rotation speed of 80 rpm and a revolution speed of 25 rpm to obtain a solid kneaded product. To the kneaded product, 100 parts by mass of ion-exchanged water and 10 parts by mass of triethylene glycol were added, and the mixture was stirred and mixed for 10 minutes using a juicer mixer. By mixing the ion-exchanged water and Proxel-GXL (Lonza Japan Co., Ltd.), an aqueous pigment dispersion was obtained with a pigment concentration of 15.0% by mass, a triethylene glycol concentration of 12.0% by mass, a Proxel-GXL concentration of 0.1% by mass, and a nonvolatile content of 18.2% by mass.

[0099] [Production of aqueous inkjet ink] 20.0 parts by mass of the pigment dispersion obtained above, 3.3 parts by mass of the aqueous inkjet binder, 8.0 parts by mass of 2-pyrrolidinone (manufactured by BASF), 8.0 parts by mass of triethylene glycol mono-n-butyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.), 3.0 parts by mass of glycerin (manufactured by Kao Corporation), 0.5 parts by mass of Surfynol 440 (nonionic surfactant, manufactured by Evonik Japan Co., Ltd.), and 57.3 parts by mass of ion-exchanged water were stirred for 1 hour. Next, the pH was adjusted to within the range of 9 to 9.8 using a 5% by mass aqueous potassium hydroxide solution, and the solution was filtered through a filter with a pore size of 5 to 10 μm to obtain an aqueous inkjet ink (pigment concentration 3.0%, urethane solid concentration 1.0%).

[0100] [Evaluation of abrasion resistance] The aqueous inkjet ink obtained above was filled into a blank ink cartridge for a commercially available inkjet printer, ENVY4500 (manufactured by HP), and a solid print was made on the printing surface of photo printing paper (HP Advanced Photo Paper, manufactured by HP) at a print density setting of 100%. After the print was dried at room temperature for 1 minute, the printed surface was rubbed back and forth three times with the same paper as the printer's paper using a Gakushin friction tester under a load of 200 g. Next, the printed surface of the printed matter was scanned to convert it into image data, and the pixel survival rate (%) was calculated based on the following formula, and the scratch resistance was evaluated based on the following criteria. Pixel survival rate (%) = (number of pixels in the colored area after the scratch test) / (number of pixels in the colored area before the scratch test) × 100 〇: 40% or more △: 20% or more but less than 40% ×: Less than 20%

[0101] [Evaluation of washing durability] After dyeing the entire surface of the cotton broadcloth, it was dried at 150°C for 5 minutes. A washing solution prepared in accordance with JIS L0844:2011 was then heated to 50°C, and the cotton broadcloth was immersed (30 minutes). It was then agitated in a food mixer for 1 minute, and the removed test sample was washed with water and then dried. The optical density (OD) of the cotton broadcloth after agitation in the mixer was measured using an X-Rite integrating sphere spectrophotometer. The OD retention rate (%) was calculated using the following formula, and the washability was evaluated according to the following criteria. OD retention rate (%) = (OD of cotton broadcloth after stirring) / (OD of cotton broadcloth before immersion in laundry liquid) × 100 〇: 50% or more △: 45% or more but less than 50% ×: Less than 45%

[0102] Table 2 shows the formulations and evaluation results of the aqueous inkjet ink binders (1) to (8) and (R1) obtained above.

[0103] [Table 2]

[0104] It was confirmed that the printed matter obtained from Examples 1 to 8, which are binders for aqueous inkjet inks of the present invention, had excellent abrasion resistance and washing resistance.

[0105] On the other hand, Comparative Example 1 is an example in which a urethane resin not containing the acrylic polymer (a2), which is an essential component of the present invention, was used, and it was confirmed that the resulting printed matter was poor in abrasion resistance and washing resistance.

Claims

1. A binder for an aqueous inkjet ink, comprising a composite resin (A) and an aqueous medium (B), wherein the composite resin (A) forms core-shell type particles having a shell portion containing a polyurethane (a1) having an acid group and a core portion containing an acrylic polymer (a2), The monomer raw material of the acrylic polymer (a2) contains an alkyl(meth)acrylate having 4 to 10 carbon atoms and a hydroxyl group-containing (meth)acrylate, The alkyl(meth)acrylate having 4 to 10 carbon atoms is methyl methacrylate, the hydroxyl group-containing (meth)acrylate is 2-hydroxyethyl (meth)acrylate, The glass transition temperature of the acrylic polymer (a2) is in the range of 20 to 110° C., The polyurethane (a1) has an acid value in the range of 10 to 30 mgKOH / g.

2. 2. The binder for aqueous ink-jet inks according to claim 1, wherein a mass ratio (a1 / a2) of the polyurethane (a1) to the acrylic polymer (a2) is from 95 / 5 to 50 / 50.

3. An aqueous ink-jet ink comprising the binder for aqueous ink-jet inks according to claim 1 or 2.

4. A printed layer formed from the aqueous ink-jet ink according to claim 3.

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