Water-based inkjet ink binder, water-based inkjet ink, and printing layer

Abstract

This invention provides a binder for water-based inkjet inks, characterized in that it contains a composite resin (A) and an aqueous medium (B). The composite resin (A) forms core-shell type particles having a shell and a core. The shell comprises a polyurethane (a1) with acid groups, and the core comprises an acrylic polymer (a2). The invention also provides an aqueous inkjet ink containing the binder and a printing layer. This water-based inkjet ink binder is suitable for printing on various recording media due to its excellent abrasion resistance on printed materials such as ordinary paper, coated paper, and films, and its washability on fabrics.

Description

Technical Field

[0001] This invention relates to binders for water-based inkjet inks, water-based inkjet inks, and printing layers. Background Technology

[0002] Inkjet (IJ) recording devices are a printing method that uses tiny droplets of ink composition to fly and adhere to recording media such as paper for printing. Driven by the increasing demand for on-demand printing, IJ printers have been rapidly expanding their applications in recent years, including industrial wide-format applications, textile applications, and flexible packaging applications.

[0003] As for inkjet inks used in the aforementioned inkjet recording apparatus, inks containing polycarbonate-based urethane resins with an elongation at break of 300% or more have been proposed (see Patent Document 1). However, such inks suffer from insufficient abrasion resistance and washability for printed materials that have been subject to higher requirements in recent years.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6119919 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The problem to be solved by the present invention is to provide a binder for water-based inkjet inks that can produce printed materials with excellent abrasion resistance and washability.

[0009] Methods for solving problems

[0010] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that a binder for water-based inkjet ink containing a specific composite resin and a water-based medium can solve the above-mentioned problems, thus completing the invention.

[0011] That is, the present invention relates to a binder for water-based inkjet ink, characterized in that it contains a composite resin (A) and an aqueous medium (B), wherein the composite resin (A) forms a core-shell type particle having a shell and a core, wherein the shell comprises a polyurethane (a1) having an acid group, and the core comprises an acrylic polymer (a2).

[0012] Invention Effects

[0013] The water-based inkjet ink binder of the present invention has excellent abrasion resistance on printed materials such as ordinary paper, coated paper, and film, as well as washability on fabrics, and can therefore be suitable for printing on various recording media. Detailed Implementation

[0014] The water-based inkjet ink binder of the present invention is a water-based inkjet ink binder containing a composite resin (A) and an aqueous medium (B). The composite resin (A) forms a core-shell type particle having a shell and a core. The shell contains a polyurethane (a1) having acid groups, and the core contains an acrylic polymer (a2) having hydroxyl groups.

[0015] The core-shell type particles of the above-mentioned composite resin (A) have the form in which the above-mentioned polyurethane (a1) introduces part or all of the above-mentioned acrylic polymer (a2) into the interior and covers it, and are dispersed in the above-mentioned aqueous medium (B).

[0016] The polyurethane (a1) constituting the shell of the composite resin (A) can be obtained by reacting a polyol with a polyisocyanate. By using a polyol with acid groups as a component of the polyol, the acid groups of the polyurethane (a1) can be easily introduced into the polyurethane (a1).

[0017] Examples of the aforementioned polyols containing acid groups include diols containing carboxyl or sulfonic acid groups, with diols containing carboxyl groups being preferred. Examples of diols containing carboxyl groups include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvalerate. 2,2-dimethylolpropionic acid is preferred among these. Alternatively, polyester polyols containing carboxyl groups, obtained by reacting the aforementioned polyols containing carboxyl groups with various polycarboxylic acids, can also be used. Examples of the aforementioned polycarboxylic acids 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 their anhydrides. It should be noted that these polyols can be used alone or in combination of two or more.

[0018] Examples of polyols containing sulfonic acid groups 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 their salts, with low molecular weight polyols that are examples of substances that can be used in the manufacture of the aforementioned polyester polyols having aromatic structures. It should be noted that these polyols can be used alone or in combination of two or more.

[0019] Other polyols that can be used in combination with the aforementioned polyols having acid groups include, for example, polyether polyols, polyester polyols, and polycarbonate polyols.

[0020] Examples of the aforementioned polyether polyols include polyether polyols obtained by addition polymerization of epoxides using one or more compounds having two or more active hydrogen atoms as initiators.

[0021] Examples of initiators mentioned above 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, glycerol, trimethylolethane, trimethylolpropane, sorbitol, sucrose, aconitine, trimellitic acid, triphenyltetrate, phosphoric acid, ethylenediamine, diethylenetriamine, triisopropanolamine, pyrogallol, dihydroxybenzoic acid, hydroxyphthalic acid, and 1,2,3-propanetrithiol.

[0022] Examples of the aforementioned epoxides include ethylene oxide, propylene oxide, butane oxide, phenyl ethylene oxide, epichlorohydrin, and tetrahydrofuran.

[0023] In addition, examples of the aforementioned polyester polyols include aliphatic polyester polyols obtained by esterification of low molecular weight polyols with polycarboxylic acids, aromatic polyester polyols, polyesters obtained by ring-opening polymerization of cyclic ester compounds such as ε-caprolactone, and their copolyesters.

[0024] Examples of low molecular weight polyols used in the manufacture of the aforementioned polyester polyols 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, neopentanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,11-decanediol. Aliphatic polyols with molecular weights of 50–300, such as monoalkyldiol, 1,12-dodecanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, glycerol, trimethylolpropane, bis(trimethylolpropane), trimethylolpropane, and pentaerythritol; polyols with alicyclic structures, such as cyclohexanediol and hydrogenated bisphenol A; and polyols with aromatic structures, such as bisphenol A and bisphenol F.

[0025] In addition, examples of the aforementioned polycarboxylic acids 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 their anhydrides or esters.

[0026] As the aforementioned polycarbonate polyol, for example, a polycarbonate polyol obtained by reacting a carbonate with a polyol, or a polycarbonate polyol obtained by reacting a carbonyl chloride with bisphenol A, etc., can be used.

[0027] As the aforementioned carbonates, methyl carbonate, dimethyl carbonate, ethyl carbonate, diethyl carbonate, cyclic carbonate, diphenyl carbonate, etc., can be used.

[0028] Polyols capable of reacting with the aforementioned carbonates may include, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 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, and 3-methyl-1,5-pentanediol. Alcohols, 2-ethyl-1,3-hexanediol, 2-methyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2-butyl-12-ethylpropanediol, 2-methyl-1,8-octanediol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanediol, hydroquinone, resorcinol, bisphenol-A, bisphenol-F, 4,4'-biphenol and other low molecular weight dihydroxy compounds, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and other polyether polyols, polyhexyl adipate, polyhexyl succinate, polycaprolactone and other polyester polyols, etc.

[0029] Regarding the amount of the aforementioned polyols containing acid groups used, the total amount of polyols used in the manufacture of the aforementioned polyurethane (a1) is preferably 3 to 50 by mass.

[0030] Examples of the aforementioned polyisocyanates include aromatic diisocyanates such as phenylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate; and aliphatic or aliphatic cyclic diisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, phenylene diisocyanate, and tetramethylphenylene diisocyanate. However, from the perspective of further improving abrasion resistance and washability, diisocyanates with an aliphatic cyclic structure are preferred. It should be noted that these polyisocyanates can be used alone or in combination of two or more.

[0031] The molar ratio (NCO / OH) of the isocyanate group (NCO) in the polyisocyanate to the hydroxyl group (OH) in the polyol is preferably 0.9 to 2.

[0032] In addition, the polyurethane (a1) mentioned above can be a polyurethane that has been polymerized with chain extenders such as polyamines.

[0033] As the aforementioned polyamines, for example, ethylenediamine, 1,2-propanediamine, 1,6-hexanediamine, piperazine, 2,5-dimethylpiperazine, isophorone diamine, 4,4'-dicyclohexylmethyldiamine, 3,3'-dimethyl-4,4'-dicyclohexylmethyldiamine, 1,4-cyclohexanediamine, and other diamines can be used; N-hydroxymethylaminoethylamine, N-hydroxyethylaminoethylamine, N-hydroxypropylaminopropylamine, N-ethylaminoethylamine, N-methylaminopropylamine, etc., having one primary amino group and Diamines with one secondary amino group; polyamines such as diethylenetriamine, dipropylenetriamine, and triethylenetetramine; hydrazine compounds such as hydrazine, N,N'-dimethylhydrazine, and 1,6-hexanedihydrazine; diacylhydrazine compounds such as succinic dihydrazine, adipic dihydrazine, glutaric dihydrazine, and isophthalic dihydrazine; and aminourea compounds such as β-aminourea propionic hydrazine, 3-aminourea-propyl-hydrazylcarbamate, and aminourea-3-aminourea-methyl-3,5,5-trimethylcyclohexane. It should be noted that these polyamines can be used alone or in combination of two or more.

[0034] The above-mentioned polyamine is preferably used when the equivalent ratio of the amino group of the polyamine to the isocyanate group of the urethane prepolymer is 0.8 to 1.

[0035] The chain-promoting reaction described above is preferably carried out by mixing the aqueous dispersion with the chain extender such as the polyamine after manufacturing the aqueous dispersion of polyurethane.

[0036] Regarding the acid value of the polyurethane (a1) mentioned above, from the perspective of further improving the balance between water dispersibility, abrasion resistance and washability, it is preferably 10 to 70, and more preferably 15 to 65.

[0037] The acid value of the polyurethane (a1) of the present invention is a value calculated based on the composition of the raw materials.

[0038] Regarding the weight-average molecular weight of the polyurethane (a1) mentioned above, from the perspective of further improving the balance between water dispersibility, abrasion resistance and washability, it is preferably 10,000 to 500,000, and more preferably 10,000 to 300,000.

[0039] In this invention, unless otherwise specified, the weight-average molecular weight and number-average molecular weight are the values ​​determined by gel permeation chromatography (GPC) using polystyrene as a standard sample.

[0040] From the perspective of further improving the water dispersibility of the above-mentioned composite resin (A), the acid groups of the above-mentioned polyurethane (a1) are preferably neutralized by an alkaline compound.

[0041] Examples of the aforementioned basic compounds 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. However, from the perspective of further improving abrasion resistance and washability, metal hydroxides are preferred, and potassium hydroxide is more preferred. It should be noted that these basic compounds can be used alone or in combination of two or more.

[0042] The acrylic polymer (a2) constituting the core of the above-mentioned composite resin (A) can be obtained by polymerization of (meth)acrylic monomers and other unsaturated monomers as needed.

[0043] Examples of the aforementioned (meth)acrylate monomers include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, neopentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, cyclopentyl methacrylate, and cyclohexyl methacrylate, which are alkyl (meth)acrylates with 4 to 10 carbon atoms.

[0044] Alkyl (meth)acrylates with 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.

[0045] (Meth)phenyl acrylate and other (meth)acrylate aryl esters;

[0046] Aryl (meth)acrylates with 10 to 20 carbon atoms, such as benzyl (meth)acrylate and phenethyl (meth)acrylate;

[0047] (Meth)acrylate phenoxyethyl ester and other (meth)acrylate aryloxyalkyl esters;

[0048] 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-cyclohexanediol mono(meth)acrylate, N-(2-hydroxyethyl)(meth)acrylamide, glycerol 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, lactone-modified (meth)acrylate with hydroxyl groups at the end, and other hydroxyl-containing (meth)acrylates.

[0049] (Meth)acrylates containing nitrogen atoms;

[0050] Polyethylene glycol (meth)acrylate, methoxy polyethylene glycol (meth)acrylate, polyethylene glycol-polypropylene glycol copoly(meth)acrylate, methoxy polyethylene glycol-polypropylene glycol copoly(meth)acrylate, polyethylene glycol-poly1,4-butanediol copoly(meth)acrylate, methoxy polyethylene glycol-poly1,4-butanediol copoly(meth)acrylate, etc. (meth)acrylates containing polyoxyethylene;

[0051] (Methacrylonitrile), (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N-hydroxymethyl(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-vinylimidazolium, N-vinylcarbazole, N-vinylquinoline, N-vinylpiperidine, and other (meth)acrylic acid monomers containing nitrogen atoms; etc. It should be noted that these (meth)acrylic acid monomers can be used alone or in combination of two or more.

[0052] Other unsaturated monomers mentioned above include, for example, methyl crotonate, ethyl crotonate, and other alkyl crotonate esters.

[0053] Dimethyl maleate, dibutyl maleate, dimethyl fumarate, dibutyl fumarate, dimethyl itaconic acid, dibutyl itaconic acid and other unsaturated dicarboxylic acid alkyl esters;

[0054] Aromatic vinyl monomers such as styrene, p-tert-butylstyrene, α-methylstyrene, vinyltoluene, vinylpyridine, chlorostyrene, and chloromethylstyrene;

[0055] Nitrogen-containing monomers such as crotonitrile, N-vinylformamide, N-vinylpyrrolidone, N-vinylimidazolium, N-vinylcarbazole, N-vinylquinoline, and N-vinylpiperidine;

[0056] Halogenated olefins such as vinylidene fluoride, vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, vinyl chloride, and vinylidene chloride; α-olefins such as ethylene, propylene, isobutylene, and 1-butene;

[0057] Vinyl acetate, vinyl propionate, vinyl pentanoate, vinyl tert-carbonate, vinyl benzoate, vinyl neodecanoate, and other vinyl carboxylic acids;

[0058] Alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether; cyclohexyl vinyl ether and other cycloalkyl vinyl ethers;

[0059] Acrolein, methyl vinyl ketone, and other carbonyl monomers;

[0060] Fluorinated alkyl monomers such as perfluorocyclohexyl (meth)acrylate, diperfluorocyclohexyl fumarate, and N-isopropylfluorooctanoic acid sulfonamide ethyl (meth)acrylate.

[0061] Maleic anhydride, citraconic anhydride, zetamicin anhydride, itaconic anhydride, tetrahydrophthalic anhydride and other unsaturated dicarboxylic acid anhydrides;

[0062] Glycidyl methacrylate, allyl glycidyl ether, tetrahydrofurfuryl methacrylate and other cyclic ether monomers;

[0063] Vinyltrichlorosilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane and other silyl-containing monomers;

[0064] 2-Hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 2-hydroxyethyl allyl ether and other hydroxyl-containing monomers;

[0065] Vinyl sulfonic acid, 3-acryloyloxypropane-1-sulfonic acid, 3-acryloyloxyoctoxybenzenesulfonic acid, 3-acryloyloxybenzenediazosulfonic acid, 3-acryloyloxydiazobenzene-4'-sulfonic acid, 2-acryloylamino-21-methylpropane-1-sulfonic acid, 2-acryloylamide-2-methylpropanesulfonic acid, acrylonitrile-tert-butylsulfonic acid, and other vinyl-containing sulfonic acid compounds and their salts; etc. It should be noted that these monomers can be used alone or in combination of two or more.

[0066] In this invention, "(meth)acrylic monomers" refers to one or both of acrylic monomers and methacrylic monomers, and "(meth)acrylates" refers to one or both of acrylic esters and methacrylates.

[0067] In the monomer raw materials of the above-mentioned acrylic polymer (a2), from the viewpoint of further improving abrasion resistance and washability, it is preferable to include alkyl (meth)acrylates with 4 to 10 carbon atoms. More preferably, the alkyl (meth)acrylates with 4 to 10 carbon atoms in the monomer raw materials are 10 to 100% by mass, further preferably 40 to 100% by mass, and particularly preferably 50 to 100% by mass.

[0068] Regarding the glass transition temperature of the aforementioned acrylic polymer (a2), from the perspective of further improving abrasion resistance and washability, it is preferably -30 to 110°C, more preferably 0 to 110°C, and even more preferably 20 to 110°C.

[0069] It should be noted that, in this invention, the glass transition temperature is a value calculated according to the FOX formula.

[0070] FOX formula: 1 / Tg = W1 / Tg1 + W2 / Tg2 + ...

[0071] (Tg: the glass transition temperature to be determined, W1: the weight percentage of component 1, Tg1: the glass transition temperature of the homopolymer of component 1)

[0072] The glass transition temperatures of the homopolymers of each component were taken from the values ​​recorded in the "Adhesion Technology Handbook" by Nikkan Kogyo Shimbun or the "Polymer Handbook" by Wiley-Interscience.

[0073] When polymerizing the above-mentioned acrylic polymer (a2), a coexisting polymerization initiator is preferred. As the polymerization initiator, azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylpropanediamine) dihydrochloride, 4,4'-azobis(4-cyanopentanoic acid), and 2,2'-azobis(2-amynylpropane) dihydrochloride can be used; benzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxypentanoate, tert-butyl peroxybenzoate, etc. Organic peroxides include tert-butyl 2-ethylhexanoate, di-tert-butyl peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, decanoyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, tert-butyl lauryl peroxide, tert-butyl benzoate peroxide, cumene hydroperoxide, and p-menthol hydroperoxide; inorganic peroxides include hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate.

[0074] The polymerization initiator is preferably 0.005 to 5 parts by mass relative to 100 parts by mass of the monomer raw material of the acrylic polymer (a2), more preferably 0.01 to 1 part by mass, and even more preferably 0.02 to 0.2 parts by mass.

[0075] Regarding the mass ratio (a1 / a2) of the polyurethane (a1) to the acrylic polymer (a2), from the perspective of further improving abrasion resistance and washability, it is preferably 95 / 5 to 50 / 50, and more preferably 90 / 10 to 65 / 35.

[0076] As the aforementioned aqueous medium (B), examples include water, water-miscible organic solvents, and mixtures thereof. Examples of water-miscible organic solvents include alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, 1,2-propanediol, and 1,3-butanediol; 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 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, with ketone solvents being preferred.

[0077] Considering safety and reduced environmental burden, the aqueous medium (B) is preferably only water, or a mixture of water and a water-miscible organic solvent, and more preferably only water. The water content in the aqueous medium (B) is preferably 50% by mass or more, and more preferably 70% by mass or more.

[0078] The content of the above-mentioned aqueous medium (B) in the binder for aqueous inkjet ink is preferably 30 to 80% by mass, more preferably 50 to 70% by mass.

[0079] The binder for water-based inkjet inks of the present invention may further include, as additive (C), crosslinking agents, plasticizers, antistatic agents, waxes, surfactants, light stabilizers, flow modifiers, dyes, leveling agents, rheology control agents, ultraviolet absorbers, antioxidants, photocatalytic compounds, preservatives, viscosity modifiers, pH modifiers, chelating agents, etc.

[0080] The content of the above-mentioned additive (C) is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the above-mentioned composite resin (A).

[0081] The composite resin (A) described above can be obtained by polymerizing the monomer raw material of the acrylic polymer (a2) in the presence of the polyurethane (a1) described above.

[0082] The binder for water-based inkjet inks of the present invention can be obtained, for example, by the following steps: Step (I) neutralizing some or all of the acid groups of the polyurethane (a1) with an alkaline compound, dispersing the resulting neutralized product in an aqueous medium (B), thereby producing an aqueous dispersion of the polyurethane (a1); and then, in Step (II), supplying (meth)acrylic acid monomers and other unsaturated monomers as needed to the resulting aqueous dispersion of the polyurethane (a1) and performing free radical polymerization. At this time, since hydrophobic monomers are introduced into the particles of the polyurethane (a1), core-shell type particles are formed having a shell containing the polyurethane (a1) and a core containing the acrylic polymer (a2). Furthermore, the additive (C) can be coexisted during the free radical polymerization as needed, or the additive (C) can be added after the polymerization reaction.

[0083] The water-based inkjet ink of the present invention contains the above-mentioned binder and colorant for water-based inkjet inks, and may further contain organic solvents, surface conditioners, pigment dispersants, drying inhibitors, penetrants, surfactants, etc.

[0084] Examples of colorants include dyes and pigments, with pigments being preferred.

[0085] As for the aforementioned pigments, compounds classified as pigments in the Color Index (published by The Society of Dyers and Colourists) can be used, including inorganic pigments and organic pigments.

[0086] Examples of such inorganic pigments include iron oxide; carbon black (carbon black manufactured using methods such as contact method, furnace method, and pyrolysis method); and titanium oxide.

[0087] Examples of the aforementioned carbon blacks include #2300, #2200B, #990, #900, #960, #980, #33, #40, #45, #45L, #52, HCF88, MA7, MA8, MA100, etc. (manufactured by Mitsubishi Chemical Corporation); Raven series (5750, 5250, 5000, 3500, 1255, 700, etc.) (manufactured by Columbia Corporation); Regal series (400R, 330R, 660R, etc.), Mogul series (L, 700, etc.), Monarch series (800, 880, 900, 1000, 10, 1300, 1400, etc.) (manufactured by Cabot Corporation); Color Black series (FW1, FW2, FW2V, FW18, FW200, S150, S160, S1), Printex series (35, U, V, 1400U, etc.), Special Black series (6, 5, 4, 4A, etc.), NIPEX series (150, 160, 170, 180, 95, 90, 85, 80, 75, etc.) (all manufactured by Orion Engineered Carbons Co., Ltd.)

[0088] As organic pigments, one or more can be used. Based on their chemical structure, examples include azo lake pigments, insoluble azo pigments, condensed azo pigments, chelated azo pigments, and other azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene pigments, violet ketone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo sulfide pigments, isoindoline pigments, and quinophthalone pigments; dye chelates such as basic dye chelates and acid dye chelates; nitro pigments; nitroso pigments; and aniline black, etc.

[0089] Specifically, examples of the aforementioned organic pigments include:

[0090] 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, etc.

[0091] CI pigments include reds 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, and other magenta pigments;

[0092] CI pigment blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 60, 63, 66 and other cyan pigments;

[0093] CI pigments include orange 5, 13, 16, 17, 34, 36, 43, 51, 64, 71, and other orange pigments;

[0094] CI pigments include purple 1, 3, 5: 1, 16, 19, 23, 38, etc.

[0095] CI pigments include green pigments 1, 4, 7, 8, 10, 17, 18, and 36.

[0096] 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, 264, etc.

[0097] Regarding the primary particle diameter of the aforementioned pigment, from the viewpoint of dispersibility, it is preferably 25 μm or less, more preferably 10 μm or less, and even more preferably 1 μm or less. From the viewpoint of stability, it can be, for example, 10 μm or more, or 30 nm or more. The aforementioned primary particle diameter can be measured using a transmission electron microscope (TEM).

[0098] Regarding the volume average particle size of the aforementioned pigments, from the viewpoint of dispersibility, it is preferably 1 μm or less, more preferably 250 nm or less, and even more preferably 200 nm or less. From the viewpoint of stability, it can be, for example, 10 nm or more, or 50 nm or more. The volume average particle size of the aforementioned pigments can be determined using laser diffraction.

[0099] The content of the aforementioned pigment in the aforementioned colorant is preferably 80% by mass or more, more preferably 9% by mass or more, even more preferably 95% by mass or more, and the upper limit is 100% by mass.

[0100] The content of the aforementioned colorant in the solid component 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, preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0101] The aforementioned pigment dispersant is a compound having both hydrophilic and hydrophobic parts, and it improves the dispersibility of pigments in aqueous media. Examples of such pigment dispersants include styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylate-(meth)acrylic acid copolymers, and (meth)acrylate-(meth)acrylic acid copolymers. When using the aforementioned styrene-acrylic acid copolymers, alkaline compounds such as potassium hydroxide can coexist in the aforementioned aqueous pigment dispersion.

[0102] The content of the pigment dispersant relative to 100 parts by weight of the colorant is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 20 parts by weight or more, preferably 100 parts by weight or less, more preferably 70 parts by weight or less, and even more preferably 50 parts by weight or less.

[0103] As the aforementioned organic solvents, hydrophilic organic solvents (organic solvents miscible with water at 25°C) are preferred. Specifically, examples 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, pentanol, and 2-methoxyethanol; ether solvents such as tetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane; amide solvents such as dimethylformamide and N-methylpyrrolidone; and solvents such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, and polypropylene glycol. Diol solvents; butanediol, pentanediol, hexanediol and diols of the same group; propylene glycol ester solvents; diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether, dipropylene glycol monoethyl ether, triethylene glycol monoethyl ether and other diol ether solvents; sulfolane; γ-butyrolactone and other lactone solvents; N-methylpyrrolidone, N-(2-hydroxyethyl)pyrrolidone, 2-pyrrolidone and other lactam solvents; acetonitrile solvents; glycerol; glycerol derivatives such as glycerol with added polyoxyethylene; and mixed solvents of one or more of these solvents.

[0104] From the viewpoint of dispersibility and storage stability, the organic solvent is preferably 1 to 300 parts by mass relative to 100 parts by mass of the pigment, more preferably 4 to 200 parts by mass.

[0105] The aforementioned water-based inkjet ink can be manufactured by first mixing and dispersing the aforementioned colorant, pigment dispersant, organic solvent, aqueous medium, and an alkaline compound as needed to prepare a colorant dispersion, and then mixing the aforementioned resin composition, drying inhibitor, penetrant, surfactant, and other additives. When preparing the aforementioned colorant dispersion, examples of mixing and dispersion methods include wet dispersion and compounding dispersion, with wet dispersion being preferred.

[0106] As a drying inhibitor, it is preferable to use a drying inhibitor that is miscible with aqueous media and can prevent clogging of the inkjet printer nozzle. Examples include glycerol, ethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol mono-n-butyl ether, polyethylene glycol with a molecular weight of less than 2000, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, erythritol, pentaerythritol, etc. Among these, glycerol and triethylene glycol are preferred as drying inhibitors because of their high safety and ability to impart drying properties and excellent ejection performance to the ink. The content of the above-mentioned drying inhibitor in the above-mentioned aqueous inkjet ink is preferably 3 to 50% by mass.

[0107] Examples of the aforementioned penetrants include lower alcohols such as ethanol and isopropanol, and glycol monoethers of alkyl alcohols such as ethylene glycol hexyl ether, diethylene glycol butyl ether, and propylene glycol propyl ether. Regarding the content of the aforementioned penetrant, from the viewpoint of improving the permeability of the ink to the recording medium and adjusting the diameter of the ink droplets on the recording medium, it is preferably 0.01 to 10% by mass in the aforementioned aqueous inkjet ink.

[0108] Examples of surfactants mentioned above 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.

[0109] Examples of anionic surfactants include alkylbenzene sulfonates, alkylphenyl sulfonates, alkylnaphthalene sulfonates, higher fatty acid salts, sulfate salts of higher fatty acid esters, sulfonates of higher fatty acid esters, sulfate salts and sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, and polyoxyethylene alkyl ether phosphates. Specific examples of these surfactants include dodecylbenzene sulfonate, isopropylnaphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutyldiphenyl sulfonate, and dibutylphenylphenol disulfonate.

[0110] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, dehydrated sorbitol fatty acid esters, polyoxyethylene dehydrated sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerol fatty acid esters, polyoxyethylene glycerol fatty acid esters, polyglycerol fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkanolamides, alkyl alkanolamides, acetylenol, ethylene oxide adducts of acetylenol, and polyethylene glycol-polypropylene glycol block copolymers. Among these, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid esters, dehydrated sorbitol fatty acid esters, polyoxyethylene dehydrated sorbitol fatty acid esters, fatty acid alkanolamides, acetylenol, ethylene oxide adducts of acetylenol, and polyethylene glycol-polypropylene glycol block copolymers are preferred.

[0111] Other surfactants that can be used include silicone surfactants such as polysiloxane ethylene oxide adducts; fluorinated surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylidene perfluoroalkyl ethers; and biosurfactants such as 4,5-dicarboxy-γ-pentadecanolactone, rhamnolipids, and lysophosphatidylcholine.

[0112] Regarding the content of the surfactant, from the viewpoint of effectively preventing bleeding of printed images, the content 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.

[0113] Water-based inks used in inkjet printing can be used for printing on various recording media. These recording media can include absorbent recording media such as photocopying paper (PPC paper) commonly used in copiers, recording media with an absorbent layer of ink, non-absorbent recording media without ink absorption, non-absorbent recording media with low ink absorbency, fabrics, films, etc.

[0114] The water-based inkjet ink binder of the present invention is useful in printing on various recording media due to its excellent storage stability, ejection properties, and the abrasion resistance and washability of the printed matter.

[0115] Example

[0116] The present invention will be described in more detail below with specific examples. It should be noted that the weight-average molecular weight and average particle size are values ​​measured under the following measurement conditions.

[0117] [GPC Measurement Conditions]

[0118] Measurement apparatus: High-speed GPC apparatus (TOSOH Corporation "HLC-8220GPC")

[0119] Chromatographic column: Use the following chromatographic columns manufactured by TOSOH Corporation in series.

[0120] "TSKgel G5000" (7.8mm I.D. × 30cm) × 1 stick

[0121] "TSKgel G4000" (7.8mm I.D. × 30cm) × 1 stick

[0122] "TSKgel G3000" (7.8mm I.D. × 30cm) × 1 stick

[0123] "TSKgel G2000" (7.8mm I.D. × 30cm) × 1 stick

[0124] Detector: RI (Differential Refractometer)

[0125] Column temperature: 40℃

[0126] Eluent: Tetrahydrofuran (THF)

[0127] Flow rate: 1.0 mL / min

[0128] Injection volume: 100 μL (tetrahydrofuran solution with a sample concentration of 4 mg / mL)

[0129] Standard samples: A standard curve was prepared using the following monodisperse polystyrene.

[0130] (Monodisperse polystyrene)

[0131] "TSKgel Standard Polystyrene A-500" manufactured by TOSOH Corporation

[0132] "TSKgel Standard Polystyrene A-1000" manufactured by TOSOH Corporation

[0133] "TSKgel Standard Polystyrene A-2500" manufactured by TOSOH Corporation

[0134] "TSKgel Standard Polystyrene A-5000" manufactured by TOSOH Corporation

[0135] "TSKgel Standard Polystyrene F-1" manufactured by TOSOH Corporation

[0136] "TSKgel Standard Polystyrene F-2" manufactured by TOSOH Corporation

[0137] "TSKgel Standard Polystyrene F-4" manufactured by TOSOH Corporation

[0138] "TSKgel Standard Polystyrene F-10" manufactured by TOSOH Corporation

[0139] "TSKgel Standard Polystyrene F-20" manufactured by TOSOH Corporation

[0140] "TSKgel Standard Polystyrene F-40" manufactured by TOSOH Corporation

[0141] "TSKgel Standard Polystyrene F-80" manufactured by TOSOH Corporation

[0142] "TSKgel Standard Polystyrene F-128" manufactured by TOSOH Corporation

[0143] "TSKgel Standard Polystyrene F-288" manufactured by TOSOH Corporation

[0144] "TSKgel Standard Polystyrene F-550" manufactured by TOSOH Corporation

[0145] [Particle size determination conditions]

[0146] The water-based inkjet ink was diluted with water and binder to prepare a diluted dispersion with a concentration of 0.1% by mass. The diluted dispersion was then used to measure the particle size using a particle size analyzer (Microtrac BEL Co., Ltd.'s "Nanotrac Wave II": calculated using dynamic light scattering method). The 50% median particle size was set as the average particle size.

[0147] (Synthetic Example 1: Synthesis of acrylic macromonomer (1))

[0148] 700 parts by mass of methyl ethyl ketone were added to a four-necked flask equipped with a thermometer, a stirring device, a reflux condenser and a nitrogen inlet tube. 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 supplied to the above reaction vessel to allow them to react, thereby obtaining an acrylic macromonomer (1) as a vinyl polymer with two hydroxyl groups at one end and a number average molecular weight of 3000.

[0149] (Manufacturing Example 1: Manufacturing of polyurethane (a1-1) with acid groups)

[0150] 50.9 parts by mass of PTMG1k (PTMG1000, manufactured by Mitsubishi Chemical; polytetramethylene ether glycol with a number average molecular weight of 1000) and 12.6 parts by mass of 2,2-dimethylolpropionic acid (DMPA) were added to a four-necked flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet, and stirred thoroughly. Then, 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 reaction was carried out at 75°C for 4 hours. After the reaction, methyl ethyl ketone (MEK) was added to bring 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 were added to the obtained urethane prepolymer solution to neutralize the acid groups. Then, deionized water was added under vigorous stirring to bring the solids concentration to 18% to emulsify the polyurethane. After the reaction was completed, MEK was removed by vacuum distillation to obtain an aqueous dispersion of polyurethane (a1-1) with acid groups. The non-volatile component of this aqueous dispersion was 30% by mass.

[0151] (Manufacturing Example 2: Manufacturing of polyurethane (a1-2) with acid groups)

[0152] Except for changing the raw material formulation as shown in Table 1, an aqueous dispersion of polyurethane (a1-2) with acid groups was obtained in the same manner as in Manufacturing Example 1. The non-volatile component of this aqueous dispersion is 30% by mass.

[0153] (Manufacturing Example 3: Manufacturing of polyurethane (al-3) with acid groups)

[0154] Except for changing the raw material formulation as shown in Table 1, a urethane prepolymer solution with acid groups was obtained in the same manner as in Manufacturing Example 1. 1.9 parts by mass of potassium hydroxide was added to the obtained urethane prepolymer solution to neutralize the acid groups. Then, under vigorous stirring, deionized water was added to bring the solids concentration to 18%, and 2.7 parts by mass of ethylenediamine was added dropwise to initiate a chain-promoting reaction. After the reaction was complete, MEK was removed by vacuum distillation to obtain an aqueous dispersion of polyurethane (a1-3) with acid groups. The non-volatile component of this aqueous dispersion was 30% by mass.

[0155] (Manufacturing Example 4: Manufacturing of polyurethane (a1-4) with acid groups)

[0156] Except for changing the raw material formulation as shown in Table 1, an aqueous dispersion of polyurethane (a1-4) with acid groups was obtained in the same manner as in Manufacturing Example 3. The non-volatile component of this aqueous dispersion is 30% by mass.

[0157] (Manufacturing Example 5: Manufacturing of polyurethane (a1-5) with acid groups)

[0158] Except for changing the raw material formulation as shown in Table 1, an aqueous dispersion of polyurethane (a1-5) with acid groups was obtained in the same manner as in Manufacturing Example 1. The non-volatile component of this aqueous dispersion is 30% by mass.

[0159] (Manufacturing Example 6: Manufacturing of polyurethane (a1-6) with acid groups)

[0160] Except for changing the raw material formulation as shown in Table 1, an aqueous dispersion of polyurethane (a1-6) with acid groups was obtained in the same manner as in Manufacturing Example 1. The non-volatile component of this aqueous dispersion is 30% by mass.

[0161] The formulations of the acid-group polyurethanes (a1-1) to (a1-6) obtained above are shown in Table 1.

[0162] Table 1

[0163]

[0164] The abbreviations in Table 1 are shown below.

[0165] PTMG1k: Mitsubishi Chemical's "PTMG1000"; polytetramethylene ether glycol with a number average molecular weight of 1000.

[0166] Excenol 2020: AGC-manufactured "Excenol 2020"; polypropylene glycol with a number average molecular weight of 2000.

[0167] UH-100: "ETERNACOLL UH-100" manufactured by Ube Industries; a crystalline polycarbonate diol with a number average molecular weight of 1000.

[0168] UH-200: "ETERNACOLL UH-200" manufactured by Ube Industries; a crystalline polycarbonate diol with a number average molecular weight of 2000.

[0169] G3450J: "DURANOL G3450J" manufactured by Asahi Kasei; number average molecular weight 800

[0170] (Example 1: Manufacturing of binder (1) for water-based inkjet ink)

[0171] 233.4 parts by mass of an aqueous dispersion of the acid-containing polyurethane (a1-1) obtained in Manufacturing Example 1 were mixed with 236.6 parts by mass of deionized water. 15 parts by mass of methyl methacrylate and 15 parts by mass of 2-hydroxyethyl (meth)acrylate were then reacted using 0.01 parts by mass of ammonium persulfate (APS) in a one-step emulsion polymerization process (reaction temperature 80°C). After removing unreacted monomers, the mixture was concentrated, and the water content was adjusted to 20% by mass. This resulted in an aqueous dispersion of the composite resin, yielding an aqueous inkjet ink binder (1). The mass ratio (a1 / a2) was 70 / 30, and the glass transition temperature of the acrylic polymer was 78°C. Furthermore, the particle size distribution of the composite resin exhibited a single peak, confirming the formation of core-shell particles with an average particle size of 24 nm.

[0172] (Examples 2-6: Manufacturing of binders (2)-(6) for water-based inkjet inks)

[0173] Except that the aqueous dispersion of the acid-based polyurethane (a1-1) used in Example 1 was changed to an aqueous dispersion of the acid-based polyurethane (a1-2) to (a1-6), the aqueous dispersions of the composite resin were obtained as in Example 1, and the binders (2) to (6) for water-based inkjet inks were obtained as in Example 1. The mass ratio (a1 / a2) was 70 / 30 for all of them. In addition, the particle size distribution of the composite resin showed a single peak, confirming the formation of core-shell particles. Regarding the average particle size, the binder (2) for water-based inkjet inks was 83 nm, the binder (3) for water-based inkjet inks was 44 nm, the binder (4) for water-based inkjet inks was 45 nm, the binder (5) for water-based inkjet inks was 111 nm, and the binder (6) for water-based inkjet inks was 123 nm.

[0174] (Example 7: Manufacturing of binder (7) for water-based inkjet ink)

[0175] 236.6 parts by mass of ion-exchanged water were added to 233.4 parts by mass of an aqueous dispersion of the acid-containing polyurethane (a1-2) obtained in Manufacturing Example 1. 30 parts by mass of methyl methacrylate were reacted under conditions of one-step emulsion polymerization of monomers using 0.01 parts by mass of ammonium persulfate (APS) (reaction temperature 80°C). After concentration to remove unreacted monomers, the water content was adjusted to 20% by mass, resulting in an aqueous dispersion of the composite resin, thus obtaining an aqueous inkjet ink binder (7). The mass ratio (a1 / a2) was 70 / 30. The glass transition temperature of the acrylic polymer was 105°C. Furthermore, the particle size distribution of the composite resin showed a single peak, confirming the formation of core-shell particles with an average particle size of 115 nm.

[0176] (Example 8: Manufacturing of binder (8) for water-based inkjet ink)

[0177] 233.4 parts by mass of an aqueous dispersion of the acid-containing polyurethane (a1-2) obtained in Manufacturing Example 1 were mixed with 236.6 parts by mass of ion-exchanged water. 20 parts by mass of ethyl acrylate and 10 parts by mass of styrene were then reacted using a one-step emulsion polymerization of monomers with 0.01 parts by mass of ammonium persulfate (APS) (reaction temperature 80°C). After concentration to remove unreacted monomers, the water content was adjusted to 20% by mass, resulting in an aqueous dispersion of the composite resin, thus obtaining an aqueous inkjet ink binder (8). The mass ratio (a1 / a2) was 70 / 30. The glass transition temperature of the acrylic polymer was 9°C. Furthermore, the particle size distribution of the composite resin showed a single peak, confirming the formation of core-shell particles with an average particle size of 121 nm.

[0178] (Comparative Example 1: Binder (R1) for Water-based Inkjet Ink)

[0179] The aqueous dispersion of the polyurethane (a1-1) with acid groups obtained in Manufacturing Example 1 is designated as a binder (R1) for water-based inkjet inks.

[0180] [Preparation of Pigment Dispersions]

[0181] Add 50 parts by weight of CI Pigment Red 122 (manufactured by DIC Co., Ltd., “FASTOGEN Super Magenta RY”), CI Pigment Blue 15:3 (manufactured by DIC Co., Ltd., SBG-SD), and 10 parts by weight of styrene-acrylic acid copolymer (weight average molecular weight 11000, acid value 180mgKOH / g) to a 0.5L jacketed container of a mini planetary mixer (Aikosha Co., Ltd. mini-PLM). While heating the jacketed container to 80°C, stir for 10 minutes at a rotation speed of 80 rpm and a revolution speed of 25 rpm.

[0182] Then, while maintaining the temperature of the jacketed tank at 80°C, 5.3 parts by mass of a 34% by mass potassium hydroxide aqueous solution and 30 parts by mass of triethylene glycol were added to the above 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 mixture.

[0183] Add 100 parts by weight of deionized water and 10 parts by weight of triethylene glycol to the above mixture, and mix for 10 minutes using a blender. Mix the deionized water with Proxel-GXL (LONZA JAPAN Co., Ltd.) to obtain an aqueous pigment dispersion with a pigment concentration of 15.0% by weight, a triethylene glycol concentration of 12.0% by weight, a Proxel-GXL concentration of 0.1% by weight, and a non-volatile component concentration of 18.2% by weight.

[0184] [Manufacturing of Water-Based Inkjet Ink]

[0185] 20.0 parts by weight of the pigment dispersion obtained above, 3.3 parts by weight of the above-mentioned water-based inkjet binder, 8.0 parts by weight of 2-pyrrolidone (manufactured by BASF), 8.0 parts by weight of triethylene glycol mono-n-butyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.), 3.0 parts by weight of glycerin (manufactured by Kao Corporation), 0.5 parts by weight of Surfynol 440 (nonionic surfactant, manufactured by Evonik Japan Co., Ltd.), and 57.3 parts by weight of ion-exchanged water were stirred for 1 hour.

[0186] Then, the pH was adjusted to the range of 9 to 9.8 using a 5% potassium hydroxide aqueous solution, and the resulting ink 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 solids concentration 1.0%).

[0187] [Evaluation of abrasion resistance]

[0188] The water-based inkjet ink obtained above was filled into an empty ink cartridge of a commercially available ENVY4500 inkjet printer (manufactured by HP). A full-page print with 100% print density was then performed on the printing surface of photo printing paper (HP premium photo paper, manufactured by HP). After drying the print at room temperature for 1 minute, the printing surface was rubbed three times back and forth using a vibration-type abrasion tester under a load of 200g with the same paper as the printing paper.

[0189] Then, the printed surface of the above-mentioned printed material was scanned to digitize the image data, and the pixel retention rate (%) was calculated based on the following formula. The abrasion resistance was evaluated using the following benchmarks.

[0190] Pixel retention rate (%) = (Number of pixels in the shaded area after the swiping test) / (Number of pixels in the shaded area before the swiping test) × 100

[0191] ○:More than 40%

[0192] △: 20% or more but less than 40%

[0193] ×: Less than 20%

[0194] [Evaluation of washability]

[0195] After fully dyeing the cotton fleece fabric, it was dried at 150°C for 5 minutes. Then, a washing solution prepared based on JIS L0844:2011 was heated to 50°C and used to impregnate the cotton fleece fabric (for 30 minutes). The fabric was then stirred in a food mixer for 1 minute, and the resulting test sample was washed with water and dried. The optical density (OD) of the cotton fleece fabric after stirring was measured using an integrating sphere X-Rite spectrophotometer. The OD retention rate (%) was calculated based on the following formula, and the wash resistance was evaluated using the following criteria.

[0196] OD retention rate (%) = (OD of cotton fleece after stirring) / (OD of cotton fleece before washing liquid immersion) × 100

[0197] ○:More than 50%

[0198] △: 45% or more but less than 50%

[0199] ×: Less than 45%

[0200] The results of the compatibility and evaluation of the water-based inkjet inks obtained above with binders (1) to (8) and (R1) are shown in Table 2.

[0201] Table 2

[0202]

[0203] The printed materials obtained by Examples 1 to 8, which are the binders for water-based inkjet inks of the present invention, are confirmed to have excellent abrasion resistance and washability.

[0204] On the other hand, Comparative Example 1 is an example that uses a urethane resin that does not contain an acrylic polymer (a2), which is an essential component of the present invention; however, it was found that the resulting prints had poor abrasion resistance and washability.

Claims

1. A binder for water-based inkjet inks, characterized in that, The mixture contains a composite resin A and an aqueous medium B. The composite resin A forms core-shell type particles having a shell and a core. The shell comprises a polyurethane a1 with acid groups, and the core comprises an acrylic polymer a2. The monomer raw materials of the acrylic polymer a2 contain alkyl (meth)acrylates with 4 to 10 carbon atoms and alkyl (meth)acrylates containing hydroxyl groups, wherein the alkyl (meth)acrylates with 4 to 10 carbon atoms are methyl methacrylates. The hydroxyl-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℃. The acid value of the polyurethane a1 is in the range of 10 mg KOH / g to 30 mg KOH / g.

2. The binder for water-based inkjet ink according to claim 1, wherein, The mass ratio of the polyurethane a1 to the acrylic polymer a2, a1 / a2, is 95 / 5 to 50 / 50.

3. An aqueous inkjet ink comprising the binder for aqueous inkjet inks as described in claim 1 or 2.

4. A printing layer formed from the aqueous inkjet ink of claim 3.

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