Binder for inkjet ink and inkjet ink

Abstract

This binder for an inkjet ink is made to contain a polyurethane resin (E), which is a chain elongation product, by a polyamine having at least two amino groups and / or imino groups of a neutralized product of an isocyanate group-terminated prepolymer that is a reaction product of (A) a polyisocyanate, (B) a diol, (C) a compound having an anionic hydrophilic group and at least two active hydrogens, and (D) a trivalent or higher polyol, wherein the (B) diol contains at least one selected from the group consisting of (B1) a polycarbonate diol having a structural unit derived from a diol having a branched structure and having 3-10 carbon atoms, and (B2) a polycarbonate diol having a structural unit derived from a diol having a linear structure and an odd number of 3-9.

Description

Binder for inkjet ink and inkjet ink

[0001] The present invention relates to a binder for an inkjet ink and an inkjet ink, and more particularly to a binder for an inkjet ink and an inkjet ink containing a polyurethane resin.

[0002]

[0003] Image formation using the inkjet method involves ejecting minute droplets of ink from nozzles in a recording head and causing them to land on a recording medium to form an image. Solvent-based or water-based inkjet inks have traditionally been used for image formation using this inkjet method. However, solvent-based inkjet inks have problems such as the odor of the solvent and the health effects of volatile components, and therefore there is a growing need for water-based inkjet inks.

[0003] For example, Japanese Patent Laid-Open Publication No. 2022-98703 (Patent Document 1) discloses an aqueous inkjet ink containing a binder resin composition for aqueous inkjet inks, which comprises a urethane resin, a basic compound, and an aqueous medium, wherein the urethane resin is a reaction product of a polyol, a polyisocyanate, and a polyamine compound, the polyol comprises a crystalline polycarbonate diol and a diol having an acid group, the polyisocyanate comprises an alicyclic polyisocyanate, the polyamine compound comprises a linear diamine, and the urethane resin has an acid value of 15 mg KOH / g or more and 60 mg KOH / g or less, and also describes that the inkjet ink achieves abrasion resistance and wash resistance of printed matter.

[0004] Furthermore, Japanese Patent Laid-Open No. 2022-146158 (Patent Document 2) describes an aqueous polyurethane resin dispersion for inkjet inks, which contains water and a polyurethane resin obtained by reacting a polyol component with a polyisocyanate component, wherein the polyurethane resin is a polyurethane resin having a carboxyl group and / or a carboxylate anion group, the polyol component is a polyol component containing polytetramethylene ether glycol, and the weight ratio of the polytetramethylene ether glycol is 1 / 100 of the total weight of the polyol component and the polyisocyanate component. The article discloses an aqueous polyurethane resin dispersion in which the weight ratio of the polyisocyanate component is 10 to 70% by weight based on the total weight of the polyol component and the polyisocyanate component, the polyisocyanate component contains isophorone diisocyanate, the weight ratio of the isophorone diisocyanate is 25 to 70% by weight based on the total weight of the polyol component and the polyisocyanate component, the acid value of the polyurethane resin is 15 to 40 mgKOH / g, and the content of urea groups in the polyurethane resin is 0.45 mol / kg or less, and it also describes that the polyurethane resin has excellent blocking resistance and adhesion.

[0005] JP 2022-98703 A JP 2022-146158 A

[0006] However, the aqueous inkjet ink described in Patent Document 1 and the inkjet ink containing an aqueous polyurethane resin dispersion described in Patent Document 2 did not provide sufficient adhesion of the printed layer to the substrate (particularly a plastic substrate). Furthermore, conventional aqueous inkjet inks did not necessarily have sufficient water resistance.

[0007] The present invention has been made in view of the problems associated with the above-mentioned conventional techniques, and aims to provide a binder that is capable of forming a printing layer that has excellent adhesion to a substrate and excellent water resistance, and an inkjet ink using the binder.

[0008] As a result of extensive research to achieve the above object, the present inventors have found that by using an aqueous dispersion containing a polyurethane resin synthesized using at least one of a polycarbonate diol having structural units derived from a diol with a branched structure and 3 to 10 carbon atoms and a polycarbonate diol having structural units derived from a diol with a linear structure and an odd number of carbon atoms of 3 to 9, and a trivalent or higher polyol, as a binder for an inkjet ink, a printed layer having excellent adhesion to a substrate and excellent water resistance can be formed, leading to the completion of the present invention.

[0009] That is, the present invention provides the following aspects: [1] An ink-jet ink binder containing a polyurethane resin which is a chain-extended product of a neutralized isocyanate-terminated prepolymer, which is the reaction product of (A) a polyisocyanate, (B) a diol, (C) a compound having an anionic hydrophilic group and at least two active hydrogen atoms, and (D) a polyol with a valence of three or more, with (E) a polyamine having two or more amino and / or imino groups, wherein the diol (B) comprises at least one selected from the group consisting of (B1) a polycarbonate diol having a structural unit derived from a diol having a branched structure and 3 to 10 carbon atoms and (B2) a polycarbonate diol having a straight-chain structure and an odd-numbered diol having 3 to 9 carbon atoms. [2] The ink-jet ink binder according to [1], wherein the polyurethane resin has an acid value of 5 to 50 mgKOH / g. [3] The binder for ink-jet ink according to [1] or [2], wherein the proportion of the (D) polyol is 0.1 to 1.5% by mass relative to the total amount of the (B) diol, the (C) compound, and the (D) polyol. [4] The binder for ink-jet ink according to any one of [1] to [3], wherein the total proportion of the (B1) polycarbonate diol and the (B2) polycarbonate diol is 50% by mass or more and the total proportion of the (B1) polycarbonate diol, the (B2) polycarbonate diol, the (C) compound, and the (D) polyol is 100% by mass or less relative to the total amount of the (B) diol, the (C) compound, and the (D) polyol. [5] An ink-jet ink containing the binder for ink-jet ink according to any one of [1] to [4], a pigment, and an aqueous medium.

[0010] According to the present invention, it is possible to form a printing layer that has excellent adhesion to a substrate and excellent water resistance.

[0011] The present invention will be described in detail below based on preferred embodiments thereof.

[0012] [Binder for Inkjet Ink] The binder for inkjet ink of the present invention (hereinafter also referred to as "binder") contains a polyurethane resin which is a chain-extended product of a neutralized isocyanate-terminated prepolymer which is a reaction product of (A) a polyisocyanate, (B) a diol including a specific polycarbonate diol, (C) a compound having an anionic hydrophilic group and at least two active hydrogen atoms (hereinafter also referred to as "anionic hydrophilic group-containing active hydrogen compound"), and (D) a trivalent or higher polyol, with a polyamine having two or more amino groups and / or imino groups (E).

[0013] (A) Polyisocyanate The (A) polyisocyanate used in the present invention is not particularly limited, and examples thereof include aromatic polyisocyanate compounds, aliphatic polyisocyanate compounds, and alicyclic polyisocyanate compounds that have been conventionally used. Examples of aromatic polyisocyanate compounds include m-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate (1,5-NDI), tolidine diisocyanate, tetramethylxylylene diisocyanate (TMXDI), and xylylene diisocyanate (XDI). Examples of aliphatic polyisocyanate compounds include tetramethylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate, etc. Examples of alicyclic polyisocyanate compounds include isophorone diisocyanate (IPDI), hydrogenated xylylene diisocyanate (H6XDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate, norbornane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, etc. These polyisocyanates may be used alone or in combination of two or more. Among these polyisocyanates, aliphatic polyisocyanates and alicyclic polyisocyanates are preferred from the viewpoint of obtaining a non-yellowing polyurethane resin.

[0014] (B) Diol The (B) diol used in the present invention comprises at least one selected from the group consisting of (B1) polycarbonate diols having structural units derived from diols with a branched structure and a carbon number of 3 to 10, and (B2) polycarbonate diols having structural units derived from diols with a linear structure and an odd number of carbon atoms of 3 to 9. By blending at least one of such (B1) polycarbonate diols and (B2) polycarbonate diols in an inkjet ink, a printed layer with excellent adhesion to a substrate can be formed.

[0015] In the present invention, the (B1) polycarbonate diol is preferably a polycarbonate diol having a structural unit derived from a diol having a branched structure and a carbon number of 3 to 10 and a structural unit derived from a diol having a linear structure and a carbon number of 3 to 10, or a polycarbonate diol having structural units derived only from a diol having a branched structure and a carbon number of 3 to 10. Furthermore, the (B2) polycarbonate diol is preferably at least one selected from the group consisting of a polycarbonate diol having a structural unit derived from a diol having a linear structure and a carbon number of 3 to 9, an odd number, and a diol having a linear structure and a carbon number of 4 to 10, and a polycarbonate diol having structural units derived only from a diol having a linear structure and a carbon number of 3 to 9, an odd number.

[0016] The number average molecular weight of the (B1) polycarbonate diol and the (B2) polycarbonate diol is preferably 400 to 4000, and more preferably 800 to 3000. If the number average molecular weight of the (B1) polycarbonate diol and the (B2) polycarbonate diol is less than the lower limit, the adhesion of the formed printing layer to the substrate may decrease, while if the number average molecular weight of the (B1) polycarbonate diol and the (B2) polycarbonate diol exceeds the upper limit, the viscosity of the polycarbonate diol itself tends to be too high, making it difficult to handle.

[0017] Examples of the diols having a branched structure and an integer of 3 to 10 carbon atoms include 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, and 2,2-dimethyl-1,3-propanediol. Examples of the diols having a linear structure and an odd number of carbon atoms from 3 to 9 include 1,3-propanediol, 1,5-pentanediol, 1,7-heptanediol, and 1,9-nonanediol. Examples of the diols having a linear structure and an even number of carbon atoms from 4 to 10 include 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, and 1,10-decanediol.

[0018] Specific examples of the (B1) polycarbonate diol include polycarbonate diols derived from 3-methyl-1,5-pentanediol / 1,6-hexanediol (for example, Kuraray Polyol C-590 (number average molecular weight: 500), Kuraray Polyol C-1090 (number average molecular weight: 1000), Kuraray Polyol C-2050 (number average molecular weight: 2000), Kuraray Polyol C-2090 (number average molecular weight: 2000), and Kuraray Polyol C-3090 (number average molecular weight: 3000), all manufactured by Kuraray Co., Ltd.), polycarbonate diols derived from 2-methyl-1,3-propanediol (for example, ETERNACOLL UP-50 (number average molecular weight: 500), ETERNACOLL UP-100 (number average molecular weight: 1000), and ETERNACOLL UP-200 (number average molecular weight: 2000), all manufactured by UBE Co., Ltd.), and polycarbonate diols derived from 2-methyl-1,3-propanediol (for example, ETERNACOLL UP-50 (number average molecular weight: 500), ETERNACOLL UP-100 (number average molecular weight: 1000), and ETERNACOLL UP-200 (number average molecular weight: 2000), all manufactured by UBE Co., Ltd.). UP-200 (number average molecular weight: 2000)), polycarbonate diols derived from 2,2-dimethyl-1,3-propanediol (for example, BENEBiOL NL1005B (number average molecular weight 1000), BENEBiOL NL2005B (number average molecular weight 2000), BENEBiOL NL1030B (number average molecular weight 1000), BENEBiOL NL2030B (number average molecular weight 2000) manufactured by Mitsubishi Chemical Corporation).

[0019] Specific examples of the (B2) polycarbonate diol include polycarbonate diols derived from 1,5-pentanediol / 1,6-hexanediol (for example, Duranol T5650E (number average molecular weight: 500), Duranol T5650J (number average molecular weight: 800), Duranol T5651 (number average molecular weight: 1000), and Duranol T5652 (number average molecular weight: 2000), all manufactured by Asahi Kasei Corporation; and ETERNACOLL PH-50 (number average molecular weight: 500), ETERNACOLL PH-100 (number average molecular weight: 1000), ETERNACOLL PH-200 (number average molecular weight: 2000), all manufactured by UBE Corporation). PH-300 (number average molecular weight: 3000)), and polycarbonate diol derived from 1,3-propanediol (for example, HS PD-2003 (weight average molecular weight: 2000) manufactured by Toyokuni Oil Mills Co., Ltd.).

[0020] In the present invention, in addition to the (B1) polycarbonate diol and the (B2) polycarbonate diol, a diol other than the (B1) polycarbonate diol and the (B2) polycarbonate diol (hereinafter also referred to as "other diol") may be used in combination. Examples of the other diol include polycarbonate diols other than the (B1) polycarbonate diol and the (B2) polycarbonate diol (hereinafter also referred to as "other polycarbonate diol"), polyester diols, polyether diols, and low-molecular-weight diols having a number-average molecular weight of 400 or less. These other diols may be used alone or in combination of two or more.

[0021] Examples of other polycarbonate diols include polycarbonate diols obtained by reacting glycols having a linear structure and an even number of carbon atoms, such as 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, and diethylene glycol, with diphenyl carbonate, phosgene, etc. These other polycarbonate diols may be used alone or in combination of two or more.

[0022] Examples of polyester diols include diol components such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 300 to 1000 polyethylene glycol, dipropylene glycol, tripropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanedimethanol, bisphenol A, bisphenol S, hydrogenated bisphenol A, hydroquinone, and alkylene oxide adducts thereof, and dimer acids. , succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic anhydride, fumaric acid, 1,3-cyclopentanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, 1,2-bisphenoxyethane-p,p'-dicarboxylic acid, anhydrides or ester-forming derivatives of dicarboxylic acids, polyester diols obtained by ring-opening polymerization of cyclic ester compounds such as ε-caprolactone, and polyester diols copolymerized therewith. These polyester diols may be used alone or in combination of two or more.

[0023] Examples of polyether diols include polymers of alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide; and alkylene oxide adducts of alkylene diols such as ethylene glycol, propylene glycol, and 1,4-pentanediol. Such alkylene oxide polymers and adducts may be homopolymers or homoadducts of one type of alkylene oxide, or copolymers or coadducts of two or more types of alkylene oxides. In the case of copolymers or coadducts, they may be random polymers or random adducts, or block polymers or block adducts. The molecular weight of such polyether diols is preferably 400 to 5,000. These polyether diols may be used alone or in combination of two or more types.

[0024] Examples of low-molecular-weight diols include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, nonanediol, and neopentyl glycol. These low-molecular-weight diols may be used alone or in combination of two or more. From the viewpoints of adhesion of the printed layer to the substrate and water resistance, the content of this low-molecular-weight diol is preferably less than 5% by mass relative to the total amount of the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) trivalent or higher polyol.

[0025] In the present invention, it is preferable that the ratio of the total amount of the (B1) polycarbonate diol and the (B2) polycarbonate diol to the total amount of the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) polyol [(B1 + B2) / (B + C + D)] is 50 mass% or more, and the ratio of the total amount of the (B1) polycarbonate diol, the (B2) polycarbonate diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) polyol [(B1 + B2 + C + D) / (B + C + D)] is 100 mass% or less. In this case, it is preferable that the amount of the (C) anionic hydrophilic group-containing active hydrogen compound is such that the acid value of the resulting polyurethane resin falls within the range described below, and it is preferable that the amount of the (D) polyol is such that the proportion of the (D) polyol falls within the range described below.

[0026] In the present invention, from the viewpoint of adhesion of the formed printing layer to the substrate, the ratio of the total amount of the (B1) polycarbonate diol and the (B2) polycarbonate diol to the total amount of the (B) diol, the (C) compound, and the (D) polyol [(B1+B2) / (B+C+D)] is preferably 50 to 98 mass%, more preferably 80 to 95 mass%.

[0027] (C) Anionic Hydrophilic Group-Containing Active Hydrogen Compound The anionic hydrophilic group-containing active hydrogen compound (C) used in the present invention is a compound having a carboxy group (—COOH), a carboxylate group (—COO － ), sulfo group (—SO ３ H), sulfonate group (—SO ３ －(C) Anionic hydrophilic group-containing active hydrogen compounds are compounds having anionic hydrophilic groups such as 2,2-dimethylolpropionic acid (DMPA), 2,2-dimethylolbutanoic acid (DMBA), 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dihydroxymaleic acid, 2,6-dihydroxybenzoic acid, and the like. Furthermore, polyester polyols having pendant carboxy groups obtained by reacting a diol having a carboxy group with an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, or the like can also be used as the (C) anionic hydrophilic group-containing active hydrogen compound. When synthesizing a polyester polyol having pendant carboxy groups, a diol not having a carboxy group may be used in combination with a diol having a carboxy group. These anionic hydrophilic group-containing active hydrogen compounds may be used alone or in combination of two or more.

[0028] In the present invention, the proportion of the (C) anionic hydrophilic group-containing active hydrogen compound is preferably set so that the acid value of the resulting polyurethane resin falls within the range described below, from the viewpoints of the storage stability of the resulting binder and the water resistance of the resulting printed layer.

[0029] (D) Polyol The (D) polyol used in the present invention is a trivalent or higher polyol. By incorporating a trivalent or higher polyol into an inkjet ink, a printed layer with excellent adhesion to the substrate and excellent water resistance can be formed. Examples of such (D) polyols include low-molecular-weight trivalent or higher polyols with a molecular weight of 500 or less, such as trimethylolpropane, pentaerythritol, and sorbitol. Compounds with a molecular weight of 500 or less, obtained by adding one or more alkylene oxides to such low-molecular-weight trivalent or higher polyols or low-molecular-weight trivalent or higher polyalkylene polyamines with a molecular weight of 500 or less, can also be used as the (D) polyol. Examples of the low-molecular-weight polyalkylene polyamines include ethylene diamine, diethylene triamine, and triethylene tetramine. Examples of the alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide. These polyols may be used alone or in combination. Among these polyols, tri- to tetrahydric polyols are preferred, and trihydric polyols are more preferred, from the viewpoint of the adhesion of the printed layer to the substrate and water resistance.

[0030] In the present invention, the proportion of the (D) polyol is preferably 0.1 to 1.5 mass %, more preferably 0.2 to 1.0 mass %, based on the total amount of the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) polyol. If the proportion of the (D) polyol is less than the lower limit, the crosslink density of the resulting polyurethane resin tends to be low, and the water resistance of the resulting printed layer may be insufficient. On the other hand, if the proportion of the (D) polyol exceeds the upper limit, the crosslink density of the polyurethane resin tends to be too high, and the adhesion of the resulting printed layer to the substrate may be reduced.

[0031] (E) Polyamine The (E) polyamine used in the present invention has two or more amino groups and / or two or more imino groups. Examples of such (E) polyamine include diamines such as ethylenediamine, propylenediamine, tetramethylenediamine, hexamethylenediamine, diaminocyclohexylmethane, hydrazine, piperazine, 2-methylpiperazine, isophoronediamine, norboranediamine, diaminodiphenylmethane, tolylenediamine, and xylylenediamine; polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and iminobispropylamine; and diprimary amines. and amidoamines derived from monocarboxylic acids; water-soluble amine derivatives such as monoketimines of diprimary amines; and hydrazine derivatives such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, itaconic acid dihydrazide, 1,1'-ethylenehydrazine, 1,1'-trimethylenehydrazine, and 1,1'-(1,4-butylene)dihydrazine. These polyamines may be used alone or in combination of two or more. Among these polyamines, ethylenediamine, hydrazine, piperazine, isophoronediamine, norbornanediamine, diethylenetriamine, and triethylenetetramine are preferred.

[0032] In the present invention, the proportion of the polyamine (E) is preferably an amount containing 0.8 to 1.2 equivalents of amino groups relative to the free isocyanate groups of the isocyanate-terminated prepolymer described below.

[0033] (Isocyanate-Terminated Prepolymer and Neutralized Product Thereof) The isocyanate-terminated prepolymer used in the present invention is a reaction product of the (A) polyisocyanate, the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) polyol.

[0034] The method for producing such an isocyanate-terminated prepolymer is not particularly limited, and examples include the conventionally known single-stage so-called one-shot method and the multi-stage isocyanate polyaddition reaction method. The reaction temperature is preferably 40 to 150°C. In this case, if necessary, a reaction catalyst such as dibutyltin dilaurate, stannous octoate, dibutyltin di-2-ethylhexoate, triethylamine, triethylenediamine, N-methylmorpholine, or bismuth tris(2-ethylhexanoate), or a reaction inhibitor such as phosphoric acid, sodium hydrogen phosphate, paratoluenesulfonic acid, adipic acid, or benzoyl chloride may be added.

[0035] Furthermore, an organic solvent that does not react with isocyanate groups may be added during or after the reaction. Examples of such organic solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, dimethylformamide, dimethyl sulfoxide, toluene, xylene, ethyl acetate, butyl acetate, and methylene chloride. Among these organic solvents, methyl ethyl ketone, toluene, and ethyl acetate are particularly preferred. Furthermore, these organic solvents can be removed by heating and reducing the pressure after the prepolymer is emulsified and dispersed and chain-extended.

[0036] When producing an isocyanate-terminated prepolymer, the molar ratio (NCO / OH) of the isocyanate groups to the hydroxyl groups in the raw material is preferably 1.1 / 1.0 to 1.5 / 1.0, and more preferably 1.25 / 1.0 to 1.35 / 1.0. By adjusting the molar ratio of the isocyanate groups to the hydroxyl groups in the raw material within the above range, an isocyanate-terminated prepolymer having the desired free isocyanate group content can be obtained. If the molar ratio of the isocyanate groups to the hydroxyl groups in the raw material is below the above lower limit, the viscosity of the resulting isocyanate-terminated prepolymer tends to be too high, making it difficult to emulsify and disperse. On the other hand, if the molar ratio of the isocyanate groups to the hydroxyl groups in the raw material exceeds the above upper limit, the proportion of urethane bonds and urea bonds increases, the hardness of the resulting polyurethane resin becomes too high, and the adhesion of the resulting printed layer to the substrate may be reduced.

[0037] The content of free isocyanate groups in the isocyanate group-terminated prepolymer obtained in this manner is preferably 0.2 to 4.0% by mass, and more preferably 0.6 to 3.0% by mass. If the free isocyanate group content is less than the lower limit, the viscosity of the obtained isocyanate group-terminated prepolymer tends to be too high, making it difficult to emulsify and disperse, while if the free isocyanate group content exceeds the upper limit, the hardness of the obtained polyurethane resin tends to be too high, potentially reducing the adhesion of the formed printing layer to the substrate.

[0038]

[0033] Note that the (A) polyisocyanate, the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) polyol all have a plurality of reaction sites, and the isocyanate group-terminated prepolymer obtained by reacting such (A) polyisocyanate, the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) polyol has a complex structure and cannot be directly represented by a general formula (structural formula).

[0039] (Neutralized Product of Isocyanate-Terminated Prepolymer) The neutralized product of the isocyanate-terminated prepolymer used in the present invention is obtained by neutralizing the anionic hydrophilic groups in the isocyanate-terminated prepolymer. Such a neutralized product of the isocyanate group-terminated prepolymer may be produced by (i) neutralizing the anionic hydrophilic groups in the isocyanate group-terminated prepolymer obtained by reacting the (A) polyisocyanate, the (B) diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol by a known method, or by (ii) mixing the (A) polyisocyanate, the (B) diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol, neutralizing the anionic hydrophilic groups in the (C) anionic hydrophilic-group-containing active hydrogen compound by a known method, and then reacting the neutralized (C) anionic hydrophilic-group-containing active hydrogen compound, the (A) polyisocyanate, the (B) diol, and the (D) polyol. The neutralized product of the isocyanate group-terminated prepolymer can also be produced by (iii) reacting the (A) polyisocyanate, the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound in which the anionic hydrophilic group is a salt of an anionic hydrophilic group, and the (D) polyol.

[0040] In the production methods (i) and (ii) above, the basic compound used to neutralize the anionic hydrophilic group is not particularly limited, and examples thereof include amines such as trimethylamine, triethylamine, tri-n-propylamine, tributylamine, N-methyl-diethanolamine, N,N-dimethylmonoethanolamine, N,N-diethylmonoethanolamine, and triethanolamine; alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; ammonia, etc. Among these, tertiary amines such as trimethylamine, triethylamine, tri-n-propylamine, tributylamine, and N,N-dimethylmonoethanolamine are particularly preferred.

[0041] In the production methods (i) and (ii) above, when neutralizing the anionic hydrophilic groups, the amount of the neutralizing basic compound used is preferably 0.5 to 1.5 equivalents, more preferably 0.6 to 1.4 equivalents, and particularly preferably 0.7 to 1.3 equivalents, relative to the anionic hydrophilic groups. If the amount of the neutralizing basic compound used is less than the lower limit, the emulsifiability and storage stability of the polyurethane resin tend to decrease. On the other hand, adding the neutralizing basic compound in an amount exceeding the upper limit does not further improve the emulsifiability and storage stability of the polyurethane resin, and is therefore economically undesirable.

[0042] (Polyurethane Resin) The polyurethane resin used in the present invention is a chain-extended product obtained by chain-extending a neutralized product of the isocyanate-terminated prepolymer using the (E) polyamine.

[0043] (Emulsification and Dispersion) During chain elongation of the neutralized isocyanate-terminated prepolymer, the neutralized isocyanate-terminated prepolymer is first emulsified and dispersed in water. The emulsification and dispersion method is not particularly limited, and examples thereof include conventionally known methods using a homomixer, homogenizer, disper, or the like. The neutralized isocyanate-terminated prepolymer can be emulsified and dispersed in water at a temperature within a range of 0 to 40°C without the addition of an emulsifier. This can suppress the reaction between the isocyanate group and water. Furthermore, when emulsifying and dispersing the neutralized isocyanate-terminated prepolymer, a reaction inhibitor such as phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, paratoluenesulfonic acid, adipic acid, or benzoyl chloride may be added as necessary.

[0044] (Chain Extension) Next, the neutralized isocyanate-terminated prepolymer thus emulsified and dispersed in water is chain-extended using the (E) polyamine to form an aqueous polyurethane resin.

[0045] The chain extension method is not particularly limited, and for example, a method of adding the (E) polyamine to an emulsion dispersion of the neutralized isocyanate-terminated prepolymer to extend the chain, or a method of adding the emulsion dispersion of the neutralized isocyanate-terminated prepolymer to the (E) polyamine to extend the chain is preferred. The reaction between the neutralized isocyanate-terminated prepolymer and the (E) polyamine is completed at a reaction temperature of 20 to 50° C., usually within 30 to 120 minutes after mixing the neutralized isocyanate-terminated prepolymer and the (E) polyamine.

[0046] Such chain extension may be carried out simultaneously with, after, or before the emulsification and dispersion. In addition, when the obtained polyurethane resin contains an organic solvent, it is preferable to remove the organic solvent under reduced pressure at a temperature of 30 to 80°C.

[0047] Like the (A) polyisocyanate, the (B) diol, the (C) anionic hydrophilic group-containing active hydrogen compound, and the (D) polyol, the (E) polyamine also has a plurality of reaction sites, and the chain-extended product of the neutralized isocyanate-terminated prepolymer (polyurethane resin) obtained by chain-extending the neutralized product of the isocyanate-terminated prepolymer using such a (E) polyamine also has a complex structure, similar to the isocyanate-terminated prepolymer, and cannot be directly represented by a general formula (structural formula).

[0048] The acid value of the polyurethane resin thus obtained is preferably 5 to 50 mgKOH / g, and more preferably 10 to 40 mgKOH / g. If the acid value of the polyurethane resin is less than the lower limit, the storage stability of the binder tends to decrease, whereas if the acid value of the polyurethane resin is greater than the upper limit, the water resistance of the resulting printed layer tends to decrease.

[0049] (Binder) The binder of the present invention contains the polyurethane resin. In such a binder, the polyurethane resin is typically present in a state of dispersion in water. The content of the polyurethane resin in the binder is preferably 10 to 60% by mass, more preferably 20 to 50% by mass. If the content of the polyurethane resin is below the lower limit, it tends to be difficult to add other additive components in the required amounts when preparing the inkjet ink. On the other hand, if the content of the polyurethane resin is above the upper limit, the viscosity tends to be high, making the ink difficult to handle. The content of the polyurethane resin is determined by precisely weighing approximately 1 g of the binder (aqueous dispersion containing a polyurethane resin) in a thin layer on a Petri dish, heating it at 105±5°C for 30 minutes, and then precisely weighing the mass. The ratio of the remaining mass after heating to the mass before heating is expressed as a percentage.

[0050] [Inkjet Ink] The inkjet ink of the present invention contains the binder of the present invention, a pigment, and an aqueous medium.

[0051] (Pigment) The pigment used in the present invention is not particularly limited as long as it is a pigment that can be used in inkjet inks, and examples thereof include organic pigments and inorganic pigments with the following numbers listed in the Color Index.

[0052] Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, and Pigment Orange 13, 16, 20, and 36 are examples.

[0053] Examples of blue or cyan pigments include Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36, and 60. Examples of green pigments include Pigment Green 7, 26, 36, and 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, and 193. Examples of black pigments include Pigment Black 7, 28, and 26.

[0054] Commercially available pigments include, for example, Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromofine Orange 3700L, 6730, Chromofine Scarlet 6750, Chromofine Magenta 6880, 6886, 6891N, 6790, 6887, Chromofine Violet RE, Chromofine Red 6820, 6830, and Chromofine Blue HS-3. , 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P, Chromofine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromofine Black A-1103, Seika First Yellow 10GH, A -3, 2035, 2054, 2200, 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seika First Red 8040, C405 (F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seika First Carmine 6B1476T- 7, 1483LT, 3840, 3870, Seika First Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika First Maroon 460N, Seika First Orange 900, 2900, Seika Light Blue C718, A612, Cyanine Blue 4933M, 4933GN-EP, 4940, 4973 (all manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.); KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (all manufactured by DIC Corporation);Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow1705, Colortex Orange 202, Colortex Red101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex Brown B610N, Colortex Violet 600, Pigment Red 122, Colortex Blue 516, 517, 518, 519, A818, P-908, 510, Colortex Green 402, 403, Colortex Black 702, U905 (all manufactured by Sanyo Dye Co., Ltd.); Lionol Yellow 1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (all manufactured by Toyo Ink Co., Ltd.), Toner Magenta E02, Permanent Rubin F6B, Toner Yellow HG, Permanent Yellow GG-02, Hostaperm Blue B2G (all manufactured by Hoechst Industrie); Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (all manufactured by Clariant); carbon black #2600, #2400, #2350, #2200, #1000, #990, #980, #970, #960, #950, #850, MCF88, #750, #650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, #52, #50, #47, #45, #45L, #40, #33, #32, #30, #25, #20, #10, #5, #44, and CF9 (all manufactured by Mitsubishi Chemical Corporation).

[0055] (Aqueous Medium) The aqueous medium used in the present invention is not particularly limited, and may be, for example, water alone, a water-compatible organic solvent (water-soluble organic solvent) alone, or a mixed solvent of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include monohydric alcohols such as methanol, ethanol, propanol, pentanol, hexanol, cyclohexanol, and benzyl alcohol; dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, polypropylene glycol, and 1,2-hexanediol; trihydric or higher polyhydric alcohols such as glycerin, trimethylolpropane, and hexanetriol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, and diethylene glycol monomethyl ether. Examples of suitable water-soluble organic solvents include polyhydric alcohol ethers such as ethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, and triethylenetetramine; amides such as formamide, N,N-dimethylformamide, and N,N-dimethylacetamide; heterocycles such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2-oxazolidone, and 1,3-dimethyl-2-imidazolidine; sulfoxides such as dimethyl sulfoxide; and sulfones such as sulfolane. Among these water-soluble organic solvents, those having a hydroxyl group and a boiling point of 100° C. or higher are preferred, and examples thereof include glycerin, propylene glycol, 1,3-propanediol, ethylene glycol, 1,2-hexanediol, and triethylene glycol monobutyl ether are preferred.

[0056] (Additives) In addition to the binder, the pigment, and the aqueous medium, the inkjet ink of the present invention may contain other additives as needed, such as surfactants, preservatives, antifungals, antirust agents, pH adjusters, etc.

[0057] Examples of surfactants include anionic, cationic, amphoteric, and nonionic surfactants. Examples of anionic surfactants include fatty acid salts, alkyl sulfates, alkyl sulfate esters, alkylbenzenesulfonates, alkylnaphthalenesulfonates, dialkylsulfosuccinates, alkyl phosphate ester salts, alkylnaphthalenesulfonate-formaldehyde condensates, and polyoxyethylene alkyl sulfate ester salts. Examples of cationic surfactants include amine salts, tetraalkyl quaternary ammonium salts, trialkyl quaternary ammonium salts, alkylpyridinium salts, and alkylquinolinium salts. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylamines, ethylene oxide adducts of polypropylene glycol, acetylene glycol, and ethylene oxide adducts of acetylene glycol.

[0058] Examples of antiseptics and antifungal agents include aromatic halogen compounds (eg, Preventol CMK), methylene dithiocyanate, halogen-containing nitrogen-sulfur compounds, and 1,2-benzisothiazolin-3-one (eg, PROXELGXL).

[0059] Examples of the pH adjuster include urea and sodium hydroxide.

[0060] In the inkjet ink of the present invention, the content of the binder (aqueous dispersion containing the polyurethane resin) is preferably 1 to 50% by mass, and more preferably 2 to 30% by mass, based on the total mass of the inkjet ink. If the content of the binder is less than the lower limit, the adhesion of the formed printing layer to the substrate and water resistance tend to decrease, while if the content of the binder exceeds the upper limit, the viscosity of the inkjet ink increases, and image quality and storage stability tend to decrease.

[0061] The content of the pigment is preferably 0.1 to 30% by mass, and more preferably 1 to 10% by mass, based on the total mass of the inkjet ink. If the content of the pigment is less than the lower limit, the color of the printed matter tends to be light and the shielding effect tends to be lost, while if the content of the pigment is more than the upper limit, the viscosity of the inkjet ink tends to increase, which tends to deteriorate the image quality and the ejection properties and storage stability.

[0062] Furthermore, the content of the aqueous medium is preferably 0.1 to 90% by mass, and more preferably 1 to 50% by mass, of the total inkjet ink. If the content of the aqueous medium is less than the lower limit, the viscosity of the inkjet ink cannot be adjusted, and image quality tends to deteriorate. On the other hand, if the content of the aqueous medium exceeds the upper limit, water resistance tends to deteriorate.

[0063] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The free isocyanate group content and the acid value of the polyurethane resin were measured by the following methods.

[0064] (Free Isocyanate Group Content) 0.3 g of urethane prepolymer was placed in an Erlenmeyer flask, and 10 ml of 0.1 N dibutylamine toluene solution was added to dissolve the urethane prepolymer. Next, several drops of bromophenol blue solution were added, and the mixture was titrated with 0.1 N hydrochloric acid methanol solution. The free isocyanate group content NCO% was determined using the following formula: NCO%=(a-b)×0.42×f / x (wherein a: titration amount of 0.1 N hydrochloric acid methanol solution when only 10 ml of 0.1 N dibutylamine toluene solution was titrated, b: titration amount of 0.1 N hydrochloric acid methanol solution when the solution containing the urethane prepolymer was titrated, f: factor of the 0.1 N hydrochloric acid methanol solution, and x: amount of urethane prepolymer).

[0065] (Acid Value of Polyurethane Resin) The acid value of the polyurethane resin was measured in accordance with the potentiometric titration method in 3.2 of JIS K0070 (1992). The polyurethane resin aqueous dispersion was dissolved in tetrahydrofuran (THF) and subjected to potentiometric titration with a potassium hydroxide ethanol titrant using an automatic potentiometric titrator COM-1700 (manufactured by HIRANUMA Corporation). The acid value of the polyurethane resin was calculated in terms of the content of the polyurethane resin in the polyurethane resin aqueous dispersion.

[0066] The raw materials for the polyurethane resins prepared in the examples and comparative examples are shown below.

[0067] <(A) Polyisocyanate> H12MDI: dicyclohexylmethane diisocyanate ("Desmodur W" manufactured by Covestro) HDI: hexamethylene diisocyanate ("Desmodur H" manufactured by Covestro).

[0068] <(B) Diols> ((B1) Polycarbonate Diols) C-2090: Polycarbonate diol manufactured by Kuraray Co., Ltd. (using 3-methyl-1,5-pentanediol / 1,6-hexanediol as raw materials), trade name "Kuraray Polyol C-2090", number average molecular weight 2000. UP-200: Polycarbonate diol manufactured by UBE Corporation (using 2-methyl-1,3-propanediol as raw materials), trade name "ETERNACOLL UP-200", number average molecular weight 2000. NL2005B: Polycarbonate diol manufactured by Mitsubishi Chemical Corporation (using 2,2-dimethyl-1,3-propanediol / 1,4-butanediol as raw materials), trade name "BENEBiOL NL2005B", number average molecular weight 2000. C-1090: Polycarbonate diol (made using 3-methyl-1,5-pentanediol / 1,6-hexanediol as raw materials) manufactured by Kuraray Co., Ltd., trade name "Kuraray Polyol C-1090", number average molecular weight 1000. C-3090: Polycarbonate diol (made using 3-methyl-1,5-pentanediol / 1,6-hexanediol as raw materials) manufactured by Kuraray Co., Ltd., trade name "Kuraray Polyol C-3090", number average molecular weight 3000. ((B2) Polycarbonate diol) T5652: Polycarbonate diol (made using 1,5-pentanediol / 1,6-hexanediol as raw materials) manufactured by Asahi Kasei Corporation, trade name "Duranol T5652", number average molecular weight 2000. PD-2003: Polycarbonate diol (using 1,3-propanediol as a raw material) manufactured by Toyokuni Oil Mills Co., Ltd., trade name "HS PD-2003", number average molecular weight 2000. (Other diols) UH-200: Polycarbonate diol (using 1,6-hexanediol as a raw material) manufactured by UBE Corporation, trade name "ETERNACOLL UH-200", number average molecular weight 2000. G4672: Polycarbonate diol (using 1,4-butanediol / 1,6-hexanediol as raw materials) manufactured by Asahi Kasei Corporation, trade name "Duranol G4672", number average molecular weight 2000.PTMG2000: Polyether diol (polytetramethylene ether glycol) manufactured by Mitsubishi Chemical Corporation, trade name "PTMG2000", number average molecular weight 2000. 1,4-BD: 1,4-butanediol.

[0069] (C) Anionic Hydrophilic Group-Containing Active Hydrogen Compounds DMPA: Dimethylolpropionic acid.

[0070] <(D) Polyol> TMP: trimethylolpropane.

[0071] <Neutralizing amines> TEA: triethylamine.

[0072] <(E) Polyamine> HDZ: hydrazine monohydrate DETA: diethylenetriamine.

[0073] Example 1 Preparation of Inkjet Ink Binder Into a four-neck flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube, 205.1 parts by mass of (B1) a polycarbonate diol ("Kuraray Polyol C-2090" manufactured by Kuraray Co., Ltd., number average molecular weight 2000) made from 3-methyl-1,5-pentanediol / 1,6-hexanediol as a raw material, 1.4 parts by mass of (D) trimethylolpropane as a polyol having 3 or more hydroxyl groups, 18.0 parts by mass of dimethylolpropionic acid as (C) an anionic hydrophilic group-containing active hydrogen compound, and a solvent were added. After uniformly mixing, 44.0 parts by mass of dicyclohexylmethane diisocyanate and 28.2 parts by mass of hexamethylene diisocyanate as (A) polyisocyanate, and 0.04 parts by mass of bismuth tris(2-ethylhexanoate) as a catalyst were added, and the mixture was reacted at 80°C for 240 minutes to obtain a methyl ethyl ketone solution of an isocyanate group-terminated urethane prepolymer having a free isocyanate group content of 1.78% by mass relative to the isocyanate group-terminated prepolymer, which was then cooled to 40°C.

[0074] To this solution, 12.9 parts by mass of triethylamine was added at 40°C to carry out a neutralization reaction. Subsequently, 707.5 parts by mass of water was gradually added to the resulting solution while stirring, emulsifying and dispersing the neutralized product of the terminal isocyanate group-containing urethane prepolymer. 3.4 parts by mass of hydrazine monohydrate and 1.0 part by mass of diethylenetriamine were added as (E) polyamines to the resulting emulsion dispersion, and the mixture was stirred at 40±5°C for 90 minutes. After that, a solvent removal (methyl ethyl ketone removal) treatment was carried out at 40°C under reduced pressure to obtain an aqueous polyurethane resin dispersion (binder for inkjet inks) with a solids concentration (i.e., polyurethane resin concentration) of 30.0% by mass.

[0075] Tables 1 and 2 show the acid value of the polyurethane resin, the ratio of the (D) polyol to the total amount of the (B) diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol [D / (B+C+D)], the ratio of the total amount of the (B1) polycarbonate diol and the (B2) polycarbonate diol to the total amount of the (B) diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol [(B1+B2) / (B+C+D)]], and the ratio of the total amount of the (B1) polycarbonate diol, the (B2) polycarbonate diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol [(B1+B2+C+D) / (B+C+D)]] in the obtained aqueous polyurethane resin dispersion (binder for inkjet ink).

[0076] <Preparation of Inkjet Ink> 27 parts by mass of the obtained inkjet ink binder (8.1 parts by mass as polyurethane resin), 25 parts by mass of a carbon black aqueous dispersion as a pigment (self-dispersion carbon black dispersion "Aqua-Black(R) 162" manufactured by Tokai Carbon Co., Ltd., solids concentration 19% by mass), 10 parts by mass of propylene glycol, 2 parts by mass of 1,2-hexanediol, 2 parts by mass of 2-pyrrolidone, and 34 parts by mass of water as an aqueous medium were charged into a container and mixed for 10 minutes to prepare an inkjet ink.

[0077] Examples 2 to 17 and Comparative Examples 1 to 5 Aqueous dispersions of polyurethane resins (binders for inkjet inks) were prepared, and further inkjet inks were prepared in the same manner as in Example 1, except that the types and amounts of (A) polyisocyanate, (B) diol, (C) anionic hydrophilic group-containing active hydrogen compound, (D) polyol, neutralized amine, and (E) polyamine shown in Tables 1 and 2 were used. Tables 1 and 2 show the acid value of the polyurethane resin, the ratio of the (D) polyol to the total amount of the (B) diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol [D / (B+C+D)], the ratio of the total amount of the (B1) polycarbonate diol and the (B2) polycarbonate diol to the total amount of the (B) diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol [(B1+B2) / (B+C+D)]], and the ratio of the total amount of the (B1) polycarbonate diol, the (B2) polycarbonate diol, the (C) anionic hydrophilic-group-containing active hydrogen compound, and the (D) polyol [(B1+B2+C+D) / (B+C+D)]] in the obtained aqueous polyurethane resin dispersion (binder for inkjet ink).

[0078] <Dispersion Stability of Inkjet Ink Binder> 200 g of inkjet ink binder was sealed in a transparent 200 ml bottle and then left to stand in an oven at 45°C for 7 days. After standing, the bottle was visually inspected for the presence or absence of polyurethane resin sediment, and the dispersion stability of the binder was evaluated according to the following criteria. The results are shown in Tables 1 and 2. (Evaluation Criteria) A: No resin sedimentation. B: Resin sedimentation.

[0079] <Preparation of Test Pieces> An inkjet ink was applied to a polyester film (PET) ("Espet E-5102" manufactured by Toyobo Co., Ltd., biaxially stretched film, corona-treated, thickness 12 μm) and a polypropylene film (OPP) ("Pylen P-2161" manufactured by Toyobo Co., Ltd., biaxially stretched film, corona-treated, thickness 30 μm) using a bar coater so that the thickness after drying would be 1 μm, and then dried at 90° C. for 10 minutes to prepare test pieces in which the ink was coated (printed) on each resin film.

[0080] <Adhesion> In accordance with JIS K5600-5-6:1999, 100 (10 × 10) squares were formed on the dried film surface (printed layer) of the printed ink of the test piece by making 1 mm-wide cuts with a cutter knife. A peel test was conducted on this printed layer using adhesive tape ("Cellotape (registered trademark)" manufactured by Nichiban Co., Ltd.), and the number of squares remaining on the test piece after the tape was peeled off was counted, and the adhesion of the printed layer was evaluated according to the following criteria. The results are shown in Tables 1 and 2. (Evaluation criteria) 5: 100 squares remaining. 4: 99 to 95 squares remaining. 3: 94 to 85 squares remaining. 2: 84 to 65 squares remaining. 1: 64 squares or less remaining.

[0081] <Water Resistance> The test piece was immersed in water at 20°C for 24 hours. After removing the test piece from the water, the surface moisture was lightly wiped off with a cloth. Then, 100 (10 × 10) squares were formed on the dried surface of the printed ink (printed layer) of the test piece by making 1 mm-wide cuts with a utility knife in accordance with JIS K5600-5-6:1999. A peel test was conducted on this printed layer using adhesive tape ("Cellotape (registered trademark)" manufactured by Nichiban Co., Ltd.). The number of squares remaining on the test piece after tape peeling was counted, and the water resistance of the printed layer was evaluated according to the following criteria. The results are shown in Tables 1 and 2. (Evaluation Criteria) 5: 100 squares remaining. 4: 99-95 squares remaining. 3: 94-85 squares remaining. 2: 84-65 squares remaining. 1: 64 squares or less remaining.

[0082]

[0083]

[0084] As shown in Tables 1 and 2, it was found that by using as the diol (B) at least one of (B1) a polycarbonate diol having a structural unit derived from a diol with a branched structure and 3 to 10 carbon atoms and (B2) a polycarbonate diol having a structural unit derived from a diol with a linear structure and an odd number of carbon atoms of 3 to 9, and by using as the binder of the inkjet ink an aqueous dispersion containing a polyurethane resin synthesized using (D) a trivalent or higher polyol, a printed layer having excellent adhesion to the substrate and excellent water resistance was formed (Examples 1 to 17).

[0085] On the other hand, it was found that when other diols were used instead of the (B1) polycarbonate diol and the (B2) polycarbonate diol (Comparative Examples 1 to 3), when a short-chain diol was used instead of the (D) trivalent or higher polyol (Comparative Example 4), and when no (D) trivalent or higher polyol was used (Comparative Example 5), the adhesion of the printing layer to the substrate and the water resistance were reduced.

[0086] As described above, according to the present invention, it is possible to obtain an inkjet ink that is capable of forming a printed layer that has excellent adhesion to a substrate and excellent water resistance. Therefore, the inkjet ink of the present invention is useful as an ink for printing on various recording media.

Claims

1. A binder for inkjet inks comprising (A) a polyisocyanate, (B) a diol, (C) a compound having an anionic hydrophilic group and at least two active hydrogens, and (D) a polyurethane resin which is a chain extension product of a neutralized isocyanate-terminated prepolymer which is a reaction product of a trivalent or higher polyol, with (E) a polyamine having two or more amino and / or imino groups, wherein the diol (B) comprises at least one selected from the group consisting of (B1) a polycarbonate diol having a structural unit derived from a diol having a branched structure and 3 to 10 carbon atoms, and (B2) a polycarbonate diol having a structural unit derived from a diol having a linear structure and an odd number of carbon atoms of 3 to 9.

2. The ink-jet ink binder according to claim 1, wherein the acid value of the polyurethane resin is 5 to 50 mg KOH / g.

3. The binder for ink-jet inks according to claim 1, wherein the ratio of the polyol (D) is 0.1 to 1.5 mass % based on the total amount of the diol (B), the compound (C) and the polyol (D).

4. The binder for ink-jet ink according to claim 1, wherein the total amount of the (B1) polycarbonate diol and the (B2) polycarbonate diol is 50% by mass or more and the total amount of the (B1) polycarbonate diol, the (B2) polycarbonate diol, the (C) compound and the (D) polyol is 100% by mass or less based on the total amount of the (B) diol, the (C) compound and the (D) polyol.

5. An ink-jet ink comprising the ink-jet ink binder according to any one of claims 1 to 4, a pigment and an aqueous medium.

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