Aqueous ink composition for inkjet printing, and printed matter

Abstract

Provided is an aqueous ink composition used in an inkjet recording method, the aqueous ink composition comprising a coloring material, an aqueous medium, a binder resin, and wax, wherein the binder resin includes a urethane resin, and the wax includes polyethylene wax. According to the present invention, it is possible to obtain: an aqueous ink composition for inkjet printing, from which printed matter having excellent scratch resistance is formed and which has ink stability and ink ejection properties; and printed matter printed with said ink composition for inkjet printing.

Description

Aqueous ink composition for inkjet printing and printed matter

[0001] The present invention relates to an aqueous ink composition for inkjet printing and a printed matter.

[0002] Inkjet recording is a recording method in which ink droplets are ejected directly from extremely fine nozzles onto a recording material, depositing them on the material to produce characters or images. This method not only offers the advantages of low noise and ease of operation, but also allows for easy colorization. For these reasons, inkjet recording is used not only in office and home output devices but also in industrial applications. Inkjet inks include solvent inks, UV inks, and water-based inks. Among these, water-based inks have attracted attention for their environmental friendliness, and their use on a wide range of recording media has expanded, from copy paper to specialty paper with ink-receiving layers, cardboard, textile printing, and even printing on recording media with low or no ink absorption. Accordingly, there is a growing need for high-performance water-based inks for inkjet printing (see, for example, Patent Document 1). Inkjet printing inks can be broadly divided into two types: dye inks and pigment inks. Due to issues with dye inks' water resistance, weather resistance, and lightfastness, pigment inks have recently become more widely used. However, pigment inks have a problem with abrasion resistance (fixability), in that the pigment accumulates on the printing paper, and the pigment on the paper can be rubbed off by external factors, damaging the image. Therefore, attempts have been made to improve this by adding binder resins or the like to enhance adhesion to the recording medium. However, there is a strong demand for further improvement in abrasion resistance, including for recording media such as coated paper and non-absorbent films. Meanwhile, with the increasing performance of inkjet printers and the like, various performance requirements for water-based inks are increasing year by year. For example, there is a demand for ink ejection stability that does not cause clogging of the ink ejection nozzles of inkjet printers over time and does not cause ink ejection failure or abnormal ejection direction over a long period of time, and for inks produced by mixing pigments, dyes, and other additives with binder resins, that do not cause separation or aggregation over time.

[0003] As described above, it is becoming increasingly important for inkjet printing inks to simultaneously achieve the quality of printed matter when the ink is fixed on a recording medium and the performance required of the inkjet ink itself.

[0004] Japanese Patent Application Laid-Open No. 2006-282760

[0005] As the fields of use of inkjet printed matter expand, higher levels of abrasion resistance are required. However, there remains a problem that, for example, when a strong external force is applied locally, the printed image may fade, deteriorate, or be damaged due to the falling off of pigment, etc.

[0006] When attempts are made to improve abrasion resistance by using a resin or the like in the ink, problems such as poor ink stability and ink ejection properties arise. The problem to be solved by the present invention is to provide an aqueous ink composition for inkjet printing that has excellent abrasion resistance of printed matter as well as ink stability and ink ejection properties, and a printed matter printed with the ink composition for inkjet printing.

[0007] As a result of extensive research into solving the above problems, the present inventors discovered that the above problems can be solved by using a urethane resin as a binder resin constituting an aqueous ink composition, and further using polyethylene wax, and thus completed the present invention.

[0008] The present invention has the following aspects. [1] An aqueous ink composition for use in an inkjet recording system, comprising a colorant, an aqueous medium, a binder resin, and a wax, wherein the binder resin comprises a urethane resin and the wax comprises a polyethylene wax. [2] The aqueous ink composition of [1], wherein the urethane resin is a reaction product of essential raw materials, including a polyol (a), a polyisocyanate (b), and a neutralizing agent (c), and the polyisocyanate (b) comprises one or more polyisocyanates selected from the group consisting of aromatic polyisocyanates (b1) and alicyclic polyisocyanates (b2). [3] The aqueous ink composition of [1] or [2], wherein the urethane resin has an acid value in the range of 20 to 60 mgKOH / g. [4] The aqueous ink composition of [2], wherein the urethane resin further comprises an amine compound (d) as a raw material. [5] The aqueous ink composition of [1] or [2], wherein the melting point of the polyethylene wax is 150°C or lower. [6] A printed matter obtained by printing the aqueous ink composition of [1] or [2] on the surface of a recording medium.

[0009] According to the present invention, it is possible to provide a water-based ink composition for ink-jet printing that can provide a printed matter having excellent abrasion resistance, and that has excellent ink stability and ink ejection properties.

[0010] Preferred embodiments of the present invention are described below. However, the present invention is not limited to the following embodiments. In this specification, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. Individually stated upper and lower limits can be arbitrarily combined. Furthermore, the term "aqueous ink composition" refers to an ink composition in which the water content of the total solvent is 40% by mass or more and which is substantially free of water-insoluble solvents whose solubility in water at 20°C is less than 0.5 g / 100 mL (the content is 1% by mass or less of the total solvent). This aqueous ink composition provides sufficient abrasion resistance not only when printed on recording media with excellent ink absorption, such as copy paper (PPC paper) commonly used in copiers, or recording media having an ink-absorbing layer, but also when printed on recording media with poor ink absorption or no ink absorption, such as cardboard, art paper such as printing paper, coated paper, lightweight coated paper, lightly coated paper, and plastic film.

[0011] The components of the aqueous ink composition will be described in detail below.

[0012] The coloring material used in the present invention may be a known or commonly used pigment, dye, or the like, and may contain one or both of a pigment and a dye. From the viewpoint of producing a printed matter having excellent weather resistance, the coloring material preferably contains a pigment. The pigment may be coated with a resin. That is, a coloring agent in which a pigment is coated with a resin can also be used as the coloring material.

[0013] The pigment is not particularly limited, and organic and inorganic pigments commonly used in aqueous gravure inks or aqueous inkjet inks can be used. The pigment may contain either an organic pigment or an inorganic pigment, or both. Furthermore, both non-acid-treated and acid-treated pigments can be used. Examples of inorganic pigments include titanium oxide, antimony red, red iron oxide, cadmium red, cadmium yellow, cobalt blue, Prussian blue, ultramarine blue, carbon black, and graphite. Examples of organic pigments include quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, and azo pigments.

[0014] Examples of pigments (black pigments) that can be used in black inks include C.I. Pigment Black 1, 6, 7, 8, 10, 26, 27, and 28. Among these, C.I. Pigment Black 7 is preferably used. Specific examples of black pigments include No. 2300, No. 2200B, No. 900, No. 960, No. 980, No. 995B, No. 33, No. 40, No. 45, No. 45L, and No. 50L manufactured by Mitsubishi Chemical Corporation. 52, HCF88, MA7, MA8, MA100, etc.; Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc., manufactured by Birla Carbon Corporation; BLACK PEARLS 880, BLACK PEARLS 4750, Regal 400R, Regal 330R, Regal 660R, Mogul L, Mogul 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc., manufactured by Cabot Corporation; Color Black, manufactured by Orion Engineered Carbons Examples of suitable polyesters include FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35, U, V, 1400U, Special Black 6, 5, 4, 4A, NIPEX150, NIPEX160, NIPEX170, and NIPEX180.

[0015] Specific examples of pigments (yellow pigments) that can be used in yellow inks include C.I. 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, and 185. Specific examples of pigments (magenta pigments) that can be used in magenta inks include C.I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112, 122, 123, 146, 176, 184, 185, 202, 209, 269, and 282; C.I. Pigment Violet 19, and the like.

[0016] Specific examples of pigments (cyan pigments) that can be used in cyan inks include C.I. Pigment Blue 1, 2, 3, 15, 15:3, 15:4, 15:6, 16, 22, 60, 63, and 66. Of these, C.I. Pigment Blue 15:3 is preferably used.

[0017] Specific examples of pigments (white pigments) that can be used in white ink include alkaline earth metal sulfates, carbonates, finely powdered silicic acid, silicas such as synthetic silicates, calcium silicate, alumina, alumina hydrate, titanium oxide, zinc oxide, talc, clay, and the like.

[0018] To ensure stable dispersion of the pigment in the ink, it is preferable to employ a means for effectively dispersing the pigment in the aqueous medium. One such means is the use of a pigment dispersant. Examples of pigment dispersants that can be used include polyvinyl alcohols, polyvinylpyrrolidones, acrylic resins such as acrylic acid-acrylic ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, and styrene-α-methylstyrene-acrylic acid-acrylic ester copolymers, aqueous resins such as styrene-maleic acid copolymers, styrene-maleic anhydride copolymers, and vinylnaphthalene-acrylic acid copolymers, as well as salts of these aqueous resins. Examples of pigment dispersants that can be used include the Ajisper PB series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Disperbyk series manufactured by BYK Japan, the EFKA series manufactured by BASF, the SOLSPERSE series manufactured by The Lubrizol Japan Co., Ltd., and the TEGO series manufactured by Evonik. Furthermore, compounds exemplified as polymer (G) in WO 2018 / 190139 can also be used as pigment dispersants. Alternatively, a dispersibility-imparting group (hydrophilic functional group and / or its salt) or an active species having a dispersibility-imparting group may be bonded (grafted) to the surface of the pigment directly or indirectly via an alkyl group, an alkyl ether group, an aryl group, or the like. Such self-dispersing pigments can be produced, for example, by vacuum plasma treatment, oxidation treatment with hypohalous acid and / or hypohalous acid salts, oxidation treatment with ozone, a wet oxidation method in which the pigment surface is oxidized with an oxidizing agent in water, or a method in which a carboxy group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface. When using such self-dispersing pigments, there is no need to include a pigment dispersant, which can suppress foaming and other problems caused by the pigment dispersant, making it easier to obtain an aqueous ink composition with excellent ejection stability.Furthermore, when the self-dispersing pigment is used, the significant increase in viscosity caused by the pigment dispersant is suppressed, making it possible to incorporate a larger amount of pigment, and making it easier to produce printed matter with high print density. Commercially available products can also be used as the self-dispersing pigment. Examples of commercially available products include Microjet CW-1 (trade name; manufactured by Orient Chemical Industries Co., Ltd.), CAB-O-JET 200, and CAB-O-JET 300 (all trade names; manufactured by Cabot Corporation).

[0019] Examples of the dyes include azo dyes such as monoazo and disazo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoimine dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, naphthalimide dyes, perinone dyes, phthalocyanine dyes, and triarylmethane dyes.

[0020] From the viewpoint of ensuring sufficient print density, the content of the colorant is, for example, 1% by mass or more, preferably 1.5% by mass, and more preferably 2% by mass or more, relative to the total amount of the aqueous ink composition. From the viewpoint of easily suppressing the occurrence of streaks and easily obtaining better image fastness while maintaining excellent dispersion stability of the colorant, the content of the colorant is, for example, 15% by mass or less, preferably 13% by mass, and more preferably 10% by mass or less, relative to the total amount of the aqueous ink composition. From these viewpoints, the content of the colorant is 1 to 15% by mass, preferably 1.5 to 13% by mass, and more preferably 2 to 10% by mass, relative to the total amount of the aqueous ink composition.

[0021] The aqueous medium used in the present invention is, for example, water, and specifically, pure water or ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, etc. The content of the aqueous medium is 30 to 97% by mass, preferably 35 to 95% by mass, more preferably 40 to 90% by mass, and particularly preferably 45 to 90% by mass, relative to the total amount of the aqueous ink composition, from the viewpoint of easily achieving high ink stability and ejection stability.

[0022] The aqueous ink composition may contain a solvent component other than water (e.g., a water-soluble organic solvent) for the purpose of adjusting viscosity, etc. However, when a mixed solvent of water and a solvent component other than water (e.g., a water-soluble organic solvent) is used, the content of water in the entire solvent is 40% by mass or more, and preferably 50% by mass or more. As the water-soluble organic solvent, any known water-soluble organic solvent used in inkjet inks can be used. The urethane resin used in the present invention is a reaction product of essential raw materials: polyol (a), polyisocyanate (b), and neutralizer (c).

[0023] Examples of the polyol (a) include polyether polyol (a1), polyester polyol (a2), polycarbonate polyol (a3), etc. The polyol (a) may be used alone or in combination of two or more thereof.

[0024] Examples of the polyether polyol (a1) include those obtained by addition polymerization of alkylene oxide using one or more compounds having two or more active hydrogen atoms as an initiator as needed. Examples of the initiator include ethylene glycol, diethylene glycol, triethylene glycol, trimethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, glycerin, trimethylolethane, trimethylolpropane, sorbitol, sucrose, aconite sugar, trimellitic acid, hemimellitic acid, phosphoric acid, ethylenediamine, diethylenetriamine, triisopropanolamine, pyrogallol, dihydroxybenzoic acid, hydroxyphthalic acid, and 1,2,3-propanetrithiol.

[0025] Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, and tetrahydrofuran.

[0026] Examples of the polyester polyol (a2) include polyester polyols obtained by reacting a low-molecular-weight polyol with a polycarboxylic acid; polyester polyols obtained by ring-opening polymerization of a cyclic ester compound such as ε-caprolactone; and polyester polyols obtained by copolymerizing these.

[0027] The low-molecular-weight polyol used in the production of the polyester polyol may be one or more kinds, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,1-decanediol. aliphatic polyols having a molecular weight of 50 or more and 300 or less, such as hexanediol, 1,11-undecanediol, 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, glycerin, trimethylolpropane, ditrimethylolpropane, trimethylolpropane, and pentaerythritol; polyols having an alicyclic structure, such as cyclohexanedimethanol and hydrogenated bisphenol A; and polyols having an aromatic structure, such as bisphenol A and bisphenol F.

[0028] The polycarboxylic acid may be used alone or in combination of two or more kinds. Examples thereof include aliphatic polycarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; alicyclic polycarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and cyclohexanetricarboxylic acid; aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and anhydrides or esters thereof.

[0029] Specific examples of the polycarbonate polyol (a3) ​​include an esterification reaction product of a carbonate ester and a polyhydric alcohol, and a reaction product of a polyhydric alcohol and phosgene.

[0030] The carbonate ester may be used alone or in combination of two or more kinds, and examples thereof include aliphatic carbonates, alicyclic carbonates (hereinafter, carbonates containing an alicyclic structure may be referred to as "alicyclic"), and aromatic carbonates (hereinafter, carbonates containing an aromatic structure may be collectively referred to as "aromatic"). Examples of the aliphatic carbonate include saturated aliphatic carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, di-n-butyl carbonate, diisobutyl carbonate, ethyl-n-butyl carbonate, and ethyl isobutyl carbonate; and unsaturated aliphatic carbonates such as ethylene carbonate, trimethylene carbonate, tetramethylene carbonate, 1,2-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,3-pentylene carbonate, 1,4-pentylene carbonate, 1,5-pentylene carbonate, 2,3-pentylene carbonate, and 2,4-pentylene carbonate. Examples of aromatic carbonates include diphenyl carbonate and dibenzyl carbonate.

[0031] The polyhydric alcohol may be one or more types, and examples thereof include linear or branched diols such as ethylene glycol, propylene glycol, butanediol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, polyethylene glycol, and polypropylene glycol; alicyclic diols such as 1,4-cyclohexanedimethanol and hydrogenated bisphenol A; and tri- or higher functional polyols such as trimethylolmethane, trimethylolpropane, ditrimethylolpropane, pentaerythritol, and dipentaerythritol. It is more preferable to use a polyether polyol (a1) and a polycarbonate polyol (a3) ​​as the polyol (a) from the viewpoint of improving ink stability and the abrasion resistance of printed matter.

[0032] By increasing the content of the polycarbonate polyol (a3), the scratch resistance of the resulting printed matter tends to be improved.

[0033] The polyol (a) also includes a diol (a4) having an acid group. Examples of the diol (a4) having an acid group include diols having a carboxyl group or a sulfonic acid group, and preferably include a diol having a carboxyl group. Examples of the diol having a carboxyl group include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvaleric acid. Among these, 2,2-dimethylolpropionic acid is preferred. Polyester polyols having a carboxyl group obtained by reacting the polyol having a carboxyl group with various polycarboxylic acids can also be used. Examples of the polycarboxylic acid include aliphatic polycarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; alicyclic polycarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and cyclohexanetricarboxylic acid; aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and acid anhydrides thereof. The polyol (a) also includes a vinyl polymer (a5) having two hydroxyl groups at one end.

[0034] The vinyl polymer (a5) having two hydroxyl groups at one end can be obtained, for example, by radical polymerization of a chain transfer agent having two hydroxyl groups and a mercapto group or the like with a vinyl monomer.

[0035] Examples of the chain transfer agent having two hydroxyl groups and a mercapto group or the like include 3-mercapto-1,2-propanediol (thioglycerin), 1-mercapto-1,1-methanediol, 1-mercapto-1,1-ethanediol, 2-mercapto-1,3-propanediol, 2-mercapto-2-methyl-1,3-propanediol, 2-mercapto-2-ethyl-1,3-propanediol, 1-mercapto-2,3-propanediol, 2-mercaptoethyl-2-methyl-1,3-propanediol, and 2-mercaptoethyl-2-ethyl-1,3-propanediol.

[0036] Examples of the vinyl monomer that can be used include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, phenyl (meth)acrylate, and benzyl (meth)acrylate; (meth)acrylic acid, β-carboxyethyl (meth)acrylate, and 2-(meth)acryloylpropionic acid.

[0037] Examples of the polyol (a) include the above-mentioned polyols and diols as well as low-molecular-weight polyols (a6).

[0038] The low-molecular-weight polyol (a6) is a polyol having a molecular weight of less than 500 (preferably 450 or less, more preferably 400 or less, with a lower limit of about 50), and examples thereof include aliphatic polyols such as ethylene glycol, diethylene glycol, 1,2-propylene glycol, dipropylene glycol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanediol, 1,6-hexanediol, and cyclohexanedimethanol; cyclobutanediol; alicyclic polyols such as bisphenol A, cyclopentanediol, 1,4-cyclohexanediol, cycloheptanediol, cyclooctanediol, butylcyclohexanediol, cyclohexanedimethanol, hydroxypropylcyclohexanol, dicyclohexanediol, hydrogenated bisphenol A, 1,3-adamantanediol, 1,1'-bicyclohexylidenediol, and cyclohexanetriol; and aromatic polyols such as bisphenol A, bisphenol F, bisphenol AD, and ethylene oxide and propylene oxide adducts thereof.

[0039] Examples of the polyisocyanate (b) include aromatic polyisocyanates (b1), alicyclic polyisocyanates (b2), and aliphatic polyisocyanates (b3).

[0040] Examples of the aromatic polyisocyanate (b1) include phenylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, polymethylene polyphenyl polyisocyanate, and carbodiimidized diphenylmethane polyisocyanate.

[0041] Examples of the alicyclic polyisocyanate (b2) include norbornane diisocyanate, isophorone diisocyanate, cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, dimer acid diisocyanate, etc. Examples of the aliphatic polyisocyanate (b3) include hexamethylene diisocyanate, lysine diisocyanate, etc. The above-mentioned polyisocyanates (b) can be used alone or in combination of two or more.

[0042] The content of the polyisocyanate (b) in the raw materials for the urethane resin is preferably in the range of 10 to 60% by mass, more preferably in the range of 20 to 50% by mass, because this allows for the production of an aqueous ink composition having excellent ink stability, ink ejection properties, and abrasion resistance.

[0043] The neutralizing agent (c) is an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide.

[0044] As the neutralizing agent (c), a neutralizing agent other than the alkali metal hydroxide (hereinafter, sometimes referred to as "other neutralizing agent") can be used in combination, if necessary.

[0045] Examples of the other neutralizing agents include triethylamine, ammonia, morpholine, monoethanolamine, and diethylethanolamine.

[0046] The amount of the neutralizer (c) used is preferably in the range of 1 to 15% by mass, more preferably 2 to 10% by mass, of the raw materials for the urethane resin, because this allows for the production of an aqueous ink composition having excellent ink stability, ink ejection properties, and abrasion resistance.

[0047] The urethane resin used in the present invention is a reaction product of essential raw materials, such as polyol (a), polyisocyanate (b), and neutralizing agent (c), and, if necessary, an amine compound (d) may be used as a chain extender. Examples of the amine compound (d) include diamines such as ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-4,4'-dicyclohexylmethanediamine, and 1,4-cyclohexanediamine; and amines containing one primary amino group and one secondary amino group, such as N-hydroxymethylaminoethylamine, N-hydroxyethylaminoethylamine, N-hydroxypropylaminopropylamine, N-ethylaminoethylamine, and N-methylaminopropylamine. Diamines contained therein include polyamines such as diethylenetriamine, dipropylenetriamine, and triethylenetetramine, hydrazines such as hydrazine, N,N'-dimethylhydrazine, and 1,6-hexamethylenebishydrazine, dihydrazides such as succinic acid dihydrazide, adipic acid dihydrazide, glutaric acid dihydrazide, sebacic acid dihydrazide, and isophthalic acid dihydrazide, and semicarbazides such as β-semicarbazide propionic acid hydrazide, 3-semicarbazide-propyl-carbazate, and semicarbazide-3-semicarbazidemethyl-3,5,5-trimethylcyclohexane. These amine compounds can be used alone or in combination of two or more.

[0048] By using the amine compound (d), the tensile strength of the resulting urethane resin is increased, which tends to improve the scratch resistance of printed matter.

[0049] The acid value of the urethane resin is 15 mgKOH / g or more, preferably 20 mgKOH / g or more, more preferably 25 mgKOH / g or more, and even more preferably 30 mgKOH / g or more, and is 75 mgKOH / g or less, preferably 70 mgKOH / g or less, more preferably 65 mgKOH / g or less, and more preferably 60 mgKOH / g or less. An acid value in the range of 20 to 60 mgKOH / g is preferred, and a range of 30 to 60 mgKOH / g is more preferred, since an aqueous ink composition having excellent ink stability, ejection stability, and abrasion resistance can be obtained.

[0050] The method for producing the urethane resin is not particularly limited, and any method may be used. For example, the urethane resin may be produced by reacting all of the reaction raw materials including the polyol compound (a), the polyisocyanate (b), and the neutralizing agent (c) at once, or by reacting the reaction raw materials sequentially.

[0051] The weight average molecular weight of the urethane resin is preferably 10,000 or more, more preferably 20,000 or more, more preferably 50,000 or more, and is preferably 2,000,000 or less, more preferably 1,000,000 or less, and even more preferably 500,000 or less.

[0052] In the present invention, the weight-average molecular weight and number-average molecular weight can be measured using gel permeation chromatography, with polystyrene as a standard sample. The urethane resin is preferably dissolved or dispersed in a solvent, and more preferably in an emulsion state. The solvent is preferably an aqueous medium, and more preferably the same aqueous medium as the aqueous medium used in the aqueous ink composition. The urethane resins can be used alone or in combination. From the viewpoint of suppressing mottling and white streaks during printing, the content of the urethane resin is preferably 10.0% by mass or less, and may be 8.0% by mass or less, or 6.0% by mass or less, relative to the total amount of the aqueous ink composition. From the viewpoint of achieving better setting properties, the content of the urethane resin is preferably 0.5% by mass or more, and may be 0.75% by mass or more, or 1.0% by mass or more, relative to the total amount of the aqueous ink composition. From these viewpoints, the content of the urethane resin is preferably 0.5 to 6.0% by mass relative to the total amount of the aqueous ink composition.

[0053] The content of the urethane resin is preferably 500 parts by mass or less, and may be 400 parts by mass or less, or 300 parts by mass or less, relative to 100 parts by mass of the colorant, from the viewpoint of suppressing mottling and white streaks during printing. The content of the urethane resin is preferably 8 parts by mass or more, and may be 12 parts by mass or more, or 16 parts by mass or more, relative to 100 parts by mass of the colorant, from the viewpoint of obtaining better setting properties. From these viewpoints, the content of the urethane resin is preferably 8 to 300 parts by mass relative to 100 parts by mass of the colorant. The aqueous ink composition of the present invention may contain a resin other than the urethane resin as a binder resin. The content of the urethane resin relative to 100 parts by mass of the total amount of binder resin is preferably 80 parts by mass or more, and may be 90 parts by mass or more, 95 parts by mass or more, or 100 parts by mass.

[0054] The wax used in the aqueous ink composition of the present invention is a polyethylene wax, and the polyethylene wax has a skeleton derived from polyethylene (polyethylene skeleton). The polyethylene skeleton mainly has structural units derived from ethylene. The polyethylene skeleton may be a homopolyethylene (ethylene homopolymer) skeleton, a block polyethylene (block copolymer of ethylene and another olefin) skeleton, or a random polyethylene (random copolymer of ethylene and another olefin) skeleton. Examples of the other olefin include alkenes such as propylene, isobutylene, 1-butene, 1-pentene, and 1-hexene. These components may be linear or branched. The number of carbon atoms of the other olefin component is, for example, 2 to 6. The content of the ethylene component in the polyethylene skeleton (the content of structural units derived from ethylene) is, for example, 60 mol% or more, and may be 70 mol% or more. When the polyethylene skeleton is a block polyethylene skeleton or a random polyethylene skeleton, the content of the ethylene component in the polyethylene skeleton (the content of structural units derived from ethylene) is, for example, 95 mol% or less, and may be 90 mol% or less. The content of the polyethylene skeleton in the polyethylene wax is, for example, 50 to 99% by mass, based on the total amount of the polyethylene wax. The content of the polyethylene skeleton in the polyethylene wax may be 50% by mass or more, 60% by mass or more, or 70% by mass or more, and may be 99% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the polyethylene wax. From the viewpoint of obtaining better image fastness, the polyethylene wax preferably contains a high-density oxidized polyethylene wax or a modified polyethylene wax. In this embodiment, the synergistic effect of using a urethane resin in combination with a high-density oxidized polyethylene wax or a modified polyethylene wax tends to obtain better setting properties, image fastness, and mottle suppression. The density of the polyethylene wax may, for example, be 0.95 g / cm or more, and 0.95 to 1.1 g / cm.The melting point (Tm) of the polyethylene wax is, for example, 160°C or lower, preferably 150°C or lower, more preferably 140°C or lower, and may be 135°C or lower, or 130°C or lower. The melting point (Tm) of the oxidized polyethylene wax is, for example, 40°C or higher, preferably 120°C or higher, and more preferably 125°C or higher. From these viewpoints, the melting point (Tm) is 40 to 160°C, preferably 120 to 150°C, and more preferably 125 to 140°C. The melting point (Tm) is a value measured using a melting point measuring device in accordance with JIS K 0064. The polyethylene wax is, for example, in a particulate form. From the viewpoint of preventing clogging of an inkjet head, the average particle diameter of the particulate polyethylene wax is, for example, 10 to 200 nm. The average particle diameter of the particulate polyethylene wax may be 20 nm or higher or 30 nm or higher, and may be 100 nm or lower or 60 nm or lower. The average particle size is the d50 diameter in the volume-based particle size distribution measured by a laser scattering method using a laser scattering particle size analyzer (e.g., Microtrac). The polyethylene wax is preferably dissolved or dispersed in a solvent, and more preferably in an emulsion state. The solvent is preferably an aqueous medium, and more preferably the same aqueous medium as the aqueous medium used in the aqueous ink composition. The polyethylene wax may be used alone or in combination of two or more. Commercially available polyethylene waxes may also be used. Preferred commercially available products include AQUACER 515, AQUACER 531, and AQUACER 1547, manufactured by BYK. From the viewpoint of excellent image fastness, the content of the polyethylene wax is preferably 0.1% by mass or more, and may be 0.2% by mass or more, or 0.3% by mass or more, relative to the total amount of the aqueous ink composition. The content of the polyethylene wax may be, for example, 5% by mass or less, 3% by mass or less, or 2% by mass or less, relative to the total amount of the aqueous ink composition, from the viewpoint of easily achieving sufficient ejection stability.From these viewpoints, the content of the polyethylene wax may be 0.1 to 5% by mass with respect to the total amount of the aqueous ink composition. From the viewpoint of excellent image fastness, the content of the polyethylene wax is preferably 1.6 parts by mass or more, and may be 4 parts by mass or more or 6 parts by mass or more, relative to 100 parts by mass of the colorant. From the viewpoint of easily obtaining sufficient ink ejection properties, the content of the polyethylene wax may be, for example, 500 parts by mass or less, 350 parts by mass or less, or 200 parts by mass or less, relative to 100 parts by mass of the colorant. From these viewpoints, the content of the polyethylene wax may be 1.6 to 500 parts by mass with respect to 100 parts by mass of the colorant. From the viewpoint of excellent setting ability and image fastness and further suppression of mottling, the ratio of the content of the polyethylene wax to the content of the urethane resin (content of oxidized polyethylene wax / content of urethane resin) is, for example, 0.03 to 10. The ratio may be 0.03 or more, 0.1 or more, 0.2 or more, or 0.3 or more, and may be 10 or less, 2.0 or less, or 1.5 or less. In this embodiment, it is particularly preferable that the ratio of the urethane resin content to the polyethylene wax content be within the above range. The aqueous ink composition may contain a wax other than polyethylene wax. However, the content of polyethylene wax relative to 100 parts by mass of the total amount of wax is preferably 80 parts by mass or more, and may be 90 parts by mass or more, 95 parts by mass or more, or 100 parts by mass. In addition to the above-mentioned components, the aqueous ink composition of the present invention may further contain other additives such as surfactants, wetting agents (drying inhibitors), penetrants, preservatives, viscosity modifiers, pH adjusters, chelating agents, plasticizers, antioxidants, and UV absorbers, as needed. These components may be used alone or in combination of two or more. The use of a surfactant facilitates good wetting and spreading of the aqueous ink composition ejected from the nozzles of the inkjet head on the surface of a recording medium after landing, thereby making it easier to prevent streak-like printing defects. Furthermore, by using a surfactant, the surface tension of the aqueous ink composition can be reduced, which makes it easier to improve the leveling properties of the aqueous ink composition.As the surfactant, various anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used. From the viewpoint of easily suppressing the occurrence of streak-like printing defects, the surfactant is preferably at least one selected from the group consisting of anionic surfactants and nonionic surfactants. Examples of anionic surfactants include alkylbenzenesulfonates, alkylphenylsulfonates, alkylnaphthalenesulfonates, higher fatty acid salts, sulfate ester salts of higher fatty acid esters, sulfonates of higher fatty acid esters, sulfate ester salts and sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. Specific examples of these include dodecylbenzenesulfonates, isopropylnaphthalenesulfonates, monobutylphenylphenol monosulfonates, monobutylbiphenylsulfonates, and dibutylphenylphenol disulfonates.Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkylolamides, alkylalkanolamides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers. Of these, preferred is one or more selected from the group consisting of polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid alkylolamides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers. The aqueous ink composition preferably contains an acetylene-based surfactant, from the viewpoint of easily suppressing the occurrence of streak-like printing defects. The acetylene-based surfactant is a surfactant having an acetylene structure in the molecule. From the viewpoint of easily suppressing the occurrence of streak-like printing defects, the acetylene-based surfactant preferably contains one or more selected from the group consisting of acetylene glycol and oxyethylene adducts of acetylene glycol. From the viewpoint of easily suppressing the occurrence of streak-like printing defects, the content of the acetylene-based surfactant is preferably 80 to 100% by mass, more preferably 85 to 99.9% by mass, even more preferably 90 to 99.5% by mass, and particularly preferably 95 to 99.3% by mass, relative to the total amount of surfactants.Other surfactants that can be used include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers; and biosurfactants such as spiculisporic acid, rhamnolipid, and lysolecithin. The surfactant content is preferably 0.001 to 5% by mass, more preferably 0.001 to 3% by mass, even more preferably 0.001 to 2% by mass, particularly preferably 0.01 to 2% by mass, extremely preferably 0.1 to 2% by mass, very preferably 0.5 to 2% by mass, even more preferably 0.8 to 2% by mass, and even more preferably 1 to 1.6% by mass, based on the total amount of the aqueous ink composition. Aqueous ink compositions containing surfactants at these content levels exhibit good wettability of the ejected droplets on the surface of the substrate, facilitate sufficient wetting and spreading on the substrate, and are effective in preventing streaky printing defects. Furthermore, aqueous ink compositions containing surfactants within the above ranges are effective in improving the leveling properties of the coating film. From the same viewpoint, the content of the acetylene surfactant is preferably within the above-mentioned ranges. The humectant can be used for the purpose of preventing the aqueous ink composition from drying out in the ejection nozzles of the inkjet head. The humectant is preferably one that is miscible with water and has the effect of preventing clogging of the ejection orifices of the inkjet head, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols having a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, mesoerythritol, pentaerythritol, and glycerin. A solid humectant can also be used as the humectant. Examples of such humectants include urea and urea derivatives. Examples of the urea derivatives include ethylene urea, propylene urea, diethyl urea, thiourea, N,N-dimethyl urea, hydroxyethyl urea, hydroxybutyl urea, ethylene thiourea, and diethyl thiourea.These may be used alone or in combination of two or more. From the viewpoint of easily obtaining printed matter with excellent setting properties, it is preferable to use at least one selected from the group consisting of urea, ethylene urea, and 2-hydroxyethyl urea. The content of the humectant may be 3 to 50% by mass based on the total amount of the aqueous ink composition. Examples of penetrants include lower alcohols such as ethanol and isopropyl alcohol, and glycol monoethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, and tripropylene glycol monobutyl ether. The content of the penetrant is preferably 3% by mass or less, more preferably 1% by mass or less, based on the total amount of the aqueous ink composition, and even more preferably the aqueous ink composition is substantially free of penetrant. The pH of the aqueous ink composition is preferably 7.0 or higher, more preferably 7.5 or higher, and even more preferably 8.0 or higher, in order to improve the storage stability and ejection stability of the ink, and to improve the wetting spread, print density, and abrasion resistance when printed on a recording medium.The upper limit of the pH of the aqueous ink composition is preferably 11.0 or less, more preferably 10.5 or less, and even more preferably 10.0 or less, in order to suppress deterioration of components constituting the ink application or ejection device (e.g., ink ejection ports, ink flow paths, etc.) and to reduce the effects of ink adhesion to skin. From these viewpoints, the pH of the aqueous ink composition is preferably 7.0 to 11.0. Note that the above pH is measured at 25°C. The viscosity of the aqueous ink composition is, for example, 1.0 mPa·s or more and less than 10.0 mPa·s at 25°C. When the viscosity of the aqueous ink composition is within this range, when used in an inkjet recording system, the apparent deviation of the landing position on the recording medium caused by deflection of the ink droplets tends to be reduced, and the occurrence of streaks in the printed material tends to be effectively prevented. Furthermore, aqueous ink compositions having a viscosity within this range tend to have excellent storage stability and ejection stability in inkjet recording systems. The viscosity of the aqueous ink composition at 25°C is preferably 1.2 mPa·s or more, and more preferably 1.3 mPa·s or more. The viscosity of the aqueous ink composition at 25°C is preferably 8.0 mPa·s or less, and more preferably 7.0 mPa·s or less. The above viscosity is a value measured, for example, using a cone-plate rotational viscometer equivalent to an E-type viscometer, under the following conditions: Measuring device: TV-22 viscometer (TV-22, manufactured by Toki Sangyo Co., Ltd.) Calibration standard solution: JS20 Measurement temperature: 25°C Rotation speed: 10 to 100 rpm Injection amount: 1200 μL The surface tension of the aqueous ink composition is, for example, 20 to 40 mN / m at 25°C. When the surface tension of the aqueous ink composition is within this range, when used in an inkjet recording method, the wettability of the ejected droplets on the surface of the recording medium tends to be good, and the ink tends to spread sufficiently after landing. The surface tension of the aqueous ink composition at 25° C. is preferably 25 mN / m or more, and more preferably 27 mN / m or more. The surface tension of the aqueous ink composition at 25° C. is preferably 35 mN / m or less, and more preferably 32 mN / m or less. The aqueous ink composition of the embodiment described above can be produced by mixing the above-mentioned components.The above-mentioned components may be mixed all at once or sequentially. For example, the binder resin (e.g., urethane resin) and wax (e.g., oxidized polyethylene wax) may be dissolved or dispersed in an aqueous medium before mixing. Furthermore, the pigment as a colorant may be dispersed in an aqueous medium together with a pigment dispersant before mixing. For mixing, a dispersing machine such as a bead mill, ultrasonic homogenizer, high-pressure homogenizer, paint shaker, ball mill, roll mill, sand mill, sand grinder, Dyno Mill, Dispermat, SC Mill, or Nanomizer can be used. After mixing, centrifugation, filtration, or the like may be performed as needed. The aqueous ink composition of the present invention obtained by the above method can be used for inkjet printing using an inkjet printer, for example, for inkjet printing on recording media such as paper, plastic film, metal film, or sheet. The inkjet method is not particularly limited, and known methods such as continuous jetting (charge-controlled type, spray type, etc.) and on-demand type (piezo type, thermal type, electrostatic suction type, etc.) can be used.

[0055] A printed matter printed using the aqueous ink composition of the present invention is a printed matter obtained by printing the aqueous ink composition of the above embodiment on the surface of a recording medium. It comprises a recording medium and an ink coating film printed on the surface of the recording medium. The ink coating film formed on the surface of the recording medium is, for example, a dried product of the aqueous ink composition and contains the solid components of the aqueous ink composition of the above embodiment (e.g., the colorant, the urethane resin, and the oxidized polyethylene wax). This printed matter has excellent abrasion resistance, and is therefore less likely to cause deterioration of the printed image due to loss of pigments, etc., and has an image with high color density, so it can be used for a variety of purposes, such as photographic printing by inkjet printing and printed matters obtained by high-speed inkjet printing.

[0056] The present invention will be described in detail below with reference to examples and comparative examples. It should be noted that the present invention is not limited to the examples listed below. <Production of Urethane Resin> (Production Example 1: Synthesis of Aqueous Urethane Resin Dispersion 1) 500.0 parts by mass of EXCENOL 1020 (manufactured by AGC, a polypropylene glycol-type polyether polyol having a number average molecular weight of 1000, hereinafter sometimes referred to as PPG1000), a polymer diol, and 42.2 parts by mass of 2,2-dimethylolpropionic acid (DMPA), an acid group diol, were placed in a four-neck flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube, and the mixture was thoroughly stirred. Next, 320.7 parts by mass of hydrogenated 4,4'-diphenylmethane diisocyanate (H12MDI) as polyisocyanate, 0.16 parts by mass of dibutyltin dilaurate (DBTDL) as catalyst, and methyl ethyl ketone (MEK) as solvent were added to a non-volatile content of 80%, and the mixture was thoroughly stirred and reacted at 100°C. After confirming the completion of the reaction by measuring the NCO concentration, MEK was added, and the mixture was stirred for 30 minutes and cooled to 40°C or below, yielding a urethane prepolymer solution with a non-volatile content of 60%. A 48% aqueous potassium hydroxide solution was added to the obtained urethane prepolymer solution in an amount necessary to neutralize 100% of the acid groups of the DMPA, and the acid groups were neutralized by stirring for 15 minutes. Next, ion-exchanged water in an amount twice the amount of the prepolymer solution was gradually added under strong stirring to emulsify the urethane, and then 22.0 parts by mass of ethylenediamine (EDA), an amine compound, was added as a chain extender, and the mixture was stirred for 3 hours at 40° C. to carry out a chain extension reaction. After completion of the reaction, MEK was distilled off under reduced pressure, and the nonvolatile content was adjusted with ion-exchanged water to synthesize aqueous urethane resin dispersion 1 having a nonvolatile content of 30% and an acid value of solids of 20 mgKOH / g. (Production Example 2: Synthesis of aqueous urethane resin dispersion 2) Aqueous urethane resin dispersion 2 having a nonvolatile content of 30% and an acid value of solids of 45 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the amounts of Exenol 1020 in Production Example 1 were changed from 500.0 parts by mass to 350.0 parts by mass, DMPA in Production Example 1 from 42.2 parts by mass to 93.9 parts by mass, H12MDI in Production Example 1 from 320.7 parts by mass to 413.2 parts by mass, and EDA in Production Example 1 from 22.0 parts by mass to 28.4 parts by mass.(Production Example 3: Synthesis of aqueous urethane resin dispersion 3) Aqueous urethane resin dispersion 3 having a nonvolatile content of 30% and an acid value of solids of 40 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the EXCENOL 1020 in Production Example 1 was changed to 400.0 parts by mass of ETERNACOLL UH-100 (a crystalline polycarbonate diol manufactured by UBE having a number average molecular weight of 1000), the DMPA from 42.2 parts by mass to 85.3 parts by mass, the H12MDI from 320.7 parts by mass to 409.3 parts by mass, and the EDA from 22.0 parts by mass to 28.1 parts by mass. (Production Example 4: Synthesis of aqueous urethane resin dispersion 4) Aqueous urethane resin dispersion 4 having a nonvolatile content of 30% and a solid acid value of 55 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the Exenol 1020 in Production Example 1 was changed to 300.0 parts by mass of Polylite OD-X-2155 (manufactured by DIC, crystalline polycarbonate diol having a number average molecular weight of 1000), the DMPA from 42.2 parts by mass to 116.7 parts by mass, H12MDI from 320.7 parts by mass to 460.4 parts by mass, and EDA from 22.0 parts by mass to 31.6 parts by mass. (Production Example 5: Synthesis of aqueous urethane resin dispersion 5) Aqueous urethane resin dispersion 5 having a nonvolatile content of 30% and an acid value of solids of 50 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the amount of Exenol 1020 in Production Example 1 was changed from 500.0 parts by mass to 350.0 parts by mass, the amount of DMPA in Production Example 1 was changed from 42.2 parts by mass to 98.6 parts by mass, the amount of H12MDI in Production Example 1 was changed to 361.8 parts by mass of isophorone dizocyanate (IPDI), and the amount of EDA in Production Example 1 was changed from 22.0 parts by mass to 29.3 parts by mass. (Production Example 6: Synthesis of aqueous urethane resin dispersion 6) Aqueous urethane resin dispersion 6 having a nonvolatile content of 30% and a solid acid value of 51 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the amounts of Exenol 1020 in Production Example 1 were changed from 500.0 parts by mass to 350.0 parts by mass, DMPA in Production Example 1 to 93.9 parts by mass, H12MDI in Production Example 1 to 320.7 parts by mass, IPDI in Production Example 1 to 175.1 parts by mass, and toluene diisocyanate (TDI) in Production Example 1 to 137.2 parts by mass, and EDA in Production Example 1 to 28.4 parts by mass.(Production Example 7: Synthesis of aqueous urethane resin dispersion 7) Aqueous urethane resin dispersion 7 having a nonvolatile content of 30% and a solid acid value of 52 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the amounts of Exenol 1020 in Production Example 1 were changed from 500.0 parts by mass to 350.0 parts by mass, DMPA in Production Example 1 to 98.6 parts by mass, H12MDI in Production Example 1 to 320.7 parts by mass, IPDI in Production Example 1 to 180.9 parts by mass, and 1,4-bis(isocyanatomethyl)cyclohexane (H6XDI) in Production Example 1 to 156.6 parts by mass, and EDA in Production Example 1 to 29.3 parts by mass. (Production Example 8: Synthesis of aqueous urethane resin dispersion 8) Aqueous urethane resin dispersion 8 having a nonvolatile content of 30% and a solid acid value of 43 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the amounts of Exenol 1020 in Production Example 1 were changed from 500.0 parts by mass to 400.0 parts by mass, DMPA in Production Example 1 from 42.2 parts by mass to 80.5 parts by mass, H12MDI in Production Example 1 from 320.7 parts by mass to IPDI from 166.8 parts by mass and hexamethylene diisocyanate (HDI) from 126.2 parts by mass, and EDA in Production Example 1 from 22.0 parts by mass to 22.5 parts by mass. (Production Example 9: Synthesis of aqueous urethane resin dispersion 9) Aqueous urethane resin dispersion 9 having a nonvolatile content of 30% and an acid value of solids of 45 mgKOH / g was synthesized in the same manner as in Production Example 1, except that the amounts of Exenol 1020 in Production Example 1 were changed from 500.0 parts by mass to 350.0 parts by mass, DMPA from 42.2 parts by mass to 93.9 parts by mass, H12MDI from 320.7 parts by mass to 413.2 parts by mass, and EDA from 22.0 parts by mass to 23.6 parts by mass of hydrazine (HYD) monohydrate. (Production Example 10: Synthesis of aqueous urethane resin dispersion 10) A four-necked flask equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen inlet tube was charged with 500.0 parts by mass of PTMG1000 (a polymer diol manufactured by Mitsubishi Chemical, a polytetramethylene glycol-type polyether polyol having a number average molecular weight of 1000), 289.2 parts by mass of H12MDI, and 197.3 parts by mass of MEK. After thorough mixing, 0.16 parts by mass of DBTDL was added and reacted at 75 ° C. After confirming the completion of the reaction by NCO concentration measurement, 176.8 parts by mass of MEK was added and cooled to 40 ° C. or less, and 83.8 parts by mass of DMPA and 0.10 parts by mass of DBTDL were added. Thereafter, the mixture was heated again to 75 ° C., and the reaction was continued.After 10 hours, the reaction was terminated by adding 2.0 parts by mass of methanol. Next, 207.9 parts by mass of MEK was added to obtain an organic solvent solution of urethane resin. A 48% aqueous potassium hydroxide solution was added to the obtained urethane solution in an amount necessary to neutralize 100% of the acid groups of the DMPA, and the acid groups were neutralized by stirring for 15 minutes. Next, ion-exchanged water was gradually added in an amount twice the amount of the urethane solution under strong stirring to emulsify the urethane. After completion of the emulsification, MEK was distilled off under reduced pressure, and the nonvolatile content was adjusted with ion-exchanged water to synthesize an aqueous urethane resin dispersion 10 with a nonvolatile content of 30% and a solid acid value of 40 mgKOH / g. (Production Example 11: Synthesis of aqueous urethane resin dispersion 11) A four-neck flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube was charged with 700.0 parts by mass of MEK, and then 291 parts by mass of methyl (meth)acrylate, 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 reaction vessel and reacted to obtain a solvent solution of a vinyl polymer (VP-1) having two hydroxyl groups at one end and having a number average molecular weight of 3,000. Next, 250.0 parts by mass of the polymer diol Exenol 1020, 750.0 parts by mass of the VP-1 solution, and 228.8 parts by mass of H12MDI were added to a four-neck flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube. After thorough mixing, 0.20 parts by mass of DBTDL was added and the mixture was allowed to react at 75°C. After confirming the completion of the reaction by NCO concentration measurement, the mixture was cooled to below 40°C, and 75.8 parts by mass of DMPA and 0.15 parts by mass of DBTDL were added. The mixture was then reheated to 75°C and the reaction continued. After 12 hours, the reaction was terminated by adding 2.0 parts by mass of methanol. Next, 254.6 parts by mass of MEK was added to obtain an organic solvent solution of urethane resin. A 48% aqueous potassium hydroxide solution was added to the resulting urethane solution in an amount necessary to neutralize 100% of the acid groups of the DMPA, and the acid groups were neutralized by stirring for 15 minutes. Next, ion-exchanged water in an amount twice the amount of the urethane solution was gradually added under vigorous stirring to emulsify the urethane.After the emulsification was completed, MEK was distilled off under reduced pressure, and the nonvolatile content was adjusted with ion-exchanged water to synthesize an aqueous urethane resin dispersion 11 having a nonvolatile content of 30% and a solid acid value of 40 mgKOH / g.

[0057]

[0058] <Preparation of Wax> The following polyethylene waxes were prepared as waxes. AQUACER 515: BYK Corporation, trade name, high-density oxidized polyethylene wax emulsion, melting point 135°C, non-volatile content 35% AQUACER 531: BYK Corporation, trade name, modified polyethylene wax emulsion, melting point 130°C, non-volatile content 45% <Production of Pigment Dispersion> 50 parts by mass of C.I. Pigment Red 122 ("FASTOGEN Super Magenta RY" manufactured by DIC Corporation), and 10 parts by mass of a styrene-acrylic acid copolymer (weight average molecular weight of 11,000, acid value of 180 mgKOH / g) were added in this order, and the mixture was stirred for 10 minutes at a rotation speed of 80 rpm and a revolution speed of 25 rpm while the temperature of the jacketed tank was heated to 80°C.

[0059] Next, with the temperature of the jacketed tank maintained at 80°C, 5.3 parts by mass of a 34% by mass aqueous potassium hydroxide solution and 30 parts by mass of triethylene glycol were added to the composition, and the mixture was kneaded for 60 minutes at a rotation speed of 80 rpm and a revolution speed of 25 rpm, thereby obtaining a solid kneaded product.

[0060] To the kneaded product, 100 parts by mass of ion-exchanged water and 10 parts by mass of triethylene glycol were added, and the mixture was stirred and mixed for 10 minutes using a juicer mixer. By mixing the ion-exchanged water and Proxel-GXL (Lonza Japan Co., Ltd.), an aqueous pigment dispersion having a pigment concentration of 15.0% by mass, a triethylene glycol concentration of 12.0% by mass, a Proxel-GXL concentration of 0.1% by mass, and a non-volatile content of 18.2% by mass was obtained. <Preparation of Pigment Inks for Inkjet Printing> (Examples 1 to 26) 20.0 parts by mass of the pigment dispersion obtained above (corresponding to a pigment concentration of 3.0% in the ink), the aqueous urethane resin dispersions obtained in Preparation Examples 1 to 11, polyethylene wax, 8.0 parts by mass of 2-pyrrolidinone, 8.0 parts by mass of triethylene glycol mono-n-butyl ether, 3.0 parts by mass of glycerin, 0.5 parts by mass of Surfynol 440 (manufactured by Air Products), and ion-exchanged water were mixed to obtain aqueous ink compositions for inkjet printing in Examples 1 to 26. The amounts of the aqueous urethane resin dispersion and polyethylene wax added were adjusted so that the nonvolatile content of each was the value shown in the table. Ion-exchanged water was added so that the total amount of each ink component added was 100 parts by mass. Note that the above contents are all based on the total amount of the aqueous ink composition. (Comparative Examples 1 to 10) The aqueous ink compositions for inkjet printing in Comparative Examples 1 to 10 were obtained in the same manner as in the Examples, except that the urethane resin dispersion or wax was not used, or the following polypropylene wax was used as the wax component. Arrowbase DA-1010: Product name, manufactured by Unitika Ltd., polypropylene wax emulsion, melting point 75°C, non-volatile content 25% Arrowbase DC-1010: Product name, manufactured by Unitika Ltd., polypropylene wax emulsion, melting point 140°C, non-volatile content 25% The following evaluations were carried out using the aqueous ink compositions obtained in the above Examples and Comparative Examples. <Abrasion Resistance> The aqueous ink composition for inkjet printing obtained above was applied to photographic printing paper (HP Advanced Photo Paper, manufactured by HP Corporation) using a bar coater #3 to obtain a test ink coating. The coating was allowed to dry at room temperature for one day, and then a friction test was carried out using a Gakushin friction tester. During the test, plain paper was attached to the friction arm, and the arm was moved back and forth 20 times under a load of 200 g.The degree of abrasion on the ink-coated surface was evaluated visually, and samples evaluated as A or B were evaluated as having sufficient abrasion resistance for practical use. [Evaluation Criteria] A: No scratches were observed on the coated surface, and no peeling of the coloring material was observed. B: Slight scratches were observed on the coated surface, but no peeling of the coloring material was observed. C: Significant scratches were observed on the coated surface, and some peeling of the coloring material was observed. <Scratch Resistance> The aqueous ink composition for inkjet printing obtained above was applied to photographic printing paper (HP Advanced Photo Paper, manufactured by HP Corporation) using a bar coater #3 to obtain a test ink-coated product. After drying the coated product at room temperature for one day, it was scratched with a plastic guitar pick and the degree of scratches was evaluated visually. Samples evaluated as A or B were evaluated as having sufficient abrasion resistance for practical use. [Evaluation Criteria] A: No scratches were observed on the coated surface, and no peeling of the coloring material was observed. B: Slight scratches were observed on the coated surface. C: Significant scratches were observed on the coated surface, and some peeling of the coloring material was observed. <Ink Dischargeability> The aqueous ink composition for inkjet printing obtained above was filled into a black ink cartridge of a commercially available inkjet printer, ENVY4500 (manufactured by HP), and a solid print was performed on a transparent OHP sheet at a print density setting of 100% to obtain a printed material for evaluation. An unprinted OHP sheet was used as a reference, and the absorbance (value at the maximum peak near 536 nm) of the printed surface of the OHP sheet was measured. The absorbance was compared with that of the binder-free ink, and the dischargeability index was calculated according to the following formula: Dischargeability index = (absorbance of binder-added ink) / (absorbance of binder-free ink). A dischargeability index of 0.80 or higher was rated A, 0.70 to 0.79 was rated B, 0.60 to 0.69 was rated C, and 0.59 or lower was rated D. A rating of A or B was deemed to have sufficient dischargeability for practical use. <Ink storage stability> The aqueous ink for inkjet printing obtained above was diluted, and the particle size by volume (MV) was measured by detecting scattered light of laser light using a Nanotrac particle size distribution analyzer "UPA150" manufactured by Microtrac Bell Co., Ltd. in an environment of 25°C. The ink was then stored at 60°C for one week, and the MV was measured in the same manner after storage. Ink samples with an MV increase rate of less than 10% before and after storage were rated A, and samples with an MV increase rate of 10% or more were rated B. Ink samples with a rating of B were evaluated as having insufficient storage stability.

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Claims

1. An aqueous ink composition for use in an inkjet recording method, comprising a colorant, an aqueous medium, a binder resin, and a wax, wherein the binder resin comprises a urethane resin, and the wax comprises a polyethylene wax.

2. The aqueous ink composition according to claim 1, wherein the urethane resin is a reaction product of essential raw materials, that is, polyol (a), polyisocyanate (b) and neutralizing agent (c), and the polyisocyanate (b) contains one or more polyisocyanates selected from the group consisting of aromatic polyisocyanates (b1) and alicyclic polyisocyanates (b2).

3. The aqueous ink composition according to claim 1 or 2, wherein the acid value of the urethane resin is in the range of 20 to 60 mgKOH / g.

4. The aqueous ink composition according to claim 2, wherein the urethane resin further contains an amine compound (d) as a raw material.

5. The aqueous ink composition according to claim 1 or 2, wherein the polyethylene wax has a melting point of 150° C. or lower.

6. A printed matter obtained by printing the aqueous ink composition according to claim 1 or 2 on the surface of a recording medium.

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