White ink composition

Abstract

The present invention aims to provide a white ink that is easily redispersible and can be redispersed even with minimal shaking, at most, or even without shaking. As a solution, a white ink composition is provided, comprising: a titanium oxide pigment comprising 5.0 to 20.0% by mass of the ink composition; a solid component of an alkali-soluble resin having styrene, stearyl acrylate and / or lauryl acrylate, and acrylic acid as constituent units, comprising 3.0 to 60.0 parts by mass of an alkali-soluble resin having a weight-average molecular weight of 10,000 or greater, an acid value of 100 mgKOH / g or greater, and a glass transition temperature of 50°C or greater, relative to 100 parts by mass of the pigment in the ink composition; and a surfactant.

Description

Technical Field

[0001] The present invention relates to a white ink composition. Background Art

[0002] As described in Patent Documents 1 and 2, it is known that a styrene acrylic resin or various dispersants are formulated in a white ink composition, but the properties of the precipitate produced when a titanium oxide pigment is precipitated have not been studied.

[0003] Patent Literature

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-4368

[0005] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-84072 Summary of the Invention

[0006] Typical ink compositions, especially those containing titanium oxide, tend to settle over time, forming sediments. Furthermore, even if the settled ink composition is shaken, it is difficult to redisperse it, unless it is vigorously shaken hundreds of times.

[0007] Therefore, it is desired to obtain a white ink characterized by being easily redispersible and being able to be redispersed by shaking with relatively weak force for at most several dozen times or without shaking at all.

[0008] The present inventors conducted intensive studies to solve the above-mentioned problems and, as a result, found that the above-mentioned problems can be solved by setting a specific composition, thereby completing the present invention.

[0009] That is, the present invention is as follows.

[0010] 1. A white ink composition comprising:

[0011] 5.0 to 20.0% by mass of the titanium oxide pigment in the ink composition,

[0012] The solid content of an alkali-soluble resin having styrene, stearyl acrylate and / or lauryl acrylate, and acrylic acid as constituent units, a weight-average molecular weight of 10,000 or more, an acid value of 100 mgKOH / g or more, and a glass transition temperature of 50°C or more, is 3.0 to 60.0 parts by mass per 100 parts by mass of the pigment in the ink composition.

[0013] and surfactants.

[0014] 2. The white ink composition according to item 1, wherein the solid content of the alkali-soluble resin is 10.0 to 30.0 parts by mass based on 100 parts by mass of the pigment in the ink composition.

[0015] According to the present invention, there is an effect of easily redispersing a temporarily precipitated pigment in a white ink composition containing titanium oxide as a coloring pigment. DETAILED DESCRIPTION

[0016] The white ink composition of the present invention is preferably an aqueous white ink composition, which will be described below in order.

[0017] First, the glass transition temperature and weight average molecular weight in the present invention are defined as follows.

[0018] Glass transition temperature

[0019] The glass transition temperature of the resin in the present invention is a theoretical glass transition temperature obtained by the following Wood's equation when the resin is an acrylic copolymer resin.

[0020] Wood type: 1 / Tg=W1 / Tg1+W2 / Tg2+W3 / Tg3+ +Wx / Tgx

[0021] [wherein, Tg1~Tgx represent monomers 1, 2, 3 that constitute the resin x, W1 to Wx represent the glass transition temperature of the homopolymer of monomers 1, 2, and 3. x represents the respective polymerization fractions, and Tg represents the theoretical glass transition temperature. The glass transition temperature in Wood's equation is an absolute temperature.]

[0022] For resins other than acrylic copolymers, the glass transition temperature is the theoretical glass transition temperature determined by thermal analysis. The thermal analysis method is based on JIS K7121 (Determination of Transition Temperature of Plastics). For example, a Perkin Elmer Pyris1 DSC can be used to measure the glass transition temperature at a heating rate of 20°C / min and a nitrogen flow rate of 20 mL / min.

[0023] <Weight average molecular weight>

[0024] The weight-average molecular weight of the resin in the present invention can be measured by gel permeation chromatography (GPC). For example, a Waters 2690 (Waters) GPC apparatus can be used, with a PLgel 5μ MIXED-D (Polymer Laboratories) column and tetrahydrofuran as the developing solvent. Chromatographic analysis can be performed at a column temperature of 25°C, a flow rate of 1 mL / min, an RI detector, a sample injection concentration of 10 mg / mL, and an injection volume of 100 μL. The weight-average molecular weight can be determined as polystyrene-equivalent.

[0025] <Titanium oxide pigment>

[0026] The present invention contains a titanium oxide pigment in an amount of 5.0 to 20.0% by mass of the ink composition.

[0027] Furthermore, the titanium oxide pigment preferably accounts for 50.0% by mass or more, more preferably 55.0% by mass or more, and even more preferably 60.0% by mass or more of the solid content (total of pigment and resin component) of the white ink composition of the present invention. Furthermore, the titanium oxide pigment preferably accounts for 98.0% by mass or less, more preferably 90.0% by mass or less, and even more preferably 80.0% by mass or less.

[0028] As the titanium oxide pigment that can be used in the present invention, known pigments can be used.

[0029] Titanium oxide pigments may be unsurface-treated or surface-treated with one or more selected from silica, alumina, zirconium dioxide, and organosilicon compounds. The average particle size of the titanium oxide pigment is preferably 0.15 to 0.30 μm. Titanium oxide pigments treated with silica, alumina, or an organic compound are also preferred.

[0030] Examples of surface-treated titanium oxide include R-960 (silica-coated titanium oxide pigment) (DuPont), CR-50, R-630, R-680 (alumina-coated titanium oxide pigment), R-780, R-850, R-550 (alumina and silica-coated titanium oxide pigment), CR-50-2, PF-736, R-980 (titanium oxide pigment coated with alumina and an organic substance), CR-57, and CR-Super70 (titanium oxide pigment coated with alumina, zirconium dioxide, and an organic substance).

[0031] Titanium oxide pigments treated with silica, alumina, and organic compounds

[0032] As titanium oxide pigments treated with silica, alumina, and an organic compound, which can be used in the present invention, known pigments can be used. Alternatively, no pigments may be used. In particular, the amounts of silica, alumina, and organic matter in the pigment are preferably such that the titanium oxide content in the titanium oxide pigment is within a range of 90.0 to 98.0% by mass. The average particle size of the titanium oxide pigment is preferably 0.15 to 0.30 μm.

[0033] As such titanium oxide pigments, PF-690, PF-691, PF-711, PC-3, CR-80, CR-90, CR-90-2, CR-93 (Ishihara Sangyo Co., Ltd.) and the like can be used.

[0034] In addition, the average particle size is a value measured by a Coulter counter method.

[0035] <Alkali-soluble resin>

[0036] As the alkali-soluble resin in the present invention, a resin having styrene, stearyl acrylate and / or lauryl acrylate, or acrylic acid as a constituent unit can be used as a specific alkali-soluble resin.

[0037] Such a specific alkali-soluble resin has a weight average molecular weight of 10,000 or more, more preferably 13,000 or more, preferably 50,000 or less, more preferably 40,000 or less, and even more preferably 30,000 or less.

[0038] The solid content of the alkali-soluble resin can be set to 3.0 to 60.0% by mass relative to the mass of the pigment in the white ink composition, more preferably 4.0% by mass or more, even more preferably 10.0% by mass or more, more preferably 45.0% by mass or less, and even more preferably 30.0% by mass or less.

[0039] When the specific alkali-soluble resin is used, a water-dispersible resin or other alkali-soluble resin may be used in combination.

[0040] The alkali-soluble resin is preferably composed of monomers having a mass ratio of styrene / stearyl acrylate and / or lauryl acrylate / acrylic acid of 20 to 80 / 5 to 25 / 15 to 30.

[0041] The alkali-soluble resin may be used with a bifunctional or higher-functional crosslinking agent from the viewpoint of appropriately crosslinking with the resin to suppress aggregation of the pigment.

[0042] The bifunctional or higher crosslinking agent may be a crosslinking agent having two or more reactive functional groups in the molecule in order to react with the functional groups of the alkali-crosslinkable resin. Examples of such reactive functional groups include epoxy, hydroxyl, isocyanate, amino, and aziridinyl groups. The bifunctional or higher crosslinking agent may be used alone or in combination of two or more.

[0043] The acid value of the alkali-soluble resin is 100 mgKOH / g or higher, preferably 125 mgKOH / g or higher, and more preferably 150 mgKOH / g, from the perspective of improving solubility in aqueous media. Furthermore, the acid value of the alkali-soluble resin is preferably 300 mgKOH / g or lower, and more preferably 250 mgKOH / g or lower, from the perspective of improving the water resistance of printed materials. The acid value is the theoretical value, calculated based on the composition of the monomers used to synthesize the alkali-soluble resin, and is the number of milligrams of potassium hydroxide theoretically required to neutralize 1 gram of the alkali-soluble resin.

[0044] The glass transition temperature of the alkali-soluble resin is 50°C or higher, preferably 60°C or higher, and more preferably 70°C or higher. From the perspective of improving the folding resistance of printed materials, the glass transition temperature of the alkali-soluble resin is preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 80°C or lower.

[0045] (Water-dispersible resin)

[0046] The white ink composition of the present invention may contain a water-dispersible resin. As the water-dispersible resin, one or more selected from styrene acrylic resin emulsions, polyurethane resin emulsions, and polyolefin resin emulsions may or may not be used in combination.

[0047] When other water-dispersible resins are used in combination, the solid content ratio of the water-dispersible resin in the white ink composition is preferably 10.0% by mass or less, and more preferably 8.0% by mass or less.

[0048] Styrene acrylic resin emulsions are emulsions of styrene acrylic resin dispersed in water. They can be produced by emulsion polymerization, dispersion polymerization, suspension polymerization, pulverization, or solution / bulk polymerization, followed by post-emulsification. Detailed information on these methods and stabilizers is described in "Emulsion Polymerization and Emulsion Polymers" (PA Lovell, MS El-Aasser, John Wiley & Sons Ltd., England, 1977, incorporated herein by reference).

[0049] Examples of commercially available styrene acrylic resin emulsions include M6963 (acid value less than 10 mgKOH / g, Japan Coatings Resin Co., Ltd.), J-450, J-734, J-7600, J-352, J-390, J-7100, J-741, J-74J, J-511, J-840, J-775, HRC-1645, HPD-71, PDX-6102B, JDX-5050 (styrene acrylic resin emulsion, BASF), UC-3900 (styrene acrylic resin emulsion, Toagosei Co., Ltd.), AP4710 (acrylic-silicone resin emulsion, Showa Highpolymer Co., Ltd.), SF460, SF460S, SF420, SF110, SF300, SF361 (polyurethane resin emulsion, Unicar Co., Ltd.), W-6020, W-5025, W-5661, W-6010 (polyurethane resin emulsion, Mitsui Chemicals Co., Ltd.), etc.

[0050] The polyurethane resin emulsion is an emulsion obtained by dispersing a polyurethane resin in water. Any of anionic, cationic, and nonionic polyurethane resins can be used, with anionic and nonionic polyurethane resins being preferred. Examples of the polyurethane resin include polyether polyurethane resins, polyester polyurethane resins, polyester and polyether polyurethane resins, and polycarbonate polyurethane resins. The polyurethane resin emulsions can be used alone or in combination of two or more.

[0051] Examples of commercially available polyurethane resin emulsions include "SUPER FLEXSTAR 210" (Dai-ichi Kogyo Seiyaku Co., Ltd., anionic polyester-based polyurethane resin), "SUPER FLEXSTAR 130" (Dai-ichi Kogyo Seiyaku Co., Ltd., anionic polyether-based polyurethane resin), "SUPER FLEXSTAR 500M" (Dai-ichi Kogyo Seiyaku Co., Ltd., nonionic polyester-based polyurethane resin), "SUPER FLEXSTAR 460" (Dai-ichi Kogyo Seiyaku Co., Ltd., anionic polycarbonate-based polyurethane resin), "Impranil DLP1380" (Sumika Covestro Urethane Co., Ltd., anionic polyester-based polyurethane resin), "BAYBOND PU407" (Sumika Covestro Urethane Co., Ltd., anionic / nonionic polyester-based polyurethane resin), and SUPER FLEXSTAR 420NS (Dai-ichi Kogyo Seiyaku Co., Ltd., anionic polycarbonate-based polyurethane resin).

[0052] The polyolefin resin emulsion is an emulsion of a polyolefin resin dispersed in water. Examples of the polyolefin resin include polyethylene resin, polypropylene resin, polybutene resin, and polyolefin resins obtained by copolymerizing two or more of ethylene, propylene, and butene. Furthermore, the polyolefin resin may include modified polyolefin resins in which amino groups, carboxyl groups, hydroxyl groups, acryloyl groups, or other polymer chains have been introduced into the polyolefin chain; oxidized polyolefin resins in which a portion of the polyolefin chain has been oxidized; and halogenated polyolefin resins in which a portion of the polyolefin chain has been treated with a halogen. These polyolefin resin emulsions may be used alone or in combination of two or more.

[0053] Examples of commercially available polyolefin resin emulsions include "CHEMIPEARL S100" (Mitsui Chemicals, Ltd., polyethylene resin emulsion), "CHEMIPEARL XEP800H" (Mitsui Chemicals, Ltd., polypropylene resin emulsion), and "ARROWBASE TC-4010" (UNITIKA, polypropylene resin emulsion).

[0054] The resin emulsion of the present invention may contain any known resin emulsion (other resin emulsion) used in white ink compositions, other than the styrene acrylic resin emulsion, the polyurethane resin emulsion, and the polyolefin resin emulsion, as long as the effects of the present invention are not impaired. Examples of such other resin emulsions include acrylic resin emulsions, polyvinyl acetate resin emulsions, and polyvinyl chloride resin emulsions.

[0055] The solid content concentration of the styrene acrylic resin emulsion, the polyurethane resin emulsion and / or the polyolefin resin emulsion in the total solid content of the water-dispersible resin is preferably 70.0% by mass or more, more preferably 80.0% by mass or more, further preferably 90.0% by mass or more, and most preferably 95.0% by mass or more, from the viewpoint of improving the coating film resistance such as scratch resistance.

[0056] <Other water-soluble resins (alkali-soluble resins)>

[0057] Examples of other water-soluble resins (alkali-soluble resins) include acrylic copolymer resins, maleic copolymer resins, polyester resins obtained by polycondensation, and polyurethane resins. Materials for synthesizing such alkali-soluble resins include, for example, those disclosed in Japanese Patent Application Laid-Open No. 2000-94825, and acrylic copolymer resins, maleic copolymer resins, polyester resins, polyurethane resins, and the like that can be obtained using the materials described in the publication. Furthermore, resins obtained from materials other than these may also be used. The alkali-soluble resins may be used alone or in combination of two or more.

[0058] In addition, as the water-soluble resin, a non-alkali-soluble water-soluble resin may be used in some cases.

[0059] The content of the other alkali-soluble resin may be 1.0 parts by mass or more, preferably 5.0 parts by mass or more, relative to 100 parts by mass of the pigment, from the perspective of improving the dispersibility of the pigment. The content of the other alkali-soluble resin is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 60 parts by mass or less, relative to 100 parts by mass of the pigment, from the perspective of reducing the viscosity of the aqueous inkjet composition.

[0060] As the acrylic copolymer resin, for example, one obtained by polymerizing a mixture of an anionic group-containing monomer and other copolymerizable monomers in a solvent in the presence of a common radical initiator (e.g., dibenzoyl peroxide, t-butyl perbenzoate, azobisisobutyronitrile, etc.) can be used.

[0061] Examples of the anionic group-containing monomer include monomers having at least one anionic group selected from a carboxyl group, a sulfonic acid group, and a phosphonic acid group. Among them, monomers having a carboxyl group are particularly preferred.

[0062] Examples of the monomer having a carboxyl group include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, 2-carboxyethyl (meth)acrylate, 2-carboxypropyl (meth)acrylate, maleic anhydride, fumaric anhydride, and maleic acid half ester. Examples of the monomer having a sulfonic acid group include ethyl methacrylate and phosphonic acid ethyl methacrylate.

[0063] As other monomers copolymerizable with the anionic group-containing monomer, a hydrophobic group-containing monomer is preferred from the viewpoint of improving adsorption to the pigment.

[0064] Examples of the hydrophobic group-containing monomer include monomers having a long-chain alkyl group, such as (meth)acrylic acid, and other free-radically polymerizable unsaturated carboxylic acids having 8 or more carbon atoms (e.g., 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, 2-hydroxystearyl (meth)acrylate, etc.), alkyl vinyl ethers having 8 or more carbon atoms (e.g., dodecyl vinyl ether, etc.), and vinyl esters of fatty acids having 8 or more carbon atoms (e.g., vinyl 2-ethylhexanoate, vinyl laurate, vinyl stearate, etc.). Examples of monomers having an alicyclic hydrocarbon group include cyclohexyl (meth)acrylate, and examples of monomers having an aromatic hydrocarbon group include benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, and other styrene-based monomers. These hydrophobic group-containing units may be used alone or in combination of two or more.

[0065] As other monomers copolymerizable with the anionic group-containing monomer, a hydrophilic group-containing monomer may be included from the viewpoint of suppressing aggregation of the alkali-soluble resin in the aqueous medium.

[0066] Examples of the monomer containing a hydrophilic group include, for example, a monomer having an (poly)oxyalkylene chain, and esters of a single-end alkyl-capped (poly)alkylene glycol such as methoxypolyethylene glycol, methoxypolyethylene polypropylene glycol, ethoxypolyethylene glycol, ethoxypolyethylene polypropylene glycol, propoxypolyethylene glycol, propoxypolyethylene polypropylene glycol, and a free-radical polymerizable unsaturated carboxylic acid such as (meth)acrylic acid, or ethylene oxide adducts and / or propylene oxide adducts of a free-radical polymerizable unsaturated carboxylic acid such as (meth)acrylic acid. Examples of the monomer containing a basic group include vinyl pyrrolidones such as 1-vinyl-2-pyrrolidone and 1-vinyl-3-pyrrolidone, vinyl pyrrolidone such as 2-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine, 1-vinylimidazole ... Examples include vinylimidazoles such as vinyl-2-methylimidazole, vinylpiperidines such as 3-vinylpiperidine and N-methyl-3-vinylpiperidine, nitrogen-containing derivatives of (meth)acrylic acid such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, (meth)acrylamide, N-methanol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-methoxy (meth)acrylamide, N-ethoxy (meth)acrylamide, N-dimethylacrylamide, and N-propylacrylamide. Examples of monomers having a hydroxyl group include hydroxyalkyl (meth)acrylic acid esters such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate. Examples of monomers having an epoxy group include glycidyl (meth)acrylate. These hydrophilic group-containing monomers may be used alone or in combination of two or more.

[0067] Examples of other copolymerizable monomers other than the hydrophobic group-containing monomer and the hydrophilic group-containing monomer include alkyl (meth)acrylates having less than 8 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, and hexyl (meth)acrylate. Other copolymerizable monomers other than the hydrophobic group-containing monomer and the hydrophilic group-containing monomer may be used alone or in combination of two or more.

[0068] Surfactants

[0069] The surfactant of the present invention contains an alkyl sulfonate and / or a polyoxyethylene alkyl ether sulfate.

[0070] The alkyl sulfonate is a higher alcohol sulfuric acid ester salt, and is a compound represented by the general formula (1): R1SO3M (in the formula (1), R1 is a straight-chain or branched alkyl or alkenyl group having 6 or more and 18 or less carbon atoms, and M is a cation). In the formula (1), M includes alkali metal ions such as sodium and potassium, ammonium ions, and the like. Examples of the alkyl sulfonate include lauryl sulfate, LATEMUL PS (Kao Corporation), SUNNOL LM-1130 (LION SPECIALTY CHEMICALS Co., Ltd.), and SANDET LNM (Sanyo Chemical Co., Ltd.). The alkyl sulfonates can be used alone or in combination of two or more.

[0071] The polyoxyethylene alkyl ether sulfate is a compound represented by the general formula (2): R2O(AO)mSO3M (in formula (2), R2 is a linear or branched alkyl or alkenyl group having 6 to 18 carbon atoms, AO is a linear or branched oxyalkylene group having 2 to 4 carbon atoms, m is the average number of moles of AO added, and M is a cation). Examples of the polyoxyethylene alkyl ether sulfate include SANDET EN (Sanyo Chemical Co., Ltd.), SUNNOL LMT-1430 (LION SPECIALTY CHEMICALS Co., Ltd.), and ADEKA HOPE YES-25 (ADEKA Corporation). For example, the polyoxyethylene alkyl ether sulfates can be used alone or in combination of two or more.

[0072] The surfactant of the present invention may contain known surfactants (other surfactants) used in white ink compositions other than the alkyl sulfonates and / or polyoxyethylene alkyl ether sulfates, as long as the effects of the present invention are not impaired. Examples of such other surfactants include nonionic surfactants, cationic surfactants, anionic surfactants, amphoteric surfactants, and betaine surfactants. Specific examples of such other surfactants include silicone surfactants, fluorine-based surfactants, and acetylene-based surfactants. These other surfactants may be used alone or in combination of two or more.

[0073] Examples of the silicone surfactant include BYK-347, BYK-377, and BYK-3455 (BYK Chemicals Japan Ltd.).

[0074] Examples of the fluorine-based surfactant include F-410, F-444, and F-553 (all from DIC Corporation), FS-65, FS-34, FS-35, FS-31, and FS-30 (all from DuPont Corporation).

[0075] Examples of the acetylene surfactant include SURFYNOL 104E, SURFYNOL 104H, SURFYNOL 104A, SURFYNOL 104BC, SURFYNOL 104DPM, SURFYNOL 104PA, SURFYNOL 104PG-50, SURFYNOL 420, SURFYNOL 440, SURFYNOL 465, DYNOL 607, DYNOL 609, OLFINE E1004, OLFINE E1010, OLFINE E1020, OLFINE PD-001, OLFINE PD-002W, OLFINE PD-004, OLFINE PD-005, OLFINE EXP.4001, OLFINE EXP.4200, OLFINE EXP.4123, and OLFINE One or more products sold under the trade name EXP.4300 (Nissin Chemical Industry Co., Ltd.)

[0076] <Water-soluble solvent>

[0077] The water-soluble solvent of the present invention can be any known water-soluble solvent used in white ink compositions without particular limitation. Examples thereof include monohydric alcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, nitrogen-containing compounds, ketones, ethers, and esters. These water-soluble solvents can be used alone or in combination of two or more.

[0078] Examples of the monohydric alcohols include methanol, ethanol, 1-propanol, 1-butanol, and 3-methoxy-3-methyl-1-butanol.

[0079] Examples of the polyol include ethylene glycol, propylene glycol, glycerol, diethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, neopentyl glycol, 1,2-hexanediol, 1,6-hexanediol, 1,2-cyclohexanediol, heptanediol, and 1,8-octanediol.

[0080] Examples of the lower alkyl ethers of the polyols include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol monopropyl ether, ethylene glycol isopropyl ether, ethylene glycol monobutyl ether, ethylene glycol isobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, and dipropylene glycol mono-n-butyl ether.

[0081] Examples of the nitrogen-containing compound include pyrrolidone and N-methyl-2-pyrrolidone.

[0082] Examples of the ketones include acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diisopropyl ketone, cyclopentanone, and cyclohexanone.

[0083] Examples of the ethers include isopropyl ether, n-butyl ether, tetrahydrofuran, tetrahydropyran, and 1,4-dioxane.

[0084] Examples of the esters include propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, ethyl butyrate, butylene phthalate, dioctyl phthalate; and cyclic esters such as ε-caprolactone and ε-caprolactam.

[0085] From the viewpoint of suppressing the drying of the ink composition in the inkjet head and facilitating the formation of an ink layer (film) on the substrate, the water-soluble solvent preferably contains at least one selected from monohydric alcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, and nitrogen-containing compounds, and more preferably contains at least one selected from propylene glycol, glycerol, diethylene glycol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and 3-methoxy-3-methyl-1-butanol.

[0086] Water

[0087] The water used in the present invention includes water used as an aqueous medium in the pigment dispersion described below, water contained in the resin emulsion, and water added for concentration adjustment of the white ink composition of the present invention. Examples of such water include ion-exchanged water, pure water, distilled water, and industrial water. These waters may be used alone or in combination of two or more.

[0088] The proportion of water (including water contained in each component) in the white ink composition of the present invention is preferably 40.0% by mass or more, more preferably 50.0% by mass or more, from the viewpoint of improving the drying properties of the coating film. Furthermore, from the viewpoint of improving ejection stability, it is preferably 70.0% by mass or less, more preferably 60.0% by mass or less.

[0089] <Basic compounds>

[0090] The white ink composition of the present invention preferably contains a basic compound from the perspective of dissolving the alkali-soluble resin. Examples of such basic compounds include inorganic basic compounds such as sodium hydroxide and potassium hydroxide; and organic basic compounds such as ammonia, methylamine, ethylamine, monoethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dibutylethanolamine, diethanolamine, N-methyldiethanolamine, triethanolamine, morpholine, N-methylmorpholine, and N-ethylmorpholine. These basic compounds can be used alone or in combination of two or more.

[0091] The proportion of the alkaline compound in the white ink composition of the present invention may be an amount sufficient to dissolve the alkali-soluble resin in the medium. Generally, from the viewpoint of improving the dispersion stability of the alkali-soluble resin, the proportion is preferably 0.05% by mass or more, more preferably 0.1% by mass or more. From the viewpoint of improving the water resistance of printed materials, the proportion is preferably 1.0% by mass or less, more preferably 0.5% by mass or less.

[0092] The white ink composition of the present invention may further contain additives such as known resins, pigment dispersants, mildew inhibitors, rust inhibitors, thickeners, antioxidants, ultraviolet absorbers, storage life enhancers, defoaming agents, and pH adjusters, depending on the intended purpose. Resin particles may or may not be added to prevent pigment precipitation in the white ink composition.

[0093] <Method for Preparing White Ink Composition>

[0094] The method for preparing (producing) the white ink composition of the present invention is not particularly limited, and the above-mentioned components may be added sequentially or simultaneously and mixed.

[0095] Among them, for example, there is (1) a method for preparing a white ink composition, which comprises mixing an aqueous resin varnish obtained by dissolving an alkali-soluble resin in water, a pigment, and, if necessary, a pigment dispersant, etc. in the presence of the alkaline compound, and then preparing a pigment dispersion (ink base) using various dispersers such as a ball mill, an attritor, a roller mill, a sand mill, and a stirred mill. Subsequently, the remaining materials are further added to prepare a white ink composition.

[0096] Another example is (2) a method for preparing a white ink composition, wherein after dispersing the pigment by the above method, an alkali-soluble resin is precipitated on the pigment surface by an acid precipitation method or an ion exchange method described in the re-published patent publication No. WO2005 / 116147, thereby obtaining a resin-coated pigment. The obtained resin-coated pigment is then neutralized with an alkaline compound and redispersed in water using various dispersing devices (such as a high-speed stirring device), and the remaining materials are further added to prepare a white ink composition.

[0097] The initial viscosity of the white ink composition of the present invention after production is preferably 2.0 to 15.0 mPa s, more preferably 3.0~12.0mPa The viscosity can be measured, for example, by an E-type viscometer (trade name "RE100L Viscometer," manufactured by Toki Sangyo Co., Ltd.).

[0098] <Primer Coat Composition>

[0099] When printing with the white ink composition of the present invention, a printed layer or primer layer based on a primer composition may be pre-formed on the surface of the printed object. This primer composition may contain an aggregation accelerator to promote aggregation of the white ink composition. Suitable primer compositions include, for example, the colorless ink composition described in Japanese Patent Application Publication No. 2009-190379, the primer ink composition described in Japanese Patent Application Publication No. 6424266, and the primer ink described in Japanese Patent Application Publication No. 2017-88646.

[0100] Examples of the aggregation accelerator include water-soluble polyvalent metal salts, organic acids, and cationic polymers. The aggregation accelerators may be used alone or in combination of two or more.

[0101] Examples of the water-soluble polyvalent metal salt include dissociated salts of alkaline earth metals such as Ca and Mg. Specifically, examples of the water-soluble polyvalent metal salt include calcium nitrate, CaCl2, Ca(OH)2, (CH3COO)2Ca, MgCl2, Mg(OH)2, (CH3COO)2Mg, (HCOO)2Ca, and MgSO4. Among these, calcium salts are preferred, with calcium nitrate, CaCl2, Ca(OH)2, (CH3COO)2Ca, and (HCOO)2Ca being particularly preferred.

[0102] Examples of the organic acid include lactic acid, malic acid, citric acid, oxalic acid, malonic acid, acetic acid, propionic acid, and fumaric acid.

[0103] Examples of the cationic polymer include polymers having primary to tertiary amino groups and polymers having quaternary ammonium salt groups. Specifically, the cationic polymer includes homopolymers of monomers having primary to tertiary amino groups, their salts, or quaternary ammonium salt groups (cationic monomers), or copolymers or polycondensates of these cationic monomers with other monomers (hereinafter referred to as "non-cationic monomers"). The cationic polymer can be used in the form of either a water-soluble polymer or water-dispersible emulsion particles.

[0104] The content of the coagulation accelerator is generally preferably 1.0% by mass or more in the primer composition from the viewpoint of improving the clarity and permeation resistance of the printed material, and is preferably 15.0% by mass or less, more preferably 10.0% by mass or less in the primer composition from the viewpoint of improving the water resistance of the printed material.

[0105] The primer composition may contain a resin emulsion from the viewpoint of improving the abrasion resistance and adhesion of the primer. The resin emulsion preferably has good stability even in the presence of an aggregation accelerator and may be used alone or in combination of two or more.

[0106] Examples of the resin emulsion include acrylic resin emulsions, polyester resin emulsions, polyurethane resin emulsions, polyvinyl acetate resin emulsions, polyvinyl chloride resin emulsions, polybutadiene resin emulsions, and polyolefin resin emulsions. Among these, acrylic resin emulsions, polyvinyl acetate resin emulsions, and polyolefin resin emulsions are preferred.

[0107] Examples of the acrylic resin emulsion include acrylic resin emulsions, styrene-acrylic resin emulsions, acrylic acid-vinyl acetate resin emulsions, acrylic acid-vinyl chloride resin emulsions, acrylic acid-silicone resin emulsions, and acrylic acid-colloidal silica resin emulsions. Among these, styrene-acrylic resin emulsions are preferred. Furthermore, the glass transition temperature of the resin contained in the acrylic resin emulsion is preferably 0°C or lower.

[0108] The polyvinyl acetate-based resin emulsion preferably has a glass transition temperature of the resin contained in the polyvinyl acetate-based resin emulsion of 0° C. or higher and 50° C. or lower in order to achieve good adhesion to a recording medium.

[0109] The polyolefin resin emulsion is a chlorinated polyolefin resin emulsion obtained by chlorinating and emulsifying a polyolefin resin. Examples of the chlorinated polyolefin resin emulsion include chlorinated polypropylene resin emulsion and chlorinated polyethylene resin emulsion. The degree of chlorination is preferably 5 to 30%.

[0110] The resin solid content of the resin emulsion is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, in the primer composition from the viewpoint of improving adhesion to the substrate, and is preferably 10.0% by mass or less, more preferably 5.0% by mass or less, in the primer composition from the viewpoint of improving storage stability.

[0111] The primer composition may contain a hydrazide compound to improve the adhesion between the primer and the substrate through interaction with the substrate surface of the printed object. The hydrazide compound is preferably a dihydrazide compound, for example, 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, etc.

[0112] The content of the hydrazide compound is generally about 0.2% by mass or more and 5% by mass or less in the primer composition.

[0113] The undercoat composition may contain a surfactant from the viewpoint of improving leveling properties on the substrate. As the surfactant, the same surfactant as that which can be mixed with the above-mentioned white ink composition can be mixed.

[0114] In addition to the above-mentioned components, the primer composition may also contain any other components as needed. Examples of such optional components include water-soluble organic solvents and various additives. Examples of such additives include preservatives, defoamers, and the like.

[0115] Examples of the water-soluble organic solvent include monohydric alcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, ketones, ethers, esters, nitrogen-containing compounds, etc. From the perspective of drying properties of the resulting primer layer, it is preferred not to use a water-soluble organic solvent.

[0116] Examples of the preservative improver include hindered amines, UV absorbers, and antioxidants. Examples of the hindered amine include N-CH3 type, NH type, and N-OR type. Examples of the UV absorber include phenyl ketone type UV absorbers, benzotriazole type UV absorbers, salicylic acid type UV absorbers, hydroxyphenol triazine type UV absorbers, cyanoacrylate type UV absorbers, and nickel complex salt type UV absorbers. Examples of the antioxidant include phenolic antioxidants, amine type antioxidants, sulfur type antioxidants, and phosphorus type antioxidants.

[0117] Examples of the defoaming agent include silicone-based defoaming agents and PLURONIC (registered trademark)-based defoaming agents.

[0118] <Production of Primer Coating Composition>

[0119] The primer composition can be produced by adding the aggregation accelerator to water, and optionally the resin emulsion, the hydrazide compound, the surfactant, the water-soluble organic solvent, and various additives, followed by stirring and mixing using a disperser or the like.

[0120] <Printed Materials>

[0121] The printed article can be obtained by printing an ink set comprising the white ink composition and, if necessary, the undercoat composition. Specifically, the article can be obtained by applying the undercoat composition to a substrate, drying it to form an undercoat layer, and then printing the white ink composition onto the undercoat layer using an inkjet printer. The undercoat composition can be applied using various coating devices, including blade coaters, air knife coaters, roll coaters, bar coaters, gravure coaters, bar blade coaters, lip coaters, curtain coaters, die coaters, and inkjet printers.

[0122] The inkjet printing method can appropriately adopt conventionally known conditions. For example, a method can be exemplified in which the undercoat composition (or the white ink composition) is placed in an ink cartridge, the ink cartridge is mounted on an inkjet recording apparatus such as a single-pass method, and inkjet printing is performed by ejecting the ink from a nozzle onto the substrate (or undercoat).

[0123] Examples of the substrate include non-absorbent printing media such as coated paper, inkjet paper, and inkjet glossy paper; polyolefin films, polyester films, nylon films, and general plastic substrates such as polyvinyl chloride sheets; uncoated papers such as plain paper and offset printing paper; and fabrics such as cotton. Among these, non-absorbent printing media are preferred, and plastic substrates are more preferred, from the viewpoint of good adhesion of the primer layer.

[0124] Example

[0125] (Example)

[0126] Pigments

[0127] CR-90-2 (trade name, titanium oxide treated with silica, alumina, and organic matter, average particle size 0.25 μm, DBP oil absorption 20 ml / 100 g, Ishihara Sangyo Co., Ltd.)

[0128] <Additives>

[0129] SURFYNOL 465 (Nissin Chemical Industry Co., Ltd.), an acetylene dione surfactant

[0130] <Water-based resin varnish>

[0131] 20 parts by mass of styrene / stearyl acrylate / acrylic acid or styrene / lauryl acrylate / acrylic acid copolymers as alkali-soluble resins shown in Table 1 were dissolved in a mixed solution of 2.5 parts by mass of potassium hydroxide and 77.5 parts by mass of water to obtain aqueous resin varnishes A to K having a solid content of 20%.

[0132] [Table 1]

[0133]

[0134] <Preparation of Pigment Dispersion>

[0135] To 40.0 parts by mass of the above-mentioned aqueous resin varnishes A to K, 20.0 parts by mass of water was added and mixed to prepare a resin varnish for pigment dispersion. Furthermore, 40.0 parts by mass of CR-90-2 was added to the varnish, stirred and mixed, and then kneaded using a wet circulating mill to obtain pigment dispersions A to F and I to M. At this time, pigment dispersions A to F were prepared using the above-mentioned aqueous resin varnishes A to F, pigment dispersion I was prepared using the above-mentioned aqueous resin varnish G, pigment dispersion J was prepared using the above-mentioned aqueous resin varnish H, pigment dispersion K was prepared using the above-mentioned aqueous resin varnish I, pigment dispersion L was prepared using the above-mentioned aqueous resin varnish J, and pigment dispersion M was prepared using the above-mentioned aqueous resin varnish K.

[0136] Separately, 50.0 parts by mass of water was added to 10.0 parts by mass of the aqueous resin varnish A and mixed to prepare a resin varnish for pigment dispersion. 40.0 parts by mass of CR-90-2 was further added to this varnish, stirred and mixed, and then kneaded using a wet circulation mill to obtain a pigment dispersion G.

[0137] Separately, 30.0 parts by mass of water was added to 50.0 parts by mass of the aqueous resin varnish A and mixed to prepare a resin varnish for pigment dispersion. Furthermore, 20.0 parts by mass of CR-90-2 was added to this varnish, stirred and mixed, and then kneaded using a wet circulation mill to obtain a pigment dispersion H.

[0138] Separately, 58.0 parts by mass of water were added to 2.0 parts by mass of the aqueous resin varnish A and mixed to prepare a resin varnish for pigment dispersion. Furthermore, 40.0 parts by mass of CR-90-2 were added to this varnish, stirred and mixed, and then kneaded using a wet circulation mill to obtain a pigment dispersion O.

[0139] Separately, 10.0 parts by mass of water was added to 70.0 parts by mass of the aqueous resin varnish A and mixed to prepare a resin varnish for pigment dispersion. Furthermore, 20.0 parts by mass of CR-90-2 was added to this varnish, stirred and mixed, and then kneaded using a wet circulation mill to obtain a pigment dispersion P.

[0140] <Preparation of White Ink Composition>

[0141] Each white ink composition was prepared by mixing so as to have the content described in Table 2.

[0142] For example, in Example 1, pigment dispersion A is mixed with aqueous resin varnish A, and 25 parts by mass of a substance formulated so that the resin in the varnish is adjusted to 20.0% by mass relative to the pigment, as well as a water-soluble solvent, a surfactant, and water are added to make 100 parts by mass as a white ink composition.

[0143] <Preparation of Primer Coating Composition>

[0144] 2.0 parts by mass of calcium acetate, 0.5 parts by mass of SURFYNOL 465, and 97.5 parts by mass of water were stirred and mixed to obtain a primer composition.

[0145] <Evaluation of Softness and Redispersibility of Sediment of White Ink Composition>

[0146] To evaluate the hardness of the sediment, 800 mL of the white ink composition prepared above was prepared, filled into a 1 L sample bottle, and allowed to stand at room temperature for one month. After one month, the appearance of the ink composition was observed to reveal titanium oxide sediment at the bottom. The sediment was scraped with a spatula to assess its softness. Furthermore, to evaluate its redispersibility, the ink composition was stirred at 400 rpm for 10 minutes using a disperser, and visual observation was made to determine whether the sediment redispersed.

[0147] [Evaluation criteria for softness of sediment]

[0148] ○: The sediment is soft and non-sticky, and there is no resistance when scraping with a spatula

[0149] △: The hardness of the sediment is medium, non-sticky, and there is a slight resistance when scraping with a spatula

[0150] ×: The sediment is hard and sticky. There is great resistance when scraping with a spatula, and the sediment is penetrated.

[0151] [Evaluation criteria for redispersibility]

[0152] ○: Redispersion

[0153] △: Most of the particles are redispersed, but some sediment remains.

[0154] ×: No change in sediment

[0155] <Evaluation of Discharge Properties of Ink Compositions>

[0156] The white ink composition was loaded into an ink cartridge of an evaluation printer equipped with an Epson head, and printed on masking paper, and the image quality of the printed matter was evaluated.

[0157] [Evaluation criteria for ejection properties]

[0158] ○: No printing errors, stable ejection

[0159] △: Slight printing errors, can be sprayed

[0160] ×: Printing is disordered and cannot be ejected stably

[0161] Image quality evaluation

[0162] Evaluation masking paper was prepared by applying the primer composition onto masking paper using a #4 wire bar manufactured by Marukyo Giken. Using an Epson PX105 printer, the white ink compositions of Examples 1-10 and Comparative Examples 1-9 were printed as thin lines with a width of approximately 0.3 mm on the evaluation masking paper. The printed area was visually observed for thickening of the thin lines due to bleeding of the ink composition, and the image quality was evaluated.

[0163] [Image quality evaluation criteria]

[0164] 0: No bleeding, thin lines are straight, and printing is completed with its original thickness

[0165] △: The thin line is straight, and some thickening is observed, but no thickening of more than 2 times is observed.

[0166] ×: The thin line is not straight, or the overall thickness is observed to be more than 2 times

[0167] <Evaluation of Storage Stability of Ink Composition>

[0168] The white ink composition was filled into a glass bottle and allowed to stand at 60° C. for 4 weeks, and then the viscosity of the aqueous pigment-based inkjet ink composition was measured.

[0169] [Evaluation criteria for storage stability]

[0170] ○: Change rate from initial viscosity is less than 10%

[0171] △: The change rate from the initial viscosity is more than 10% and less than 20%

[0172] ×: Change rate from initial viscosity is 20% or more

[0173] [Table 2]

[0174]

[0175]

[0176] According to Examples 1 to 10, which are examples according to the present invention, the ink composition has soft sediment, excellent redispersibility and ejectability, and also excellent image quality and storage stability after printing.

[0177] However, Comparative Examples 1 and 2, in which the glass transition temperature of the alkali-soluble resin is relatively low, exhibit particularly poor redispersibility. Comparative Example 3, in which the weight-average molecular weight of the alkali-soluble resin is relatively low, exhibits particularly poor storage stability. Comparative Example 4, in which the acid value of the alkali-soluble resin is relatively low, exhibits particularly poor image quality. Comparative Example 5, in which the weight-average molecular weight and acid value of the alkali-soluble resin are relatively low, exhibits particularly poor image quality and storage stability. Comparative Example 6, in which the content of the alkali-soluble resin in the ink composition is relatively low, exhibits particularly poor image quality and storage stability. Comparative Example 7, in which the content of the alkali-soluble resin in the ink composition is relatively high, exhibits particularly poor ejection properties, image quality, and storage stability. Comparative Example 8, in which the pigment concentration is relatively low, exhibits particularly poor image quality. Conversely, Comparative Example 9, in which the pigment concentration is relatively high, exhibits particularly poor ejection properties, image quality, and storage stability.

Claims

1. A white ink composition, characterized in that contain: 5.0 to 20.0% by mass of titanium oxide pigment in the ink composition, The solid content of an alkali-soluble resin having styrene, stearyl acrylate and / or lauryl acrylate, and acrylic acid as constituent units, wherein the mass ratio of the constituent units is styrene / stearyl acrylate and / or lauryl acrylate / acrylic acid = 20-80 / 5-25 / 15-30, and having a weight average molecular weight of 10,000 or more, an acid value of 100 mgKOH / g or more, and a glass transition temperature of 50°C or more, is 10.0 to 45.0 parts by mass per 100 parts by mass of the pigment in the ink composition. and surfactants.

2. The white ink composition according to claim 1, wherein The solid content of the alkali-soluble resin is 10.0 to 30.0 parts by mass relative to 100 parts by mass of the pigment in the white ink composition.

3. The white ink composition according to claim 1 or 2, characterized in that The titanium oxide pigment is a titanium oxide pigment treated with silicon dioxide, aluminum oxide and an organic compound.

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