White ink composition

Abstract

To provide a white ink that is easy to redisperse and can be redispersed with several tens of gentle shakes at most or without shaking at all.SOLUTION: There is provided a white ink composition comprising: a titanium oxide pigment, an amount of which is 5.0-20.0 mass% of the ink composition; an alkali-soluble resin comprising constituent units of styrene, stearyl acrylate and / or lauryl acrylate, and acrylic acid and having a weight-average molecular weight of 10,000 or higher, an acid value of 100 mgKOH / g or greater, and a glass transition temperature of 50°C or higher, the amount of which is 3.0-60.0 pts.mass on a solid basis per 100 pts.mass of the pigment in the ink composition; and a surfactant.SELECTED DRAWING: None

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 to blend a styrene-acrylic resin and various dispersants in a white ink composition, but the properties of the precipitate when the titanium oxide pigment precipitates are not particularly examined.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, an ink composition is likely to cause sedimentation and precipitation over time, especially when it contains titanium oxide. In addition, even if the precipitated ink composition is shaken, it is difficult to redisperse it easily, and it is difficult to redisperse it without shaking it hundreds of times with a strong force. Therefore, it has been desired to obtain a white ink that is easy to redisperse and can be redispersed with at most several tens of shakes with a weak force or without shaking at all.

Means for Solving the Problems

[0005] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by setting a specific composition, and have completed the present invention. That is, the present invention is as follows. 1. 5.0 to 20.0% by mass of titanium oxide pigment in the ink composition A 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 with respect to 100 parts by mass of the pigment in the ink composition, a surfactant, and contains a white ink composition. 2. The white ink composition according to 1, wherein the solid content of the alkali-soluble resin is 10.0 to 30.0 parts by mass with respect to 100 parts by mass of the pigment in the ink composition. [Effect of the Invention]

[0006] According to the present invention, in a white ink composition containing titanium oxide as a coloring pigment, there is an effect that the pigment once precipitated can be easily redispersed. [Embodiments for Carrying Out the Invention]

[0007] The white ink composition of the present invention is preferably an aqueous white ink composition, which will be described in order below. First, the glass transition temperature and the weight average molecular weight in the present invention are defined as follows. [Glass Transition Temperature] The glass transition temperature of the resin in the present invention is the theoretical glass transition temperature determined by the following Wood's equation when the resin is an acrylic copolymer resin. Wood's equation: 1 / Tg = W1 / Tg1 + W2 / Tg2 + W3 / Tg3 + ······ + Wx / Tgx [In the formula, Tg1 to Tgx are the glass transition temperatures of the respective homopolymers of monomers 1, 2, 3 ··· x constituting the resin, W1 to Wx are the polymerization fractions of monomers 1, 2, 3 ··· x, and Tg represents the theoretical glass transition temperature. However, the glass transition temperature in Wood's equation is an absolute temperature.]

[0008] The glass transition temperature of the resin is the theoretical glass transition temperature determined by thermal analysis when the resin is other than an acrylic copolymer resin. As a method of thermal analysis, in accordance with JIS K7121 (Method for Measuring the Transition Temperature of Plastics), for example, the glass transition temperature can be measured using a PerkinElmer Pyris1 DSC under the conditions of a heating rate of 20 °C / min and a nitrogen gas flow rate of 20 milliliters / min.

[0009] <Weight average molecular weight> The weight average molecular weight of the resin in the present invention can be measured by gel permeation chromatography (GPC). For example, using a Waters 2690 as the GPC apparatus and a PLgel, 5 μm, MIXED-D (Polymer Laboratories) as the column, with tetrahydrofuran as the eluent solvent, a column temperature of 25 °C, a flow rate of 1 milliliter / min, an RI detector, a sample injection concentration of 10 milligrams / milliliter, and an injection volume of 100 microliters, chromatography is performed and the weight average molecular weight in terms of polystyrene is determined.

[0010] <Titanium oxide pigment> In the present invention, the titanium oxide pigment is contained in the ink composition in an amount of 5.0 to 20.0% by mass. Alternatively, 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 in the solid content (total of pigment and resin content) of the white ink composition of the present invention. Also, it is 98.0% by mass or less, preferably 90.0% by mass or less, and more preferably 80.0% by mass or less. Known titanium oxide pigments can be used as the titanium oxide pigment that can be used in the present invention. Titanium oxide without surface treatment may be used, or a titanium oxide pigment treated with one or more selected from silica, alumina, zirconia, organosilicon compounds, etc. may be used. And the average particle diameter of the titanium oxide pigment is preferably 0.15 to 0.30 μm. Note that a titanium oxide pigment treated with silica, alumina, and an organic compound is preferred. Examples of the 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 (alumina- and organic substance-coated titanium oxide pigment), CR-57, CR-Super70 (alumina-, zirconia- and organic substance-coated titanium oxide pigment), and the like.

[0011] <Titanium oxide pigment treated with silica, alumina, and organic compounds> As the titanium oxide pigment treated with silica, alumina, and organic compounds that can be used in the present invention, known ones can be used, or they may not be used. In particular, the amounts of silica, alumina, and organic substances in the pigment are preferably such that the titanium oxide content in the titanium oxide pigment is in the range of 90.0 to 98.0% by mass, and the average particle diameter of this titanium oxide pigment is preferably 0.15 to 0.30 μm. As such a titanium oxide pigment, PF-690, PF-691, PF-711, PC-3, CR-80, CR-90, CR-90-2, CR-93 (Ishihara Sangyo Co., Ltd.), etc. can be used. The average particle diameter is a value measured by the Coulter counter method.

[0012] <Alkali-soluble resin> As the alkali-soluble resin in the present invention, a resin having styrene, stearyl acrylate and / or lauryl acrylate, and acrylic acid as constituent units can be adopted as a specific alkali-soluble resin. Such a specific alkali-soluble resin has a weight average molecular weight of 10,000 or more. Further, 13,000 or more is preferable, 50,000 or less is preferable, 40,000 or less is more preferable, and 30,000 or less is even more preferable. The solid content of the alkali-soluble resin can be 3.0 to 60.0% by mass based on 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. When using this specific alkali-soluble resin, a water-dispersible resin or other alkali-soluble resins may be used in combination.

[0013] The alkali-soluble resin preferably has a monomer mass ratio of styrene / stearyl acrylate and / or lauryl acrylate / acrylic acid = 20 to 80 / 5 to 25 / 15 to 30. From the viewpoint of appropriately crosslinking the resin to suppress pigment aggregation, a crosslinking agent having two or more functional groups may be used for the alkali-soluble resin.

[0014] The crosslinking agent having two or more functional groups may be any one 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 the reactive functional group include an epoxy group, a hydroxyl group, an isocyanate group, an amino group, and an aziridine group. The crosslinking agent having two or more functional groups can be used alone or in combination of two or more.

[0015] The acid value of the alkali-soluble resin is 100 mgKOH / g or more, and from the viewpoint of enhancing solubility in an aqueous medium, 125 mgKOH / g or more is preferable, and 150 mgKOH / g or more is more preferable. Also, from the viewpoint of improving the water resistance of the printed matter, the acid value of the alkali-soluble resin is preferably 300 mgKOH / g or less, and more preferably 250 mgKOH / g or less. The acid value is the theoretical acid value obtained arithmetically by calculating the number of milligrams of potassium hydroxide theoretically required to neutralize 1 g of the alkali-soluble resin based on the composition of the monomers used to synthesize the alkali-soluble resin.

[0016] 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 viewpoint of improving the folding resistance of the printed matter, 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.

[0017] (Water-dispersible resin) The white ink composition of the present invention can 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 be used in combination, or may not be used in combination. When other water-dispersible resins are used in combination, the proportion of the solid content 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.

[0018] The styrene-acrylic resin emulsion is an emulsion in which a styrene-acrylic resin is dispersed in water, and can be produced by emulsion polymerization, dispersion polymerization, suspension polymerization, grinding, or solution / bulk polymerization followed by post-emulsification. Detailed information on this method and stabilizers is described in "Emulsion Polymerization and Emulsion Polymer" (P.A. Lovell, M.S. El-Aasser, John Wiley & Sons Ltd., England, 1977, incorporated herein by reference). Examples of commercially available styrene-acrylic resin emulsions include M6963 (acid value less than 10 mgKOH / g, Japan Coating 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 (urethane resin emulsion, Nippon Unicar Co., Ltd.), W-6020, W-5025, W-5661, W-6010 (urethane resin emulsion, Mitsui Chemicals, Inc.), and the like.

[0019] The urethane resin emulsion is an emulsion in which a urethane resin is dispersed in water, and any of anionic, cationic, and nonionic types can be used, but anionic and nonionic types are preferred. Examples of the urethane resin include polyether-based urethane resin, polyester-based urethane resin, polyester-polyether-based urethane resin, polycarbonate-based urethane resin, and the like. The urethane resin emulsion can be used alone or in combination of two or more.

[0020] Examples of commercially available polyurethane resin emulsions include "Superflex 210" (Daiichi Kogyo Seiyaku Co., Ltd., anionic polyester-based polyurethane resin), "Superflex 130" (Daiichi Kogyo Seiyaku Co., Ltd., anionic polyether-based polyurethane resin), "Superflex 500M" (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., nonionic polyester-based polyurethane resin), "Superflex 460" (Daiichi Kogyo Seiyaku Co., Ltd., anionic polycarbonate-based polyurethane resin), "Impranil DLP1380" (Sumika Covestro Polyurethanes Co., Ltd., anionic polyester-based polyurethane resin), "Vibond PU407" (Sumika Covestro Polyurethanes Co., Ltd., anionic / nonionic polyester-based polyurethane resin), Superflex 420NS (Daiichi Kogyo Seiyaku Co., Ltd., anionic polycarbonate-based polyurethane resin), and the like.

[0021] The polyolefin resin emulsion is an emulsion in which a polyolefin resin is dispersed in water. Examples of the polyolefin resin include a polyethylene resin, a polypropylene resin, a polybutylene resin, and a polyolefin resin obtained by copolymerizing two or more of ethylene, propylene, and butylene. Further, the polyolefin resin may be a modified polyolefin resin in which an amino group, a carboxyl group, a hydroxyl group, an acryloyl group, or another polymer chain is introduced into the polyolefin chain; an oxidized polyolefin resin in which a part of the polyolefin chain is oxidized; a halogenated polyolefin resin in which a part is treated with a halogen; and the like. The polyolefin resin emulsion can be used alone or in combination of two or more.

[0022] Examples of commercially available polyolefin resin emulsions include "Chemparl S100" (Mitsui Chemicals, Inc., polyethylene-based resin emulsion), "Chemparl XEP800H" (Mitsui Chemicals, Inc., polypropylene-based resin emulsion), "Arrowbase TC-4010" (Unitika Ltd., polypropylene-based resin emulsion), and the like.

[0023] The resin emulsion of the present invention may contain, within a range that does not impair the effects of the present invention, known resin emulsions (other resin emulsions) used in white ink compositions other than the styrene-acrylic resin emulsion, the polyurethane resin emulsion, and the polyolefin resin emulsion. Examples of such other resin emulsions include acrylic resin emulsions, polyvinyl acetate resin emulsions, polyvinyl chloride resin emulsions, and the like.

[0024] In the total solid content of the water-dispersible resin, the solid content concentration of the styrene-acrylic resin emulsion, the polyurethane resin emulsion, and / or the polyolefin resin emulsion is preferably 70.0% by mass or more, more preferably 80.0% by mass or more, still more 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 abrasion resistance.

[0025] <Other water-soluble resins (alkali-soluble resins)> Examples of other water-soluble resins (alkali-soluble resins) include acrylic copolymer resins, maleic acid copolymer resins, polyester resins obtained by polycondensation reactions, and polyurethane resins. Materials for synthesizing such alkali-soluble resins are disclosed, for example, in JP-A-2000-94825, and acrylic copolymer resins, maleic acid copolymer resins, polyester resins, polyurethane resins, etc. obtained using the materials described in that publication can be used. Furthermore, resins obtained using other materials than these are also available. The alkali-soluble resins can be used alone or in combination of two or more. Note that, in some cases, water-soluble resins that are not alkali-soluble can also be employed as the water-soluble resin.

[0026] The content of other alkali-soluble resins may be 1.0 part by mass or more, preferably 5.0 parts by mass or more, from the viewpoint of enhancing the dispersibility of the pigment, with respect to 100 parts by mass of the pigment. From the viewpoint of reducing the viscosity of the aqueous inkjet composition, the content of other alkali-soluble resins 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, with respect to 100 parts by mass of the pigment.

[0027] Examples of the acrylic copolymer resin include those obtained by polymerizing a mixture of other monomers copolymerizable with an anionic group-containing monomer in a solvent in the presence of a usual radical generator (for example, benzoyl peroxide, tertiary butyl peroxybenzoate, azobisisobutyronitrile, etc.).

[0028] Examples of the anionic group-containing monomer include monomers having at least one anionic group selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic acid group. Among these, monomers having a carboxyl group are particularly preferred.

[0029] 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, maleic acid half ester, etc. Examples of the monomer having a sulfonic acid group include sulfonylethyl methacrylate, etc. Examples of the monomer having a phosphonic acid group include phosphonoethyl methacrylate, etc.

[0030] From the viewpoint of improving the adsorptivity with the pigment, the other monomer copolymerizable with the anionic group-containing monomer preferably contains a hydrophobic group-containing monomer.

[0031] Examples of the hydrophobic group-containing monomer include, as monomers having a long-chain alkyl group, alkyl esters of radical-polymerizable unsaturated carboxylic acids such as (meth)acrylic acid 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.), vinyl esters of fatty acids having 8 or more carbon atoms (e.g., vinyl 2-ethylhexanoate, vinyl laurate, vinyl stearate, etc.); as monomers having an alicyclic hydrocarbon group, cyclohexyl (meth)acrylate, etc.; as monomers having an aromatic hydrocarbon group, styrene-based monomers such as benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, etc. The hydrophobic group-containing monomer can be used alone or in combination of two or more.

[0032] As other monomers copolymerizable with the anionic group-containing monomer, hydrophilic group-containing monomers can be included from the viewpoint of suppressing aggregation of the alkali-soluble resin in an aqueous medium.

[0033] Examples of the hydrophilic group-containing monomer include, as monomers having a (poly)oxyalkylene chain, esterified products of one-terminal alkyl-blocked (poly)alkylene glycols such as methoxypolyethylene glycol, methoxypolyethylene polypropylene glycol, ethoxypolyethylene glycol, ethoxypolyethylene polypropylene glycol, propoxypolyethylene glycol, and propoxypolyethylene polypropylene glycol with radically polymerizable unsaturated carboxylic acids such as (meth)acrylic acid, and ethylene oxide adducts and / or propylene oxide adducts to radically polymerizable unsaturated carboxylic acids such as (meth)acrylic acid; examples of the basic group-containing monomer include vinylpyrrolidones such as 1-vinyl-2-pyrrolidone and 1-vinyl-3-pyrrolidone, vinylpyridines such as 2-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine, and 5-ethyl-2-vinylpyridine, vinylimidazoles such as 1-vinylimidazole and 1-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-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-methoxy (meth)acrylamide, N-ethoxy (meth)acrylamide, N-dimethylacrylamide, and N-propylacrylamide; examples of the monomer having a hydroxyl group include hydroxyalkyl esters of (meth)acrylic acid such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate; and examples of the monomer having an epoxy group include glycidyl (meth)acrylate. The hydrophilic group-containing monomer can be used alone or in combination of two or more kinds.

[0034] Examples of the copolymerizable other monomers other than the hydrophobic group-containing monomer and the hydrophilic group-containing monomer include alkyl esters of (meth)acrylic acid 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. The copolymerizable other monomers other than the hydrophobic group-containing monomer and the hydrophilic group-containing monomer can be used alone or in combination of two or more.

[0035] <Surfactant> The surfactant of the present invention contains an alkyl sulfonate and / or a polyoxyethylene alkyl ether sulfate.

[0036] The alkyl sulfonate is a higher alcohol sulfate ester salt and is a compound represented by the general formula (1): R1SO3M (in the formula (1), R1 is a linear or branched alkyl group or alkenyl group having 6 to 18 carbon atoms, and M is a cation). In the formula (1), examples of M include alkali metal ions such as sodium and potassium, and ammonium ions. Examples of the alkyl sulfonate include lauryl sulfate, Latemul PS (manufactured by Kao Corporation), Sunol LM-1130 (manufactured by Lion Corporation), and Sanded LNM (manufactured by Sanyo Chemical Industries, Ltd.). The alkyl sulfonate can be used alone or in combination of two or more.

[0037] The polyoxyethylene alkyl ether sulfate is a compound represented by the general formula (2): R2O(AO)mSO3M (wherein, R2 is a linear or branched alkyl group 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 Sanded EN (Sanyo Chemical Industries, Ltd.), Sannol LMT-1430 (Lion Corporation), Adeka Hope YES-25 (ADEKA Corporation), and the like. For example, the polyoxyethylene alkyl ether sulfate can be used alone or in combination of two or more kinds.

[0038] The surfactant of the present invention can contain, within a range not impairing the effects of the present invention, known surfactants (other surfactants) used in white ink compositions other than the alkyl sulfonate and / or polyoxyethylene alkyl ether sulfate. Examples of the other surfactants include nonionic surfactants, cationic surfactants, anionic surfactants, amphoteric surfactants, and betaine surfactants. Specific examples of the other surfactants include, for example, silicone-based surfactants, fluorine-based surfactants, and acetylene-based surfactants. The other surfactants can be used alone or in combination of two or more kinds.

[0039] Examples of the silicone-based surfactants include BYK-347, BYK-377, BYK-3455 (BIG CHEMIE JAPAN CO., LTD.), and the like.

[0040] Examples of the fluorine-based surfactants include, for example, F-410, F-444, F-553 (all of the above, DIC Corporation), FS-65, FS-34, FS-35, FS-31, FS-30 (all of the above, DuPont Corporation), and the like.

[0041] Examples of the acetylene-based surfactant include one or more selected from those commercially available under trade names such as 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, Olfin E1004, Olfin E1010, Olfin E1020, Olfin PD-001, Olfin PD-002W, Olfin PD-004, Olfin PD-005, Olfin EXP.4001, Olfin EXP.4200, Olfin EXP.4123, Olfin EXP.4300 (manufactured by Nissin Chemical Industry Co., Ltd.).

[0042] <Water-soluble solvent> As the water-soluble solvent of the present invention, known water-soluble solvents used in white ink compositions can be used without particular limitation. Examples include monoalcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, nitrogen-containing compounds, ketones, ethers, esters, and the like. The water-soluble solvents can be used alone or in combination of two or more.

[0043] Examples of the monoalcohols include methanol, ethanol, 1-propanol, 1-butanol, 3-methoxy-3-methyl-1-butanol, and the like.

[0044] Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, glycerin, diethylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,2-pentanediol, 1,5-pentanediol, neopentyl glycol, 1,2-hexanediol, 1,6-hexanediol, 1,2-cyclohexanediol, heptanediol, 1,8-octanediol, and the like.

[0045] Examples of the lower alkyl ethers of the polyhydric alcohol 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, dipropylene glycol mono-n-butyl ether, and the like.

[0046] Examples of the nitrogen-containing compound include pyrrolidone, N-methyl-2-pyrrolidone, and the like.

[0047] Examples of the ketones include acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diisopropyl ketone, cyclopentanone, cyclohexanone, and the like.

[0048] Examples of the ethers include isopropyl ether, n-butyl ether, tetrahydrofuran, tetrahydropyran, 1,4-dioxane, and the like.

[0049] 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, dibutyl phthalate, dioctyl phthalate; cyclic esters such as ε-caprolactone and ε-caprolactam, and the like.

[0050] From the viewpoints of suppressing drying of the ink composition in the inkjet nozzle and facilitating formation of an ink layer (film) on the substrate, the water-soluble solvent preferably contains at least one selected from the group consisting of monoalcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, and nitrogen-containing compounds, and more preferably contains at least one selected from the group consisting of propylene glycol, glycerin, diethylene glycol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and 3-methoxy-3-methyl-1-butanol.

[0051] <Water> The water in the white ink composition of the present invention includes water as an aqueous medium contained in the pigment dispersion liquid described later, water contained in the resin emulsion, and water added for adjusting the concentration of the white ink composition of the present invention. Examples of the water include ion-exchanged water, pure water, distilled water, and industrial water. The water can be used alone or in combination of two or more.

[0052] From the viewpoint of improving the drying property of the coating film, the proportion of the water (including the 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, and from the viewpoint of improving the ejection stability, it is preferably 70.0% by mass or less, more preferably 60.0% by mass or less.

[0053] <Basic compound> In the white ink composition of the present invention, from the viewpoint of dissolving the alkali-soluble resin, it is preferably contained a basic compound. Examples of the basic compound include inorganic basic compounds such as sodium hydroxide and potassium hydroxide; 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. The basic compound can be used alone or in combination of two or more kinds.

[0054] The proportion of the basic compound in the white ink composition of the present invention may be an amount that dissolves the alkali-soluble resin in the medium. Usually, from the viewpoint of enhancing the dispersion stability of the alkali-soluble resin, 0.05% by mass or more is preferable, 0.1% by mass or more is more preferable, and from the viewpoint of enhancing the water resistance of the printed matter, 1.0% by mass or less is preferable, 0.5% by mass or less is more preferable.

[0055] In the white ink composition of the present invention, additives such as known resins, pigment dispersants, antifungal agents, rust preventives, thickeners, antioxidants, ultraviolet absorbers, storage improvers, defoamers, and pH adjusters can be further added according to the purpose. However, for preventing pigment precipitation in the white ink composition, resin particles may or may not be blended.

[0056] <Method for preparing white ink composition> The method for preparing (manufacturing) the white ink composition of the present invention is not particularly limited, and the above components may be added in order or simultaneously and mixed. Among them, for example, (1) an aqueous resin varnish obtained by dissolving an alkali-soluble resin in water in the presence of the basic compound, a pigment, and if necessary, a pigment dispersant, etc. are mixed, and then a pigment dispersion liquid (ink base) is prepared using various dispersing machines such as a ball mill, an attritor, a roll mill, a sand mill, an agitator mill, etc. Next, there is a method of further adding the remaining materials to prepare a white ink composition. Also, after dispersing the pigment by the above method, a resin-coated pigment is obtained by depositing an alkali-soluble resin on the pigment surface by an acid precipitation method or ion exchange means described in the re-published patent WO2005 / 116147. Next, the obtained resin-coated pigment is neutralized with a basic compound, redispersed in water using various dispersers (such as a high-speed stirring device), and the remaining materials are further added to prepare a white ink composition.

[0057] The white ink composition of the present invention has an initial viscosity after production in the range of 2.0 to 15.0 mPa·s, preferably 3.0 to 12.0 mPa·s. The viscosity can be measured, for example, by an E-type viscometer (trade name "RE100L viscometer", manufactured by Toki Sangyo Co., Ltd.).

[0058] <Primer composition> When printing is performed with the white ink composition of the present invention, a printed layer or a coated layer with a primer composition can be provided in advance on the surface of the object to be printed. The primer composition can contain a flocculation accelerator that promotes the aggregation of the white ink composition. Examples of such primer compositions include the colorless ink composition described in JP-A-2009-190379, the primer ink composition described in Japanese Patent No. 6424266, and the primer ink described in JP-A-2017-88646.

[0059] Examples of the flocculation accelerator include water-soluble polyvalent metal salts, organic acids, cationic polymers, etc. The flocculation accelerator can be used alone or in combination of two or more.

[0060] Examples of the water-soluble polyvalent metal salt include dissociable 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, MgSO4, etc. Among these, calcium salts are preferred, and calcium nitrate, CaCl2, Ca(OH)2, (CH3COO)2Ca, (HCOO)2Ca are preferred.

[0061] Examples of the organic acid include lactic acid, malic acid, citric acid, oxalic acid, malonic acid, acetic acid, propionic acid, fumaric acid, and the like.

[0062] Examples of the cationic polymer include polymers having primary to tertiary amino groups, polymers having quaternary ammonium bases, and the like. Specifically, the cationic polymer includes homopolymers of monomers having primary to tertiary amino groups and their salts, monomers having quaternary ammonium bases (cationic monomers), and copolymers or polycondensates of the cationic monomers and other monomers (hereinafter referred to as "non-cationic monomers"). The cationic polymer can be used in any form of a water-soluble polymer or water-dispersible latex particles.

[0063] From the viewpoint of improving the clarity and anti-bleeding properties of the printed matter, the content of the flocculation accelerator is usually preferably 1.0% by mass or more in the primer composition, and from the viewpoint of improving the water resistance of the printed matter, it is preferably 15.0% by mass or less, more preferably 10.0% by mass or less in the primer composition.

[0064] The primer composition can contain a resin emulsion from the viewpoint of improving the abrasion resistance and adhesion of the primer. The resin emulsion is preferably one having good stability even in the presence of the flocculation accelerator, and can be used alone or in combination of two or more.

[0065] 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, polyolefin resin emulsions, and the like. Among these, acrylic resin emulsions, polyvinyl acetate resin emulsions, and polyolefin resin emulsions are preferred.

[0066] Examples of the acrylic resin emulsion include acrylic resin emulsion, styrene-acrylic resin emulsion, acrylic-vinyl acetate resin emulsion, acrylic-vinyl chloride resin emulsion, acrylic-silicone resin emulsion, acrylic-colloidal silica resin emulsion, etc. Among these, styrene-acrylic resin emulsion is preferred. Further, the glass transition temperature of the resin contained in the acrylic resin emulsion is preferably 0°C or lower.

[0067] Since the polyvinyl acetate resin emulsion has good adhesion to the recording medium, the glass transition temperature of the resin contained in the polyvinyl acetate resin emulsion is preferably 0°C or higher and 50°C or lower.

[0068] As the polyolefin resin emulsion, a chlorinated polyolefin resin emulsion obtained by chlorinating a polyolefin resin and emulsifying it is preferred. Examples of the chlorinated polyolefin resin emulsion include chlorinated polypropylene resin emulsion, chlorinated polyethylene resin emulsion, etc. The degree of chlorination is preferably 5 to 30%.

[0069] From the viewpoint of usually improving the adhesion to the substrate, the content of the resin solid 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 the storage stability, it is preferably 10.0% by mass or less, more preferably 5.0% by mass or less in the primer composition.

[0070] Since the primer composition can improve the adhesion between the primer and the substrate by interacting with the surface of the substrate of the object to be printed, it can contain a hydrazide compound. The hydrazide compound is preferably a dihydrazide compound, and examples thereof include 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, and the like.

[0071] The content of the hydrazide compound is usually about 0.2% by mass or more and 5.0% by mass or less in the primer composition.

[0072] The primer composition can contain a surfactant from the viewpoint of improving the leveling property on the substrate. As the surfactant, the same surfactants as those that can be blended in the white ink composition described above can be blended.

[0073] In addition to the above-described components, the primer composition may be blended with optional components as necessary. Examples of the optional components include water-soluble organic solvents and various additives. Examples of the additives include preservative improvers and defoamers.

[0074] Examples of the water-soluble organic solvent include monoalcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, ketones, ethers, esters, nitrogen-containing compounds, and the like. In view of the drying property of the resulting primer layer, it is preferable not to use a water-soluble organic solvent.

[0075] Examples of the preservative improver include hindered amines, ultraviolet absorbers, antioxidants, etc. Examples of the hindered amine include N-CH3 type, N-H type, N-OR type, etc. Examples of the ultraviolet absorber include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, hydroxyphenyltriazine-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, nickel complex salt-based ultraviolet absorbers, etc. Examples of the antioxidant include phenolic antioxidants, amine antioxidants, sulfur antioxidants, phosphorus antioxidants, etc.

[0076] Examples of the defoamer include silicone-based defoamers, Pluronic (registered trademark)-based defoamers, etc.

[0077] <Manufacture of Primer Composition> The primer composition can be produced by adding the aggregation accelerator, the resin emulsion, the hydrazide compound, the surfactant, the water-soluble organic solvent, and various additives to water and stirring and mixing them with a disper or the like.

[0078] <Printed Matter> To obtain a printed matter, an ink set having the white ink composition and, if necessary, the primer composition is printed. Specifically, it can be obtained by an image forming method in which the primer composition is applied and dried on a substrate to form a primer layer, and then the white ink composition is printed on the primer layer using an inkjet printer. Examples of the coating method of the primer composition include coating methods using various coating devices such as a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a rod blade coater, a lip coater, a curtain coater, a die coater, and an inkjet.

[0079] The printing method using an inkjet can appropriately adopt conventionally known conditions. For example, the primer composition (or the white ink composition) is housed in an ink cartridge, the ink cartridge is attached to an inkjet recording apparatus such as a single-pass system, and inkjet printing is performed by ejecting from a nozzle onto a substrate (or a primer layer).

[0080] Examples of the substrate include non-absorbent printing media such as coated papers like art paper, inkjet dedicated paper, and inkjet glossy paper, plastic-based substrates such as polyolefin films, polyester films, nylon films, and polyvinyl chloride sheets; uncoated papers such as plain paper and offset paper; and fabrics such as cotton. Among these, from the viewpoint of good adhesion of the primer layer, non-absorbent printing media are preferred, and plastic-based substrates are more preferred.

[0081] (Example) <Pigment> CR-90-2 (trade name "CR-90-2", titanium oxide treated with silica, alumina, and an organic substance, average particle diameter 0.25 μm, DBP oil absorption 20 ml / 100 g, Ishihara Sangyo Co., Ltd.) <Additive> Surfynol 465 (Nissin Chemical Industry Co., Ltd.), an acetylene diol-based surfactant

[0082] <Aqueous resin varnish> 20 parts by mass of styrene / stearyl acrylate / acrylic acid or styrene / lauryl acrylate / acrylic acid copolymer, which is an alkali-soluble resin shown in Table 1, was 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 with a solid content of 20%.

[0083]

Table 1

[0084] <Preparation of pigment dispersion> 20.0 parts by mass of water was added to and mixed with 40.0 parts by mass of the above aqueous resin varnishes A to K to prepare a resin varnish for pigment dispersion. To this varnish, 40.0 parts by mass of CR-90-2 was further added, and after stirring and mixing, kneading was performed with a wet circulation mill to obtain pigment dispersions A to F, I to M. At this time, pigment dispersions A to F were obtained using the above aqueous resin varnishes A to F respectively, pigment dispersion I was obtained using the above aqueous resin varnish G, pigment dispersion J was obtained using the above aqueous resin varnish H, pigment dispersion K was obtained using the above aqueous resin varnish I, pigment dispersion L was obtained using the above aqueous resin varnish J, and pigment dispersion M was obtained using the above aqueous resin varnish K. Also, 50.0 parts by mass of water was added to and mixed with 10.0 parts by mass of the above aqueous resin varnish A to prepare a resin varnish for pigment dispersion. To this varnish, 40.0 parts by mass of CR-90-2 was further added, and after stirring and mixing, kneading was performed with a wet circulation mill to obtain pigment dispersion G. Also, 30.0 parts by mass of water was added to and mixed with 50.0 parts by mass of the above aqueous resin varnish A to prepare a resin varnish for pigment dispersion. To this varnish, 20.0 parts by mass of CR-90-2 was further added, and after stirring and mixing, kneading was performed with a wet circulation mill to obtain pigment dispersion H. Also, 58.0 parts by mass of water was added to and mixed with 2.0 parts by mass of the above aqueous resin varnish A to prepare a resin varnish for pigment dispersion. To this varnish, 40.0 parts by mass of CR-90-2 was further added, and after stirring and mixing, kneading was performed with a wet circulation mill to obtain pigment dispersion O. Also, 10.0 parts by mass of water was added to and mixed with 70.0 parts by mass of the above aqueous resin varnish A to prepare a resin varnish for pigment dispersion. To this varnish, 20.0 parts by mass of CR-90-2 was further added, and after stirring and mixing, kneading was performed with a wet circulation mill to obtain pigment dispersion P.

[0085] <Preparation of white ink composition> Each white ink composition was prepared by mixing so as to have the contents described in Table 2. For example, in Example 1, 25 parts by mass of a mixture of a pigment dispersion A and an aqueous resin varnish A, formulated such that the resin content in the varnish with respect to the pigment is 20.0% by mass, and a water-soluble solvent, a surfactant, and water were added to make 100 parts by mass to obtain a white ink composition.

[0086] <Preparation of Primer Composition> 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.

[0087] <Evaluation of Softness and Redispersibility of Sediment in White Ink Composition> For the evaluation of the hardness of the sediment, 800 mL of the white ink composition produced above was prepared, filled into a 1 L sample bottle, and left standing at room temperature for 1 month. After 1 month, the appearance of the ink composition was observed, and titanium oxide had sedimented at the bottom. The softness of the sediment was evaluated by scraping the bottom with a spatula. Also, for the evaluation of redispersibility, the ink composition was stirred using a disper at a rotational speed of 400 rpm for 10 minutes, and it was visually observed whether the sediment was redispersed.

[0088] [Evaluation Criteria for Softness of Sediment] ○: The sediment is soft and not sticky, and there is no resistance when scraped with a spatula. △: The hardness of the sediment is intermediate, not sticky, and there is a little resistance when scraped with a spatula. ×: The sediment is hard and sticky, and there is a large resistance when scraped with a spatula, and the spatula pierces the sediment.

[0089] [Evaluation Criteria for Redispersibility] ○: Redisperses. △: Most redisperses, but a little sediment remains. ×: No change in the sediment.

[0090] <Evaluation of Dischargeability of Ink Composition> The evaluation printer cartridge equipped with an Epson head was filled with the white ink composition, printed on masking paper, and the print quality of the printed matter was evaluated. [Evaluation Criteria for Ejection Performance] ○: Those with no printing distortion and capable of stable ejection △: Those with some printing distortion but still capable of ejection ×: Those with printing distortion and unable to eject stably

[0091] [Image Quality Evaluation] The primer composition was applied to the masking paper with a wire bar of Maruwa Giken #4 to prepare the masking paper for evaluation. Using the Epson printer PX105, the white ink compositions of Examples 1 to 10 and Comparative Examples 1 to 9 were printed in a thin line with a width of about 0.3 mm on the masking paper for evaluation. The image quality of the printed part was evaluated by visually observing the thickening of the thin line due to the bleeding of the ink composition. [Evaluation Criteria for Image Quality] 〇: Those with no bleeding, the thin line is straight, and printed with the original thickness △: The thin line is straight, with partial thickening observed, but no thickening more than twice the original thickness ×: The thin line is not straight, or overall thickening more than twice the original thickness is observed

[0092] [Evaluation of Storage Stability of Ink Composition] The white ink composition was filled into a glass bottle and left standing at 60 °C for 4 weeks, and then the viscosity of the ink composition for aqueous pigment type inkjet was measured. [Evaluation Criteria for Storage Stability] ○: Those with a change rate from the initial viscosity of less than 10% △: Those with a change rate from the initial viscosity of 10% or more and less than 20% ×: Those with a change rate from the initial viscosity of 20% or more

[0093]

Table 2

[0094] According to Examples 1 to 10 which are examples along the lines of the present invention, the sediment of the ink composition was soft, excellent in redispersibility and ejectability, and also excellent in image quality after printing and storage stability. However, according to Comparative Examples 1 and 2 in which the glass transition temperature of the water-dispersible resin was low, it was particularly inferior in redispersibility. According to Comparative Example 3 in which the weight-average molecular weight of the water-dispersible resin was low, it was particularly inferior in storage stability. According to Comparative Example 4 in which the acid value of the water-dispersible resin was low, it was particularly inferior in image quality. According to Comparative Example 5 in which the weight-average molecular weight and acid value of the water-dispersible resin were low, it was particularly inferior in image quality and storage stability. According to Comparative Example 6 in which the content of the water-dispersible resin in the ink composition was small, it was particularly inferior in image quality and storage stability. According to Comparative Example 7 in which the content of the water-dispersible resin in the ink composition was too large, it was particularly inferior in ejectability, image quality and storage stability. According to Comparative Example 8 in which the pigment concentration was low, it was particularly inferior in image quality. Conversely, according to Comparative Example 9 in which the pigment concentration was high, it was particularly inferior in ejectability, image quality and storage stability.

Claims

1. 5.0 to 20.0% by mass of titanium oxide pigment in the ink composition, Styrene, stearyl acrylate and / or lauryl acrylate, acrylic acid as constituent units, the mass ratio of the constituent units being styrene / stearyl acrylate and / or lauryl acrylate / acrylic acid = 20 to 80 / 5 to 25 / 15 to 30, the weight average molecular weight being 10,000 or more, the acid value being 100 mgKOH / g or more, and the glass transition temperature being 50°C or more of the solid content of an alkali-soluble resin, 3.0 to 60.0 parts by mass with respect to 100 parts by mass of the pigment in the ink composition, Surfactant, Containing, White ink composition.

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 with respect to 100 parts by mass of the pigment in the white ink composition.

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