White ink composition for water-based inkjet printing

Abstract

To provide a white ink composition for water-based inkjet printing that achieves high white image density in a printed object and exhibits high redispersibility after pigment settling, storage stability, and discharge stability.SOLUTION: There is provided a white ink composition for water-based inkjet printing that contains: a titanium oxide pigment; a polymer dispersing agent including an anionic group-containing resin; a surfactant; and water. The ink composition contains 4.0 pts.mass to 16.0 pts.mass of the titanium oxide pigment relative to 100 pts.mass of the ink composition. The titanium oxide pigment includes titanium oxide and a surface treatment agent for treating the surface of the titanium oxide. The titanium oxide pigment satisfies the condition that the ratio of the mass of the titanium oxide to the total mass of the surface treatment agent is 90:10 to 80:20. The weight average molecular weight of the anionic group-containing resin is 5,000 or more and 50,000 or less. The anionic group-containing resin content is 7.0 pts.mass or more relative to 100 pts.mass of the titanium oxide pigment.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a white ink composition for aqueous ink-jet printing, and more particularly to a white ink composition containing a specific titanium oxide pigment. [Background technology]

[0002] In white ink compositions for aqueous inkjet printing, titanium oxide pigment is often blended as a white pigment. Since titanium oxide pigment has a high specific gravity, ink compositions containing titanium oxide pigment may cause sedimentation or aggregation of the titanium oxide pigment. In particular, ink compositions for aqueous inkjet printing need to have a low viscosity in order to obtain ejection stability during printing, so that the titanium oxide pigment is prone to sedimentation or aggregation; during storage of the ink composition or during pauses in printing, the titanium oxide pigment may sediment or aggregate in the ink flow path of the inkjet printer. In addition, even if an attempt is made to redisperse the titanium oxide pigment that has settled or aggregated in the white ink composition, it may be difficult.

[0003] Several solutions have been proposed to such problems. Patent Document 1 describes a water-based ink for inkjet printing that contains a rutile titanium oxide pigment and a polymer dispersant; by making a predetermined amount or more of the constituent units of the polymer dispersant be derived from an anionic group-containing monomer, the ink can be easily redispersed even if the titanium oxide pigment settles (has good redispersibility during settling).

[0004] Furthermore, Patent Document 2 describes a method for storing in a tank an aqueous inkjet white ink composition containing a surface-treated titanium oxide pigment and a pigment dispersant, and describes how maintaining the temperature of the white ink composition at -5 to -35°C prevents the titanium oxide pigment from settling and makes it easy to redisperse the titanium oxide pigment even if it does settle.

[0005] Furthermore, Patent Document 3 describes an ink composition for UV-curable inkjet recording that contains a surface-treated titanium oxide pigment and a polymer dispersant having an acidic polar group, and claims that by subjecting the titanium oxide pigment to a specific surface treatment, an ink composition with excellent ejection stability is obtained. Patent Document 4 describes an ink composition for inkjet recording that contains a titanium oxide pigment and a polymer dispersant, and claims that by using a sulfonic acid group-containing polymer dispersant as the polymer dispersant, the ink dispersion stability is improved and clogging of the inkjet nozzle is suppressed.

[0006] On the other hand, Patent Document 5 describes a white ink composition for preprint printing containing surface-treated titanium oxide, in which the surface-treated titanium oxide has a predetermined particle size and oil absorption amount, and the titanium oxide content of the surface-treated titanium oxide is set within a certain range, thereby achieving high whiteness and hiding power. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6881836 [Patent Document 2] Patent Publication No. 2021-178908 [Patent Document 3] JP 2004-59857 A [Patent Document 4] JP 2007-99833 A [Patent Document 5] JP 2016-98262 A Summary of the Invention [Problem to be solved by the invention]

[0008] As described in Cited Documents 1 to 4, techniques have been proposed for suppressing sedimentation of titanium oxide pigment, improving redispersibility, improving ejection stability, etc. in aqueous white ink compositions for inkjet printing that contain a titanium oxide pigment and a polymeric pigment dispersant. However, these techniques do not pay attention to the relationship between the amount of surface treatment of the titanium oxide pigment (or the titanium oxide content) and suppression of sedimentation of the titanium oxide pigment, etc.

[0009] The present inventors have found that, in a white ink composition containing a titanium oxide pigment and a polymeric pigment dispersant, by setting the surface treatment amount of the titanium oxide pigment (or the titanium oxide content) within a certain range, the white image density of a print produced by the white ink composition is increased, and the redispersibility during sedimentation, storage stability, and ejection stability of the white ink composition are also improved. In other words, the present invention provides a white ink composition for aqueous inkjet printing that produces a high white image density in a print, and that has high redispersibility during sedimentation, storage stability, and ejection stability. [Means for solving the problem]

[0010] That is, the present invention relates to an aqueous white ink composition for ink-jet printing, as shown below. [1] A water-based white ink composition for ink-jet printing, comprising a titanium oxide pigment, a polymer dispersant containing an anionic group-containing resin, a surfactant, and water, comprising: The titanium oxide pigment is contained in an amount of 4.0 parts by mass to 16.0 parts by mass relative to 100 parts by mass of the ink composition; The titanium oxide pigment includes titanium oxide and a surface treatment agent that treats a surface of the titanium oxide; The titanium oxide pigment satisfies the condition that the mass of the titanium oxide: the total mass of the surface treatment agent = 90:10 to 80:20; The weight average molecular weight of the anionic group-containing resin is 5,000 or more and 50,000 or less; The aqueous white ink composition for ink-jet printing, wherein the content of the anionic group-containing resin is 7.0 parts by mass or more per 100 parts by mass of the titanium oxide pigment.

[0011] Furthermore, as a preferred embodiment, the present invention relates to an aqueous white ink composition for ink-jet printing, as shown below. [2] The aqueous white ink composition for ink-jet printing according to [1] above, wherein the anionic group-containing resin has an acid value of 470 mgKOH / g or more and 830 mgKOH / g or less. [3] The aqueous white ink composition for ink-jet printing according to [1] or [2] above, wherein the content of the anionic group-containing resin is 25.0 parts by mass or less per 100 parts by mass of the titanium oxide pigment. [4] The water-based white ink composition for ink-jet printing according to any one of [1] to [3] above, wherein the titanium oxide pigment has an average primary particle size in the range of 100 nm to 600 nm. Effect of the Invention

[0012] The aqueous white ink composition for inkjet printing of the present invention has high redispersibility during sedimentation, storage stability, and ejection stability, and can provide printed matter with high white image density, and therefore can be widely used as a white ink composition for inkjet printing. For example, it can be used as an inkjet printing ink composition for white-line printing, and can be used in inkjet textile printing, etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 1. Water-based white ink composition for inkjet printing The aqueous white ink composition for inkjet printing of the present invention (hereinafter, also simply referred to as the "white ink composition") contains 1) a titanium oxide pigment, 2) a polymeric dispersant, 3) a surfactant, and 4) a solvent containing water, and may further contain 5) other optional components.

[0014] 1-1.Titanium oxide pigment The titanium oxide pigment contained in the white ink composition is a titanium oxide (TiO 2 ) and a treatment agent (surface treatment agent) for treating the surface of the titanium oxide core. The surface treatment agent for titanium oxide is alumina (Al 2 O 3etc.), silica (SiO 2 etc.), zirconia (ZrO 2 The titanium oxide may be an inorganic oxide (or inorganic hydrate) such as zinc oxide or magnesium oxide, or an organic substance such as stearic acid; however, inorganic oxides (or inorganic hydrates) are preferred, and one or both of alumina and silica are more preferred. The surface treatment of titanium oxide is carried out by a wet treatment in a solution (aqueous treatment, etc.) or a dry treatment in a solid phase (gas phase treatment, etc.), which are well known to those skilled in the art.

[0015] The ratio of "mass of titanium oxide" to "total mass of surface treatment agents" in the titanium oxide pigment (mass of titanium oxide:total mass of surface treatment agents) is 90:10 to 80:20, preferably 87:13 to 80:20, and more preferably 85:15 to 80:20. The titanium oxide content in the titanium oxide pigment is preferably 90 mass% or less, more preferably 87 mass% or less, and even more preferably 85 mass% or less; on the other hand, it is preferably 80 mass% or more.

[0016] When the total mass of the surface treatment agent relative to the mass of titanium oxide in the titanium oxide pigment increases, the dispersibility (particularly sedimentation redispersibility) of the titanium oxide pigment in the white ink composition is improved. The mechanism of improvement is not particularly limited; however, it is considered that the titanium oxide pigment is more easily adsorbed to the anionic group-containing resin described below when the surface treatment agent is present on the surface of the titanium oxide pigment than when the titanium oxide is exposed. In addition, by treating the surface of the titanium oxide with a surface treatment agent, the surface of the pigment is roughened and the surface area is increased, and as a result, the titanium oxide pigment may be more easily adsorbed to the anionic group-containing resin. If the total mass of the surface treatment agent relative to the mass of titanium oxide is excessively large (i.e., if the titanium oxide content is too low), the function as a white pigment is reduced, and the white image density of the obtained printed matter may not be sufficiently high.

[0017] The amount of the surface treatment agent in the titanium oxide pigment (i.e., the content ratio between the "mass of titanium oxide" and the "total mass of the surface treatment agent") can be measured by a method known to those skilled in the art; for example, the amount of inorganic treatment can be analyzed by X-ray fluorescence analysis (XRF), atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectroscopy (ICP), etc. to analyze the amount of inorganic surface treatment such as alumina, silica, zirconia, etc., and the amount of inorganic adsorbed or attached to the titanium oxide surface can be quantified. In addition, the particle surface of the titanium oxide pigment can be analyzed by X-ray photoelectron spectroscopy (ESCA, Electron Spectroscopy for Chemical Analysis), etc. Preferably, the amount of the surface treatment agent in the titanium oxide pigment is determined by X-ray fluorescence analysis.

[0018] The particle size of the titanium oxide pigment is preferably 100 nm or more, more preferably 200 nm or more, in terms of average primary particle size; on the other hand, it is preferably 600 nm or less. When the average primary particle size is 100 nm or more, the white density of the coating film obtained from the white ink composition is improved; when it is 600 nm or less, the inkjet dischargeability of the white ink composition is easily stabilized. The average primary particle size of the titanium oxide pigment can be measured using a transmission electron microscope.

[0019] The crystal type of titanium oxide in the titanium oxide pigment is not particularly limited and may be rutile type (tetragonal crystal), anatase type (tetragonal crystal), brookite type (orthorhombic crystal), etc., but is preferably rutile type. By using rutile type titanium oxide, the crystal stability and the hiding power of the white ink composition are likely to be improved. Titanium oxide can be produced by a gas phase method or liquid phase method known to those skilled in the art, but in order to increase the crystallinity of titanium oxide, it is preferable to produce it by a gas phase method.

[0020] The content of the titanium oxide pigment in the white ink composition is 4.0 parts by mass or more, preferably 7.0 parts by mass or more, relative to 100 parts by mass of the ink composition; on the other hand, it is 16.0 parts by mass or less, preferably 13.0 parts by mass or less. By making the content of the titanium oxide pigment 4.0 parts by mass or more relative to 100 parts by mass of the ink composition, it is possible to impart sufficient coloring power to the white ink composition (to form a printed matter with a high white image density), and by making it 16.0 parts by mass or less, it is possible to increase the fluidity of the white ink composition and improve sedimentation redispersibility, storage stability, ejection properties, etc.

[0021] Titanium oxide pigments can be obtained from the market. Examples of titanium oxide pigments that satisfy the condition of "mass of titanium oxide: total mass of surface treatment agent = 90:10 to 80:20" or titanium oxide pigments with "titanium oxide content of 80 to 90 mass%" include: TIPAQUE CR-85 (titanium oxide content 88%), TIPAQUE CR-90 (titanium oxide content 90%), TIPAQUE CR-93 (titanium oxide content 90%), TIPAQUE PFR209 (titanium oxide content 89%) (all from Ishihara Sangyo Kaisha); TIPURE TS-6300 (titanium oxide content 82%), TIPURE R-960 (titanium oxide content 90%) (all from Chemours); TITONE R-7E (titanium oxide content 85%), TITONE R-62N (titanium oxide content 89%), TITONE R-45M (titanium oxide content 89%) (both from Sakai Chemical Industry Co., Ltd.); and JR-805 (titanium oxide content 88%) (both from Teika Co., Ltd.). The above titanium oxides may be used alone or in combination of two or more kinds.

[0022] 1-2. Polymer dispersants The polymer dispersant contained in the white ink composition includes an anionic group-containing resin. The anionic group-containing resin is a resin in which at least a portion of its monomer units contains an anionic group. The anionic group refers to an acidic group such as a carboxylic acid group, a sulfonic acid group, or a phosphoric acid group. The anionic group contained in the anionic group-containing resin promotes the adsorption of the anionic group-containing resin to the titanium oxide pigment, thereby enhancing the dispersibility (particularly the sedimentation and redispersibility) of the titanium oxide pigment in the white ink composition.

[0023] In the anionic group-containing resin, the acid group may form a salt, for example, a sodium salt or a potassium salt. When the acid group of the anionic group-containing resin forms a salt, the solubility of the anionic group-containing resin in water is increased, and thus the anionic group-containing resin can be dissolved as a varnish in the white ink composition.

[0024] The anionic group-containing resin has an acid value, which is preferably 400 mgKOH / g or more, more preferably 470 mgKOH / g or more, and even more preferably 560 mgKOH / g or more; on the other hand, it is preferably 900 mgKOH / g or less, more preferably 830 mgKOH / g or less, and even more preferably 780 mgKOH / g or less. When the acid value of the anionic group-containing resin is 470 mgKOH / g or more, the presence rate of the anionic group increases and the anionic group is easily adsorbed to the titanium oxide pigment, so that the precipitation and redispersibility of the white ink composition can be improved. On the other hand, when the acid value of the anionic group-containing resin is 900 mgKOH / g or less, the image density of the white ink composition is easily increased, and the ejection property of the white ink composition is also easily stabilized.

[0025] The acid value of the anionic group-containing resin can be measured in accordance with JIS K 0070.

[0026] The weight average molecular weight of the anionic group-containing resin is 5000 or more, and preferably 10000 or more; on the other hand, it is preferably 50000 or less, and preferably 30000 or less. When the weight average molecular weight of the anionic group-containing resin is 5000 or more, the sedimentation and redispersibility of the white ink composition can be improved. On the other hand, when the weight average molecular weight of the anionic group-containing resin is 50000 or less, the ejection properties of the white ink composition tend to be stable.

[0027] The weight average molecular weight of the polymer dispersant may be a weight average molecular weight calculated in terms of polystyrene, and can be measured by gel permeation chromatography.

[0028] Examples of the anionic group-containing monomer that constitutes the anionic group-containing resin include acrylic acid, methacrylic acid, maleic acid, and sulfonic acid group-containing vinyl monomers (such as styrene sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid).

[0029] In addition, the anionic group-containing resin preferably contains, as its monomer units, a hydrophobic monomer together with the anionic group-containing monomer, and may further contain a nonionic monomer, etc., so long as the effects of the present invention are not impaired.

[0030] The hydrophobic monomer constituting the anionic group-containing resin may be an alkyl (meth)acrylate, an aromatic group-containing monomer, etc. The alkyl (meth)acrylate preferably has an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms; examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (iso or tertiary)butyl (meth)acrylate, (iso)amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl (meth)acrylate [lauryl (meth)acrylate, etc.], (iso)stearyl (meth)acrylate, etc. The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group of 6 to 22 carbon atoms, which may have a substituent containing a hetero atom; it may be a styrene-based monomer (e.g., styrene, 2-methylstyrene, divinylbenzene, etc.), an aromatic group-containing (meth)acrylate (e.g., benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc.), etc.

[0031] Examples of the nonionic monomer constituting the anionic group-containing resin include polyalkylene glycol (meth)acrylate. When the anionic group-containing resin contains a nonionic monomer as a monomer unit, the sedimentation and redispersibility of the white ink composition can be improved in some cases.

[0032] Examples of the polyalkylene glycol (meth)acrylate include polyethylene glycol mono(meth)acrylate, methoxypolyethylene glycol mono(meth)acrylate, ethoxypolyethylene glycol mono(meth)acrylate, propoxypolyethylene glycol mono(meth)acrylate, butoxypolyethylene glycol mono(meth)acrylate, octoxypolyethylene glycol mono(meth)acrylate, and stearoxypolyethylene glycol mono(meth)acrylate.

[0033] The anionic group-containing resin can be obtained by copolymerizing a predetermined monomer by a known polymerization method (e.g., solution polymerization method) and neutralizing the anionic group of the obtained copolymer with a neutralizing agent, etc. The anionic group-containing resin may be a random copolymer or a block copolymer of the predetermined monomer.

[0034] 1-3.Surfactants The surfactant contained in the white ink composition can improve the dispersibility (particularly the sedimentation and redispersibility) of the titanium oxide pigment in the white ink composition. The surfactant may be a nonionic surfactant, a silicone-based surfactant, or the like. The content of the surfactant in the white ink composition may be appropriately set in consideration of the dispersibility, etc., and may be in the range of 0.1 to 2.0% by mass, preferably 0.2 to 1.5% by mass.

[0035] The nonionic surfactant may be an acetylene glycol surfactant or an alcohol ethoxylate surfactant.

[0036] Acetylene glycol surfactants are compounds that have both acetylene alcohol or acetylene bonds and glycol units, and can be represented by the following structural formula 1. The acetylene bond site is a hydrophobic site, and the alcohol site or glycol site is a hydrophilic site, and can exhibit a surface active function. [ka]

[0037] In the above structural formula 1, R 1 and R 2 each independently represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms; R 3 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group; R represents an alkylene group having 2 to 6 carbon atoms; m represents 0 to 40; and X represents a hydrogen atom or a group represented by the following structural formula 2. [ka]

[0038] In the above structural formula 2, R 4 and R 5 each independently represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms; R 6 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group; R represents an alkylene group having 2 to 6 carbon atoms; and n represents 0 to 40.

[0039] Specific examples of acetylene glycol surfactants include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, and ethylene oxide adducts thereof.

[0040] Acetylene glycol surfactants are also available on the market, and are available under the trade names: SURFYNOL 104E, SURFYNOL 104H, SURFYNOL 104A, SURFYNOL 104BC, SURFYNOL 104DPM, SURFYNOL 104PA, SURFYNOL 104PG-50, SURFYNOL 420, SURFYNOL 440, SURFYNOL 465, SURFYNOL 485, Olfine 1004, Olfine E1004, Olfine E1010, Olfine E1020 (Nissin Chemical Industry Co., Ltd.), and the like.

[0041] Alcohol ethoxylate surfactants are compounds in which a polyoxyethylene chain and an alkyl group are bonded by an ether bond. A -O-(CH 2 CH 2 O) d The alkyl group (R -H) in the alcohol ethoxylate surfactants is sometimes called poly(oxyethylene) alkyl ether. AThere is no limitation on the number of carbon atoms in the alkyl group (R A ) preferably has about 11 to 15 carbon atoms, and more preferably has about 12 to 13 carbon atoms; furthermore, the average number of moles of added ethyleneoxy chains (d) is preferably about 3 to 15, and more preferably has the average number of moles of added ethyleneoxy groups of about 5 to 10.

[0042] Examples of alcohol ethoxylate surfactants include those sold under the trade names EMULGEN 705, EMULGEN 104, EMULGEN 106, EMULGEN 707, EMULGEN 1108, EMULGEN 1118S-70, EMULGEN 1135S-70, and EMULGEN 1150S-60 (Kao Corporation); those sold under the trade names ADEKA TOLL LA-675B and ADEKA TOLL LA-775 (ADEKA Corporation); those sold under the trade name TRITON (registered trademark) HW1000 (Dow Corporation); and those sold under the trade name SANNONIC SS70 (Sanyo Chemical Industries, Ltd.).

[0043] Silicone surfactants are dimethylpolysiloxanes (chemical formula: (C 2 H 6 OSi) n ) or a modified form thereof, but a surfactant obtained by modifying a polysiloxane with a polyether (a polyether-modified silicone-based surfactant) is preferred. The polyether-modified silicone-based surfactant can suppress an excessive increase in the viscosity of the ink.

[0044] Polyether-modified silicone surfactants have a structure in which the side chain and / or terminal hydrocarbon groups of silicone oil are replaced with polyether groups. As the polyether group, polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups (EO) and propyleneoxy groups (PO) are added in a block or random manner are suitable, and compounds in which polyether groups are graft-bonded to a silicone main chain, compounds in which silicone and polyether groups are bonded in a block form, etc. can be used.

[0045] Silicone surfactants can be obtained from the market, and specific examples include KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF640, KF-642, KF643, KF-644, KF6020, KF6011, etc. (Shin-Etsu Chemical Co., Ltd. KF series); Silface SAG (Nissin Chemical Co., Ltd.); BYK-345, 347, 348, 349, etc. (BYK series from BYK-Chemie Co., Ltd.); TEGO GLIDE 410, 450, etc., TEGO Twin 400, etc. (Evonik Co., Ltd.). These surfactants may be used alone or in combination of two or more types.

[0046] 1-4. Solvents containing water The white ink composition contains a solvent. The solvent contains at least water and preferably contains a water-soluble organic solvent. The water-soluble organic solvent may be a polyhydric alcohol, a glycol ether, or the like.

[0047] Examples of polyhydric alcohols include 1,2-alkanediols such as ethylene glycol, propylene glycol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol; diethylene glycol, polyethylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, glycerin, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol.

[0048] The glycol ether may be an alkylene glycol monoalkyl ether, an alkylene glycol dialkyl ether, or the like. The alkyl group of the alkylene glycol monoalkyl ether may be either a straight chain or a branched chain. Specific examples of the alkylene glycol monoalkyl ether include ethylene glycol ethyl ether, ethylene glycol isopropyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol isopropyl ether, diethylene glycol isobutyl ether, diethylene glycol butyl ether, triethylene glycol methyl ether, dipropylene glycol butyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, and the like.

[0049] The type and amount of the solvent in the white ink composition may be selected so as to set the viscosity and fluidity of the white ink composition within a predetermined range. These solvents may be used alone or in combination.

[0050] 1-5.Other optional ingredients The white ink composition may contain various additives, such as a water-dispersible resin, a wetting agent, a penetrating agent, a dispersant, a viscosity modifier, an antifoaming agent, an antifungal agent, an antirust agent, and an ultraviolet absorbing agent, as necessary.

[0051] The water-dispersible resin contained in the white ink composition is usually a resin emulsion, and may be a nonionic resin emulsion and / or an anionic resin emulsion. The water-dispersible resin (resin emulsion) may be a urethane resin, an acrylic resin, a styrene-acrylic resin, a fluorene resin, a polyolefin resin, a rosin-modified resin, a terpene resin, a polyester resin, a polyamide resin, an epoxy resin, a vinyl chloride resin, a vinyl chloride-vinyl acetate copolymer, an ethylene-vinyl acetate resin, or the like.

[0052] When the white ink composition is used in inkjet textile printing (described later), a urethane-based resin is preferable from the viewpoint of reducing stickiness of the coating film. The urethane-based resin may be any of a polyether type containing an ether bond, a polyester type containing an ester bond, a polycarbonate type containing a carbonate bond, etc. Among these, a polycarbonate-type or polyether-type urethane-based resin having a crosslinkable group is more preferable from the viewpoint of improving the friction fastness of the image of the printed textile.

[0053] Examples of the crosslinkable group possessed by the urethane resin include an isocyanate group, a silanol group, a carboxyl group, and a hydroxyl group, and a substituent (blocked isocyanate group) in which the isocyanate group is chemically protected (capped or blocked) is preferable. The blocked isocyanate group is deprotected and activated by the application of heat, forming a crosslinked bond (e.g., a urethane bond, a urea bond, an allophanate bond, etc.). In addition, it is preferable that the crosslinkable group of the urethane resin having the crosslinkable group is provided in three or more per molecule, and in such a case, a crosslinked structure is formed by the reaction of the crosslinkable group.

[0054] The content of the water-dispersible resin (resin emulsion) in the white ink composition, calculated as solid content, relative to the total mass of the ink (100 mass%), is preferably 1 mass% or more, more preferably 2.5 mass% or more, and even more preferably 3 mass% or more; and is preferably 20 mass% or less, more preferably 15 mass% or less, and even more preferably 12 mass% or less.

[0055] The white ink composition may or may not have active energy ray curing properties. A white ink composition that has active energy ray curing properties may contain a polymerizable compound and a polymerization initiator.

[0056] 1-6. Preparation of aqueous white ink composition for inkjet printing The procedure for producing the aqueous white ink composition for inkjet printing is not particularly limited, but the composition can be obtained by preparing a dispersion of titanium oxide pigment, mixing this with water and, if necessary, various additives, and stirring the mixture.

[0057] 1-7. Physical properties of aqueous white ink composition for inkjet printing Since the white ink composition is used for inkjet printing, the viscosity is set so that it has a viscosity suitable for inkjet printing and also has high dispersibility (particularly, sedimentation and redispersibility). The viscosity of the white ink composition at 25°C is preferably 3.0 mPa·s or more, more preferably 4.5 mPa·s or more, and even more preferably 5.0 mPa·s or more; on the other hand, it is preferably 12.0 mPa·s or less, more preferably 9.0 mPa·s or less, even more preferably 7.5 mPa·s or less, and even more preferably 6.5 mPa·s or less. The viscosity of the white ink composition can be measured using an E-type viscometer.

[0058] The pH of the white ink composition is not particularly limited, but from the viewpoint of enhancing dispersibility, it is preferably 5.5 or more, more preferably 6.0 or more, and even more preferably 6.5 or more; on the other hand, from the viewpoints of component resistance and skin irritation, it is preferably 11.0 or less, more preferably 10.0 or less, even more preferably 9.5 or less, and even more preferably 9.0 or less.

[0059] 2. Uses of the aqueous inkjet printing white ink composition 2-1. About inkjet printing The aqueous white ink composition for inkjet printing of the present invention can be used for inkjet printing. The white ink composition of the present invention has good storage stability and good ejection stability, and therefore can form a high-quality white image with high white density when inkjet printed. Furthermore, the white ink composition of the present invention has high sedimentation and redispersibility, and therefore can be redispersed by a simple means even if the titanium oxide pigment settles in the inkjet printing device (for example, in an ink tank or ink flow path), and is therefore suitable for inkjet printing.

[0060] There is no particular limitation on the inkjet recording method of the white ink composition of the present invention. Examples of inkjet recording methods include a charge control method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink to eject ink using radiation pressure, and a thermal inkjet method that heats the ink to form bubbles and uses the generated pressure. Inkjet recording methods include a method of ejecting a large number of low-concentration inks called photo inks in a small volume, a method of improving image quality by using multiple inks of substantially the same hue but different concentrations, and a method of using colorless and transparent ink. The white ink composition of the present invention is particularly suitable as an inkjet recording ink for a drop-on-demand method (pressure pulse method) using a piezoelectric element.

[0061] The white ink composition of the present invention may be used for underprinting (also referred to as "whiteout printing") on a printed material. "Whiteout printing" means that the white ink composition is printed in advance on a portion of the printed material where an ink composition of a desired color is to be printed (or that the white ink composition is printed solidly on the entire printed material); this masks the underlying printed material and prevents the color of the printed portion from mixing with the desired color. Whiteout printing is often performed particularly when a "light-colored ink composition" is printed on a printed material. The white ink composition of the present invention can form a printing layer with a high white image density, and therefore can more reliably mask the underlying printed material when used for whiteout printing.

[0062] The white ink composition of the present invention can be printed on any substrate. Examples of substrates include paperboard, resin film, corrugated cardboard, fabric, etc. When the substrate is fabric, it can be printed by, for example, the inkjet printing method described below.

[0063] 2-2. About inkjet printing The white ink composition of the present invention can also be used in an inkjet textile printing method. The inkjet textile printing method is a method of printing an image on a fabric using a pretreatment liquid, a white ink composition, and a chromatic ink composition. That is, the inkjet textile printing method may include, in this order, 1) step A of preparing a fabric pretreated with a pretreatment liquid, 2) step B of inkjet coating the white ink composition on the pretreated fabric, and 3) step C of inkjet coating a chromatic ink composition on an ink layer formed by coating the white ink composition. The white ink composition of the present invention can be used as the white ink composition in step B.

[0064] [Process A] In the step A of preparing a fabric pretreated with a pretreatment liquid, the pretreatment liquid may be applied to the fabric by applying the pretreatment liquid to the fabric or by immersing the fabric in the pretreatment liquid, etc. Alternatively, a fabric pretreated by another person may be obtained and used in the inkjet printing method.

[0065] The material of the fabric to be pretreated in the inkjet printing method is not particularly limited, and may be any conventional fabric on which an image is formed by the inkjet printing method, such as natural fibers such as cotton, linen, wool, silk, etc.; synthetic fibers such as polypropylene, polyester, acetate, triacetate, polyamide, polyurethane, etc.; biodegradable fibers such as polylactic acid, etc., or blends of these fibers may also be used.

[0066] The pretreatment liquid for pretreating the fabric may be a pretreatment liquid that has been conventionally used in inkjet printing methods. The pretreatment liquid is capable of aggregating the components of the white ink composition and the chromatic ink composition on the fabric. The pretreatment liquid preferably contains a) a polyvalent metal salt and b) a water-dispersible resin, and usually contains c) an aqueous medium, and may further contain other optional components.

[0067] By pretreating the fabric, it is possible to improve the color development of the image in the printed material. The pretreatment of the fabric is performed by applying a pretreatment liquid to the fabric. For example, the fabric can be immersed in the pretreatment liquid, or the pretreatment liquid can be applied to the fabric by various coating (rotor) means, spraying (spray) means, inkjet printing means, etc. After the pretreatment liquid is applied to the fabric, the solvent of the applied pretreatment liquid is dried, but there may be cases where it is not dried.

[0068] [Process B] The inkjet textile printing method includes a step B of inkjet coating a white ink composition on a pretreated fabric. That is, the white ink composition is inkjet coated on the pretreated fabric to form a white ink layer on the pretreated fabric. The white ink layer may be formed on a part or all (preferably all) of the pretreated area of ​​the fabric where a chromatic ink composition described below is to be applied. In applying the white ink composition, the white ink composition may be applied once or multiple times (that is, it may be repeatedly applied and overcoated).

[0069] In step B, by using the white ink composition of the present invention, a white ink layer having a high white image density can be formed on the fabric, and the fabric can be more reliably shielded, thereby further improving the color development of the image formed with the chromatic ink compositions in step C described below.

[0070] [Process C] The inkjet textile printing method of the present invention includes a step C of inkjet coating a chromatic ink composition on a white ink layer formed by coating a white ink composition on a fabric. That is, the chromatic ink composition is applied by an inkjet technique to the fabric on which a white ink layer has been formed, to print a chromatic image. The chromatic ink composition can be applied on a part or all of the white ink layer formed on the fabric. The chromatic ink composition may be applied once or multiple times (that is, it may be repeatedly applied and overcoated).

[0071] [Image fixing process, etc.] The inkjet printing method preferably includes a step of applying a chromatic ink composition to a fabric to print an image, and then fixing the image to the fabric by heating. The fabric is preferably heated to 100 to 180° C., and the heating means is not particularly limited, and a heat press machine, an iron, a dryer, a heating dryer, etc. can be used. EXAMPLES

[0072] A. Preparation of White Ink Composition A-1. Materials used in preparation of white ink composition A-1-1. Titanium oxide (1) to (3) were used as surface-treated titanium oxide pigments. Titanium dioxide pigment (1) Product name: "TiPure TS6300" manufactured by Chemours Surface treatment agent "Silica and Alumina" Mass of titanium oxide: Total mass of surface treatment agent (silica and alumina) = 82:18 Average primary particle size: 0.53μm Titanium dioxide pigment (2) Product name: "TIPAQUE PFR209" manufactured by Ishihara Sangyo Kaisha Surface treatment agent "Silica and Alumina" Mass of titanium oxide: Total mass of surface treatment agent (silica and alumina) = 89:11 Average primary particle size: 0.25μm Titanium dioxide pigment (3) Product name: "TIPAQUE CR-80" manufactured by Ishihara Sangyo Kaisha Surface treatment agent "Silica and Alumina" Mass of titanium oxide: Total mass of surface treatment agent (silica and alumina) = 93:7 Average primary particle size: 0.25μm

[0073] A-1-2. The following anionic group-containing resin varnishes 1 to 9 were prepared. 25.0 parts by mass of anionic group-containing resin 1 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 15,000, acid value 650 mgKOH / g) was dissolved in a mixed liquid of 10.3 parts by mass of potassium hydroxide and 64.7 parts by mass of water to obtain anionic group-containing resin varnish 1 with a resin solid content of 25.0% by mass. 25.0 parts by mass of anionic group-containing resin 2 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 5,000, acid value 650 mgKOH / g) was dissolved in a mixed liquid of 10.3 parts by mass of potassium hydroxide and 64.7 parts by mass of water to obtain anionic group-containing resin varnish 2 having a resin solid content of 25.0% by mass. 25.0 parts by mass of anionic group-containing resin 3 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 50,000, acid value 650 mgKOH / g) was dissolved in a mixed liquid of 10.3 parts by mass of potassium hydroxide and 64.7 parts by mass of water to obtain anionic group-containing resin varnish 3 having a resin solid content of 25.0% by mass. 25.0 parts by mass of anionic group-containing resin 4 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 15,000, acid value 550 mgKOH / g) was dissolved in a mixed liquid of 8.8 parts by mass of potassium hydroxide and 66.2 parts by mass of water to obtain anionic group-containing resin varnish 4 with a resin solid content of 25.0% by mass. 25.0 parts by mass of anionic group-containing resin 5 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 15,000, acid value 800 mgKOH / g) was dissolved in a mixed liquid of 12.7 parts by mass of potassium hydroxide and 62.3 parts by mass of water to obtain anionic group-containing resin varnish 5 having a resin solid content of 25.0% by mass. 25.0 parts by mass of anionic group-containing resin 6 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 3,000, acid value 650 mgKOH / g) was dissolved in a mixed liquid of 10.3 parts by mass of potassium hydroxide and 64.7 parts by mass of water to obtain anionic group-containing resin varnish 6 having a resin solid content of 25.0% by mass. 25.0 parts by mass of anionic group-containing resin 7 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 60,000, acid value 650 mgKOH / g) was dissolved in a mixed liquid of 10.3 parts by mass of potassium hydroxide and 64.7 parts by mass of water to obtain anionic group-containing resin varnish 7 with a resin solid content of 25.0 mass%. 25.0 parts by mass of anionic group-containing resin 8 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 15,000, acid value 450 mgKOH / g) was dissolved in a mixed liquid of 8.0 parts by mass of potassium hydroxide and 67.0 parts by mass of water to obtain anionic group-containing resin varnish 8 having a resin solid content of 25.0 mass%. 25.0 parts by mass of anionic group-containing resin 9 (acrylic acid / lauryl acrylate / styrene copolymer: weight average molecular weight 15,000, acid value 850 mgKOH / g) was dissolved in a mixed liquid of 13.5 parts by mass of potassium hydroxide and 61.5 parts by mass of water to obtain anionic group-containing resin varnish 9 having a resin solid content of 25.0 mass%.

[0074] A-1-3. Other materials ·Water dispersible resin Product name: NeoRez R-966, manufactured by DSM Polyether Polyurethane Resin Solids content 33% Surfactants Product name: Olfin E1010, manufactured by Nissin Chemical Co., Ltd. Polyoxyethylene (10) acetylenic glycol ether

[0075] A-2. Preparation of Water-Based White Ink Base: Water-based white ink bases (A) to (O) were prepared using the titanium oxide pigment shown in A-1 and anionic group-containing resin varnish. 18 parts of anionic group-containing resin varnish 1 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (A). 18 parts of anionic group-containing resin varnish 1 and 37 parts of water were mixed, and then 45 parts of titanium oxide (2) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (B). 12.6 parts of anionic group-containing resin varnish 1 and 42.4 parts of water were mixed, and 45 parts of titanium oxide (1) was further added and stirred, and then the mixture was milled in a wet circulation mill to obtain a water-based white ink base (C). 43.2 parts of anionic group-containing resin varnish 1 and 11.8 parts of water were mixed, and 45 parts of titanium oxide (1) was further added and stirred, and then the mixture was milled in a wet circulation mill to obtain a water-based white ink base (D). 18 parts of anionic group-containing resin varnish 2 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (E). 18 parts of anionic group-containing resin varnish 3 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (F). 18 parts of anionic group-containing resin varnish 4 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (G). 18 parts of anionic group-containing resin varnish 5 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (H). 18 parts of anionic group-containing resin varnish 1 and 37 parts of water were mixed, and then 45 parts of titanium oxide (3) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (I). 9 parts of anionic group-containing resin varnish 1 and 46 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (J). 46.8 parts of anionic group-containing resin varnish 1 and 8.2 parts of water were mixed, and 45 parts of titanium oxide (1) was further added and stirred, and then the mixture was milled in a wet circulation mill to obtain a water-based white ink base (K). 18 parts of anionic group-containing resin varnish 6 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (L). 18 parts of anionic group-containing resin varnish 7 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (M). 18 parts of anionic group-containing resin varnish 8 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (N). 18 parts of anionic group-containing resin varnish 9 and 37 parts of water were mixed, and then 45 parts of titanium oxide (1) was added and mixed with stirring. The mixture was then ground in a wet circulation mill to obtain a water-based white ink base (O).

[0076] A-3. Preparation of Water-Based White Ink Composition White ink compositions having the formulations shown in Tables 1 and 2 were prepared using the water-based white ink bases (A) to (O) prepared in A-2, a water-dispersible resin, and a surfactant.

[0077] B. Preparation of printed items B-1. Preparation of pretreatment liquid for inkjet printing To 83.7 parts of water, 10 parts of calcium nitrate tetrahydrate, 6.0 parts of a nonionic styrene-acrylic self-crosslinking resin emulsion having a glass transition temperature of -30°C (product name: Movinyl 966A, manufactured by Japan Coating Resins, solid content 45 mass%), and 0.3 parts of Acetylenol E100 (HLB 13.5, ethylene oxide adduct of acetylene glycol, manufactured by Kawaken Fine Chemicals Co., Ltd.) were added and stirred to obtain a pretreatment liquid for inkjet textile printing.

[0078] B-2. Preparation of printed items A 100% cotton black fabric was impregnated with 10 g of the pretreatment liquid per A4 size, and dried by heating for 1 minute at 170°C using a heat press machine to obtain a print medium. A solid image was printed on the print medium using the aqueous white ink compositions prepared using the aqueous white ink bases (A) to (O) using an evaluation printer equipped with a SPECTRA head, and then heated for 4 minutes at 170°C using a conveyor oven to produce a print of each white ink composition.

[0079] C. Evaluation of Water-Based White Ink Composition and Printed Materials The water-based white ink composition prepared in A-3 was evaluated for sedimentation redispersibility, storage stability, and ink-jet dischargeability, and the printed material produced in B-2 was evaluated for image density.

[0080] C-1. Evaluation of sedimentation and redispersibility 100 g of the water-based white ink compositions of the Examples and Comparative Examples were filled into a 100 ml sample bottle and left to stand in an environment of 60° C. for 4 weeks, and then the sample bottle was shaken up and down to redisperse the sediment (until no sediment was observable), and the number of shakes required was measured and the sedimentation redispersibility was evaluated according to the following criteria. ◎ Redispersed less than 50 times ○ Redispersed 50 to 100 times △ Redispersed 100 to 200 times × Redispersion was not possible within 200 attempts

[0081] C-2. Evaluation of storage stability In the sedimentation and redispersibility test of C-1, the viscosity (initial viscosity) of the water-based white ink composition when filled into the sample bottle and the viscosity of the water-based white ink composition after redispersing the sediment were each measured, and the storage stability was evaluated according to the following criteria. ◎ The change in viscosity from the initial viscosity is less than 5% ○ The change rate from the initial viscosity is 5% or more and less than 10% △ The change in viscosity from the initial viscosity is between 10% and 20%. × The change in viscosity from the initial viscosity is 20% or more.

[0082] C-3. Evaluation of inkjet ejection properties The water-based white ink compositions of the Examples and Comparative Examples were subjected to continuous actual printing operations using an inkjet printer (an evaluation printer equipped with a head manufactured by SPECTRA Corporation), and the presence or absence of nozzle missing in the obtained white images was confirmed, and the inkjet dischargeability was evaluated according to the following criteria. ◎ No ejection problems were observed in any of the nozzles during continuous printing for over one hour. ○ During continuous printing operation of 15 minutes or more and less than 1 hour, no ejection problems are observed in any nozzle. △: During continuous printing operation of 15 minutes or more and less than 1 hour, there are nozzles that are unable to eject ink. × All nozzles are unable to eject during continuous printing for 15 minutes or more but less than 1 hour.

[0083] C-4. Evaluation of image density of printed matter The lightness (L*) of the printed matter was measured using a color difference meter (product name "DR-321", manufactured by Konica Minolta) and evaluated according to the following criteria. ◎ Lightness L* was 90 or higher ○ Lightness L* was 80 or more and less than 90 △ Lightness L* was 60 or more and less than 80 × Lightness L* was less than 60

[0084] [Table 1]

[0085] [Table 2]

[0086] As shown in Comparative Example 1 in Table 2, it was found that the white ink composition containing titanium oxide pigment (3) (CR-80) with a titanium oxide content of 93% by mass in the titanium oxide pigment had poor sedimentation and redispersibility, and once the pigment settled, it was difficult to redisperse. In contrast, as shown in Examples 1 and 2 in Table 1, the white ink compositions containing titanium oxide pigments (1) or (2) (TS-6300 or PRF209) with titanium oxide contents of 82% or 89% by mass in the titanium oxide pigment had sufficient sedimentation and redispersibility.

[0087] Furthermore, as can be seen from a comparison between Example 1 and Example 2 in Table 1, the white ink composition containing titanium oxide pigment (1) (TS-6300), in which the titanium oxide content in the titanium oxide pigment is 82% by mass, has higher sedimentation and redispersibility than the white ink composition containing titanium oxide pigment (2) (PRF209), in which the titanium oxide content in the titanium oxide pigment is 89% by mass. Thus, it can be seen that the titanium oxide content in the titanium oxide pigment (or the amount of surface treatment in the titanium oxide pigment) is an important factor in the sedimentation and redispersibility of the white ink composition.

[0088] As shown in Comparative Example 2 in Table 2, a white ink composition in which the titanium oxide pigment content in the ink composition was 3.0% by mass did not provide sufficient white image density (brightness) to the resulting printed matter. Furthermore, as shown in Comparative Example 3, a white ink composition in which the titanium oxide pigment content was 18.0% by mass was prone to inkjet ejection defects and also tended to deteriorate in sedimentation and redispersibility. In contrast, as shown in Examples 1, 3, and 4 in Table 1, white ink compositions in which the titanium oxide pigment contents were 10.0%, 5.0%, and 15.0% by mass provided sufficient white image density (brightness) to the resulting printed matter, were less likely to cause ejection defects, and also had sufficient sedimentation and redispersibility.

[0089] As shown in Comparative Example 4 in Table 2, when the content of the anionic group-containing resin relative to the titanium oxide pigment was 5%, the sedimentation redispersibility and storage stability tended to deteriorate. In contrast, as shown in Examples 1, 5, 6, and 11, when the content of the anionic group-containing resin relative to the titanium oxide pigment was 10 mass%, 7 mass%, 24 mass%, and 26 mass%, both the sedimentation redispersibility and storage stability were evaluated as being sufficient.

[0090] As can be seen from the comparison of Examples 1, 5, 6, and 11, as the content of the anionic group-containing resin increases, the sedimentation redispersibility and storage stability tend to improve, and as the content of the anionic group-containing resin decreases, the ejection properties and image density tend to improve. Among them, Example 1 was highly evaluated for both sedimentation redispersibility and storage stability, showing a good balance.

[0091] As shown in Comparative Example 5 of Table 2, when the weight average molecular weight of the anionic group-containing resin was 3000, the sedimentation redispersibility tended to decrease, and as shown in Comparative Example 6, when the weight average molecular weight of the anionic group-containing resin was 60000, the ejection properties of the white ink composition tended to decrease. In contrast, as shown in Examples 1, 7, and 8, when the weight average molecular weight of the anionic group-containing resin was 15000, 5000, or 50000, both the sedimentation redispersibility and the ejection properties were evaluated as being sufficient.

[0092] As shown in Examples 1 and 8 to 13 in Tables 1 and 2, when the acid value of the anionic group-containing resin was in the range of 450 mgKOH / g to 850 mgKOH / g, the precipitation redispersibility, the dischargeability, and the image density were all evaluated as being sufficient. In particular, as the acid value of the anionic group-containing resin increased, the precipitation redispersibility tended to improve, and as the acid value decreased, the dischargeability and the image density tended to improve. [Industrial Applicability]

[0093] The aqueous white ink composition for inkjet printing of the present invention has high redispersibility during sedimentation, storage stability, and ejection stability, and can form a printed layer with high white density by an inkjet recording method. Therefore, the white ink composition of the present invention can be used, for example, as an ink for white-line printing or as a white ink in inkjet textile printing.

Claims

1. A water-based white ink composition for ink-jet printing, comprising a titanium oxide pigment, a polymer dispersant containing an anionic group-containing resin, a surfactant, and water, The ink composition contains the titanium oxide pigment in an amount of 4.0 parts by mass to 16.0 parts by mass based on 100 parts by mass of the ink composition, The titanium oxide pigment contains titanium oxide and a surface treatment agent that treats a surface of the titanium oxide, the titanium oxide pigment satisfies the condition that the mass of the titanium oxide: the total mass of the surface treatment agent = 90:10 to 80:20; The weight average molecular weight of the anionic group-containing resin is 5,000 or more and 50,000 or less, The aqueous white ink composition for ink-jet printing, wherein the content of the anionic group-containing resin is 7.0 parts by mass or more based on 100 parts by mass of the titanium oxide pigment.

2. 2. The aqueous white ink composition for ink-jet printing according to claim 1, wherein the anionic group-containing resin has an acid value of 470 mg KOH / g or more and 830 mg KOH / g or less.

3. 3. The aqueous white ink composition for ink-jet printing according to claim 1, wherein a content of the anionic group-containing resin is 25.0 parts by mass or less with respect to 100 parts by mass of the titanium oxide pigment.

4. 3. The aqueous white ink composition for ink-jet printing according to claim 1, wherein the titanium oxide pigment has an average primary particle size in the range of 100 nm to 600 nm.

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