White ink composition for water-based inkjet printing

Abstract

The present invention addresses the problem of providing 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.　The present invention provides, as a means for solving the problem, 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 4.0-16.0 parts by mass of the titanium oxide pigment relative to 100 parts by 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 5,000-50,000. The anionic group–containing resin content is not less than 7.0 parts by mass relative to 100 parts by mass of the titanium oxide pigment.

Description

Water-based white ink composition for inkjet printing

[0001] The present invention relates to a white ink composition for aqueous inkjet printing, and more specifically to a white ink composition containing a specific titanium oxide pigment.

[0002] White ink compositions for aqueous inkjet printing often contain titanium oxide pigment as a white pigment. Because titanium oxide pigment has a high specific gravity, ink compositions containing such pigments can experience sedimentation or aggregation of the titanium oxide pigment. In particular, ink compositions for aqueous inkjet printing must have a low viscosity to ensure ejection stability during printing, making them prone to sedimentation or aggregation; during storage of the ink composition or during pauses in printing, sedimentation or aggregation of the titanium oxide pigment can occur in the ink flow path of the inkjet printer. Furthermore, attempts to redisperse titanium oxide pigment that has settled or aggregated in the white ink composition can be difficult.

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

[0004] Furthermore, Patent Document 2 describes a method for storing an aqueous inkjet white ink composition containing a surface-treated titanium oxide pigment and a pigment dispersant in a tank, in which the temperature of the white ink composition is maintained at −5 to −35° C., thereby suppressing precipitation of the titanium oxide pigment and facilitating redispersion even if precipitation does occur.

[0005] Furthermore, Patent Document 3 discloses that in an ultraviolet-curable ink jet recording printing ink composition containing a surface-treated titanium oxide pigment and a polymer dispersant having an acidic polar group, an ink composition with excellent ejection stability is obtained by performing a specific surface treatment on the titanium oxide pigment. Patent Document 4 discloses that in an ink jet ink composition containing a titanium oxide pigment and a polymer dispersant, the ink dispersion stability is improved and clogging of ink jet nozzles is suppressed by using a sulfonic acid group-containing polymer dispersant as the polymer dispersant.

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

[0007] Japanese Patent No. 6881836 Japanese Patent Application Laid-Open No. 2021-178908 Japanese Patent Application Laid-Open No. 2004-59857 Japanese Patent Application Laid-Open No. 2007-99833 Japanese Patent Application Laid-Open No. 2016-98262

[0008] As described in Cited Documents 1 to 4, techniques have been proposed for aqueous white ink compositions for inkjet printing containing a titanium oxide pigment and a polymeric pigment dispersant, with the aim of suppressing sedimentation of the titanium oxide pigment, improving redispersibility, improving ejection stability, etc. However, these techniques do not pay attention to the relationship between the amount of surface treatment of the titanium oxide pigment (or titanium oxide content) and suppressing 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 an item printed with 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 achieves a high white image density of printed items, and that has high redispersibility during sedimentation, storage stability, and ejection stability.

[0010] That is, the present invention relates to the following aqueous white ink composition for inkjet printing: [1] A white ink composition for inkjet printing containing a titanium oxide pigment, a polymer dispersant containing an anionic group-containing resin, a surfactant, and water, wherein: the titanium oxide pigment is contained in an amount of 4.0 parts by mass to 16.0 parts by mass per 100 parts by mass of the ink composition; the titanium oxide pigment contains titanium oxide and a surface treatment agent that treats the surface of the titanium oxide; the ratio of the mass of the titanium oxide to the total mass of the surface treatment agent in the titanium oxide pigment 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; and 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, the present invention relates to the following aqueous white ink compositions for inkjet printing as preferred embodiments: [2] The aqueous white ink composition for inkjet 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 inkjet 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 aqueous white ink composition for inkjet 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.

[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 a 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.

[0013] 1. Regarding the aqueous 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 polymer 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 comprises titanium oxide (TiO2) as a core and a treatment agent (surface treatment agent) for treating the surface of the titanium oxide core. The surface treatment agent for titanium oxide may be an inorganic oxide (or inorganic hydrate) such as alumina (Al2O3, etc.), silica (SiO2, etc.), zirconia (ZrO2, etc.), zinc oxide, magnesium oxide, or an organic substance such as stearic acid; however, an inorganic oxide (or inorganic hydrate) is preferred, and one or both of alumina and silica are more preferred. The surface treatment of titanium oxide can be carried out by a wet treatment (aqueous treatment, etc.) carried out in a solution or a dry treatment (gas-phase treatment, etc.) carried out in a solid phase, as known to those skilled in the art.

[0015] The ratio of the "mass of titanium oxide" to the "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% by mass or less, more preferably 87% by mass or less, and even more preferably 85% by mass or less; on the other hand, it is preferably 80% by mass or more.

[0016] Increasing the total mass of the surface treatment agents relative to the mass of titanium oxide in a titanium oxide pigment improves the dispersibility (particularly sedimentation and redispersibility) of the titanium oxide pigment in a white ink composition. The mechanism of this improvement is not particularly limited; however, it is believed that the titanium oxide pigment is more easily adsorbed to the anionic group-containing resin described below when a surface treatment agent is present on the surface of the titanium oxide pigment than when the titanium oxide is exposed. Furthermore, treating the surface of the titanium oxide with a surface treatment agent roughens the pigment surface, increasing its surface area, which may result in the titanium oxide pigment being more easily adsorbed to the anionic group-containing resin. If the total mass of the surface treatment agents relative to the mass of titanium oxide is excessively high (i.e., if the titanium oxide content is too low), the functionality of the titanium oxide as a white pigment may be reduced, and the white image density of the resulting printed matter may not be sufficiently high.

[0017] The amount of surface treatment agent in a titanium oxide pigment (i.e., the ratio of the "mass of titanium oxide" to the "total mass of surface treatment agents") can be measured by methods 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, or zirconia, and quantify the amount of inorganic material adsorbed or attached to the titanium oxide surface. Furthermore, the particle surface of titanium oxide pigments can also be analyzed using X-ray photoelectron spectroscopy (ESCA, Electron Spectroscopy for Chemical Analysis). Preferably, the amount of surface treatment agent in a 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 ejection properties of the white ink composition are likely to be stabilized. The average primary particle size of the titanium oxide pigment can be measured using a transmission electron microscope.

[0019] The crystal form of titanium oxide in the titanium oxide pigment is not particularly limited and may be rutile (tetragonal), anatase (tetragonal), brookite (orthorhombic), or the like, with rutile being preferred. Rutile titanium oxide tends to improve the stability of the crystals and the hiding power of the white ink composition. Titanium oxide can be produced by a gas phase method or liquid phase method known to those skilled in the art, but production by a gas phase method is preferred in order to enhance the crystallinity of titanium oxide.

[0020] The content of the titanium oxide pigment in the white ink composition is 4.0 parts by mass or more, and 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, and preferably 13.0 parts by mass or less. By ensuring that the content of the titanium oxide pigment is 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 ensuring that the content is 16.0 parts by mass or less, it is possible to increase the fluidity of the white ink composition and improve sedimentation and redispersibility, storage stability, ejection properties, etc.

[0021] Titanium oxide pigments are also commercially available. 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 having "a 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 manufactured by Sakai Chemical Industry Co., Ltd.); and JR-805 (titanium oxide content: 88%) (both manufactured by Teika Corporation). The above titanium oxides may be used alone or in combination.

[0022] 1-2. Polymer Dispersant The polymer dispersant contained in the white ink composition includes an anionic group-containing resin. An anionic group-containing resin is a resin in which at least a portion of its monomer units contain an anionic group. The anionic group refers to an acidic group such as a carboxylic acid group, a sulfonic acid group, or a phosphate 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 improving 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, such as 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 increases, and 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, 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 anionic group-containing resin has an acid value of 470 mgKOH / g or more, the presence rate of anionic groups increases, making it easier for the anionic group to be adsorbed to the titanium oxide pigment, thereby improving the sedimentation and redispersibility of the white ink composition. On the other hand, when the anionic group-containing resin has an acid value of 900 mgKOH / g or less, the image density of the white ink composition is likely to be increased and the ejection properties of the white ink composition are also likely to be stable.

[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 5,000 or more, and preferably 10,000 or more; on the other hand, it is preferably 50,000 or less, and preferably 30,000 or less. When the weight-average molecular weight of the anionic group-containing resin is 5,000 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 50,000 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 converted into 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 styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid).

[0029] Furthermore, the anionic group-containing resin preferably contains a hydrophobic monomer as a monomer unit together with the anionic group-containing monomer, and may further contain a nonionic monomer or the like, as 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 [such as lauryl(meth)acrylate], and (iso)stearyl(meth)acrylate. 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; examples of the aromatic group-containing monomer include styrene-based monomers (e.g., styrene, 2-methylstyrene, and divinylbenzene), aromatic group-containing (meth)acrylates (e.g., benzyl (meth)acrylate, phenoxyethyl (meth)acrylate), and the like.

[0031] Examples of nonionic monomers that constitute 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 polyalkylene glycol (meth)acrylates 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 predetermined monomers by a known polymerization method (e.g., solution polymerization) and neutralizing the anionic groups of the resulting copolymer with a neutralizing agent. The anionic group-containing resin may be a random copolymer or a block copolymer of the predetermined monomers.

[0034] 1-3. Surfactant 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 set appropriately taking into consideration the dispersibility and the like, but may be in the range of 0.1 to 2.0% by mass, and 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 contain both acetylene alcohol or acetylene bonds and glycol units, and can be represented by the following structural formula 1. The acetylene bond site serves as a hydrophobic site, and the alcohol site or glycol site serves as a hydrophilic site, allowing them to exhibit surfactant properties.

[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.

[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 commercially available 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 A The number of carbon atoms in the alkyl group (R ) and the average number of moles of ethyleneoxy chains added (d) are not limited. A ) preferably has about 11 to 15 carbon atoms, more preferably about 12 to 13 carbon atoms; and the average number of moles of added ethyleneoxy chains (d) is preferably about 3 to 15, more preferably 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 Chemical Company); and those sold under the trade name SANNONIC SS70 (Sanyo Chemical Industries, Ltd.).

[0043] Silicone surfactants are dimethylpolysiloxanes (chemical formula: (C2H6OSi) n The polysiloxanes and their modified products are preferably polysiloxanes modified with polyethers (polyether-modified silicone surfactants). Polyether-modified silicone surfactants can prevent excessive increases in ink viscosity.

[0044] The polyether-modified silicone surfactant has a structure in which the hydrocarbon groups at the side chains and / or terminals of silicone oil are substituted 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 manner, 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. (KF series from Shin-Etsu Chemical Co., Ltd.); Silface SAG (Nissin Chemical Industry Co., Ltd.); BYK-345, 347, 348, 349, etc. (BYK series from BYK-Chemie); TEGO GLIDE 410, 450, etc., TEGO Twin 400, etc. (Evonik). These surfactants may be used alone or in combination.

[0046] 1-4. Water-Containing Solvent The white ink composition contains a solvent. The solvent preferably contains at least water and 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 that the viscosity and fluidity of the white ink composition can be set within a predetermined range. These solvents may be used alone or in combination.

[0050] 1-5. Other Optional Components 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 absorber may be added to the white ink composition as needed.

[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 anionic resin emulsion. The water-dispersible resin (resin emulsion) may be a urethane-based resin, an acrylic-based resin, a styrene-acrylic-based resin, a fluorene-based resin, a polyolefin-based resin, a rosin-modified resin, a terpene-based resin, a polyester-based resin, a polyamide-based resin, an epoxy-based resin, a vinyl chloride-based resin, a vinyl chloride-vinyl acetate copolymer, an ethylene-vinyl acetate-based resin, or the like.

[0052] When the white ink composition is used in inkjet textile printing (described later), a urethane-based resin is preferred 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. Of these, a polycarbonate-type or polyether-type urethane-based resin that also has a crosslinkable group is more preferred from the viewpoint of improving the rubbing fastness of the image of the printed textile.

[0053] Examples of crosslinkable groups possessed by urethane-based resins include isocyanate groups, silanol groups, carboxyl groups, and hydroxyl groups, and a substituent in which the isocyanate group is chemically protected (capped or blocked) (blocked isocyanate group) is preferred. 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.). Furthermore, it is preferred that the urethane-based resin having crosslinkable groups has three or more crosslinkable groups per molecule, and in such a case, a crosslinked structure is formed by the reaction of the crosslinkable groups.

[0054] The content of the water-dispersible resin (resin emulsion) in the white ink composition, in terms of solid content, relative to the total mass (100 mass%) of the ink, 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 be actinic energy ray-curable. A white ink composition that is actinic energy ray-curable may contain a polymerizable compound and a polymerization initiator.

[0056] 1-6. Production of aqueous white ink composition for inkjet printing There are no particular restrictions on the procedure for producing the aqueous white ink composition for inkjet printing. 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 the Aqueous White Ink Composition for Inkjet Printing Because the white ink composition is used for inkjet printing, it has a viscosity that allows for inkjet printing, and the viscosity is set from the viewpoint of enhancing 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; and 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 higher, more preferably 6.0 or higher, and even more preferably 6.5 or higher; on the other hand, from the viewpoints of component resistance and skin irritation, it is preferably 11.0 or lower, more preferably 10.0 or lower, even more preferably 9.5 or lower, and even more preferably 9.0 or lower.

[0059] 2. Uses of the aqueous white ink composition for inkjet printing 2-1. Regarding 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 is capable of forming a high-quality white image with a 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 the ink tank or ink flow path), making it suitable for inkjet printing.

[0060] There are no particular limitations on the inkjet recording method for 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 with the radiation pressure to eject the ink, and a thermal inkjet method that heats the ink to form bubbles and uses the generated pressure. Inkjet recording methods include a method that ejects a large number of low-concentration inks, known as photo inks, in a small volume, a method that uses multiple inks of substantially the same hue but different densities to improve image quality, and a method that uses a colorless, 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) that uses 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 substrate. "Whiteout printing" refers to printing the white ink composition in advance on a portion of the substrate where an ink composition of a desired color will be printed (or printing it solidly over the entire substrate); this masks the underlying substrate 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 substrate. The white ink composition of the present invention can form a printed layer with a high white image density, and therefore can more reliably mask the underlying substrate when used in whiteout printing.

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

[0063] 2-2. Inkjet Textile 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 color ink composition. That is, the inkjet textile printing method can include, in this order: 1) step A of preparing a fabric that has been pretreated with a pretreatment liquid; 2) step B of inkjet coating the white ink composition onto the pretreated fabric; and 3) step C of inkjet coating chromatic color ink compositions onto an ink layer formed by applying the white ink composition. The white ink composition of the present invention can be used as the white ink composition in step B.

[0064] [Step A] In 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 that has been 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. Examples include natural fibers such as cotton, linen, wool, and silk; synthetic fibers such as polypropylene, polyester, acetate, triacetate, polyamide, and polyurethane; and biodegradable fibers such as polylactic acid, and blends of these fibers may also be used.

[0066] The pretreatment liquid for pretreating the fabric may be a pretreatment liquid conventionally used in inkjet textile printing methods. The pretreatment liquid is capable of aggregating the components of the white ink composition and the chromatic color 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] Pretreating a fabric can improve the color development of an image on a printed item. The pretreatment of a fabric is carried out 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, spray means, inkjet printing means, or the like. After applying the pretreatment liquid to the fabric, the solvent of the applied pretreatment liquid is dried, but there are also cases where it is not dried.

[0068] [Step B] The inkjet printing method includes step B of inkjet coating a white ink composition onto a pretreated fabric. That is, the white ink composition is inkjet coated onto the pretreated fabric to form a white ink layer on the pretreated fabric. The white ink layer may be formed on part or all (preferably all) of the pretreated area of ​​the fabric where the chromatic ink compositions described below are 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 applied repeatedly to form overcoats).

[0069] In step B, by using the white ink composition of the present invention, a white ink layer with 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] [Step C] The inkjet textile printing method of the present invention includes step C of inkjet coating a chromatic ink composition on a white ink layer formed by applying a white ink composition to a fabric. In other words, a chromatic ink composition is applied by inkjet technique to a fabric on which a white ink layer has been formed, thereby printing a chromatic image. The chromatic ink composition can be applied on part or all of the white ink layer formed on the fabric. The chromatic ink composition may be applied once or multiple times (in other words, it may be applied repeatedly to form overcoats).

[0071] [Image Fixing Step, 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 image can be heated to preferably 100 to 180°C. The heating means is not particularly limited, and a heat press, iron, dryer, heating dryer, etc. can be used.

[0072] A. Preparation of White Ink Composition A-1. Materials used in preparation of white ink composition A-1-1. Titanium oxides (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." Titanium dioxide mass: total mass of surface treatment agent (silica and alumina) = 82:18. Average primary particle size: 0.53 μm. Titanium dioxide pigment (2) Product name: "TIPAQUE PFR209" manufactured by Ishihara Sangyo Kaisha. Surface treatment agent "silica and alumina." Titanium dioxide mass: total mass of surface treatment agent (silica and alumina) = 89:11. Average primary particle size: 0.25 μm. Titanium dioxide pigment (3) Product name: "TIPAQUE CR-80" manufactured by Ishihara Sangyo Kaisha. Surface treatment agent "silica and alumina." Titanium dioxide mass: total mass of surface treatment agent (silica and alumina) = 93:7. Average primary particle size: 0.25 μm.

[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 mg KOH / g) was dissolved in a mixed solution 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 solids 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 mg KOH / g) was dissolved in a mixed solution 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 with a resin solids 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 mg KOH / 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 with a resin solids content of 25.0 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 mg KOH / 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 solids content of 25.0 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 mg KOH / 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 with a resin solids content of 25.0 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 mg KOH / 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 with a resin solids content of 25.0 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 mg KOH / 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 solids 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 mg KOH / 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 with a resin solids 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 solids content of 25.0% by mass.

[0074] A-1-3. Other materials Water-dispersible resin: Product name: NeoRez R-966, manufactured by DSM Polyether polyurethane resin Solid content: 33% Surfactant: Product name: Olfine 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 and anionic group-containing resin varnish shown in A-1. 18 parts of anionic group-containing resin varnish 1 and 37 parts of water were added and mixed, followed by 45 parts of titanium oxide (1), stirring and mixing, and then milling in a wet circulation mill to obtain water-based white ink base (A). 18 parts of anionic group-containing resin varnish 1 and 37 parts of water were added and mixed, followed by 45 parts of titanium oxide (2), stirring and mixing, and then milling in a wet circulation mill to obtain water-based white ink base (B). 12.6 parts of anionic group-containing resin varnish 1 and 42.4 parts of water were added and mixed, followed by 45 parts of titanium oxide (1), stirring and mixing, and then milling in a wet circulation mill to obtain water-based white ink base (C). - 43.2 parts of anionic group-containing resin varnish 1 and 11.8 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (D). - 18 parts of anionic group-containing resin varnish 2 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (E). - 18 parts of anionic group-containing resin varnish 3 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (F). - 18 parts of anionic group-containing resin varnish 4 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (G). - 18 parts of anionic group-containing resin varnish 5 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (H). - 18 parts of anionic group-containing resin varnish 1 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (3) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (I).- 9 parts of anionic group-containing resin varnish 1 and 46 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (J). - 46.8 parts of anionic group-containing resin varnish 1 and 8.2 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (K). - 18 parts of anionic group-containing resin varnish 6 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain aqueous white ink base (L). - 18 parts of anionic group-containing resin varnish 7 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain an aqueous white ink base (M). - 18 parts of anionic group-containing resin varnish 8 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain an aqueous white ink base (N). - 18 parts of anionic group-containing resin varnish 9 and 37 parts of water were added and mixed, then 45 parts of titanium oxide (1) was added and stirred and mixed, and the mixture was then milled in a wet circulation mill to obtain an aqueous white ink base (O).

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

[0077] B. Production of Printed Materials 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. (trade name: Movinyl 966A, manufactured by Japan Coating Resins Co., Ltd., solids content 45% by 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 printing.

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

[0079] C. Evaluation of Water-Based White Ink Composition and Printed Material 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 aqueous 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, after which the sediment was redispersed by shaking the sample bottle up and down (until no sediment was observable), and the number of shakes required was measured and the sedimentation and redispersibility was evaluated according to the following criteria: ◎ Redispersed in less than 50 shakes ○ Redispersed in 50 to less than 100 shakes △ Redispersed in 100 to less than 200 shakes × Unable to redisperse within 200 shakes

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

[0082] C-3. Evaluation of inkjet discharge properties The aqueous white ink compositions of the Examples and Comparative Examples were subjected to continuous actual printing using an inkjet printer (an evaluation printer equipped with a head manufactured by SPECTRA), and the resulting white images were checked for missing nozzles, and the inkjet discharge properties were evaluated according to the following criteria: ◎ No ejection defects were observed in any of the nozzles during continuous actual printing for one hour or more. ○ No ejection defects were observed in any of the nozzles during continuous actual printing for 15 minutes or more but less than one hour. △ During continuous actual printing for 15 minutes or more but less than one hour, some nozzles became unable to eject. × During continuous actual printing for 15 minutes or more but less than one hour, all nozzles became unable to eject.

[0083] C-4. Evaluation of image density of printed textiles The lightness (L*) of printed textiles 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 more ○ 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]

[0085]

[0086] As shown in Comparative Example 1 in Table 2, the white ink composition blended with titanium oxide pigment (3) (CR-80), which had a titanium oxide content of 93% by mass, had poor sedimentation and redispersibility, and it was found that once the pigment had settled, it was difficult to redisperse. In contrast, as shown in Examples 1 and 2 in Table 1, the white ink compositions blended with titanium oxide pigments (1) or (2) (TS-6300 or PRF209), which had titanium oxide contents of 82% or 89% by mass, 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), which has a titanium oxide content of 82 mass %, has higher sedimentation and redispersibility than the white ink composition containing titanium oxide pigment (2) (PRF209), which has a titanium oxide content of 89 mass %. This shows that the titanium oxide content of the titanium oxide pigment (or the amount of surface treatment on the titanium oxide pigment) is an important factor in determining 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 relative to the ink composition was 3.0% by mass did not impart sufficient white image density (brightness) to the resulting printed textile. Furthermore, as shown in Comparative Example 3, a white ink composition in which the titanium oxide pigment content was 18.0% by mass tended to cause inkjet ejection defects and also tended to exhibit poor 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 imparted sufficient white image density (brightness) to the resulting printed textile, were less likely to cause ejection defects, and also exhibited 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%, 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%, 7%, 24%, and 26% by mass, both sedimentation redispersibility and storage stability were evaluated as being sufficient.

[0090] As can be seen from a comparison of Examples 1, 5, 6, and 11, there was a tendency for the sedimentation redispersibility and storage stability to improve as the content of the anionic group-containing resin increased, and there was a tendency for the ejection properties and image density to improve as the content of the anionic group-containing resin decreased. In particular, Example 1 was highly rated for both sedimentation redispersibility and storage stability, demonstrating a good balance.

[0091] As shown in Comparative Example 5 in Table 2, when the weight average molecular weight of the anionic group-containing resin was 3,000, the sedimentation and redispersibility tended to decrease, and as shown in Comparative Example 6, when the weight average molecular weight of the anionic group-containing resin was 60,000, the jetting 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 15,000, 5,000, or 50,000, both the sedimentation and redispersibility and the jetting 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 sedimentation redispersibility, jetting property, and image density were all evaluated as being sufficient. In particular, as the acid value of the anionic group-containing resin increased, the sedimentation redispersibility tended to improve, and as the acid value decreased, the jetting property and image density tended to improve.

[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 a 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 whitening printing or as a white ink in inkjet textile printing.

Claims

1. A white ink composition for aqueous inkjet printing, comprising a titanium oxide pigment, a polymer dispersant containing an anionic group-containing resin, a surfactant, and water, wherein the titanium oxide pigment is contained in an amount of 4.0 to 16.0 parts by mass per 100 parts by mass of the ink composition, the titanium oxide pigment contains titanium oxide and a surface treatment agent for treating the surface of the titanium oxide, and the titanium oxide pigment satisfies a condition of a ratio of the mass of the titanium oxide to the total mass of the surface treatment agent of 90:10 to 80:20, the anionic group-containing resin has a weight average molecular weight of 5,000 or more and 50,000 or less, and 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.

2. The aqueous white ink composition for ink-jet printing according to claim 1, wherein the acid value of the anionic group-containing resin is from 470 mg KOH / g to 830 mg KOH / g.

3. The aqueous white ink composition for ink-jet printing according to claim 1 or 2, 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 aqueous white ink composition for ink-jet printing according to claim 1 or 2, wherein the titanium oxide pigment has an average primary particle size in the range of 100 nm to 600 nm.

Images