JP2020084072A - Pigment dispersion, and ink for inkjet - Google Patents

Abstract

To provide a pigment dispersion less in viscosity change and hardly generating coarse particles after long term storage, and an ink for inkjet.SOLUTION: There is provided a pigment consisting of an inorganic pigment (A) and a polymer (B) having a monomer unit having one or more anionic groups, in which content of the polymer (B) is over 7.0 pts.mass and 45 pts.mass or less based on 100 pts.mass of the inorganic pigment (A), and the anionic group of the monomer unit having the anionic group is one or more kinds selected from a carboxyl group and a sulfonate group.SELECTED DRAWING: None

Description

The present invention relates to a pigment dispersion that can be used in molded articles, paints, textile printing agents, stationery inks, printing inks, flexographic printing inks, inkjet inks and the like.

In various printings (gravure printing method, flexographic printing method, silk screen printing, etc.), when printing on a non-white recording medium (for example, resin film, paperboard, cloth, cardboard, etc.), after applying white ink A method in which a chromatic color ink or a black ink is applied to make a printed image stand out and visibility is improved is used.

Even in the inkjet printing method, white ink may be used for the same purpose. The white ink generally uses an inorganic pigment. The inorganic pigment has a high refractive index of light as compared with the organic pigment and can obtain a good whiteness.

However, in the white ink using the inorganic pigment, the specific gravity of the inorganic pigment is heavy and the white ink is likely to settle. Therefore, it has been required that the inorganic pigment be easily redispersed by shaking or stirring after the passage of time.

Patent Document 1 contains titanium oxide and at least one anionic group-containing monomer unit selected from acrylic acid, methacrylic acid, maleic acid, and sulfonic acid group-containing vinyl monomer in an amount of 72% by mass or more, and a mass average molecular weight. A pigment dispersion containing a polymer having a ratio of 3,000 or more and 50,000 or less and containing 1% by mass or more and 7% by mass or less of the polymer with respect to titanium oxide is disclosed.

Patent Document 2 discloses a pigment dispersion containing titanium oxide, a polycarboxylic acid salt, a polyacrylic acid salt, or the like.

JP, 2017-75302, A JP, 2018-158994, A

In the inkjet printing, since a droplet of ink is ejected from a fine nozzle to print, a desired image cannot be formed in many cases due to a change in viscosity of the ink and the presence of coarse particles. The conventional white ink has a problem that when it is stored for a long period of time after the pigment dispersion is prepared, the viscosity is increased and coarse particles are increased to deteriorate the printed image.

It is an object of the present invention to provide a pigment dispersion that causes little change in viscosity after long-term storage and hardly causes coarse particles, and an inkjet ink.

The pigment dispersion of the present invention is a pigment dispersion comprising an inorganic pigment (A) and a polymer (B) having a monomer unit having one or more anionic groups,
The content of the polymer (B) is more than 7.0 parts by mass and 45 parts by mass or less with respect to 100 parts by mass of the inorganic pigment (A),
The anionic group of the monomer unit having the anionic group is at least one selected from a carboxyl group and a sulfonic acid group.

According to the present invention described above, it is possible to provide a pigment dispersion that causes little change in viscosity after long-term storage and does not easily generate coarse particles, and an inkjet ink.

First, the terms used in this specification are defined. "(Meth)acryloyl" is "acryloyl and methacryloyl". “(Meth)acrylic” is “acrylic and methacrylic”. “(Meth)acrylic acid” is “acrylic acid and methacrylic acid”. "(Meth)acrylate" is "acrylate and methacrylate". The monomer is an ethylenically unsaturated group-containing monomer. Further, “C.I.” means a color index (C.I.).

The pigment dispersion of the present invention is a pigment dispersion comprising an inorganic pigment (A) and a polymer (B) having a monomer unit having one or more anionic groups,
The content of the polymer (B) is more than 7.0 parts by mass and 45 parts by mass or less with respect to 100 parts by mass of the inorganic pigment (A),
The anionic group of the monomer unit having the anionic group is at least one selected from a carboxyl group and a sulfonic acid group.
The pigment dispersion of the present invention can be used for various coloring applications, for example, resin moldings, general paints, automotive paints, textiles, stationery inks (for example, ballpoint pens, fountain pens, etc.). , Gravure printing inks, flexographic printing inks, inkjet inks, and the like. Among these, inkjet ink is more preferable. In the present specification, an aspect in which the pigment dispersion is applied to an inkjet ink will be mainly described.

In the pigment dispersion of the present invention, the anionic group of the polymer (B) acts as an adsorption group that is adsorbed on the surface of the inorganic pigment (A). In addition, the repulsion of the anionic group can suppress the reaggregation of the inorganic pigment (A), and can suppress the increase in viscosity with time and the increase in coarse particles with time. These effects can be obtained by using an appropriate amount of the polymer (B) adsorbed on the surface of the inorganic pigment (A). When the amount of the polymer (B) used is inappropriate, even if the viscosity immediately after the pigment dispersion is prepared and the amount of coarse particles are good, it deteriorates after long-term storage.

(Inorganic pigment (A))
In this specification, the inorganic pigment (A) is particles of a metal compound that can be used as a white ink. Examples of the inorganic pigment (A) include metal oxides, barium sulfate, calcium carbonate and the like. Examples of the metal oxide include titanium dioxide (hereinafter referred to as titanium oxide), barium titanate, zirconium oxide, zinc oxide, silicon dioxide (silica), aluminum oxide (alumina) magnesium oxide, and the like. Among these, titanium oxide is preferable from the viewpoint of reproducing the refractive index showing high whiteness and the hue of conventional printing ink. The crystal structure of titanium oxide includes rutile type (tetragonal), anatase type (tetragonal), and brookite type (orthorhombic). From the viewpoint of crystal stability, whiteness, and availability, the rutile type is used. Titanium oxide is preferred.

The inorganic pigment (A) is preferably a coated pigment having a first coating layer coated on the surface of the metal compound particles with at least one selected from the group consisting of silica and alumina. When the inorganic pigment (A) is, for example, titanium oxide, it has a property of decomposing organic substances due to photocatalytic activity, and therefore the surface of the titanium oxide particles is preferably surface-treated with an inorganic oxide such as silica or alumina. Further, when the inorganic pigment (A) is, for example, barium sulfate or calcium carbonate, it is preferable to perform surface treatment with an inorganic oxide in order to improve the affinity with other components during the preparation of the pigment dispersion.

The surface treatment of titanium oxide is preferably performed by, for example, alumina treatment, silica treatment, coating with an inorganic hydrate containing zinc, magnesium, zirconium or the like to form the first coating layer. Among these, alumina treatment, silica treatment, and treatment with alumina and silica are preferable from the viewpoint of improving the dispersibility of titanium oxide after coating. The titanium oxide on which the first coating layer is formed has a higher affinity for the solvent when producing the ink or the like. In the case of alumina treatment, if the pH at the time of dispersion is set appropriately, the surface of the particles will exceed the isoelectric point and the dispersibility will be good. In addition, the silica treatment lowers the isoelectric point of the particle surface, which improves the dispersibility and facilitates the coating with the polymer (B).

The inorganic pigment (A) is preferably formed by using an organic compound such as polyol to form the second coating layer on the first coating layer. This makes it possible to suppress dry aggregation when the inorganic pigment (A) is once pulverized, so that the dispersibility is improved when a composition such as an ink is produced thereafter.

The shape of the inorganic pigment (A) is not particularly limited, and may be granular or needle-like. From the viewpoint of whiteness, the average primary particle diameter of the inorganic pigment (A) is preferably 0.1 μm or more, more preferably 0.15 μm or more, and further preferably 0.2 μm or more. From the viewpoint of redispersibility, the average primary particle diameter is preferably 0.6 μm or less, more preferably 0.5 μm or less, still more preferably 0.4 μm or less. The measuring method of the average primary particle diameter is an average value calculated by selecting any 20 particles from an enlarged image of a scanning electron microscope. If the particle image is, for example, elliptical, the length in the vertical axis direction is used.

Commercially available products of titanium oxide include, for example, trade name: Taipaque R, CR, PF series manufactured by Ishihara Sangyo Co., Ltd., product name: R series manufactured by Sakai Chemical Industry Co., Ltd., trade name: JR, MT series, titanium manufactured by Teika. Trade name: KURONOS KR series manufactured by Kogyo Co., Ltd., trade name: TR series manufactured by Fuji Titanium Industry Co., Ltd., and the like.

(Polymer (B))
In the present specification, the polymer (B) has a monomer unit having one or more anionic groups, and the anionic group of the monomer unit having an anionic group is at least 1 selected from a carboxyl group and a sulfonic acid group. It is a seed.

(Monomer unit constituting polymer (B))
The polymer (B) essentially includes a monomer unit having one or more anionic groups, and a monomer unit having no anionic group can be used in combination, if necessary.

(Monomer unit having an anionic group)
The anionic group of the monomer unit having an anionic group is preferably a carboxyl group or a sulfonic acid group. Due to the presence of the anionic group, the polymer (B) is easily adsorbed on the inorganic pigment (A), and the repulsive force due to negative charging works, so that the inorganic pigments (A) are less likely to aggregate.
Examples of the monomer having an anionic group include acrylic acid, methacrylic acid, styrenesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid.

(Monomer unit without anionic group)
The monomer unit having no anionic group is preferably, for example, a nonionic monomer, a styrene-based monomer, an aromatic group-containing monomer other than the styrene-based monomer, or an alkyl group-containing monomer.
Examples of the nonionic monomer include alkylene glycol (meth)acrylate.

Examples of the alkylene glycol (meth)acrylate include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxypropyl (meth)acrylate, diethylene glycol monomethyl ether (meth)acrylate, diethylene glycol monoethyl ether ( (Meth)acrylate, diethylene glycol mono-2-ethylhexyl ether (meth)acrylate, dipropylene glycol monomethyl ether (meth)acrylate, triethylene glycol monomethyl ether (meth)acrylate, triethylene glycol monoethyl ether (meth)acrylate, tripropylene glycol Monomethyl ether (meth)acrylate, tetraethylene glycol monomethyl ether (meth)acrylate, polyethylene glycol monomethyl ether (meth)acrylate, polypropylene glycol monomethyl ether (meth)acrylate, polyethylene glycol monolauryl ether (meth)acrylate, polyethylene glycol monostearyl ether Alkylene glycol monoalkyl ether (meth)acrylates such as (meth)acrylates and octoxy polyethylene glycol-polypropylene glycol (meth)acrylates;
Phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, phenoxyhexaethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, paracumylphenoxyethyl (meth)acrylate, parac Milphenoxyethylene glycol (meth)acrylate, paracumylphenoxy polyethylene glycol (meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate, nonylphenoxy polypropylene glycol (meth)acrylate, and nonylphenoxy poly(ethylene glycol-propylene glycol) (meth) ) An alkylene glycol (meth)acrylate having an aromatic ring such as acrylate; and the like.
Commercial products of nonionic monomers are, for example, NK ester M-230G, 450G, 900G (above, manufactured by Shin-Nakamura Chemical Co., Ltd.), Bremmer PME-1000, 4000 (above, manufactured by NOF CORPORATION), light ester. 041MA (manufactured by Kyoeisha Chemical Co., Ltd.) and the like.

Examples of the hydrophobic monomer include styrene-based monomers, aromatic group-containing monomers other than styrene-based monomers, and alkyl group-containing monomers.
Examples of the styrene-based monomer include styrene, α-methylstyrene, styrene macromer and the like. Examples of the aromatic group-containing monomer other than the styrene-based monomer include benzyl (meth)acrylate, benzyl, phenoxy (meth)acrylate, and the like. Examples of the alkyl group-containing monomer include methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (iso)butyl (meth)acrylate, (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, ( Examples thereof include iso)stearyl (meth)acrylate and behenyl (meth)acrylate.

Examples of the aromatic group-containing monomer include styrene-based monomers and aromatic group-containing (meth)acrylates. Examples of the styrene-based monomer include styrene, 2-methylstyrene, and divinylbenzene, and examples of the aromatic group-containing (meth)acrylate include benzyl (meth)acrylate.

(Production of polymer (B))
The polymer (B) can be synthesized by polymerizing a monomer mixture. Examples of the polymerization include solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, and the like, and solution polymerization is preferable from the viewpoint of easy control of molecular weight and molecular weight distribution.

The solvent used in the solution polymerization is not particularly limited, and examples thereof include water, an aliphatic alcohol, and a mixed solvent of one or more of these and water. The water is preferably ion-exchanged water, distilled water, or purified water rather than tap water or the like.

It is preferable to use a polymerization initiator for the polymerization. Examples of the polymerization initiator include azo compounds and peroxides. Examples of the azo compound include azobisisobutyronitrile and azobis2,4-dimethylvaleronitrile. Peroxides include, for example, cumene hydroperoxide, t-butyl hydroperoxide, benzoyl peroxide, diisopropyl peroxycarbonate, di t-butyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, t-butyl peroxide. Oxy-2-ethylhexanoate and the like can be mentioned.
The amount of the polymerization initiator used is preferably about 0.001 to 5 parts by mass with respect to 100 parts by mass of the monomer mixture.

A chain transfer agent can be used for the polymerization. This makes it easy to adjust the molecular weight of the polymer (B). Examples of the chain transfer agent include mercaptans.

In the present specification, the polymer (B) is preferably one or more selected from polyacrylic acid and polyacrylic acid salt from the viewpoint of repulsive force due to adsorption of the inorganic pigment (A) and negative charging, and polyacrylic acid is more preferable. preferable. The polyacrylic acid is preferably a sulfonic acid group-containing polyacrylic acid.

The anionic group of the polymer (B) preferably forms a salt. Examples of the base include ammonia, organic amines such as dimethylaminoethanol and triethylamine, and alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide.

Commercially available products of polyacrylic acid are, for example, Aron T-50 (Mw 6,000), Aron A-10SL (Mw 5,000), Aron A-30SL (6,000) (all manufactured by Toagosei Co., Ltd.), Aqualic. DL, Aquaric YS (all manufactured by Nippon Shokubai Co., Ltd.) and the like can be mentioned. Examples of commercially available sulfonic acid group-containing polyacrylic acid include Aron A-6012 (Mw 10,000) (manufactured by Toagosei Co., Ltd.), Aqualic GL, Aqualic LS (all manufactured by Nippon Shokubai Co., Ltd.) and the like.

The mass average molecular weight (Mw) of the polymer (B) is preferably 1,000 or more, more preferably 3,000 or more, still more preferably 5,000 or more. The upper limit of the mass average molecular weight is preferably 50,000 or less, more preferably 30,000 or less, and even more preferably 10,000 or less. Due to the appropriate mass average molecular weight, there is little change in viscosity during long-term storage, and it is difficult for coarse particles to increase.

The content of the polymer (B) is more than 7.0 parts by mass and 45 parts by mass or less with respect to 100 parts by mass of the inorganic pigment (A). The content of the polymer (B) is preferably more than 11 parts by mass, more preferably more than 15 parts by mass. Further, it is preferably 40 parts by mass or less, and more preferably 35 parts by mass or less. When contained in an appropriate amount, there is little change in viscosity during long-term storage, and it is difficult for coarse particles to increase.

(Method for producing pigment dispersion)
In the production of the pigment dispersion, for example, the inorganic pigment (A), the polymer (B), water, and if necessary, an additive such as an antifoaming agent are mixed and premixed. Then, the obtained mixture is obtained by dispersing with a disperser or the like.
Examples of the premixing include disperser, planetary mixer, and kneader. The premixing is carried out at least for the purpose of obtaining a form in which the mixture can be easily introduced into the disperser, but from the viewpoint of improving dispersibility in the disperser and adsorbing the inorganic pigment (A) and the polymer (B), It may be positioned as a kneading step in consideration of shear strength.

Examples of the disperser include a kneading and mixing device such as a kneader used for premixing, a post-layer, a ball mill, a bead mill, and a colloid mill. The bead mill preferably uses media such as glass beads and zirconia beads, more preferably bead mills, and even more preferably zirconia beads. The diameter of the zirconia beads is preferably 1.2 mmΦ or less, more preferably 1.0 mmΦ or less, and even more preferably 0.8 mmΦ or less. The smaller the bead diameter, the smaller the impact on the inorganic pigment (A) due to the collision of the beads, and the suppression of overdispersion (crushing of the primary particles of the inorganic pigment (A)), and the viscosity and coarse particles are less likely to increase Stable It is easy to obtain a good pigment dispersion.

The dispersion temperature is preferably 10° C. or higher and 40° C. or lower from the viewpoint of dispersibility of the inorganic pigment (A) and bead wear. In addition, it is more preferably 35° C. or lower, and further preferably 30° C. or lower.
The dispersion time is until the pigment dispersion reaches the intended dispersion particle size, reduction of coarse particles, and whiteness, but from the viewpoint of adsorption of the polymer (A) and crushing of the inorganic pigment (A). It is preferably 1 hour or longer, more preferably 2 hours or longer, still more preferably 3 hours or longer. Further, it is 100 hours or less, more preferably 75 hours or less, and further preferably 50 hours or less.

The volume average particle size distribution (d50) of the pigment dispersion when the inorganic pigment (A) is dispersed is preferably 100 nm or more and 600 nm or less, more preferably 200 nm or more and 400 nm or less, and further preferably 240 nm or more and 380 nm or less. The moderate particle size distribution (d50) further improves the whiteness of the white ink and the stability of the pigment dispersion during long-term storage.

A solvent can be used to prepare the pigment dispersion. The solvent may be water or a mixed solvent of one or more aliphatic alcohols and water. The water is preferably ion-exchanged water, distilled water, or purified water rather than tap water or the like.

(Inkjet ink)
The inkjet ink herein includes a pigment dispersion. Further, the inkjet ink can be prepared by appropriately adding a material selected from a resin, a basic substance, water, a water-soluble solvent, a surfactant, a cross-linking agent and the like in addition to the pigment dispersion.

Examples of the resin include polyester resin, polyurethane resin, polyepoxy resin, polyamide resin, polyether resin, silicone resin, polyolefin resin, polystyrene resin, polyvinyl alcohol resin, polyvinyl ester resin, polyacrylic acid resin, unsaturated carvone resin. Examples thereof include acid resins, celluloses, rosins, and natural rubber.

The inkjet ink of the present specification preferably further contains a resin having a hydrophobic group and a hydrophilic group (hereinafter referred to as resin (X)). When the resin (X) is contained, the water resistance of the film formed by printing the inkjet ink is further improved. The resin (X) can be produced, for example, by polymerizing a hydrophobic-containing monomer and a hydrophilic group-containing monomer.

The resin (X) can be synthesized by polymerizing a monomer mixture. Examples of the polymerization include solution polymerization, bulk polymerization, emulsion polymerization and suspension polymerization.

Examples of the hydrophobic group include aromatic groups and alkyl groups. Of these, aromatic groups are preferred. Examples of the monomer that imparts a hydrophobic group to the resin (X) include styrene, benzyl acrylate, benzyl methacrylate, phenoxy acrylate, lauryl acrylate, stearyl acrylate, and behenyl acrylate. In addition, vinyl compounds having hydrophobic oligomers such as macromonomers and polymers in their side chains are also included. Examples of commercially available products include styrene macromers (for example, AS-6 (manufactured by Toagosei Co., Ltd.)), vinyl compounds having a hydrophobic acrylic resin in a side chain (for example, AA-6 (manufactured by Toagosei Co., Ltd.)), hydrophobic And vinyl compounds having a urethane resin as a side chain, vinyl compounds having a hydrophobic ester resin as a side chain, vinyl compounds having a hydrophobic ether resin as a side chain, and the like.

The hydrophilic group is a group that forms a salt, and examples thereof include a nonionic group (for example, a hydroxyl group and an alkylene oxide group) such as a carboxyl group, a sulfonic acid group, a phosphoric acid group, a phosphonic acid group, and an amino group. .. Of these, a carboxyl group is preferred. The monomer that imparts a hydrophilic group to the resin (X) is, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, or the like. Further, a vinyl monomer (for example, Bremmer PME-1000, 4000 (manufactured by NOF CORPORATION)) to which a hydrophilic alkylene oxide polymer is bonded may be used.

When the resin (X) is used as an inkjet ink, it is preferable that the monomer mixture contains a hydrophobic group-containing monomer in an amount of more than 50 mol% from the viewpoint of further improving the water resistance of the coating film formed.

Commercially available products of the resin (X) are, for example, Joncryl series (manufactured by BASF) represented by Joccryl 690, 67 in the case of styrene (meth)acrylic resin, X-1 (manufactured by Starlight PMC), styrene (anhydrous). If it is a maleic acid resin, SMA resin series represented by SMA1440, SMA2625, SMA3840, etc. (manufactured by CrayValley), and if it is (meth)acrylic resin, VS-1057, X-310, TS-1316 (manufactured by Starlight PMC). Etc.

The content of the resin (X) is preferably 20 parts by mass to 150 parts by mass with respect to 100 parts by mass of the inorganic pigment (A). The amount is more preferably 35 parts by mass to 135 parts by mass, further preferably 50 parts by mass to 120 parts by mass.

Examples of the basic substance include inorganic bases and organic bases. Examples of the inorganic base include potassium hydroxide, sodium hydroxide, sodium hydrogen carbonate, sodium carbonate and the like. As the organic base, for example, a primary to tertiary amine can be used. For example, alkylamines such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine. Alkanolamines such as aminoethanol, methylaminoethanol, dimethylaminoethanol, ethylaminoethanol, diethylaminoethanol, diethanolamine, triethanolamine; amines having nonionic groups such as methoxypoly(oxyethylene/oxypropylene)-2-propylamine. Is mentioned.

The water-soluble solvent acts to prevent the ink from drying and to improve the dispersion stability. Further, the penetrability into the substrate and the wet spreadability after inkjet printing are further improved.
Water-soluble solvents include, for example, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, propylene carbonate, ethylene carbonate and the like. Can be mentioned.

Examples of the surfactant include anionic surfactants, cationic surfactants, nonionic surfactants and amphoteric surfactants.

The crosslinking agent improves the strength of the film after printing. As the crosslinking agent, for example, a glycidyl crosslinking agent, a carbodiimide crosslinking agent, an oxazoline crosslinking agent, an isocyanate crosslinking agent, an aziridine crosslinking agent, or the like can be used.

(Method for producing inkjet ink)
An example of a method for producing an inkjet ink will be described.
For pigment dispersions, resins, basic substances, water, water-soluble solvents and, if necessary, surface-active agents such as anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc. It is prepared by adding an agent, a pH adjusting agent, and other components.
The pigment dispersion is prepared by adding the desired components while stirring and thoroughly stirring. When stirring, it can be heated if necessary.

The stirrer is, for example, a high speed mixer, a homogenizer, a planetary mixer, a trimix, a kneader, an extruder, a horizontal sand mill, a vertical sand mill, an annular bead mill, a paint shaker, a ball mill, or the like, a disperser equipped with an ultrasonic oscillator. A two-roll mill, a three-roll mill, etc. may be mentioned.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not particularly limited to the examples. In addition, in an Example, "part" is a "mass part" and "%" represents the "mass %."

The materials used in the examples are described below.
(Inorganic pigment (A))
Taipaque CR-58 (made by Ishihara Sangyo Co., Ltd.)
Titanium dioxide (rutile type)
Average primary particle size: 0.28 μm
Compound forming the first coating layer: Alumina Typake CR-80 (manufactured by Ishihara Sangyo Co., Ltd.)
Titanium dioxide (rutile type)
Average primary particle size: 0.25 μm
Compound forming the first coating layer: alumina, silica

(Polymer (B))
-Polymer having a carboxyl group as an anionic group Aron A-10SL (manufactured by Toagosei Co., Ltd.)
Polyacrylic acid Mw 5,000
Nonvolatile content 40%
-Sodium salt of a polymer having a carboxyl group and a sulfonic acid group as an anionic group Aron A-6012 (manufactured by Toagosei Co., Ltd.)
Polyacrylic acid sulfonic acid type copolymer sodium Mw 10,000
Nonvolatile content 40%

.Resin (X) having an aromatic group as a hydrophobic group and a carboxyl group as a hydrophilic group
Joncryl 690 (BASF)
Styrene acrylic resin Mw16,500
Nonvolatile content 98.5%

(Water-soluble solvent)
Diethylene glycol mono-n-butyl ether Propylene glycol

(Surfactant)
・Nonionic surfactant Surfynol DF110D (manufactured by EVONIK)

(Preservative)
Proxel GXL (Lonza)

The evaluation methods of the pigment dispersion and the ink are shown below.

(Preparation of Aron A-10SL NaOH aqueous solution)
Sodium hydroxide (50.0 parts) was dissolved in ion-exchanged water (50.0 parts) to prepare a 50.0% sodium hydroxide aqueous solution. 69.5 parts of Aron A-10SL (40% non-volatile content) were weighed in a 200 ml glass bottle, and 30.0 parts of 50% sodium hydroxide aqueous solution was added thereto. At this time, the glass bottle container was ice-cooled and 50% sodium hydroxide aqueous solution was added while maintaining the temperature at 50°C or lower. After adding the 50% sodium hydroxide aqueous solution, confirm the pH of the mixed solution, and further add 0.5 part of the 50% sodium hydroxide aqueous solution and stir to adjust the pH to the range of 9.2 to 9.5. Then, an Aron A-10SL NaOH aqueous solution having a Aron A-10SL concentration of 28.1% was obtained.

(Preparation of Joncryl 690 NaOH aqueous solution)
Sodium hydroxide (50.0 parts) was dissolved in ion-exchanged water (50.0 parts) to prepare a 50.0% sodium hydroxide aqueous solution. 20.0 parts of Joncryl 690 crushed in a 200 ml glass bottle was weighed, 73.2 parts of ion-exchanged water was added thereto, and the mixture was heated with a disper so that the liquid temperature became 50°C. To this, 6.8 parts of 50% sodium hydroxide aqueous solution was added and stirred until Joncryl 690 was dissolved to obtain a Joncryl 690 NaOH aqueous solution having a concentration of 20% Joncryl 690.

(Preparation Example 1 Preparation of Pigment Dispersion (1))
To a 225 ml glass bottle, 9.3 parts of Aron A-10SL NaOH aqueous solution and 55.7 parts of ion-exchanged water were added and well stirred, 160 parts of 0.8 mm zirconia beads were added, and finally TAIPAKE CR-80. Was added to a shaker (Automatic shaker SK450 manufactured by Sakata Inx Engineering Co., Ltd.) and dispersed for 6 hours. After the dispersion, the beads were removed to obtain a pigment dispersion (1). The particle size distribution (d50) of the pigment dispersion was measured by diluting with ion-exchanged water using Nanotrac Wave (manufactured by Microtrac Bell). The value of d50 of the volume average particle diameter was used.

(Preparation Examples 2 to 19 Preparation of Pigment Dispersions (2) to (19))
Pigment dispersions (2) to (19) were produced in the same manner as in Production Example 1 except that the amounts of the inorganic pigment (A), the polymer (B) and the amount used in Table 1 were changed. The particle size distribution was measured by the same method as in Preparation Example 1. The evaluation results are as shown in Table 1.

(Example 1)
An inkjet ink (1) was produced using the pigment dispersion (1) produced in Production Example 1.
An ink component (ink component liquid) other than the pigment dispersion (1) was mixed in advance, and this was added to the pigment dispersion (1) with stirring to prepare.
To prepare ink components other than the pigment dispersion, 100 ml of a glass container was charged with 24.7 parts of ion-exchanged water, 7.0 parts of diethylene glycol mono-n-butyl ether, 23.0 parts of propylene glycol, 1.5 parts of Surfynol DF110D, 0.2 parts of Proxel GXL and 15.0 parts of Joncyrl 690 NaOH aqueous solution as a resin consisting of a hydrophobic group and a hydrophilic group were weighed out and mixed with a disper to prepare an ink component liquid.
28.6 parts of Pigment Dispersion (1) was weighed in a 200 ml glass container, and 71.4 parts of the ink component liquid was added while stirring with a disper at a liquid temperature of 25° C., and the mixture was stirred for 30 minutes. (1) was obtained. The composition of the obtained ink is shown in Table 3.

(Examples 2-17, Comparative Examples 1-2)
Inkjet inks (2) of Examples 2 to 17 and Comparative Examples 1 and 2 in the same manner as in Example 1 except that the materials and the amounts used in Tables 3 to 4 were changed. To (19) were produced.

(Evaluation of inkjet ink)
To evaluate the dispersion state of the inkjet ink after long-term storage, an accelerated evaluation of the inkjet ink at 70° C. for 4 weeks was performed. The results are shown in Tables 3-4.

(Method of measuring viscosity)
The rate of change in viscosity was evaluated immediately after producing the inkjet ink and after 4 weeks at 70°C.
The viscosity was measured using an E-type viscometer (“ELD type viscometer” manufactured by Toki Sangyo Co., Ltd.) at a rotor (name 1°34′×R24) at 25° C. and a rotation speed of 20 rpm, and the value after 3 minutes was measured. The viscosity was evaluated. The viscometer was calibrated using a standard solution for viscometer calibration JS10 (manufactured by Nippon Grease Co., Ltd.).
The evaluation criteria are as follows.
◯: Viscosity change rate after storage at 70°C for 4 weeks is less than ±10% (good)
Δ: Viscosity change rate after storage at 70° C. for 4 weeks ±10% or more and less than ±20% (no problem in practical use)
X: Viscosity change rate after storage at 70°C for 4 weeks ±20% or more (not practical)

(Particle size distribution (d50))
The rate of change in the particle size distribution (d50) immediately after the inkjet ink was prepared and after 4 weeks at 70° C. was evaluated.
The particle size distribution (d50) was measured by diluting with ion-exchanged water using Nanotrac Wave (manufactured by Microtrac Bell). The value of d50 of the volume average particle diameter was used.
The evaluation criteria are as follows.
◯: d50 change rate after storage at 70° C. for 4 weeks is less than ±10% (good)
Δ: Change rate of d50 after storage at 70° C. for 4 weeks is ±10% or more and less than ±20% (no problem in practical use)
×: Change rate of d50 after storage at 70°C for 4 weeks is ±20% or more (not practical)

(Coarse particles)
Coarse particles were evaluated immediately after the ink jet ink was produced and after 70° C. for 4 weeks.
The change in coarse particles was evaluated by the ink passage time during vacuum filtration using a 25 mmφ glass fiber filter (GF/B opening 1.0 μm manufactured by GE Healthcare Life Science). If the number of coarse particles is large or the number of coarse particles increases after storage, the filter becomes clogged and the passage time becomes long. Further, when the coarse particles are excessive, the filter is clogged and the ink cannot be completely filtered. Generally, the filter used in the path for supplying ink to the inkjet head is larger than 1 μm, and it can be said that it is sufficient if the filter passes the filtration according to this test method.
(Evaluation condition)
The evaluation ink was prepared by the method described in Example 1 so that the nonvolatile content of the inorganic pigment in the pigment dispersion was 10%. A suction vessel (VT-500 0.5L made by ADVANTEC) with a vacuum pump attached via a cock and a funnel with a 15 ml scale and a 25 mmφ glass fiber filter (GF/B GE Healthcare Life Science) A 25 mm diameter filter holder (manufactured by ADVANTEC) on which was placed was placed. A decompression pump (Aspirator A-1000S manufactured by Tokyo Rikagaku Kikai Co., Ltd.) was operated using a cock so that the inside of the suction vessel was not decompressed, and 15 ml of ink was measured using a funnel memory. Next, the opening time of the pump and the suction vessel was started, and the time taken for the total amount of ink to pass through the filter was measured. When the filtration filter was clogged within 60 seconds and the pigment dispersion did not pass through, the amount of ink remaining in the funnel was measured. The evaluation criteria are as follows.
◯: Ink transit time is less than 35 seconds (good)
Δ: Ink transit time is 35 seconds or more and less than 60 seconds (no problem in practical use)
×: Ink transit time is 60 seconds or more (not practical)

(Whiteness)
Immediately after the ink jet ink was produced, the whiteness was evaluated visually and by L* value. A transparent film (TAC50 125×300 m ² R1 manufactured by MBS Co., Ltd.) is set on a coating table (K101 control coater RK Print Coat Instruments), and a meter bar K101 wet 12 μm (RK Print Coat Instruments) is used to speed After applying the ink in No. 6, it was dried at 80° C. for 3 minutes. The dried film was placed on a uniform density plate (density 2.0, semi-gloss type, manufactured by Fujifilm Co., Ltd.), and the L* value was measured using X-rite i1 (manufactured by Videojet X-Rite Co., Ltd.) to obtain whiteness. did. The measurement conditions were: observation light source: D50, observation field of view: 2°, density: DIN, white reference: Abs, filter: No, M factor: M0. The L* value when measuring CIELabLab was used. The evaluation criteria are as follows.
◯: Both L* value and visual observation are sufficient (good)
Δ: Either L* value or visual inspection is insufficient (no problem)
X: Both L* value and visual inspection are insufficient (defective)

From the results of Tables 2 and 3, the content of the polymer (B) exceeds 7.0 parts by mass with respect to 100 parts by mass of the inorganic pigment (A), and at 45 parts by mass or less, the viscosity and the increase of coarse particles increase. It can be seen that suppressed and good whiteness can be obtained.

Claims (7)

A pigment dispersion comprising an inorganic pigment (A) and a polymer (B) having a monomer unit having one or more anionic groups,
The content of the polymer (B) is more than 7.0 parts by mass and 45 parts by mass or less with respect to 100 parts by mass of the inorganic pigment (A),
The pigment dispersion, wherein the anionic group of the monomer unit having the anionic group is at least one selected from a carboxyl group and a sulfonic acid group. The pigment dispersion according to claim 1, wherein the inorganic pigment (A) is a coated pigment having a first coating layer coated on the surface of the metal compound particles with at least one selected from the group consisting of silica and alumina. body. The pigment dispersion according to claim 1 or 2, wherein the inorganic pigment (A) is rutile type titanium oxide. The pigment dispersion according to any one of claims 1 to 3, wherein the inorganic pigment (A) has an average primary particle diameter of 0.1 µm to 0.6 µm. The polymer (B) having a monomer unit having one or more anionic groups is one or more selected from polyacrylic acid and a polyacrylic acid salt, and the polymer according to claim 1. Pigment dispersion An inkjet ink, comprising the pigment dispersion according to claim 1. The inkjet ink according to claim 6, further comprising a resin having a hydrophobic group and a hydrophilic group.