Water-based pigment dispersions

Abstract

To provide: an aqueous pigment dispersion having a small dispersion particle diameter of the pigment and excellent storage stability at ordinary temperature; and an aqueous ink having excellent dischargeability and decap characteristics when using in an inkjet recording system.SOLUTION: Provided are: an aqueous pigment dispersion comprising an aluminum lake pigment (A) and a pigment dispersant (B), where the pigment dispersant (B) is a polymer containing a structural unit derived from an anionic group-containing monomer (b-1) and a structural unit derived from a hydrophilic nonionic monomer (b-2) containing an oxyalkylene group; and an aqueous ink for inkjet recording, comprising the aqueous pigment dispersion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based pigment dispersion and a water-based ink for ink-jet printing containing the water-based pigment dispersion. [Background technology]

[0002] Inkjet recording is a method of ejecting ink droplets from extremely fine nozzles directly onto a recording medium, causing them to adhere to the recording medium, resulting in printed matter with characters and images recorded on it. Unlike conventional recording methods, this method does not use plates, and so it is expected to be used in a wide range of fields as on-demand printing that can handle small-lot, high-mix production. Recently, there has been research into applying inkjet recording to pharmaceuticals and food.

[0003] For example, Patent Document 1 describes an edible pigment composition containing at least a lake pigment, a pigment dispersant, and a dispersion stabilizer, with the aim of providing a pigment composition, an inkjet aqueous ink composition, etc., that has excellent dispersion stability (storage stability) of the lake pigment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-127589 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, aluminum lake pigments are pigments that have carboxyl groups and sulfonic acid groups and are formed by adsorbing food dyes, which are originally water-soluble, onto the surface of aluminum hydroxide gel due to the coagulation action of polycationized aluminum hydroxide gel. For this reason, aluminum lake pigments are generally difficult to disperse in water, and when attempts are made to disperse them in water, they often gel while absorbing water. Furthermore, even if the pigment can be temporarily dispersed using a pigment dispersant having anionic functional groups, the aluminum ions eluted from the aluminum lake pigment degenerate the electric double layer formed by the anionic functional groups of the pigment dispersant, making it impossible to suppress aggregation caused by collisions of pigment particles due to Brownian motion, resulting in an increase in the particle size of the pigment particles and causing them to settle. In the examples of Patent Document 1, sodium polyacrylate is used as a pigment dispersant. Because sodium polyacrylate orients its carboxyl groups in the aluminum hydroxide gel, which is a polycation, it is expected to stably adsorb to the surface of the aluminum lake pigment. However, it was found that the pigment could not be refined to a particle size large enough to eject the ink in an inkjet recording system, and that the storage stability at room temperature (25°C) was insufficient. Furthermore, when applying water-based inks using aluminum lake pigments to inkjet recording systems, improved ejection performance is also required, as well as excellent decap characteristics that prevent smearing when the ink nozzle surface is left unprotected after printing and printing is restarted. An object of the present invention is to provide an aqueous pigment dispersion in which the dispersed particle size of the pigment is small and which has excellent storage stability at room temperature, and an aqueous ink which has excellent ejection properties and decap characteristics when used in an inkjet recording method. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by providing an aqueous pigment dispersion containing an aluminum lake pigment and a pigment dispersant, wherein the pigment dispersant is a polymer containing structural units derived from a specific monomer. That is, the present invention provides the following [1] and [2]. [1] An aqueous pigment dispersion containing an aluminum lake pigment (A) and a pigment dispersant (B), The aqueous pigment dispersion, wherein the pigment dispersant (B) is a polymer containing a structural unit derived from an anionic group-containing monomer (b-1) and a structural unit derived from a hydrophilic nonionic monomer (b-2) containing an oxyalkylene group. [2] A water-based ink for ink-jet recording, comprising the water-based pigment dispersion according to [1] above and a water-soluble organic solvent (C). [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an aqueous pigment dispersion in which the dispersed particle size of the pigment is small and which has excellent storage stability at room temperature, and an aqueous ink which has excellent ejection properties and decap characteristics when used in an inkjet recording method. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Water-based pigment dispersion] The aqueous pigment dispersion of the present invention (hereinafter also simply referred to as "pigment dispersion") is an aqueous pigment dispersion containing an aluminum lake pigment (A) and a pigment dispersant (B), and the pigment dispersant (B) is a polymer containing a constituent unit derived from an anionic group-containing monomer (b-1) and a constituent unit derived from a hydrophilic nonionic monomer (b-2) containing an oxyalkylene group. In this specification, the term "aqueous system" means that water accounts for the largest proportion of the medium.

[0009] The present invention has the particular effect of providing an aqueous pigment dispersion in which the dispersed particle size of the pigment is small and which has excellent storage stability at room temperature (hereinafter also referred to as "room temperature storage stability"), and further providing an aqueous ink which has excellent jetting properties and decap characteristics when used in an inkjet recording system. The reason for this is not clear, but is thought to be as follows. The pigment dispersion of the present invention contains an aluminum lake pigment, and the pigment dispersant is a polymer containing a structural unit derived from an anionic group-containing monomer and a structural unit derived from a hydrophilic nonionic monomer having an oxyalkylene group. It is believed that the anionic groups introduced into the polymer by the anionic group-containing monomer are oriented and adsorbed onto the surface of the aluminum hydroxide gel of the aluminum lake pigment, suppressing aggregation and sedimentation of the pigment particles through electrical repulsion, thereby contributing to a reduction in the dispersed particle size. Furthermore, the oxyalkylene groups introduced into the polymer by the hydrophilic nonionic monomer enhance the affinity of the aluminum lake pigment near its surface for the water contained as a medium, covering the surface of the aluminum lake pigment with a water molecule layer. This water molecule layer generates a steric repulsive force, preventing contact between pigment particles and preventing aggregation of the pigment particles, thereby suppressing an increase in the pigment particle size. As a result, the dispersed particle size of the pigment in the pigment dispersion is reduced, improving storage stability at room temperature, and further improving ejection performance and decap performance when used in inkjet recording systems.

[0010] <Aluminum Lake Pigment (A)> The pigment dispersion of the present invention contains an aluminum lake pigment (A). The aluminum lake pigment (A) comprises a dye component (α) that exhibits coloring power and an aluminum hydroxide gel (β) that adsorbs the dye. From the viewpoint of detoxifying the tar dye, the dye component (α) preferably has a hydrophilic functional group such as a sulfonic acid group or a carboxyl group introduced into the aromatic ring in the molecule, thereby giving it high water solubility. From the viewpoint of making the dye component having such a chemical structure into a water-insoluble pigment, the aluminum lake pigment (A) is prepared by adding a polymerized aluminum ion [Al n+2 (OH) 3n ] 6+ It is preferable that the dye component (α) is bound to an aluminum hydroxide gel (β) carrier present in the form of n=10 or more.

[0011] The aluminum lake pigment (A) is not particularly limited, but from the viewpoints of reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving dischargeability and decap properties, it is preferably a pigment using at least one dye component (α) selected from Yellow No. 4, Yellow No. 5, Red No. 2, Red No. 3, Red No. 40, Red No. 102, Red No. 104-(1), Green No. 3, Blue No. 1, and Blue No. 2, and more preferably one or more dye components selected from Yellow No. 4 Aluminum Lake, Yellow No. 5 Aluminum Lake, Blue No. 1 Aluminum Lake, and Red No. 104-(1) Aluminum Lake.

[0012] <Pigment dispersant (B)> The pigment dispersion of the present invention contains a pigment dispersant (B) (hereinafter also simply referred to as "dispersant (B)"). The dispersant (B) is a polymer containing a constituent unit derived from an anionic group-containing monomer (b-1) and a constituent unit derived from a hydrophilic nonionic monomer (hereinafter simply referred to as "hydrophilic nonionic monomer") (b-2) containing an oxyalkylene group. The dispersant (B) is obtained by copolymerizing raw material monomers including an anionic group-containing monomer (b-1) and a hydrophilic nonionic monomer (b-2).

[0013] (Anionic Group-Containing Monomer (b-1)) The dispersant (B) according to the present invention contains a structural unit derived from an anionic group-containing monomer (b-1). The anionic groups introduced into the polymer of the dispersant (B) by the anionic group-containing monomer (b-1) are oriented toward the aluminum hydroxide gel (β) portion of the aluminum lake pigment (A), thereby allowing the dispersant (B) to be adsorbed onto the aluminum lake pigment (A). This is thought to reduce the dispersed particle size of the pigment, improve storage stability at room temperature, and further improve dischargeability and decap properties. The anionic group is not particularly limited, but examples thereof include a carboxy group, a sulfonic acid group, and a phosphate group. From the viewpoints of reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving ejection properties and decap properties, a carboxy group is preferred. Examples of carboxy group-containing monomers include monocarboxylic acid monomers such as (meth)acrylic acid, 2-ethylacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, β-methylacrylic acid (crotonic acid), α-phenylacrylic acid, β-acryloyloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, and β-styrylacrylic acid (1-carboxy-4-phenylbutadiene-1,3); dicarboxylic acid monomers such as fumaric acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, mesaconic acid, and glutaconic acid; and tricarboxylic acid monomers such as aconitic acid and tricarboxyethylene. Among these, the anionic group-containing monomer (b-1) is preferably a carboxy group-containing monomer, more preferably a monocarboxylic acid monomer, even more preferably (meth)acrylic acid, and even more preferably methacrylic acid, from the viewpoints of reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving ejection properties and decap properties. In this specification, "(meth)acrylic acid" means one or more selected from acrylic acid and methacrylic acid. The same applies to "(meth)acrylic acid" below.

[0014] (Hydrophilic nonionic monomer containing an oxyalkylene group (b-2)) The dispersant (B) according to the present invention contains a structural unit derived from a hydrophilic nonionic monomer (b-2) containing an oxyalkylene group. In the present invention, the term "hydrophilic" of a monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the dissolved monomer is 10 g or more.

[0015] The hydrophilic nonionic monomer (b-2) is not particularly limited as long as it has an oxyalkylene group and a polymerizable group in the molecule. The oxyalkylene group preferably has a carbon number of 2 or more and 4 or less. Specific examples of the oxyalkylene group include an oxyethylene group, an oxypropylene group, and an oxybutylene group. From the viewpoints of reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving ejection properties and decap properties, the oxyalkylene group is preferably at least one selected from an oxyethylene group and an oxypropylene group, and more preferably an oxyethylene group. The polymerizable group is a group having a radically polymerizable unsaturated double bond, and includes at least one selected from a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. Of these, the polymerizable group is preferably a vinyl group, an allyl group, an acryloyl group, or a methacryloyl group. Specific examples of the hydrophilic nonionic monomer (b-2) include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; polyalkylene glycol (meth)acrylate; alkoxypolyalkylene glycol (meth)acrylate; and polyalkylene glycol monoallyl ether.

[0016] Among these, the hydrophilic nonionic monomer (b-2) preferably has a polyalkylene glycol chain, and more preferably has a polyoxyalkylene group, from the viewpoint of reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving ejection and decap properties. The average number of moles of alkylene oxide added to the polyalkylene glycol chain or polyoxyalkylene group is, from the same viewpoint as above, preferably 2 or more, more preferably 4 or more, and even more preferably 9 or more, and, from the same viewpoint as above, is preferably 120 or less, more preferably 90 or less, even more preferably 45 or less, and still more preferably 35 or less. When the average number of moles added is within the above range, storage stability at high temperatures (hereinafter also referred to as "high-temperature storage stability") can be maintained for a long period of time. The polyalkylene glycol chain or polyoxyalkylene group may contain units derived from ethylene oxide and units derived from propylene oxide. The molar ratio of the units derived from ethylene oxide (EO) to the units derived from propylene oxide (PO) [EO / PO] is preferably 1 or more, more preferably 1.1 or more, even more preferably 1.2 or more, and is preferably 9 or less, more preferably 6 or less, even more preferably 3 or less, and still more preferably 2 or less.

[0017] The structural unit derived from the hydrophilic nonionic monomer (b-2) is preferably a structural unit derived from a polyalkylene glycol (meth)acrylate represented by the following formula (1), from the viewpoints of reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving ejection properties and decap properties. In the present invention, "(meth)acrylate" means one or more selected from acrylate and methacrylate. The same applies to "(meth)acrylate" hereinafter.

[0018] [ka] (In formula (1), R 1 represents a hydrogen atom or a methyl group, and R 2 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, OA represents an oxyalkylene group having 2 to 4 carbon atoms, and n represents the average number of moles of alkylene oxide added, which is a number of 2 to 120.

[0019] In the formula (1), the number of carbon atoms in OA, which is an oxyalkylene group, is preferably 2 or more and 3 or less, more preferably 2, from the viewpoints of reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving ejection properties and decap properties. That is, from the same viewpoints as above, OA, which is an oxyalkylene group, is preferably one or more selected from an oxyethylene group and an oxypropylene group, more preferably an oxyethylene group. In the formula (1), R 1is preferably a methyl group from the viewpoint of the dispersion stability of the pigment dispersion. In the formula (1), R 2 is preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group, from the viewpoint of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, as well as improving ejection and decap properties. The alkyl group may be linear or branched. In the formula (1), n, which is the average number of moles added, is preferably 4 or more, more preferably 9 or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving ejection properties and decap properties; and from the same viewpoints as above, n is preferably a number of 90 or less, more preferably 45 or less, and even more preferably 35 or less. However, the n oxyalkylene groups may be the same or different from one another, and when the oxyalkylene groups are different from one another, they may be added in block, random, or alternate manner.

[0020] The polyalkylene glycol (meth)acrylate constituting the structural unit represented by the formula (1) is preferably at least one selected from polyethylene glycol mono(meth)acrylate, (polyethylene glycol / polypropylene glycol) (meth)acrylate, alkoxypolyethylene glycol (meth)acrylate, and alkoxy(polyethylene glycol / polypropylene glycol) (meth)acrylate, more preferably at least one selected from polyethylene glycol mono(meth)acrylate and alkoxypolyethylene glycol (meth)acrylate. Specifically, the alkoxypolyethylene glycol (meth)acrylate is preferably one or more selected from 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, more preferably one or more selected from methoxypolyethylene glycol mono(meth)acrylate, ethoxypolyethylene glycol mono(meth)acrylate, propoxypolyethylene glycol mono(meth)acrylate, butoxypolyethylene glycol mono(meth)acrylate, and octoxypolyethylene glycol mono(meth)acrylate, even more preferably one or more selected from methoxypolyethylene glycol mono(meth)acrylate, ethoxypolyethylene glycol mono(meth)acrylate, and propoxypolyethylene glycol mono(meth)acrylate, and still more preferably methoxypolyethylene glycol mono(meth)acrylate.

[0021] As described above, the hydrophilic nonionic monomer (b-2) is preferably an alkoxypolyethylene glycol mono(meth)acrylate, more preferably an alkoxypolyethylene glycol mono(meth)acrylate having an alkoxy group having from 1 to 20 carbon atoms, even more preferably an alkoxypolyethylene glycol mono(meth)acrylate having an alkoxy group having from 1 to 8 carbon atoms, still more preferably an alkoxypolyethylene glycol mono(meth)acrylate having an alkoxy group having from 1 to 3 carbon atoms, still more preferably one or more selected from methoxypolyethylene glycol mono(meth)acrylate, ethoxypolyethylene glycol mono(meth)acrylate, and propoxypolyethylene glycol mono(meth)acrylate, and still more preferably methoxypolyethylene glycol mono(meth)acrylate.

[0022] Specific examples of commercially available hydrophilic nonionic monomers (b-2) include NK Ester M-20G, 40G, 90G, 230G, 450G, and 900G (all manufactured by Shin-Nakamura Chemical Co., Ltd.); Blenmer PME-1000, 4000, and Blenmer 50POEP-800B (all manufactured by NOF Corporation); and Light Ester 041MA (manufactured by Kyoeisha Chemical Co., Ltd.).

[0023] The dispersant (B) may contain a constituent unit derived from a monomer other than the constituent unit derived from the anionic base-containing monomer (b-1) and the constituent unit derived from the hydrophilic nonionic monomer (b-2), as long as the effect of the present invention is not impaired. Examples of the other monomer include a hydrophilic nonionic monomer other than the hydrophilic nonionic monomer (b-2); or a hydrophobic monomer. In this specification, the term "hydrophobic monomer" refers to a monomer that dissolves in 100 g of ion-exchanged water at 25° C. to saturation in an amount of less than 10 g.

[0024] Examples of hydrophilic nonionic monomers other than the hydrophilic nonionic monomer (b-2) include (meth)acrylamide; N-vinyl-2-pyrrolidone; and N-alkyl(meth)acrylamides. Examples of the hydrophobic monomer include aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol. The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably at least one selected from a styrene-based monomer and an aromatic group-containing (meth)acrylate. The molecular weight of the aromatic group-containing monomer is preferably less than 500. Examples of styrene-based monomers include styrene, α-methylstyrene, 2-methylstyrene, 4-vinyltoluene (4-methylstyrene), and divinylbenzene. Examples of aromatic group-containing (meth)acrylates include phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate. The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms. Examples thereof include (meth)acrylates having a linear or branched alkyl group having from 1 to 22 carbon atoms; and (meth)acrylates having an alicyclic alkyl group such as cyclohexyl (meth)acrylate.

[0025] The content of the structural units derived from the anionic group-containing monomer (b-1) in all structural units of the dispersant (B) is preferably 3% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, and still more preferably 15% by mass or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving ejection properties and decap properties; and from the same viewpoints as above, it is preferably 55% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less, still more preferably 40% by mass or less, still more preferably 35% by mass or less, still more preferably 30% by mass or less, and still more preferably 20% by mass or less. The content of the structural units derived from the hydrophilic nonionic monomer (b-2) in all structural units of the dispersant (B) is preferably 45% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, still more preferably 60% by mass or more, still more preferably 65% ​​by mass or more, still more preferably 70% by mass or more, and still more preferably 80% by mass or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving ejection properties and decap properties; and from the same viewpoints as above, it is preferably 97% by mass or less, more preferably 93% by mass or less, still more preferably 90% by mass or less, and still more preferably 85% by mass or less.

[0026] When the dispersant (B) contains a structural unit derived from a hydrophobic monomer, the content of the structural unit derived from the hydrophobic monomer is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoints of improving the adsorption of the dispersant to the aluminum lake pigment in an aqueous medium, reducing the dispersed particle size of the pigment, improving storage stability at room temperature, and improving ejection properties and decap properties. As described above, the dispersant (B) may contain structural units other than the structural units derived from the anionic base-containing monomer (b-1) and the structural units derived from the hydrophilic nonionic monomer (b-2), as long as the effects of the present invention are not impaired. However, from the viewpoints of reducing the dispersed particle size of the pigment and improving room temperature storage stability, further improving high temperature storage stability, and improving ejection properties and decapability, the total content of the structural units derived from the anionic group-containing monomer (b-1) and the structural units derived from the hydrophilic nonionic monomer (b-2) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and still more preferably 95% by mass or more, with the upper limit being 100% by mass, even more preferably 100% by mass. In other words, the dispersant (B) is even more preferably composed only of structural units derived from the anionic group-containing monomer (b-1) and structural units derived from the hydrophilic nonionic monomer (b-2).

[0027] From the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving ejection properties and decap properties, dispersant B preferably contains a structural unit derived from (meth)acrylic acid as the anionic group-containing monomer (b-1) and a structural unit derived from alkoxypolyalkylene glycol (meth)acrylate as the monomer (b-2), and more preferably contains a structural unit derived from (meth)acrylic acid as the anionic group-containing monomer (b-1) and a structural unit derived from methoxypolyethylene glycol (meth)acrylate as the hydrophilic nonionic monomer (b-2). The dispersant B may be synthesized by a known polymerization method, or a commercially available product may be used.

[0028] As described above, in the present invention, the dispersant (B) contains oxyalkylene groups introduced by the hydrophilic nonionic monomer (b-2). This creates a steric repulsive force due to the water molecule layer covering the surface of the aluminum lake pigment, suppressing pigment particle aggregation and preventing particle size increase. This reduces the dispersed particle size of the pigment, improves room-temperature storage stability, and further improves dischargeability and decapability. These effects of the present invention are more effectively achieved when the oxyalkylene groups of the hydrophilic nonionic monomer (b-2) are preferably polyoxyalkylene groups, further improving high-temperature storage stability. These effects are believed to depend on the type of polyoxyalkylene groups introduced into the dispersant (B) (the average number of moles of alkylene oxide added) and the number of polyoxyalkylene groups. From this viewpoint, as an indicator of the type of polyoxyalkylene group (average number of moles of alkylene oxide added) and the number of polyoxyalkylene groups introduced into dispersant (B), the number of moles of hydrophilic nonionic monomer (b-2) per 100 g of dispersant (B) is preferably 0.01 or more, more preferably 0.03 or more, even more preferably 0.05 or more, and preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.3 or less, still more preferably 0.2 or less, still more preferably 0.1 or less, and even more preferably 0.08 or less. The number of moles of the hydrophilic nonionic monomer (b-2) in 100 g of the dispersant (B) can be calculated from the monomer composition of the dispersant (B) and the molecular weight of the hydrophilic nonionic monomer (b-2).

[0029] As described above, in the present invention, since the dispersant (B) has anionic groups introduced by the anionic group-containing monomer (b-1), the anionic groups are oriented and adsorbed on the surface of the aluminum hydroxide gel of the aluminum lake pigment, and it is believed that the electrical repulsion suppresses the aggregation and sedimentation of the pigment particles, thereby contributing to a reduction in the dispersed particle size. On the other hand, since the anionic groups also have the function of increasing the solubility of the dispersant (B) in aqueous media, it is believed that the dispersion stability of the pigment dispersion also depends on the type and number of anionic groups introduced into the dispersant (B). From this viewpoint, the dispersion stability of the pigment dispersion is an index of the type and number of anionic groups introduced into the dispersant (B), and the number of moles of the anionic group-containing monomer (b-1) in 100 g of the dispersant (B) is preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, still more preferably 0.15 or more, and is preferably 0.7 or less, more preferably 0.5 or less, even more preferably 0.4 or less, still more preferably 0.3 or less, and still more preferably 0.25 or less. When the number of moles of the anionic group-containing monomer (b-1) in 100 g of dispersant (B) is within the above range, the dispersion stability of the pigment dispersion in particular is improved by the number of anionic groups introduced into dispersant (B) being within an appropriate range, and the anionic groups are sufficiently adsorbed onto the surface of the aluminum hydroxide gel of the aluminum lake pigment, and the solubility of dispersant (B) in an aqueous medium can be adjusted. This is thought to improve the dispersion stability of the pigment dispersion, reduce the dispersed particle size of the pigment, improve storage stability at room temperature, and further improve ejection properties and decap properties. The number of moles of the anionic group-containing monomer (b-1) in 100 g of the dispersant (B) can be calculated from the monomer composition of the dispersant (B) and the molecular weight of the anionic group-containing monomer (b-1).

[0030] The ratio of the number of moles of structural units derived from hydrophilic nonionic monomer (b-2) to the number of moles of structural units derived from anionic group-containing monomer (b-1) contained in dispersant (B) (hereinafter also referred to as the molar ratio [monomer (b-2) / monomer (b-1)]) is preferably 0.05 or more, more preferably 0.1 mole or more, even more preferably 0.15 or more, still more preferably 0.2 or more, and still more preferably 0.25 or more, from the viewpoints of adjusting the types and numbers of anionic groups and polyoxyalkylene groups introduced into dispersant (B), improving the dispersion stability of the pigment dispersion, reducing the dispersed particle size of the pigment, improving room temperature storage stability, further improving high temperature storage stability, and improving dischargeability and decapability; and from the same viewpoints as above, it is preferably 2.5 or less, more preferably 2 or less, even more preferably 1.7 or less, still more preferably 1.5 or less, still more preferably 1.3 or less, still more preferably 1 or less, still more preferably 0.7 or less, and still more preferably 0.5 or less.

[0031] The dispersant (B) is preferably prepared by solution polymerization from the viewpoint of controlling the molecular weight. The solvent used in the solution polymerization method is not particularly limited, and preferred examples include water, aliphatic alcohols having from 1 to 3 carbon atoms, ketones having from 3 to 8 carbon atoms, esters such as ethyl acetate, and mixed solvents of one or more of these with water. Among these, water is preferred, as it can be used as is without removing the solvent when producing a pigment dispersion, which will be described later. During the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. Any polymerization initiator that is used in ordinary solution polymerization can be used, but persulfates are preferred, and ammonium persulfates are more preferred. The chain transfer agent is preferably a mercaptan, more preferably 2-mercaptoethanol. The amount of the polymerization initiator used is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the total amount of the raw material monomers of dispersant (B), from the viewpoint of the molecular weight distribution of dispersant (B), and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, from the same viewpoint as above. The amount of chain transfer agent used is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the total amount of raw material monomers of dispersant (B), from the viewpoint of the molecular weight distribution of dispersant (B), and from the same viewpoint as above, is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less.

[0032] Preferred polymerization conditions vary depending on the type of polymerization initiator, etc., but the polymerization temperature is preferably 50° C. or higher and 90° C. or lower, and the polymerization time is preferably 1 hour or higher and 20 hours or lower. When a persulfate is used as the polymerization initiator, the polymerization temperature is preferably 70°C or higher, more preferably 75°C or higher, from the viewpoint of reactivity, and is preferably 85°C or lower, more preferably 83°C or lower, from the viewpoint of the molecular weight distribution of the dispersant (B). The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon. After the polymerization reaction is completed, the produced dispersant (B) can be isolated from the reaction solution by known methods such as reprecipitation, solvent distillation, etc. Furthermore, unreacted monomers and the like can be removed from the dispersant (B) by reprecipitation, membrane separation, chromatography, extraction, etc. From the viewpoint of improving the productivity of the pigment dispersion, it is preferable that the solvent used in the polymerization reaction is not removed and the dispersant (B) is used as a solution thereof.

[0033] The acid value of the dispersant (B) is preferably 25 mgKOH / g or more, more preferably 30 mgKOH / g or more, even more preferably 50 mgKOH / g or more, and even more preferably 100 mgKOH / g or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving ejection and decap properties. From the same viewpoints as above, it is preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, even more preferably 270 mgKOH / g or less, even more preferably 230 mgKOH / g or less, even more preferably 200 mgKOH / g or less, even more preferably 150 mgKOH / g or less, and even more preferably 130 mgKOH / g or less. The acid value of the dispersant (B) can be measured by the method described in the Examples.

[0034] The polystyrene-equivalent weight-average molecular weight of dispersant (B) is preferably 5,000 or more, more preferably 20,000 or more, and even more preferably 40,000 or more, from the viewpoints of improving the dispersion stability of the pigment dispersion, improving the room-temperature storage stability, further improving the high-temperature storage stability, and improving the ejection and decap properties, and is preferably 500,000 or less, more preferably 300,000 or less, even more preferably 150,000 or less, still more preferably 100,000 or less, and even more preferably 70,000 or less, from the viewpoint of reducing the dispersed particle size of the pigment. The weight-average molecular weight of dispersant (B) can be measured by the method described in the Examples.

[0035] It is preferable that the dispersant (B) be ionized by neutralizing at least a portion of the anionic groups. This allows random electrical repulsion to be imparted to the dispersant (B), and the anionic groups of the dispersant (B) are hydrated in an aqueous medium, suppressing the formation of intramolecular hydrogen bonds. This allows the polymer chains of the dispersant (B) to be sufficiently expanded in the aqueous medium without shrinking, allowing the anionic groups of the dispersant (B) to more efficiently form ionic bonds with the aluminum of the aluminum lake pigment (A). This is thought to further reduce the dispersed particle size of the pigment, further improve both room temperature and high temperature storage stability, and further improve dischargeability and decapability. From this viewpoint, the degree of neutralization of the dispersant (B) is preferably 5 mol% or more, more preferably 7 mol% or more, even more preferably 10 mol% or more, and preferably 95 mol% or less, more preferably 90 mol% or less, even more preferably 70 mol% or less, still more preferably 50 mol% or less, still more preferably 42 mol% or less, still more preferably 40 mol% or less, still more preferably 35 mol% or less, still more preferably 32 mol% or less, still more preferably 30 mol% or less. Furthermore, from the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, and further improving storage stability at high temperatures, the degree of neutralization of the dispersant (B) is preferably 5 mol% or more, more preferably 7 mol% or more, and even more preferably 10 mol% or more, and from the same viewpoints as above, it is preferably 95 mol% or less, more preferably 90 mol% or less, even more preferably 70 mol% or less, still more preferably 50 mol% or less, still more preferably 42 mol% or less, and even more preferably 40 mol% or less. Furthermore, from the viewpoint of further improving the ejection property and decap property, the degree of neutralization of the dispersant (B) is preferably 5 mol% or more, more preferably 7 mol% or more, and even more preferably 10 mol% or more, and from the same viewpoint as above, it is preferably 95 mol% or less, more preferably 70 mol% or less, even more preferably 50 mol% or less, still more preferably 42 mol% or less, still more preferably 40 mol% or less, still more preferably 35 mol% or less, still more preferably 32 mol% or less, and even more preferably 30 mol% or less.

[0036] Examples of neutralizing agents used for neutralization include ammonia; organic amines such as ethylamine, diethylamine, trimethylamine, triethylamine, and triethanolamine; and alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, from the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving ejection properties and decap properties, alkali metal hydroxides are preferred, and sodium hydroxide is more preferred. These neutralizing agents can be used alone or in combination of two or more. The neutralizing agent is preferably used as an aqueous solution of the neutralizing agent.

[0037] (Production of Water-Based Pigment Dispersion) The method for producing the pigment dispersion of the present invention is not particularly limited, but from the viewpoint of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving dischargeability and decapability, a method in which a pigment mixture containing aluminum lake pigment (A), dispersant (B), water, and, if necessary, additives is dispersed using a disperser is preferred. The dispersion treatment of the pigment mixture may be carried out in one dispersion, or from the viewpoint of obtaining a uniform pigment dispersion, it may be carried out by pre-dispersing the pigment mixture and then further by main dispersion using a disperser. The dispersing machine is not particularly limited, and examples thereof include kneading and mixing devices such as kneaders; media-type dispersing machines such as attritors, ball mills, sand mills using glass beads or zirconia beads, and paint shakers; and colloid mills. From the viewpoint of reducing the viscosity of the pigment dispersion, the temperature of the dispersion treatment is preferably maintained at 10°C or higher and 35°C or lower, more preferably 15°C or higher and 30°C or lower, and even more preferably 18°C ​​or higher and 27°C or lower. The time for the dispersion treatment is preferably from 2 hours to 200 hours, more preferably from 3 hours to 50 hours, from the viewpoint of sufficiently pulverizing the pigment.

[0038] The nonvolatile component concentration (solid content concentration) of the pigment dispersion of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving storage stability at room temperature, further improving storage stability at high temperatures, and improving ejection and decap properties, and from the same viewpoints as above, is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, still more preferably 20% by mass or less, still more preferably 15% by mass or less, and even more preferably 12% by mass or less. The solid content concentration of the pigment dispersion is measured by the method described in the Examples.

[0039] The content of the aluminum lake pigment (A) in the pigment dispersion of the present invention is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving the room temperature storage stability of the pigment dispersion, further improving the high temperature storage stability, and facilitating the preparation of the water-based ink and improving the jetting property and decap property, and from the same viewpoints as above, is preferably 20% by mass or less, more preferably 17% by mass or less, and even more preferably 15% by mass or less. The content of the pigment dispersant (B) in the pigment dispersion of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving the room temperature storage stability of the pigment dispersion, further improving the high temperature storage stability, and improving the ejection property and decap property, and from the same viewpoints as above, is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0040] The mass ratio of the content of the aluminum lake pigment (A) to the total content of the aluminum lake pigment (A) and the pigment dispersant (B) in the pigment dispersion of the present invention, [aluminum lake pigment (A) / [aluminum lake pigment (A) + pigment dispersant (B)]], is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, still more preferably 0.40 or more, still more preferably 0.45 or more, still more preferably 0.50 or more, still more preferably 0.55 or more, and still more preferably 0.60 or more, from the viewpoints of reducing the dispersed particle size of the pigment and improving the room temperature storage stability of the pigment dispersion, further improving the high temperature storage stability, and facilitating the preparation of the water-based ink and improving the jetting and decapping properties. From the same viewpoints as above, it is preferably 0.90 or less, more preferably 0.85 or less, even more preferably 0.80 or less, still more preferably 0.75 or less, and still more preferably 0.70 or less. Furthermore, from the viewpoints of reducing the dispersed particle size of the pigment and improving the room temperature storage stability, and further improving the high temperature storage stability, the mass ratio [aluminum lake pigment (A) / [aluminum lake pigment (A) + pigment dispersant (B)]] is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, still more preferably 0.40 or more, still more preferably 0.45 or more, still more preferably 0.50 or more, still more preferably 0.55 or more, and still more preferably 0.60 or more; and from the same viewpoints as above, it is preferably 0.90 or less, more preferably 0.85 or less, even more preferably 0.80 or less, still more preferably 0.75 or less, and still more preferably 0.70 or less. Furthermore, from the viewpoint of further improving the ejection property and decap property, the mass ratio [aluminum lake pigment (A) / [aluminum lake pigment (A) + pigment dispersant (B)]] is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, still more preferably 0.40 or more, still more preferably 0.45 or more, still more preferably 0.50 or more, still more preferably 0.55 or more, and still more preferably 0.60 or more, and from the same viewpoint as above, it is preferably 0.90 or less, more preferably 0.85 or less.

[0041] The water content in the pigment dispersion of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and still more preferably 75% by mass or more, from the viewpoint of dispersion stability of the pigment dispersion, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less, from the same viewpoint as above.

[0042] (Physical properties of water-based pigment dispersions) The volume average particle size of the pigment dispersion of the present invention is preferably 200 nm or less, more preferably 170 nm or less, even more preferably 150 nm or less, and still more preferably 140 nm or less, from the viewpoint of reducing the dispersed particle size of the pigment and improving the room temperature storage stability of the pigment dispersion, further improving the high temperature storage stability, and improving the ejection property and decap property, and is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 90 nm or more, and still more preferably 110 nm or more, from the viewpoint of the productivity of the pigment dispersion. The volume average particle size of the pigment dispersion is measured by the method described in the Examples. The viscosity of the pigment dispersion of the present invention at 20°C is preferably 1 mPa·s or more, more preferably 1.5 mPa·s or more, even more preferably 2 mPa·s or more, even more preferably 2.5 mPa·s or more, even more preferably 3 mPa·s or more, even more preferably 3.5 mPa·s or more, and even more preferably 4 mPa·s or more, from the same viewpoints as above, and is preferably 20 mPa·s or less, more preferably 15 mPa·s or less, even more preferably 10 mPa·s or less, even more preferably 7 mPa·s or less, and even more preferably 6 mPa·s or less. The viscosity of the pigment dispersion at 20°C is measured by the method described in the examples. From the viewpoint of dispersion stability of the pigment dispersion, the pH of the pigment dispersion of the present invention at 20°C is preferably 4 or more, more preferably 4.5 or more, and even more preferably 5 or more, and from the viewpoint of jetting property, it is preferably 9 or less, more preferably 8 or less, even more preferably 7.5 or less, and still more preferably 7 or less. The pH of the pigment dispersion at 20°C is measured by the method described in the examples.

[0043] The pigment dispersion of the present invention contains the pigment (A) in the form of an aluminum lake, and therefore, from the viewpoint of safety, is preferably used in the food, medical, cosmetic, and other fields. In particular, the pigment dispersion of the present invention is preferably used in the cosmetic field. When the pigment dispersion of the present invention is used in the cosmetic field, the pigment dispersion is preferably used in a water-based ink to be applied to hair, skin (including lips), or nails as a cosmetic composition, and more preferably used in a water-based ink to be applied to hair. The cosmetic composition may be a hair cosmetic composition, a skin cosmetic composition, a nail cosmetic composition, or the like, and among these, it is preferably used as a hair cosmetic composition. As the hair cosmetic composition, it is preferable to apply it to hair dyes such as hair mascara and hair color; styling agents such as hair wax, hair spray, hair mousse and hair foam; hair growth agents, and the like. As cosmetic compositions for skin, it is preferable to use them in base makeup cosmetics such as makeup base cosmetics, foundations, and concealers; point makeup cosmetics such as blusher, eye shadow, mascara, eyeliner, eyebrow pencil, overcoat agents, and lipstick; UV protection cosmetics such as sunscreen emulsions and sunscreen creams; skin cleansing cosmetics such as facial washes and cleansing cosmetics; and basic cosmetics such as serums, packs, and massage cosmetics. As the nail cosmetic composition, it is preferably applied to nail-beautifying cosmetics such as nail enamel and nail gloss. When the pigment dispersion of the present invention is used in the cosmetic field, the pigment dispersion can be used in a water-based ink used for printing to decorate the surface of packaging containers for storing cosmetics, such as various compact cases for storing powder cosmetics such as foundation, eye shadow, blush, and eyebrow pencil.

[0044] The pigment dispersion of the present invention has a reduced dispersed particle size of the pigment, is excellent in room temperature storage stability and high temperature storage stability, and further, can improve ejection properties and decap properties when used in an inkjet recording method, and is therefore preferably used for inkjet recording.

[0045] [Water-based ink for inkjet printing] The water-based ink for ink-jet printing of the present invention (hereinafter also simply referred to as "water-based ink") preferably contains the water-based pigment dispersion and a water-soluble organic solvent (C) from the viewpoint of improving ejection properties and decap properties.

[0046] <Water-soluble organic solvent (C)> The water-soluble organic solvent (C) (hereinafter also referred to simply as "organic solvent (C)") preferably contains at least one water-soluble organic solvent having a boiling point of 90°C or higher, from the viewpoints of suppressing an increase in viscosity due to the pigment dispersant and improving ejection properties and decap properties. In the present invention, the "water-soluble organic solvent" is an organic solvent that is arbitrarily miscible with water.

[0047] From the viewpoint of suppressing drying of the ink in the inkjet nozzle and improving the ejection performance and decap characteristics, the boiling point of the organic solvent (C) is preferably 100°C or higher, more preferably 150°C or higher, even more preferably 200°C or higher, still more preferably 230°C or higher, still more preferably 250°C or higher, still more preferably 280°C or higher, still more preferably 290°C or higher, and preferably 400°C or lower, more preferably 370°C or lower, still more preferably 350°C or lower, still more preferably 330°C or lower, and still more preferably 320°C or lower. When two or more water-soluble organic solvents are used as the organic solvent (C), the boiling point of the organic solvent (C) is a weighted average value weighted by the content (mass %) of each water-soluble organic solvent.

[0048] Examples of the organic solvent (C) include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. It should be noted that a mixture of multiple polyhydric alcohols included in the concept of polyhydric alcohols can be used, and similarly, a mixture of multiple polyhydric alcohol alkyl ethers is preferably used.

[0049] Polyhydric alcohols include ethylene glycol (boiling point 197°C), diethylene glycol (boiling point 244°C), polyethylene glycol, propylene glycol (boiling point 188°C), dipropylene glycol (boiling point 232°C), polypropylene glycol, 1,3-propanediol (boiling point 210°C), 1,3-butanediol (boiling point 208°C), 1,4-butanediol (boiling point 230°C), and 3-methyl-1,3-butanediol. (boiling point 203 ° C), 1,5-pentanediol (boiling point 242 ° C), 1,2-hexanediol (boiling point 223 ° C), 1,6-hexanediol (boiling point 250 ° C), 2-methyl-2,4-pentanediol (boiling point 196 ° C), 1,2,6-hexanetriol (boiling point 178 ° C), 1,2,4-butanetriol (boiling point 190 ° C), 1,2,3-butanetriol (boiling point 175 ° C), petriol (boiling point 216 ° C), etc. In addition, it is preferable to use compounds with a boiling point of 250 ° C or higher, such as triethylene glycol (boiling point 285 ° C), tripropylene glycol (boiling point 273 ° C), and glycerin (boiling point 290 ° C), in combination with compounds with a boiling point of less than 250 ° C. The polyhydric alcohol may also be an alkylene oxide adduct of the polyhydric alcohol, such as a glycerin-modified ethylene oxide adduct.

[0050] Examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether (boiling point 135°C), ethylene glycol monobutyl ether (boiling point 171°C), diethylene glycol monomethyl ether (boiling point 194°C), diethylene glycol monoethyl ether (boiling point 202°C), diethylene glycol monobutyl ether (boiling point 230°C), triethylene glycol monomethyl ether (boiling point 122°C), triethylene glycol monoisobutyl ether (boiling point 160°C), tetraethylene glycol monomethyl ether (boiling point 158°C), propylene glycol monoethyl ether (boiling point 133°C), dipropylene glycol monobutyl ether (boiling point 227°C), dipropylene glycol monomethyl ether (boiling point 90°C), tripropylene glycol monomethyl ether (boiling point 100°C), and tripropylene glycol monobutyl ether. It is also preferable to use a compound having a boiling point of 250°C or higher, such as triethylene glycol monobutyl ether (boiling point 276°C), in combination with a compound having a boiling point of less than 250°C.

[0051] Examples of nitrogen-containing heterocyclic compounds include N-methyl-2-pyrrolidone (boiling point 202°C), 2-pyrrolidone (boiling point 245°C), 1,3-dimethyl-2-imidazolidinone (boiling point 220°C), and ε-caprolactam (boiling point 136°C). Examples of amides include formamide (boiling point: 210° C.), N-methylformamide (boiling point: 199° C.), and N,N-dimethylformamide (boiling point: 153° C.). Examples of amines include monoethanolamine (boiling point 170°C), diethanolamine (boiling point 217°C), triethanolamine (boiling point 208°C), and triethylamine (boiling point 90°C). Examples of sulfur-containing compounds include dimethyl sulfoxide (boiling point 189°C), etc. It is also preferable to use compounds with a boiling point of 250°C or higher, such as sulfolane (boiling point 285°C) and thiodiglycol (boiling point 282°C), in combination with compounds with a boiling point of less than 250°C.

[0052] Among these, preferred is one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers, more preferred is one or more selected from polyhydric alcohols and polyhydric alcohol-modified alkylene oxide adducts, and even more preferred is one or more selected from glycerin, 1,2-hexanediol, and glycerin-modified ethylene oxide adducts.

[0053] (Other ingredients) In addition to the aluminum lake pigment (A), dispersant (B), and water-soluble organic solvent (C), various additives may be added to the water-based ink of the present invention, such as commonly used surfactants, wetting agents, penetrating agents, dispersants other than dispersant (B), viscosity modifiers, antifoaming agents, antifungal agents, antirust agents, and ultraviolet absorbers.

[0054] From the viewpoint of print quality, the water-based ink of the present invention may further contain a surfactant. From the viewpoint of print quality, the surfactant is preferably a nonionic surfactant, and examples thereof include: (1) alkyl ethers, alkenyl ethers, alkynyl ethers, or aryl ethers of polyoxyalkylenes obtained by adding ethylene oxide, propylene oxide, or butylene oxide to saturated or unsaturated, linear or branched higher alcohols, polyhydric alcohols, or aromatic alcohols having from 8 to 22 carbon atoms; (2) esters of polyhydric fatty acids and higher alcohols having saturated or unsaturated, linear or branched hydrocarbon groups having from 8 to 22 carbon atoms; (3) polyoxyalkylene aliphatic amines having linear or branched alkyl or alkenyl groups having from 8 to 20 carbon atoms; (4) ester compounds of higher fatty acids having from 8 to 22 carbon atoms and polyhydric alcohols, or compounds obtained by adding ethylene oxide, propylene oxide, or butylene oxide to ester compounds of such polyhydric alcohols; (5) silicone-based surfactants; and (6) acetylene glycol-based surfactants.

[0055] Among these, the nonionic surfactant is preferably an acetylene glycol surfactant, specific examples of which include one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3,5-dimethyl-1-hexyne-3-ol, and ethylene oxide adducts thereof. Among these, the nonionic surfactant is more preferably one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and ethylene oxide adducts thereof, and even more preferably one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol and ethylene oxide adducts thereof.

[0056] Commercially available nonionic surfactants include, for example, the Surfynol series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals; the Acetylenol series manufactured by Kawaken Fine Chemicals Co., Ltd.; and "Emulgen 120 (polyoxyethylene lauryl ether)" manufactured by Kao Corporation.

[0057] (Production of water-based ink for inkjet printing) The water-based ink of the present invention is preferably produced by mixing the water-based pigment dispersion, the water-soluble organic solvent (C), and, if necessary, water and various additives. Filtration using a filter or the like may also be carried out. The contents of each component in the water-based ink of the present invention and the ink properties are as follows.

[0058] (Aluminum lake pigment (A) content) The content of the aluminum lake pigment (A) in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of coloring degree, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, still more preferably 7% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of improving jetting ability and decap ability.

[0059] (Pigment dispersant (B) content) The content of dispersant (B) in the water-based ink of the present invention is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.6% by mass or more, from the viewpoints of improving the dispersion stability of the water-based ink and improving the jetting and decapping properties, and from the same viewpoints as above, is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 5% by mass or less, still more preferably 3% by mass or less, and even more preferably 2.5% by mass or less. The mass ratio of the content of the aluminum lake pigment (A) to the total content of the aluminum lake pigment (A) and the pigment dispersant (B) in the water-based ink of the present invention, [aluminum lake pigment (A) / [aluminum lake pigment (A) + pigment dispersant (B)]], is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, still more preferably 0.40 or more, still more preferably 0.50 or more, and still more preferably 0.60 or more, from the viewpoints of improving the dispersion stability, jetting property, and decap property of the water-based ink; and from the same viewpoints as above, is preferably 0.90 or less, more preferably 0.85 or less, even more preferably 0.80 or less, still more preferably 0.75 or less, and still more preferably 0.70 or less.

[0060] (Water-soluble organic solvent (C) content) The content of the water-soluble organic solvent (C) in the water-based ink of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of improving jetting performance and decap performance, and from the same viewpoint as above, is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0061] (Water content) From the viewpoint of improving jetting performance and decap performance, the water content in the water-based ink of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 70% by mass or more, and from the same viewpoint as above, the water content is preferably 90% by mass or less, more preferably 85% by mass or less.

[0062] (Surfactant content) When the water-based ink of the present invention contains a surfactant, the content of the surfactant in the water-based ink is, from the viewpoint of dot diameter, preferably 0.01% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.05% by mass or more, and still more preferably 0.07% by mass or more, and, from the same viewpoint as above, is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and still more preferably 0.5% by mass or less.

[0063] (Water-based ink properties) The volume average particle size of the water-based ink of the present invention is preferably 200 nm or less, more preferably 170 nm or less, even more preferably 150 nm or less, and even more preferably 140 nm or less, from the viewpoint of improving jetting performance and decap performance, and is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 90 nm or more, and even more preferably 110 nm or more, from the viewpoint of productivity of the water-based ink. The volume average particle size of the water-based ink is measured by the method described in the Examples. From the viewpoint of improving jetting and decapability, the viscosity of the water-based ink of the present invention at 20°C is preferably 1.0 mPa·s or more, more preferably 1.5 mPa·s or more, even more preferably 2.0 mPa·s or more, still more preferably 2.5 mPa·s or more, even more preferably 3.0 mPa·s or more, and even more preferably 3.5 mPa·s or more, and from the same viewpoints as above, it is preferably 12 mPa·s or less, more preferably 9.0 mPa·s or less, even more preferably 7.0 mPa·s or less, still more preferably 5.5 mPa·s or less, and even more preferably 4.5 mPa·s or less. The viscosity of the water-based ink at 20°C is measured by the method described in the examples. From the viewpoint of dispersion stability of the water-based ink, the pH of the water-based ink of the present invention at 20°C is preferably 4 or more, more preferably 4.5 or more, and even more preferably 5 or more, and from the viewpoint of jetting ability, it is preferably 9 or less, more preferably 8 or less, even more preferably 7.5 or less, and even more preferably 7 or less. The pH of the water-based ink at 20°C is measured by the method described in the examples.

[0064] (Inkjet recording method) The ink-jet recording method using the water-based ink of the present invention is preferably a method in which the water-based ink is ejected onto a recording medium using an ink-jet recording apparatus. Since the aluminum lake pigment (A) according to the present invention has a relatively low specific gravity, an inkjet recording apparatus without a dispersing means may be used. However, it is preferable to use an inkjet recording apparatus with a dispersing means for dispersing the aluminum lake pigment (A) in the water-based ink.

[0065] When the inkjet recording apparatus has a dispersing means, the inkjet recording method preferably includes step 1 of redispersing the water-based ink by the dispersing means, and step 2 of ejecting the water-based ink redispersed in step 1 onto a recording medium. By using the water-based ink in the inkjet recording method, even if the aluminum lake pigment (A) dispersed in the water-based ink settles or aggregates during printing or after a printing pause, the aluminum lake pigment (A) can be easily redispersed by the dispersing means of the inkjet recording apparatus, thereby improving dischargeability and decap characteristics. From this perspective, the inkjet recording apparatus preferably has at least an ink discharge means, a container (ink-filled container) for filling the water-based ink, an ink flow path, and a dispersing means for dispersing the aluminum lake pigment (A) contained in the water-based ink. The ink-filled container may further have an ink pre-filled container.

[0066] As the ink ejection means, there are methods of ejecting ink using a thermal or piezo inkjet ejection head, but the thermal method is preferred from the viewpoint of ejection properties and decap characteristics. That is, in the inkjet recording method of the present invention, a method is preferred in which the water-based ink is used for a thermal method, a container filled with the water-based ink is mounted on an inkjet recording apparatus, and the water-based ink is ejected using a thermal ejection head to record on a recording medium. The dispersion means is not particularly limited as long as it is a means for dispersing the aluminum lake pigment (A) in the aqueous medium of the aqueous ink by mechanical force.

[0067] The recording medium is not particularly limited, and examples thereof include recording media used in printing in the food, medical, and cosmetic fields. Examples thereof include highly water-absorbent recording media such as plain paper and fine paper; low water-absorbent recording media such as art paper, coated paper, and synthetic resin film; and metals. Furthermore, when the water-based ink of the present invention is used as a cosmetic composition, it can also be applied to hair, skin (including lips), or nails as a recording medium. Preferred embodiments of the cosmetic composition that can be used are as exemplified for the pigment dispersion described above. Furthermore, when the water-based ink of the present invention is used as a water-based ink for printing to decorate the surface of a packaging container that contains cosmetics, the recording medium may be, as described above, various packaging containers such as various compact cases that contain powder cosmetics such as foundation, eye shadow, blush, and eyebrow pencil. [Example]

[0068] In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The various physical properties were measured by the following methods.

[0069] (1) Measurement of the acid value of pigment dispersant (B) Measurement was carried out in accordance with the potentiometric titration method of JIS K 0070.

[0070] (2) Measurement of the weight-average molecular weight of pigment dispersant (B) Using a solution of 0.2 M phosphate buffer / acetonitrile = 9 / 1 (volume ratio) as the eluent, measurements were performed by gel permeation chromatography (GPC apparatus (HLC-8320GPC) manufactured by Tosoh Corporation, columns (PW+G4000PW+G2500PW) manufactured by Tosoh Corporation, flow rate: 1.0 mL / min, temperature: 40°C) using polyethylene glycol, the weight-average molecular weight of which had been previously determined to be monodisperse, as the standard substance.

[0071] (3) Measurement of solid concentration 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 ml polypropylene container (φ=40 mm, height=30 mm), and approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed and maintained at 105°C for 2 hours to remove volatiles. The mixture was then left in the desiccator for a further 15 minutes, after which the mass was measured. The mass of the sample after devolatilization was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration (%).

[0072] (4) Measurement of the volume average particle size of water-based pigment dispersions or water-based inks The volume average particle size of the water-based pigment dispersion or water-based ink was measured using the zeta potential / particle size measurement system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) at a concentration of approximately 5 × 10 -3 %, the dispersion was placed in a measurement cell, and measurements were taken at a temperature of 25°C, with 100 cumulative cycles, and the refractive index of water (1.333) was entered as the refractive index of the dispersion solvent.

[0073] (5) pH of water-based pigment dispersion or water-based ink The pH of the aqueous pigment dispersion or ink at 20°C was measured using a tabletop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.). (6) Viscosity of water-based pigment dispersion or water-based ink The viscosity was measured at 20°C using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34' x R24, rotation speed 50 rpm).

[0074] Production Example 1 (Production of a solution of pigment dispersant (B-1)) A 2 L glass reaction vessel equipped with a dropping funnel was charged with 233 g of water, and the temperature was raised to 80° C. under a nitrogen atmosphere. Next, under a nitrogen gas atmosphere, three liquids were gradually added dropwise into the reaction vessel simultaneously over 90 minutes: a monomer solution of 17.3 g of methacrylic acid and 82.7 g of methoxypolyethylene glycol monomethacrylate (average number of moles of ethylene oxide (EO) added, n=2, manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Ester M-20G") as dropping solution 1; 13.5 g of a 7% aqueous solution of 2-mercaptoethanol as dropping solution 2; and 16 g of a 6% aqueous solution of ammonium persulfate as dropping solution 3. Next, 5.5 g of a 6% aqueous solution of ammonium persulfate was gradually added dropwise to the reaction vessel over 30 minutes, and after the completion of the addition, the mixture was aged for 1 hour at 80° C. Thereafter, the mixture was cooled to 40° C., and 1.68 g of a 48% aqueous solution of sodium hydroxide (amount of sodium hydroxide: 806 mg) was added to neutralize the mixture, and water was added to adjust the solids concentration to 20%, to obtain a solution of pigment dispersant (B-1).

[0075] Production Examples 2 to 15 (Production of Solutions of Pigment Dispersants (B-2) to (B-15)) Solutions of pigment dispersants (B-2) to (B-15) were obtained in the same manner as in Production Example 1, except that the monomer compositions and amounts of sodium hydroxide were changed to those shown in Table 1. The details of the monomers in Table 1 are as follows: MPEGMAA (n=2): Methoxypolyethyleneglycol monomethacrylate (average number of EO moles added = 2, "NK Ester M-20G" manufactured by Shin-Nakamura Chemical Co., Ltd.) MPEGMAA (n=4): Methoxypolyethyleneglycol monomethacrylate (average number of EO moles added = 4, "NK Ester M-40G" manufactured by Shin-Nakamura Chemical Co., Ltd.) MPEGMAA (n=9): Methoxypolyethyleneglycol monomethacrylate (average number of EO moles added = 9, "NK Ester M-90G" manufactured by Shin-Nakamura Chemical Co., Ltd.) MPEGMAA (n=23): Methoxypolyethyleneglycol monomethacrylate (average number of EO moles added = 23, "NK Ester M-230G" manufactured by Shin-Nakamura Chemical Co., Ltd.) MPEGMAA (n=45): Methoxypolyethyleneglycol monomethacrylate (average number of EO moles added = 45, "NK Ester M-450G" manufactured by Shin-Nakamura Chemical Co., Ltd.) MPEGMAA (n=90): Methoxypolyethyleneglycol monomethacrylate (average EO molar addition number=90, "NK Ester M-900G" manufactured by Shin-Nakamura Chemical Co., Ltd.) MPEGMAA (n=120): methoxypolyethylene glycol monomethacrylate (average number of moles of EO added=120, used was that produced in Production Example M1 below) 50POEP-800B (n=14): Octoxy (polyethylene glycol / polypropylene glycol) methacrylate (block type) (average number of EO moles added = 8, average number of propylene oxide (PO) moles added = 6, NOF Corporation "Blenmar 50POEP-800B")

[0076] Production Example M1 (Production of methoxypolyethylene glycol monomethacrylate (n=120)) Using polyethylene glycol monomethyl ether (weight average molecular weight 5,312) having an average number of moles of EO added of 120 melted at 80°C, the target product, methoxypolyethylene glycol monomethacrylate (average number of moles of EO added = 120), was obtained by the method described in Example 1 (Step 1) of JP-A-11-228636.

[0077] [Table 1]

[0078] Comparative manufacturing examples C1~C2 The following 25% aqueous polyacrylic acid solution or 35% sodium polyacrylate and water were mixed in the ratios shown in Table 2 to obtain solutions of pigment dispersants (B-C1) to (B-C2) with a solid content of 20%. 25% polyacrylic acid aqueous solution (unneutralized polyacrylic acid, Fujifilm Wako Pure Chemical Industries, Ltd., weight-average molecular weight 50,000) 35% sodium polyacrylate aqueous solution (100 mol% neutralized sodium polyacrylate, Fujifilm Wako Pure Chemical Industries, Ltd., weight-average molecular weight 60,000)

[0079] [Table 2]

[0080] Example 1-1 (Water-based pigment dispersion P-1) A 250 mL polypropylene bottle was charged with 35 parts of the pigment dispersant (B-1) solution (20% solids concentration) obtained in Production Example 1 (7 parts active pigment dispersant B-1), 13 parts of aluminum lake pigment A-1 ["BC Yellow No. 4 AL" (Yellow No. 4 Aluminum Lake, manufactured by Kishi Kasei Co., Ltd.)], and 52 parts of water. 200 g of zirconia beads with a diameter of 50 μm were added, and the mixture was dispersed in a paint shaker at 25° C. for 15 hours. The zirconia beads were removed using a 75 μm mesh, and the solids concentration was adjusted with water to obtain aqueous pigment dispersion P-1 (20% solids concentration).

[0081] Examples 1-2 to 1-15 and Comparative Examples 1-C1 to 1-C2 (Water-based Pigment Dispersions P-2 to P-15 and P-C1 to P-C2) Water-based pigment dispersions P-2 to P-15 and P-C1 to P-C2 (solid content concentration 20%) were obtained in the same manner as in Example 1-1, except that the pigment dispersant (B) was changed to a solution shown in Table 3. The obtained water-based pigment dispersions were evaluated as follows.

[0082] [evaluation] <Effect of reducing the dispersed particle size of pigment> [Volume average particle size] The volume average particle size of each of the aqueous pigment dispersions of Examples 1-1 to 1-15 and Comparative Examples 1-C1 to 1-C2 was measured. The results are shown in Table 3. The smaller the volume average particle size, the greater the effect of reducing the dispersed particle size of the pigment. A volume average particle size of 200 nm or less is excellent in reducing the dispersed particle size of the pigment.

[0083] 〔viscosity〕 The viscosity of each of the aqueous pigment dispersions of Examples 1-1 to 1-15 and Comparative Examples 1-C1 to 1-C2 was measured. The results are shown in Table 3. The viscosity of each of the aqueous pigment dispersions P-1 to P-15 of the examples was 20 mPa s or less, and when the aqueous pigment dispersions were filtered through a cellulose acetate syringe filter with a pore size of 5 μm, no decrease in filtration rate due to pressure loss occurred, which also indicates that the dispersed particle size of the pigment was reduced. On the other hand, the comparative water-based pigment dispersions P-C1 and P-C2 had high viscosities, and when an attempt was made to filter them using the same method as above, pressure loss made it difficult to pass the liquid through.

[0084] <Evaluation of room temperature storage stability> The aqueous pigment dispersions of Examples 1-1 to 1-15 and Comparative Examples 1-C1 to 1-C2 were allowed to stand at room temperature (25°C), and the presence or absence of sediment was visually confirmed, and the room temperature storage stability was evaluated according to the following evaluation criteria. The results are shown in Table 3. A: No sediment was found even after leaving it at room temperature for one week. A-: The formation of sediment was confirmed 24 hours after the start of leaving it at room temperature, but no clear supernatant layer was confirmed after leaving it at room temperature for one week. B: The formation of a precipitate was confirmed 24 hours after the start of standing at room temperature, and the formation of a clear supernatant layer was confirmed after standing at room temperature for one week.

[0085] <Evaluation of high-temperature storage stability> Each of the aqueous pigment dispersions of Examples 1-1 to 1-15 and Comparative Examples 1-C1 to 1-C2 was sealed in a glass screw tube and allowed to stand in a thermostatic bath at 60°C for 4 weeks, after which the volume average particle size and viscosity were measured, and the particle size retention rate (%) and viscosity retention rate (%) were calculated using the following formulas. The results are shown in Table 3. The closer the particle size retention rate (%) and viscosity retention rate (%) are to 100%, the more excellent the high-temperature storage stability. Particle size retention rate (%) = [Volume average particle size after storage (nm) / Volume average particle size before storage (nm)] x 100 Viscosity retention rate (%) = [Viscosity after storage (mPa·s) / Viscosity before storage (mPa·s)] x 100 Furthermore, when the fluidity of the aqueous pigment dispersions was visually confirmed after storage in a thermostatic chamber at 60°C for 4 weeks, it was confirmed that the aqueous pigment dispersions P-1 to P-15 of the examples were able to maintain their fluidity even after storage. On the other hand, the aqueous pigment dispersions P-C1 and P-C2 of the comparative examples were unable to maintain fluidity and gelled after being stored for 4 weeks in a thermostatic chamber at 60° C. Furthermore, an attempt was made to measure the volume average particle size of the gelled samples, but it was not possible to measure it.

[0086] <Evaluation of high-temperature storage stability when diluted> The aqueous pigment dispersions of Examples 1-1 to 1-15 and Comparative Examples 1-C1 to 1-C2 were each diluted two-fold with ion-exchanged water to prepare dispersions with a solids concentration of 10%. Each dispersion was then sealed in a glass screw tube and allowed to stand in a thermostatic chamber at 60°C for four weeks. The volume average particle size was then measured, and the particle size retention rate (%) was calculated using the formula above. The results are shown in Table 3. Furthermore, when the fluidity of the aqueous pigment dispersions was visually confirmed after storage in a thermostatic chamber at 60°C for 4 weeks, it was confirmed that the aqueous pigment dispersions P-1 to P-15 of the examples maintained their fluidity even after storage. On the other hand, the aqueous pigment dispersions P-C1 and P-C2 of the comparative examples were unable to maintain fluidity and gelled after being stored in a thermostatic chamber at 60°C for 4 weeks. Furthermore, although an attempt was made to measure the volume average particle size of the gelled samples, it was not possible to do so. This poses a practical problem.

[0087] [Table 3]

[0088] From Table 3, it can be seen that the aqueous pigment dispersions of the Examples have a higher effect of reducing the dispersed particle size of the pigment than the Comparative Examples, and also have excellent storage stability at room temperature. Furthermore, in an evaluation of high-temperature storage stability, the aqueous pigment dispersions of the Examples showed particle size retention rates of less than 110% when diluted to a solids concentration of 10%, indicating that an aqueous pigment dispersion with a solids concentration of 10% can be stored for long periods even at high temperatures. This shows that the pigment dispersions of the present invention can be made to have excellent high-temperature storage stability by diluting them to a level that does not interfere with their incorporation into ink.

[0089] Example 2-1 (Water-based ink I-1) The aqueous pigment dispersion P-1 (20% solids concentration) obtained in Example 1-1 was mixed with the following formulation to obtain a 4% aluminum lake pigment (A) and a 2.15% pigment dispersant (B) in the aqueous ink. The resulting mixture was filtered through a 20 mL needleless syringe fitted with a 1.2 μm pore cellulose acetate filter (2.5 cm outer diameter, manufactured by Sartorius) to remove coarse particles, yielding aqueous ink I-1. The viscosity of aqueous ink I-1 at 20°C was 4.2 mPa s. <Composition> Water-based pigment dispersion P-1 (containing 4 parts of aluminum lake pigment A-1 and 2.15 parts of pigment dispersant B-1) 30.77 parts Glycerin (boiling point 290°C) 10 parts Liponic EG-1 (trade name of Lipo Chemicals, glycerin-modified EO adduct (average number of EO moles added: 26), boiling point: 381°C) 5 parts 1,2-Hexanediol (boiling point 223°C) 3 parts Ion-exchanged water 51.23 parts

[0090] Examples 2-2 to 2-15 and Comparative Examples 2-C1 to 2-C2 (Water-Based Inks I-2 to I-15 and I-C1 to I-C2) Each water-based ink was obtained in the same manner as in Example 2-1, except that the water-based pigment dispersions shown in Table 4 were used instead of Water-based Pigment Dispersion P-1, the amount of glycerin was adjusted to the amount shown in Table 4 so that the viscosity at 20°C was between 4.0 and 4.4 mPa s, and the remaining amount of water was adjusted. However, in Comparative Examples 2-C1 and 2-C2, the viscosity could not be reduced sufficiently by simply adjusting the amount of glycerin, and the viscosities were 9.4 mPa and 15.2 mPa s, respectively.

[0091] <Evaluation of ejection properties> Each of the water-based inks of Examples 2-1 to 2-15 and Comparative Examples 2-C1 to 2-C2 was filled into a handheld printer cartridge "HC-01K" (manufactured by Ricoh Co., Ltd.) whose interior had been thoroughly washed with ion-exchanged water and dried in advance, and a Ricoh Handheld Printer (product name, manufactured by Ricoh Co., Ltd.) was used to print a solid image measuring 12.8 mm high x 30 mm wide at 100% duty on plain paper as the recording medium. All of the water-based inks I-1 to I-15 of the examples could be ejected without any problems. On the other hand, the comparative water-based inks I-C1 and I-C2 did not achieve the desired viscosity even when the glycerin content in the ink was reduced to 0%, and the ink did not fill the ink head flow path inside the cartridge, making it impossible to evaluate the ejection performance. Table 4 shows the results using the following notation. A: The ink was ejected without any problems, and a solid image was printed. B: Ink could not be ejected and a solid image could not be printed.

[0092] <Evaluation of decap characteristics> Using ink cartridges filled with the water-based inks of Examples 2-1 to 2-15 and Comparative Examples 2-C1 to 2-C2, a 12.8 mm high x 30 mm wide solid image was printed at 100% duty. The nozzle surface was then wiped with an AZPURE wiper (manufactured by AS ONE Corporation) moistened with ion-exchange water. The nozzle surface was then left facing downwards for a predetermined period of time in a windless environment at 25°C and 50% humidity. A 12.8 mm high x 30 mm wide solid image was then printed again at 100% duty. The degree of smearing at the start of printing was observed and evaluated as the time required for maintenance. The longer the time required for maintenance, the better the decap performance. The results are shown in Table 4. [Evaluation criteria (time required for maintenance)] 120 seconds: No smearing was observed even after leaving the nozzle surface for 120 seconds and printing. 90 seconds: No smearing was observed when the nozzle surface was left for 90 seconds, but smearing occurred when left for 120 seconds. 60 seconds: No smearing was observed when the nozzle surface was left for 60 seconds, but smearing occurred when left for 90 seconds. 30 seconds: No smearing was observed when the nozzle surface was left for 30 seconds, but smearing occurred when left for 60 seconds. 15 seconds: No smearing was observed when the nozzle surface was left for 15 seconds, but smearing occurred when left for 30 seconds. 0 seconds: No smearing was observed immediately after wiping, but smearing occurred when the nozzle surface was left for 15 seconds. Non-discharge: Discharge was not possible.

[0093] [Table 4]

[0094] From Table 4, it can be seen that the water-based inks of the examples are superior in ejection properties and decap characteristics to the comparative examples.

[0095] Examples 3-1 to 3-7 (Water-based Pigment Dispersions P-16 to P-22) In Example 1-1, water-based pigment dispersions P-16 to P-22 (solid concentration 20%) were obtained in the same manner as in Example 1-1, except that the amount of aluminum lake pigment (A) and the type and amount of pigment dispersant (B) solution as solids were changed as shown in Table 5.

[0096] [evaluation] <Effect of reducing the dispersed particle size of pigment> [Volume average particle size] The volume average particle size of each of the water-based pigment dispersions of Examples 3-1 to 3-7 was measured. The results are shown in Table 5. 〔viscosity〕 The viscosity of each of the aqueous pigment dispersions of Examples 3-1 to 3-7 was measured, and the results are shown in Table 5. The viscosity of water-based pigment dispersions P-16 to P-22 was all 20 mPa s or less, and when the water-based pigment dispersions were filtered through a cellulose acetate syringe filter with a pore size of 5 μm, there was no decrease in filtration rate due to pressure loss. This also indicates that the dispersed particle size of the pigment was reduced.

[0097] <Evaluation of room temperature storage stability> The aqueous pigment dispersions of Examples 3-1 to 3-7 were allowed to stand at room temperature, and the presence or absence of sediment was visually confirmed, and the room temperature storage stability was evaluated according to the above-mentioned evaluation criteria. The results are shown in Table 5.

[0098] <Evaluation of high-temperature storage stability> Each of the aqueous pigment dispersions of Examples 3-1 to 3-7 was sealed in a glass screw tube and allowed to stand in a thermostatic bath at 60°C for 4 weeks, after which the particle size was measured and the particle size retention rate (%) and viscosity retention rate (%) were calculated using the above formula. The results are shown in Table 5. Furthermore, when the fluidity of the water-based pigment dispersions after storage was checked visually, it was confirmed that water-based pigment dispersions P-16 to P-22 maintained their fluidity after storage. <Evaluation of high-temperature storage stability when diluted> Each of the aqueous pigment dispersions of Examples 3-1 to 3-7 was diluted in the same manner as above, and allowed to stand in a thermostatic chamber at 60°C for 4 weeks, after which the particle size was measured and the particle size retention rate (%) was calculated using the formula above. The results are shown in Table 5. Furthermore, when the fluidity of the water-based pigment dispersions after storage was checked visually, it was confirmed that the water-based pigment dispersions P-16 to P-22 of the examples maintained their fluidity even after storage.

[0099] [Table 5]

[0100] Table 5 shows that the aqueous pigment dispersions of the Examples have a high effect of reducing the particle size of dispersed pigments and are also excellent in storage stability at room temperature. Furthermore, in an evaluation of high-temperature storage stability, the aqueous pigment dispersions of the Examples showed particle size retention rates of less than 110% when diluted to a solids concentration of 10%, indicating that an aqueous pigment dispersion with a solids concentration of 10% can be stored for long periods even at high temperatures. This shows that the pigment dispersions of the present invention can be made to have excellent high-temperature storage stability by diluting them to a level that does not interfere with their incorporation into ink.

[0101] Examples 4-1 to 4-7 (Water-based Inks I-16 to I-22) Each water-based ink was prepared in the same manner as in Example 2-1, except that the water-based pigment dispersions shown in Table 6 were used instead of water-based pigment dispersion P-1, the amount of glycerin was adjusted to the amount shown in Table 6 so that the viscosity at 20°C was between 4.0 and 4.4 mPa s, and the remaining amount of water was adjusted accordingly. The resulting water-based inks were then evaluated for jetting performance and decap characteristics as described above. The results are shown in Table 6.

[0102] [Table 6]

[0103] From Table 6, it can be seen that the water-based inks of the examples have excellent ejection properties and decap characteristics.

[0104] Production Examples 16 to 23 (Production of Solutions of Pigment Dispersants (B-16) to (B-23)) Solutions of pigment dispersants (B-16) to (B-23) were obtained in the same manner as in Production Example 1, except that the monomer compositions and the amount of sodium hydroxide used for neutralization shown in Table 7 were changed.

[0105] [Table 7]

[0106] Examples 5-1 to 5-8 (Water-based Pigment Dispersions P-31 to P-38) Water-based pigment dispersions P-31 to P-38 (solid concentration 20%) were obtained in the same manner as in Example 1-1, except that the pigment dispersant (B) was changed to a solution shown in Table 8.

[0107] [evaluation] <Evaluation of the effect of reducing the dispersed particle size of pigments> [Volume average particle size] The volume average particle size of each of the water-based pigment dispersions of Examples 5-1 to 5-8 was measured. The results are shown in Table 8. 〔viscosity〕 The viscosity of each of the aqueous pigment dispersions of Examples 5-1 to 5-8 was measured. The results are shown in Table 8. The viscosity of water-based pigment dispersions P-31 to P-38 was all 20 mPa s or less, and when the water-based pigment dispersions were filtered through a cellulose acetate syringe filter with a pore size of 5 μm, there was no decrease in filtration rate due to pressure loss. This also indicates that the dispersed particle size of the pigment was reduced.

[0108] <Evaluation of room temperature storage stability> The aqueous pigment dispersions of Examples 5-1 to 5-8 were allowed to stand at room temperature, and the presence or absence of sediment was visually confirmed, and the room temperature storage stability was evaluated according to the above-mentioned evaluation criteria. The results are shown in Table 8.

[0109] <Evaluation of high-temperature storage stability> Each of the aqueous pigment dispersions of Examples 5-1 to 5-8 was sealed in a glass screw tube and allowed to stand in a thermostatic bath at 60°C for 4 weeks, after which the particle size was measured and the particle size retention rate (%) and viscosity retention rate (%) were calculated using the above formula. The results are shown in Table 8. Furthermore, when the fluidity of the aqueous pigment dispersions was visually confirmed after storage in a thermostatic chamber at 60°C for 4 weeks, it was confirmed that the fluidity of aqueous pigment dispersions P-31 to P-38 was maintained after storage.

[0110] [Table 8]

[0111] Table 8 shows that the aqueous pigment dispersions of the Examples have a high effect of reducing the particle size of dispersed pigments and are also excellent in storage stability at room temperature. Furthermore, in the evaluation of high-temperature storage stability, the water-based pigment dispersions of the Examples had particle size retention rates of less than 110% and viscosity retention rates of 90% or more and 110% or less, which indicates that even highly concentrated water-based pigment dispersions with a solid content of 20% can be stored at high temperatures for long periods of time.

[0112] Examples 6-1 to 6-8 (Water-based Inks I-31 to I-38) Each water-based ink was prepared in the same manner as in Example 2-1, except that the water-based pigment dispersions shown in Table 9 were used instead of water-based pigment dispersion P-1, the amount of glycerin was adjusted to the amount shown in Table 9 so that the viscosity at 20°C was between 4.0 and 4.4 mPa s, and the remaining amount of water was adjusted. The resulting water-based inks were then evaluated for jetting performance and decap performance as described above. The results are shown in Table 9.

[0113] [Table 9]

[0114] From Table 9, it can be seen that the water-based inks of the examples have excellent ejection properties and decap characteristics.

[0115] Production Example 24 (Production of a solution of pigment dispersant (B-24)) A solution of pigment dispersant (B-24) was obtained in the same manner as in Production Example 1, except that the monomer composition and the amount of sodium hydroxide used for neutralization shown in Table 10 were changed.

[0116] [Table 10]

[0117] Examples 7-1 to 7-3 (Water-based Pigment Dispersions P-41 to P-43) In Example 1-4, aluminum lake pigment A-1 was replaced with aluminum lake pigment A-2 to A-4, the type of pigment dispersant was replaced with the pigment dispersant shown in Table 11 instead of B-4, and in Example 7-3, the blending amounts were changed to those shown in Table 11. In the same manner as in Example 1-4, water-based pigment dispersions P-41 to P-43 (solid concentration 20%) were obtained. A-2: "SunCROMA FD&C Yellow 6 AL Lake" (Yellow No. 5 aluminum lake pigment, manufactured by Sun Chemical) A-3: "SunCROMA FD&C Blue 1 AL Lake" (Blue No. 1 aluminum lake pigment, manufactured by Sun Chemical) A-4: "SunCROMA FD&C Red 28 AL Lake" (Red No. 104-1 aluminum lake pigment, manufactured by Sun Chemical) [evaluation] <Evaluation of the effect of reducing the dispersed particle size of pigments> [Volume average particle size] The volume average particle size of each of the water-based pigment dispersions of Examples 7-1 to 7-3 was measured. The results are shown in Table 11. 〔viscosity〕 The viscosity of each of the aqueous pigment dispersions of Examples 7-1 to 7-3 was measured, and the results are shown in Table 11. The viscosity of water-based pigment dispersions P-41 to P-43 was all 20 mPa s or less, and when the water-based pigment dispersions were filtered through a cellulose acetate syringe filter with a pore size of 5 μm, there was no decrease in filtration rate due to pressure loss. This also indicates that the dispersed particle size of the pigment was reduced.

[0118] <Evaluation of room temperature storage stability> The aqueous pigment dispersions of Examples 7-1 to 7-3 were allowed to stand at room temperature, and the presence or absence of sediment was visually confirmed, and the room temperature storage stability was evaluated according to the above-mentioned evaluation criteria. The results are shown in Table 11.

[0119] <Evaluation of high-temperature storage stability> Each of the aqueous pigment dispersions of Examples 7-1 to 7-3 was sealed in a glass screw tube and allowed to stand in a thermostatic bath at 60°C for 4 weeks, after which the particle size was measured and the particle size retention rate (%) and viscosity retention rate (%) were calculated using the above formula. The results are shown in Table 11. Furthermore, when the fluidity of the water-based pigment dispersions after storage was checked visually, it was confirmed that water-based pigment dispersions P-41 to P-43 maintained their fluidity after storage. <Evaluation of high-temperature storage stability when diluted> Each of the aqueous pigment dispersions of Examples 7-1 to 7-3 was diluted in the same manner as above, and allowed to stand in a thermostatic chamber at 60°C for 4 weeks, after which the particle size was measured and the particle size retention rate (%) was calculated using the formula above. The results are shown in Table 11. Furthermore, when the fluidity of the aqueous pigment dispersions was visually confirmed after storage in a thermostatic chamber at 60°C for 4 weeks, it was confirmed that the aqueous pigment dispersions P-41 to P-43 of the examples maintained their fluidity even after storage.

[0120] [Table 11]

[0121] From Table 11, it can be seen that the water-based pigment dispersions of the Examples have a high effect of reducing the dispersed particle size of the pigment, and also have excellent storage stability at room temperature. Furthermore, in the evaluation of high-temperature storage stability, the water-based pigment dispersions of the Examples had particle size retention rates of less than 110% and viscosity retention rates of 90% or more and 110% or less, which indicates that even highly concentrated pigment dispersions with a solid content of 20% can be stored at high temperatures for long periods of time. Furthermore, in an evaluation of high-temperature storage stability, the aqueous pigment dispersions of the Examples showed particle size retention rates of less than 110% even when diluted to a solids concentration of 10%, demonstrating that an aqueous pigment dispersion with a solids concentration of 10% can be stored for long periods even at high temperatures. This shows that the pigment dispersions of the present invention can be made excellent in high-temperature storage stability by diluting them to a level that does not interfere with their incorporation into ink.

[0122] Examples 8-1 to 8-3 (Water-based Inks I-41 to I-43) Each water-based ink was prepared in the same manner as in Example 2-1, except that instead of water-based pigment dispersion P-1, the water-based pigment dispersions shown in Table 12 were used, the amounts of glycerin and Liponic EG-1 (glycerin-modified EO adduct) were adjusted as necessary to the amounts shown in Table 12 so that the viscosity at 20°C was between 4.0 and 4.4 mPa·s, and the remaining amount of water was adjusted. The resulting water-based inks were then evaluated for jetting performance and decap performance as described above. The results are shown in Table 12.

[0123] [Table 12]

[0124] From Table 12, it can be seen that the water-based inks of the examples have excellent jetting properties and decap characteristics. [Industrial Applicability]

[0125] According to the present invention, it is possible to provide an aqueous pigment dispersion in which the dispersed particle size of the pigment is small and which has excellent storage stability at room temperature and at high temperatures, and an aqueous ink containing the aqueous pigment dispersion has excellent ejection properties and decap characteristics, and is therefore suitable as an aqueous ink for inkjet recording. Because the aqueous pigment dispersion of the present invention contains the pigment (A) in the form of an aluminum lake, it can be used in the food, medical, cosmetic, and other fields from the standpoint of safety, and can also exert similar effects when applied to the skin, hair, or nails.

Claims

1. An aqueous pigment dispersion containing an aluminum lake pigment (A) and a pigment dispersant (B), the pigment dispersant (B) is a polymer containing a structural unit derived from an anionic group-containing monomer (b-1) and a structural unit derived from a hydrophilic nonionic monomer (b-2) containing an oxyalkylene group, and the total content of the structural units derived from the monomer (b-1) and the structural units derived from the monomer (b-2) in the polymer is 80 mass% or more.

2. 2. The water-based pigment dispersion according to claim 1, wherein the aluminum lake pigment (A) is at least one selected from Yellow No. 4 Aluminum Lake, Yellow No. 5 Aluminum Lake, Blue No. 1 Aluminum Lake, and Red No. 104-(1) Aluminum Lake.

3. The aqueous pigment dispersion according to claim 1 or 2, wherein the hydrophilic nonionic monomer (b-2) has a polyoxyalkylene group, and the average number of moles of alkylene oxide added to the polyoxyalkylene group is 2 or more and 120 or less.

4. 4. The aqueous pigment dispersion according to claim 1, wherein the hydrophilic nonionic monomer (b-2) is an alkoxypolyalkylene glycol mono(meth)acrylate.

5. The aqueous pigment dispersion according to any one of claims 1 to 4, wherein a content of the structural units derived from the hydrophilic nonionic monomer (b-2) in all structural units of the pigment dispersant (B) is 50% by mass or more and 97% by mass or less.

6. The aqueous pigment dispersion according to any one of claims 1 to 5, wherein a content of the structural units derived from the anionic group-containing monomer (b-1) in all structural units of the pigment dispersant (B) is 3% by mass or more and 50% by mass or less.

7. 7. The aqueous pigment dispersion according to claim 1, wherein a mass ratio of a content of the aluminum lake pigment (A) to a total content of the aluminum lake pigment (A) and the pigment dispersant (B) [aluminum lake pigment (A) / [aluminum lake pigment (A) + pigment dispersant (B)]] is 0.30 or more and 0.90 or less.

8. 8. The water-based ink for ink-jet printing according to claim 1, wherein the pigment dispersant (B) has an acid value of 25 mgKOH / g or more and 350 mgKOH / g or less.

9. The aqueous pigment dispersion according to any one of claims 1 to 8, wherein at least a portion of the anionic groups of the pigment dispersant (B) is neutralized, and the degree of neutralization is from 5 mol % to 70 mol %.

10. 10. The aqueous pigment dispersion according to claim 1, wherein the water content is 50% by mass or more and 95% by mass or less.

11. A water-based ink for ink-jet printing, comprising the water-based pigment dispersion according to any one of claims 1 to 10 and a water-soluble organic solvent (C).

12. The water-based ink for ink-jet printing according to claim 11, which is for use in a thermal system.

13. 13. The water-based ink for ink-jet printing according to claim 11, wherein the content of the aluminum lake pigment (A) is 2% by mass or more.

14. The water-based ink for ink-jet printing according to any one of claims 11 to 13, which has a pH of 5 or more and 7 or less.

15. Use of the water-based pigment dispersion according to any one of claims 1 to 10 in a water-based ink for ink-jet printing.

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