Aqueous pigment dispersion

Abstract

To provide an aqueous pigment dispersion having superior filterability even following prolonged storage.SOLUTION: An aqueous pigment dispersion comprises crosslinked polymer particles containing a pigment, and a polyoxyethylene glycol monoether (I) represented by a formula (1). The content of the polyoxyethylene glycol monoether (I) is 0.1 mass% or more and 4.0 mass% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous pigment dispersion.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from a very fine inkjet nozzle onto a recording medium and adhered to obtain a recording in which characters and images are recorded. This method is easy and inexpensive to achieve full color, and in addition to paper recording media such as plain paper and coated paper, synthetic resin films and the like can be used as the recording medium, and there are many advantages such as non-contact with the recording medium, so it has become extremely popular. In recent years, in order to impart weather resistance and water resistance to the obtained recordings, pigments are widely used as colorants, and aqueous inks with less environmental impact are used. In such aqueous inks, an aqueous pigment dispersion in which pigments are finely dispersed in an aqueous medium is used when preparing the ink. However, since aqueous inks and aqueous pigment dispersions contain a large amount of water and have a high water activity, deterioration due to the generation of microorganisms such as filamentous fungi becomes a problem. Therefore, in order to overcome such problems, studies have been made to enhance the antiseptic properties of aqueous inks and aqueous pigment dispersions.

[0003] For example, Patent Document 1 describes a method for producing an aqueous dispersion for inkjet recording, which has a step of heat-sterilizing an aqueous dispersion containing 10 to 30% by weight of water-insoluble polymer particles containing a colorant, 3 to 10% by weight of a compound represented by a specific formula (R 10 -O(CH2CH2O) a -H, where R 10 represents a hydrocarbon group having 3 to 6 carbon atoms and a is a number from 2 to 5.), and a preservative at 60°C or higher.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] However, it has been found that in the technique of Patent Document 1, aggregates may be generated after long-term storage of the aqueous dispersion for inkjet recording. When such an aqueous dispersion for inkjet recording is used for the preparation of ink, it causes a decrease in the filterability due to the sedimentation of aggregates. Therefore, there is a demand for an aqueous pigment dispersion that has less generation of aggregates and excellent filterability even after long-term storage. An object of the present invention is to provide an aqueous pigment dispersion having excellent filterability even after long-term storage.

MEANS FOR SOLVING THE PROBLEMS

[0006] The present inventors have found that an aqueous pigment dispersion containing crosslinked polymer particles containing a pigment and a polyoxyethylene glycol monoether represented by a specific formula can solve the above problems by having the content of the polyoxyethylene glycol monoether in the aqueous pigment dispersion within a predetermined range. That is, the present invention provides an aqueous pigment dispersion containing crosslinked polymer particles containing a pigment and a polyoxyethylene glycol monoether (I) represented by the following formula (1), RO(CH2CH2O) n H (1) (In the formula, R represents a hydrocarbon group having 3 to 6 carbon atoms, n represents the average number of moles of ethylene oxide added, and is a number of 2 or more and 5 or less.) and provides an aqueous pigment dispersion in which the content of the polyoxyethylene glycol monoether (I) is 0.1% by mass or more and 4.0% by mass or less.

EFFECTS OF THE INVENTION

[0007] According to the present invention, it is possible to provide an aqueous pigment dispersion having excellent filterability even after long-term storage.

MODE FOR CARRYING OUT THE INVENTION

[0008] [Aqueous pigment dispersion] The aqueous pigment dispersion of the present invention contains crosslinked polymer particles containing a pigment and a polyoxyethylene glycol monoether (I) represented by the following formula (1). RO(CH2CH2O) n H (1) (In the formula, R represents a hydrocarbon group having 3 to 6 carbon atoms, n represents the average number of moles of ethylene oxide added, and is a number from 2 to 5.) The content of the polyoxyethylene glycol monoether (I) is 0.1% by mass or more and 4.0% by mass or less. In the present invention, "aqueous" means that water occupies the largest proportion by mass in the medium.

[0009] According to the present invention, the filterability is excellent even after long-term storage. The reason is not clear, but it is considered as follows. The aqueous pigment dispersion of the present invention contains crosslinked polymer particles containing a pigment and a polyoxyethylene glycol monoether represented by a specific formula. This polyoxyethylene glycol monoether can impart a high antiseptic effect against filamentous fungi and the like to the aqueous pigment dispersion of the present invention. On the other hand, in the present invention, since the polymer present on the surface of the crosslinked polymer particles containing a pigment has a crosslinked structure, the swelling of the polymer can be suppressed even in the presence of the polyoxyethylene glycol monoether. Therefore, when the aqueous pigment dispersion of the present invention is stored for a long time at a high temperature such as in summer, even if the crosslinked polymer particles containing a pigment come into contact with each other, the entanglement of the polymer chains can be suppressed and the generation of aggregates can be suppressed. As a result, it is considered that an aqueous pigment dispersion excellent in filterability can be provided. Hereinafter, the filterability of the filter after the aqueous pigment dispersion is stored at a high temperature for a long time (for example, stored at 40 ° C for 6 months) is also simply referred to as "filterability".

[0010] [Crosslinked polymer particles containing a pigment] The crosslinked polymer particles containing a pigment according to the present invention (hereinafter also referred to as "pigment-containing crosslinked polymer particles") are formed of at least a pigment and a crosslinked polymer (A) and are dispersed in an aqueous medium. The form of the pigment-containing crosslinked polymer particles is not particularly limited as long as the particles are formed of at least a pigment and a crosslinked polymer (A), and the particles are those in which the crosslinked polymer (A) is adsorbed on the pigment in an aqueous pigment dispersion. As the form of the pigment-containing crosslinked polymer particles, for example, a particle form in which the pigment is encapsulated in the crosslinked polymer (A), a particle form in which the pigment is uniformly dispersed in the crosslinked polymer (A), a particle form in which the pigment is exposed on the particle surface of the crosslinked polymer (A), etc. are included, and mixtures thereof are also included.

[0011] (Pigment) The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and a lake pigment or a fluorescent pigment can also be used. Further, if necessary, a extender pigment can be used in combination therewith. Specific examples of the inorganic pigment include, for example, carbon black, titanium oxide, iron oxide, red iron oxide, metal oxides such as chromium oxide, and nacreous pigments. Particularly in black ink, carbon black is preferable. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of the organic pigment include azo pigments such as azo lake pigments and insoluble azo pigments (for example, allyl acetoacetate monoazo pigments, allyl acetoacetate disazo pigments, pyrazolone pigments, condensed disazo pigments, metal chelate azo pigments); polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. In achromatic ink, achromatic pigments such as white, black, and gray can be used, and in colored ink, colored pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred organic pigments include one or more product numbers selected from the group consisting of C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green. Examples of extender pigments include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination of two or more.

[0012] (Crosslinked Polymer (A)) As the crosslinked polymer (A) constituting the pigment-containing crosslinked polymer particles according to the present invention (hereinafter also referred to as "crosslinked polymer (A)"), it is preferably a reaction product of a polymer (a) having an acid group and a crosslinking agent. In this case, the crosslinked polymer (A) preferably has a structure containing a constituent component derived from the polymer (a) having an acid group and a constituent component derived from the crosslinking agent. Such a crosslinked structure is considered to be a three-dimensional structure in which the polymer (a) having an acid group is formed by the constituent component derived from the crosslinking agent. The crosslinked polymer (A) may be used alone or in combination of two or more.

[0013] [Polymer (a) Having an Acid Group] Examples of the acid group of the polymer (a) having an acid group include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphoric acid group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Among these, the acid group is preferably a carboxy group. The polymer (a) having an acid group may be either water-soluble or water-insoluble. Regarding the "water-solubility" and "water-insolubility" of the polymer, when the polymer dried at 105°C for 2 hours until a constant weight is dissolved in 100 g of water at 25°C until saturation, if the dissolved amount exceeds 10 g, it is judged as "water-soluble", and if it is 10 g or less, it is judged as "water-insoluble". Further, when the acid group of the polymer (a) having an acid group is neutralized with a neutralizing agent as described later, it is judged by the dissolved amount measured under the condition that the neutralizing agent is present under the condition that the mass ratio of the polymer (a) having the acid group to the neutralizing agent is the same as that in the aqueous pigment dispersion of the present invention.

[0014] Examples of the polymer skeleton of the polymer (a) having an acid group include vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds), polyesters, and polyurethanes. As the polymer (a) having an acid group, those synthesized as appropriate or commercially available products may be used. Among these, from the viewpoint of improving the filterability, the polymer (a) having an acid group is preferably a vinyl polymer having an acid group, and more preferably a vinyl polymer containing a structural unit derived from a monomer (a-1) having an acid group. Examples of such vinyl polymers include homopolymers of a monomer (a-1) having an acid group, copolymers of a monomer (a-1) having an acid group and a hydrophobic monomer (a-2), and copolymers of a monomer (a-1) having an acid group, a hydrophobic monomer (a-2), and a nonionic monomer (a-3). Here, the "hydrophobicity" of the hydrophobic monomer (a-2) means that when the monomer is dissolved in 100 g of ion-exchanged water at 25°C until saturation, the dissolved amount is less than 10 g. The nonionic monomer (a-3) is a monomer having a high affinity for water and water-soluble organic solvents, and is, for example, a monomer containing a hydroxy group or a polyalkylene glycol chain. When the polymer (a) having an acid group is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.

[0015] Examples of the monomer (a-1) having an acid group include, but are not limited to, one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. Among these, from the perspective of improving filterability, more preferably, it is one or more selected from the group consisting of acrylic acid and methacrylic acid.

[0016] The hydrophobic monomer (a-2) is preferably one or more selected from the group consisting of aromatic group-containing monomers, (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol, and macromers, and more preferably one or more selected from the group consisting of aromatic group-containing monomers and macromers. In this specification, "(meth)acrylate" means one or more selected from the group consisting of acrylate and methacrylate. "(meth)acrylate" hereinafter has the same meaning.

[0017] The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, and more preferably one or more selected from the group consisting of styrene-based monomers and aromatic group-containing (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500. The styrene-based monomer is preferably one or more selected from the group consisting of styrene and 2-methylstyrene. The aromatic group-containing (meth)acrylate is preferably one or more selected from the group consisting of benzyl (meth)acrylate and phenoxyethyl (meth)acrylate, and more preferably benzyl (meth)acrylate.

[0018] (Meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, more preferably has an alkyl group having 1 to 22 carbon atoms, and still more preferably has an alkyl group having 6 to 18 carbon atoms. For example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isoamyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate can be mentioned.

[0019] As the hydrophobic monomer, a macromer may be used. The macromer is a compound having a number average molecular weight of 500 or more and 100,000 or less and having a polymerizable functional group at one end, and from the viewpoint of improving filterability, it is preferably a compound having a number average molecular weight of 1,000 or more and 10,000 or less. The number average molecular weight is a value measured by gel permeation chromatography using chloroform containing 1 mmol / L of dodecyl dimethylamine as a solvent and using polystyrene as a standard substance. The polymerizable functional group present at one end of the macromer is preferably a methacryloyloxy group and an acryloyloxy group, and more preferably a methacryloyloxy group. From the viewpoint of improving filterability, the macromer is preferably one or more selected from the group consisting of aromatic group-containing monomer-based macromers and silicone-based macromers, and more preferably an aromatic group-containing monomer-based macromer. Examples of the aromatic group-containing monomer that constitutes the aromatic group-containing monomeric macromer include the aforementioned aromatic group-containing monomers, and one or more selected from the group consisting of styrene and benzyl (meth)acrylate are preferred, and styrene is more preferred. Specific examples of commercially available styrene-based macromers include AS-6(S), AN-6(S), HS-6(S) (manufactured by Toagosei Co., Ltd., etc.). Examples of the silicone-based macromer include organopolysiloxane having a polymerizable functional group at one end.

[0020] Examples of the nonionic monomer (a-3) include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate and polypropylene glycol mono(meth)acrylate; alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate. Among these, alkoxypolyalkylene glycol mono(meth)acrylate is preferred, and polypropylene glycol mono(meth)acrylate is more preferred. Specific examples of commercially available nonionic monomers include the "NK Ester" series manufactured by Shin-Nakamura Chemical Co., Ltd. and the "Blemmer" series manufactured by NOF Corporation. Each monomer of the polymer (a) having an acid group can be used alone or in combination of two or more.

[0021] From the viewpoint of improving the filterability, the content of the structural unit derived from the monomer (a-1) having an acid group in the polymer (a) having an acid group is preferably 5% by mass or more, more preferably 8% by mass or more, still more preferably 10% by mass or more, and from the same viewpoint as above, preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less. The content of the structural unit derived from the hydrophobic monomer (a-2) in the polymer (a) having an acid group is preferably 55% by mass or more, more preferably 60% by mass or more, still more preferably 65% by mass or more, from the viewpoint of improving the filterability, and is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less, from the same viewpoint as described above. When the polymer (a) having an acid group further contains a structural unit derived from a nonionic monomer (a-3), the content of the structural unit derived from the nonionic monomer (a-3) in the polymer (a) having an acid group is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 8% by mass or more, from the viewpoint of improving the filterability, and is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 12% by mass or less, from the same viewpoint as described above.

[0022] The acid value of the polymer (a) having an acid group is preferably 50 mgKOH / g or more, more preferably 80 mgKOH / g or more, still more preferably 180 mgKOH / g or more, even more preferably 230 mgKOH / g or more, from the viewpoint of improving the filterability, and is preferably 800 mgKOH / g or less, more preferably 500 mgKOH / g or less, still more preferably 300 mgKOH / g or less, from the same viewpoint as described above. The acid value of the polymer (a) having an acid group can be determined by the method described in the examples, but can also be calculated from the mass ratio of the constituent monomers.

[0023] The weight average molecular weight of the polymer (a) having an acid group is preferably 5,000 or more, more preferably 7,000 or more, still more preferably 10,000 or more, from the viewpoint of improving the filterability, and is preferably 500,000 or less, more preferably 300,000 or less, still more preferably 100,000 or less, even more preferably 50,000 or less, from the same viewpoint as described above. The weight average molecular weight can be determined by the method described in the examples.

[0024] Examples of commercially available polymers (a) having an acid group include polyacrylic acid such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); styrene / acrylic resins such as "Joncryl 67", "Joncryl 611", "Joncryl 678", "Joncryl 680", "Joncryl 690", "Joncryl 819" (all manufactured by BASF Japan Ltd.).

[0025] The polymer (a) having an acid group can be produced by copolymerizing the above monomer (a-1) and, if necessary, monomer (a-2) and monomer (a-3) as raw material monomers by a known polymerization method. As the polymerization method, a solution polymerization method is preferred. There is no limitation on the solvent used in the solution polymerization method, but polar solvents such as water, aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, and esters are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone, etc. are more preferred. In the polymerization, known polymerization initiators and polymerization chain transfer agents can be used. As the polymerization initiator, azo-based radical polymerization initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile) are preferred, and as the polymerization chain transfer agent, mercaptan compounds such as 2-mercaptoethanol are preferred. Although the preferred polymerization conditions vary depending on the type of polymerization initiator and the like, the polymerization temperature is preferably 50°C or higher and 90°C or lower, and the polymerization time is preferably 1 hour or longer and 10 hours or shorter. Also, the polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.

[0026] [Crosslinking agent] From the viewpoint of improving the filterability, the crosslinking agent is a polyfunctional epoxy compound having two or more crosslinkable functional groups in the molecule, preferably having two or more epoxy groups in the molecule. Such a polyfunctional epoxy compound is more preferably a compound having two or more glycidyl ether groups in the molecule, still more preferably a polyglycidyl ether compound of a polyhydric alcohol, and even more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 20 carbon atoms. The epoxy equivalent weight of the polyfunctional epoxy compound is preferably 90 g / eq. or more, more preferably 100 g / eq. or more, still more preferably 110 g / eq. or more, and preferably 300 g / eq. or less, more preferably 200 g / eq. or less.

[0027] Examples of the polyfunctional epoxy compound include polypropylene glycol diglycidyl ether (water solubility rate: 31% by mass), 1,4-butanediol diglycidyl ether (water solubility rate: 100% by mass), 1,6-hexanediol diglycidyl ether (water solubility rate: 0% by mass), trimethylolpropane polyglycidyl ether (water solubility rate: 27% by mass), pentaerythritol polyglycidyl ether (water solubility rate: 0% by mass), neopentyl glycol diglycidyl ether, diglycidyl ether of hydrogenated bisphenol A (water solubility rate: 0% by mass), ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, and one or more selected from the group consisting of polyglycerol polyglycidyl ether are preferably mentioned. Among these, from the viewpoint of improving the filterability, one or more selected from the group consisting of 1,4-butanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, and glycerol polyglycidyl ether are more preferable, and trimethylolpropane polyglycidyl ether is still more preferable.

[0028] The polyfunctional epoxy compound may be water-insoluble or water-soluble, but from the viewpoint of efficiently reacting with the acid groups in the polymer (a) having a carboxyl group in an aqueous medium to form a crosslinked structure and improving the filterability, the water solubility rate of the polyfunctional epoxy compound is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less, even more preferably 60% by mass or less, even more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 30% by mass or less. Here, the "water solubility rate" refers to the dissolution rate (mass %) when 10 parts by mass of a crosslinking agent is dissolved in 90 parts by mass of water at room temperature of 25°C.

[0029] From the viewpoint of improving filterability, the crosslinking degree of the crosslinked polymer (A) represented by the following formula (2) is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, even more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, and is preferably 80 mol% or less, more preferably 75 mol% or less. Crosslinking degree = [(molar equivalent number of crosslinkable functional groups of the crosslinking agent) / (molar equivalent number of acid groups of the polymer (a) having acid groups)] × 100 (2)

[0030] From the viewpoint of improving filterability, the acid value of the crosslinked polymer (A) is preferably 40 mgKOH / g or more, more preferably 50 mgKOH / g or more, still more preferably 60 mgKOH / g or more, even more preferably 65 mgKOH / g or more, and from the same viewpoint as above, it is preferably 200 mgKOH / g or less, more preferably 150 mgKOH / g or less, still more preferably 130 mgKOH / g or less, even more preferably 100 mgKOH / g or less, even more preferably 80 mgKOH / g or less. The acid value of the crosslinked polymer (A) can be determined by the method described in the examples, but can also be calculated by the following formula (3). Acid value of crosslinked polymer (A) (mgKOH / g) = [Acid value of polymer (a) having acid groups (mgKOH / g) × ((100 - crosslinking degree (mol%)) / 100)] (3) In the present invention, the crosslinking degree (mol%) of the crosslinked polymer (A) is represented by the above formula (2).

[0031] The acid groups of the crosslinked polymer (A) are preferably neutralized with a neutralizing agent. The neutralizing agent is preferably at least one selected from the group consisting of alkali metal hydroxides, ammonia, and organic amines, more preferably at least one selected from the group consisting of alkali metal hydroxides and organic amines, still more preferably an alkali metal hydroxide, and even more preferably sodium hydroxide. From the viewpoint of improving the filterability, the degree of neutralization of the crosslinked polymer (A) is preferably 15 mol% or more, more preferably 20 mol% or more, still more preferably 25 mol% or more, and from the same viewpoint as above, preferably 65 mol% or less, more preferably 50 mol% or less, still more preferably 35 mol% or less. The degree of neutralization is determined by the following formula to obtain the equivalent amount of the neutralizing agent used. When the total of the equivalent amount of the neutralizing agent used and the crosslinking degree of the crosslinked polymer (A) exceeds 100 mol%, the degree of neutralization of the crosslinked polymer (A) is the value obtained by subtracting the crosslinking degree (mol%) from 100 mol%. When the total of the equivalent amount of the neutralizing agent used and the crosslinking degree of the crosslinked polymer (A) does not exceed 100 mol%, the degree of neutralization of the crosslinked polymer dispersant A is synonymous with the equivalent amount of the neutralizing agent used. Equivalent amount of neutralizing agent used (mol%) = {[(mass of neutralizing agent added (g) / equivalent of neutralizing agent (g / mol)) / ((acid value (mgKOH / g) of polymer (a) having acid groups before neutralization × mass of polymer (a) having acid groups before neutralization (g)) / (56.1 × 1,000))]} × 100

[0032] <Polyoxyethylene glycol monoether (I)> The aqueous pigment dispersion of the present invention contains a polyoxyethylene glycol monoether (I) represented by the following formula (1) from the viewpoint of imparting antiseptic properties to the aqueous pigment dispersion. RO(CH2CH2O) n H (1) (In the formula, R represents a hydrocarbon group having 3 to 6 carbon atoms, n represents the average number of moles of ethylene oxide added, and is a number from 2 to 5.)

[0033] In the formula (1), R is preferably an alkyl group having 3 to 6 carbon atoms, more preferably an alkyl group having 3 to 4 carbon atoms, from the viewpoints of antiseptic property and filterability. Specific examples of R preferably include one or more selected from the group consisting of an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a hexyl group, and an isohexyl group. Among these, from the viewpoints of antiseptic property and filterability, R is more preferably one or more selected from the group consisting of a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a t-butyl group, still more preferably one or more selected from the group consisting of a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a t-butyl group, and even more preferably a butyl group. In the formula (1), n is preferably 2 or more and 4 or less, more preferably 2 or more and 3 or less, and still more preferably 3, from the viewpoints of antiseptic property and filterability. Preferable examples of the polyoxyethylene glycol monoether (I) represented by the formula (1) include polyethylene glycol monoalkyl ethers such as diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether, from the viewpoints of antiseptic property and filterability. Among them, one or more selected from the group consisting of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether are more preferable, and triethylene glycol monobutyl ether is still more preferable.

[0034] <Water> The aqueous pigment dispersion of the present invention contains water. As the water used in the aqueous ink of the present invention, pure water or ion-exchanged water is preferable from the viewpoint of preventing the mixing of unintended substances.

[0035] The aqueous pigment dispersion of the present invention may further contain additives such as water-soluble organic solvents, surfactants, viscosity modifiers, defoamers, rust inhibitors, antiseptics, and antifungal agents that are usually used in aqueous inks as wetting agents, penetrants, etc.

[0036] (Production of aqueous pigment dispersion) The aqueous pigment dispersion of the present invention is preferably obtained by a method including the following steps 1 to 3. Step 1: A step of subjecting a mixture containing a polymer (a) having an acid group, an organic solvent, a pigment, water, and, if necessary, a neutralizing agent to dispersion treatment, and removing the organic solvent from the obtained dispersion-treated product to obtain a pigment aqueous dispersion (d) containing polymer particles containing the pigment. Step 2: A step of reacting the polymer (a) having an acid group contained in the pigment aqueous dispersion (d) obtained in Step 1 with a crosslinking agent to crosslink the polymer (a) with the crosslinking agent to obtain a pigment aqueous dispersion (D) containing crosslinked polymer particles containing the pigment. Step 3: A step of mixing the pigment aqueous dispersion (D) obtained in Step 2 with polyoxyethylene glycol monoether (I) and subjecting the mixture to heat sterilization to obtain an aqueous pigment dispersion.

[0037] [Step 1] Step 1 is a step of subjecting a mixture containing a polymer (a) having an acid group, an organic solvent, a pigment, water, and, if necessary, a neutralizing agent to dispersion treatment, and removing the organic solvent from the obtained dispersion-treated product to obtain a pigment aqueous dispersion (d) containing polymer particles containing the pigment. In Step 1, from the viewpoint of improving filterability, it is preferable to subject a mixture of an aqueous dispersion of the polymer (a) having an acid group and the pigment to dispersion treatment to obtain the pigment aqueous dispersion (d). It is preferable to use the above-described neutralizing agent for preparing the aqueous dispersion of the polymer (a) having an acid group. The equivalent amount of the neutralizing agent used is preferably 10 mol% or more, more preferably 30 mol% or more, still more preferably 50 mol% or more from the viewpoint of improving filterability, and, from the same viewpoint as above, preferably 90 mol% or less, more preferably 80 mol% or less, still more preferably 70 mol% or less. The equivalent amount of the neutralizing agent used can be determined by the following formula. When the equivalent amount of the neutralizing agent used is 100 mol% or less, it is synonymous with the degree of neutralization, and when the equivalent amount of the neutralizing agent used exceeds 100 mol% in the following formula, it means that the neutralizing agent is in excess with respect to the acid groups of the polymer (a) having an acid group, and the degree of neutralization of the polymer (a) having an acid group at this time is regarded as 100 mol%. Use equivalent amount (mol%) of neutralizing agent = {[(mass of neutralizing agent added (g)) / (equivalent weight of neutralizing agent (g / mol))] / [((acid value (mg KOH / g) of polymer (a) having acid groups before neutralization) × (mass of polymer (a) having acid groups before neutralization (g))) / (56.1 × 1,000)]} × 100

[0038] In step 1, the dispersion treatment can atomize the pigment to a desired particle size only by this dispersion with shear stress, but from the viewpoint of obtaining a uniform aqueous dispersion, it is preferable to perform pre-dispersion and then further perform this dispersion. As the disperser used for pre-dispersion, generally used mixing and stirring devices such as anchor blades and disperser blades can be used. As the means for applying shear stress used for this dispersion, for example, kneaders such as roll mills and kneaders; high-pressure homogenizers such as microfluidizers; and media-type dispersers such as paint shakers and bead mills can be mentioned. Among these, from the viewpoint of reducing the particle size of the pigment, it is preferable to use a high-pressure homogenizer or a bead mill. When performing the dispersion treatment using a high-pressure homogenizer, the average particle size of the polymer particles containing the pigment can be adjusted by controlling the treatment pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less. Also, for the purpose of removing coarse particles and the like, it is preferable to obtain, as the pigment aqueous dispersion (d), something that has passed through a filter or the like.

[0039] 〔Step 2〕 Step 2 is a step of reacting polymer (a) having acid groups contained in the pigment aqueous dispersion (d) obtained in step 1 with a crosslinking agent to crosslink polymer (a) with the crosslinking agent to obtain a pigment aqueous dispersion (D) containing crosslinked polymer particles containing the pigment (hereinafter, also simply referred to as "pigment aqueous dispersion (D)"). In Step 2, the temperature of the crosslinking reaction is preferably 40°C or higher and 95°C or lower, the time of the crosslinking reaction is preferably 0.5 hours or longer, more preferably 1 hour or longer, and is preferably 10 hours or shorter, more preferably 7 hours or shorter.

[0040] [Step 3] Step 3 is a step of mixing the pigment aqueous dispersion (D) obtained in Step 2 and the polyoxyethylene glycol monoether (I) represented by the formula (1), and subjecting the mixture to heat sterilization treatment to obtain an aqueous pigment dispersion. By including Step 3 and performing heat sterilization treatment in the presence of the polyoxyethylene glycol monoether (I), the antiseptic property of the aqueous pigment dispersion can be improved. In Step 3, there is no particular limitation on the method of mixing the pigment aqueous dispersion (D) obtained in Step 2 and the polyoxyethylene glycol monoether (I). For example, it can be mixed using a conventionally known mixing device such as a homomixer, a homodisper, a wave rotor, a homogenizer, a disperser, a paint conditioner, a ball mill, a magnetic stirrer, a mechanical stirrer, etc. The polyoxyethylene glycol monoether (I) is preferably added before heating from the viewpoint of improving the sterilization effect. Further, when the aqueous pigment dispersion of the present invention further contains a preservative, from the viewpoint of improving the sterilization effect, it is preferable to add the preservative before the heat sterilization treatment and then perform the heat sterilization treatment. The temperature of the heat sterilization treatment is preferably 60°C or higher, more preferably 70°C or higher, and is preferably 95°C or lower, more preferably 80°C or lower. The time of the heat sterilization treatment is preferably 1 hour or longer, more preferably 3 hours or longer, and is preferably 24 hours or shorter, more preferably 12 hours or shorter. The heat sterilization treatment is preferably performed, for example, by putting the pigment aqueous dispersion (D) and the polyoxyethylene glycol monoether (I) in a sealed container and holding them at the above temperature and for the above time with standing or stirring.

[0041] From the viewpoint of improving filterability, the average particle diameter of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion of the present invention is preferably 50 nm or more, more preferably 70 nm or more, still more preferably 90 nm or more, and from the same viewpoint as above, preferably 600 nm or less, more preferably 500 nm or less, still more preferably 300 nm or less, even more preferably 200 nm or less, and even more preferably 150 nm or less. The average particle diameter of the pigment-containing crosslinked polymer particles can be measured by the method described in the examples.

[0042] (Composition of aqueous pigment dispersion) From the viewpoint of printing density, the solid content concentration of the aqueous pigment dispersion of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 18% by mass or more, and from the viewpoint of improving filterability, preferably 30% by mass or less, more preferably 27% by mass or less, still more preferably 25% by mass or less. The solid content concentration of the aqueous pigment dispersion is measured by the method described in the examples. From the viewpoint of printing density, the content of the pigment in the aqueous pigment dispersion of the present invention is preferably 5% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and from the viewpoint of improving filterability, preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less. From the viewpoint of improving filterability, the mass ratio of the pigment content to the total content of the pigment and the crosslinked polymer (A) in the aqueous pigment dispersion of the present invention [pigment / (pigment + crosslinked polymer (A))] is preferably 0.50 or more, more preferably 0.60 or more, still more preferably 0.70 or more, and from the same viewpoint as above, preferably 0.90 or less, more preferably 0.85 or less, still more preferably 0.80 or less. The content of the crosslinked polymer (A) in the aqueous pigment dispersion of the present invention is the total content of the polymer (a) having acid groups before crosslinking and the crosslinking agent.

[0043] The content of the polyoxyethylene glycol monoether (I) in the aqueous pigment dispersion of the present invention is 0.1% by mass or more, preferably 0.3% by mass or more, more preferably 0.5% by mass or more, still more preferably 0.7% by mass or more, from the viewpoint of antiseptic property, and is 4.0% by mass or less, preferably 3.5% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.5% by mass or less, even more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, from the viewpoint of improving filterability. The mass ratio [polyoxyethylene glycol monoether (I) / pigment-containing crosslinked polymer particles] of the content of the polyoxyethylene glycol monoether (I) to the content of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion of the present invention is preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.04 or more, from the viewpoint of antiseptic property, and is preferably 0.20 or less, more preferably 0.17 or less, still more preferably 0.12 or less, even more preferably 0.07 or less, from the viewpoint of improving filterability.

[0044] The water content in the aqueous pigment dispersion of the present invention is preferably 60% by mass or more, more preferably 65% by mass or more, still more preferably 70% by mass or more, from the viewpoint of reducing environmental load, and is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less.

[0045] (Preparation of Aqueous Ink) The aqueous pigment dispersion of the present invention can be used as an aqueous ink by mixing it with water-soluble organic solvents, dispersants, defoamers, rust inhibitors, surfactants, etc. usually used in aqueous inks. The content of the pigment-containing crosslinked polymer particles in the aqueous ink is preferably 1% by mass or more, more preferably 3% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less. The content of polyoxyethylene glycol monoether (I) in the aqueous ink is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and even more preferably 0.7% by mass or more from the viewpoint of antiseptic property, and preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and even more preferably 1.5% by mass or less from the viewpoint of improving filterability. The content of water in the aqueous ink is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more from the viewpoint of reducing environmental load, and preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less.

Examples

[0046] In the following Preparation Examples, Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The measurement methods for each physical property are as follows.

[0047] (1) Measurement of weight average molecular weight of polymer (a) having acid groups It was determined by gel permeation chromatography. The measurement conditions are shown below. GPC apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation Column: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", "TSKgel guardcolumn SuperAW-H" manufactured by Tosoh Corporation Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively Flow rate: 1 mL / min Standard substance: Monodisperse polystyrene kit with known molecular weight, "PStQuick B (F-550, F-80, F-10, F-1, A-1000)", "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" manufactured by Tosoh Corporation

[0048] (2) Measurement of acid value of polymer (a) having acid group and crosslinked polymer (A) Using a potentiometric automatic titrator (manufactured by Kyoto Electronics Industry Co., Ltd., electric burette, model number: APB-610), in the case of polymer (a) having acid groups without crosslinked structure, the polymer (a) having acid groups was dissolved in a titration solvent (toluene:acetone = 2:1 (volume ratio)) obtained by mixing toluene and acetone. In the case of crosslinked polymer (A), the aqueous pigment dispersion was dispersed in the titration solvent and titrated with 0.1N potassium hydroxide / ethanol solution by potentiometric titration method, and the inflection point on the titration curve was taken as the end point. The acid value (mgKOH / g) was calculated from the titration volume up to the end point of the potassium hydroxide solution.

[0049] (3) Measurement of solid content concentration of polymer solution Using an infrared moisture meter (FD-230 manufactured by Kett Scientific Co., Ltd.), 1.0 g of the measurement sample was dried under the conditions of a drying temperature of 150 °C and a measurement mode of 96 (monitoring time 2.5 minutes / variation width 0.05%), and then the moisture (%) of the measurement sample was measured, and the solid content concentration (%) was calculated by the following formula. Solid content concentration (%) = 100 - moisture (%) of measurement sample

[0050] (4) Measurement of solid content concentration of aqueous pigment dispersion Weighed 10.0 g of sodium sulfate, which had been made constant in a desiccator, into a 30 mL ointment container, added about 1.0 g of the sample and mixed them, then weighed accurately, held at 105 °C for 2 hours to remove volatile components, left it in the desiccator for another 15 minutes, and measured the mass. The mass of the sample after removing volatile components was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration (%).

[0051] (5) Measurement of average particle size of pigment-containing crosslinked polymer particles in aqueous pigment dispersion Cumulant analysis was performed using a laser particle analysis system (ELS-8000 manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was taken as the average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion. The concentration of the particles to be measured in the measurement sample was 5×10-3 A dispersion diluted with water to be %(in terms of solid content concentration) was used. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 integration times. The refractive index of water (1.333) was input as the refractive index of the dispersion medium.

[0052] <Preparation of Polymer (a) Having Acid Groups> Preparation Example 1-1 19.2 parts of acrylic acid, 70.8 parts of styrene, and 10.0 parts of α-methylstyrene were mixed to prepare a raw material monomer mixture. In a reaction vessel, 10.0 parts of methyl ethyl ketone (hereinafter also referred to as "MEK"), 0.3 part of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% of the above raw material monomer mixture were put in and mixed, and sufficient nitrogen gas substitution was carried out. On the other hand, into a dropping funnel, the remainder (90%) of the above raw material monomer mixture, 0.27 part of 2-mercaptoethanol, 40.0 parts of MEK, and a mixture of 1.1 parts of an azo radical polymerization initiator ("V-65", 2,2'-azobis(2,4-dimethylvaleronitrile)) manufactured by Fuji Film Wako Pure Chemical Corporation (hereinafter also referred to as "V-65") were put in. While stirring the raw material monomer in the reaction vessel under a nitrogen atmosphere, the temperature was raised to 65°C, and the mixture in the dropping funnel was dropped over 3 hours. After stirring for 2 hours from the end of dropping, a solution prepared by dissolving 0.15 part of the azo radical polymerization initiator (V-65) in 2.5 parts of MEK was added, and it was aged at 65°C for 2 hours and further at 70°C for 2 hours to obtain a solution of polymer (a1) having a carboxy group. The weight average molecular weight and acid value of polymer (a1) are shown in Table 1.

[0053] Preparation Examples 1-2, 1-3, 1-5 In Preparation Example 1-1, except that the charged amounts of the raw material monomers were changed as shown in Table 1, solutions of polymers (a2), (a3), and (a5) having carboxy groups were obtained in the same manner as in Preparation Example 1-1. The weight average molecular weight and acid value of each polymer are shown in Table 1.

[0054] Preparation Example 1-4 13.8 parts of methacrylic acid, 56.2 parts of benzyl acrylate, and 40.0 parts (20.0 parts as solids) of a styrene macromer (manufactured by Toagosei Co., Ltd., "AS-6S", number average molecular weight: 6,000, solid content concentration 50%) (hereinafter referred to as "styrene macromer"), and 10.0 parts of polypropylene glycol monomethacrylate (manufactured by NOF Corporation, "Blemmer PP-800", average number of added moles of propylene oxide 13, terminal: hydroxyl group) were mixed to prepare a raw material monomer mixture. 10 parts of MEK, 0.3 part of 2-mercaptoethanol, and 10% of the above raw material monomer mixture were placed in a reaction vessel and mixed, and nitrogen gas substitution was sufficiently performed. On the other hand, a mixture of the remaining 90% of the above raw material monomer mixture, 0.27 part of 2-mercaptoethanol, 40 parts of MEK, and 1.1 parts of an azo radical polymerization initiator (V-65) was placed in a dropping funnel, and thereafter, in the same manner as in Preparation Example 1-1, a solution of a polymer (a4) having a carboxy group was obtained. The weight average molecular weight and acid value of the polymer (a4) are shown in Table 1.

[0055]

Table 1

[0056] <Preparation of polymer aqueous dispersion (P)> Preparation Example 2-1 The solution of the polymer (a1) having a carboxy group obtained in Preparation Example 1-1 was dried under reduced pressure and then pulverized using a coffee mill to obtain a polymer (a1) having a carboxy group. 80.0 parts of the polymer (a1) having a carboxy group, 289.3 parts of ion-exchanged water, and 30.3 parts of a 5N aqueous sodium hydroxide solution (manufactured by Fujifilm Wako Pure Chemical Corporation, reagent) as a neutralizing agent (the use equivalent of the neutralizing agent (the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups of the polymer (a1) having a carboxy group) was set to 60 mol% (neutralization degree: 60 mol%)) were added to a heat-resistant flask. Neutralization and dispersion were carried out by heating at 90 °C for 5 hours while stirring at 150 rpm to obtain a polymer aqueous dispersion (P1) (solid content concentration: 20.0%).

[0057] Preparation Examples 2-2 to 2-5 In Preparation Example 2-1, polymer dispersions (P2) to (P5) (neutralization degree: 40 mol% or 60 mol%, solid content concentration: 20.0%) were obtained in the same manner as in Preparation Example 2-1, except that the type of polymer (a) having an acid group, the amount of ion-exchanged water, and the amount of 5N aqueous sodium hydroxide solution were changed as shown in Table 2.

[0058] [Table 2]

[0059] <Production of Pigment Dispersion (d)> Production Example 1-1 To 124.9 parts of the polymer dispersion (P1) obtained in Preparation Example 2-1, 370.2 parts of ion-exchanged water and 100.0 parts of C.I. Pigment Red 122 (dimethylquinacridone pigment, "IRGAPHOR MAGENTA DMQ" manufactured by Ciba Specialty Chemicals Corporation, hereinafter referred to as "PR122") were added, and using a disper ("Ultra Disper" manufactured by Asada Iron Works Co., Ltd.), the mixture was stirred at 20 °C for 60 minutes under the condition that the disper blade was rotated at 7,000 rpm. The obtained mixture was subjected to a dispersion treatment of 10 passes at a pressure of 200 MPa using a microfluidizer (trade name, manufactured by Microfluidics, model name: M-110-EH) to obtain a dispersion-treated product. The obtained dispersion-treated product was filtered through a syringe without a needle having a capacity of 25 mL (manufactured by Terumo Corporation) equipped with a syringe filter with a pore size of 5 μm ("Minisart" manufactured by Sartorius, model number: S7594-FMOSK) to remove coarse particles, thereby obtaining a pigment dispersion (d1) (solid content concentration: 21.0%).

[0060] Production Examples 1-2 to 1-10 In Production Example 1-1, pigment dispersions (d2) to (d10) (solid content concentration: 21.0%) were obtained in the same manner as in Production Example 1-1, except that the type and amount of the polymer dispersion (P) were changed as shown in Table 3. PO34: C.I. Pigment Orange 34 (Pyrazolone-based pigment, "PERMANENT ORANGE RL-01" manufactured by Clariant Chemicals) PO43: C.I. Pigment Orange 43 (Perinone pigment, "PV Fast Orange GRL" manufactured by Clariant) PG7: C.I. Pigment Green 7 (Phthalocyanine pigment, "PV Fast Green GNX" manufactured by Clariant Chemicals Japan) PV23: C.I. Pigment Violet 23 (Dioxazine pigment, "Hostaperm Violet RL SPEC." manufactured by Clariant) PR166: C.I. Pigment Red 166 (Condensed disazo-based pigment, "Chromophtal Scarlet RT" manufactured by Clariant)

[0061]

Table 3

[0062] <Production of Pigment Aqueous Dispersion (D)> Production Example 2-1 100.0 parts of the pigment aqueous dispersion (d1) obtained in Production Example 1-1 (solid content concentration: 21.0%) was placed in a glass bottle with a screw cap. 1.09 parts of trimethylolpropane polyglycidyl ether ("Denacol EX-321" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 139 g / eq., water solubility rate: 27%) (hereinafter referred to as "EX-321") as a crosslinking agent (crosslinking 70 mol% of all carboxyl groups possessed by the polymer (a1) having carboxyl groups) (crosslinking degree: 70 mol%) and 4.0 parts of ion-exchanged water were added, sealed, and heated at 70°C for 5 hours while stirring with a stirrer. Thereafter, the temperature was lowered to room temperature, and it was filtered with a 25 mL syringe without a needle equipped with the syringe filter having a pore diameter of 5 μm to obtain a pigment aqueous dispersion (D1) (solid content concentration: 21.0%).

[0063] Production Examples 2-2 to 2-19 In Production Example 2-1, pigment aqueous dispersions (D2) to (D19) (solid content concentration: 21.0%) were obtained in the same manner as in Production Example 2-1, except that the type of the pigment aqueous dispersion (d), the type and addition amount of the crosslinking agent, and the addition amount of ion-exchanged water were changed as shown in Table 4. The crosslinking agents used in Production Examples 2-7 to 2-13 are shown below. EX-214L: "Denacol EX-214L" manufactured by Nagase ChemteX Corporation, 1,4-butanediol diglycidyl ether, epoxy equivalent: 115 g / eq., water solubility rate: 100% EX-850: "Denacol EX-850" manufactured by Nagase ChemteX Corporation, polyethylene glycol diglycidyl ether, epoxy equivalent: 122 g / eq., water solubility rate: 100% EX-614B: "Denacol EX-614B" manufactured by Nagase ChemteX Corporation, sorbitol polyglycidyl ether, epoxy equivalent: 173 g / eq., water solubility rate: 94% EX-622: "Denacol EX-622" manufactured by Nagase ChemteX Corporation, sorbitol polyglycidyl ether, epoxy equivalent: 191 g / eq., water solubility rate: insoluble EX-313: "Denacol EX-313" manufactured by Nagase ChemteX Corporation, glycerol polyglycidyl ether, epoxy equivalent: 141 g / eq., water solubility rate: 99% EX-512: "Denacol EX-512" manufactured by Nagase ChemteX Corporation, polyglycerol polyglycidyl ether, epoxy equivalent: 168 g / eq., water solubility rate: 100% EX-521: "Denacol EX-521" manufactured by Nagase ChemteX Corporation, polyglycerol polyglycidyl ether, epoxy equivalent: 183 g / eq., water solubility rate: 100%

[0064]

Table 4

[0065] Example 1 As shown in Table 5, 95.2 parts of the pigment aqueous dispersion (D1), 1.0 part of triethylene glycol monobutyl ether (hereinafter also referred to as "BTG") as the polyoxyethylene glycol monoether (I), and 3.8 parts of ion-exchanged water were mixed and sterilized at 70°C for 5 hours. Then, it was filtered through the 5-μm syringe filter to obtain an aqueous pigment dispersion (1) (solid content concentration: 20.0%). The average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion (1) was 120 nm.

[0066] Examples 2 to 13, 15 to 23 In Example 1, except that the type of the pigment aqueous dispersion (D), the addition amount of the polyoxyethylene glycol monoether (I), or the addition amount of the ion-exchanged water was changed as shown in Table 5, in the same manner as in Example 1, aqueous pigment dispersions (2) to (13), (15) to (23) (all having a solid content concentration of 20.0%) were obtained respectively.

[0067] Example 14 In Example 1, except that the pigment aqueous dispersion (D1) was changed to the pigment aqueous dispersion (D4) as shown in Table 5, and the compound (I) was changed from triethylene glycol monobutyl ether to diethylene glycol monobutyl ether (hereinafter referred to as "BDG"), in the same manner as in Example 1, an aqueous pigment dispersion (14) (solid content concentration: 20.0%) was obtained.

[0068] Comparative Example 1 In Example 1, except that the pigment aqueous dispersion (D1) was changed to the pigment aqueous dispersion (d5) as shown in Table 5, in the same manner as in Example 1, an aqueous pigment dispersion (C1) (solid content concentration: 20.0%) was obtained.

[0069] The filterability of each of the aqueous pigment dispersions obtained in the examples and comparative examples was evaluated by the following method. The results are shown in Table 5. 100 g of each aqueous pigment dispersion obtained in the examples or comparative examples was added to a 100 mL plastic container, sealed, and stored at 40°C for 6 months. Then, each aqueous pigment dispersion cooled to room temperature (25°C) was filtered with a 25 mL syringe without a needle (manufactured by Terumo Corporation) equipped with a syringe filter with a pore size of 5 μm ("Minisart" manufactured by Sartorius, model number: S7594-FMOSK), and the liquid passing amount (g) until one syringe filter was blocked was measured. The larger the liquid passing amount (g), the better the filterability.

[0070]

Table 5

[0071] From Table 5, it can be seen that the aqueous pigment dispersions of the examples are excellent in filterability even after long-term storage compared to the comparative examples.

Industrial Applicability

[0072] According to the present invention, it is possible to provide an aqueous pigment dispersion excellent in filterability, in which the generation of aggregates is suppressed even after long-term storage.

Claims

1. A water-based pigment dispersion containing crosslinked polymer particles containing a pigment and a polyoxyethylene glycol monoether (I) represented by the following formula (1), RO(CH 2 CH 2 O) n H (1) (In formula (1), R represents a hydrocarbon group having 3 to 6 carbon atoms, n represents the average number of added moles of ethylene oxide, and is a number from 2 to 5.) wherein the content of the polyoxyethylene glycol monoether (I) is 0.1% by mass or more and 4.0% by mass or less.

2. The crosslinked polymer (A) constituting the crosslinked polymer particles containing the pigment is a reaction product of a polymer (a) having an acid group and a crosslinking agent, and the crosslinking degree represented by the following formula (2) is 10 mol% or more and 80 mol% or less. The water-based pigment dispersion according to claim 1. Crosslinking degree = [(molar equivalent number of crosslinkable functional groups of the crosslinking agent) / (molar equivalent number of acid groups of the polymer (a) having an acid group)] × 100 (2)

3. The water-based pigment dispersion according to claim 2, wherein the acid value of the crosslinked polymer (A) is 40 mgKOH / g or more and 200 mgKOH / g or less.

4. The water-based pigment dispersion according to claim 2 or 3, wherein the acid group of the crosslinked polymer (A) is neutralized with one or more selected from the group consisting of alkali metal hydroxides, ammonia, and organic amines.

5. The polymer (a) having an acid group is a vinyl-based polymer containing a structural unit derived from a monomer (a-1) having an acid group, and the monomer (a-1) having an acid group is selected from the group consisting of acrylic acid and methacrylic acid. The water-based pigment dispersion according to any one of claims 2 to 4.

6. The water-based pigment dispersion according to any one of claims 2 to 5, wherein the crosslinking agent is a polyfunctional epoxy compound having two or more epoxy groups in the molecule.

7. The water-based pigment dispersion according to claim 6, wherein the polyfunctional epoxy compound is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 20 carbon atoms.

8. The water-based pigment dispersion according to any one of claims 1 to 7, wherein the polyoxyethylene glycol monoether (I) is triethylene glycol monobutyl ether.

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