Method for producing a compound for pigment dispersions, and method for producing an aqueous pigment dispersion and an inkjet ink composition using the compound for pigment dispersions.

Abstract

The present invention provides a method for producing a compound for pigment dispersions that is useful for preparing aqueous pigment dispersions with excellent dispersion stability and suppression of the formation of settling components and coarse particles, and that can be used to obtain inkjet ink compositions with improved discharge characteristics such as discharge stability and discharge durability from such aqueous pigment dispersions. [Solution] A method for producing a compound for a pigment dispersion, comprising kneading a mixture containing a resin having an acid value of 180 mg KOH / g or more and 300 mg KOH / g or less, a weight-average molecular weight of 10,000 or more and 30,000 or less, and a glass transition temperature of 130°C or more and 150°C or less, and a pigment, in a range of 70°C or more and 95°C or less.

Description

Technical Field

[0001] The present invention relates to a method for producing a kneaded product for a pigment dispersion liquid, and a method for producing an aqueous pigment dispersion liquid and an ink composition for inkjet using the same.

Background Art

[0002] Aqueous inks for inkjet have excellent characteristics such as having no risk of fire or toxicity such as mutagenicity like oil-based inks, or having significantly reduced toxicity, and have become the mainstream of inkjet recording inks other than industrial uses. As an aqueous ink for inkjet recording, since it has high dissolution stability, less nozzle clogging, good color development property, and enables high-quality printing, dyes have been conventionally used as colorants. However, there is a problem that it is inferior in water resistance and light resistance of images. Since improvement of water resistance, light resistance, and long-term image quality stability is also required for household use, conversion of colorants from dyes to pigments is actively pursued in each application. While inks using pigments can be expected to have excellent water resistance and light resistance, nozzle clogging due to sedimentation is likely to occur due to the remaining of coarse pigment particles and the occurrence of aggregation. Therefore, various methods for dispersing pigments in an aqueous medium using polymer-based dispersants have been studied. For example, a kneading step of kneading a mixture having a high solid content ratio containing a pigment, a polymer dispersant, a wetting agent, and a basic compound is introduced to disperse the pigment, and then this is diluted to produce an ink composition. In this step, micronization of the pigment by crushing and prevention of aggregation by coating the surface of the micronized pigment with a resin (polymer dispersant) are performed to improve dispersion stability and reduce the number of coarse particles.

[0003] For example, Patent Document 1 discloses a method for producing an aqueous pigment dispersion for inkjet ink, comprising: a first step of kneading a styrene-acrylic resin having 50 to 90% by mass of styrene monomer units and acrylic acid monomer units or methacrylic acid monomer units, and having an acid value within a predetermined range, a pigment, a wetting agent, and a basic compound to produce a colored knead; and a second step of dispersing the colored knead in water or an aqueous medium consisting of water and a wetting agent. Patent Document 2 discloses a method for producing a compound for aqueous phthalocyanine blue pigment dispersion, which involves kneading a mixture containing an anionic resin, a phthalocyanine blue pigment, and a basic compound to produce a solid or semi-solid compound for aqueous phthalocyanine blue pigment dispersion. Patent Document 3 discloses a colored resin compound for inkjet inks containing a quinacridone pigment, a specific compound having a quinacridone skeleton, a specific styrene resin having a predetermined range of acid value and weight-average molecular weight obtained by copolymerizing a monomer containing 60% by mass or more of styrene monomer and an unsaturated aliphatic carboxylic acid having a radically polymerizable double bond relative to the total monomer components, and an alkali metal hydroxide. Patent Document 4 discloses an aqueous pigment dispersion for inkjet recording, which is obtained by mixing and stirring a solid pigment dispersion at room temperature containing carbon black having an ash content of a predetermined amount or less and a ratio of DBP oil absorption amount to specific surface area of ​​a predetermined value or less, and a copolymer having anionic groups, in an aqueous medium. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-048014 [Patent Document 2] Japanese Patent Publication No. 2004-051777 [Patent Document 3] Japanese Patent Publication No. 2005-048013 [Patent Document 4] Japanese Patent Publication No. 2013-006890 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] According to Patent Document 1, an aqueous pigment dispersion for inkjet ink obtained by this method is said to have excellent dispersion stability, especially under high-temperature heating, and to produce an aqueous ink composition that exhibits good ejection performance as a recording liquid for thermal jet inkjet systems. According to Patent Document 2, an aqueous phthalocyanine blue pigment dispersion and ink composition can be obtained that exhibits good dispersion stability and long-term storage stability of the phthalocyanine blue pigment. According to Patent Document 3, it is said to be suitable for producing a red or magenta colored pigment dispersion for inkjet ink that has excellent dispersibility and dispersion stability, exhibits little increase in particle size and viscosity even when left at high temperatures for a long period of time, and has excellent storage stability. Furthermore, according to Patent Document 4, the number of coarse particles is significantly reduced, improving the storage stability and ejection stability of the inkjet recording ink, and significantly improving the production efficiency and manufacturing yield of the ink. Thus, Patent Document 1 is an invention specifically for thermal jet ink compositions, Patent Document 2 is for cyan ink, Patent Document 3 is for magenta ink, and Patent Document 4 is for black ink. From the standpoint of broad applicability to inkjet ink compositions in general, there is still room for improvement.

[0006] Furthermore, inkjet printing is gradually replacing conventional printing methods in the printing field. In recent years, there has been a demand for further improvements in continuous printing characteristics and high-speed printing characteristics in the commercial inkjet recording field, and inkjet ink compositions that can meet these demands are needed. To further improve continuous printing characteristics and high-speed printing characteristics, it is necessary to further improve the dispersion stability and long-term storage stability of pigments in inkjet ink compositions, and to further improve ejection characteristics such as ejection stability and ejection durability. In other words, it is desirable that fine pigment particles with as uniform particle size as possible are coated with resin and stably dispersed in the liquid medium for a long period of time in the inkjet ink composition. To put it another way, there is a need for a method that can ensure micronization by crushing the pigment and prevention of aggregation by coating the surface of the micronized pigment with resin (polymeric dispersant) at the aqueous pigment dispersion stage, and even at the pigment compound stage, while also achieving industrially acceptable manufacturing efficiency and yield. From this point of view, there is still room for improvement in the inventions disclosed in Patent Documents 1 to 4.

[0007] As a result of diligent research, the inventors have found that by using a specific resin as the resin for dispersing the pigment, and kneading a mixture containing this specific resin and pigment under specific conditions, the dispersion stability and storage stability of the pigment in the aqueous pigment dispersion and inkjet ink composition prepared from the resulting kneaded product are improved, and the ejection characteristics of the inkjet ink composition are also improved. The object of the present invention is to provide a method for producing a compound for a pigment dispersion that is useful for preparing an aqueous pigment dispersion with excellent dispersion stability and storage stability, and in which the formation of settling components and coarse particles is suppressed, and that can be used to obtain an inkjet ink composition with improved discharge characteristics such as discharge stability and discharge durability from such an aqueous pigment dispersion. Another object of the present invention is to provide a method for producing an aqueous pigment dispersion using such a compound for pigment dispersions, and a method for producing an inkjet ink composition. [Means for solving the problem]

[0008] The present invention has the following aspects. [1] A method for producing a compound for a pigment dispersion, comprising kneading a mixture containing a resin having an acid value of 180 mg KOH / g or more and 300 mg KOH / g or less, a weight-average molecular weight of 10,000 or more and 30,000 or less, and a glass transition temperature of 130°C or more and 150°C or less, and a pigment, at a temperature of 70°C or more and 95°C or less. [2] A method for producing a compound for a pigment dispersion of [1], wherein the resin is a resin having anionic groups. [3] A method for producing a compound for a pigment dispersion according to [1] or [2], wherein the resin is a styrene-acrylic resin. [4] A method for producing a compound for a pigment dispersion according to any one of [1] to [3], wherein the mixture further contains a wetting agent and / or a basic compound. [5] A method for producing the pigment dispersion paste according to [4], wherein the wetting agent is a polyhydric alcohol. [6] A method for producing the pigment dispersion paste according to [4] or [5], wherein the content of the wetting agent relative to the pigment is 0.2 or more and 1.2 or less by mass ratio. [7] A method for producing a compound for a pigment dispersion according to any of [4] to [6], wherein the amount of the basic compound is such that the neutralization rate of the resin is 50% or more. [8] A method for producing a compound for a pigment dispersion according to any of [4] to [7], wherein the basic compound is an alkali metal hydroxide. [9] A method for producing a compound for a pigment dispersion according to any of [1] to [8], wherein the kneading is performed using a Henschel mixer or a planetary mixer. A method for producing an aqueous pigment dispersion, comprising the step of dispersing a compound for a pigment dispersion produced by any of the methods in [1] to [9] in an aqueous solvent. A method for producing an inkjet ink composition, comprising the step of diluting an aqueous pigment dispersion prepared by the method of

[10] with an aqueous solvent. [Effects of the Invention]

[0009] The present invention provides a method for producing a compound for pigment dispersions that is useful for preparing aqueous pigment dispersions that have excellent dispersion stability and storage stability, and suppress the formation of settling components and coarse particles. An inkjet ink composition with improved discharge characteristics such as discharge stability and discharge durability can be obtained from such aqueous pigment dispersions. [Modes for carrying out the invention]

[0010] The present invention relates to a method for producing a compound for a pigment dispersion (hereinafter also simply referred to as "the method for producing the compound of the present invention"), which involves kneading a mixture containing a resin (hereinafter simply referred to as "resin") having an acid value of 180 mg KOH / g or more and 300 mg KOH / g or less, a weight-average molecular weight of 10,000 or more and 30,000 or less, and a glass transition temperature of 130°C or more and 150°C or less, and a pigment, in a range of 70°C or more and 95°C or less. In this specification, in the manufacture of a compound for pigment dispersions, the material before kneading is referred to as the mixture, and the material during or after kneading is referred to as the compound. First, the composition of the mixture in the method for producing the kneaded product of the present invention will be described.

[0011] In the method for producing the kneaded product of the present invention, the resin is preferably a resin having anionic groups. Here, a resin having anionic groups means a resin containing monomer structural units having at least one type of anionic group, and it is preferable that the anionic group functions as a hydrophilic group. The resin having anionic groups is preferably a copolymer containing structural units derived from the above-mentioned monomer having at least one type of anionic group and structural units derived from a monomer having a hydrophobic group. Examples of monomers having anionic groups include polymerizable monomers having carboxyl groups, sulfonic acid groups, phosphate groups, etc., as anionic groups. From the viewpoint of further improving the dispersion stability of pigments in aqueous pigment dispersions prepared from the kneaded product obtained by the kneading method of the present invention, and from the viewpoint of easily obtaining an inkjet ink composition with improved discharge characteristics such as discharge stability and discharge durability from such aqueous pigment dispersions, it is preferable that the structural units derived from monomers having anionic groups are structural units derived from polymerizable monomers containing carboxyl groups, such as (meth)acrylic acid and maleic anhydride, and more preferably structural units derived from (meth)acrylic acid.

[0012] Examples of monomers having a hydrophobic group include alkyl (meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate and phenylethyl (meth)acrylate; sulfonic acid group-containing (meth)acrylates such as sulfoethyl (meth)acrylate and sulfopropyl (meth)acrylate; hydroxyl group-containing (meth)acrylates such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate; styrene compounds such as styrene, α-methylstyrene and vinyltoluene; acrylonitonyl; acrylamide; vinyl acetate; vinyl chloride; vinylpyrrolidone; vinyl alcohol; ethylene; and the like. The resin having the anionic group may contain one type of structural unit derived from these hydrophobic monomers, or two or more types. From the viewpoint of further improving the dispersion stability of the pigment in the aqueous pigment dispersion prepared from the kneaded product obtained by the kneading method of the present invention, and from the viewpoint of easily obtaining an inkjet ink composition with improved discharge characteristics such as discharge stability and discharge durability from such aqueous pigment dispersion, it is preferable that the structural unit derived from the monomer having the hydrophobic group is a structural unit derived from a styrene compound, and more preferably a structural unit derived from styrene. In the present specification, "(meth)acrylic" is a term that collectively refers to acrylic, methacrylic, and both of them. "(meth)acrylate" is a term that collectively refers to acrylate, methacrylate, and both of them.

[0013] Examples of the resin having an anionic group include styrene resins, acrylic acid resins, maleic acid resins, polyvinyl acetate resins, polyvinyl sulfonic acid resins, polyester resins, polyurethane resins, polyamide resins, polyvinyl alcohol resins, polyvinylpyrrolidone resins, cellulose resins, and the like. Among them, from the viewpoint of further improving the dispersion stability of the pigment in the aqueous pigment dispersion prepared from the kneaded product obtained by the method for producing the kneaded product of the present invention, and from the viewpoint of easily obtaining an inkjet ink composition having improved ejection characteristics such as ejection stability and ejection durability from such an aqueous pigment dispersion, the resin used in the method for producing the kneaded product of the present invention is preferably a resin having an anionic group, the structural unit derived from the monomer having an anionic group is a structural unit derived from (meth)acrylic acid, and the structural unit derived from the monomer having a hydrophobic group is a structural unit derived from a styrene-based compound, and more preferably a styrene-acrylic resin.

[0014] The content of the structural unit derived from the styrene-based compound in the styrene-acrylic resin is preferably 50% by mass or more, more preferably 70% by mass or more, based on the total amount of the styrene-acrylic resin, from the viewpoint of further improving the dispersion stability of the pigment in the aqueous pigment dispersion prepared from the kneaded product obtained by the method for producing the kneaded product of the present invention, and from the viewpoint of easily obtaining an inkjet ink composition having improved ejection characteristics such as ejection stability and ejection durability from such an aqueous pigment dispersion. The content of the structural unit derived from the styrene-based compound in the styrene-acrylic resin is preferably 95% by mass or less based on the total amount of the styrene-acrylic resin. When the content of the structural unit derived from the styrene-based compound is within the above range, the hydrophobicity of the styrene-acrylic resin increases, and in the resulting kneaded product and the prepared aqueous pigment dispersion, it is considered that the resin is more likely to be firmly coated on the pigment surface. As a result, the inkjet ink composition obtained from the aqueous pigment dispersion has improved ejection stability due to improved stability of the particle size of the resin-coated particles even when heated, and a high printing density can be obtained. Furthermore, it is also effective in improving the durability of the coating film on the recording medium.

[0015] The resin in the method for producing the kneaded product of the present invention is preferably a resin having an anionic group, and more preferably the above-described styrene-acrylic resin. The acid value of the resin is 180 mgKOH / g or more and 300 mgKOH / g or less, preferably 180 mgKOH / g or more and 250 mgKOH / g or less, and more preferably 190 mgKOH / g or more and 210 mgKOH / g or less. When the acid value of the resin is within the above range, from the viewpoints of the dispersion stability and long-term storage stability of the aqueous pigment dispersion prepared from the obtained kneaded product, and also from the aqueous pigment dispersion, an inkjet ink composition with improved ejection characteristics such as ejection stability and ejection durability can be obtained, and it is preferable from the viewpoint of easily maintaining the water resistance (durability) of printed products such as images using the inkjet ink composition. In this specification, the acid value (mgKOH / g) is the number of milligrams (mg) of potassium hydroxide (KOH) required to neutralize 1 g of the resin. The weight average molecular weight (Mw) of the resin is 10,000 or more and 30,000 or less, and preferably 10,000 or more and 17,000 or less, from the viewpoints of the dispersion stability, long-term storage stability and handling property (viscosity) of the aqueous pigment dispersion prepared from the obtained kneaded product, and also from the aqueous pigment dispersion, an inkjet ink composition with improved ejection characteristics such as ejection stability and ejection durability can be obtained. The weight average molecular weight of the resin is a value measured by gel permeation chromatography (GPC) and determined as a standard polystyrene conversion value.

[0016] The glass transition temperature (Tg) of the resin is between 130°C and 150°C. Even if the glass transition temperature of the resin is within the above range, the method for producing the compound of the present invention yields an aqueous pigment dispersion prepared from the resulting compound that exhibits excellent dispersion stability, long-term storage stability, and handling properties. Furthermore, an inkjet ink composition with excellent thermal stability and improved ejection characteristics such as ejection stability and ejection durability can be obtained from such an aqueous pigment dispersion. In addition, it is easier to maintain the water resistance (durability) of printed products such as images using such an inkjet ink composition. The glass transition temperature of the resin was measured using differential scanning calorimetry (DSC). The glass transition temperature of a resin can be adjusted by the type and content ratio of structural units derived from monomers with anionic groups and monomers with hydrophobic groups contained in the resin.

[0017] In the method for producing the kneaded product of the present invention, the pigment can be any pigment commonly used in color inks such as cyan, magenta, and yellow, as well as black ink, as inkjet inks, without any particular limitations. Examples of phthalocyanine pigments used in cyan ink include Pigment Blue 15:1 (PB 15:1), Pigment Blue 15:2 (PB 15:2), Pigment Blue 15:3 (PB 15:3), Pigment Blue 15:4 (PB 15:4), and Pigment Blue 15:6 (PB 15:6). When using these phthalocyanine pigments, phthalocyanine derivatives, which are phthalocyanine derivatives into which sulfone groups, carboxyl groups, phosphate groups, chlorosulfonyl groups, phthalimidomethyl groups, chloromethyl groups, amino groups, amide groups, etc., may be used in combination to stabilize their dispersion. Examples of quinacridone pigments used in magenta ink include CIPigment Red 122, CIPigment Red 202, CIPigment Red 209, CIPigment Violet 19; or mixtures or solid solutions of two or more of these pigments. Examples of azo pigments used in yellow ink include monoazo and disazo pigments such as CIPigment Yellow 120, 151, 154, 175, 180, 181, 1, 65, 73, 74, 116, 12, 13, 14, 17, 81, 83, 150, 155, 214, and 128. The volume-average particle size of the various pigments described above is preferably in the range of 10 to 300 nm, more preferably 50 to 180 nm, and even more preferably 80 to 150 nm.

[0018] For carbon black used in black ink, its DBP oil absorption (ml / 100g) is preferably 40ml / 100g or more, more preferably in the range of 60-200ml / 100g, and even more preferably in the range of 80-150ml / 100g. The DBP oil absorption can be measured by a method compliant with JIS K6217-4. The primary particle size of carbon black is usually preferably 60 nm or less, more preferably 40 nm or less, and even more preferably 20 nm or less. On the other hand, the primary particle size of carbon black is preferably 5 nm or more. When the primary particle size of carbon black is within the above range, the dispersion stability and long-term storage stability of the aqueous pigment dispersion prepared from the kneaded product obtained by the kneading method of the present invention tend to improve. The ash content of carbon black is preferably 1.0% by mass or less, and more preferably 0.2% by mass or less. The ash content of carbon black can be measured in accordance with JIS K6128-2. The pH of carbon black is preferably between 3 and 11, and more preferably between 6 and 9. The pH of carbon black can be measured in accordance with the old JIS K6221 standard.

[0019] In the method for producing the kneaded product of the present invention, the pigment content in the mixture used for kneading is preferably in the range of 35 to 60% by mass relative to the total mixture. For pigments used in color inks such as cyan, magenta, and yellow, a range of 40 to 60% by mass is more preferable, and for carbon black used in black ink, a range of 35 to 50% by mass is more preferable. Increasing the pigment content is advantageous from the viewpoint of improving the production efficiency of the aqueous pigment dispersion and inkjet ink composition described later, but from the viewpoint of ease of temperature control and viscosity control during kneading, the above range is preferable. In this case, it is easier to ensure the dispersion stability and storage stability of the aqueous pigment dispersion prepared from the resulting kneaded product.

[0020] In the method for producing the compound of the present invention, the ratio of pigment to resin in the mixture is preferably in the range of 0.1 to 1, and more preferably in the range of 0.2 to 0.5, as a mass ratio of resin to pigment. If the ratio of pigment to resin in the mixture is within the above range, the compound contains an amount of resin that can uniformly and stably coat the surface of the pigment, so the pigment is easily coated with resin, and the dispersion stability and storage stability when preparing the aqueous pigment dispersion described later are easily improved. Furthermore, when used as an inkjet ink composition, the amount of resin present in a state where at least a portion is dissolved or swollen in the aqueous solvent is controlled, so ink ejection failures are less likely to occur, and the ink ejection stability and ejection durability are less likely to be affected.

[0021] In the method for producing a kneaded product of the present invention, the mixture may further contain a wetting agent and / or a basic compound, preferably at least one of a wetting agent and a basic compound, and more preferably a wetting agent and a basic compound.

[0022] In the method for producing a compound of the present invention, when a mixture containing a resin (particularly a resin having anionic groups), a pigment, and a wetting agent is kneaded, the solid content ratio of the mixture can be easily adjusted to a value suitable for the kneading apparatus, making kneading easier. Furthermore, the surface of the pigment particles becomes more easily wetted by the wetting agent, and the resin, which is in a swollen state or at least partially dissolved state, is replaced by the wetting agent during kneading, thereby forming a resin coating on the surface of the pigment particles. Pigment particles coated with such resin exhibit even greater dispersion stability in aqueous pigment dispersions and inkjet ink compositions, as described later.

[0023] Examples of wetting agents include monoalcohols such as methanol, ethanol, propanol, butanol, and pentanol; Polyhydric alcohols such as propanediol, butanediol, pentanediol, hexanediol, 1,2,6-hexanetriol, glycerin, trimethylolpropane, and pentaerythritol; Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and polypropylene glycol; Glycol esters such as propylene glycol laurate; Glycol ethers such as ethylene glycol monoethyl ether (also known as cellosolve), ethylene glycol monobutyl ether, carbitol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, etc. Glycol ether esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and dipropylene glycol methyl ether acetate; Examples include lactones such as γ-butyrolactone; lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-(2-hydroxyethyl)pyrrolidone, and ε-caprolactam; and sulfolanes and 1,3-dimethylimidazolidinone. These may be used individually or in combination of two or more. Among these, polyhydric alcohols are preferred, and glycols such as diethylene glycol and triethylene glycol are more preferred. These glycols have high boiling points, low volatility, and high surface tension, and also act as drying inhibitors in aqueous pigment dispersions and ink compositions described later. They are also components that have been conventionally used and included in inkjet ink compositions. The boiling point of the wetting agent is preferably higher than the mixing temperature (mixing temperature reached) from the viewpoint of preventing volatilization during mixing, and is preferably 170°C or higher. The boiling point of the wetting agent is preferably 300°C or lower. The wetting agent can also be selected depending on the type of resin used in the method for producing the kneaded product of the present invention, and it is preferable that at least a portion of the resin dissolves or swells in the wetting agent.

[0024] In the method for producing the kneaded product of the present invention, when a wetting agent is further added to a mixture containing a resin and a pigment, the amount of the wetting agent is usually preferably in the range of 10 to 50% by mass, and more preferably in the range of 15 to 40% by mass, relative to the total amount of the mixture. Furthermore, the content of the wetting agent relative to the resin is preferably 0.2 to 12 by mass ratio, and more preferably 0.4 to 5.3 by mass ratio. Furthermore, the content of the wetting agent relative to the pigment is preferably 0.2 to 1.2 by mass ratio. When the content of the wetting agent relative to the pigment is within the above range, the surface of the pigment can be sufficiently wetted in the initial stages of kneading, and at least a portion of the resin can be dissolved or swollen, so that resin coating on the pigment surface can be carried out smoothly by kneading.

[0025] Furthermore, when the pigment is a color pigment such as cyan, magenta, or yellow as described above, the content of the wetting agent relative to the pigment is preferably 0.2 to 0.7 by mass ratio, and more preferably 0.34 to 0.44. When the pigment is carbon black, a black pigment as described above, the wetting agent content relative to the pigment is more preferably 0.50 to 1.10 by mass ratio. Furthermore, when it is a low-oil-absorption carbon black with a DBP oil absorption of 30 ml / 100g or more and less than 70 ml / 100g, the wetting agent content relative to the pigment is even more preferably 0.50 to 0.90 by mass ratio, and when it is a high-oil-absorption carbon black with a DBP oil absorption of 70 ml / 100g or more and 150 ml / 100g or less, the wetting agent content relative to the pigment is even more preferably 0.80 to 1.10 by mass ratio. When the content of the wetting agent relative to the pigment is within the aforementioned range, sufficient shear force can be applied to the mixture for kneading, preventing insufficient disintegration of the pigment and making it easier to obtain a kneaded mixture that is a uniform pigment dispersion. As a result, the dispersion stability and storage stability of the aqueous pigment dispersion prepared from the resulting kneaded mixture for pigment dispersion, as described later, tend to be improved. Furthermore, the ejection characteristics of the inkjet ink composition tend to be improved. When the amount of wetting agent relative to the pigment is large, sufficient shear force is not applied to the mixture that contributes to kneading, making it difficult to raise the temperature of the kneaded material to 70°C or higher. As a result, it becomes difficult to reduce the particle size distribution of the pigment and decrease the amount of coarse particles in the resulting pigment dispersion mixture, making it difficult to ensure sufficient dispersion stability in the aqueous pigment dispersion described later. On the other hand, if the amount of wetting agent relative to the pigment is small, the viscosity of the resulting pigment dispersion mixture tends to rise excessively, leading to excessive shear force. If the load on the mixer due to shear force exceeds the allowable range, mixing may become impossible. Furthermore, even if the temperature of the pigment dispersion mixture rises above 95°C, slightly decreasing the viscosity and bringing the load to a mixable range, the subsequent step of dispersing the mixture in an aqueous solvent will increase the viscosity of the mixture as the temperature drops due to the addition of the aqueous solvent. If the dispersion process continues in this state, the viscosity of the mixture will not decrease, making it difficult to maintain uniformity. As a result, insufficient dispersion is likely to occur, leading to an uneven mixture with partially high-viscosity areas remaining. Consequently, some of the high-viscosity areas in the aqueous pigment dispersion tend to remain in a clump-like state, which can easily cause an increase in coarse particles and the formation of precipitates.

[0026] In the method for producing the compound of the present invention, when a mixture containing a resin (particularly a resin having anionic groups), a pigment, and a basic compound is kneaded together, a compound for pigment dispersion is obtained in which the anionic groups of the resin are neutralized. As a result, the affinity of the compound for pigment dispersion with water is improved, and when preparing the aqueous pigment dispersion described later, the compound for pigment dispersion disperses more quickly in the aqueous solvent, improving production efficiency. In addition, the dispersion state of the resin-coated pigment in the resulting aqueous pigment dispersion is more easily stabilized, improving dispersion stability and storage stability. Furthermore, when basic compounds are incorporated, the interaction between the basic compounds and the resin (especially resins with anionic groups) allows the finely pulverized pigment to be sufficiently coated with the resin during kneading, thus suppressing the generation of coarse particles. This eliminates the need for a coarse particle removal step during the production of aqueous pigment dispersions, and also improves the yield.

[0027] Examples of basic compounds include organic basic compounds such as amines, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine; and inorganic basic compounds such as hydroxides or carbonates of alkali metals such as potassium and sodium, carbonates of alkaline earth metals such as calcium and barium, and ammonium hydroxide. Inorganic basic compounds are preferred from the viewpoint of easily adjusting the strength of the basicity, and among them, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide are more preferred. When alkali metal hydroxides are used as basic compounds, they are strongly basic, water-soluble, and can be added in the form of an aqueous solution. Therefore, they are preferable from the viewpoint of easily improving the dispersibility of resins containing anionic groups by neutralizing them, and thus easily obtaining aqueous pigment dispersions as described later. In the method for producing the kneaded product of the present invention, when the basic compound is used in the form of an aqueous solution, its concentration is usually preferably 20 to 50% by mass.

[0028] In the method for producing the kneaded product of the present invention, when a basic compound is further added to a mixture containing a resin and a pigment, the amount of the basic compound added is preferably such that the neutralization rate of the resin (preferably a resin having anionic groups) is 50% to 200%, and more preferably 80% to 120%. When the content of the basic compound is within the above range, the dispersion stability and storage stability of the aqueous pigment dispersion prepared from the resulting kneaded product tend to be improved. When a basic compound is included, it is preferable to mix it with the resin and pigment to form a mixture before kneading, in the method for producing the kneaded product of the present invention, from the viewpoint of facilitating the coating of the resin onto the pigment surface. In this specification, the neutralization rate is the value calculated by the following formula. A neutralization rate of 100% or more means that the resin contains more basic compounds than the base theoretically required to neutralize the acid value of the resin. Neutralization rate (%) = 100 × [{Mass of basic compound (g) × 56 × 1000} / {Resin acid value × Equivalent weight of basic compound × Amount of resin (g)}]

[0029] In the method for producing the compound of the present invention, a mixture containing a resin and a pigment, and preferably further containing the above-mentioned wetting agent and / or basic compound, is kneaded at a temperature of 70°C to 95°C to produce a compound for pigment dispersion. The resulting compound for pigment dispersion is preferably solid or semi-solid. Here, "kneading the mixture in a range of 70°C to 95°C" means that the temperature of the kneaded mixture itself, reached at the end of kneading, is controlled to be within the range of 70°C to 95°C. The temperature of the kneaded mixture itself can be measured by directly inserting a thermocouple or thermometer into the mixture. In the method for producing a kneaded product of the present invention, the resin constituting the mixture before kneading is characterized in that it has an acid value of 180 mg KOH / g or more and 300 mg KOH / g or less, an Mw of 10,000 or more and 30,000 or less, and a Tg of 130°C or more and 150°C or less.

[0030] Resins having such acid values ​​and Mw, and having the role of coating the pigment surface to improve dispersibility, are comprehensively described in the aforementioned Patent Documents 1 to 4. Specifically, Patent Document 1 discloses a styrene-acrylic resin with an acid value of 50 to 300 and an Mw of 5000 to 30000; Patent Document 2 discloses an anionic group-containing resin with an acid value of 60 to 300 and an Mw of 3000 to 50000; Patent Document 3 discloses a styrene-based resin with an acid value of 50 to 300 and an Mw of 7500 to 40000; Patent Document 4 discloses an anionic group-containing copolymer with an acid value of 50 to 300 and an Mw of 7500 to 40000; and all Tg can be in the range of 90 to 150°C. Furthermore, regarding the kneading temperature (temperature reached through kneading), Patent Document 1 states that it is preferable to satisfy the following conditions for styrene-acrylic resin: Tg ≥ 90°C and (Tg - 50°C) ≤ kneading temperature Mt ≤ (Tg + 50°C); Patent Document 2 states that 40 to 70°C is preferable; Patent Document 3 states that a range lower than the Tg of the styrene-acrylic resin and with a temperature difference of less than 50°C from Tg is preferable; and Patent Document 4 states that a range lower than the Tg of the anionic group-containing copolymer and with a temperature difference of less than 50°C from Tg is preferable. In contrast, it has been found that when a mixture containing a specific resin with an acid value of 180 mg KOH / g to 300 mg KOH / g, an Mw of 10,000 to 30,000, and a Tg of 130°C to 150°C is kneaded together with a pigment, the viscosity change of the kneaded product tends to be extreme and difficult to control. This phenomenon is thought to be due to the inclusion of a resin with a high acid value, high Mw, and high Tg, but Patent Documents 1 to 4 do not specifically mention that such problems occur, and naturally, no solutions to these problems are disclosed.

[0031] In the method for producing the compound of the present invention, when the mixing is carried out in a range of 70°C to 95°C, preferably with the addition of a basic compound, it was surprisingly found that the neutralization of the resin proceeds smoothly during mixing, even though the resin has a high Mw and high Tg. Furthermore, when a wetting agent is preferably added, in addition to controlling the mixing temperature (mixing temperature) as described above, it was found that controlling the content of the wetting agent to the pigment in the specific mass ratio described above facilitates the viscosity control of the compound, and the dissolution and swelling of at least a portion of the specific resin in the wetting agent proceeds smoothly, making it easier to coat the pigment surface with resin. Furthermore, we found that the resulting compound exhibits excellent dispersibility when dispersed in an aqueous solvent to prepare an aqueous pigment dispersion, as well as excellent dispersion stability and storage stability of the resulting aqueous pigment dispersion. We also found that the inkjet ink composition obtained from this aqueous pigment dispersion exhibits extremely suppressed generation of coarse particles, no sedimentation, excellent discharge characteristics, and superior manufacturing efficiency and yield.

[0032] The solid content ratio of the resin and pigment combined is preferably in the range of 50 to 80% by mass in the resulting pigment dispersion mixture. For pigments used in color inks such as cyan, magenta, and yellow, a range of 60 to 80% by mass is more preferable, and for carbon black used in black ink, a range of 50 to 65% by mass is more preferable. When the solid content ratio is within the above range, the viscosity of the mixture during mixing is kept moderately high, the share of the mixture from the mixer during mixing is increased, and mixing can be carried out smoothly while simultaneously promoting the pulverization of the pigment in the mixture and the coating of the pigment with the resin. Furthermore, when a mixture further containing a wetting agent and / or a basic compound is kneaded, the anionic groups of the resin are neutralized, thereby improving the dispersibility and solubility of the resin. Also, since at least a portion of the resin dissolves or swells and is kneaded with the pigment, the coating of the resin onto the pigment surface progresses more easily, and the presence of the basic compound results in a highly viscous, clay-like mixture.

[0033] In the method for producing the kneaded product of the present invention, it is preferable to perform the kneading in such a manner that the mass of the mixture does not substantially change during kneading, from the viewpoint of improving the dispersibility of the pigment during kneading without causing problems such as an increase in the viscosity of the kneaded product or an increase in the solid content ratio. In other words, in the method for producing the kneaded product of the present invention, preferably when a wetting agent and / or a basic compound is further included, it is preferable to knead the mixture in such a way that the aqueous solvent in which the wetting agent and the basic compound are dissolved does not evaporate during kneading, and the mass of the mixture (kneaded product) does not substantially change. In this case, as mentioned above, mixing becomes easier, and the pigment particles, whose surfaces are wet with the wetting agent, are replaced by the resin, which is swollen or at least partially dissolved by the mixing process, thereby facilitating the formation of a resin film on the surface of the pigment particles. Furthermore, the mixed material after mixing becomes easier to disperse in an aqueous solvent, allowing for faster dispersion, improving manufacturing efficiency, and further enhancing the dispersion stability and ejection characteristics of the inkjet ink composition produced from the prepared aqueous pigment dispersion.

[0034] From the viewpoint of carrying out the method for producing the kneaded product of the present invention in such a way that the mass of the mixture does not substantially change during kneading, it is preferable to use a kneading apparatus that can perform kneading in a closed system. When using a kneading apparatus that can perform kneading in a closed system, unlike kneading using an open system kneader such as a roll mill (roll meat mixer), changes in the composition of the kneaded product due to evaporation of the aqueous solvent in the kneaded product due to the temperature rise during kneading are suppressed, and the shear force on the kneaded product does not change easily, so the resin coating on the pigment surface proceeds smoothly. In addition, kneaded products obtained using an open system kneader tend to have a dry surface, and when preparing the aqueous pigment dispersion, it is necessary to pulverize it beforehand and further disperse the pigment after adding the aqueous solvent, which can take a long time for dispersion, and coarse particles may remain in the resulting aqueous pigment dispersion, but such concerns are not present. In this specification, "substantially unchanged mass of mixture" means that the mass change of the kneaded product during and after kneading is within 10% by mass relative to the total mass of the mixture before kneading, and any mass change within this range is permissible.

[0035] Examples of mixing devices include Henschel mixers, pressure kneaders, Banbury mixers, and planetary mixers. Among these, from the viewpoint of being able to perform mixing in a closed system, Henschel mixers or planetary mixers, which are mixing devices equipped with a stirring tank and stirring blades, are preferred, and planetary mixers are more preferred. Planetary mixers have a structure that uses two stirring blades that rotate on their own axis and revolve around each other to stir and knead the contents in the stirring tank, and there is little dead space in the stirring tank that the stirring blades do not reach. In addition, they can handle a wide range of materials to be kneaded, from high load ranges to low load ranges (i.e., from high viscosity ranges to low viscosity ranges). When mixing is performed using a Henschel mixer or planetary mixer, the mass of the mixed material does not substantially change during mixing relative to the mass of the initial mixture, allowing for the production of a mixed material for aqueous pigment dispersions with a composition similar to the initial mixture, thus improving manufacturing stability. Furthermore, because mixing is performed with high pigment and solid content concentrations from the beginning, the pigment is broken down by the shear force applied during mixing, reducing the amount of undispersed coarse particles. As a result, there is no need to remove coarse particles in subsequent processes, leading to a good yield. Furthermore, because mixing can be performed in a closed system, unlike when using a pressure kneader or Banbury mixer, the mixed material after mixing can be continuously diluted by adding an aqueous solvent, stirred and dispersed to prepare an aqueous pigment dispersion, without having to remove it from the Henschel mixer or planetary mixer.

[0036] The present invention also includes a step of dispersing a compound for a pigment dispersion obtained by the above-described manufacturing method in an aqueous solvent, and is a method for producing an aqueous pigment dispersion (hereinafter simply referred to as "the method for producing an aqueous pigment dispersion of the present invention"). The compound used for pigment dispersions is usually a semi-solid or solid paste. Aqueous pigment dispersions can be produced by dispersing this compound in an aqueous solvent (i.e., a solvent primarily composed of water). The pigments in the compound for pigment dispersions are already finely crushed and coated with resin during the production of the compound for pigment dispersions using the manufacturing method of the present invention described above. As a result, the dispersibility in aqueous solvents is good, the dispersion time for preparing aqueous pigment dispersions is short, and coarse particles are suppressed, eliminating the need for steps to remove coarse particles, thus improving manufacturing efficiency and increasing the yield of aqueous pigment dispersions. Furthermore, the kneaded product obtained by the method for producing the pigment dispersion knead of the present invention, preferably a mixture containing a pigment and the aforementioned resin, plus a wetting agent and / or a basic compound, exhibits good dispersibility in aqueous solvents due to the interaction between the resin having anionic groups and the basic compound, and therefore disperses quickly. The resulting aqueous pigment dispersion also exhibits excellent dispersion stability and storage stability.

[0037] As the aqueous solvent, water or a mixture of water and an organic solvent miscible with water can be used. Examples of organic solvents miscible with water include alcohols such as ethanol and isopropanol; and glycol ethers such as ethylene glycol monohexyl ether, diethylene glycol monobutyl ether, and propylene glycol propyl ether. Furthermore, the compounds exemplified as wetting agents in the description of the method for producing the kneaded product of the present invention may be used in mixture with water as an organic solvent miscible with water.

[0038] As a means of dispersing the compound for pigment dispersions in an aqueous solvent, any of the following can be used: a disperser using media such as an ultrasonic homogenizer, paint shaker, ball mill, attritor, basket mill, sand mill, sand grinder, dyno mill, disper mat, SC mill, spike mill, agitator mill, etc.; or a disperser that does not use media such as an ultrasonic homogenizer, nanomizer, dissolver, disper, high-speed impeller disperser, etc. Depending on the type of disperser used for dispersion, an aqueous solvent may be added to the pigment dispersion mixture beforehand and mixed to adjust the viscosity to a level suitable for processing in the disperser before dispersion. Alternatively, an aqueous solvent may be added after dispersion to adjust the solid content concentration of the resulting aqueous pigment dispersion. Furthermore, when dispersing the pigment dispersion mixture in an aqueous solvent, various additives may be added as needed.

[0039] In the present invention, a kneading method for producing a kneaded product according to the present invention can be used, for example, with a kneader equipped with the above-mentioned stirring tank and stirring blades, specifically, for example, a Henschel mixer or a planetary mixer, to obtain a kneaded product. After that, an aqueous pigment dispersion can be prepared by adding an aqueous solvent to the kneaded product in the stirring tank and mixing it. In other words, since the production of the kneaded product and the preparation of the aqueous pigment dispersion can be carried out continuously with the same apparatus, the production efficiency of the aqueous pigment dispersion can be improved. The resulting mixture can be removed as is, or an aqueous solvent can be added in a stirring tank to adjust it to a predetermined viscosity before being removed from the tank. This mixture can then be further mixed with the aqueous solvent and dispersed to obtain an aqueous pigment dispersion.

[0040] In aqueous pigment dispersions, the dispersion state of the pigment is influenced by factors such as the particle size of the pigment, the particle size of the resin-coated particles in which the pigment is coated with resin, the ratio of pigment to resin, and the composition of the resin and aqueous solvent. In the method for producing the kneaded product of the present invention, fine resin-coated particles are obtained in which the surface of fine pigment particles is thinly and uniformly coated with resin. As a result, these particles exhibit excellent dispersion stability in aqueous solvents, and their dispersion state is maintained over a long period of time. This effect enables the development of ejection stability and ejection durability in the inkjet ink composition described below.

[0041] The present invention also provides a method for producing an inkjet ink composition, comprising the step of diluting an aqueous pigment dispersion obtained by the above-described manufacturing method with an aqueous solvent. The inkjet ink composition can be manufactured by further diluting the aqueous pigment dispersion obtained as described above with an aqueous solvent. It is preferable to dilute the inkjet ink composition with an aqueous solvent so that the pigment concentration is in the range of 1 to 20% by mass. Examples of aqueous solvents include those similar to those used to disperse the pigment dispersion mixture described above. These may be the same type of aqueous solvent as the one used to disperse the pigment dispersion mixture, or a different type of aqueous solvent, but it is preferable that they be the same type of aqueous solvent. If the aqueous solvent is a mixture of water and an organic solvent that is miscible with water, it is easy to adjust the solid content concentration and viscosity of the resulting inkjet ink composition, and it also helps to prevent drying. Furthermore, if an organic solvent that is miscible with water and exhibits permeability to the recording medium is blended with the aqueous solvent, it is preferable from the viewpoint of easily adjusting the permeability of the inkjet ink composition to the recording medium and the dot size on the recording medium.

[0042] In the manufacture of inkjet ink compositions, in addition to aqueous pigment dispersions and aqueous solvents, known additives such as pH adjusters, surfactants, preservatives, chelating agents, plasticizers, antioxidants, surface tension adjusters, fade inhibitors, pigment dispersants, UV absorbers, and UV-curable resins may be added.

[0043] The viscosity of the resulting inkjet ink composition at 25°C is preferably in the range of 3 to 30 mPa·s, and more preferably in the range of 5 to 20 mPa·s, from the viewpoint of providing the inkjet ink composition with excellent dispersion stability and ease of handling, as well as improving ejection characteristics such as inkjet ejection stability and ejection durability. In the resulting inkjet ink composition, the various pigments described above are preferably included in an amount of 1 to 20% by mass of the total inkjet ink composition, and more preferably in an amount of 1 to 10% by mass.

[0044] The inkjet systems to which the inkjet ink composition obtained by the manufacturing method of the present invention can be applied are not particularly limited. Known systems such as continuous jet type (charge-controlled type, spray type, etc.) and on-demand type (piezo type, thermal type, electrostatic attraction type, etc.) can be used. The inkjet ink composition prepared from the kneaded product obtained by the manufacturing method of the present invention enables extremely stable ink ejection when applied to various inkjet systems, and in particular, it can achieve a high level of ejection characteristics such as ejection stability and ejection durability required in the field of high-speed inkjet printing.

[0045] Although an embodiment of the method for producing a compound for pigment dispersion, the method for producing an aqueous pigment dispersion, and the method for producing an inkjet ink composition of the present invention has been described above, the present invention is not limited to the configuration of the embodiment described above. For example, the method for producing a compound of the present invention may have additional configurations or steps in addition to the configuration of the above embodiment, or may be replaced with any configurations or steps that produce a similar effect. [Examples]

[0046] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. The compounds used in these examples are shown below. <Pigments> Pigment 1: Carbon black (#995B; manufactured by Mitsubishi Chemical Corporation, primary particle size 16nm, DBP oil absorption 112ml / 100g, specific surface area 250m²) 2 / g) Pigment 2: Carbon black (BP880 (BLACK PEARLS 880)); manufactured by Cabot, primary particle size 16nm, DBP oil absorption 105ml / 100g, specific surface area 220m² 2 / g) Pigment 3: Cyan pigment (FASTOGEN BLUE SBG-SD; manufactured by DIC Corporation, Pigment Blue 15:3) <Resin> Resin 1: A resin with an acid value of 202 mg KOH / g, Mw 14000, and Tg 139℃. Resin 2: A resin with an acid value of 201 mg KOH / g, Mw 11000, and Tg 136℃. Resin 3: A resin with an acid value of 186 mg KOH / g, Mw 16000, and Tg 138℃. <Humectant> TEG: Triethylene glycol <Basic compounds> Basic compound 1: 34% by mass aqueous solution of potassium hydroxide

[0047] Example 1 (1) 150 parts by mass of pigment 1, 60 parts by mass of resin 1, 141 parts by mass of TEG, and 35.65 parts by mass of basic compound 1 (mass ratio of TEG to pigment 1: 0.94) were placed in a planetary mixer (manufactured by Inoue Seisakusho Co., Ltd., product name "PLM-V-50V") with a stirring bed capacity of 50 L. The jacket was heated to 60°C, and the mixture was stirred at a rotation of 60 rpm and revolution of 20 rpm to obtain a mixture of pigment 1, resin 1, TEG, and basic compound 1. Then, kneading was continued for 60 minutes while maintaining the same rotation speed to obtain kneaded product 1. The temperature of kneaded product 1 immediately after the end of kneading (temperature reached by kneading) was 82°C. (2) Next, the amount of deionized water and solvent shown in Table 1 was gradually added to the kneaded mixture 1 in the stirring tank, and dispersion was performed using a planetary mixer (rotation 60 rpm, revolution 20 rpm) while confirming that it was uniformly mixed, and deionized water was added to disperse until the concentration of pigment 1 reached 12.8% by mass, thereby obtaining aqueous pigment dispersion 1. (3) The obtained aqueous pigment dispersion 1 was evaluated as follows.

[0048] <Measurement of the number of coarse particles in a dispersion> The number of coarse particles with a diameter of 0.5 μm or larger in aqueous pigment dispersion 1, diluted 50 to 2000 times with deionized water, was measured using an Entegris Accusizer 780 APS coarse particle count analyzer. The measurement involved filling the analyzer's measuring section with approximately 4 ml of the diluted aqueous pigment dispersion 1, and detecting the number and particle size of particles passing through the section using optical means. The dilution ratio of the aqueous pigment dispersion 1 and the mass filled into the measuring section were input as parameters during measurement. The obtained measurement results were multiplied by the dilution concentration to calculate the number of particles contained in 1 ml of the undiluted aqueous pigment dispersion 1. <Measurement of average dispersed particle size of pigments in dispersions> The average dispersed particle size of pigment 1 in aqueous pigment dispersion 1, diluted 200 to 1000 times with deionized water, was measured using a Microtrac-Bell Nanotrac particle size distribution analyzer (UPA150). In this measurement, approximately 4 ml of aqueous pigment dispersion 1 was placed in a measurement cell, and the particle size was measured by detecting the scattered light of a laser beam at 25°C. The parameters input during measurement were viscosity (viscosity of aqueous pigment dispersion 1 after dilution with deionized water), density of dispersed particles (true specific gravity of pigment 1), and density of deionized water. Three measurements were performed with a measurement time of 30 seconds, and the average value of the obtained volume-average particle size (MV) was taken as the average dispersed particle size (nm). <Dispersion stability of dispersions> The absorbance of aqueous pigment dispersion 1, diluted 10,000 times with deionized water, was measured using a UV-Vis spectrophotometer (V-760) manufactured by JASCO Corporation, and the absorbance at 500 nm was determined. If the dispersion stability of pigment 1 is poor and sedimentation occurs, the absorbance will be low.

[0049] Examples 2-9, Comparative Examples 1-2 (1) In Example 1(1), the pigment type and resin type were changed as shown in Table 1, the amounts of pigment, resin, TEG and basic compound 1 were changed to the amounts shown in Table 1, and the temperature reached by kneading with a planetary mixer was changed to the temperature shown in Table 1. The same procedure as in Example 1(1) was carried out to obtain kneaded products 2-9 and kneaded products C1-C2. (2) Next, the mixture in the stirring tank was gradually mixed with the amounts of deionized water and solvent shown in Table 1, and diluted by dispersion using a planetary mixer (rotation 60 rpm, revolution 20 rpm) while ensuring that it was uniformly mixed, to obtain aqueous pigment dispersions 2-9 and aqueous dispersions C1-C2. The pigment concentrations in each dispersion are shown in Table 1. (3) Aqueous pigment dispersions 2-9 and C1-C2 were evaluated in the same manner as in Example 1(3). The results are shown in Table 1. Regarding dispersion stability, the absorbance at 500 nm was measured for aqueous dispersions containing pigment 1 or pigment 2, and the absorbance at the maximum absorption wavelength was measured for aqueous dispersions containing pigment 3. Specifically, in Examples 6-9, the absorbance of aqueous pigment dispersions 6-9 diluted 10,000 times with deionized water was measured using a UV-Vis spectrophotometer, and the absorbance at the maximum absorption wavelength (wavelength shown in Table 1) was determined.

[0050] [Table 1]

[0051] These results indicate that the aqueous pigment dispersion prepared from the kneaded material obtained by the kneading method of the present invention exhibits excellent dispersion stability and storage stability, and the formation of settling components and coarse particles is suppressed. [Industrial applicability]

[0052] The compound for pigment dispersions obtained by the manufacturing method of the present invention is useful for preparing aqueous pigment dispersions that exhibit excellent dispersion stability and suppress the formation of sedimentary components and coarse particles. Furthermore, inkjet ink compositions with improved ejection characteristics, such as ejection stability and ejection durability, can be obtained from such aqueous pigment dispersions.

Claims

1. A method for producing a compound for a pigment dispersion, comprising kneading a mixture containing a resin having an acid value of 180 mg KOH / g or more and 300 mg KOH / g or less, a weight-average molecular weight of 10,000 or more and 30,000 or less, and a glass transition temperature of 130°C or more and 150°C or less, and a pigment, at a temperature of 70°C or more and 95°C or less.

2. The method for producing a compound for a pigment dispersion according to claim 1, wherein the resin is a resin having anionic groups.

3. The method for producing a compound for a pigment dispersion according to claim 1, wherein the resin is a styrene-acrylic resin.

4. The method for producing a compound for a pigment dispersion according to claim 1, wherein the mixture further contains a wetting agent and / or a basic compound.

5. The method for producing a compound for a pigment dispersion according to claim 4, wherein the wetting agent is a polyhydric alcohol.

6. A method for producing a compound for a pigment dispersion according to claim 4, wherein the content of the wetting agent relative to the pigment is 0.2 or more and 1.2 or less by mass ratio.

7. The method for producing a compound for a pigment dispersion according to claim 4, wherein the amount of the basic compound is such that the neutralization rate of the resin is 50% or more.

8. The method for producing a compound for a pigment dispersion according to claim 4, wherein the basic compound is an alkali metal hydroxide.

9. The method for producing a compound for a pigment dispersion according to claim 1, wherein the kneading is performed using a Henschel mixer or a planetary mixer.

10. A method for producing an aqueous pigment dispersion, comprising the step of dispersing a compound for a pigment dispersion produced by the method of any one of claims 1 to 9 in an aqueous solvent.

11. A method for producing an inkjet ink composition, comprising the step of diluting an aqueous pigment dispersion prepared by the method described in claim 10 with an aqueous solvent.

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