Method for producing pigment composition, method for producing pigment dispersion, method for producing aqueous ink, and inkjet recording method

Abstract

To provide a method for producing a pigment composition which contains micronized yellow pigment for broadening the range of color reproducibility, while exhibiting superior light resistance.SOLUTION: A method for producing a pigment composition includes a kneading step in which a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent is kneaded by a solvent salt milling process to provide a kneaded product. The pigment is at least one monoazo pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 1, and C.I. Pigment Yellow 9. The mixture further contains a compound represented by the following formula (1).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a pigment composition, a method for producing a pigment dispersion, a method for producing an aqueous ink, and an inkjet recording method.

Background Art

[0002] In recent years, an inkjet recording method has been used to record business documents using plain paper or the like as a recording medium and photographic images using glossy paper or the like as a recording medium, and its usage frequency has been increasing significantly. When forming an image using the inkjet recording method, it has become mainstream to use a pigment as a coloring material from the viewpoint of high fastness. However, when using an ink containing a pigment as a coloring material, the range of color reproducibility is inferior compared to the case of using an ink containing a dye as a coloring material. Therefore, it is becoming mainstream to use a pigment obtained by pulverizing a pigment to a fine particle size with a primary particle size of about 20 nm or more and 100 nm or less. There are many methods for making pigments finer, but wet kneading and pulverization such as solvent salt milling and dry pulverization are widely performed (Patent Document 1).

[0003] Among the pigments for inkjet recording, the yellow pigment is widely used as C.I. Pigment Yellow 74, which is a monoazo pigment, particularly inexpensive and excellent in hue and vividness. Generally, many monoazo pigments are inferior in crystal stability to heat and light, and this tendency is particularly remarkable in fine monoazo pigments. As a result, it may cause a decrease in the coloring power and vividness of the recorded matter. Various studies have been conducted to improve the crystal stability of such monoazo pigments. As an example, when wet kneading and pulverizing C.I. Pigment Yellow 74 by solvent salt milling, a method of producing a fine pigment by adding a compound having a structure similar to that of the pigment has been proposed (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] As a result of the studies by the present inventors, it was confirmed that the range of color reproducibility is expanded by using a micronized yellow pigment, but when an image is recorded on a recording medium using an ink containing the yellow pigment, the lightfastness of the recorded image decreases.

[0006] Therefore, an object of the present invention is to provide a method for producing a pigment composition having good lightfastness while containing a micronized yellow pigment for expanding the range of color reproducibility. Another object of the present invention is to provide a method for producing a pigment dispersion, a method for producing an aqueous ink, and an inkjet recording method using the pigment composition obtained by the above production method. [Means for Solving the Problems]

[0007] That is, according to the present invention, there is provided a method for producing a pigment composition including a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product, wherein the pigment is at least one monoazo pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 1, and C.I. Pigment Yellow 9, and the mixture further contains a compound represented by the following chemical formula (1).

[0008] TIFF2025092979000001.tif48170 [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for producing a pigment composition having good lightfastness while containing a yellow pigment that has been atomized to expand the range of color reproducibility. Furthermore, according to the present invention, it is possible to provide a method for producing a pigment dispersion, a method for producing an aqueous ink, and an inkjet recording method, which use the pigment composition obtained by the above-mentioned production method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0011] In order to obtain a pigment composition capable of expanding the range of color reproduction, the present inventors mixed a monoazo pigment, CI Pigment Yellow 74, a compound having a similar structure, a water-soluble inorganic salt, and an organic solvent, and then kneaded the mixture to produce a pigment composition. As a result, it was confirmed that the pigment was atomized by the kneading process, which expanded the range of color reproduction, but the lightfastness was significantly reduced. The present inventors speculate that the cause of this is as follows.

[0012] A mixture containing CI Pigment Yellow 74, a compound having a structure similar to that of CI Pigment Yellow 74, a water-soluble inorganic salt, and an organic solvent is kneaded by a solvent salt milling method to form a finely divided pigment composition having many crystal defects. The finely divided pigment composition has a wide range of color reproducibility. However, the present inventors believe that the finely divided pigment composition has many crystal defects, which causes distortion in the crystal structure and weakens the resistance to deterioration caused by external factors such as light.

[0013] Therefore, the present inventors diligently studied a method for reducing crystal defects when micronizing pigments. As a result, among the compounds represented by the following general formula (2) having a similar structure to C.I. Pigment Yellow 74, it was found that at least the compound represented by the following chemical formula (1) is effective when used in kneading by the solvent-salt milling method.

[0014] TIFF2025092979000002.tif48170

[0015] Among the compounds represented by the following general formula (2), the reason why the compound represented by chemical formula (1) (hereinafter, may be referred to as "Compound A") forms a pigment composition with particularly few crystal defects compared to other compounds is speculated by the present inventors as follows.

[0016] (i) Compound A has a molecular weight close to that of C.I. Pigment Yellow 74 among the group of compounds having a similar structure to C.I. Pigment Yellow 74. Also, (ii) Compound A has many hydrogen bonding groups (amide group, ketone group, ether group, amine group). A compound having both the above characteristics (i) and (ii) strongly adsorbs to C.I. Pigment Yellow 74 and reduces the probability of incorporating impurity components (such as o-acetetoacetanisidide and 2-methoxy-4-nitroaniline) during crystal growth. As a result, the present inventors believe that the pigment composition after crystal growth obtained using Compound A has fewer crystal defects and can maintain light resistance.

[0017] <Method for producing a pigment composition> The manufacturing method of one embodiment of the present invention is a method for manufacturing a pigment composition including a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product. The pigment is at least one monoazo pigment (hereinafter, may be simply referred to as "monoazo pigment") selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 1, and C.I. Pigment Yellow 9. Further, the mixture further contains the compound (Compound A) represented by the above chemical formula (1). Hereinafter, the kneading step, each used material, etc. will be described in detail.

[0018] 〔Kneading Step〕 In the kneading step in the manufacturing method of the pigment composition of the present embodiment, a mixture containing the above specific monoazo pigment, Compound A, a water-soluble inorganic salt, and an organic solvent is kneaded by a solvent-salt milling method to obtain a kneaded product. The solvent-salt milling method is a method of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent while applying a load to the mixture to compress it using a kneading apparatus. In the manufacturing method of the pigment composition of the present embodiment, a kneaded product containing atomized pigment, Compound A, a water-soluble inorganic salt, and an organic solvent can be obtained by the kneading step by the solvent-salt milling method.

[0019] As the kneading device, for example, batch-type and continuous-type kneading devices, as well as normal-pressure type, pressure-type, and reduced-pressure type kneading devices can be used, and a device that kneads while applying a load to the contents and compressing them can be preferably used. Further, a kneading device equipped with a material input section such as a kneading kettle and a hopper, and a stirring section such as a stirring blade, stirring wing, blade, screw, and roll for stirring the material can be preferably used. Specific kneading devices include, for example, kneading devices such as a kneader, a roll mill, a ball mill, an attritor, a sand mill, a planetary mixer, and a continuous single-screw kneader. Examples of the planetary mixer include Trimix (trade name) manufactured by Inoue Manufacturing Co., Ltd. Examples of the continuous single-screw kneader include Miracle KCK (trade name) manufactured by Asada Iron Works. Among the kneading devices listed above, it is preferable to use a planetary mixer.

[0020] Regarding the mixing ratio of the pigment, compound A, water-soluble inorganic salt, and organic solvent in the kneading process, it is preferably the following ratio based on the total usage amount of the pigment. In the kneading process, the usage amount of compound A is preferably 0.04 times or more and 0.21 times or less, and more preferably 0.05 times or more and 0.20 times or less, in terms of mass ratio to the total usage amount of the pigment. When the above mass ratio is 0.05 times or more, the possibility of impurities such as o-acetoacetanisidide and 2-methoxy-4-nitroaniline being incorporated during crystal growth during kneading is reduced. Therefore, it is easy to obtain a pigment with few crystal defects, and the light resistance of the obtained pigment composition is likely to increase. On the other hand, when the above mass ratio is 0.20 times or less, crystal growth during kneading is likely to be promoted, the refinement of the pigment can be moderately suppressed, and the light resistance of the obtained pigment composition is likely to increase.

[0021] In addition, the amount of the water-soluble inorganic salt used in the kneading step is preferably 3.0 times or more and 20.0 times or less, more preferably 5.0 times or more and 10.0 times or less, based on the total amount of the pigments used. The amount of the organic solvent used in the kneading step is preferably 0.5 times or more and 5.0 times or less, more preferably 0.8 times or more and 3.0 times or less, based on the total amount of the pigments used.

[0022] The temperature during kneading in the kneading step is preferably 15°C or higher and 95°C or lower, more preferably 20°C or higher and 90°C or lower. When the temperature during kneading is 20°C or higher, crystal growth is likely to be promoted, and the refinement of the pigment is moderately suppressed, so the light resistance of the obtained pigment composition is likely to increase. On the other hand, when the temperature during kneading is 90°C or lower, the rate of crystal growth is moderately suppressed, so that compound A having a structure similar to that of the monoazo pigment is preferentially incorporated, and the incorporation of impurities such as o-acetetoacetanisidide and 2-methoxy-4-nitroaniline is likely to be suppressed. As a result, a pigment with few crystal defects is obtained, and the light resistance of the obtained pigment composition is likely to increase. The kneading time in the kneading step is preferably 1 hour or more and 10 hours or less, more preferably 2 hours or more and 8 hours or less.

[0023] When producing the kneaded product, in addition to the mixture containing the monoazo pigment, compound A, water-soluble inorganic salt, and organic solvent, a pigment derivative may be added for the purpose of adjusting crystal growth and crystal dislocation of the pigment. As the pigment derivative to be added, a pigment derivative having the same structure as the pigment as the parent body is preferable, but a pigment derivative having a different structure may also be used. Examples of the substituent of the pigment derivative include a hydroxyl group, a carboxy group, a carbamoyl group, a sulfonic acid group, a sulfonamide group, and a phthalimidomethyl group. In addition, organic dyes also include light yellow aromatic polycyclic compounds such as naphthalene-based and anthraquinone-based compounds that are not generally called dyes. In particular, a pigment derivative having a basic group can be preferably used because of its large dispersion effect on the pigment. These can be used alone or in combination of two or more.

[0024] (Pigment) As the pigment, a specific monoazo pigment which is a yellow pigment is used. Specifically, from the viewpoints of color development property and dispersibility, at least one monoazo pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 1, and C.I. Pigment Yellow 9 is used. In addition to these specific monoazo pigments, other monoazo pigments may be further used. Examples of the other monoazo pigments include C.I. Pigment Yellow 2, 3, 4, 5, 6, 7, 10, 49, 65, 73, 75, 97, 98, 105, 111, 116, 130, 165, 167, and 205, etc. One or more of these may be used.

[0025] (Dye Derivative) In the kneading step, a dye derivative such as Compound A can be further added to the mixture containing the monoazo pigment, the water-soluble inorganic salt, and the organic solvent. It is considered that the dye derivative can inhibit the crystal growth of the pigment by adsorbing on the pigment surface and can make the primary particle size finer. Also, it is considered that the dye derivative can enhance the dispersion stability by imparting polarity to the pigment surface and interacting with the resin added when forming the coloring composition.

[0026] As the pigment derivative, known pigment derivatives having an acidic group, a basic group, a neutral group, etc. in the organic pigment residue can be used. Examples of the pigment derivative having an acidic group include compounds having an acidic substituent such as a sulfo group, a carboxy group, and a phosphate group, and amine salts thereof. Examples of the pigment derivative having a basic group include compounds having a basic substituent such as a sulfonamide group and a tertiary amino group at the terminal. Examples of the pigment derivative having a neutral group include compounds having a neutral substituent such as a phenyl group and a phthalimidoalkyl group. Examples of the organic pigment include diketopyrrolopyrrole-based pigments, anthraquinone-based pigments, quinacridone-based pigments, dioxazine-based pigments, perinone-based pigments, perylene-based pigments, thiazine indigo-based pigments, triazine-based pigments, benzimidazolone-based pigments, indole-based pigments such as benzisoindole, isoindoline-based pigments, isoindolinone-based pigments, quinophthalone-based pigments, naphthol-based pigments, fluorene-based pigments, metal complex-based pigments, azo-based pigments such as azo, disazo, and polyazo, and the like.

[0027] Specific examples of the azo-based pigment derivative include, in addition to Patent Document 2, known pigment derivatives described in JP-A-2012-21120, JP-A-2010-260997, JP-A-2008-231340, JP-A-2008-231338, JP-A-2008-156465, JP-A-2008-24733, and the like. Note that in these documents, the pigment derivative may be described as a derivative, a pigment derivative, a dispersant, a pigment dispersant, or simply a compound, etc. However, a compound having a substituent such as an acidic group, a basic group, or a neutral group in the above-described organic pigment residue is synonymous with the pigment derivative. These pigment derivatives can be used alone or in combination of two or more.

[0028] In the kneading step in the method for producing the pigment composition of the present embodiment, a compound represented by the following general formula (2) can be used as the monoazo pigment derivative. In the kneading step, among the compounds represented by the general formula (2), in the general formula (2), X 2 is -CONH-C6H5, X 5 and X 10is -OCH3, others (X 1 , X 3 , X 4 , X 6 , X 7 , X 8 , X 9 ) is -H, at least compound A is used. In the kneading step, in addition to compound A, one or more of the compounds represented by the general formula (2) other than compound A may also be used.

[0029] TIFF2025092979000003.tif50170

[0030] X in the general formula (2) 1 to X 5 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an alkoxycarbonyl group having 1 to 5 carbon atoms, a carboxy group, a nitro group, a sulfone group, a carbamoyl group, an N-phenylcarbamoyl group, a sulfamoyl group, or a trifluoromethyl group. Also, X 1 to X 5 may form an optionally substituted heterocyclic structure in which adjacent groups are combined to further contain a nitrogen atom, an oxygen atom, or a sulfur atom.

[0031] X in the general formula (2) 6 to X 10 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an acetylamino group, a carboxy group, a sulfone group, a nitro group, or a group represented by the following general formula (3).

[0032] TIFF2025092979000004.tif12170

[0033] In the general formula (3), Y 1 represents -SO2NR'- or -CONR'- R' represents a hydrogen atom, an alkyl group having 20 or less carbon atoms which may have a substituent, an alkenyl group having 20 or less carbon atoms which may have a substituent, or an aryl group having 20 or less carbon atoms which may have a substituent. Y2 represents a direct bond connecting Y 1 and Y 3 , an alkylene group having 20 or fewer carbon atoms which may have a substituent, an alkenylene group having 20 or fewer carbon atoms which may have a substituent, an arylene group having 20 or fewer carbon atoms which may have a substituent, or -Y 2a -Y 2b -Y 2c - represents. Y 2a and Y 2c each independently represent an alkylene group having 20 or fewer carbon atoms which may have a substituent, an alkenylene group having 20 or fewer carbon atoms which may have a substituent, or an arylene group having 20 or fewer carbon atoms which may have a substituent. Y 2b represents a direct bond connecting Y 2a and Y 2c , -O-, -CO-, -NR'-, or -SO2-. Y 3 represents a hydrogen atom, -OR 1 , -COOR 1 , -NR 1 R 2 , or -R 1 represents. Here, R 1 and R 2 each independently represent a hydrogen atom, an alkyl group having 20 or fewer carbon atoms which may have a substituent, an alkenyl group having 20 or fewer carbon atoms which may have a substituent, or an aryl group having 20 or fewer carbon atoms which may have a substituent. Further, R 1 and R 2 may be combined together to form an optionally substituted heterocyclic structure containing an additional nitrogen atom, oxygen atom, or sulfur atom. Further, R', R 1 , and R 2 each independently may be combined with Y 2 to form an optionally substituted heterocyclic structure containing an additional nitrogen atom, oxygen atom, or sulfur atom.

[0034] Examples of the halogen atom in X 1 to X 10 in the general formula (2) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. X 1 to X 10Examples of the alkyl group having 1 to 5 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, sec-pentyl group, and neopentyl group. X in the general formula (2) 1 to X 10 Examples of the alkoxy group having 1 to 5 carbon atoms include methoxy group, ethoxy group, propoxy group, butoxy group, tert-butoxy group, pentyloxy group, and neopentyloxy group. X in the general formula (2) 1 to X 5 Examples of the alkoxycarbonyl group having 1 to 5 carbon atoms include methoxycarbonyl group, ethoxycarbonyl group, tert-butoxycarbonyl group, and pentyloxycarbonyl group. X in the general formula (2) 1 to X 5 In, the optionally substituted heterocyclic structure formed by adjacent groups being integrated to include a further nitrogen atom, oxygen atom, or sulfur atom is not particularly limited. Examples of the heterocyclic structure include indole group, benzimidazolone group, benzofuryl group, benzothienyl group, pyrrole group, and quinoline group.

[0035] Examples of the optionally substituted alkyl group having 20 or less carbon atoms for R', R 1 and R 2 include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, octadecyl group, isopropyl group, isobutyl group, isopentyl group, sec-butyl group, tert-butyl group, sec-pentyl group, tert-pentyl group, tert-octyl group, neopentyl group, cyclopropyl group, cyclobutyl, and cyclopentyl group. R', R 1 and R 2Examples of the alkenyl group having 20 or less carbon atoms which may have a substituent include vinyl group, 1-propenyl group, allyl group, 2-butenyl group, 3-butenyl group, isopropenyl group, isobutenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, 3-hexenyl group, 1-octenyl group, 1-octadecenyl group, cyclopentenyl group, cyclohexenyl group, 1,3-butadienyl group, cyclohexadienyl group, cyclopentadienyl group, trifluoroethenyl group, 1-chloroethenyl group, 2,2-dibromoethenyl group, and 4-hydroxy-1-butenyl group. R', R 1 and R 2 Examples of the aryl group having 20 or less carbon atoms which may have a substituent include phenyl group, biphenyl group, indenyl group, tolyl group, xylyl group, p-cyclohexylphenyl group, p-cumenyl group, and m-carboxyphenyl group.

[0036] Also, Y mentioned in the description of the general formula (3) 2 , Y 2a and Y 2c Examples of the alkylene group having 20 or less carbon atoms which may have a substituent include methylene group, ethylene group, trimethylene group, tetramethylene group, propylene group, ethylmethylene group, chloromethylene group, dimethylmethylene group, and bis(trifluoromethyl)methylene group. Y 2 , Y 2a and Y 2c Examples of the alkenylene group having 20 or less carbon atoms which may have a substituent include vinylene group, 1-methylvinylene group, propenylene group, 1-butenylene group, 2-butenylene group, 1-pentenylene group, and 2-pentenylene group. Y 2 , Y 2a and Y 2cExamples of the arylene group having 20 or less carbon atoms which may have a substituent include an o-phenylene group, an m-phenylene group, a p-phenylene group, a 4-methyl-1,2-phenylene group, a 4-chloro-1,2-phenylene group, a 4-hydroxy-1,2-phenylene group, a 2-methyl-1,4-phenylene group, and a p,p'-biphenylylene group. R 1 and R 2 which are combined together to form an optionally substituted heterocyclic structure containing an additional nitrogen atom, oxygen atom, or sulfur atom are not particularly limited. Examples of the heterocyclic structure include an indole group, a benzimidazolone group, a benzofuryl group, a benzothienyl group, a pyrrole group, and a quinoline group. Also, R', R 1 , and R 2 which are each independently combined with Y 2 to form an optionally substituted heterocyclic structure containing an additional nitrogen atom, oxygen atom, or sulfur atom are not particularly limited. Examples of the heterocyclic structure include an indole group, a benzimidazolone group, a benzofuryl group, a benzothienyl group, a pyrrole group, and a quinoline group.

[0037] As the compound represented by the general formula (2) other than compound A, one or more of the following compounds are preferable. · A compound in which X 9 in the general formula (2) is an aromatic amide and the others are a hydrogen atom, a methoxy group, or a nitro group. · A compound in which any one of X 1 to X 5 in the general formula (2) is a sulfone group and the others are a hydrogen atom, a methoxy group, or a nitro group. · A compound in which X 8 in the general formula (2) is a -SO2NHC4H9 group and the others are a hydrogen atom, a methoxy group, or a nitro group. · A compound in which X 8 in the general formula (2) is a -CONH(CH2)3N(C2H5)2 group and the others are a hydrogen atom, a methoxy group, or a nitro group.

[0038] Monoazo pigments and compounds represented by the general formula (2) such as Compound A (monoazo pigment derivatives) can be obtained by diazotizing aromatic amines and then coupling them with acetoacetanilide compounds by known methods described in Patent Document 2 and the like. For example, methods include adding a diazotized product of an aromatic amine to a slurry containing an acetoacetanilide compound, or adding an alkaline aqueous solution of an acetoacetanilide compound to an aqueous solution of a diazotized product of an aromatic amine. Further, methods include simultaneously and gradually adding an aqueous solution of a diazotized product of an aromatic amine and an alkaline aqueous solution of an acetoacetanilide compound at a constant flow rate into an aqueous solution prepared in advance by adding a base such as acetic acid and sodium hydroxide. As the aromatic amine, for example, an aniline derivative (aniline having a substituent of X 1 to X 5 in the benzene ring) can be used. As the acetoacetanilide compound, for example, an acetoacetanilide derivative (acetoacetanilide having a substituent of X 1 to X 5 or X 6 to X 10 in the benzene ring) can be used.

[0039] (Water-soluble inorganic salt) The water-soluble inorganic salt used in the kneading step utilizes its high hardness to crush the pigment in the kneading step, contributing to the refinement of the primary particles of the pigment. The water-soluble inorganic salt is not particularly limited as long as it is an inorganic salt soluble in water. Specific examples of the water-soluble inorganic salt include sodium chloride, potassium chloride, sodium sulfate, zinc chloride, calcium chloride, and magnesium chloride, and mixtures of two or more of them. Among them, from the perspective of price, it is preferable to use sodium chloride.

[0040] Regarding the particle size of the water-soluble inorganic salt, in the volume-based particle size distribution, the cumulative 50% particle size (median particle size; D 50 ) is 1 μm or more and 250 μm or less, and the cumulative 95% particle size (D 95) is preferably 500 μm or less. Particularly when a fine pigment is desired, the water-soluble inorganic salt used as a grinding aid is also preferably fine. Specifically, in the particle size distribution based on volume, the cumulative 50% particle size (D 50 ) is 1 μm or more and 10 μm or less, and the cumulative 95% particle size (D 95 ) is more preferably a water-soluble inorganic salt of 20 μm or less.

[0041] For D of the water-soluble inorganic salt 50 and D 95 , values measured using an optical microscope can be adopted. Specifically, the particle sizes of 500 water-soluble inorganic salt particles are measured using an optical microscope, and a method of calculating D 50 and D 95 from the particle size distribution based on volume can be mentioned. For the water-soluble inorganic salt used in the examples described later, D 50 and D 95 were also determined by the above measurement method.

[0042] As the quality of the water-soluble inorganic salt, the water content is also important. Industrial grade salt usually contains 1.0 mass% or more of water. From the viewpoint of suppressing the spread of the particle size distribution of the refined pigment and easily adjusting the average primary particle size of the pigment to be in the range of 10 nm or more and 100 nm or less, the water content of the water-soluble inorganic salt is preferably 3.0 mass% or less, and more preferably 1.5 mass% or less.

[0043] (organic solvent) The organic solvent used in the kneading step is for wetting the mixture of the pigment and the water-soluble inorganic salt and making a dough (a mass formed by kneading) of appropriate firmness. Thereby, a strong load is likely to be applied to the kneaded material, increasing the grinding effect and promoting the refinement of the pigment.

[0044] The organic solvent is not particularly limited, but water-soluble organic solvents such as alcohols, glycols, and ethers are preferred. Specific water-soluble organic solvents include, for example, 2-(methoxymethoxy)ethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, liquid polyethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, low molecular weight polypropylene glycol, aniline, pyridine, tetrahydrofuran, dioxane, methanol, ethanol, isopropanol, n-propanol, isobutanol, n-butanol, ethylene glycol, propylene glycol, propylene glycol monomethyl ether acetate, ethyl acetate, isopropyl acetate, acetone, methyl ethyl ketone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone. One of the above water-soluble organic solvents may be used alone, or two or more thereof may be mixed and used as necessary. Among them, it is preferable to use highly viscous water-soluble organic solvents such as ethylene glycol, diethylene glycol, and polyethylene glycol.

[0045] 〔Other steps〕 Through the above kneading process, a kneaded product containing a pigment, Compound A, a water-soluble inorganic salt, an organic solvent, etc. can be obtained. In the method for producing the pigment composition of the present embodiment, it is preferable to perform a step of removing the water-soluble inorganic salt and the organic solvent from the kneaded product obtained by the above kneaded process. As the method, for example, after putting the kneaded product into water at a predetermined ratio with respect to the kneaded product to obtain a pigment suspension (slurry), the water-soluble inorganic salt and the organic solvent can be removed from the kneaded product by filtering and washing this pigment suspension. The filtration method is not particularly limited, but it is preferable to adopt a method of separating by passing the above pigment suspension through an ultrafiltration membrane or a dialysis membrane, or a method of separating with a high-pressure filter press, etc.

[0046] Through the steps including the above filtration, etc., a wet cake of the pigment composition from which the water-soluble inorganic salt and the organic solvent have been separated is obtained. Considering the growth of bacteria, it is preferable to dry the obtained wet cake so that the water content is 5% by mass or less. As the drying method, for example, batch or continuous drying for dehydrating and / or desolventizing the wet cake by heating at 80°C or higher and 120°C or lower by a heat source installed in a dryer can be mentioned. Examples of the dryer include a box-type dryer, a band dryer, and a spray dryer.

[0047] <Method for Producing Pigment Dispersion> It is possible to produce a pigment dispersion using the pigment composition obtained by the method for producing the pigment composition described above. The method for producing the pigment dispersion includes a dispersion step of mixing the pigment composition obtained by the method for producing the pigment composition described above, a dispersant, and water, and dispersing the pigment composition in water with the dispersant. As the pigment composition, it is preferable to use a pigment composition containing a pigment and Compound A obtained after removing the water-soluble inorganic salt and the organic solvent from the kneaded product obtained in the method for producing the pigment composition described above. As the water, it is preferable to use deionized water such as ion-exchanged water or pure water.

[0048] 〔Dispersion Step〕 As a dispersion method for dispersing a pigment in water as a dispersion medium, for example, a resin-dispersed pigment using a resin as a dispersant, a self-dispersing pigment in which a hydrophilic group is bonded to the particle surface of the pigment, or the like can be used. Further, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, a microcapsule pigment in which the particle surface of the pigment is coated with a resin, or the like can be used. In order to disperse the above-described pigment composition in water as a dispersion medium, it is preferable to use a resin (resin dispersant) or a surfactant as a dispersant. Among them, it is more preferable to use a resin (resin having an anionic group) capable of stably dispersing the pigment in the dispersion medium by the action of the anionic group.

[0049] As the resin, a resin obtained by copolymerizing a polymerizable hydrophobic monomer and a polymerizable hydrophilic monomer, having a structural unit derived from the hydrophobic monomer, and a structural unit derived from a hydrophilic monomer having an anionic group is preferable. Examples of the hydrophobic monomer include styrene, α-methylstyrene, n-butyl acrylate, n-hexyl acrylate, benzyl methacrylate, and the like. One or more of the hydrophobic monomers can be used. Examples of the hydrophilic monomer include hydrophilic monomers having a carboxy group such as acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propyl acrylic acid, isopropyl acrylic acid, itaconic acid, and fumaric acid; hydrophilic monomers having a sulfonic acid group such as styrene sulfonic acid, sulfonic acid-2-propylacrylamide, acrylic acid-2-sulfonic acid ethyl, methacrylic acid-2-sulfonic acid ethyl, and butylacrylamide sulfonic acid; hydrophilic monomers having a phosphonic acid group such as methacrylic acid-2-phosphonic acid ethyl and acrylic acid-2-phosphonic acid ethyl; and the like. One or more of the hydrophilic monomers can be used.

[0050] The weight-average molecular weight of the resin used as a dispersant is preferably 1,000 or more and 30,000 or less, more preferably 3,000 or more and 15,000 or less. The weight-average molecular weight of the resin can be a value in terms of standard polystyrene measured using gel permeation chromatography (GPC). The acid value (mgKOH / g) of the resin is preferably 40 mgKOH / g or more and 300 mgKOH / g or less, more preferably 100 mgKOH / g or more and 250 mgKOH / g or less. The acid value of the resin can be a value measured by a potentiometric titration apparatus using a potassium hydroxide-methanol titrant. The amount of the resin used is preferably 10% by mass or more and 50% by mass or less based on the amount of the pigment used.

[0051] When dispersing the pigment composition in a dispersion medium, a dispersing device can be used. Examples of the dispersing device include an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a sand mill, a sand grinder, a dyno mill, a dispermat, an SC mill, a spike mill, a nanomizer, an agitator mill, and a planetary mill.

[0052] The content (% by mass) of the pigment in the pigment dispersion is preferably 1.0% by mass or more and 50.0% by mass or less, more preferably 5.0% by mass or more and 30.0% by mass or less based on the total mass of the pigment dispersion.

[0053] The pigment composition and the pigment dispersion containing the same can be suitably used for any application that requires a coloring function. Examples of such applications include paints, printing inks, colored molded articles, toners for electrostatic charge image development, color filters for liquid crystal display devices, and inks for inkjet. Among these, aqueous inks for inkjet are preferred.

[0054] <Method for manufacturing ink> It is possible to produce an aqueous ink using the pigment dispersion obtained by the above-described method for producing a pigment dispersion. The method for producing the aqueous ink includes a step of mixing a component containing the pigment dispersion obtained by the above-described method for producing a pigment dispersion and a water-soluble organic solvent. When preparing the ink in this step, in addition to the aforementioned pigment dispersion and water-soluble organic solvent, water and other additives used as necessary can be blended as the above components to prepare the ink.

[0055] (Colorant) Since the ink contains the pigment dispersion obtained by the above-described method for producing a pigment dispersion, it contains the pigment composition obtained by the above-described method for producing a pigment composition as a colorant. The content (mass%) of the pigment in the ink is preferably 0.1 mass% or more and 15.0 mass% or less, more preferably 1.0 mass% or more and 10.0 mass% or less, based on the total mass of the ink.

[0056] (Aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. As the aqueous medium for the ink, water or a mixed solvent of water and a water-soluble organic solvent can be used. Deionized water (ion-exchanged water) is preferably used as the water. The content (mass%) of water in the ink is preferably 40.0 mass% or more and 95.0 mass% or less, more preferably 50.0 mass% or more and 95.0 mass% or less, based on the total mass of the ink.

[0057] As the water-soluble organic solvent, any of those conventionally commonly used in inks for inkjet can be used. Examples of the water-soluble organic solvent include alkyl alcohols having 1 to 4 carbon atoms, amides, ketones, keto alcohols, ethers, polyalkylene glycols, glycols, alkylene glycols having 2 to 6 carbon atoms in the alkylene group, polyhydric alcohols, alkyl ether acetates, alkyl ethers of polyhydric alcohols, nitrogen-containing compounds, and sulfur-containing compounds. These water-soluble organic solvents can be used alone or in combination of two or more as necessary. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less, more preferably 3.0% by mass or more and 40.0% by mass or less, based on the total mass of the ink.

[0058] (Other Additives) In order to maintain properties such as moisture retention, the ink may contain solid compounds having moisture retention at normal temperature, such as urea, urea derivatives, trimethylolpropane, and trimethylolethane, in addition to the above-described components. The content (% by mass) of such a compound in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, more preferably 3.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. Further, the ink may contain various additives such as surfactants, pH adjusters, rust preventives, antiseptics, fungicides, antioxidants, and anti-reduction agents as necessary in addition to the above-described components.

[0059] <Inkjet Recording Method> The ink obtained by the above-described method for producing an ink is preferably used in an inkjet recording method. The inkjet recording method is an inkjet recording method in which the aqueous ink obtained by the above-described method for producing an aqueous ink is ejected from an inkjet recording head and an image is recorded on a recording medium. Examples of the method of ejecting the ink include a method of ejecting the ink by applying mechanical energy to the ink and a method of ejecting the ink by applying thermal energy to the ink.

[0060] <Ink Cartridge> When using the above ink in an inkjet recording method, an ink cartridge can be used. The ink cartridge includes the above ink and an ink storage unit for storing the ink. Furthermore, it may be an ink cartridge configured to have an ink storage unit and a recording head.

Examples

[0061] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Regarding the amounts of components, "parts" and "%" are based on mass unless otherwise specified.

[0062] <Synthesis of Monoazo Pigment> (Synthesis of C.I. Pigment Yellow 74) 67.2 g of 2-methoxy-4-nitroaniline as a diazo component was added to 500 g of water, stirred to prepare a suspension, and further ice was added to adjust the temperature to 5°C or lower. 105 g of 35% hydrochloric acid was added thereto, and the mixture was stirred for 1 hour while maintaining the temperature at 5°C or lower. Then, an aqueous solution prepared by adding 28.0 g of sodium nitrite to 72.0 g of water was added, and diazotization was carried out by stirring for 1 hour. 0.5 g of sulfamic acid was added to the reaction mixture to eliminate nitrous acid, and a diazonium aqueous solution was prepared.

[0063] On one hand, 84.5 g of o-acetacetanisidide and 164 g of 25% aqueous sodium hydroxide solution were added to 140 g of water as coupler components, and stirred until completely dissolved. This was then poured into an aqueous solution prepared by mixing 82.0 g of 80% acetic acid and 420 g of water to prepare a coupler slurry. The prepared coupler slurry was heated to 40 °C, and the above diazonium aqueous solution was added dropwise thereto over 1 hour. After completion of the dropping, stirring was carried out at the same temperature for 1 hour to complete the reaction. After completion of the reaction, the slurry was heated to 90 °C, stirred for 1 hour, and then filtered through a Buchner funnel with a diameter of 285 mm. During filtration, 25 L of ion-exchanged water was poured over for washing, dried, and pulverized to obtain 150 g of C.I. Pigment Yellow 74, which is a monoazo pigment.

[0064] (Synthesis of C.I. Pigment Yellow 1) In the synthesis of the above C.I. Pigment Yellow 74, 67.2 g of 2-methoxy-4-nitroaniline used as the diazo component was changed to 60.8 g of 4-methyl-2-nitroaniline. Also, in the synthesis of the above C.I. Pigment Yellow 74, 84.5 g of o-acetacetanisidide used as the coupler component was changed to 72.2 g of acetoacetanilide. Otherwise in the same manner, 132 g of C.I. Pigment Yellow 1, which is a monoazo pigment, was obtained.

[0065] (Synthesis of C.I. Pigment Yellow 9) In the synthesis of the above C.I. Pigment Yellow 74, 67.2 g of 2-methoxy-4-nitroaniline used as the diazo component was changed to 60.8 g of 4-methyl-2-nitroaniline. Also, in the synthesis of the above C.I. Pigment Yellow 74, 84.5 g of o-acetacetanisidide used as the coupler component was changed to 78.0 g of N-acetacetyl-o-toluidine. Otherwise in the same manner, 137 g of C.I. Pigment Yellow 9, which is a monoazo pigment, was obtained.

[0066] <Manufacture of Pigment Composition> The respective components shown in the middle column of Table 1 were mixed and kneaded for 8 hours at the kneading temperature shown in the right column of Table 1 using a planetary mixer (trade name "Trimix", manufactured by Inoue Seisakusho) to perform a micronization treatment of the pigment and obtain a kneaded product. In this way, in the production of Pigment Compositions 1 to 31, a kneaded product containing a pigment, a water-soluble inorganic salt, and an organic solvent was obtained by a kneading step using the solvent salt milling method. By thoroughly washing, filtering, and drying each of the obtained kneaded products, the water-soluble inorganic salt and the organic solvent were removed from the kneaded products to obtain Pigment Compositions 1 to 33. The meanings of the abbreviations in Table 1 and the structural formulas of Compounds B to G are shown below.

[0067] TIFF2025092979000005.tif232170

[0068] · PY74: C.I. Pigment Yellow 74 · PY1: C.I. Pigment Yellow 1 · PY9: C.I. Pigment Yellow 9 · PY73: C.I. Pigment Yellow 73 · PY213: C.I. Pigment Yellow 213 · NaCl: D 50 where D 95 is 250 μm and D · CaCl2: D 50 where D 95 is 250 μm and D · DEG: Diethylene glycol · DMSO: N,N-Dimethylformamide

[0069] · Compound B: In General Formula (2), X 9 is an aromatic amide, and the others (X 1 to X 8 and X 10 are -H, -OCH3, or NO2). · Compound C: In General Formula (2), X 1 to X 5 any one of which is -SO3H, and the others are -H, -OCH3, or -NO2). · Compound D: In General Formula (2), X8 is -CONH-(CH2)3-N(C2H5)2, and the others (X 1 to X 7 , X 9 and X 10 ) are -H, -OCH3, or -NO2. · Compound E: In general formula (2), X 8 is -SO2NH-C4H9, and the others (X 1 to X 7 , X 9 and X 10 ) are -H, -OCH3, or -NO2. · Compound F: A compound represented by the following chemical formula (F). · Compound G: A compound represented by the following chemical formula (G).

[0070] TIFF2025092979000006.tif45170

[0071] TIFF2025092979000007.tif37170

[0072] <Synthesis of Resin> A water-soluble random copolymer resin was synthesized according to the procedure shown below. After putting 200.0 parts of isopropanol into a flask equipped with a stirrer, a nitrogen inlet tube, a reflux condenser, and a thermometer, the temperature was raised to 85°C with stirring under a nitrogen atmosphere. The monomer mixture shown in Table 2 and the polymerization initiator were each added dropwise into the flask over 2 hours while maintaining the temperature at 80°C. The internal temperature was maintained at 80°C and stirred for 4 hours to synthesize the resin. After adding 0.9 equivalents of potassium hydroxide and an appropriate amount of ion-exchanged water to the acid value of the resin, isopropanol was removed under reduced pressure to obtain an aqueous resin solution, which is an alkaline aqueous solution of Resin 1. The content of Resin 1 (solid content) in this aqueous resin solution was 20.0%. The meanings of the abbreviations in Table 2 are shown below. St: Styrene nBA: n-Butyl acrylate AA: Acrylic acid Coincidence initiator: A solution prepared by dissolving 5.0 parts of "Perkadox L-W75(LS)" (manufactured by Kayaku Akzo, dibenzoyl peroxide, purity 75%) in 10.0 parts of isopropanol

[0073] TIFF2025092979000008.tif23170

[0074] <Preparation of pigment dispersion liquid> Using each of the obtained pigment compositions 1 to 33, pigment dispersion liquids 1 to 33 with numbers corresponding to the numbers of the pigment compositions were prepared. Specifically, 20 parts of the pigment composition of the type (number) shown in Table 3 below, 30 parts of the aqueous solution of Resin 1, and 50 parts of ion-exchanged water were mixed, and dispersion treatment was performed at a treatment pressure of 200 MPa using a high-pressure homogenizer (trade name "Starburst", manufactured by Sugino Machine). Thereafter, an appropriate amount of ion-exchanged water was added to obtain pigment dispersion liquids 1 to 33 with a pigment content of 15.0%.

[0075] <Preparation of ink> Using each of the obtained pigment dispersion liquids 1 to 33, inks 1 to 33 with numbers corresponding to the numbers of the pigment dispersion liquids were prepared. Specifically, using the pigment dispersion liquids of the type (number) shown in Table 3 below, the following components containing the pigment dispersion liquid were mixed, and after sufficient stirring, pressure filtration was performed using a microfilter (manufactured by Fujifilm) with a pore size of 2.5 μm to prepare inks 1 to 33. Acetylenol E60 shown below is the trade name of a surfactant manufactured by Kawaken Fine Chemicals. Also, Proxel GXL(S) is the trade name of a preservative manufactured by Lonza Japan. (Components of ink) Pigment dispersion liquid (any one of 1 to 33) 20.0 parts Glycerin 7.0 parts Triethylene glycol 2.0 parts 2-Pyrrolidone 2.0 parts Triethylene glycol monobutyl ether 2.0 parts Acetylenol E60 1.0 part Proxel GXL(S) 0.3 part Ion-exchanged water 65.7 parts

[0076] <Evaluation> (Evaluation of light resistance) As an inkjet recording apparatus, a product named "ImagePROGRAF Pro-1000" (manufactured by Canon) was prepared. In this inkjet recording apparatus, an image recorded under the condition of applying about 4 ng of ink per drop to a unit area of 1 / 1,200 inch × 1 / 1,200 inch at a resolution of 1,200 dpi × 1,200 dpi is defined as having a recording duty of 100%. Using the above inkjet recording apparatus, images of each ink were recorded on a recording medium in the fine art smooth printing mode without color correction. For each recorded image, a weather resistance tester (product name "Super Xenon Weather Meter SX75", manufactured by Suga Test Instruments Co., Ltd.) was used, and a light resistance test was performed under the conditions of an illuminance of 180 W / m 2 , a black panel temperature of 60 °C, and a relative humidity of 50%. Before and after the light resistance test, a spectrophotometer (product name "Spectrolino", manufactured by Gretag Macbeth) was used to measure the optical density (O.D. value; initial and after the test) of each image. For three locations where the initial O.D. values of each image were "0.6", "1.0", and "maximum value", the time point (number of days) when the O.D. value after the test decreased to 70% of the initial O.D. value was determined as the lifespan, and the light resistance of the image was evaluated according to the following evaluation criteria. In this example, "AA" and "A" were set as acceptable levels and "B" as an unacceptable level according to the following evaluation criteria. The evaluation results are shown in the right column of Table 3. AA: 125 days or more and less than 150 days (equivalent to 125 years or more) A: 100 days or more and less than 125 days (equivalent to 100 years or more) B: 80 days or more and less than 100 days (equivalent to 80 years or more)

[0077] TIFF2025092979000009.tif169170

[0078] Note that the disclosure of this embodiment includes the following methods. (Method 1) A method for manufacturing a pigment composition including a kneading step of kneading a mixture including a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product, The pigment is at least one monoazo pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 1, and C.I. Pigment Yellow 9. A method for producing a pigment composition, characterized in that the mixture further contains a compound represented by the following chemical formula (1).

[0079] TIFF2025092979000010.tif48170

[0080] (Method 2) The method for producing a pigment composition according to Method 1, wherein the amount of the compound represented by the chemical formula (1) used in the kneading step is 0.05 times or more and 0.20 times or less in terms of the mass ratio to the total amount of the pigments used. (Method 3) The method for producing a pigment composition according to Method 1 or 2, wherein the temperature during kneading in the kneading step is 20°C or higher and 90°C or lower. (Method 4) A method for producing a pigment dispersion liquid, characterized by including a dispersion step of mixing a pigment composition, a dispersant, and water obtained by the method for producing a pigment composition according to any one of Methods 1 to 3, and dispersing the pigment composition in the water with the dispersant. (Method 5) A method for producing an aqueous ink, characterized by including a step of mixing a pigment dispersion liquid obtained by the method for producing a pigment dispersion liquid according to Method 4 and a component containing a water-soluble organic solvent. (Method 6) An inkjet recording method of ejecting ink from an inkjet recording head and recording an image on a recording medium, wherein the ink is an aqueous ink obtained by the method for producing an aqueous ink according to Method 5.

Claims

1. A method for producing a pigment composition, comprising a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product, wherein the pigment is at least one monoazo pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 1, and C.I. Pigment Yellow 9, and the mixture further contains a compound represented by the following chemical formula (1), characterized in that it is a method for producing a pigment composition.

2. The method for producing a pigment composition according to claim 1, wherein the amount of the compound represented by the chemical formula (1) used in the kneading step is 0.05 times or more and 0.20 times or less in terms of mass ratio with respect to the total amount of the pigment used.

3. The method for producing a pigment composition according to claim 1, wherein the temperature during kneading in the kneading step is 20°C or higher and 90°C or lower.

4. A method for producing a pigment dispersion liquid, comprising a dispersion step of mixing a pigment composition obtained by the method for producing a pigment composition according to any one of claims 1 to 3, a dispersant, and water, and dispersing the pigment composition in the water by the dispersant.

5. A method for producing an aqueous ink, comprising a step of mixing a pigment dispersion liquid obtained by the method for producing a pigment dispersion liquid according to claim 4 and a component containing a water-soluble organic solvent.

6. An inkjet recording method of ejecting ink from an inkjet recording head and recording an image on a recording medium, wherein the ink is an aqueous ink obtained by the method for producing an aqueous ink according to claim 5, characterized in that it is an inkjet recording method.

Images