Method for producing pigment composition, method for producing pigment dispersion, method for producing water-based ink, and inkjet recording method

Abstract

To provide a method for producing a pigment composition which enables production of a pigment composition having superior ozone resistance.SOLUTION: A method for producing a pigment composition comprises a kneading step in which a mixture containing a pigment, a water-soluble inorganic salt, an organic solvent, and a water-insoluble antioxidant is kneaded by a solvent salt milling technique to provide a kneaded product.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, the market using pigments has expanded in various fields such as color filters and inks for inkjet. Along with this, pigments are required to have not only high color characteristics but also various reliabilities such as stability and filterability when used as a coloring composition, and suitability when applied to a substrate. In particular, due to the spread of various recording devices using the inkjet method, inkjet inks are being used to obtain recordings installed outdoors, such as posters for outdoor exhibitions and recordings for building materials. Therefore, there is an increasing demand for aqueous inks containing pigments as colorants (hereinafter sometimes referred to as "pigment inks") to have excellent ozone resistance so that recordings can be installed even in high-temperature and high-humidity outdoor environments.

[0003] For example, Patent Document 1 discloses an ink using a phthalocyanine pigment excellent in ozone resistance and the like. By using a pigment composed of a dye having a specific functional group like the ink disclosed in Patent Document 1, it becomes possible to obtain a recording excellent in ozone resistance. However, high color development and ozone resistance are in a trade-off relationship, and even if attempts like those disclosed in Patent Document 1 are made, if the molecular structure of the pigment is limited, there is also a limit to the improvement of ozone resistance. Under such circumstances, instead of seeking a solution in the molecular structure of the pigment, using additives and the like have also been proposed. For example, Patent Document 2 proposes an aqueous ink for inkjet containing a pigment, a styrene resin, an aqueous medium, and polycarbonate-modified urethane resin particles encapsulating an ultraviolet absorber and an antioxidant.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the ink disclosed in the above Patent Document 2, it is said that high color development property and light resistance can be achieved. However, since the antioxidant does not exist in the vicinity of the pigment, the actual situation is that it has not reached the level of ozone resistance that has been increasing in recent years.

[0006] Therefore, an object of the present invention is to provide a method for producing a pigment composition capable of producing a pigment composition excellent in ozone resistance. 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 mixture further contains a water-insoluble antioxidant.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a method for producing a pigment composition capable of producing a pigment composition excellent in ozone resistance. Further, 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 using the pigment composition obtained by the above production method.

Embodiments for Carrying Out the Invention

[0009] 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.

[0010] The present inventors have conducted various studies to improve the ozone resistance of aqueous pigment inks using antioxidants. When a water-soluble antioxidant was added directly to the aqueous pigment ink, the ozone resistance could not be improved. The present inventors speculate that this is because when the aqueous pigment ink to which the water-soluble antioxidant was added was applied to a recording medium, the antioxidant was also absorbed into the recording medium together with the water, and the antioxidant's effect could not be fully imparted to the pigment on the recording medium.

[0011] Therefore, the water-insoluble antioxidant was directly added to the aqueous pigment ink, but it was suspended in water, and the color development and storage stability were reduced, and the performance of the ink could not be maintained. Furthermore, when a dispersion of the water-insoluble antioxidant dispersed in water was directly added to the aqueous pigment ink, the color development and storage stability were not reduced, and the performance of the ink could be maintained. Then, an image was recorded on a recording medium by an inkjet recording method using the aqueous pigment ink to which the aqueous dispersion of the water-insoluble antioxidant was added, and the ozone resistance was measured using the obtained recorded matter, and the improvement of the ozone resistance was confirmed. However, the ozone resistance desired by the present inventors could not be satisfied. Unlike the water-soluble antioxidant, the water-insoluble antioxidant is thought to remain on the recording medium in the recorded matter. However, the present inventors speculate that the water-insoluble antioxidant could not remain in the vicinity of all the pigments on the recording medium, and the role of the antioxidant could not be fully exerted.

[0012] The inventors considered that the ozone resistance could be improved by retaining a water-insoluble antioxidant on the surface of the pigment. Therefore, the pigment and the water-insoluble antioxidant were mixed and stirred in an organic solvent, and then the obtained pigment composition after washing was incorporated into an aqueous ink and the ozone resistance was measured in the same manner as described above. However, the ozone resistance did not improve. It is presumed that the water-insoluble antioxidant could not be retained on the pigment surface by simple stirring.

[0013] Therefore, the inventors focused on the solvent-salt milling method as a technique for retaining the water-insoluble antioxidant on the pigment surface. 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. In the solvent-salt milling method, the pigment is pulverized by the water-soluble inorganic salt to create an energetically unstable fracture surface, and the fracture surfaces of the finely pulverized pigments adsorb to each other and crystal growth occurs, whereby the particle diameter of the pigment is adjusted. The inventors considered that a strong adsorptive force is required to retain the water-insoluble antioxidant on the pigment surface. The fracture surface of the pigment created by the solvent-salt milling method has a strong adsorptive ability, and it was considered that the water-insoluble antioxidant could be retained on the pigment surface by adding the water-insoluble antioxidant during the kneading step by the solvent-salt milling method.

[0014] The inventors kneaded a mixture containing a pigment, a water-soluble inorganic salt, a water-insoluble antioxidant, and an organic solvent by the solvent-salt milling method to prepare a kneaded product. After washing this kneaded product, a pigment composition, a dispersant, and water were blended to prepare a pigment dispersion. Then, an aqueous ink was prepared using the pigment dispersion, and when the ozone resistance was measured in the same manner as described above using this ink, a significant improvement in the ozone resistance was confirmed.

[0015] <Method for producing pigment composition> The manufacturing method according to an 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 above mixture further contains a water-insoluble antioxidant. Hereinafter, the kneading step, each material used, and the like will be described in detail.

[0016] 〔Kneading Step〕 In the kneading step in the method for manufacturing the pigment composition of the present embodiment, a mixture containing a pigment, a water-insoluble antioxidant, 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 device. In the method for manufacturing the pigment composition of the present embodiment, a kneaded product containing a refined pigment, a water-insoluble antioxidant, a water-soluble inorganic salt, and an organic solvent can be obtained by the kneading step by the solvent-salt milling method.

[0017] As the kneading device, for example, batch-type and continuous-type, 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 to compress them can be preferably used. Also, 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 examples of the kneading device include kneading devices such as a kneader, a roll mill, a ball mill, an attritor, a sand mill, a planetary mixer, and a continuous single-shaft kneader. Examples of the planetary mixer include Trimix (trade name) manufactured by Inoue Manufacturing Co., Ltd. Examples of the continuous single-shaft 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.

[0018] In the kneading process, the amount of the water-insoluble antioxidant used is preferably 0.1% by mass or more and 15.0% by mass or less, more preferably 0.5% by mass or more and 10.0% by mass or less, in terms of mass ratio to the amount of the pigment used. When the amount of the water-insoluble antioxidant used is 0.5% by mass or more based on the amount of the pigment used, the ozone resistance of the resulting pigment composition is more likely to be further improved. From this perspective, the amount of the water-insoluble antioxidant used based on the amount of the pigment used is more preferably 1.0% by mass or more. On the other hand, if the water-insoluble antioxidant covers the entire surface of the pigment, it is considered that the antioxidant function of the water-insoluble antioxidant can be sufficiently imparted. From this perspective and from the viewpoints of the storage stability and ejection stability of the ink when preparing an inkjet ink using the resulting pigment composition, the amount of the water-insoluble antioxidant used based on the amount of the pigment used is more preferably 10.0% by mass or less.

[0019] Regarding the mixing ratio of the pigment, the water-soluble inorganic salt, and the organic solvent in the kneading process, it is preferably the following ratio based on the amount of the pigment used. In the kneading process, the amount of the water-soluble inorganic salt used 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, in terms of mass ratio to the amount of the pigment used. Also, in the kneading process, the amount of the organic solvent used 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, in terms of mass ratio to the amount of the pigment used.

[0020] The kneading time in the kneading process is preferably 1 hour or more and 10 hours or less, more preferably 2 hours or more and 8 hours or less. When the kneading time is 2 hours or more, the adsorption amount of the water-insoluble antioxidant on the pigment surface is likely to be sufficient, and the ozone resistance is likely to be improved. On the other hand, when the kneading time is 8 hours or less, it is easy to suppress the aggregation of the pigments, and it is easy to suppress the broadening of the particle size distribution of the resulting pigment composition.

[0021] (Shearing force) In the method for producing the pigment composition of the present embodiment, in order to adsorb the water-insoluble antioxidant on the pigment surface, it is important to expose the crushed surface of the pigment during kneading. Therefore, kneading is performed by a solvent-salt milling method that applies a strong load to the pigment. When specifically expressing this "applying a load", it can be expressed by the "shearing rate". The shearing rate during kneading in the kneading step is preferably 10 s -1 or more, and from the viewpoint of easily applying a shearing force to the pigment itself, it is more preferably 15 s -1 or more, and even more preferably 20 s -1 or more.

[0022] (Pigment) Examples of pigments used in the kneading process include carbon black and organic pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of organic pigments include water-insoluble azo pigments such as toluidine red, toluidine maroon, C.I. Pigment Red 150, Hansa yellow, benzidine yellow, C.I. Pigment Yellow 74, and pyrazolone red; water-soluble azo pigments such as lithol red, heliobordeaux, pigment scarlet, and permanent red 2B; phthalocyanine pigments such as copper phthalocyanine blue and copper phthalocyanine green; quinacridone pigments such as quinacridone red and quinacridone magenta; perylene pigments such as perylene red and perylene scarlet; isoindolinone pigments such as isoindolinone yellow and isoindolinone orange; benzimidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red; pyranthrone pigments such as pyranthrone red and pyranthrone orange; as well as indigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, and dioxazine violet. Of course, it is not limited to these. One of the above pigments may be used alone, or two or more may be used in combination.

[0023] (Non-water-soluble antioxidant) An antioxidant is a compound that has the effect of stopping a chain reaction by scavenging radicals and decomposing itself. In addition, the antioxidant used in the method for producing the pigment composition of the present embodiment needs to stay on the pigment surface in the aqueous pigment ink. Here, when a water-soluble antioxidant is used, the water-soluble antioxidant elutes from the pigment surface during purification of the pigment composition, preparation of the pigment dispersion, and preparation of the aqueous pigment ink. Therefore, the water-soluble antioxidant does not exist on the pigment surface, and improvement in ozone resistance cannot be obtained. Therefore, a water-insoluble antioxidant is used in the method for producing the pigment composition of the present embodiment. Here, it is more preferable that the water-insoluble antioxidant is not dissolved in water, but the "water-insoluble antioxidant" in the present disclosure refers to an antioxidant having a solubility in water at 25 °C of less than 10% by mass.

[0024] Examples of suitable water-insoluble antioxidants include hindered amine-based antioxidants, hindered phenol-based antioxidants, phosphite-based antioxidants, phosphonite-based antioxidants, and thioether-based antioxidants. It is more preferable to use one or more of these water-insoluble antioxidants.

[0025] Specific non-water-soluble antioxidants include, for example, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-(hexane-1,6-diyl)bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 branched alkyl ester, 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(mesitylene-2,4,6-triyl)tri-p-cresol, calcium diethyl bis{[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl}phosphonate / polyethylene wax, 4,6-bis(octylthiomethyl)-o-cresol, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, tris(2,4-di-tert-butylphenyl) phosphite / pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate, N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, reaction product of N-phenylbenzenamine / 2,4,4-trimethylpentene, 2,6-di-tert-butyl-4-[(4,6-bis(octylthio)-1,3,5-triazin-2-yl)amino]phenol, 3,9 - Bis[2 - [3 - (3 - tert - butyl - 4 - hydroxy - 5 - methylphenyl)propionyloxy]-1,1 - dimethylethyl]-2,4,8,10 - tetraoxo - spiro(5,5)undecene, triphenyl phosphite, tris(2,4 - di - tert - butylphenyl)phosphite, bis[2,4 - bis(1,1 - dimethylethyl)-6 - methylphenyl]ethyl ester phosphorous acid, 2’,3 - bis[3 - [3,5 - di - tert - butyl - 4 - hydroxyphenyl]propionohydrazide], didodecyl - 3,3’ - thiodipropionate, and dioctadecyl - 3,3’ - thiodipropionate, etc. can be mentioned. One or more of these antioxidants can be used.,

[0026] (Water - soluble inorganic salt) The water - soluble inorganic salt used in the kneading process utilizes its high hardness to crush the pigment in the kneading process and contributes 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 water - soluble inorganic salts include, for example, 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.,

[0027] 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 preferably 1 μm or more and 250 μm or less, and the cumulative 95% particle size (D 95 ) is preferably 500 μm or less. When particularly fine pigments are desired, it is preferable that the water - soluble inorganic salt used as a grinding aid is also fine. Specifically, in the volume - based particle size distribution, the cumulative 50% particle size (D 50 ) is preferably 1 μm or more and 50 μm or less, and the cumulative 95% particle size (D 95 ) is preferably 100 μm or less for the water - soluble inorganic salt.,

[0028] The D 50 and D 95It is possible to obtain values measured using an optical microscope. Specifically, the particle diameters of 500 water-soluble inorganic salts are measured using an optical microscope, and a method for calculating D 50 and D 95 from the volume-based particle size distribution is exemplified. For the water-soluble inorganic salts used in the examples described later, D 50 and D 95 were also determined by the above measurement method.

[0029] (Organic solvent) The organic solvent used in the kneading step serves, as a first role, to wet the mixture of the pigment and the water-soluble inorganic salt and to make a dough (a lump formed by kneading) of appropriate firmness. As a result, in the solvent-salt milling method, a strong load is likely to be applied to the kneaded material, increasing the grinding effect and playing a part in generating a crushed surface of the pigment.

[0030] The organic solvent is not particularly limited, but organic solvents such as alcohols, glycols, ethers, and aprotic polar solvents are preferred. Specifically, 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 can be mentioned. One of the above water-soluble organic solvents may be used alone, or two or more thereof may be mixed and used as necessary.

[0031] Also, in the kneading step, it is preferable that the organic solvent plays a second role of dissolving the water-insoluble antioxidant. Therefore, the organic solvent used in the kneading step preferably contains a first organic solvent capable of dissolving the water-insoluble antioxidant. By using, as the organic solvent in the kneading step, a first organic solvent capable of dissolving the water-insoluble antioxidant, it is possible to further improve the ozone resistance of the resulting pigment composition. As the first organic solvent, it is more preferable to use an organic solvent that completely dissolves the water-insoluble antioxidant, but an organic solvent capable of dissolving 10% by mass or more of the water-insoluble antioxidant at 25°C is used as the first organic solvent capable of dissolving the water-insoluble antioxidant. The fact that the first organic solvent can dissolve 10% by mass or more of the water-insoluble antioxidant means that the ratio (mass%) of the mass of the water-insoluble antioxidant dissolved in the first organic solvent to the mass of the first organic solvent is 10% by mass or more. For example, it means that 10 g or more of the water-insoluble antioxidant is dissolved in 100 g of the first organic solvent.

[0032] The ratio of the amount of the first organic solvent used to the total amount of the organic solvents used in the kneading step is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on the total amount of the organic solvents used. Also, the above ratio of the amount of the first organic solvent used may be 100% by mass, that is, only the organic solvent corresponding to the first organic solvent (only one or two or more of the first organic solvents) may be used as the organic solvent.

[0033] For example, when the water-insoluble antioxidant contains a hindered phenol antioxidant, it is possible to dissolve the hindered phenol antioxidant with N-methylpyrrolidone or N,N-dimethylformamide. By dissolving the water-insoluble antioxidant during the production of the pigment composition, the water-insoluble antioxidant can be efficiently adsorbed onto the pigment. Therefore, it is more preferable that the water-insoluble antioxidant contains a hindered phenol antioxidant and the organic solvent contains at least one of N-methylpyrrolidone and N,N-dimethylformamide. Furthermore, it is even more preferable that the water-insoluble antioxidant contains a hindered phenol antioxidant and the organic solvent contains N,N-dimethylformamide.

[0034] (Other materials) When producing a kneaded product in the kneading step, in addition to the mixture containing a pigment, a water-insoluble antioxidant, a water-soluble inorganic salt, and an organic solvent, a dye derivative may be added for the purpose of adjusting crystal growth and crystal dislocation of the pigment. As the dye derivative to be added, a dye derivative having the same structure as the pigment as the parent body is preferable, but a dye derivative having a different structure may also be used. Examples of the substituents of the dye 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 dye derivative having a basic group can be preferably used because it has a great effect on dispersing the pigment. These can be used alone or in combination of two or more.

[0035] 〔Other steps〕 Through the above kneading process, a kneaded product containing a pigment, a water-insoluble antioxidant, 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.

[0036] Through the step 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. The obtained wet cake is preferably dried to a water content of 5% by mass or less in consideration of the growth of bacteria. 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.

[0037] <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 a water-insoluble antioxidant 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.

[0038] 〔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 having a hydrophilic group bonded to the particle surface of the pigment, etc. 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, etc. can be used. In order to disperse the above-described pigment composition in water as the dispersion medium, it is preferable to use a resin (resin dispersant) or a surfactant as the dispersant. Among them, it is more preferable to use a resin (resin having an anionic group) capable of stably dispersing the pigment composition in the dispersion medium by the action of the anionic group.

[0039] As the resin, a resin having a structural unit derived from a hydrophobic monomer and a structural unit derived from a hydrophilic monomer having an anionic group, which is obtained by copolymerizing a polymerizable hydrophobic monomer and a polymerizable hydrophilic monomer, is preferable. Examples of the hydrophobic monomer include styrene, α-methylstyrene, n-butyl acrylate, n-hexyl acrylate, benzyl methacrylate, etc. 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, propylacrylic acid, isopropylacrylic 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; etc. One or more of the hydrophilic monomers can be used.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] The pigment composition and the pigment dispersion containing the same can be suitably used in 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.

[0044] <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 above-described 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.

[0045] (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.

[0046] (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.

[0047] 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 (mass %) of the water-soluble organic solvent in the ink is preferably 3.0 mass % or more and 50.0 mass % or less, more preferably 3.0 mass % or more and 40.0 mass % or less, based on the total mass of the ink.

[0048] (Other Additives) In the ink, in order to maintain moisture retention and the like, in addition to the above-described components, solid compounds having moisture retention at normal temperature such as urea, urea derivatives, trimethylolpropane, and trimethylolethane may be contained. The content (mass %) of such a compound in the ink is preferably 0.1 mass % or more and 20.0 mass % or less, more preferably 3.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink. Further, in the ink, various additives such as a surfactant, a pH adjuster, a rust preventive, a preservative, a fungicide, an antioxidant, and a reduction preventive may be contained as necessary in addition to the above-described components.

[0049] <Inkjet Recording Method> The ink obtained by the above-described ink production method 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 aqueous ink production method 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.

[0050] <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.

Example

[0051] 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. Unless otherwise specified, "parts" and "%" described with respect to component amounts are based on mass.

[0052] <Preparation of Pigment> The following pigments were prepared. · Copper phthalocyanine blue (hereinafter, may be referred to as "PB15:3"). · C.I. Pigment Red 150 (hereinafter, may be referred to as "PR150"). · C.I. Pigment Yellow 74 (hereinafter, may be referred to as "PY74").

[0053] <Preparation of Antioxidant> (Hindered Phenol Antioxidant) To 100 parts of water, 20 parts of a hindered phenol antioxidant with the trade name "Sumilizer BBM-S" (manufactured by Sumitomo Chemical Tex) was added and stirred for 30 minutes. Then, the antioxidant was recovered on filter paper by filtration, and after drying, its mass was measured. Since 95% or more of the added antioxidant mass could be recovered on the filter paper, it was determined that the above hindered phenol antioxidant is a water-insoluble antioxidant. Also, the solubility in diethylene glycol, N-methylpyrrolidone, and dimethylformamide was confirmed in the same manner except that the organic solvents described in Table 1 below were used instead of water, and the results in Table 1 were obtained.

[0054] TIFF2025102451000001.tif50170

[0055] (Phosphite-based antioxidant) To 100 parts of water, 20 parts of the phosphite-based antioxidant with the trade name "ADEKA STAB 1178" (manufactured by ADEKA) was added and stirred for 30 minutes. Then, the antioxidant was recovered on filter paper by filtration, and after drying, the mass was measured. Since 95% or more of the added antioxidant mass could be recovered on the filter paper, the above phosphite-based antioxidant was judged to be a water-insoluble antioxidant. Also, the solubility in diethylene glycol, N-methylpyrrolidone, and dimethylformamide was confirmed in the same manner except that the organic solvents described in Table 2 below were used instead of water, and the results in Table 2 were obtained.

[0056] TIFF2025102451000002.tif49170

[0057] (Thioether-based antioxidant) To 100 parts of water, 20 parts of the thioether-based antioxidant with the trade name "ADEKA STAB AO-503" (manufactured by ADEKA) was added and stirred for 30 minutes. Then, the antioxidant was recovered on filter paper by filtration, and after drying, the mass was measured. Since 95% or more of the added antioxidant mass could be recovered on the filter paper, the above thioether-based antioxidant was judged to be a water-insoluble antioxidant. Also, the solubility in diethylene glycol, N-methylpyrrolidone, and dimethylformamide was confirmed in the same manner except that the organic solvents described in Table 3 below were used instead of water, and the results in Table 3 were obtained.

[0058] TIFF2025102451000003.tif48170

[0059] (Hindered amine-based antioxidant) To 100 parts of water, 20 parts of “ADEKA STAB LA-72” (manufactured by ADEKA), a hindered amine antioxidant, was added and stirred for 30 minutes. Thereafter, the antioxidant was recovered on filter paper by filtration, and after drying, its mass was measured. Since 95% or more of the added antioxidant mass could be recovered on the filter paper, the above hindered amine antioxidant was judged to be a water-insoluble antioxidant. Also, the solubility in diethylene glycol, N-methylpyrrolidone, and dimethylformamide was confirmed in the same manner except that the organic solvents shown in Table 4 below were used instead of water, and the results in Table 4 were obtained.

[0060] TIFF2025102451000004.tif49170

[0061] (Sodium L-ascorbate) To 100 parts of water, 20 parts of sodium L-ascorbate was added and stirred for 30 minutes. Thereafter, sodium L-ascorbate was recovered on filter paper by filtration, and after drying, its mass was measured. Since 10% or less of the added sodium L-ascorbate mass could be recovered on the filter paper, sodium L-ascorbate was judged to be a water-soluble antioxidant.

[0062] <Manufacture of Pigment Composition> (Pigment Compositions 1 to 5, 7 to 16) Copper phthalocyanine blue was used as the pigment. Each component (unit: part) shown in the upper row of Table 5 (Tables 5-1 to 5-3) was mixed to obtain a mixture. As the sodium chloride, those with D 50 being 150 μm and D 95 being 300 μm were used. The above mixture was kneaded for 8 hours under the kneading conditions shown in the lower row of Table 5 using a planetary mixer (trade name “Trimix”, manufactured by Inoue Seisakusho; indicated as “1” in “Kneading Apparatus No.” in the lower row of Table 5). In this way, each kneaded product was obtained by the solvent salt milling method. By sufficiently washing, filtering, and drying the obtained kneaded product, water-soluble inorganic salts and organic solvents were removed from the kneaded product to obtain Pigment Compositions 1 to 5 and 7 to 16.

[0063] (Pigment Composition 6) 100 parts of copper phthalocyanine blue, 10 parts of a hindered phenol antioxidant (trade name "Sumilizer BBM-S", manufactured by Sumitomo Chemical Tex), 1000 parts of sodium chloride, 190 parts of diethylene glycol, and 10 parts of N-methylpyrrolidone were mixed. This mixture was charged into a kneader (trade name "PBV-03", manufactured by Irie Shokai), and kneaded at a temperature of 30°C and a shear rate of 20 s -1 for 8 hours to prepare a kneaded product by the solvent salt milling method. The obtained kneaded product was thoroughly washed, filtered, and dried to remove water-soluble inorganic salts and organic solvents from the kneaded product, thereby obtaining Pigment Composition 6.

[0064] (Pigment Composition 17) 100 parts of copper phthalocyanine blue and 1 part of a hindered phenol antioxidant (trade name "Sumilizer BBM-S", manufactured by Sumitomo Chemical Tex) were mixed and added to a container containing 10000 parts of N-methylpyrrolidone, and stirred for 1 hour. Thereafter, filtration and washing with water were repeated to obtain Pigment Composition 17.

[0065] TIFF2025102451000005.tif93170

[0066] TIFF2025102451000006.tif94170

[0067] TIFF2025102451000007.tif94170

[0068] (Pigment Compositions 18 - 28) C.I. Pigment Red 150 was used as the pigment. The components (unit: parts) shown in the upper row of Table 6 (Table 6-1 and Table 6-2) were mixed. This mixture was kneaded for 8 hours under the kneading conditions shown in the lower row of Table 6 using a planetary mixer (trade name "Trimix", manufactured by Inoue Seisakusho; indicated as "1" in the "Kneading Apparatus No." in the lower row of Table 6). In this way, each kneaded product was obtained by the solvent salt milling method. The obtained kneaded product was thoroughly washed, filtered, and dried to remove water-soluble inorganic salts and organic solvents from the kneaded product, thereby obtaining Pigment Compositions 18 - 28.

[0069] (Pigment Composition 29) 100 parts of C.I. Pigment Red 150 and 1 part of a hindered phenol antioxidant (trade name "Sumilizer BBM-S", manufactured by Sumitomo Chemical Tex) were mixed and added to a container containing 10,000 parts of N-methylpyrrolidone, and stirred for 1 hour. Then, filtration and washing with water were repeated to obtain Pigment Composition 29.

[0070] TIFF2025102451000008.tif93170

[0071] TIFF2025102451000009.tif93170

[0072] (Pigment Compositions 30 - 40) C.I. Pigment Yellow 74 was used as the pigment. Each component (unit: part) shown in the upper row of Table 7 (Table 7-1 and Table 7-2) was mixed. This mixture was kneaded for 8 hours under the kneading conditions shown in the lower row of Table 7 using a planetary mixer (trade name "Trimix", manufactured by Inoue Manufacturing Co., Ltd.; indicated as "1" in the "Kneading Equipment No." in the lower row of Table 7). In this way, each kneaded product was obtained by the solvent salt milling method. The obtained kneaded product was thoroughly washed, filtered, and dried to remove water-soluble inorganic salts and organic solvents from the kneaded product, thereby obtaining Pigment Compositions 30 - 40.

[0073] (Pigment Composition 41) 100 parts of C.I. Pigment Yellow 74 and 1 part of a hindered phenol antioxidant (trade name "Sumilizer BBM-S", manufactured by Sumitomo Chemical Tex) were mixed and added to a container containing 10,000 parts of N-methylpyrrolidone, and stirred for 1 hour. Then, filtration and washing with water were repeated to obtain Pigment Composition 41.

[0074] TIFF2025102451000010.tif92170

[0075] TIFF2025102451000011.tif94170

[0076] <Synthesis of Resin> Resins 1 and 2, which are water-soluble random copolymers, were 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 8 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 each resin. After adding 0.9 equivalent of potassium hydroxide and an appropriate amount of ion-exchanged water based on the acid value of the resin, isopropanol was removed under reduced pressure to obtain Resin Aqueous Solutions 1 and 2, which are alkaline aqueous solutions of Resins 1 and 2. The content of the resin (solid content) in Resin Aqueous Solutions 1 and 2 was both 20.0%. The meanings of the abbreviations in Table 8 are shown below. St: Styrene nBA: n-Butyl acrylate AA: Acrylic acid Polymerization initiator: A solution prepared by dissolving 5.0 parts of the product named "Perkadox L-W75(LS)" (manufactured by Kayaku Akzo, dibenzoyl peroxide, purity 75%) in 10.0 parts of isopropanol

[0077] TIFF2025102451000012.tif36170

[0078] <Preparation of Pigment Dispersion> (Preparation of Pigment Dispersions 1 - 8, 10 - 19, 22 - 34, 37 - 49, 52) Each component shown in Table 9 (Table 9-1 to Table 9-3) (pigment composition, resin aqueous solution, and ion-exchanged water; unit: part) was mixed, and using a high-pressure homogenizer (product name "Starburst", manufactured by Sugino Machine), dispersion treatment was performed at a treatment pressure of 200 MPa. Then, an appropriate amount of ion-exchanged water was added to obtain Pigment Dispersions 1 - 8, 10 - 19, 22 - 34, 37 - 49, and 52 with a pigment content of 15.0%.

[0079] (Preparation of Pigment Dispersion 9) Mix each of the components shown in Table 9-1 (pigment composition, aqueous resin solution, and ion-exchanged water; unit: part), put them into a batch vertical sand mill (manufactured by Imex), fill it with 150.0 parts of zirconia beads with a diameter of 0.3 mm, and perform a dispersion treatment for 5 hours while cooling with water. Then, add an appropriate amount of ion-exchanged water to obtain Pigment Dispersion 9 with a pigment content of 15.0%.

[0080] (Preparation of Pigment Dispersions 20, 35, and 50) Mix the pigment composition, aqueous resin solution, and ion-exchanged water (unit: part) shown in Table 9 (Tables 9-1 to 9-3), and use a high-pressure homogenizer (trade name "Starburst", manufactured by Sugino Machine) to perform a dispersion treatment at a treatment pressure of 200 MPa. Then, add an appropriate amount of ion-exchanged water and the amount of water-soluble antioxidant shown in Table 9 to obtain Pigment Dispersions 20, 35, and 50 with a pigment content of 15.0%. As the water-soluble antioxidant, sodium L-ascorbate was used.

[0081] (Preparation of Pigment Dispersions 21, 36, and 51) Mix the pigment composition, aqueous resin solution, and ion-exchanged water (unit: part) shown in Table 9 (Tables 9-1 to 9-3), and use a high-pressure homogenizer (trade name "Starburst", manufactured by Sugino Machine) to perform a dispersion treatment at a treatment pressure of 200 MPa. Then, add an appropriate amount of ion-exchanged water and the amount of water-insoluble antioxidant shown in Table 9 to obtain Pigment Dispersions 21, 36, and 51 with a pigment content of 15.0%. As the water-insoluble antioxidant, a dispersion in which a water-insoluble antioxidant is dispersed in water (trade name "LX-803A", manufactured by ADEKA) was used.

[0082] TIFF2025102451000013.tif148170

[0083] TIFF2025102451000014.tif108170

[0084] TIFF2025102451000015.tif108170

[0085] (Preparation of Ink) Using each of the obtained pigment dispersions 1 to 52, inks 1 to 52 with numbers corresponding to the numbers of the pigment dispersions were prepared as shown in Table 10 (Tables 10-1 to 10-3) below. Specifically, using the types (numbers) of pigment dispersions shown in Table 10 below, the following components containing the pigment dispersion were mixed, stirred well and dispersed, and then pressure filtration was performed using a microfilter with a pore size of 3.0 μm (manufactured by Fujifilm) to prepare inks 1 to 52. Acetylenol E100 shown below is the trade name of a surfactant manufactured by Kawaken Fine Chemicals Co., Ltd. (Components of Ink) Pigment dispersion (any one of 1 to 52) 33.0 parts Glycerin 10.0 parts Triethylene glycol 7.0 parts Acetylenol E100 0.1 part Ion-exchanged water 49.9 parts

[0086] <Evaluation> Inks 1 to 52 were each filled into an ink cartridge and set in an inkjet recording apparatus (trade name "PIXUS PRO-10", manufactured by Canon) equipped with a recording head that discharges ink by thermal energy. The resolution of this inkjet recording apparatus is 2400 dpi × 1200 dpi. Then, an image recorded under the condition of applying 1 drop of 30.4 ng of ink droplets to a unit area of 1 / 600 inch × 1 / 600 inch is defined as having a recording duty of 100%. Using the above inkjet recording apparatus, a solid image with a recording duty of up to 140% was recorded on a recording medium (trade name "Canon Photo Paper, Glossy Gold GL-101", manufactured by Canon). Table 10 shows each ink and the corresponding examples and comparative examples.

[0087] In the obtained solid image, an ozone weather meter (model OMS-H, manufactured by Suga Test Instruments Co., Ltd.) was used, and it was left standing for 3 hours at an ozone concentration of 12 ppm, a temperature inside the tank of 24 °C, and a humidity of 60% RH. When the initial optical density (O.D. value) of each solid image was "0.5", the O.D. value after 300 hours (equivalent to 100 years) was measured, and the ratio of the O.D. value after 300 hours (residual O.D. value) to the initial O.D. value was calculated and used as an evaluation index for ozone resistance. For the measurement of the O.D. value, a spectrophotometer (trade name "Spectrolino", manufactured by Gretag Macbeth) was used. The ozone resistance was evaluated according to the evaluation criteria shown below. In this example, according to the following evaluation criteria, "A", "B", and "C" were set as acceptable levels, and "D" and "E" were set as unacceptable levels. The evaluation results are shown in Table 10. A: The residual O.D. value was 95% or more. B: The residual O.D. value was 90% or more and less than 95%. C: The residual O.D. value was 80% or more and less than 90%. D: The residual O.D. value was 50% or more and less than 80%. E: The residual O.D. value was less than 50%.

[0088] TIFF2025102451000016.tif144170

[0089] TIFF2025102451000017.tif104170

[0090] TIFF2025102451000018.tif105170

[0091] Note that the disclosure of this embodiment includes the following methods. (Method 1) 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 mixture further contains a water-insoluble antioxidant, which is a method for producing a pigment composition. (Method 2) The method for producing a pigment composition according to Method 1, wherein the amount of the water-insoluble antioxidant used in the kneading step is 0.5% by mass or more and 10.0% by mass or less based on the amount of the pigment used, by mass ratio. (Method 3) The shear rate during kneading in the kneading step is 15 s -1 or more, and the method for producing a pigment composition according to Method 1 or 2. (Method 4) The method for producing a pigment composition according to any one of Methods 1 to 3, wherein the organic solvent contains a first organic solvent capable of dissolving the water-insoluble antioxidant. (Method 5) The water-insoluble antioxidant contains a hindered phenol-based antioxidant, and the method for producing a pigment composition according to any one of Methods 1 to 4, wherein the organic solvent contains at least one of N-methylpyrrolidone and N,N-dimethylformamide. (Method 6) The water-insoluble antioxidant contains a hindered phenol-based antioxidant, and the method for producing a pigment composition according to any one of Methods 1 to 5, wherein the organic solvent contains N,N-dimethylformamide. (Method 7) A method for producing a pigment dispersion liquid, comprising 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 6, and dispersing the pigment composition in the water by the dispersant. (Method 8) 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 Method 7 and a component containing a water-soluble organic solvent. (Method 9) An inkjet recording method in which ink is ejected from an inkjet recording head and an image is recorded on a recording medium, wherein the ink is an aqueous ink obtained by the method for producing an aqueous ink according to Method 8.

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 mixture further contains a water-insoluble antioxidant. A method for producing a pigment composition, characterized by this.

2. The method for producing a pigment composition according to claim 1, wherein the amount of the water-insoluble antioxidant used in the kneading step is 0.5% by mass or more and 10.0% by mass or less in terms of mass ratio with respect to the amount of the pigment used.

3. The shear rate during kneading in the kneading step is 15 s －１ or more, and the method for producing a pigment composition according to claim 1.

4. The method for producing a pigment composition according to claim 1, wherein the organic solvent contains a first organic solvent capable of dissolving the water-insoluble antioxidant.

5. The water-insoluble antioxidant contains a hindered phenol-based antioxidant, and the method for producing a pigment composition according to claim 1, wherein the organic solvent contains at least one of N-methylpyrrolidone and N,N-dimethylformamide.

6. The water-insoluble antioxidant contains a hindered phenol-based antioxidant, and the method for producing a pigment composition according to claim 1, wherein the organic solvent contains N,N-dimethylformamide.

7. A method for producing a pigment dispersion, 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 6, a dispersant, and water, and dispersing the pigment composition in the water by the dispersant.

8. A method for producing an aqueous ink, comprising a step of mixing a pigment dispersion obtained by the method for producing a pigment dispersion according to claim 7 and a component containing a water-soluble organic solvent.

9. An inkjet recording method of ejecting an ink from an inkjet recording head and recording an image on a recording medium, wherein the ink is the aqueous ink obtained by the method for producing an aqueous ink according to claim 8. An inkjet recording method, characterized by this.

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