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 light 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 ultraviolet absorber 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 inkjet recording devices, inkjet inks are being used to obtain recordings installed outdoors, such as outdoor display posters 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 light resistance so that recordings can be installed even in outdoor environments.

[0003] For example, Patent Document 1 discloses an ink composition using an insoluble azo pigment excellent in light resistance and the like. By using a pigment with high crystallinity as the pigment as in the ink composition disclosed in Patent Document 1, it is possible to obtain a recording with excellent light resistance. In particular, conventionally, there are pigments that are inferior in light resistance among pigments with excellent chroma, and it is known that pigments with high crystallinity are useful as pigments that are excellent in both chroma and light resistance. However, high color development and light resistance are in a trade-off relationship, and even if attempts such as those disclosed in Patent Document 1 are made, there is a limit to the improvement of light resistance when the molecular structure of the pigment is limited. Under such circumstances, it has also been proposed to use additives rather than seeking a solution in the molecular structure of the pigment. For example, Patent Document 2 proposes an aqueous ink for inkjet containing a pigment, a styrene-based resin, an aqueous medium, and polycarbonate-modified urethane resin particles encapsulating an ultraviolet absorber and a light stabilizer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the ink disclosed in Patent Document 2, since the ultraviolet absorber and the light stabilizer do not exist in the vicinity of the pigment, the actual situation is that it has not reached the level of light 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 light 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 ultraviolet absorber.

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 light 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 lightfastness of aqueous pigment inks using ultraviolet absorbers. When a water-soluble ultraviolet absorber was added directly to the aqueous pigment ink, the lightfastness could not be improved. The present inventors speculate that this is because when the aqueous pigment ink to which the ultraviolet absorber was added was applied to a recording medium, the ultraviolet absorber was also absorbed into the recording medium together with the water, and the ultraviolet light striking the pigment on the recording medium could not be sufficiently absorbed.

[0011] Therefore, the non-water-soluble ultraviolet absorber 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 in which the non-water-soluble ultraviolet absorber was 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 non-water-soluble ultraviolet absorber was added, and the light fastness was measured using the obtained recorded matter, and the light fastness was confirmed to be improved. However, the light fastness desired by the present inventors could not be satisfied. Unlike the water-soluble ultraviolet absorber, the non-water-soluble ultraviolet absorber is thought to remain on the recording medium in the recorded matter. However, the present inventors speculate that the non-water-soluble ultraviolet absorber could not remain in the vicinity of all the pigments on the recording medium, and the role of the ultraviolet absorber could not be fully exerted.

[0012] The inventors thought that the lightfastness could be improved by retaining a water-insoluble ultraviolet absorber on the surface of the pigment. Therefore, the pigment and the water-insoluble ultraviolet absorber were mixed and stirred in an organic solvent, and then the obtained pigment composition after washing was contained in an aqueous ink and the lightfastness was measured in the same manner as described above. However, the lightfastness did not improve. It is presumed that the water-insoluble ultraviolet absorber 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 ultraviolet absorber 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 compressing the mixture by applying a load thereto. In the solvent-salt milling method, the pigment is pulverized by the water-soluble inorganic salt to create an energetically unstable crushing surface, and the crushed surfaces of the finely crushed pigments adsorb to each other and crystal growth occurs, whereby the particle size of the pigment is adjusted. The inventors thought that a strong adsorptive force was required to retain the water-insoluble ultraviolet absorber on the pigment surface. The crushing surface of the pigment created by the solvent-salt milling method has a strong adsorptive ability, and it was thought that the water-insoluble ultraviolet absorber could be retained on the pigment surface by adding the water-insoluble ultraviolet absorber during the kneading step by the solvent-salt milling method.

[0014] The inventors blended a pigment, a water-soluble inorganic salt, a water-insoluble ultraviolet absorber, and an organic solvent, kneaded them by the solvent-salt milling method to prepare a kneaded product, and 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 lightfastness was measured in the same manner as described above using this ink, a significant improvement in lightfastness was confirmed. As described above, it is presumed that a crushing surface was generated on the pigment in the kneading step by the solvent-salt milling method, the water-insoluble ultraviolet absorber adsorbed to the crushing surface, and the lightfastness was improved by covering the pigment surface with the water-insoluble ultraviolet absorber.

[0015] <Method for producing a pigment composition> The manufacturing method of 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 ultraviolet absorber. Hereinafter, the kneading step, each material used, and the like will be described in detail.

[0016] 〔Kneading Step〕 In the kneading step in the manufacturing method of the pigment composition of the present embodiment, a mixture containing a pigment, a water-insoluble ultraviolet absorber, 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 manufacturing method of the pigment composition of the present embodiment, a kneaded product containing a refined pigment, a water-insoluble ultraviolet absorber, 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, and kneading devices such as normal pressure type, pressure type, and reduced pressure type can be used, and a device that kneads while applying a load to the contents to compress them can be preferably used. In addition, a kneading device provided with a material input section such as a kneading kettle and a hopper, and a stirring section such as a stirring blade, stirring vane, 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.

[0018] In the method for producing the pigment composition of the present embodiment, in order to adsorb the water-insoluble ultraviolet absorber on the pigment surface, it is important to create a crushed surface of the pigment during kneading. Therefore, kneading is performed by the 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 "shear rate". The shear rate during kneading in the kneading step is preferably 10 s -1 or more, and from the viewpoint of more easily applying a shearing force to the pigment itself, 15 s -1 or more is more preferable, and 20 s -1 or more is even more preferable.

[0019] The temperature during kneading in the kneading step is preferably 0°C or higher and 130°C or lower, more preferably 10°C or higher and 120°C or lower, and even more preferably 10°C or higher and 90°C or lower.

[0020] The kneading time in the kneading step is preferably 1 hour or longer and 10 hours or shorter, and more preferably 2 hours or longer and 8 hours or shorter. When the kneading time is 2 hours or longer, the adsorption amount of the water-insoluble ultraviolet absorber on the pigment surface tends to be sufficient, and the light resistance tends to be improved. On the other hand, from the viewpoint of processing efficiency, the kneading time is preferably 8 hours or shorter.

[0021] In the kneading process, the amount of the water-insoluble ultraviolet absorber 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, based on the amount of the pigment used. When the amount of the water-insoluble ultraviolet absorber used is 0.5% by mass or more based on the amount of the pigment used, the light resistance of the resulting pigment composition is more likely to be further improved. From this perspective, the ratio of the amount of the water-insoluble ultraviolet absorber used based on the amount of the pigment used is more preferably 0.8% by mass or more. On the other hand, if the water-insoluble ultraviolet absorber covers the entire surface of the pigment, it is considered that the ultraviolet absorption function of the water-insoluble ultraviolet absorber can be sufficiently imparted. From this perspective and from the viewpoints of the storage stability and ejection stability of the ink prepared using the resulting pigment composition, the ratio of the amount of the water-insoluble ultraviolet absorber used based on the amount of the pigment used is more preferably 10.0% by mass or less, and even more preferably 8.0% by mass or less. The ratio (% by mass) of the amount of the water-insoluble ultraviolet absorber used based on the amount of the pigment used as described above is determined by {mass of the water-insoluble ultraviolet absorber used / mass of the pigment used} × 100 in the kneading process.

[0022] Regarding the mixing ratio of the pigment, water-soluble inorganic salt, and organic solvent in the kneading process, the following ratios are preferably used 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 the 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 the mass ratio to the amount of the pigment used.

[0023] (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.

[0024] (Water-insoluble ultraviolet absorber) An ultraviolet absorber is a compound having a chemical structure that absorbs light in the ultraviolet region and emits it to the outside as thermal energy. Generally, a compound having a maximum wavelength in the ultraviolet region is defined as an ultraviolet absorber. Similarly, in the present disclosure, a compound having a maximum wavelength in the range of 280 nm or more and 350 nm or less is used as the ultraviolet absorber.

[0025] The ultraviolet absorber used in the method for producing the pigment composition of the present embodiment needs to remain on the pigment surface in the aqueous pigment ink. Here, if a water-soluble ultraviolet absorber is used, the water-soluble ultraviolet absorber will elute from the pigment surface during the purification of the pigment composition, the preparation of the pigment dispersion, and the preparation of the aqueous pigment ink. Therefore, the ultraviolet absorber will not be present on the pigment surface, and the improvement of light resistance cannot be obtained. Accordingly, in the method for producing the pigment composition of the present embodiment, a water-insoluble ultraviolet absorber is used. Here, the water-insoluble ultraviolet absorber is more preferably insoluble in water, but the "water-insoluble ultraviolet absorber" in the present disclosure refers to an ultraviolet absorber having a solubility in water at 25°C of less than 10% by mass.

[0026] Examples of suitable water-insoluble ultraviolet absorbers include benzotriazole derivatives, benzophenone derivatives, cyanoacrylate derivatives, and triazine derivatives. These may be referred to as benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and triazine-based ultraviolet absorbers, respectively. It is more preferable to use one or more of these ultraviolet absorbers.

[0027] Specific non-water-soluble ultraviolet absorbers include, for example, 2-(2H-benzotriazol-2-yl)-p-cresol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol, 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol], the reaction product of methyl-3-[3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl]propionate / polyethylene glycol 300, 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol, 2,2-bis{[2-cyano-3,3-diphenylacryloyl-oxy]methyl}propane-1,3-diyl = bis(2-cyano-3,3-diphenylacrylate), ethyl 2-cyano-3,3-diphenylacrylate, 2-ethylhexyl 2-cyano-3,3-diphenylacrylate, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol, and 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, etc. One or more of these non-water-soluble ultraviolet absorbers can be used.

[0028] (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, 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, for example, sodium chloride, potassium chloride, sodium sulfate, zinc chloride, calcium chloride, and magnesium chloride, and mixtures of two or more of them. Among these, it is preferable to use sodium chloride from the perspective of cost.

[0029] 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 10 μm or less, and the cumulative 95% particle size (D 95 ) is preferably 20 μm or less for the water-soluble inorganic salt.

[0030] For D 50 and D 95 of the water-soluble inorganic salt, 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 for calculating D 50 and D 95 from the volume-based particle size distribution 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.

[0031] (Organic solvent) The organic solvent used in the kneading process serves, as a first role, to moisten a mixture containing a pigment, a water-insoluble ultraviolet absorber, and a water-soluble inorganic salt and to form 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.

[0032] 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.

[0033] In addition, in the kneading process, it is preferable that the organic solvent plays a second role of dissolving the water-insoluble ultraviolet absorber. Therefore, the organic solvent used in the kneading process preferably contains a first organic solvent capable of dissolving the water-insoluble ultraviolet absorber. In the kneading process, it is more preferable to use the first organic solvent capable of dissolving the water-insoluble ultraviolet absorber for a part of the organic solvent. By dissolving the water-insoluble ultraviolet absorber using the first organic solvent capable of dissolving the water-insoluble ultraviolet absorber in the kneading process, the water-insoluble ultraviolet absorber can be efficiently adsorbed onto the pigment. Therefore, it is possible to further improve the light resistance of the obtained pigment composition.

[0034] As the first organic solvent, it is more preferable to use an organic solvent that completely dissolves the water-insoluble ultraviolet absorber. However, at the temperature during the kneading treatment, an organic solvent capable of dissolving 10% by mass or more of the water-insoluble ultraviolet absorber is used as the first organic solvent capable of dissolving the water-insoluble ultraviolet absorber. The fact that the first organic solvent can dissolve 10% by mass or more of the water-insoluble ultraviolet absorber means that the ratio (mass%) of the mass of the water-insoluble ultraviolet absorber 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 ultraviolet absorber dissolves in 100 g of the first organic solvent.

[0035] The ratio of the amount of the first organic solvent used to the total amount of the organic solvents used in the kneading process is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% 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 is preferably 100% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0036] For example, when a benzotriazole derivative is used as the water-insoluble ultraviolet absorber, it can be dissolved in N-methylpyrrolidone or N,N-dimethylformamide, so they can be used as the first organic solvent. By dissolving the water-insoluble ultraviolet absorber during the production of the pigment composition, the water-insoluble ultraviolet absorber can be efficiently adsorbed onto the pigment. Therefore, it is preferable that the water-insoluble ultraviolet absorber contains a benzotriazole derivative and the organic solvent contains at least one of N-methylpyrrolidone and N,N-dimethylformamide. More preferably, the water-insoluble ultraviolet absorber contains a benzotriazole derivative and the organic solvent contains N,N-dimethylformamide.

[0037] (Other materials) When producing a kneaded product in the kneading step, in addition to the mixture containing the pigment, the water-insoluble ultraviolet absorber, the water-soluble inorganic salt, and the organic solvent, a dye derivative may be added for the purpose of adjusting the 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 of its great effect on the dispersion of the pigment. These can be used alone or in combination of two or more.

[0038] 〔Other processes〕 Through the above kneading process, a kneaded product containing a pigment, a water-insoluble ultraviolet absorber, 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.

[0039] Through the process 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.

[0040] <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 ultraviolet absorber 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.

[0041] 〔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, 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 a dispersion medium, it is preferable to use a resin (resin dispersant) or a surfactant as a dispersant. Among these, it is more preferable to use a resin (a resin having an anionic group) capable of stably dispersing the pigment composition in the dispersion medium by the action of an anionic group.

[0042] As the resin, a resin obtained by copolymerizing a polymerizable hydrophobic monomer and a polymerizable hydrophilic monomer, having a structural unit derived from a 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, propylacrylic acid, isopropylacrylic acid, itaconic acid, and fumaric acid; hydrophilic monomers having a sulfonic acid group such as styrenesulfonic acid, sulfonic acid-2-propylacrylamide, acrylic acid-2-sulfoethyl, methacrylic acid-2-sulfoethyl, and butylacrylamidesulfonic acid; hydrophilic monomers having a phosphonic acid group such as methacrylic acid-2-phosphonoethyl and acrylic acid-2-phosphonoethyl; and the like. One or more of the hydrophilic monomers can be used.

[0043] 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.

[0044] 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.

[0045] 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. The content (mass) of the water-insoluble ultraviolet absorber in the pigment dispersion 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 based on the content (% by mass) of the pigment in the pigment dispersion. This ratio is more preferably 0.8% by mass or more and 8.0% by mass or less.

[0046] 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.

[0047] <Method for manufacturing ink> It is possible to manufacture an aqueous ink using the pigment dispersion obtained by the method for manufacturing the pigment dispersion described above. The method for manufacturing the aqueous ink includes a step of mixing a component containing the pigment dispersion obtained by the method for manufacturing the pigment dispersion described above 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.

[0048] (Colorant) Since the ink contains the pigment dispersion obtained by the method for manufacturing the pigment dispersion described above, it contains the pigment composition obtained by the method for manufacturing the pigment composition described above as a colorant. The content (% by mass) of the pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. The content (mass) of the water-insoluble ultraviolet absorber in the ink 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, based on the content (% by mass) of the pigment in the ink. This ratio is more preferably 0.8% by mass or more and 8.0% by mass or less.

[0049] (Aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. As the aqueous medium, 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 (% by mass) of water in the ink is preferably 40.0% by mass or more and 95.0% by mass or less, more preferably 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the ink.

[0050] As the water-soluble organic solvent, any of those conventionally generally 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.

[0051] (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 (% 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, in the ink, various additives such as a surfactant, a pH adjuster, a rust preventive, a preservative, a fungicide, an antioxidant, and an anti-reduction agent may be contained as necessary in addition to the above-described components.

[0052] <Inkjet Recording Method> The ink obtained by the above-described method for manufacturing 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 manufacturing aqueous ink is ejected from an inkjet recording head and an image is recorded on a recording medium. Examples of the method for ejecting the ink include a method in which mechanical energy is applied to the ink to eject the ink, and a method in which thermal energy is applied to the ink to eject the ink.

[0053] <Ink Cartridge> When using the above-described ink in an inkjet recording method, an ink cartridge can be used. The ink cartridge includes the above-described ink and an ink storage unit for storing the ink. Further, an ink cartridge configured to have an ink storage unit and a recording head may be used.

Examples

[0054] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but 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.

[0055] <Preparation of Pigment> The following pigments were prepared. · C.I. Pigment Yellow 74 (hereinafter, may be referred to as "PY74"). · C.I. Pigment Red 150 (hereinafter, may be referred to as "PR150"). · Copper phthalocyanine blue (hereinafter, may be referred to as "PB15:3").

[0056] <Preparation of Ultraviolet Absorbent> (Benzotriazole derivative) To 100 parts of water, 20 parts of the benzotriazole derivative (benzotriazole-based ultraviolet absorber) with the trade name "Tinuvin 360" (manufactured by BASF) was added, and the mixture was stirred for 30 minutes. Thereafter, the benzotriazole derivative was recovered on filter paper by filtration, and after drying, its mass was measured. Since 95% or more of the added mass of the benzotriazole derivative could be recovered on the filter paper, it was determined that this benzotriazole derivative is a water-insoluble ultraviolet absorber.

[0057] Instead of 100 parts of water, 20 parts of an organic solvent was used, and the amount of the above benzotriazole derivative used was changed to 6 parts. In the same manner as above, the solubility of the benzotriazole derivative in the organic solvent was confirmed. As the organic solvents, diethylene glycol, N-methylpyrrolidone, and N,N-dimethylformamide were used. As shown in the results in Table 1, since N-methylpyrrolidone and N,N-dimethylformamide dissolved 25% or more of the above benzotriazole derivative based on the mass of the organic solvent, it was determined that the above benzotriazole derivative could be dissolved. On the other hand, since the solubility of the above benzotriazole derivative in diethylene glycol was 5% or less, it was determined that diethylene glycol could not dissolve the above benzotriazole derivative.

[0058] TIFF2025102450000001.tif49170

[0059] (cyanoacrylate derivative) To 100 parts of water, 20 parts of the cyanoacrylate derivative (cyanoacrylate-based ultraviolet absorber) with the trade name "Uvinul 3035" (manufactured by BASF) was added, and the mixture was stirred for 30 minutes. Thereafter, the above cyanoacrylate derivative was recovered on filter paper by filtration, and after drying, its mass was measured. Since 95% or more of the added mass of the cyanoacrylate derivative could be recovered on the filter paper, it was determined that this cyanoacrylate derivative is a water-insoluble ultraviolet absorber.

[0060] Instead of using 100 parts of water, 20 parts of an organic solvent were used, and the amount of the above-mentioned cyanoacrylate derivative was changed to 6 parts. In the same manner as above, the solubility of the cyanoacrylate derivative in the organic solvent was confirmed. As the organic solvents, diethylene glycol, N-methylpyrrolidone, and N,N-dimethylformamide were used. As shown in the results in Table 2, since N-methylpyrrolidone and N,N-dimethylformamide dissolved 25% or more of the above-mentioned cyanoacrylate derivative with respect to the mass of the organic solvent, it was determined that the above-mentioned cyanoacrylate derivative could be dissolved. On the other hand, since the solubility of the above-mentioned cyanoacrylate derivative in diethylene glycol was 5% or less, it was determined that diethylene glycol could not dissolve the above-mentioned cyanoacrylate derivative.

[0061] TIFF2025102450000002.tif49170

[0062] (Benzophenone derivative) To 100 parts of water, 20 parts of the benzophenone derivative (benzophenone-based ultraviolet absorber) with the trade name "Uvinul 3049" (manufactured by BASF) were added and stirred for 30 minutes. Thereafter, the above-mentioned benzophenone derivative was recovered on filter paper by filtration, and after drying, the mass was measured. Since 95% or more of the added mass of the benzophenone derivative could be recovered on the filter paper, it was determined that this benzophenone derivative was a water-insoluble ultraviolet absorber.

[0063] Instead of using 100 parts of water, 20 parts of an organic solvent were used, and the amount of the above benzophenone derivative was changed to 6 parts. Similar to the above, the solubility of the benzophenone derivative in the organic solvent was confirmed. As the organic solvents, diethylene glycol, N-methylpyrrolidone, and N,N-dimethylformamide were used. As shown in the results in Table 3, since N-methylpyrrolidone and N,N-dimethylformamide dissolved 25% or more of the above benzophenone derivative based on the mass of the organic solvent, it was determined that the above benzophenone derivative could be dissolved. On the other hand, since the solubility of the above benzophenone derivative in diethylene glycol was 5% or less, it was determined that diethylene glycol could not dissolve the above benzophenone derivative.

[0064] TIFF2025102450000003.tif50170

[0065] (2-Hydroxy-4-methoxy-5-sulfoxynatrium) To 100 parts of water, 20 parts of 2-hydroxy-4-methoxy-5-sulfoxynatrium were added and stirred for 30 minutes. Then, 2-hydroxy-4-methoxy-5-sulfoxynatrium was recovered on filter paper by filtration, and after drying, the mass was measured. Since 10% or less of the added mass of 2-hydroxy-4-methoxy-5-sulfoxynatrium could be recovered on the filter paper, it was determined that 2-hydroxy-4-methoxy-5-sulfoxynatrium was a water-soluble ultraviolet absorber.

[0066] <Manufacture of Pigment Composition> (Pigment Compositions 1 to 5, 7 to 15) C.I. Pigment Yellow 74 (PY74) was used as the pigment. Each component (unit: part) shown in the upper row of Table 4 (Tables 4-1 to 4-3) was mixed to obtain a mixture. As the ultraviolet absorbers, the same benzotriazole derivative, cyanoacrylate derivative, benzophenone derivative, and water-soluble ultraviolet absorber (2-hydroxy-4-methoxy-5-sulfoxynatrium) whose solubility was verified were used. As sodium chloride, D 50was 250 μm, D 95 with a size of 425 μm was used. The above mixture was kneaded for 8 hours under the kneading conditions shown in the middle row of Table 4 using a planetary mixer (trade name "Trimix", manufactured by Inoue Seisakusho; indicated as "1" in the "Kneading Equipment No." in the middle row of Table 4). In this way, each kneaded product was obtained by the solvent-salt milling method. By thoroughly washing, filtering, and drying the obtained kneaded product, water-soluble inorganic salts and organic solvents were removed from the kneaded product, and Pigment Compositions 1 to 5 and 7 to 15 were obtained. The "Water-insoluble UV Absorbent / Pigment (%)" shown in the lower row of Table 4 represents the ratio (%) of the amount (parts) of the water-insoluble UV absorbent used based on the amount (parts) of the pigment used in the kneading process (the same applies to Tables 5 and 6).

[0067] (Pigment Composition 6) 100 parts of C.I. Pigment Yellow 74 (PY74), 10 parts of the above benzotriazole derivative, 1000 parts of the above 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. By thoroughly washing, filtering, and drying the obtained kneaded product, water-soluble inorganic salts and organic solvents were removed from the kneaded product, and Pigment Composition 6 was obtained.

[0068] (Pigment Composition 16) 100 parts of C.I. Pigment Yellow 74 (PY74) and 1 part of the above benzotriazole derivative were mixed and added to a container containing 10000 parts of N-methylpyrrolidone, and stirred for 1 hour. Then, filtration and washing with water were repeated to obtain Pigment Composition 16.

[0069] TIFF2025102450000004.tif94170

[0070] TIFF2025102450000005.tif94170

[0071] TIFF2025102450000006.tif94170

[0072] (Pigment Compositions 17 - 26) C.I. Pigment Red 150 (PR150) was used as the pigment. Each component (unit: part) shown in the upper row of Table 5 (Table 5 - 1 and Table 5 - 2) was mixed to obtain a mixture. The components used, other than the pigment, were the same as those used in the production of the above - mentioned pigment composition containing PY74. The above - mentioned mixture was kneaded for 8 hours under the kneading conditions shown in the middle row of Table 5 using a planetary mixer (trade name "Trimix", manufactured by Inoue Seisakusho; indicated as "1" in the "Kneading Apparatus No." in the middle row of Table 5). 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, and Pigment Compositions 17 - 26 were obtained.

[0073] (Pigment Composition 27) 100 parts of C.I. Pigment Red 150 (PR150) and 1 part of the above - mentioned benzotriazole derivative were mixed and added to a container containing 10000 parts of N - methylpyrrolidone, and stirred for 1 hour. Then, filtration and repeated water washing were carried out to obtain Pigment Composition 27.

[0074] TIFF2025102450000007.tif95170

[0075] TIFF2025102450000008.tif94170

[0076] (Pigment Compositions 28 - 37) Copper phthalocyanine blue (PB15:3) was used as the pigment. Each component (unit: part) shown in the upper row of Table 6 (Table 6-1 and Table 6-2) was mixed to obtain a mixture. The components used, other than the pigment, were the same as those used in the production of the pigment composition containing PY74 described above. The above mixture was kneaded for 8 hours under the kneading conditions shown in the middle 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 middle 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, and pigment compositions 28 to 37 were obtained.

[0077] (Pigment Composition 38) 100 parts of copper phthalocyanine blue (PB15:3) and 1 part of the above benzotriazole derivative were mixed and added to a container containing 10,000 parts of N-methylpyrrolidone, and stirred for 1 hour. Then, filtration and water washing were repeated to obtain pigment composition 38.

[0078] TIFF2025102450000009.tif94170

[0079] TIFF2025102450000010.tif94170

[0080] <Preparation of Aqueous Resin Solution> 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 7 and the polymerization initiator were each dropped 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 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 resin aqueous solutions 1 and 2, which are alkaline aqueous solutions of Resins 1 and 2. The content of the resin (solid content) in both resin aqueous solutions 1 and 2 was 20.0%. The meanings of the abbreviations in Table 7 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 name "Perkadox L-W75(LS)" (manufactured by Kayaku Akzo, dibenzoyl peroxide, purity 75%) in 10.0 parts of isopropanol

[0081] TIFF2025102450000011.tif36170

[0082] <Preparation of pigment dispersion> (Pigment dispersions 1 to 8, 10 to 18, 21 to 32, 35 to 46, 49) Each component shown in Table 8 (Tables 8-1 to 8-3) (pigment composition, resin aqueous solution, and ion-exchanged water; unit: part) was mixed, and dispersion treatment was performed at a treatment pressure of 200 MPa using a high-pressure homogenizer (product name "Starburst", manufactured by Sugino Machine). Thereafter, an appropriate amount of ion-exchanged water was added to obtain pigment dispersions 1 to 8, 10 to 18, 21 to 32, 35 to 46, and 49 with a pigment content of 15.0%.

[0083] (Pigment dispersion 9) Mix each of the components shown in Table 8-1 (pigment composition, aqueous resin solution, and ion-exchanged water; unit: part), put them into a batch vertical sand mill (manufactured by Aimax), 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%.

[0084] (Pigment Dispersions 19, 33, 47) Mix the pigment composition, aqueous resin solution, and ion-exchanged water (unit: part) shown in Table 8 (Table 8-1 to Table 8-3), 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 ultraviolet absorber shown in Table 8 to obtain Pigment Dispersions 19, 33, and 47 with a pigment content of 15.0%. As the water-soluble ultraviolet absorber, 2-hydroxy-4-methoxy-5-sulfoxonatrium was used.

[0085] (Pigment Dispersions 20, 34, 48) Mix the pigment composition, aqueous resin solution, and ion-exchanged water (unit: part) shown in Table 8 (Table 8-1 to Table 8-3), 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 ultraviolet absorber shown in Table 8 to obtain Pigment Dispersions 20, 34, and 48 with a pigment content of 15.0%. As the water-insoluble ultraviolet absorber, a dispersion liquid in which the water-insoluble ultraviolet absorber is dispersed in water (trade name "HOSTAVIN 3315 DISP" (active ingredient 52%), manufactured by Clariant Chemicals) was used.

[0086] TIFF2025102450000012.tif147170

[0087] TIFF2025102450000013.tif108170

[0088] TIFF2025102450000014.tif107170

[0089] <Preparation of Ink> Using each of the obtained pigment dispersions 1 to 49, inks 1 to 49 corresponding to the numbers of the pigment dispersions were prepared as shown in Table 9 (Tables 9-1 to 9-3) below. Specifically, using the types (numbers) of pigment dispersions shown in Table 9 below, the following components containing the pigment dispersion were mixed, stirred well and dispersed, and then pressure filtration was performed with a microfilter (manufactured by Fujifilm) having a pore size of 3.0 μm to prepare inks 1 to 49. 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 49) 33.0 parts Glycerin 10.0 parts Triethylene glycol 7.0 parts Acetylenol E100 0.1 part Ion-exchanged water 49.9 parts

[0090] Inks 1 to 49 were respectively filled into ink cartridges 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. And 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, solid images with a recording duty up to 140% were recorded on a recording medium (glossy paper; trade name "Canon Photo Paper Gloss Gold GL-101", manufactured by Canon). Table 9 shows each ink and the corresponding examples and comparative examples.

[0091] In the obtained solid image, using a weather resistance tester (trade name "Xenon Weather Meter X75SC", manufactured by Suga Test Instruments Co., Ltd.), the illuminance was 0.39 W / m 2, a light resistance test was conducted under the conditions of a black panel temperature of 60 °C and a humidity of 70% RH in the tank. When the initial (before the test) optical density (O.D. value) of each image was "0.5", the O.D. value after 300 hours (equivalent to 100 years) of the light resistance test 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 light resistance. A spectrophotometer (trade name "Spectrolino", manufactured by Gretag Macbeth) was used to measure the O.D. value. The light resistance was evaluated according to the following evaluation criteria set for each main pigment.

[0092] (Evaluation criteria in Examples 1 to 16 and Comparative Examples 1 to 5) A: The residual O.D. value was 90% or more. B: The residual O.D. value was 70% or more and less than 90%. C: The residual O.D. value was 50% or more and less than 70%. D: The residual O.D. value was less than 50%. With the above evaluation criteria, "A", "B", and "C" were set as acceptable levels, and "D" was set as an unacceptable level.

[0093] (Evaluation criteria in Examples 17 to 25 and Comparative Examples 6 to 10) A: The residual O.D. value was 90% or more. B: The residual O.D. value was 70% or more and less than 90%. C: The residual O.D. value was 50% or more and less than 70%. D: The residual O.D. value was less than 50%. With the above evaluation criteria, "A", "B", and "C" were set as acceptable levels, and "D" was set as an unacceptable level.

[0094] (Evaluation criteria in Examples 26 to 34 and Comparative Examples 11 to 15) 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 less than 90%. With the above evaluation criteria, "A" was set as an acceptable level, and "B" and "C" were set as unacceptable levels.

[0095] TIFF2025102450000015.tif139170

[0096] TIFF2025102450000016.tif99170

[0097] TIFF2025102450000017.tif99170

[0098] Incidentally, 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 including 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 includes a water-insoluble ultraviolet absorber, characterized in that it is a method for producing a pigment composition. (Method 2) The method for producing a pigment composition according to Method 1, wherein the shear rate during kneading in the kneading step is 15 s -1 or more. (Method 3) The method for producing a pigment composition according to Method 1 or 2, wherein the amount of the water-insoluble ultraviolet absorber 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. (Method 4) The method for producing a pigment composition according to any one of Methods 1 to 3, wherein the organic solvent includes a first organic solvent capable of dissolving the water-insoluble ultraviolet absorber. (Method 5) The water-insoluble ultraviolet absorber includes a benzotriazole derivative, and the organic solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide, characterized in that it is a method for producing a pigment composition according to any one of Methods 1 to 4. (Method 6) The water-insoluble ultraviolet absorber includes a benzotriazole derivative, and the organic solvent includes N,N-dimethylformamide, characterized in that it is a method for producing a pigment composition according to any one of Methods 1 to 5. (Method 7) 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 Items 1 to 6, a dispersant, and water, and dispersing the pigment composition in the water with 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 of ejecting an 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 8.

Claims

1. A method for manufacturing 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 ultraviolet absorber. A method for manufacturing a pigment composition, characterized by this.

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

3. The method for manufacturing a pigment composition according to Claim 1, wherein the amount of the water-insoluble ultraviolet absorber 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.

4. The method for manufacturing a pigment composition according to Claim 1, wherein the organic solvent contains a first organic solvent capable of dissolving the water-insoluble ultraviolet absorber.

5. The water-insoluble ultraviolet absorber contains a benzotriazole derivative, and The method for manufacturing 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 ultraviolet absorber contains a benzotriazole derivative, and The method for manufacturing a pigment composition according to Claim 1, wherein the organic solvent contains N,N-dimethylformamide.

7. A method for manufacturing a pigment dispersion, characterized by including a dispersion step of mixing a pigment composition, a dispersant, and water obtained by the method for manufacturing a pigment composition according to any one of Claims 1 to 6, and dispersing the pigment composition in the water with the dispersant.

8. A method for manufacturing an aqueous ink, characterized by including a step of mixing a pigment dispersion obtained by the method for manufacturing 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 an aqueous ink obtained by the method for manufacturing an aqueous ink according to Claim 8. An inkjet recording method, characterized by this.

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