Pigment dispersions and water-based inks

Abstract

The present invention provides a pigment dispersion with good storage stability, which uses a halogen-free pigment as a coloring material that can replace CI Pigment Red 254, a typical red pigment. [Solution] The pigment dispersion contains a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, and water. The first pigment is a pigment that does not have a halogen element as a substituent and is at least one selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment. The second pigment is a pigment that does not have a halogen element as a substituent and is at least one selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton. The first dispersant and the second dispersant are copolymers having units derived from styrene-based monomers and units derived from (meth)acrylic acid-based monomers.

Description

[Technical Field]

[0001] The present invention relates to a pigment dispersion and an aqueous ink. [Background technology]

[0002] Among printing inks, colorants used in red ink include CI Pigment Red 254, a halogenated diketopyrrolol pigment.

[0003] Pigments such as the above-mentioned halogenated diketopyrrolole pigments may contain polychlorinated biphenyls (PCBs), which are residues of raw materials used in their synthesis or decomposition products. PCBs are chemical substances that are difficult to decompose in the natural environment and are therefore subject to regulation. For this reason, in order to reduce the amount of harmful substances such as PCBs remaining in pigments, synthesis reaction conditions that are less likely to produce impurities and methods for removing impurities from pigments have been proposed (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2022-534336 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, there has been a trend to refrain from using halogenated pigments that have halogen atoms such as chlorine atoms as substituents in their molecules, such as CI Pigment Red 254. This has led to a demand for the development of water-based inks that use pigments that can replace CI Pigment Red 254 as coloring materials, as well as red pigment dispersions for producing such water-based inks.

[0006] Therefore, an object of the present invention is to provide a pigment dispersion having good storage stability, which uses as a colorant a halogen-free pigment that can replace CI Pigment Red 254, a typical red pigment. Another object of the present invention is to provide a water-based ink having excellent ejection stability, which uses as a colorant a halogen-free pigment that can replace CI Pigment Red 254, a typical red pigment. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided a pigment dispersion comprising a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, and water, wherein the first pigment is a pigment that does not have a halogen atom as a substituent and is at least one selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment; the second pigment is a pigment that does not have a halogen atom as a substituent and is at least one selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton; and the first dispersant and the second dispersant are copolymers having units derived from a styrene-based monomer and units derived from a (meth)acrylic acid-based monomer.

[0008] The present invention also provides an aqueous ink comprising a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, a water-soluble organic solvent, and water, wherein the first pigment is a pigment that does not have a halogen atom as a substituent and is at least one selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment; the second pigment is a pigment that does not have a halogen atom as a substituent and is at least one selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton; and the first dispersant and the second dispersant are copolymers having units derived from a styrene-based monomer and units derived from a (meth)acrylic acid-based monomer. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a pigment dispersion having good storage stability, which uses as a colorant a halogen-free pigment that can replace CI Pigment Red 254, a typical red pigment. Furthermore, according to the present invention, it is possible to provide a water-based ink having excellent ejection stability, which uses as a colorant a halogen-free pigment that can replace CI Pigment Red 254, a typical red pigment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink dissociated into ions, but for convenience it will be expressed as "containing a salt." Furthermore, in this specification, aqueous ink may be simply referred to as "ink." Unless otherwise specified, physical property values ​​are values ​​at room temperature (25°C) and normal pressure (1 atmosphere). When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0011] The present inventors investigated the creation of pigment dispersions using halogen-free pigments to replace CI Pigment Red 254 as colorants. Specifically, they attempted to create pigment dispersions in which magenta and yellow pigments, both of which do not have halogen elements as substituents, were dispersed separately or simultaneously in a liquid medium. However, they found that dispersions containing mixed colorants sometimes resulted in unclear hues or color separation. In particular, depending on the type of dispersant used, interactions between individual pigments and the dispersant could prevent the desired particle size and number of coarse particles (i.e., the number of coarse particles), or the pigment dispersions could become thicker or coarser during long-term storage.

[0012] Therefore, the present inventors investigated combinations of pigments that have a vivid hue and are less likely to cause color separation, as well as combinations of dispersants that are less likely to cause thickening or coarsening of particle size during dispersion. As a result, they found that it was necessary to combine the following first and second pigments, and further to use the following copolymers as the first dispersant for dispersing the first pigment and the second dispersant for dispersing the second pigment. By including these components in a pigment dispersion, it is possible to obtain a pigment dispersion (red pigment dispersion) that exhibits a red hue and has good storage stability. The first pigment is a pigment that does not have a halogen element as a substituent, and is at least one selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment. The second pigment is also a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton. The first dispersant and the second dispersant are copolymers having a unit derived from a styrene-based monomer and a unit derived from a (meth)acrylic acid-based monomer.

[0013] <Pigment dispersion> The pigment dispersion of the present invention contains a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, and water. The components and properties of the pigment dispersion are described below.

[0014] (pigment) The pigment dispersion contains a first pigment and a second pigment. The first pigment is a pigment that does not have a halogen element as a substituent and is at least one selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment. The second pigment is also a pigment that does not have a halogen element as a substituent. Of the pigments, the second pigment is at least one selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton. At least two types of pigments, the first pigment and the second pigment, are used in the pigment dispersion. Multiple types of each of the first pigment and the second pigment may be used.

[0015] An example of a violet pigment having a perylene skeleton that does not have a halogen atom as a substituent is CI Pigment Violet 29. An example of a violet pigment having a benzimidazolone skeleton that does not have a halogen atom as a substituent is CI Pigment Violet 32. An example of a quinacridone pigment that does not have a halogen atom as a substituent is CI Pigment Red 122, CI Pigment Violet 19, or a solid solution having CI Pigment Violet 19. An example of a solid solution having CI Pigment Violet 19 that does not have a halogen atom as a substituent is a solid solution of CI Pigment Violet 19 and CI Pigment Red 122, or a solid solution of CI Pigment Violet 19, CI Pigment Red 122, and CI Pigment Red 202.

[0016] Examples of yellow pigments having a monoazo skeleton that does not have a halogen element as a substituent include CI Pigment Yellow 74 and CI Pigment Yellow 151. Examples of yellow pigments having a disazo skeleton that does not have a halogen element as a substituent include CI Pigment Yellow 155 and CI Pigment Yellow 180. Examples of yellow pigments having a benzimidazolone skeleton that does not have a halogen element as a substituent include CI Pigment Yellow 180. Examples of yellow pigments having an isoindoline skeleton that does not have a halogen element as a substituent include CI Pigment Yellow 185.

[0017] The first pigment is preferably at least one selected from the group consisting of CI Pigment Violet 29, CI Pigment Violet 32, CI Pigment Red 122, CI Pigment Violet 19, and a solid solution containing CI Pigment Violet 19. These pigments are halogen-free pigments that do not contain halogen elements in their molecules.

[0018] The second pigment is preferably at least one selected from the group consisting of CI Pigment Yellow 74, CI Pigment Yellow 151, CI Pigment Yellow 155, CI Pigment Yellow 180, and CI Pigment Yellow 185. These pigments are halogen-free pigments that do not contain halogen elements in their molecules.

[0019] The combination of the above-mentioned preferred specific examples of the first pigment and the second pigment makes it easier to obtain a pigment dispersion that has a clearer hue and is less susceptible to color separation. Furthermore, by using the above-mentioned preferred specific examples of the first pigment and the second pigment in combination, and further using a specific dispersant described below in combination, it is possible to more effectively prevent thickening and coarsening of the particle size during the preparation of the pigment dispersion.

[0020] From the viewpoint of dispersibility and storage stability, it is preferable to use the first pigment and the second pigment whose average particle diameter (cumulative 50% particle diameter (D50) of the volume-based particle size distribution) is adjusted to about 100 nm or more and 200 nm or less using a salt milling method or the like.

[0021] The cumulative 50% particle size (D50) of the volume-based particle size distribution of the pigments (first pigment and second pigment) in the pigment dispersion is preferably 100 nm or more and 200 nm or less, and more preferably 100 nm or more and 160 nm or less. Furthermore, the cumulative 90% particle size (D90) of the volume-based particle size distribution of the pigments in the pigment dispersion is preferably 200 nm or more and 350 nm or less, and more preferably 250 nm or more and 300 nm or less. By using the preferred combination of the first pigment and the second pigment described above, the D50 and D90 of the pigments in the pigment dispersion can be easily adjusted to fall within the above-mentioned ranges. In this specification, the cumulative 50% particle size (D50) and cumulative 90% particle size (D90) of the volume-based particle size distribution of the pigments are values ​​measured using a dynamic light scattering particle size distribution analyzer.

[0022] Furthermore, the number of particles with a particle diameter of 0.5 μm or more and less than 5.0 μm (i.e., the number of coarse particles) per 15 mass% of the pigment based on the total mass of the pigment dispersion liquid is 1.0 × 10 10 Preferably, it is 1.0 × 10 or less. 9 It is more preferable that the number of coarse particles in the pigment dispersion is within the above range by using the preferred combination of the first pigment and the second pigment described above. In this specification, the number of coarse particles is determined by measuring the number of particles with a particle diameter of 0.5 μm or more and less than 5.0 μm in a sample liquid obtained by diluting the pigment dispersion with water to an arbitrary ratio using a particle size distribution analyzer, and calculating the value per 15% by mass of the pigment from the measured value.

[0023] The content ratio of the first pigment to the second pigment in the pigment dispersion can be adjusted depending on the target red hue. The content ratio of the first pigment to the second pigment in the pigment dispersion, in mass ratio, is preferably in the range of 90:10 to 20:80 (first pigment:second pigment), and more preferably in the range of 80:20 to 30:70 (first pigment:second pigment).

[0024] The content (mass %) of the pigment (total of the first pigment and the second pigment) in the pigment dispersion is preferably 1 mass % or more and 30 mass % or less, and more preferably 5 mass % or more and 20 mass % or less, based on the total mass of the pigment dispersion.

[0025] (dispersant) The pigment dispersion contains a first dispersant for dispersing a first pigment and a second dispersant for dispersing a second pigment. Hereinafter, the first dispersant and the second dispersant may be collectively referred to simply as "dispersants." Dispersants are components for dispersing pigments in pigment dispersions or inks.

[0026] Both the first dispersant and the second dispersant are copolymers having a unit derived from a styrene-based monomer and a unit derived from a (meth)acrylic acid-based monomer. Therefore, the first dispersant and the second dispersant may be the same or different. From the viewpoint of easily obtaining a pigment dispersion with even better storage stability, it is preferable that the first dispersant and the second dispersant are the same dispersant. In this case, the pigment dispersion may contain one or more common dispersants as the first dispersant and the second dispersant.

[0027] Examples of styrene-based monomers include styrene, α-methylstyrene, 4-methylstyrene, and 2-chlorostyrene. One of these styrene-based monomers may be used alone, or two or more may be used in combination. In this specification, the term "(meth)acrylic acid-based monomer" encompasses acrylic acid, methacrylic acid, and salts thereof. One of these (meth)acrylic acid-based monomers may be used alone, or two or more may be used in combination. Examples of salts of (meth)acrylic acid include alkali metal salts and ammonium salts. Examples of alkali metal salts include sodium salts and potassium salts.

[0028] The copolymer used as a dispersant may contain, in addition to the styrene-based monomer and the (meth)acrylic acid-based monomer, units derived from other polymerizable monomers copolymerizable therewith. Examples of other polymerizable monomers include (meth)acrylic acid esters; acrylamide, methacrylamide, and derivatives thereof; acrylonitrile, methacrylonitrile, and derivatives thereof; and unsaturated carboxylic acid monomers other than (meth)acrylic acid. Among these, (meth)acrylic acid esters are preferred. Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. One of these may be used alone, or two or more may be used in combination.

[0029] The copolymer used as the dispersant is preferably a copolymer of a styrene-based monomer and a (meth)acrylic acid-based monomer, or a copolymer of a styrene-based monomer, a (meth)acrylic acid ester, and a (meth)acrylic acid-based monomer. Furthermore, the acid group (carboxylic acid group) in the copolymer used as the dispersant may be in the form of a salt neutralized with a basic compound such as potassium hydroxide. By using these copolymers as dispersants, pigment aggregation and sedimentation are less likely to occur, and a pigment dispersion with even better storage stability is more likely to be obtained. The copolymer may be in the form of a random copolymer, a block copolymer, or a graft copolymer.

[0030] In the copolymer, the mass ratio of the units derived from the (meth)acrylic acid-based monomer to the units derived from the styrene-based monomer is preferably 0.1 or more and 1.0 or less, more preferably 0.2 or more and 0.4 or less. When the mass ratio of the units derived from the (meth)acrylic acid-based monomer to the units derived from the styrene-based monomer is within the above range, the continuous ejection stability of an ink prepared using a pigment dispersion containing this copolymer as a dispersant can be improved. Specifically, even when this ink is continuously ejected from an inkjet recording head, deposition of deposits in the ink flow path of the recording head and in the vicinity of the ejection orifices, kogation, and the like are less likely to occur, thereby maintaining stable ejection performance. Therefore, the pigment dispersion is useful as a pigment dispersion for preparing aqueous inkjet inks. Furthermore, the pigment dispersion is particularly useful as a pigment dispersion for preparing aqueous inkjet inks that are ejected from a recording head (so-called thermal-type recording head) by the action of thermal energy.

[0031] The mass ratio can be calculated by dividing the content (% by mass) of units derived from acrylic acid-based monomers in the copolymer by the content (% by mass) of units derived from styrene-based monomers in the copolymer. Alternatively, for convenience, the mass ratio can be calculated by dividing the amount (parts by mass or % by mass of all monomers) of acrylic acid-based monomers used in synthesizing the copolymer by the amount (parts by mass or % by mass of all monomers) of styrene-based monomers used in synthesizing the copolymer.

[0032] The acid value of the copolymer used as a dispersant is preferably 50 mgKOH / g or more and 300 mgKOH / g or less. By using a copolymer having an acid value within the above range as a dispersant, it is possible to prepare an inkjet ink that is less susceptible to ejection defects, even when ejected from a thermal type recording head. In this specification, the acid value of the copolymer can be a value measured by a potentiometric titrator using a potassium hydroxide-ethanol titrant.

[0033] The weight-average molecular weight of the copolymer used as a dispersant is preferably from 1,000 to 30,000, and more preferably from 3,000 to 15,000. In this specification, the weight-average molecular weight of the copolymer can be measured as a value converted into standard polystyrene by gel permeation chromatography (GPC).

[0034] The content (mass%) of the dispersant (total of the first dispersant and the second dispersant) in the pigment dispersion is preferably 0.2 to 15% by mass, and more preferably 1 to 10% by mass, based on the total mass of the pigment dispersion. Furthermore, the content (mass%) of the dispersant (total of the first dispersant and the second dispersant) in the pigment dispersion is preferably 0.2 to 0.5 times the content (mass%) of the pigment (total of the first pigment and the second pigment).

[0035] (water) The pigment dispersion is an aqueous pigment dispersion containing water as a dispersion medium. As the water, deionized water or ion-exchanged water is preferably used. The content (mass %) of water in the pigment dispersion is preferably 70 mass % or more and 90 mass % or less based on the total mass of the pigment dispersion.

[0036] (Other ingredients) In addition to the above components, the pigment dispersion may further contain other components as needed, such as resins other than the dispersant, surfactants, waxes, low surface tension organic solvents, wetting agents, penetrating agents, antifoaming agents, preservatives, viscosity adjusters, pH adjusters, chelating agents, plasticizers, antioxidants, and ultraviolet absorbers.

[0037] (Method of manufacturing pigment dispersion liquid) The pigment dispersion can be produced, for example, by mixing the above-mentioned components and then dispersing them using a dispersing device. Specifically, the pigment dispersion can be produced by a dispersing method that can appropriately control dispersion conditions such as dispersion time, peripheral speed, and, if necessary, the type and particle size of the media used. Examples of dispersing devices include roll mills, bead mills, paint shakers, sand mills, agitator mills, nanomizers, homogenizers, microfluidizers, ultimizers, high-shear homomixers, and ultrasonic dispersers.

[0038] Alternatively, a pigment dispersion can be obtained by mixing a first pigment dispersion containing a first pigment, a first dispersant, and water with a second pigment dispersion containing a second pigment, a second dispersant, and water. In this case, the first pigment, the first dispersant, and water can be mixed in advance and subjected to a dispersion treatment to prepare a first pigment dispersion in which the first pigment is dispersed in water by the first dispersant. Similarly, the second pigment, the second dispersant, and water can be mixed in advance and subjected to a dispersion treatment to prepare a second pigment dispersion in which the second pigment is dispersed in water by the second dispersant.

[0039] (Applications of pigment dispersions) The pigment dispersion can be suitably used in any application requiring a coloring function. Examples of such applications include paints, printing inks, colored molded products, toners for developing electrostatic images, color filters for liquid crystal displays, and aqueous inks for inkjet printers. Among these, the pigment dispersion is preferably used in aqueous inks for inkjet printers. The use of the pigment dispersion makes it possible to easily prepare the aqueous inks described below.

[0040] <Water-based ink> The aqueous ink of the present invention contains a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, a water-soluble organic solvent, and water. By incorporating these components into the ink, it is possible to prepare an aqueous ink (aqueous red pigment ink) exhibiting a red hue. The first pigment, the second pigment, the first dispersant, and the second dispersant are all the same as those described above for the pigment dispersion. From the viewpoint of easily preparing the aqueous ink, it is preferable that the aqueous ink contains the pigment dispersion described above.

[0041] The content (% by mass) of the pigment (total of the first pigment and the second pigment) in the ink is preferably 0.1% to 15% by mass, and more preferably 1% to 10% by mass, based on the total mass of the ink. The content (% by mass) of the dispersant (total of the first dispersant and the second dispersant) in the ink is preferably 0.02% to 7.5% by mass, and more preferably 0.2% to 5% by mass, based on the total mass of the ink.

[0042] (aqueous medium) The ink is an aqueous ink containing water and a water-soluble organic solvent as an aqueous medium. The water contained in the ink is preferably deionized water or ion-exchanged water. The water content (mass %) in the ink is preferably 50% to 95% by mass, and more preferably 50% to 90% by mass, based on the total mass of the ink. The water content (mass %) in the ink is preferably 3% to 48% by mass, and more preferably 3% to 25% by mass, based on the total mass of the ink.

[0043] Examples of the water-soluble organic solvent include glycol ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, and triethylene glycol monobutyl ether; alkanols having 1 to 4 carbon atoms such as methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, isobutanol, and t-butanol; carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; ketones or ketoalcohols such as acetone, methyl ethyl ketone, and 2-methyl-2-hydroxypentan-4-one; cyclic ethers such as tetrahydrofuran and dioxane; Examples of suitable water-soluble organic solvents include glycols such as ethanol, triethylene glycol, tetraethylene glycol, propylene glycol, and butylene glycol; polyethylene glycols having an average molecular weight of 200 to 2,000, more specifically, number-average molecular weights of 200, 400, 600, 1,000, and 2,000; acetylene glycol derivatives; polyhydric alcohols such as glycerin, 1,3-butanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, and 1,2,6-hexanetriol; heterocycles such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and N-methylmorpholine; and sulfur-containing compounds such as thiodiglycol and dimethyl sulfoxide. These water-soluble organic solvents may be used singly or in combination.

[0044] (Other ingredients) In addition to the above components, the ink may contain various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and antireducing agents, as needed.

[0045] (Water-based ink manufacturing method) When preparing an aqueous ink, it is preferable to use the pigment dispersion liquid described above. Specifically, it is more preferable to prepare the ink by adding a water-soluble organic solvent or water (ion-exchanged water or deionized water) to the pigment dispersion liquid, stirring the mixture, and then filtering it. This ink can also be prepared without using the pigment dispersion liquid described above. Specifically, it is possible to prepare the ink by using the first pigment dispersion liquid and the second pigment dispersion liquid described above, by mixing the first pigment dispersion liquid, the second pigment dispersion liquid, a water-soluble organic solvent, and water, stirring the mixture, and then filtering it. [Example]

[0046] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0047] <Methods for measuring physical properties> (Viscosity of pigment dispersion) The viscosity (mPa·s) of the pigment dispersion was measured at 25°C using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.).

[0048] (D50 and D90 of the volume-based particle size distribution of pigment) A sample liquid was prepared by diluting the pigment dispersion 10,000 times (by mass) with pure water. The volume-based particle size distribution of the pigment in the sample liquid was measured using a dynamic light scattering particle size distribution analyzer (trade name "Nanotrac UPA-EX150", manufactured by Nikkiso). The cumulative 50% particle size (D50 (nm)) and cumulative 90% particle size (D90 (nm)) of the particle size distribution were then determined. The measurement conditions are shown below. [Measurement conditions] Setzero:30s Measurement time: 120 seconds Measurement count: 3 times Particle refractive index: 1.8 Solvent: Water Filter: Standard Sensitivity: Standard

[0049] (Number of particles with a particle size of 0.5 μm or more and less than 5.0 μm) A sample liquid was prepared by diluting the pigment dispersion 10,000 times (by mass) with pure water. The number of particles with a particle diameter of 0.5 μm or more and less than 5.0 μm in the sample liquid was measured using a particle size distribution analyzer (product name "AccuSizer780APS" manufactured by Particle Sizing System) under the following measurement conditions. From the measured values, the number of particles with a particle diameter of 0.5 μm or more and less than 5.0 μm per 15% of the pigment was calculated based on the total mass of the pigment dispersion. [Measurement conditions] Measurement time: 60 seconds Number of channels: 128 ·Flow rate: 60mL / min Sample loop capacity: 1 mL First dilution ratio: 30 times Second stage dilution ratio: 40x

[0050] <Production of pigment dispersion> (Pigment dispersion 1) CI Pigment Violet 29 (PV29) was used as the first pigment, and CI Pigment Yellow 74 (PY74) was used as the second pigment. A mixture was obtained by mixing 12.0 parts of the first pigment (PV29), 3.0 parts of the second pigment (PY74), 7.5 parts of a dispersant, and 77.5 parts of ion-exchanged water. The dispersant used was a resin obtained by neutralizing a random copolymer (acid value 120 mg KOH / g, weight-average molecular weight 8,000) obtained by conventionally polymerizing 73 parts of styrene, 10 parts of butyl acrylate, and 17 parts of acrylic acid with an aqueous potassium hydroxide solution. The above mixture was charged into a batch-type vertical sand mill (manufactured by Imex) filled with 85 parts of 0.3 mm zirconia beads. After 3 hours of dispersion treatment with water cooling, the mixture was centrifuged to remove undispersed material, including coarse particles. The mixture was then pressure filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare Pigment Dispersion 1 having a pigment content (solid content) of 10.0% and a resin (copolymer) content of 3.0%.

[0051] (Pigment dispersions 2 to 13) Pigment dispersions 2 to 13 were obtained in the same manner as the above-described pigment dispersion 1, except that the combinations of the first pigment and the second pigment shown in Table 1 were used instead of the combination of the first pigment and the second pigment used in the preparation of pigment dispersion 1.

[0052] (Pigment Dispersion 14) A mixture was prepared by mixing 15.0 parts of CI Pigment Violet 29 (PV29) as the first pigment, 7.5 parts of a dispersant, and 77.5 parts of ion-exchanged water. The dispersant used was a resin obtained by neutralizing a random copolymer (acid value 120 mgKOH / g, weight-average molecular weight 8,000) prepared by conventional polymerization of 73 parts of styrene, 10 parts of butyl acrylate, and 17 parts of acrylic acid with an aqueous potassium hydroxide solution. The mixture was placed in a batch-type vertical sand mill (manufactured by Imex) packed with 85 parts of 0.3 mm zirconia beads. After dispersing for 3 hours with water cooling, the mixture was centrifuged to remove undispersed material, including coarse particles. The mixture was then pressure-filtered through a 3.0 μm pore-size microfilter (manufactured by Fujifilm) to prepare a first pigment dispersion with a pigment content (solids) of 10.0% and a resin (copolymer) content of 3.0%. Next, a second pigment dispersion was prepared in the same manner as the first pigment dispersion, except that CI Pigment Yellow 74 (PY74) was used as the second pigment instead of the first pigment (PV29) used in preparing the first pigment dispersion. The first pigment dispersion and the second pigment dispersion were then mixed in a mass ratio of first pigment dispersion:second pigment dispersion = 4:1 to prepare pigment dispersion 14, which had a pigment content (solid content) of 10.0% and a resin (copolymer) content of 3.0%.

[0053] (Pigment Dispersion 15) A random copolymer (acid value 120 mgKOH / g, weight average molecular weight 8,000) prepared by polymerizing 63 parts of benzyl methacrylate, 20 parts of butyl acrylate, and 17 parts of acrylic acid in a conventional manner was neutralized with an aqueous potassium hydroxide solution to obtain a resin. Pigment dispersion 15 was prepared in the same manner as the above-mentioned pigment dispersion 1, except that this resin was used as a dispersant.

[0054] (Pigment Dispersion 16) Pigment Dispersion 16 was prepared in the same manner as the first pigment dispersion in Pigment Dispersion 14, except that CI Pigment Red 254 (PR254) was used instead of CI Pigment Violet 29 (PV29).

[0055] The obtained pigment dispersions 1 to 16 were pigment dispersions exhibiting a red hue (red pigment dispersions). The physical properties and evaluation results of the obtained pigment dispersions are shown in Table 1. The meanings of the abbreviations in Table 1 are as follows: PV29: CI Pigment Violet 29 PV32: CI Pigment Violet 32 PR122: CI Pigment Red 122 PV19: CI Pigment Violet 19 Quinacridone solid solution: A quinacridone solid solution consisting of CI Pigment Violet 19 (PV19) and CI Pigment Red 122 (PR122) in a mass ratio of 70:30. PR254: CI Pigment Red 254 PY74: CI Pigment Yellow 74 PY151: CI Pigment Yellow 151 PY155: CI Pigment Yellow 155 PY180: CI Pigment Yellow 180 PY185: CI Pigment Yellow 185

[0056] <Evaluation of pigment dispersion> (Storage stability) The pigment dispersion was placed in a sealed container and stored in a thermostatic chamber at 60°C for 60 days. After cooling to room temperature, the viscosity (mPa·s), D50 (nm) and D90 (nm) of the pigment, and the number of particles with a particle size of 0.5 μm or more and less than 5.0 μm were measured. These were then compared with the physical property values ​​before storage, and the storage stability of the pigment dispersion was evaluated according to the evaluation criteria shown below. The results are shown in Table 1. A: For all physical properties, including the viscosity of the pigment dispersion, the D50 and D90 of the pigment, and the number of particles with a particle size of 0.5 μm or more and less than 5.0 μm, the rate of change from the physical property value before storage was 10% or less. C: The rate of change in at least one of the physical properties of the viscosity of the pigment dispersion, the D50 and D90 of the pigment, and the number of particles with a particle diameter of 0.5 μm or more and less than 5.0 μm, based on the physical property value before storage, was more than 10%.

[0057] TIFF2026044392000001.tif121170

[0058] <Ink Preparation> (Ink 1) The components shown below were mixed and thoroughly stirred, then pressure filtered through a 2.5 μm pore size Fluoropore filter to obtain Ink 1 (water-based red pigment ink 1). Among the components shown below, "Acetylenol E100" is the trade name of a nonionic acetylene glycol surfactant (manufactured by Kawaken Fine Chemicals). Furthermore, "Proxel GXL(S)" is the trade name of a preservative (manufactured by Arch Chemicals). (Ink 1) Pigment dispersion 1 30.0 parts Glycerin 10.0 parts 1,2-Hexanediol 5.0 parts Polyethylene glycol (number average molecular weight 1,000) 3.0 parts Acetylenol E100 0.5 parts Proxel GXL(S) 0.2 parts 51.3 parts ion-exchanged water

[0059] (Ink 2-16) Inks 2 to 16 (water-based red pigment inks 2 to 16) were obtained in the same manner as Ink 1 above, except that pigment dispersion 1 was replaced with the pigment dispersions shown in Table 2.

[0060] <Ink evaluation> (Continuous discharge stability) Each ink cartridge was filled with ink and set in an inkjet recording device (product name "PIXUS iP3100", manufactured by Canon) that ejects ink from a recording head using thermal energy. After continuously recording a solid image on 200 sheets of A4-sized paper, a nozzle check pattern was recorded. The recorded nozzle check pattern was visually inspected and the continuous ejection stability was evaluated according to the evaluation criteria shown below. The results are shown in Table 2. A: There was no disturbance in the nozzle check pattern and printing was successful. B: Slight disturbance was observed in the nozzle check pattern. C: Non-ejection and irregularities were clearly observed in the nozzle check pattern, and normal printing was not possible.

[0061] (deposit) Each ink cartridge was filled with ink and set in an inkjet recording device (product name "PIXUS iP3100", manufactured by Canon) that ejects ink from the recording head using thermal energy. After continuously recording solid images on 200 sheets of A4-sized paper, the recording head was removed and the heater and the inside of the nozzle were observed under an optical microscope. The deposits were then evaluated according to the following evaluation criteria. The results are shown in Table 2. A: The deposits were barely visible. C: The deposits were visible throughout the area.

[0062] TIFF2026044392000002.tif117170

[0063] The disclosure of this embodiment includes the following configuration. (Configuration 1) A pigment dispersion containing a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, and water, the first pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment; the second pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton; A pigment dispersion liquid, wherein the first dispersant and the second dispersant are copolymers having a unit derived from a styrene-based monomer and a unit derived from a (meth)acrylic acid-based monomer. (Configuration 2) The first pigment is at least one selected from the group consisting of CI Pigment Violet 29, CI Pigment Violet 32, CI Pigment Red 122, CI Pigment Violet 19, and a solid solution containing CI Pigment Violet 19; 2. The pigment dispersion according to claim 1, wherein the second pigment is at least one selected from the group consisting of CI Pigment Yellow 74, CI Pigment Yellow 151, CI Pigment Yellow 155, CI Pigment Yellow 180, and CI Pigment Yellow 185. (Configuration 3) The pigment dispersion according to Configuration 1 or 2, wherein the mass ratio of the units derived from the (meth)acrylic acid-based monomer to the units derived from the styrene-based monomer in the copolymer is 0.2 or more and 0.4 or less. (Configuration 4) The pigment dispersion liquid according to any one of Configurations 1 to 3, which is used in an aqueous inkjet ink. (Configuration 5) A water-based ink containing a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, a water-soluble organic solvent, and water, the first pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment; the second pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton; The aqueous ink is characterized in that the first dispersant and the second dispersant are copolymers having a unit derived from a styrene-based monomer and a unit derived from a (meth)acrylic acid-based monomer. (Configuration 6) The first pigment is at least one selected from the group consisting of CI Pigment Violet 29, CI Pigment Violet 32, CI Pigment Red 122, CI Pigment Violet 19, and a solid solution containing CI Pigment Violet 19; 6. The aqueous ink according to claim 5, wherein the second pigment is at least one selected from the group consisting of CI Pigment Yellow 74, CI Pigment Yellow 151, CI Pigment Yellow 155, CI Pigment Yellow 180, and CI Pigment Yellow 185. (Configuration 7) The aqueous ink according to Configuration 5 or 6, wherein the mass ratio of the units derived from the (meth)acrylic acid-based monomer to the units derived from the styrene-based monomer in the copolymer is 0.2 or more and 0.4 or less. (Configuration 8) The aqueous ink according to any one of Configurations 5 to 7, which is an aqueous ink for inkjet use.

Claims

1. A pigment dispersion liquid containing a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, and water, the first pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment; the second pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton; a first dispersant and a second dispersant each being a copolymer having a unit derived from a styrene-based monomer and a unit derived from a (meth)acrylic acid-based monomer;

2. The first pigment is at least one selected from the group consisting of C.I. Pigment Violet 29, C.I. Pigment Violet 32, C.I. Pigment Red 122, C.I. Pigment Violet 19, and a solid solution having C.I. Pigment Violet 19; 2. The pigment dispersion according to claim 1, wherein the second pigment is at least one selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 151, C.I. Pigment Yellow 155, C.I. Pigment Yellow 180, and C.I. Pigment Yellow 185.

3. 2. The pigment dispersion according to claim 1, wherein the mass ratio of the units derived from the (meth)acrylic acid-based monomer to the units derived from the styrene-based monomer in the copolymer is 0.2 or more and 0.4 or less.

4. The pigment dispersion according to claim 1, which is used in an aqueous inkjet ink.

5. An aqueous ink containing a first pigment, a second pigment, a first dispersant for dispersing the first pigment, a second dispersant for dispersing the second pigment, a water-soluble organic solvent, and water, the first pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a violet pigment having a perylene skeleton, a violet pigment having a benzimidazolone skeleton, and a quinacridone pigment; the second pigment is a pigment that does not have a halogen element as a substituent, and is at least one pigment selected from the group consisting of a yellow pigment having a monoazo skeleton, a yellow pigment having a disazo skeleton, a yellow pigment having a benzimidazolone skeleton, and a yellow pigment having an isoindoline skeleton; The aqueous ink is characterized in that the first dispersant and the second dispersant are copolymers having a unit derived from a styrene-based monomer and a unit derived from a (meth)acrylic acid-based monomer.

6. The first pigment is at least one selected from the group consisting of C.I. Pigment Violet 29, C.I. Pigment Violet 32, C.I. Pigment Red 122, C.I. Pigment Violet 19, and a solid solution having C.I. Pigment Violet 19; 6. The aqueous ink according to claim 5, wherein the second pigment is at least one selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 151, C.I. Pigment Yellow 155, C.I. Pigment Yellow 180, and C.I. Pigment Yellow 185.

7. The aqueous ink according to claim 5 , wherein the mass ratio of the units derived from the (meth)acrylic acid-based monomer to the units derived from the styrene-based monomer in the copolymer is 0.2 or more and 0.4 or less.

8. The aqueous ink according to claim 5, which is an aqueous ink for ink-jet printing.

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