Pigment dispersion liquid and aqueous ink

Abstract

To provide a pigment dispersion capable of preparing an aqueous ink for inkjet, using a halogen-free pigment as a coloring material, and excellent in storage stability, and to provide an aqueous ink for inkjet using the same.SOLUTION: The pigment dispersion contains a pigment, a dispersant for dispersing the pigment, and water. The pigment is at least one selected from the group consisting of C. I. Pigment Green 8, C. I. Pigment Violet 29, and C. I. Pigment Violet 37. The aqueous ink for inkjet contains the pigment dispersion.SELECTED DRAWING: None

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 green ink include the halogenated copper phthalocyanine pigment CI Pigment Green 7. Colorants used in blue ink include the halogenated dioxane pigment CI Pigment Violet 23.

[0003] In addition to the halogenated copper phthalocyanine pigments and halogenated dioxane pigments mentioned above, pigments such as azo pigments may contain polychlorinated biphenyls (PCBs), which are residues or decomposition products of the raw materials used in their synthesis. PCBs are chemical substances that do not easily 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 do not produce impurities and methods for removing impurities from pigments have been proposed (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7173353 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, there has been a trend toward refraining from using halogenated pigments that have halogen atoms such as chlorine atoms as substituents in their molecules, such as CI Pigment Green 7 and CI Pigment Violet 23. This has led to a demand for the development of aqueous inks that use pigments that can replace CI Pigment Green 7 and CI Pigment Violet 23 as coloring materials, as well as pigment dispersions for producing such aqueous inks.

[0006] Therefore, an object of the present invention is to provide a pigment dispersion that contains a halogen-free pigment as a colorant and has excellent storage stability, which can be used to prepare an aqueous inkjet ink. Another object of the present invention is to provide an aqueous inkjet ink that uses this pigment dispersion. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided a pigment dispersion containing a pigment, a dispersant for dispersing the pigment, and water, wherein the pigment is at least one selected from the group consisting of CI Pigment Green 8, CI Pigment Violet 29, and CI Pigment Violet 37. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a pigment dispersion that contains a halogen-free pigment as a colorant and has excellent storage stability, which can be used to prepare an aqueous inkjet ink. Furthermore, according to the present invention, it is possible to provide an aqueous inkjet ink that uses this pigment dispersion. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in further detail below with reference to preferred embodiments. Water-based inkjet inks are sometimes simply referred to as "ink." Physical property values ​​are those at room temperature (25°C) and atmospheric pressure (1 atmosphere) unless otherwise specified.

[0010] The present inventors investigated the selection of halogen-free pigments to replace CI Pigment Green 7 and CI Pigment Violet 23. Specifically, various pigments were mixed with dispersants (resins) and then dispersed using a high-shear homomixer to prepare aqueous pigment dispersions. A pigment that satisfied the following criteria (i) to (iii) was then extracted, leading to the present invention. Specifically, the pigment used in the pigment dispersion of the present invention is at least one selected from the group consisting of CI Pigment Green 8, CI Pigment Violet 29, and CI Pigment Violet 37. (i) The particle size and number of coarse particles of the pigment in the pigment dispersion are similar to those in a pigment dispersion prepared using CI Pigment Green 7 or the like. (ii) Even if the pigment dispersion is stored for a long period of time, there is little change in viscosity or pigment particle size. (iii) The inkjet ink prepared using the pigment dispersion exhibits good ejection performance from thermal recording heads. Furthermore, because halogen-free pigments can be used, the technology described herein may contribute to the realization of a sustainable society, such as a decarbonized / recycling-based society.

[0011] <Pigment dispersion> The pigment dispersion of the present invention contains a pigment, a dispersant for dispersing the pigment, and water. The pigment is at least one pigment selected from the group consisting of CI Pigment Green 8, CI Pigment Violet 29, and CI Pigment Violet 37. The components constituting the pigment dispersion of the present invention will be described in detail below.

[0012] (pigment) The pigment is at least one selected from the group consisting of CI Pigment Green 8, CI Pigment Violet 29, and CI Pigment Violet 37. These pigments are halogen-free pigments that do not have halogen atoms in their molecules.

[0013] The cumulative 50% particle size (D50) of the volume-based particle size distribution of the pigment in the pigment dispersion is preferably 100 nm or more and 200 nm or less, and more preferably 100 nm or more and 120 nm or less. The cumulative 90% particle size (D90) of the volume-based particle size distribution of the pigment in the pigment dispersion is preferably 100 nm or more and 200 nm or less, and more preferably 180 nm or more and 200 nm or less. The number of particles with a particle size of 0.5 μm or more and less than 5.0 μm (i.e., coarse particles) per 15% of the pigment based on the total mass of the pigment dispersion is 1.0×10 12 Preferably, it is 5.0 × 10 or less. 10 By using the above-mentioned three types of pigments, the particle size and the number of coarse particles of the pigment in the pigment dispersion can be set within the above ranges.

[0014] (dispersant) A dispersant is a component for dispersing a pigment in a pigment dispersion or ink. The type of dispersant is not particularly limited. To prepare a pigment dispersion for use in an aqueous inkjet ink, it is preferable to use a resin such as a copolymer as the dispersant. That is, it is preferable to use a copolymer having a first unit and a second unit as the dispersant. The first unit is preferably a unit derived from a styrene-based monomer. The second unit is preferably a unit derived from at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid ester, and a methacrylic acid ester. By using such a copolymer as a dispersant, aggregation and sedimentation of the pigment are less likely to occur, and the pigment can be dispersed in a good state, resulting in a pigment dispersion with better storage stability.

[0015] Examples of styrene-based monomers include styrene, α-methylstyrene, 4-methylstyrene, and 2-chlorostyrene. Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, butyl methacrylate, and methyl-2-ethylhexyl methacrylate. The copolymer may be in the form of a random copolymer, a block copolymer, or a graft copolymer.

[0016] The second unit is preferably a unit derived from (i) acrylic acid or methacrylic acid, and (ii) an acrylic acid ester or a methacrylic acid ester. That is, the dispersant is preferably a copolymer having a first unit derived from a styrene-based monomer and a second unit derived from (i) acrylic acid or methacrylic acid, and (ii) an acrylic acid ester or a methacrylic acid ester. In addition, the acid group (carboxylic acid group) in the copolymer used as the dispersant may be neutralized with a basic compound such as potassium hydroxide.

[0017] In the copolymer, the content (mass %) of the second unit relative to the content (mass %) of the first unit is preferably 0.1 to 1.0 times, more preferably 0.2 to 0.4 times. Using a copolymer in which the content of the second unit relative to the content of the first unit falls within the above-mentioned mass ratio range as a dispersant can improve the continuous ejection stability of ink prepared using a pigment dispersion containing this dispersant. Specifically, even when this ink is continuously ejected, deposits and kogation are less likely to occur in the ink flow path of the recording head and near the ejection orifices, and ejection performance can be stably maintained. Therefore, this is particularly useful as a pigment dispersion for preparing inkjet ink to be ejected from a thermal-type recording head.

[0018] The copolymer used as a dispersant preferably has an acid value of 50 mgKOH / g to 300 mgKOH / g. By using a copolymer having an acid value within this 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.

[0019] The weight-average molecular weight of the copolymer is preferably from 1,000 to 30,000, and more preferably from 3,000 to 15,000.The content of the dispersant in the pigment dispersion is preferably from 20 to 50 parts by mass per 100 parts by mass of the pigment.

[0020] (water) The pigment dispersion is an aqueous pigment dispersion containing water as a dispersion medium. The water is preferably deionized water or ion-exchanged water. The water content (mass %) in the pigment dispersion is preferably 70% by mass or more and 85% by mass or less, based on the total mass of the pigment dispersion.

[0021] (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.

[0022] (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 that can be used include roll mills, bead mills, paint shakers, sand mills, agitator mills, nanomizers, homogenizers, microfluidizers, ultimizers, high-shear homomixers, and ultrasonic dispersers.

[0023] <Water-based ink> The above-described pigment dispersion liquid can be used to prepare an aqueous inkjet ink. That is, the aqueous inkjet ink of the present invention contains the above-described pigment dispersion liquid. For example, the aqueous inkjet ink can be obtained by adding a water-soluble organic solvent and water to the pigment dispersion liquid, followed by stirring and filtering.

[0024] The ink of the present invention contains the above-mentioned pigment dispersion liquid. Therefore, the ink of the present invention is usually an aqueous ink containing a pigment, a dispersant for dispersing the pigment, and water.

[0025] (aqueous medium) The ink can typically contain an aqueous medium, which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the ink is preferably 50.0% to 95.0% by mass, based on the total mass of the ink. The water-soluble organic solvent content (mass %) in the ink is preferably 3.0% to 50.0% by mass, based on the total mass of the ink.

[0026] 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; ethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and diethylene glycol monobutyl ether; Examples of suitable acrylic copolymers include glycols such as ethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, and butylene glycol; polyethylene glycols having an average molecular weight of 200 or more and 2,000 or less, more specifically, average molecular weights of 200, 400, 600, 1,000, and 2,000; acetylene glycol derivatives; polyhydric alcohols such as glycerin, 3-butanediol, 1,5-pentanediol, 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.

[0027] (Other ingredients) In addition to the above components, the ink may contain various additives, such as surfactants, pH adjusters, rust inhibitors, preservatives, anti-mold agents, antioxidants, anti-reducing agents, evaporation promoters, and chelating agents, as needed. [Example]

[0028] 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.

[0029] <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.).

[0030] (Cumulative 50% particle size (D50) and cumulative 90% particle size (D90) of the volume-based particle size distribution of pigment) A sample liquid was prepared by diluting the pigment dispersion liquid 10,000 times (by mass) with pure water. The D50 (nm) and D90 (nm) of the prepared sample liquid were measured using a particle size distribution analyzer (trade name "UPA150EX", manufactured by Nikkiso Co., Ltd.). The measurement conditions are as follows: [Measurement conditions] Setzero:30s Measurement time: 120 seconds Measurement count: 3 times Particle refractive index: 1.8 Solvent: Water Filter: Standard Sensitivity: Standard

[0031] (Number of particles with a particle diameter 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. Using a particle size distribution analyzer (product name "Accusixer780APS" manufactured by Particle Sizing System), the number of particles with a particle diameter of 0.5 μm or more and less than 5.0 μm in the prepared sample liquid was measured. The measurement conditions are shown below. 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, based on the total mass of the pigment dispersion, was calculated. [Measurement conditions] Measurement time: 60 seconds Number of channels: 128 ·Flow rate: 60mL / min Sample loop capacity: 1 mL First dilution ratio: 30x Second stage dilution ratio: 40x

[0032] <Production of pigment dispersion> (Pigment dispersion 1) A mixture was prepared by mixing 15.0 parts of CI Pigment Green 8, 7.5 parts of dispersant, and 77.5 parts of ion-exchange 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 73.0 parts of styrene, 10.0 parts of butyl acrylate, and 17.0 parts of acrylic acid with potassium hydroxide. The resulting mixture was placed in 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 3.0 μm pore-size microfilter (manufactured by Fujifilm) to obtain Pigment Dispersion 1, which had a pigment content (solids content) of 10.0% and a resin content of 3.0%.

[0033] (Pigment dispersions 2 to 5) Pigment dispersions 2 to 4 and 6 to 8 were obtained in the same manner as in the above-described pigment dispersion 1, except that the pigments shown in Table 1 were used instead of CI Pigment Green 8.

[0034] The physical properties and evaluation results of the obtained pigment dispersion are shown in Table 1. The meanings of the abbreviations in Table 1 are as follows: PG8: CI Pigment Green 8 PV29: CI Pigment Violet 29 PV37: CI Pigment Violet 37 PG7: CI Pigment Green 7 PV23: CI Pigment Violet 23

[0035] <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 of the pigment dispersion, the pigment D50, the pigment D90, 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 of the pigment, the 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, the rate of change from the physical property value before storage was 10% or less. C: The change rate of any of the physical properties of the pigment dispersion, namely the viscosity, D50 of the pigment, 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%.

[0036] TIFF2026006145000001.tif62170

[0037] <Ink Preparation> (Ink 1) The components shown below were mixed and thoroughly stirred, and then pressure filtered through a 2.5 μm pore size Fluoropore filter to obtain Ink 1. Among the components shown below, "Acetylenol E100" is the trade name of a nonionic acetylene glycol surfactant (manufactured by Kawaken Fine Chemicals). Also, "Proxel GXL(S)" is the trade name of a preservative (manufactured by Arch Chemicals). 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 Ion-exchanged water: 51.3 parts

[0038] (Ink 2-5) Inks 2 to 5 were obtained in the same manner as Ink 1 described above, except that pigment dispersion liquid 1 was replaced with the pigment dispersion liquid of the type shown in Table 2.

[0039] <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 or irregularities were clearly observed in the nozzle check pattern, and normal printing was not possible.

[0040] (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.

[0041] TIFF2026006145000002.tif55170

[0042] The disclosure of this embodiment includes the following configuration. (Configuration 1) A pigment dispersion containing a pigment, a dispersant for dispersing the pigment, and water, The pigment dispersion is characterized in that the pigment is at least one selected from the group consisting of CI Pigment Green 8, CI Pigment Violet 29, and CI Pigment Violet 37. (Configuration 2) The pigment dispersion according to Configuration 1, wherein the dispersant is a copolymer having a first unit derived from a styrene-based monomer and a second unit derived from at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid ester, and a methacrylic acid ester. (Configuration 3) The pigment dispersion according to Configuration 2, wherein the content (mass%) of the second unit in the copolymer is 0.2 to 0.4 times the content (mass%) of the first unit in terms of mass ratio. (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 inkjet ink containing the pigment dispersion liquid according to Configuration 4.

Claims

1. A pigment dispersion containing a pigment, a dispersant for dispersing the pigment, and water, The pigment dispersion liquid is characterized in that the pigment is at least one selected from the group consisting of C. I. Pigment Green 8, C. I. Pigment Violet 29, and C. I. Pigment Violet 37.

2. 2. The pigment dispersion according to claim 1, wherein the dispersant is a copolymer having a first unit derived from a styrene-based monomer and a second unit derived from at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid ester, and a methacrylic acid ester.

3. 3. The pigment dispersion according to claim 2, wherein the content (% by mass) of the second unit in the copolymer is 0.2 to 0.4 times the content (% by mass) of the first unit in terms of a mass ratio.

4. The pigment dispersion according to any one of claims 1 to 3, which is used in an aqueous inkjet ink.

5. A water-based inkjet ink comprising the pigment dispersion liquid according to claim 4.

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