Ink set

Abstract

To provide an ink set which includes a combination of special color inks using a halogen-free pigment as a color material and can record an image excellent in a color reproduction region.SOLUTION: The ink set has a combination of at least two aqueous inks selected from the group consisting of a green ink, a red ink, and a blue ink, each containing a pigment, a dispersant for dispersing the pigment, and water. The pigment in the green ink is a combination of a blue pigment such as (i) C. I. Pigment Green 8 or (ii) C. I. Pigment Blue 15:3 and a yellow pigment such as C. I. Pigment Yellow 74.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink set. [Background technology]

[0002] In recent years, it has become mainstream to use pigments as coloring materials in printing inks. However, when recording an image using pigment inks of the three basic primary colors, yellow (Y), magenta (M), and cyan (C), there is a problem that the color reproduction range is narrower than when recording an image using dye inks of the same three basic primary colors. To solve this problem, it has been proposed to use special color inks using coloring materials with hues other than the three basic primary colors, such as red (R), green (G), blue (B), orange (O), and violet (V) (Patent Document 1).

[0003] Among printing inks, colorants used in green ink include CI Pigment Green 7, a halogenated copper phthalocyanine pigment, colorants used in blue ink include CI Pigment Violet 23, a halogenated dioxane pigment, and colorants used in red ink include CI Pigment Red 254, a halogenated diketopyrrolopyrrole pigment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-354886 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, there has been a trend away from using halogenated pigments, which have halogen atoms such as chlorine atoms as substituents in their molecules. This has led to a demand for the development of ink sets that can record images with a sufficiently wide color reproduction range while still using halogen-free pigments as colorants.

[0006] Therefore, an object of the present invention is to provide an ink set that includes a combination of special color inks that use halogen-free pigments as coloring materials, and that is capable of recording images with an excellent color reproduction range. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided an ink set having a combination of at least two aqueous inks selected from the group consisting of a green ink, a red ink, and a blue ink, each of which contains a pigment, a dispersant for dispersing the pigment, and water, wherein the pigment in the green ink is (i) CI Pigment Green 8 or (ii) a combination of at least one selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60 with 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; and the pigment in the red ink is (iii) CI Pigment Red 185 or (iv) CI Pigment Violet 29, CI Pigment Violet 32, CI Pigment Red 1 and at least one pigment selected from the group consisting of CI Pigment Violet 22, CI Pigment Violet 19, and a solid solution containing CI Pigment Violet 19, and at least one pigment 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; and the pigment in the blue ink is (v) CI Pigment Violet 37, or (vi) a combination of at least one pigment 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, and at least one pigment selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an ink set that includes a combination of special color inks that use halogen-free pigments as coloring materials, and that is capable of recording images with an excellent color reproduction range. 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, CI Pigment Violet 23, and CI Pigment Red 254. Specifically, various pigments were mixed with dispersants (resins), and then dispersed using a high-shear homomixer to prepare aqueous pigment dispersions. Pigments that met the following criteria (i) and (ii) were then extracted. (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 when the pigment dispersion is stored for a long period of time, there is little change in viscosity or pigment particle size. In addition, because halogen-free pigments can be used, the technology described in this specification can contribute to the realization of a sustainable society, such as a decarbonized / recycling-based society.

[0011] Next, inks were prepared using the extracted pigments, and the color reproduction range of images recorded by combining the prepared inks with cyan ink, magenta ink, and yellow ink was confirmed. As a result, it was found that an ink set combining at least two inks selected from the group consisting of green ink, red ink, and blue ink prepared using the pigments shown below is effective, leading to the present invention.

[0012] The pigment used in the green ink is (i) CI Pigment Green 8, or (ii) a combination of at least one pigment selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60, and at least one pigment 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.

[0013] The pigment used in the red ink is (iii) CI Pigment Red 185, or (iv) a combination of 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, and 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.

[0014] The pigment used in the blue ink is (v) CI Pigment Violet 37, or (vi) a combination of 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, and at least one selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60.

[0015] <Ink set> The ink set of the present invention has a combination of at least two aqueous inks selected from the group consisting of a green ink, a red ink, and a blue ink, each of which contains a pigment, a dispersant for dispersing the pigment, and water. The pigment in the green ink is (i) CI Pigment Green 8 or the combination described below in (ii). The pigment in the red ink is (iii) CI Pigment Red 185 or the combination described below in (iv). The pigment in the blue ink is (v) CI Pigment Violet 37 or the combination described below in (vi). The ink set of the present invention is described in detail below. (ii) A combination of at least one selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60 and 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. (iv) A combination of 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, and 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. (vi) A combination of 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, and at least one selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60.

[0016] (water-based ink) The ink set of the present invention comprises a combination of at least two inks suitable for inkjet printing, selected from the group consisting of a green ink, a red ink, and a blue ink. In other words, the ink set of the present invention is an aqueous ink set suitable for inkjet printing.

[0017] [Pigment] The pigments used in the green ink, red ink, and blue ink are all halogen-free pigments that do not contain halogen atoms in their molecules. For the green ink, CI Pigment Green 8 is used, or a mixture of blue and yellow pigments adjusted to the desired hue is used. The blue pigment is at least one selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60. The yellow 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. To express a green hue by mixing blue and yellow pigments, the mass ratio of the blue pigment (B) to the yellow pigment (Y) is preferably in the range of B:Y = 70:30 to 20:80.

[0018] The red ink uses CI Pigment Red 185, or a mixture of a violet pigment or red pigment and a yellow pigment adjusted to the desired hue. The violet pigment and red pigment are 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. The yellow 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. To express a red hue by mixing a violet pigment or red pigment with a yellow pigment, the mass ratio of the violet pigment (V) and red pigment (R) to the yellow pigment (Y) is preferably in the range of (V+R):Y=70:30 to 20:80.

[0019] For the blue ink, CI Pigment Violet 37 is used, or a mixture of a violet pigment or a red pigment and a blue pigment is used to adjust the desired hue. The violet pigment and the red pigment are 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. The blue pigment is at least one selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60. To express a blue hue by mixing a violet pigment or a red pigment with a blue pigment, the mass ratio of the violet pigment (V) and the red pigment (R) to the blue pigment (B) is preferably in the range of (V+R):B=70:30 to 20:80.

[0020] The average particle size of the pigment (the cumulative 50% particle size (D50) of the volume-based particle size distribution) is preferably 100 nm or more and 200 nm or less, and more preferably 100 nm or more and 120 nm or less. By using a pigment having an average particle size within the above range, the dispersibility of the pigment and the storage stability of the pigment dispersion and ink can be improved. The average particle size of the pigment can be appropriately adjusted by processing using a method such as salt milling.

[0021] [Dispersant] The dispersant is a component for dispersing the pigment in the ink. The type of dispersant is not particularly limited. To prepare 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, acrylic acid esters, and methacrylic acid esters. 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 or ink with excellent storage stability.

[0022] 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.

[0023] 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.

[0024] 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 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 an inkjet ink ejected from a thermal-type recording head.

[0025] 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, an inkjet ink that is less likely to cause ejection defects can be obtained, even when ejected from a thermal type recording head.

[0026] 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 ink is preferably from 20 to 50 parts by mass per 100 parts by mass of the pigment.

[0027] The dispersants in the green ink, red ink, and blue ink are preferably the same. If the dispersants in each ink are the same, the difference in the aggregation properties of the pigments in the inks applied to the recording medium will not be large, making it possible to record images with superior gloss.

[0028] [Aqueous medium] The ink is an aqueous ink containing water as a dispersion medium. The ink can typically contain water or an aqueous medium that is 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. Furthermore, 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.

[0029] 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.

[0030] [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.

[0031] (Ink manufacturing method) The ink can be prepared, for example, by adding a water-soluble organic solvent and water to a pigment dispersion, followed by stirring and filtering. The pigment dispersion can be produced, for example, by mixing the above-mentioned components, including the pigment, and then dispersing the mixture 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. [Example]

[0032] 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.

[0033] <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.).

[0034] (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

[0035] (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: 30 times Second stage dilution ratio: 40x

[0036] <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%.

[0037] (Pigment dispersions 2 to 13) Pigment dispersions 2 to 13 were obtained in the same manner as in the above-described pigment dispersion 1, except that the pigments shown in Table 1 were used in the types and amounts (parts) instead of CI Pigment Green 8.

[0038] (Pigment Dispersion 14) 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 according to a conventional method was neutralized with potassium hydroxide to obtain a resin. Pigment dispersion 14 was then prepared in the same manner as in the above-described pigment dispersion 1, except that the obtained resin was used as a dispersant.

[0039] 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 PB15:3: CI Pigment Blue 15:3 PR185: CI Pigment Red 185 PV29: CI Pigment Violet 29 PV37: CI Pigment Violet 37 PY74: CI Pigment Yellow 74 PG7: CI Pigment Green 7 PV23: CI Pigment Violet 23 PR254: CI Pigment Red 254 PR122: CI Pigment Red 122

[0040] <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 5% or less. B: 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 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%.

[0041] TIFF2026006146000001.tif120170

[0042] <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

[0043] (Ink 2-15) Inks 2 to 15 were obtained in the same manner as Ink 1 above, except that the types and amounts (parts) of pigment dispersions shown in Table 2 were used.

[0044] TIFF2026006146000002.tif128170

[0045] <Evaluation> (color reproduction area) The prepared inks were combined as shown in Table 3 to form ink sets 1 to 4. The inks constituting each ink set were filled into ink cartridges and installed in an inkjet recording device (trade name "PIXUS Pro9500," manufactured by Canon) that ejects ink from a recording head using thermal energy. The cyan ink (C ink) was installed in the cyan position, the magenta ink in the magenta position, and the yellow ink (Y ink) in the yellow position. The green ink (G ink) was installed in the green position, the red ink (R ink) in the red position, and the blue ink (B ink) in the blue position. An image pattern containing a multi-color solid image was then recorded on a recording medium (trade name "Canon Photo Paper Glossy Gold GL-101," manufactured by Canon).

[0046] Using a spectrophotometer (trade name "Spectorolino", manufactured by Gretag Macbeth), the image recorded under the conditions of light source: D50, field of view: 2° was measured, and * and b * were measured respectively. * and b * is a standard defined by the CIE (International Commission on Illumination) * b * a in the display system * and b * For each image, a * is the horizontal axis, b * On the vertical axis, the area of ​​the color gamut formed by the ink set was calculated from the plot of the outermost angle, and the color reproduction range was evaluated according to the evaluation criteria shown below. The results are shown in Table 3. A: The color gamut area was equal to or greater than the color gamut area formed with ink set 1. B: The color gamut area was less than the color gamut area formed with ink set 1.

[0047] TIFF2026006146000003.tif48170

[0048] The disclosure of this embodiment includes the following configuration. (Configuration 1) An ink set having a combination of at least two water-based inks selected from the group consisting of a green ink, a red ink, and a blue ink, each of which contains a pigment, a dispersant for dispersing the pigment, and water, The pigment in the green ink is (i) CI Pigment Green 8, or (ii) a combination of at least one selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60, and 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; The pigment in the red ink is (iii) CI Pigment Red 185, or (iv) a combination of 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, and 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; The pigment in the blue ink is (v) CI Pigment Violet 37, or (vi) An ink set comprising a combination of at least one pigment 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, and at least one pigment selected from the group consisting of CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60. (Configuration 2) The ink set according to Configuration 1, wherein the dispersant in the green ink, the dispersant in the red ink, and the dispersant in the blue ink are all copolymers having a first unit derived from a styrene-based monomer and a second unit derived from at least one selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid ester, and a methacrylic acid ester. (Configuration 3) The ink set 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 ink set according to any one of Configurations 1 to 3, wherein the green ink, the red ink, and the blue ink are all water-based inks for inkjet printing.

Claims

1. An ink set having a combination of at least two water-based inks selected from the group consisting of a green ink, a red ink, and a blue ink, each of which contains a pigment, a dispersant for dispersing the pigment, and water, The pigment in the green ink is (i) C.I. Pigment Green 8, or (ii) A combination of at least one selected from the group consisting of C.I. Pigment Blue 15:3, C.I. Pigment Blue 16, and C.I. Pigment Blue 60, and 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; The pigment in the red ink is (iii) C.I. Pigment Red 185, or (iv) A combination of 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 containing C.I. Pigment Violet 19, and 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; The pigment in the blue ink is (v) C.I. Pigment Violet 37, or (vi) An ink set characterized by a combination of 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 containing C.I. Pigment Violet 19, and at least one selected from the group consisting of C.I. Pigment Blue 15:3, C.I. Pigment Blue 16, and C.I. Pigment Blue 60.

2. 2. The ink set according to claim 1, wherein the dispersant in the green ink, the dispersant in the red ink, and the dispersant in the blue ink are all copolymers having a first unit derived from a styrene-based monomer and a second unit derived from at least one selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid ester, and a methacrylic acid ester.

3. The ink set 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. 4. The ink set according to claim 1, wherein the green ink, the red ink, and the blue ink are all water-based inks for inkjet printing.

Images