Ink set

Abstract

The present invention addresses the problem of providing an ink set which has excellent chromaticity of primary colors and secondary colors, in particular, excellent chromaticity of green, and excellent abrasion resistance of printed images. Specifically, the ink set comprises: a yellow ink containing a binder, a dispersion resin, an aqueous solvent, and C.I. Pigment yellow 74 as a pigment; and a cyan ink containing a binder, a dispersion resin, an aqueous solvent, and C.I. Pigment blue 15: 3 as a pigment, in which the volume average particle diameter of the C.I. Pigment yellow 74 is 80-120 nm and the content of the C.I. Pigment yellow 74 is 4.0-10.0 mass% relative to the total amount of the yellow ink, and the volume average particle diameter of the C.I. Pigment blue 15: 3 is 80-100 nm and the content of the C.I. Pigment blue 15: 3 is more than 2.5 mass% and less than 5.5 mass% relative to the total amount of the cyan ink.

Description

Technical Field

[0001] The present invention relates to an ink set. More specifically, the present invention particularly relates to an ink set suitable as an ink for inkjet that has improved green chroma. Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from very fine nozzles onto a recording member and adhered thereto to obtain characters and images. This method not only has the advantages of low noise and good operability of the apparatus used, but also has the advantages of being easily colorized and being able to use plain paper as the recording member. Therefore, it has been widely used as an output device in offices and homes in recent years.

[0003] On the other hand, in industrial printers, with the improvement of the inkjet recording method technology, it is also expected to be used as an output device for digital printing, and in some cases, the replacement from analog printers is being promoted. In addition, as an ink for the inkjet recording method (inkjet ink), from the viewpoint of environmental aspects and the like, the demand for water-based ink has increased instead of conventional solvent-based ink and UV ink (for example, refer to Patent Document 1).

[0004] In the printing quality (printing quality) of water-based ink, high chroma is generally required. For example, in Patent Document 2, an inkjet recording ink set composed of yellow ink, magenta ink, and cyan ink containing a specific pigment and a specific type of dispersant is disclosed, which improves the chroma of an image and has excellent storage stability of the ink.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-12226

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-41906 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] In order to improve the chroma of primary colors and secondary colors of ink, it is necessary to leave the pigment as a coloring agent near the paper surface. As a means for this, miniaturization of ink droplets is considered. However, if the ink droplets are miniaturized, there is a tendency for the image density to decrease. If the pigment concentration is increased, the decrease in image density can be suppressed. On the other hand, there are problems such as a decrease in the storage stability of the ink or a decrease in chroma caused by aggregation of the pigment component.

[0011] In addition, not only for ordinary paper, but also when extending inkjet-based printing to recording media with poor ink absorbency or non-ink absorbency such as coated paper, in order to prevent the fixing property of the ink and the printed image from peeling off due to the influence of friction, moisture, etc., it is necessary to improve the fastness of the image. Specifically, it is necessary to achieve an improvement in abrasion resistance. From this perspective, it is considered to further contain a binder component in the ink, but there is a problem of a decrease in the color density of the printed matter, and there is still room for improvement in the ink sets disclosed in Patent Document 2 and the like.

[0012] An object of the present invention is to provide an ink set having excellent color densities of primary colors and secondary colors, particularly excellent abrasion resistance of a printed image.

[0013] The inventors of the present invention repeatedly conducted in-depth studies and found that by using a specific pigment in a specific concentration range in each of the cyan and yellow inks, and preferably further containing a specific binder in the ink, the above problems can be solved, and thus the present invention was completed.

[0014] Means for solving the problem

[0015] The present invention has the following aspects.

[0016] [1] An ink set, comprising:

[0017] A yellow ink containing a binder, a dispersion resin, an aqueous solvent, and C.I. Pigment Yellow 74 as a pigment; and

[0018] A cyan ink containing a binder, a dispersion resin, an aqueous solvent, and C.I. Pigment Blue 15:3 as a pigment,

[0019] The volume average particle diameter of the C.I. Pigment Yellow 74 is 80 to 120 nm, and the content relative to the total amount of the yellow ink is 4.0 to 10.0% by mass,

[0020] The volume average particle diameter of the C.I. Pigment Blue 15:3 is 80 to 100 nm, and the content relative to the total amount of the cyan ink exceeds 2.5% by mass and is less than 5.5% by mass.

[0021] [2] The ink set according to [1], wherein the minimum film-forming temperature of the binder is 25°C or higher, and the volume average particle diameter of the binder is equal to or less than the volume average particle diameter of at least one of the C.I. Pigment Yellow 74 and C.I. Pigment Blue 15:3.

[0022] [3] The ink set according to [1] or [2], further comprising a magenta ink containing a binder, a dispersion resin, an aqueous solvent, and a solid solution pigment,

[0023] The solid solution pigment is composed of C.I. Pigment Red 122 and C.I. Pigment Violet 19,

[0024] in the solid solution pigment, the mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 is 4 / 1 to 1 / 1,

[0025] the volume average particle diameter of the solid solution pigment is 90 to 130 nm,

[0026] the ratio of the concentration of the solid solution pigment contained in the magenta ink to the concentration of the pigment contained in the cyan ink is 1.5 or more.

[0027] [4] The ink set according to any one of [1] to [3] further includes a black ink.

[0028] Advantages of the Invention

[0029] According to the present invention, it is possible to provide an ink set with excellent chroma of primary colors and secondary colors, particularly excellent chroma of green, and excellent rubbing resistance of printed images. Detailed Description of the Invention

[0030] The present invention relates to an ink set, which includes: a yellow ink containing a binder, a dispersion resin, an aqueous solvent, and C.I. Pigment Yellow 74 as a pigment; and a cyan ink containing a binder, a dispersion resin, an aqueous solvent, and C.I. Pigment Blue 15:3 as a pigment. Among them, the volume average particle diameter of the C.I. Pigment Yellow 74 is 80 to 120 nm, and its content relative to the total amount of the yellow ink is 4.0 to 10.0% by mass. The volume average particle diameter of the C.I. Pigment Blue 15:3 is 80 to 100 nm, and its content relative to the total amount of the cyan ink exceeds 2.5% by mass and is less than 5.5% by mass.

[0031] The primary colors and secondary colors of the ink set of the present invention have excellent chroma. In particular, it is possible to improve the chroma of green (c ＊ ) without reducing the color rendering properties of the chroma of cyan and red as secondary colors.

[0032] In addition, in the ink set of the present invention, preferably, the minimum film-forming temperature of the binder is 25°C or higher, and the volume average particle diameter of the binder is equal to or less than the volume average particle diameter of at least one of the C.I. Pigment Yellow 74 and C.I. Pigment Blue 15:3, whereby the rubbing resistance of the printed image is excellent.

[0033] Hereinafter, each component of the ink set of the present invention will be described.

[0034] [Yellow Ink]

[0035] In the ink set of the present invention, the pigment contained in the yellow ink is C.I. Pigment Yellow 74. The content of C.I. Pigment Yellow 74 relative to the total amount of the yellow ink is 4.0 to 10.0% by mass, more preferably in the range of 4.5 to 9.0% by mass.

[0036] The volume average particle diameter of C.I. Pigment Yellow 74 is 80 to 120 nm, more preferably in the range of 90 to 110 nm. In addition, the volume average particle diameter of C.I. Pigment Yellow 74 is obtained by the dynamic light scattering method, laser diffraction method, etc., which are general measurements for pigment dispersion particles. For example, in the case of using the dynamic light scattering method, as the pigment particles of the dispersion liquid, Nanotrac Wave II manufactured by Microtrac, a laser scattering type particle size measuring device, can be used, and the dilution ratio is adjusted so that the loading index value is 1, and the volume average particle diameter of C.I. Pigment Yellow 74 is measured according to the set conditions of a measurement time of 180 seconds and a repeated measurement number of 3.

[0037] The binder contained in the yellow ink is used for the purpose of fixing the pigment in the ink on the recording medium. Different from the dispersion resin described later, the binder does not adsorb on the surface of the pigment, etc. in the ink, and is dispersed in the aqueous solvent separately from the pigment and the dispersion resin and exists in the ink.

[0038] The minimum film-forming temperature of the binder is preferably 25°C or higher. Although it also depends on the glass transition temperature of the components constituting the binder, it is generally more preferably in the range of 25°C to 60°C, and further preferably in the range of 30°C to 45°C. By making the minimum film-forming temperature of the binder within the above range, film formation is effectively carried out under general drying conditions, and the abrasion resistance is excellent.

[0039] The volume average particle diameter of the binder is preferably equal to or less than the volume average particle diameter of at least one of the volume average particle diameter of C.I. Pigment Yellow 74, which is the pigment constituting the yellow ink, and the volume average particle diameter of C.I. Pigment Blue 15:3, which is the pigment constituting the cyan ink, and more preferably equal to or less than the volume average particle diameters of both.

[0040] More specifically, the volume average particle diameter of the binder is preferably 100 nm or less, more preferably in the range of 40 to 80 nm. If the volume average particle diameter of the binder is within the above range, aggregation of the pigments in the ink can be suppressed, the dispersion stability can be improved, the ejection stability and storage stability can be improved, and in addition, the abrasion resistance of the printed image can be improved.

[0041] It should be noted that the volume average particle diameter of the binder is obtained by dynamic light scattering method, laser diffraction method, etc., which are general methods for measuring dispersed particles. For example, in the case of using the dynamic light scattering method, Nanotrac WaveII manufactured by Microtrac can be used as a laser scattering type particle size measuring device. The dilution ratio is adjusted so that the load index value is 1, and the volume average particle diameter of the binder is measured under the set conditions of a measurement time of 180 seconds and a repeated measurement number of 3.

[0042] Examples of the binder include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinylpyrrolidone, acrylic resin, urethane resin, olefin resin, modified polyolefin resin (acid-modified polypropylene, etc.), dextran, dextrin, carrageenan (κ, ι, λ, etc.), agar, pullulan, water-soluble polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose, etc. These can be used alone or in combination of two or more.

[0043] As the binder, for example, a vinyl polymer (A1) having a glass transition temperature (Tg) of 50 to 100 °C and having a structural unit derived from an aromatic vinyl monomer, or a vinyl polymer (A) which is a vinyl halide polymer (A2) having a Tg of 50 to 100 °C can be used.

[0044] Examples of the vinyl polymer (A1) include copolymers having a structural unit derived from an aromatic vinyl monomer and a structural unit derived from a (meth)acrylic monomer. Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, etc., and styrene is preferred. Examples of the (meth)acrylic monomer include (meth)acrylic acid; (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester, (meth)acrylic acid butyl ester, (meth)acrylic acid pentyl ester, (meth)acrylic acid neopentyl ester, (meth)acrylic acid hexyl ester, (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid octyl ester, etc. (meth)acrylic esters. As the vinyl polymer (A1), styrene-acrylic resin is preferred.

[0045] Relative to the total amount of the vinyl polymer (A1), the content of the structural unit derived from the aromatic vinyl monomer is preferably in the range of 50 to 99% by mass, more preferably 80 to 99% by mass. In addition, relative to the total amount of the vinyl polymer (A1), the content of the structural unit derived from the (meth)acrylic monomer is preferably in the range of 1 to 50% by mass, more preferably 1 to 20% by mass.

[0046] As the halogenated vinyl polymer (A2), for example, (co)polymers of vinyl chloride, chlorinated polyolefins, and chlorinated rubbers can be mentioned. A vinyl chloride-acrylic polymer having a structural unit derived from a vinyl chloride monomer and a structural unit derived from a (meth)acrylic monomer is preferred. The (meth)acrylic monomer is as described above.

[0047] Relative to the total amount of the halogenated vinyl polymer (A2), the content of the structural unit derived from the vinyl chloride monomer is preferably in the range of 30 to 90% by mass, more preferably in the range of 50 to 80% by mass. In addition, relative to the total amount of the halogenated vinyl polymer (A2), the content of the structural unit derived from the (meth)acrylic monomer is preferably in the range of 10 to 70% by mass, more preferably in the range of 20 to 50% by mass.

[0048] The vinyl polymer (A) can be produced by emulsion polymerization, solution polymerization, suspension polymerization, bulk polymerization, etc. A vinyl polymer (A) having a core-shell structure is more preferred. For example, a vinyl polymer having a core-shell structure can be mentioned, in which a structural unit derived from an aromatic vinyl monomer or a structural unit derived from a vinyl chloride monomer is locally present in the core part, and a structural unit derived from a (meth)acrylic monomer is locally present in the shell part. The vinyl polymer (A) having a core-shell structure can be produced, for example, by polymerizing a monomer component containing a (meth)acrylic monomer to produce a polymer (x) constituting the shell, and then supplying an aromatic vinyl monomer or the like to a reaction vessel and polymerizing it inside the particles of the polymer (x) to form a core part.

[0049] As the vinyl polymer (A), commercially available products can be used. For example, "JONCRYL PDX-7700", "JONCRYL PDX-7780", "JONCRYL 89-E", "JONCRYL 89J" (all are trade names (JONCRYL is a registered trademark), manufactured by BASF Japan Co., Ltd.); "Hiros X BE7503" (manufactured by Seiko PMC Co., Ltd.), "VINYBLAN 745", "VINYBLAN747" (manufactured by Nissin Chemical Industry Co., Ltd.), etc.

[0050] As the binder, from the viewpoint of being able to improve the ejection stability of the ink and being able to improve the printing density and image fastness of the obtained printed matter at low cost, a styrene-acrylic resin is more preferred.

[0051] The weight average molecular weight (Mw) of the binder is preferably from 100,000 to 1,000,000, more preferably from 300,000 to 750,000. It should be noted that the Mw of the binder is a value measured by converting with standard polystyrene using a gel permeation chromatograph (GPC), and is obtained by the GPC-MALS method in which a multi-angle light scattering detector is connected to the GPC according to the measurement conditions described below.

[0052] GPC main body: LC1100 series manufactured by Agilent Technologies

[0053] Column: SHODEX SB806MHQ manufactured by Showa Denko KK

[0054] Eluent: N / 3 phosphate buffer solution (pH 3) containing N / 10 sodium nitrate

[0055] Flow rate: 1.0 ml / minute

[0056] Detector 1: DAWN, a multi-angle light scattering detector manufactured by Wyatt Technology

[0057] Detector 2: RI-101, a differential refractive index detector manufactured by Showa Denko KK

[0058] The acid value of the binder is preferably 50 mgKOH / g or less, more preferably in the range of 10 to 50 mgKOH / g, and further preferably in the range of 10 to 30 mgKOH / g.

[0059] The content of the binder is preferably in the range of 0.4 to 3.0% by mass, more preferably in the range of 0.4 to 1.5% by mass, relative to the total amount of the yellow ink. If the content of the binder is within the above range, the ejection stability and storage stability of the ink are improved. In addition, the image fastness of the printed matter can be further improved, and there is a tendency that the ink does not peel off and the abrasion resistance is excellent when water is dropped on the printed matter or when rubbed with a water-containing cloth or the like.

[0060] The dispersion resin contained in the yellow ink has the following functions: as a stable dispersion mechanism for the pigment, the dispersion resin is adsorbed on the surface of the pigment, and the pigment is stably dispersed in water and solvent components other than water by steric hindrance or electrostatic repulsion. The dispersion resin is different from the aforementioned binder and exists in a state of being adsorbed on the surface of the pigment or covering a part or all of the surface of the pigment. The dispersion resin corresponds to the solid component of the yellow ink.

[0061] Examples of the dispersion resin include polyvinyl alcohol-based resins, polyvinylpyrrolidone-based resins, acrylic resins such as acrylic acid-acrylate copolymers, styrene-acrylic copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylate copolymers, styrene-α-methylstyrene-acrylic copolymers, styrene-α-methylstyrene-acrylic acid-acrylate copolymers, etc., styrene-maleic acid copolymers, styrene-maleic anhydride copolymers, water-based resins of vinylnaphthalene-acrylic acid copolymers, and salts of the above water-based resins.

[0062] As the dispersion resin, commercially available products can be used, such as the "Ajisper (registered trademark)" PB series manufactured by Ajinomoto Fine-Techno Co., Inc., the "DISPER (registered trademark) BYK" series manufactured by BYK-Chemie GmbH, the "EFKA (registered trademark)" series manufactured by BASF SE, the "SOLSPERSE (registered trademark)" series manufactured by Lubrizol Japan Ltd., the "TEGO (registered trademark) Dispers" series manufactured by Evonik Industries AG, etc. In addition, as the dispersion resin, a compound exemplified as the polymer (G) in WO2018 / 190139 can also be used. These dispersion resins can be subjected to a crosslinking treatment using a crosslinking agent after pigment dispersion.

[0063] Among the above, as the dispersion resin, styrene-acrylic resins are preferred, and styrene-acrylic random copolymer resins are more preferred.

[0064] The weight average molecular weight (Mw) of the dispersion resin is preferably in the range of 5,000 to 50,000, more preferably in the range of 10,000 to 30,000. It should be noted that the Mw of the dispersion resin is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene conversion, and is obtained by the same measurement method as the measurement of the weight average molecular weight of the above binder.

[0065] The acid value of the dispersion resin is preferably 50 mgKOH / g or more, preferably in the range of 80 to 200 mgKOH / g, and more preferably in the range of 90 to 150 mgKOH / g.

[0066] The content of the dispersion resin is preferably in the range of 0.5 to 2.5% by mass, more preferably in the range of 0.8 to 2.0% by mass, relative to the total amount of the yellow ink.

[0067] The water-based solvent constituting the yellow ink preferably contains a polar term (δ P ) of Hansen solubility parameter (HSP) of 9 or less, and a hydrogen bond term (δ H) is one or more of aqueous solvents with a value of 18 or less. When containing such an aqueous solvent, its content is preferably in the range of 0.1% by mass or more and less than 4.0% by mass, more preferably in the range of 0.3 to 3.5% by mass, and still more preferably in the range of 0.3 to 1.5% by mass, relative to the total amount of the yellow ink. It is considered that if these aqueous solvents are contained, aggregation of the pigment can be suppressed, the wettability of the pigment surface can be improved, and the dispersion stability is excellent.

[0068] Here, the Hansen solubility parameter divides the solubility parameter (SP value: δ) introduced by Hildebrand into a dispersion term δ D , a polar term δ P and a hydrogen bond term δ H These three components are parameters that represent the polarity of substances in three-dimensional space, and the relationship of the following formula holds.

[0069] δ[(cal / cm 3 ) 0.5 = (δ D 2 + δ P 2 + δ H 2 ) 0.5

[0070] The above-mentioned dispersion term δ D , polar term δ P and hydrogen bond term δ H have been determined by Hansen and subsequent researchers for many, for example, they are published in VII-698 to 711 of Polymer Handbook (Fourth Edition). In addition, the Hansen solubility parameters related to many solvents and resins have been investigated. For example, the solubility parameters of these are described in Industrial Solvents Handbook (written by Wesley L. Archer). In addition, the software of Hansen Solubility Parameters in Practice (HSPiP) can also be used to calculate them.

[0071] The polar term of the HSP of the above-mentioned aqueous solvent is preferably 3 or more and 9 or less, and more preferably 4 or more and 7 or less. In addition, the hydrogen bond term of the HSP of the above-mentioned aqueous solvent is preferably 3 or more and 18 or less, and still more preferably 4 or more and 17.5 or less. When both the polar term and the hydrogen bond term of the HSP satisfy the above ranges, it is considered that the wettability of the pigment surface in the yellow ink is further improved and the dispersion stability is excellent.

[0072] From the viewpoints of ejection stability of the ink and prevention of drying of the ink for inkjetting in the ejection nozzles of the inkjet head, the boiling point of the above aqueous solvent at atmospheric pressure is preferably 150°C or higher, more preferably in the range of 150°C to 350°C.

[0073] Examples of such aqueous solvents include 3-methoxy-3-methyl-1-butanol (δ P = 6.3, δ H = 12.9, boiling point 174°C), 3-methoxy-1-butanol (δ P = 5.4, δ H = 13.6, boiling point 158°C), 1,2-hexanediol (δ P = 6.6, δ H = 17.1, boiling point 223°C), etc.

[0074] As the water contained in the yellow ink, pure water or ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, etc., which have removed impurities such as ionic impurities as much as possible, is preferred. The water can be sterilized by ultraviolet irradiation or addition of hydrogen peroxide, etc.

[0075] From the viewpoints of the property (drying property) of being able to dry rapidly on the surface of the recording medium after printing and ejection stability, the content of water is preferably in the range of 30 to 90% by mass, more preferably in the range of 40 to 80% by mass, relative to the total amount of the yellow ink.

[0076] The yellow ink may also contain other aqueous solvents other than the above aqueous solvent. The other aqueous solvents can have functions such as adjusting the viscosity of the ink, further improving the ejection stability during printing by the inkjet printing method, preventing drying of the ink for inkjetting in the ejection nozzles of the inkjet head, adjusting the above drying property, etc.

[0077] Examples of other aqueous solvents include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol with a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, isopropyl glycol, isobutylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,2-hexanediol, 1,6-hexanediol, meso-erythritol, pentaerythritol, glycerol, etc. Among them, solvents with a boiling point in the range of 180 to 300°C are preferred, and propylene glycol or glycerol is more preferred. In addition, when using propylene glycol and glycerol together as other aqueous solvents, aggregation and precipitation of pigments in the ink are less likely to occur, the dispersion stability can be maintained, and the viscosity can be adjusted to a desired value. From the viewpoints of improving the ejection stability during printing by the inkjet printing method and facilitating improvement of the drying property of the ink after printing, it is preferred.

[0078] The content of other aqueous solvents is preferably in the range of 0.1 to 35% by mass, more preferably in the range of 15 to 35% by mass, relative to the total amount of the yellow ink.

[0079] 〔Cyan Ink〕

[0080] The pigment contained in the cyan ink is C.I. Pigment Blue 15:3. The content of C.I. Pigment Blue 15:3 relative to the total amount of the cyan ink is greater than 2.5% by mass and less than 5.5% by mass, more preferably in the range of 2.7 to 5.3% by mass, and further preferably in the range of 3.0 to 4.0% by mass.

[0081] The volume average particle diameter of C.I. Pigment Blue 15:3 is 80 to 100 nm, more preferably in the range of 85 to 95 nm. It should be noted that the volume average particle diameter of C.I. Pigment Blue 15:3 is obtained by the dynamic light scattering method, laser diffraction method, etc., which are general measurements for pigment dispersed particles. An example of the measurement method is the same as that for the volume average particle diameter of C.I. Pigment Yellow 74 described above.

[0082] The binder contained in the cyan ink is the same as the binder contained in the yellow ink, and the details are as described above. The content of the binder in the cyan ink is preferably in the range of 0.4 to 3.0% by mass, more preferably in the range of 0.4 to 1.5% by mass, relative to the total amount of the cyan ink. If the content of the binder is within the above range, the ejection stability and storage stability of the ink are improved. In addition, the image fastness of the printed matter can be further improved. When water is dropped on the printed matter or when it is rubbed with a water-containing cloth, etc., there is also a tendency that the ink does not peel off and the abrasion resistance is excellent.

[0083] The dispersion resin contained in the cyan ink is the same as the dispersion resin contained in the yellow ink, and the details are as described above. The content of the dispersion resin in the cyan ink is preferably in the range of 0.3 to 2.5% by mass, more preferably in the range of 0.5 to 2.0% by mass, relative to the total amount of the cyan ink.

[0084] The aqueous solvent contained in the cyan ink is the same as the aqueous solvent contained in the yellow ink, and the details are as described above. In addition, the preferred content of the aqueous solvent and water is also the same as that of the yellow ink.

[0085] In the ink set of the present invention, if the content of the pigment (C.I. Pigment Yellow 74) in the yellow ink and the content of the pigment (C.I. Pigment Blue 15:3) in the cyan ink simultaneously satisfy the above ranges, while ensuring the dispersion stability, ejection stability, storage stability, and sufficient printing density of the pigment, the chroma of the primary colors and secondary colors of the obtained printed matter is excellent. In particular, it is possible to improve the chroma of green (c in particular without reducing the chroma of cyan and red as secondary colors.＊ )。

[0086] [Magenta ink]

[0087] The ink set of the present invention may further include magenta ink. The pigment contained in the magenta ink is a solid solution pigment composed of C.I. Pigment Red 122 and C.I. Pigment Violet 19. These pigments can be commercially available products respectively.

[0088] The mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 in the solid solution pigment (C.I. Pigment Red 122 / C.I. Pigment Violet 19) is 4 / 1 to 1 / 1, more preferably in the range of 3.5 / 1 to 2.5 / 1. If the mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 is within the above range, the chroma of red is excellent.

[0089] The manufacturing method of the solid solution pigment is not particularly limited, and known methods disclosed in, for example, Japanese Patent Laid-Open No. 11-49998, Japanese Patent Laid-Open No. 2000-319534, Japanese Patent Laid-Open No. 2003-253150, etc. can be applied. It should be noted that in this specification, the solid solution pigment refers to a pigment existing as a mixed crystal (a state of crystallization in a mixed state) of multiple pigment molecules, which is different from a simple mixture of two or more pigments. Whether a solid solution pigment is formed can be confirmed by X-ray diffraction analysis. In the case of a mixture of two pigments, its X-ray diffraction pattern can obtain a pattern that is an overlap of the X-ray diffraction patterns of the respective pigments, and its peak intensity is proportional to the mixing ratio. On the other hand, in the case of forming a solid solution pigment, a diffraction pattern peculiar to the formed crystal is shown.

[0090] The content of the solid solution pigment relative to the total amount of the magenta ink is 4.0 to 10.0% by mass, more preferably in the range of 5.0 to 9.0% by mass.

[0091] The volume average particle diameter of the solid solution pigment is 80 to 150 nm, more preferably in the range of 90 to 130 nm. It should be noted that the volume average particle diameter of the solid solution pigment is obtained by dynamic light scattering method, laser diffraction method, etc., which are general measurements of pigment dispersion particles. An example of the measurement method is the same as the measurement method of the volume average particle diameter of C.I. Pigment Yellow 74 described above.

[0092] The binder contained in the magenta ink is the same as the binders contained in the yellow ink and the cyan ink, and the details are as described above. The content of the binder in the magenta ink is preferably in the range of 0.4 to 3.0% by mass, more preferably in the range of 0.4 to 1.5% by mass, relative to the total amount of the magenta ink. If the content of the binder is within the above range, the ejection stability and storage stability of the ink are improved. In addition, the image fastness of the printed matter can be further improved, and there is also a tendency that the ink does not peel off and has excellent abrasion resistance when water is dropped on the printed matter or when it is rubbed with a water-containing cloth or the like.

[0093] The dispersion resin contained in the magenta ink is the same as the dispersion resins contained in the yellow ink and the cyan ink, and the details are as described above. The content of the dispersion resin in the magenta ink is preferably in the range of 0.3 to 2.5% by mass, more preferably in the range of 0.5 to 2.0% by mass, relative to the total amount of the magenta ink.

[0094] The aqueous solvent contained in the magenta ink is the same as the aqueous solvents contained in the yellow ink and the cyan ink, and the details are as described above. In addition, the preferred contents of the aqueous solvent and water are also the same as those of the yellow ink and the cyan ink.

[0095] When the ink set of the present invention further includes a magenta ink, the ratio of the concentration of the solid solution pigment contained in the magenta ink to the concentration of the pigment contained in the cyan ink (magenta / cyan concentration ratio) is preferably 1.5 or more, more preferably in the range of 1.5 to 3.0. If the magenta / cyan concentration ratio is within the above range, there is a tendency that the chromaticity balance of the secondary color is excellent.

[0096] [Black ink]

[0097] The ink set of the present invention may further include a black ink. The colorant of the black ink is not particularly limited. As the inorganic pigment, for example, iron oxide, carbon black produced by methods such as the contact method, the furnace method, or the thermal method can be used.

[0098] In addition, examples of the black pigment include C.I. Pigment Black 1, 6, 7, 8, 10, 26, 27, 28, etc. Specific examples of commercially available products include No.2300, No.2200B, No.900, No.960, No.980, No.33, No.40, No.45, No.45L, No.52, MCF88, MA7, MA8, MA10, etc. manufactured by Mitsubishi Chemical Corporation; Raven5750, Raven5250, Raven5000, Raven3500, Raven1255, Raven700, etc. manufactured by Columbia; Regal400R, Regal330R, Regal660R, Mogul L, Mogul700, Monarch800, Monarch880, Monarch900, Monarch1000, Monarch1100, Monarch1300, Monarch1400, etc. manufactured by Cabot; Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex35, Printex U, Printex V, Printex 1400U, SpecialBlack6, SpecialBlack5, Special Black4, SpecialBlack 4A, etc. manufactured by Degussa; NIPEX150, NIPEX160, NIPEX170, NIPEX180, etc. manufactured by Orion Engineered Carbons.

[0099] The details and the preferred content ranges of the binder, dispersion resin, and aqueous solvent contained in the black ink are the same as those of the magenta ink described above.

[0100] In addition, as the black pigment, a self-dispersing pigment in which a dispersibility-imparting group (hydrophilic functional group and / or its salt) or an active species of a dispersibility-imparting group is directly or indirectly bonded (grafted) via an alkyl group, an alkyl ether group, an aryl group, etc. on the surface of the pigment can also be used. As commercially available self-dispersing pigments manufactured industrially, for example, Microjet CW-1, BONJET BLACK CW-1, BONJET BLACK CW-1S, BONJET BLACK CW-2, BONJET BLACK CW-3 (the above are trade names; manufactured by Orient Chemical Industries, Ltd.), CAB-O-JET200, CAB-O-JET300 (the above are trade names; manufactured by Cabot Corporation), SENSIJET Black SDP100, SENSIJET Black SDP1000, SENSIJET Black SDP2000 (the above are trade names; manufactured by Sensient Technologies Corporation), etc. can be cited. It should be noted that in the case of using a self-dispersing pigment, the above-mentioned dispersion resin is not required.

[0101] Each ink constituting the ink set of the present invention may further contain a surfactant. If a surfactant is contained, after the ink ejected from the ejection port of the inkjet head lands on the object to be printed, it is likely to wet and spread well on the surface, and it is easy to prevent the occurrence of printing defects. In addition, the surface tension of the ink is reduced, and the leveling property is easily improved.

[0102] Examples of the surfactant include an anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant, etc., and an anionic surfactant or a nonionic surfactant is preferred.

[0103] Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate or sulfonate of higher fatty acid ester, sulfate or sulfonate of higher alcohol ether, higher alkyl sulfosuccinate, polyoxyethylene alkyl ether carboxylate, sulfate, phosphate or alkyl phosphate of polyoxyethylene alkyl ether, etc.

[0104] Examples of the nonionic surfactant include ethylene glycol-based surfactants, silicone-based surfactants, fluorine-based surfactants, and acetylenic diol-based surfactants.

[0105] Examples of the ethylene glycol-based surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene glycerol fatty acid esters, polyglycerol fatty acid esters, polyoxyethylene alkyl amines, polyoxyethylene fatty acid amides, polyoxyethylene / polyoxypropylene block copolymers, and the like.

[0106] Examples of the silicone-based surfactants include polysiloxane-based compounds, polyether-modified silicone oxides, and the like. Examples of commercially available products of the silicone-based surfactants include the "BYK (registered trademark)" series manufactured by BYK-Chemie Japan Co., Ltd., the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd., and the like.

[0107] Examples of the fluorine-based surfactants include perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers, perfluoroalkyl phosphates, perfluoroalkyl betaines, perfluoroalkyl amine oxides, and the like. Examples of commercially available products of the fluorine-based surfactants include the "MEGAFAC (registered trademark)" series manufactured by DIC Corporation, the "FTERGENT (registered trademark)" series manufactured by NEOS Corporation, the "Novec (registered trademark)" series manufactured by Sumitomo 3M Limited, and the like.

[0108] The acetylenic diol-based surfactants are surfactants having a carbon-carbon triple bond in the molecule, and examples thereof include acetylenic diol (having an acetylene bond and two hydroxyl groups in the same molecule) surfactants, and surfactants obtained by adding alkylene oxides such as ethylene oxide and propylene oxide to acetylenic diols. For example, 2,4,7,9-tetramethyl-5-decyn-4,7-diol and alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4-dimethyl-5-decyn-4-ol and alkylene oxide adducts of 2,4-dimethyl-5-decyn-4-ol, and the like. Examples of commercially available products of the acetylenic diol-based surfactants include the "Surfynol (registered trademark)" series manufactured by Evonik Corporation, the "Olfine (registered trademark)" series manufactured by Nikko Chemicals Co., Ltd.; the "Acetylenol (registered trademark)" series manufactured by Kawaken Fine Chemicals Co., Ltd.

[0109] Among the above, from the viewpoint of easily preventing the occurrence of printing defects, acetylenic diol-based surfactants are more preferred.

[0110] In addition, the HLB value of the surfactant is preferably 15 or less, more preferably 10 or less. The HLB value of the surfactant is preferably 2.5 or more, more preferably 3.5 or more. If the HLB value of the surfactant is within the above range, the wettability of the pigment surface is improved, the dispersion stability is improved, and the ejection stability and storage stability of the ink are further improved. The HLB value of the surfactant is further preferably in the range of 3.5 to 9.

[0111] Here, the "HLB (Hydrophilic-Lipophilic Balance) value" of the surfactant is a value defined by the following calculation formula (Griffin formula) by the Griffin method.

[0112] HLB value = 20 × [sum of chemical formula weights of hydrophilic moieties] / molecular weight

[0113] When each ink constituting the ink set of the present invention further contains a surfactant, its content is preferably in the range of 0.01 to 5% by mass, more preferably in the range of 0.1 to 2% by mass, relative to the total amount of each ink.

[0114] One type of surfactant can be used, or two or more types can be used.

[0115] Each ink constituting the ink set of the present invention may further contain other additives such as a pH adjuster, a preservative, a polyolefin wax, an antioxidant, a viscosity modifier, a wetting agent (drying inhibitor), a penetrant, a chelating agent, a plasticizer, an ultraviolet absorber, etc., according to need, in addition to the above components.

[0116] Examples of the pH adjuster include potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, diethanolamine, triethanolamine, triisopropanolamine, potassium carbonate, sodium carbonate, sodium bicarbonate, etc.

[0117] Examples of the preservative include sodium benzoate, sodium pentachlorophenolate, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-benzisothiazolin-3-one, etc. As the preservative, commercially available products can be used, such as "ACTICIDE (registered trademark) B20" (trade name, manufactured by THOR Japan Co., Ltd.), "Proxel (registered trademark) GXL" (trade name, manufactured by SC Johnson & Son, Inc.), etc.

[0118] Examples of the polyolefin wax include waxes or copolymers made from olefins such as ethylene, propylene, and butene or their derivatives, such as polyethylene-based waxes, polypropylene-based waxes, polybutene-based waxes, and their modified waxes. Among them, from the viewpoint of being able to improve the image fastness of the printed matter, oxidized polyethylene wax obtained by oxidatively modifying polyethylene wax is preferred. As the polyolefin wax, commercially available products can be used, such as the "AQUACER (registered trademark)" series (manufactured by BYK-Chemie Japan Co., Ltd.), etc.

[0119] Examples of the antioxidant include phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur antioxidants, etc.

[0120] When each of the inks constituting the ink set of the present invention further contains other additives, the amount thereof is preferably in the range of 0.01 to 5% by mass, more preferably in the range of 0.02 to 3% by mass, relative to the total amount of each ink.

[0121] The method for preparing each ink constituting the ink set of the present invention is not particularly limited and can be prepared by mixing the above components. The above components can be mixed together or sequentially. For example, the binder can be mixed after being dissolved or dispersed in water or other solvents. In addition, the pigment can also be mixed after being dispersed in water or other solvents together with the dispersion resin. When mixing, dispersers such as a bead mill, an ultrasonic homogenizer, a high-pressure homogenizer, a paint stirrer, a ball mill, a roll mill, a sand mill, a sand grinder, a Dyno mill, a Dispermat, an SC mill, and a Nanomizer can be used.

[0122] Regarding the viscosity of each ink constituting the ink set of the present invention at 25°C, from the viewpoints of excellent storage stability and ejection stability, and reducing the deviation of the landing position on the recording medium due to flight bending and easily suppressing the generation of stripes in the printed matter when used in an inkjet recording method, it is preferably in the range of 2.0 to 12.0 mPa·s, more preferably in the range of 2.5 to 5.0 mPa·s, and further preferably in the range of 3.0 to 4.0 mPa·s.

[0123] It should be noted that the viscosity of the ink is, for example, a value measured using a cone-plate type (cone-plate type) rotational viscometer equivalent to an E-type viscometer under the following conditions.

[0124] Measuring device: TVE-25 type viscometer (manufactured by Toki Sangyo Co., Ltd., TVE-25L)

[0125] Calibration standard liquid: JS20

[0126] Measuring temperature: 25°C

[0127] Rotation speed: 10 to 100 rpm

[0128] Injection volume: 1200 μL

[0129] The surface tension of each ink constituting the ink set of the present invention at 25°C is preferably 20 mN / m or more, more preferably 25 mN / m or more. This surface tension is preferably 40 mN / m or less, more preferably 35 mN / m or less. If the surface tension is within this range, when used in an inkjet recording method, there is a tendency that the wettability of the ejected droplets on the surface of the recording medium becomes good and there is sufficient wetting spread after landing.

[0130] From the viewpoints of improving the storage stability and ejection stability of the ink, improving the wetting spread, printing density, and image fastness during printing on a recording medium, and suppressing the deterioration of the ink coating or components constituting the ejection device (ink ejection port, ink flow path, etc.), the pH of each ink constituting the ink set of the present invention is preferably 7.0 to 11.0 at 25°C, more preferably 7.5 to 10.5.

[0131] The ink set of the present invention can be applied to various inkjet recording methods such as thermal jet, piezoelectric, continuous inkjet, roll coating, spray coating, etc., and recording devices using these recording methods.

[0132] As the recording medium to which the droplets of the ink set of the present invention adhere, in addition to plain paper, it is also possible to use cast gloss paper obtained by applying a coating to the surface of plain paper and forming an ink receiving layer with excellent surface gloss by the casting method; polymer coated gloss paper having an inkjet recording layer mainly composed of a resin, etc.

[0133] The above describes the ink set of the present invention, but the present invention is not limited to the configuration of the above-described embodiments. For example, the ink set of the present invention can add any other configuration to the configuration of the above-described embodiments, or can be replaced with any configuration that exhibits the same function.

[0134] Examples

[0135] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the following examples. The pigments, compounds, etc. used in the following examples, etc. are shown below.

[0136] <Pigments>

[0137] Yellow: C.I. Pigment Yellow 74 (“Hansa Yellow 5GX01” (trade name, manufactured by CLARIANT Corporation, volume average particle diameter: 90 nm)

[0138] Cyan: C.I. Pigment Blue 15:3 (“FASTOGEN BLUE SBG-SD” (trade name, manufactured by DIC Corporation, volume average particle diameter: 90 nm)

[0139] Magenta: Solid solution pigment with a mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 of 3 / 1 (manufactured by DIC Corporation, volume average particle diameter: 110 nm)

[0140] <Aqueous Solvents>

[0141] PG: Propylene glycol (δ P = 10.4, δ H = 21.3, boiling point 188°C)

[0142] Gly: Glycerol (δ P = 11.3, δ H = 27.2, boiling point 290 °C)

[0143] <Binder>

[0144] Binder 1: Styrene - acrylic resin (MFT: 36 °C, volume average particle size 60 nm, Mw 500000, acid value 20 mg KOH / g, manufactured by DIC Corporation)

[0145] <Surfactant>

[0146] SF420: "Surfynol 420" (trade name, manufactured by Evonik Corporation, HLB value = 4)

[0147] <Preservative>

[0148] B20: "ACTICIDE B20" (trade name, manufactured by Thor Japan)

[0149] <Dispersion resin>

[0150] Styrene - acrylic random copolymer resin (Mw 18000, acid value 110 mg KOH / g)

[0151] <Preparation of pigment dispersion>

[0152] <Pigment dispersion Y (yellow)>

[0153] Charge 150 g of yellow pigment, 60 g of dispersion resin, 75 g of PG, and 19.4 g of 34 mass% aqueous potassium hydroxide solution into a 1.0 L high - speed mixer (manufactured by EIRICH Corporation, Japan), and knead for 25 minutes at a rotor circumferential speed of 2.94 m / s and a disk circumferential speed of 1 m / s. Then, while continuing to stir, slowly add 306 g of ion - exchanged water to the kneaded material in the high - speed mixer, and further add 12 g of PG and 127.5 g of ion - exchanged water to make the pigment concentration reach 20 mass% and mix, thereby obtaining an aqueous pigment dispersion with a pigment concentration of 20 mass% (pigment dispersion Y).

[0154] <Pigment dispersion C (cyan)>

[0155] Prepare pigment dispersion C (pigment concentration: 20 mass%) in the same manner as pigment dispersion Y, except that cyan pigment is used instead of yellow pigment.

[0156] <Pigment dispersion M (magenta)>

[0157] A pigment dispersion M (pigment concentration: 20% by mass) was prepared in the same manner as pigment dispersion Y, except that magenta pigment was used instead of yellow pigment.

[0158] 1. Preparation of Ink Sets

[0159] Examples 1 to 3 and Comparative Examples 1 to 3

[0160] The pigment dispersion Y, pigment dispersion C, pigment dispersion M, binder, aqueous solvent, surfactant, preservative, and distilled water were mixed and stirred at the composition ratios shown in Table 1 to prepare yellow ink, cyan ink, and magenta ink, respectively, to obtain ink sets.

[0161] It should be noted that the contents in Table 1 are based on the total amount of each ink.

[0162] 2. Evaluation of Ink Sets

[0163] 2-1. Evaluation of Chroma

[0164] The cyan ink, magenta ink, and yellow ink of the ink sets of each example and comparative example were respectively filled into the color ink cartridges of an inkjet printer (PX-S740) manufactured by EPSON, and full-color images of each primary color of cyan, magenta, and yellow and full-color images of secondary colors of red, green, and blue composed of combinations of these three primary colors were printed on ordinary inkjet paper (trade name "NEXT-IJ<70>", manufactured by Nippon Paper Industries Co., Ltd., basis weight 81.4 g / m 2 )

[0165] The full-color images of each color were colorimetrically measured with a spectrophotometer (trade name "eXact", manufactured by X-rite) under the following measurement conditions, and the chroma of each color image was calculated by the following formula based on the a value and b value of each color image.

[0166] Chroma = √(a 2 + b 2 )

[0167] As the measurement conditions, the following conditions were used.

[0168] Observation illumination / Observer viewing angle: D65 / 2°

[0169] Concentration state: ISO state T

[0170] ΔE: CIE ΔE*(1976)

[0171] In addition, the evaluation criteria for the c* (chroma) of red, green, and blue are as follows.

[0172] <Red>

[0173] ×: <50 △: 50 to less than 55 ○: 55 to 60 ◎: > 60

[0174] <Green>

[0175] ×: <40 △: 40 to less than 45 ○: 45 to 50 ◎: > 50

[0176] <Blue>

[0177] ×: <35 △: 35 to less than 39 ○: 39 to 43 ◎: > 43

[0178] 2-2. Rub resistance (coated paper)

[0179] The ink sets of each example and comparative example were respectively filled into an inkjet printer (PX-S740) manufactured by EPSON, and full-color printing was performed on coated paper (trade name “SWORDiJET (registered trademark) 4.3 Gloss”, manufactured by Mitsubishi Paper Mills, basis weight 104.7 g / m 2 ) to obtain an ink coating film. The obtained coating film was dried at room temperature (25 °C) for 12 hours. Then, using a Gakushin type friction tester RT-300 (manufactured by Dainichi Kagaku Seiki Co., Ltd.), the same paper as the printing substrate was used as the friction member, and the dried coating film was rubbed 50 times with a load of 100 g / cm 2 The peeling condition of the coating film was visually observed, and the rub resistance (image fastness) was evaluated according to the following criteria.

[0180] <Evaluation criteria>

[0181] ○: No damage was observed on the printed matter, or even if damage was observed, it was only a small amount. ×: A large amount of damage was observed on the printed matter, and partial thick coloring was observed on the paper of the friction member

[0182] The above results are summarized in Table 1.

[0183] [Table 1]

[0184]

[0185] As shown in the above examples, in the ink sets that meet the requirements of the present invention, the chroma of red, green, and blue as secondary colors is excellently balanced, and in particular, the chroma of green can be improved.

[0186] On the other hand, in Comparative Examples 1 and 2 where the content of yellow ink and the pigment content of cyan ink do not meet the requirements of the present invention, the chroma of green is poor. In Comparative Example 1 where the pigment content of cyan ink is lower than the requirement of the present invention, the chroma of blue also decreases. On the other hand, in Comparative Example 2 where it is higher than the requirement of the present invention, the chroma of red decreases. In Comparative Example 3 that does not contain a binder and meets the requirements of the present invention, the rub resistance of the printed matter decreases.

[0187] In addition, in the ink set that satisfies the provisions of the present invention, by suppressing the aggregation of pigments in the ink with each other and improving the dispersion stability, it is possible to achieve a balance between the ink density (OD) and the improvement of chroma of the printed matter.

[0188] Industrial applicability

[0189] The ink set of the present invention improves the chroma of primary colors and secondary colors, especially the chroma of green, and the abrasion resistance of the printed image is excellent. Therefore, it is particularly useful as an ink for inkjet printers for industrial use.

Claims

1. An ink set comprising: A yellow ink containing a binder, a dispersion resin, an aqueous solvent, and CI Pigment Yellow 74 as a pigment; and A cyan ink containing a binder, a dispersion resin, an aqueous solvent and CI Pigment Blue 15:3 as a pigment, The volume average particle size of the CI Pigment Yellow 74 is 80 to 120 nm, and the content thereof is 4.0 to 10.0% by mass relative to the total amount of the yellow ink. The volume average particle size of the CI Pigment Blue 15:3 is 80 to 100 nm, and the content of the CI Pigment Blue 15:3 relative to the total amount of the cyan ink is more than 2.5% by mass and less than 5.5% by mass.

2. The ink set according to claim 1, wherein the binder has a minimum film-forming temperature of 25° C. or higher. The volume average particle size of the binder is less than or equal to the volume average particle size of at least one of the CI Pigment Yellow 74 and the CI Pigment Blue 15:

3.

3. The ink set according to claim 1 or 2, further comprising a magenta ink containing a binder, a dispersion resin, an aqueous solvent and a solid solution pigment, The solid solution pigment consists of CI Pigment Red 122 and CI Pigment Violet 19, The mass ratio of CI Pigment Red 122 to CI Pigment Violet 19 in the solid solution pigment, i.e., CI Pigment Red 122 / CI Pigment Violet 19, is 4 / 1 to 1 / 1. The volume average particle size of the solid solution pigment is 90 to 130 nm, A ratio of a concentration of a solid solution pigment contained in the magenta ink to a concentration of a pigment contained in the cyan ink is 1.5 or more. The ink set according to claim 1 or 2, further comprising black ink.

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