Ink set

Abstract

To provide an ink set excellent in chroma of a primary color and a secondary color, particularly of green, and excellent in scratch resistance of a printed image.SOLUTION: An ink set includes: a yellow ink including a binder, a dispersed resin, an aqueous solvent, and C.I. pigment yellow 74 as a pigment; and a cyan ink including a binder, a dispersed resin, an aqueous solvent, and C.I. pigment blue 15:3 as a pigment, where a volume average particle size of the C.I. pigment yellow 74 is 80 to 120nm, a content of the yellow ink to a total amount is 4.0 to 10.0 mass%, a volume average particle size of the C.I. pigment blue 15:3 is 80 to 100 nm, and a content of the cyan ink to the total amount is more than 2.5 mass% and less than 5.5 mass%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an ink set. More specifically, the present invention relates to an ink set suitable for ink-jet inks, which has improved chroma, particularly of green. [Background technology]

[0002] Inkjet recording is a method of recording in which ink droplets are ejected from extremely fine nozzles directly onto a recording medium to produce characters or images. This method has the advantages of low noise and good operability of the equipment used, as well as the ease of colorization and the ability to use plain paper as the recording medium, and therefore has come to be widely used in output devices in offices and homes in recent years. Meanwhile, with technological improvements in inkjet recording methods, industrial printers are also expected to be used as output devices for digital printing, and in some cases analog printers are being replaced by inkjet recording methods. In addition, as ink for inkjet recording methods (inkjet ink), there is an increasing demand for water-based inks instead of conventional solvent inks and UV inks, due to environmental considerations and other factors (see, for example, Patent Document 1). In the printing quality (printing quality) of aqueous inks, high chroma is generally required. For example, Patent Document 2 discloses an ink set for inkjet recording consisting of a yellow ink, a magenta ink, and a cyan ink, which contains a specific pigment and a specific type of dispersant, and is said to improve the chroma of images and have excellent storage stability of the inks. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-12226 A [Patent Document 2] JP 2005-41906 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to increase the saturation of the primary and secondary colors of the ink, it is necessary to keep the pigment, which is the coloring material, close to the surface of the paper, and one possible way to achieve this is to make the ink droplets smaller. However, making the ink droplets smaller tends to reduce image density. Increasing the pigment concentration can suppress the decrease in image density, but on the other hand, there are issues such as a decrease in the storage stability of the ink and a tendency for the pigment components to aggregate and cause a decrease in saturation. Furthermore, when expanding printing by the inkjet method to recording media that are poorly or non-absorbent of ink, such as coated paper and not just plain paper, it is necessary to improve the fixability of the ink and the robustness of the image, specifically, the abrasion resistance, so that the printed image does not peel off due to friction, moisture, etc. From this perspective, it is possible to further include a binder component in the ink, but this poses the problem of a decrease in saturation of the printed matter, and there is still room for improvement in the ink set disclosed in Patent Document 2.

[0005] An object of the present invention is to provide an ink set which has excellent saturation of primary and secondary colors, particularly excellent saturation of green, and which has excellent abrasion resistance of printed images. As a result of extensive research, the inventors discovered that the above-mentioned problems can be solved by using a specific pigment in a specific concentration range in each of the cyan and yellow inks, and preferably by further adding a specific binder to the ink, and thus completed the present invention. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A yellow ink containing a binder, a dispersing resin, an aqueous solvent, and CI Pigment Yellow 74 as a pigment; An ink set comprising a binder, a dispersion resin, an aqueous solvent, and a cyan ink containing CI Pigment Blue 15:3 as a pigment, the volume average particle diameter of the CI Pigment Yellow 74 is 80 to 120 nm, and the content of the CI Pigment Yellow 74 relative to the total amount of the yellow ink is 4.0 to 10.0 mass %, The ink set, wherein the volume average particle diameter 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 mass % and less than 5.5 mass %. [2] The minimum film-forming temperature of the binder is 25°C or higher; The ink set according to [1], wherein the volume average particle diameter of the binder is equal to or smaller than the volume average particle diameter of at least one of CI Pigment Yellow 74 and CI Pigment Blue 15:3. [3] Further, a magenta ink containing a binder, a dispersion resin, an aqueous solvent, and a solid solution pigment is provided, the solid solution pigment is composed 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 is 4 / 1 to 1 / 1; The volume average particle size of the solid solution pigment is 90 to 130 nm, The ink set according to [1] or [2], wherein 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 greater. [4] The ink set according to any one of [1] to [3], further comprising a black ink. Effect of the Invention

[0007] According to the present invention, it is possible to provide an ink set which has excellent saturation of primary and secondary colors, particularly excellent saturation of green, and which has excellent abrasion resistance of printed images. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present invention provides 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 diameter of the CI Pigment Yellow 74 is 80 to 120 nm, and the content of the CI Pigment Yellow 74 relative to the total amount of the yellow ink is 4.0 to 10.0 mass %, In the ink set, the volume average particle diameter 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 mass % and less than 5.5 mass %.

[0009] The ink set of the present invention is excellent in chroma of primary and secondary colors. In particular, the chroma of green (c * ) can be improved. 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 smaller than the volume average particle diameter of at least one of the CI Pigment Yellow 74 and CI Pigment Blue 15:3, so that the ink set has excellent abrasion resistance of printed images. Each of the components of the ink set of the present invention will now be described.

[0010] [Yellow ink] In the ink set of the present invention, the pigment contained in the yellow ink is CI Pigment Yellow 74. The content of CI Pigment Yellow 74 relative to the total amount of the yellow ink is 4.0 to 10.0% by mass, and more preferably in the range of 4.5 to 9.0% by mass. The volume average particle diameter of CI Pigment Yellow 74 is 80 to 120 nm, and more preferably in the range of 90 to 110 nm. The volume average particle diameter of CI Pigment Yellow 74 is determined by a dynamic light scattering method, a laser diffraction method, or the like, which are general measurements of pigment dispersion particles. For example, in the case of the dynamic light scattering method, the pigment particles, which are a dispersion liquid, are diluted with a laser scattering type particle size measuring device, Nanotrac Wave II, manufactured by Microtrac, Inc., and the volume average particle diameter of CI Pigment Yellow 74 can be measured under the set conditions of a measurement time of 180 seconds and a number of repeated measurements of 3, with the dilution ratio adjusted so that the loading index value is 1.

[0011] The binder contained in the yellow ink is used for the purpose of fixing the pigment in the ink to the recording medium. Unlike the dispersion resin described below, the binder is not adsorbed to the surface of the pigment in the ink, but is present in the ink dispersed in the aqueous solvent separately from the pigment and dispersion resin. The minimum film-forming temperature of the binder is preferably 25° C. or higher, and although it depends on the glass transition temperature of the components constituting the binder, it is usually more preferably in the range of 25° C. to 60° C., and even more preferably in the range of 30° C. to 45° C. When the minimum film-forming temperature of the binder is within the above range, film formation proceeds effectively under general drying conditions, and excellent abrasion resistance is achieved.

[0012] The volume average particle diameter of the binder is preferably equal to or smaller than at least one of the volume average particle diameters of CI Pigment Yellow 74, a pigment constituting the yellow ink, and CI Pigment Blue 15:3, a pigment constituting the cyan ink, and more preferably equal to or smaller than both of them. More specifically, the volume average particle diameter of the binder is preferably 100 nm or less, and more preferably in the range of 40 to 80 nm. When the volume average particle diameter of the binder is within the above range, aggregation of pigments in the ink can be suppressed, dispersion stability can be increased, ejection stability and storage stability can be improved, and the scratch resistance of the printed image can be improved. The volume average particle diameter of the binder can be determined by general measurements of dispersed particles, such as dynamic light scattering and laser diffraction. For example, in the case of dynamic light scattering, the volume average particle diameter of the binder can be measured using Nanotrac Wave II, a laser scattering type particle size measuring device manufactured by Microtrac, by adjusting the dilution ratio so that the loading index value is 1, setting the measurement time to 180 seconds and the number of repeated measurements to 3.

[0013] Examples of binders include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinylpyrrolidone, acrylic resins, urethane resins, olefin resins, modified polyolefin resins (acid-modified polypropylene, etc.), dextran, dextrin, carrageenan (κ, ι, λ, etc.), agar, pullulan, water-soluble polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose, etc. These may be used alone or in combination of two or more.

[0014] As the binder, for example, a vinyl polymer (A1) having a structural unit derived from an aromatic vinyl monomer and a glass transition temperature (Tg) of 50 to 100°C, or a halogenated vinyl polymer (A2) having a Tg of 50 to 100°C can be used. The vinyl polymer (A1) may be a copolymer 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, and p-methylstyrene, and among these, styrene is preferred. Examples of the (meth)acrylic monomer include (meth)acrylic acid; and (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate. The vinyl polymer (A1) is preferably a styrene-acrylic resin. The content of the structural units derived from aromatic vinyl monomers in the total amount of the vinyl polymer (A1) is preferably in the range of 50 to 99 mass%, more preferably 80 to 99 mass%, and the content of the structural units derived from (meth)acrylic monomers in the total amount of the vinyl polymer (A1) is preferably in the range of 1 to 50 mass%, more preferably 1 to 20 mass%.

[0015] Examples of the vinyl halide polymer (A2) include vinyl chloride (co)polymers, chlorinated polyolefins, and chlorinated rubbers, and vinyl chloride-acrylic polymers having structural units derived from vinyl chloride monomers and structural units derived from (meth)acrylic monomers are preferred. The (meth)acrylic monomers are as described above. The content of the structural units derived from vinyl chloride monomers in the total amount of the halogenated vinyl polymer (A2) is preferably in the range of 30 to 90 mass%, more preferably in the range of 50 to 80 mass%, and the content of the structural units derived from (meth)acrylic monomers in the total amount of the halogenated vinyl polymer (A2) is preferably in the range of 10 to 70 mass%, more preferably in the range of 20 to 50 mass%.

[0016] 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 in which a structural unit derived from an aromatic vinyl monomer or a structural unit derived from a vinyl chloride monomer is localized in the core portion and a structural unit derived from a (meth)acrylic monomer is localized in the shell portion can be mentioned. The vinyl polymer (A) having a core-shell structure can be produced, for example, by polymerizing a monomer component including 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 within the particles of the polymer (x) to form a core portion.

[0017] Commercially available vinyl polymers (A) may be used. Examples include "JONCRYL PDX-7700", "JONCRYL PDX-7780", "JONCRYL 89-E", and "JONCRYL 89J" (all trade names (JONCRYL is a registered trademark), manufactured by BASF Japan Ltd.), "Hi-Loss X BE7503" (manufactured by Seiko PMC Co., Ltd.), "Vinyblan 745", and "Vinyblan 747" (manufactured by Nissin Chemical Industry Co., Ltd.).

[0018] Of the above-mentioned binders, styrene-acrylic resins are more preferred from the viewpoints of improving the ejection stability of the ink, reducing costs, and improving the print density and image fastness of the resulting printed matter.

[0019] The weight average molecular weight (Mw) of the binder is preferably 100,000 to 1,000,000, and more preferably 300,000 to 750,000. The Mw of the binder is a value measured in terms of standard polystyrene by gel permeation chromatography (GPC), and was determined by a GPC-MALS method in which a multi-angle light scattering detector was connected to the GPC under the measurement conditions described below. GPC main unit: Agilent Technologies LC1100 series Column: Showa Denko SHODEX SB806MHQ Eluent: N / 3 phosphate buffer (pH 3) containing N / 10 sodium nitrate Flow rate: 1.0ml / min Detector 1: Wyatt Technology, multi-angle light scattering detector DAWN Detector 2: Showa Denko Co., Ltd., differential refractive index detector RI-101

[0020] 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 even more preferably in the range of 10 to 30 mgKOH / g.

[0021] The binder content 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, based on the total amount of the yellow ink. When the binder content is in 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 even when water is dropped onto the printed matter or when the printed matter is rubbed with a cloth containing water, the ink tends to not peel off and has excellent abrasion resistance.

[0022] The dispersing resin contained in the yellow ink serves as a means for stably dispersing the pigment, and has the role of adsorbing the dispersing resin to the pigment surface and stably dispersing the pigment in water and solvent components other than water by steric hindrance or electrostatic repulsion. Unlike the binder described above, the dispersing resin exists in a state where it is adsorbed to the pigment surface or where it coats a part or all of the pigment surface. The dispersing resin corresponds to the solid content of the yellow ink.

[0023] Examples of the dispersing resin include polyvinyl alcohols, polyvinylpyrrolidones, acrylic resins such as acrylic acid-acrylic acid ester copolymers, styrene-acrylic resins such as styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, and styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers, aqueous resins of styrene-maleic acid copolymers, styrene-maleic anhydride copolymers, and vinylnaphthalene-acrylic acid copolymers, and salts of the above aqueous resins. Commercially available dispersion resins can be used, such as the "Ajisper (registered trademark)" PB series manufactured by Ajinomoto Fine-Techno Co., Ltd., the "DISPER (registered trademark) BYK" series manufactured by BYK-Chemie, the "EFKA (registered trademark)" series manufactured by BASF, the "SOLSPERSE (registered trademark)" series manufactured by Lubrizol Japan, and the "TEGO (registered trademark) Dispers" series manufactured by Evonik. In addition, compounds exemplified as polymer (G) in WO2018 / 190139 can also be used as dispersion resins. These dispersion resins may be crosslinked with a crosslinking agent after the pigment is dispersed. Among the above, the dispersing resin is preferably a styrene-acrylic resin, and more preferably a styrene-acrylic random copolymer resin.

[0024] The weight average molecular weight (Mw) of the dispersing resin is preferably 5,000 to 50,000, and more preferably 10,000 to 30,000. The Mw of the dispersing resin is a value measured in terms of standard polystyrene by gel permeation chromatography (GPC), and is determined by the same measurement method as that for measuring the weight average molecular weight of the binder described above.

[0025] The acid value of the dispersing resin is preferably 50 mgKOH / g or more, more preferably in the range of 80 to 200 mgKOH / g, and further preferably in the range of 90 to 150 mgKOH / g. The content of the dispersion resin is preferably in the range of 0.5 to 2.5% by mass, and more preferably in the range of 0.8 to 2.0% by mass, based on the total amount of the yellow ink.

[0026] The aqueous solvent that constitutes the yellow ink has a polarity term (δ P ) is 9 or less, and the hydrogen bond term (δ H It is preferable that the yellow ink contains one or more aqueous solvents having a molecular weight of 18 or less. When such an aqueous solvent is contained, the 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 even more preferably in the range of 0.3 to 1.5% by mass, based on the total amount of the yellow ink. It is believed that the inclusion of such an aqueous solvent suppresses pigment aggregation and makes it possible to increase the wettability of the pigment surface, resulting in excellent dispersion stability.

[0027] Here, the Hansen solubility parameter is the solubility parameter (SP value: δ) introduced by Hildebrand, multiplied by the dispersion term δ D , polar term δ P , and the hydrogen bond term δ H This parameter takes into account the polarity of the substance and is expressed in three-dimensional space, and the following relationship holds: δ[(cal / cm 3 ) 0.5 ]]=(δ D 2 +δ P 2 +δ H 2 ) 0.5 The dispersion term δ D , polar term δ P , and the hydrogen bond term δ H Many of these have been calculated by Hansen and subsequent researchers, and are listed, for example, in Polymer Handbook (4th edition) VII-698-711. In addition, Hansen solubility parameters for many solvents and resins have been investigated, and these solubility parameters are listed, for example, in Industrial Solvents Handbook (by Wesley L. Archer). They can also be calculated using the Hansen Solubility Parameters in Practice (HSPiP) software.

[0028] The polarity term of the HSP of the above-mentioned aqueous solvent is preferably from 3 to 9, and more preferably from 4 to 7. The hydrogen bond term of the HSP of the above-mentioned aqueous solvent is preferably from 3 to 18, and even more preferably from 4 to 17.5. When both the polarity term and the hydrogen bond term of the HSP satisfy the above-mentioned ranges, it is believed that the wettability of the pigment surface in the yellow ink is further improved, and the dispersion stability is excellent. The boiling point of the aqueous solvent under atmospheric pressure is preferably 150° C. or higher, and more preferably in the range of 150° C. to 350° C., from the viewpoints of ink ejection stability and preventing drying of the inkjet ink in the ejection nozzles of the inkjet head. Such an aqueous solvent is, for example, 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℃), 1,2-hexanediol (δP = 6.6, δ H = 17.1, boiling point 223°C).

[0029] The water contained in the yellow ink is preferably pure water or ultrapure water from which impurities such as ionic impurities have been removed as much as possible, such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, etc. The water may be sterilized by ultraviolet irradiation, addition of hydrogen peroxide, etc. From the viewpoints of the property of being able to dry quickly on the surface of the recording medium after printing (drying property) and ejection stability, the water content is preferably in the range of 30 to 90 mass % relative to the total amount of the yellow ink, and more preferably in the range of 40 to 80 mass %.

[0030] The yellow ink may contain an aqueous solvent other than the aqueous solvents described above. The other aqueous solvent can have the role of adjusting the viscosity of the ink, the role of further improving the ejection stability when printing by the inkjet printing method, the role of preventing the inkjet ink from drying in the ejection nozzles of the inkjet head, the role of adjusting the drying property described above, etc.

[0031] Examples of other aqueous solvents include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols having a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, isopropylene 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, mesoerythritol, pentaerythritol, glycerin, etc. Among them, solvents having a boiling point in the range of 180 to 300° C. are preferred, and propylene glycol or glycerin is more preferred. Furthermore, when propylene glycol and glycerin are used in combination as other aqueous solvents, aggregation and precipitation of the pigment in the ink are less likely to occur, and the viscosity can be adjusted to a desired level while maintaining dispersion stability, which is preferable from the standpoint of improving the ejection stability when printing by an inkjet printing method and of making it easier to improve the drying properties of the ink after printing. The content of the other aqueous solvent is preferably in the range of 0.1 to 35% by mass, and more preferably in the range of 15 to 35% by mass, relative to the total amount of the yellow ink.

[0032] [Cyan ink] The pigment contained in the cyan ink is CI Pigment Blue 15:3. The content of CI Pigment Blue 15:3 relative to the total amount of the cyan ink is more than 2.5 mass% and less than 5.5 mass%, more preferably in the range of 2.7 to 5.3 mass%, and even more preferably in the range of 3.0 to 4.0 mass%.

[0033] The volume average particle diameter of CI Pigment Blue 15:3 is 80 to 100 nm, and more preferably 85 to 95 nm. The volume average particle diameter of CI Pigment Blue 15:3 is determined by a general measurement method for pigment dispersion particles, such as dynamic light scattering method or laser diffraction method, and an example of the measurement method is the same as the measurement method for the volume average particle diameter of CI Pigment Yellow 74 described above. 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 mass % relative to the total amount of the cyan ink, and more preferably in the range of 0.4 to 1.5 mass %. When the content of the binder is in 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 even when water is dropped on the printed matter or when the printed matter is rubbed with a cloth containing water, the ink does not peel off, and tends to have excellent abrasion resistance.

[0034] The dispersion resin contained in the cyan ink is the same as that 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 mass % of the total amount of the cyan ink, and more preferably in the range of 0.5 to 2.0 mass %. 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. The suitable contents of the aqueous solvent and water are also the same as those of the yellow ink.

[0035] In the ink set of the present invention, when the content of the pigment (CI Pigment Yellow 74) in the yellow ink and the content of the pigment (CI Pigment Blue 15:3) in the cyan ink both satisfy the above-mentioned ranges, the pigment dispersion stability, ejection stability, storage stability, and sufficient print density are ensured, while the chroma of the primary and secondary colors of the resulting printed matter is excellent. In particular, the chroma of the secondary colors, blue and red, is not reduced, and the chroma of green in particular (c * ) can be improved.

[0036] [Magenta ink] The ink set of the present invention may further include a magenta ink. The pigment contained in the magenta ink is a solid solution pigment consisting of CI Pigment Red 122 and CI Pigment Violet 19. Commercially available products can be used as these pigments. In the solid solution pigment, the mass ratio of CI Pigment Red 122 to CI Pigment Violet 19 (CI Pigment Red 122 / CI Pigment Violet 19) is 4 / 1 to 1 / 1, and more preferably in the range of 3.5 / 1 to 2.5 / 1. When the mass ratio of CI Pigment Red 122 to CI Pigment Violet 19 is within the above-mentioned range, the chroma of red is excellent. The method for producing the solid solution pigment is not particularly limited, and known methods disclosed in JP-A-11-49998, JP-A-2000-319534, JP-A-2003-253150, etc. can be applied. In this specification, the solid solution pigment means a pigment that exists as a mixed crystal (crystallized in a mixed state) of multiple pigment molecules, and is different from a simple mixture of two or more pigments. Whether or not a solid solution pigment is formed can be confirmed by X-ray diffraction analysis. In the case of a mixture of two pigments, the X-ray diffraction pattern obtained is a pattern equivalent to the superposition of the X-ray diffraction patterns of each pigment, and the peak intensity is proportional to the blending ratio. On the other hand, when a solid solution pigment is formed, the formed crystal shows its own diffraction pattern.

[0037] The content of the solid solution pigment relative to the total amount of the magenta ink is 4.0 to 10.0% by mass, and preferably in the range of 5.0 to 9.0% by mass. The volume average particle diameter of the solid solution pigment is 80 to 150 nm, and preferably 90 to 130 nm. The volume average particle diameter of the solid solution pigment is determined by a general measurement method for pigment dispersion particles, such as dynamic light scattering method or laser diffraction method, and an example of the measurement method is the same as the measurement method for the volume average particle diameter of CI Pigment Yellow 74 described above. The binder contained in the magenta ink is the same as the binder 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, based on the total amount of the magenta ink. When the content of the binder is in 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 even when water is dropped on the printed matter or when the printed matter is rubbed with a cloth containing water, the ink tends to not peel off and has excellent abrasion resistance.

[0038] The dispersion resin contained in the magenta ink is the same as the dispersion resin 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 mass % of the total amount of the magenta ink, and more preferably in the range of 0.5 to 2.0 mass %. The aqueous solvent contained in the magenta ink is the same as the aqueous solvent contained in the yellow ink and the cyan ink, and the details are as described above. The suitable contents of the aqueous solvent and water are also the same as those of the yellow ink and the cyan ink.

[0039] When the ink set of the present invention further comprises 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, and more preferably in the range of 1.5 to 3.0. When the magenta / cyan concentration ratio is within the above range, the secondary colors tend to have an excellent balance of saturation.

[0040] [Black ink] The ink set of the present invention may further include a black ink. The coloring material of such a black ink is not particularly limited. As an inorganic pigment, for example, iron oxide or carbon black produced by a contact method, a furnace method, a thermal method, or the like can be used. Examples of black pigments include CI Pigment Black 1, 6, 7, 8, 10, 26, 27, and 28. 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, and MA100 manufactured by Mitsubishi Chemical Corporation; Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, and Raven 700 manufactured by Columbia Chemical Corporation; and Regal 400R, Regal 330R, Regal 660R, Mogul L, and Mogul manufactured by Cabot Corporation. 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc.; Degussa's Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35, Printex U, V, 1400U, Special Black 6, 5, 4, 4A, etc.; Orion Engineered Carbons' NIPEX150, NIPEX160, NIPEX170, NIPEX180, etc.

[0041] The details and suitable content ranges of the binder, dispersing resin, and aqueous solvent contained in the black ink are the same as those in the magenta ink described above. 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 having a dispersibility-imparting group is directly or indirectly bonded (grafted) to the surface of the pigment via an alkyl group, an alkyl ether group, an aryl group, or the like may be used. Examples of self-dispersing pigments that are industrially manufactured and commercially available include Microjet CW-1, BONJET BLACK CW-1, BONJET BLACK CW-1S, BONJET BLACK CW-2, BONJET BLACK CW-3 (all trade names; manufactured by Orient Chemical Industries Co., Ltd.), CAB-O-JET200, CAB-O-JET300 (all trade names; manufactured by CABOT Corporation), SENSIJET Black SDP100, SENSIJET Black SDP1000, SENSIJET Black SDP2000 (all trade names; manufactured by Sensient Technologies Co., Ltd.). When a self-dispersing pigment is used, the above-mentioned dispersing resin is not required.

[0042] Each ink constituting the ink set of the present invention may further contain a surfactant. When the ink contains a surfactant, the ink discharged from the nozzle of the inkjet head easily wets and spreads on the surface after landing on the print medium, which makes it easier to prevent printing defects. In addition, the surface tension of the ink is reduced, which makes it easier to improve the leveling property. Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, with anionic surfactants and nonionic surfactants being preferred. Examples of the anionic surfactant include alkylbenzenesulfonates, alkylphenylsulfonates, alkylnaphthalenesulfonates, higher fatty acid salts, sulfates or sulfonates of higher fatty acid esters, sulfates or sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, sulfates, phosphates or alkyl phosphates of polyoxyethylene alkyl ethers, and the like.

[0043] Examples of the nonionic surfactant include glycol surfactants, silicone surfactants, fluorine surfactants, and acetylene diol surfactants. Examples of glycol surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, polyoxyethylene-polyoxypropylene block copolymers, and the like.

[0044] Examples of silicone surfactants include polysiloxane compounds, polyether-modified organosiloxanes, etc. Examples of commercially available silicone surfactants include the "BYK (registered trademark)" series manufactured by BYK Japan and the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd. Examples of fluorosurfactants include perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers, perfluoroalkyl phosphates, perfluoroalkyl betaines, perfluoroalkyl amine oxides, etc. Examples of commercially available fluorosurfactants include the "Megafac (registered trademark)" series manufactured by DIC Corporation, the "Ftergent (registered trademark)" series manufactured by Neos Corporation, and the "Novec (registered trademark)" series manufactured by Sumitomo 3M Limited.

[0045] Acetylene diol surfactants are surfactants having a carbon-carbon triple bond in the molecule, and examples thereof include acetylene diol (having an acetylene bond and two hydroxyl groups in the same molecule) surfactants, and surfactants in which alkylene oxides such as ethylene oxide and propylene oxide are added to acetylene diol. Examples of such surfactants include alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol and 2,4-dimethyl-5-decyne-4-ol. Commercially available acetylene diol surfactants include, for example, the "Surfynol (registered trademark)" series manufactured by Evonik, the "Olfine (registered trademark)" series manufactured by Nissin Chemical Industry Co., Ltd., and the "Acetylenol (registered trademark)" series manufactured by Kawaken Fine Chemical Co., Ltd.

[0046] Among the above, acetylene diol surfactants are more preferred from the viewpoint of easily preventing the occurrence of printing defects. 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. When the HLB value of the surfactant is within the above range, the wettability of the pigment surface is increased, 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 more preferably in the range of 3.5 to 9. Here, the "HLB (Hydrophilic-Lipophilic Balance) value" of a surfactant is a value defined by the following calculation formula (Griffin formula) according to the Griffin method. HLB value = 20 x [sum of chemical formula weights of hydrophilic parts] / molecular weight When each ink constituting the ink set of the present invention further contains a surfactant, the content thereof is preferably in the range of 0.01 to 5 mass %, and more preferably in the range of 0.1 to 2 mass %, based on the total amount of each ink. The surfactant may be used alone or in combination of two or more.

[0047] In addition to the components described above, each of the inks 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 adjuster, a wetting agent (an agent for preventing drying), a penetrating agent, a chelating agent, a plasticizer, and an ultraviolet absorber, as necessary.

[0048] Examples of pH adjusters include potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, diethanolamine, triethanolamine, triisopropanolamine, potassium carbonate, sodium carbonate, and sodium hydrogen carbonate. Examples of preservatives include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazolin-3-one, etc. Commercially available preservatives may be used, such as "ACTICIDE (registered trademark) B20" (trade name, manufactured by Thor Japan Co., Ltd.) and "Proxel (registered trademark) GXL" (trade name, manufactured by SC Johnson Co., Ltd.).

[0049] Examples of polyolefin waxes include waxes or copolymers produced from olefins such as ethylene, propylene, and butylene, or derivatives thereof, such as polyethylene wax, polypropylene wax, polybutylene wax, and modified waxes thereof. Among them, oxidized polyethylene wax, which is obtained by oxidizing and modifying polyethylene wax, is preferred from the viewpoint of improving image fastness of printed matter. Commercially available polyolefin waxes may be used, such as the "AQUACER (registered trademark)" series (manufactured by BYK Japan). Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. When each ink 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 mass %, more preferably 0.02 to 3 mass %, based on the total amount of each ink.

[0050] There is no particular limitation on the method of preparing each ink constituting the ink set of the present invention, and the inks can be prepared by mixing the above-mentioned components. The above-mentioned components may be mixed all at once or sequentially. For example, the binder may be dissolved or dispersed in water or another solvent and then mixed. Also, the pigment may be dispersed together with the dispersion resin in water or another solvent and then mixed. When mixing, a dispersing machine such as a bead mill, ultrasonic homogenizer, high-pressure homogenizer, paint shaker, ball mill, roll mill, sand mill, sand grinder, Dyno Mill, Dispermat, SC Mill, Nanomizer, etc. can be used.

[0051] The viscosity at 25°C of each of the inks constituting the ink set of the present invention 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 even more preferably in the range of 3.0 to 4.0 mPa·s, from the viewpoints of providing excellent storage stability and ejection stability, and also of reducing deviation in the landing position on a recording medium caused by deflection of ink droplets when used in an inkjet recording system, and of easily suppressing the occurrence of streaks in printed matter. The viscosity of the ink is a value measured, for example, using a cone-plate type rotational viscometer equivalent to an E-type viscometer under the following conditions. Measurement equipment: TVE-25 type viscometer (Toki Sangyo Co., Ltd., TVE-25L) Calibration standard solution: JS20 Measurement temperature: 25℃ Rotation speed: 10~100rpm Injection volume: 1200μL

[0052] 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. The 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, the ink tends to have good wettability on the surface of the recording medium from the ejected droplets, and to have sufficient wetting and spreading after landing.

[0053] The pH at 25°C of each of the inks constituting the ink set of the present invention is preferably 7.0 to 11.0, and more preferably 7.5 to 10.5, from the viewpoints of improving the storage stability and ejection stability of the ink, and improving the wetting spread, print density, and image fastness when printed on a recording medium, and from the viewpoints of suppressing deterioration of the members constituting the ink application or ejection device (ink ejection orifices, ink flow paths, etc.).

[0054] The ink set of the present invention can be applied to various ink jet recording methods such as thermal jet type, piezoelectric type, continuous ink jet type, roller application type, spray application type, and the like, as well as to recording devices using these recording methods. Examples of recording media to which droplets of the ink set of the present invention are deposited include plain paper, cast glossy paper in which a coating is applied to the surface of plain paper and an ink-receiving layer with excellent surface gloss is formed by a casting method to impart gloss to the surface, and polymer-coated glossy paper in which an inkjet recording layer containing a resin as a main component is formed.

[0055] Although the ink set of the present invention has been described above, the present invention is not limited to the configuration of the above-mentioned embodiment. For example, the ink set of the present invention may have any other optional configuration in addition to the configuration of the above-mentioned embodiment, or may be replaced with any configuration that exhibits the same function. EXAMPLES

[0056] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples. The pigments, compounds, etc. used in the examples are shown below.

[0057] <Pigments> Yellow: CI Pigment Yellow 74 ("Hansa Yellow 5GX01" (product name, CLARIANT, volume average particle size: 90 nm) Cyan: CI Pigment Blue 15:3 ("FASTOGEN BLUE SBG-SD" (product name, manufactured by DIC Corporation, volume average particle size: 90 nm) Magenta: Solid solution pigment with a mass ratio of CI Pigment Red 122 and CI Pigment Violet 19 of 3 / 1 (manufactured by DIC, volume average particle size: 110 nm) <Aqueous solvent> PG: Propylene glycol (δ P = 10.4, δ H =21.3, boiling point 188℃) Gly: glycerin (δ P = 11.3, δ H =27.2, boiling point 290℃)

[0058] <Binder> Binder 1: Styrene-acrylic resin (MFT: 36°C, volume average particle size 60 nm, Mw 500000, acid value 20 mgKOH / g, manufactured by DIC) <Surfactant> SF420: "Surfynol 420" (product name, manufactured by Evonik, HLB value = 4) <Preservatives> B20: "ACTICIDE B20" (product name, manufactured by Thor Japan) <Dispersion resin> Styrene-acrylic random copolymer resin (Mw 18000, acid value 110mgKOH / g)

[0059] <Preparation of pigment dispersion> <Pigment Dispersion Y (Yellow)> 150g of yellow pigment, 60g of dispersion resin, 75g of PG, and 19.4g of 34% by mass potassium hydroxide aqueous solution were charged into a 1.0L intensive mixer (manufactured by Nippon Eirich Co., Ltd.) and kneaded for 25 minutes at a rotor peripheral speed of 2.94m / s and a pan peripheral speed of 1m / s. Next, 306g of ion-exchanged water was gradually added to the kneaded material in the intensive mixer while continuing to stir, and then 12g of PG and 127.5g of ion-exchanged water were further added and mixed so that the pigment concentration was 20% by mass, thereby obtaining an aqueous pigment dispersion (pigment dispersion Y) with a pigment concentration of 20% by mass.

[0060] <Pigment Dispersion C (Cyan)> Pigment dispersion C (pigment concentration: 20% by mass) was prepared in the same manner as for pigment dispersion Y, except that a cyan pigment was used instead of the yellow pigment. <Pigment Dispersion M (Magenta)> Pigment dispersion M (pigment concentration: 20% by mass) was prepared in the same manner as for pigment dispersion Y, except that a magenta pigment was used instead of the yellow pigment.

[0061] 1. Preparation of Ink Set Examples 1 to 3 and Comparative Examples 1 to 3 Pigment Dispersion Y, Pigment Dispersion C, Pigment Dispersion M, binder, aqueous solvent, surfactant, preservative, and distilled water were mixed and stirred in the composition ratios shown in Table 1 to prepare yellow ink, cyan ink, and magenta ink, respectively, to obtain ink sets. The contents in Table 1 are all based on the total amount of each ink.

[0062] 2. Ink set evaluation 2-1. Evaluation of saturation The cyan ink, magenta ink, and yellow ink of the ink sets of each of the Examples and Comparative Examples were filled into color ink cartridges of an EPSON inkjet printer (PX-S740), and printed on plain inkjet paper (product name "NEXT-IJ <70> ”, manufactured by Nippon Paper Industries Co., Ltd., basis weight 81.4g / m 2 ) were printed with full solid images in each of the primary colors of cyan, magenta, and yellow, as well as full solid images in the secondary colors of red, green, and blue, which are combinations of these three primary colors. The full solid image of each color was measured using a spectrophotometer (product name "eXact", manufactured by X-rite) under the measurement conditions below, and the saturation of each color image was calculated from the a value and b value of each color image using the following formula. Saturation=√(a 2 +b 2 ) The measurement conditions were as follows: Observation lighting / observer viewing angle: D65 / 2° Density status: ISO status T ΔE: CIE ΔE*(1976) The evaluation criteria for c* (chroma) for red, green, and blue are as follows: <Red> ×:<50 △:50~less than 55 ○:55~60 ◎:>60 <Green> ×:<40 △:40~less than 45 ○:45~50 ◎:>50 <Blue> ×:<35 △:35~39 or less ○:39~43 ◎:>43

[0063] 2-2. Abrasion resistance (coated paper) Each of the ink sets of the Examples and Comparative Examples was filled into an inkjet printer (PX-S740) manufactured by EPSON Corporation, and printed on coated paper (product name "SWORD iJET (registered trademark) 4.3 Gloss", manufactured by Mitsubishi Paper Mills, basis weight 104.7 g / m 2 ) was subjected to full solid printing to obtain an ink coating film. The obtained coating film was dried at room temperature (25°C) for 12 hours. Next, using a Gakushin type friction tester RT-300 (manufactured by Daiei Scientific Instruments Co., Ltd.), the same paper as the printing substrate was used as the friction element, and the coating film after drying was rubbed with a load of 100 g / cm. 2 The degree of peeling of the coating film was visually observed, and the abrasion resistance (image fastness) was evaluated according to the following criteria. <Evaluation criteria> ○: No scratches are observed on the print, or only slight scratches are observed ×: Many scratches were observed on the print, and dark coloring was observed in parts of the friction piece paper.

[0064] The above results are summarized in Table 1.

[0065] [Table 1]

[0066] As seen from the above examples, the ink set satisfying the requirements of the present invention provides a good balance of the chroma of the secondary colors red, green and blue, and can particularly improve the chroma of green. On the other hand, Comparative Examples 1 and 2, in which the yellow ink content and the cyan ink pigment content do not satisfy the requirements of the present invention, both have poor green saturation. Comparative Example 1, in which the cyan ink pigment content is lower than the requirements of the present invention, also has low blue saturation, while Comparative Example 2, in which the cyan ink pigment content is higher than the requirements of the present invention, has low red saturation. Comparative Example 3, which does not contain a binder that satisfies the requirements of the present invention, reduces the abrasion resistance of the printed matter. In addition, in an ink set that satisfies the requirements of the present invention, aggregation of pigments in the ink is suppressed and dispersion stability is improved, making it possible to achieve a balance between ink density (OD) and improved saturation in printed matter. [Industrial Applicability]

[0067] The ink set of the present invention has improved saturation of primary and secondary colors, particularly green saturation, and excellent abrasion resistance of printed images, and is therefore particularly useful as inkjet inks for industrial inkjet printers.

Claims

1. a yellow ink containing a binder, a dispersion resin, an aqueous solvent, and C.I. Pigment Yellow 74 as a pigment; a cyan ink containing a binder, a dispersing resin, an aqueous solvent, and C.I. Pigment Blue 15:3 as a pigment; 1. An ink set comprising a magenta ink containing a solid solution pigment, The C.I. Pigment Yellow 74 has a volume average particle diameter of 80 to 120 nm and is contained in an amount of 4.0 to 10.0% by mass relative to the total amount of the yellow ink; The volume average particle diameter of the C.I. Pigment Blue 15:3 is 85 to 100 nm, and the content of the C.I. 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, The solid solution pigment comprises C.I. Pigment Red 122 and C.I. Pigment Violet 19.

2. The ink set described in claim 1, wherein the magenta ink further contains a binder, a dispersion resin, and an aqueous solvent.

3. The ink set described in claim 1 or 2, wherein the acid value of the binder contained in the yellow ink, cyan ink, and / or magenta ink is 50 mg KOH / g or less.

4. The ink set described in claim 1 or 2, wherein the minimum film-forming temperature of the binder contained in the yellow ink, cyan ink, and / or magenta ink is 25°C or higher.

5. The ink set according to claim 1, wherein the weight average molecular weight (Mw) of the binder contained in the yellow ink, cyan ink, and / or magenta ink is 100,000 to 1,000,000.

6. An ink set described in claim 1 or 2, wherein the volume average particle diameter of the solid solution pigment is 80 to 150 nm.

7. An ink set described in claim 1 or 2, wherein the content of the solid solution pigment relative to the total amount of the magenta ink is 4.0 to 10.0 mass %.

8. The ink set according to claim 1 or 2, wherein 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.

9. An ink set as described in claim 1 or 2, wherein 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.

10. The ink set according to claim 1 or 2, further comprising a black ink.