Ink set

Abstract

The present invention addresses the problem of providing an ink set which has excellent rub-fastness as a printed image, and has excellent primary color and secondary color saturation, and specifically, excellent green color saturation.　Specifically, the present invention provides an ink set provided with a yellow ink containing a binder, a dispersed resin, an aqueous solvent and C.I. pigment yellow 74 as a pigment, and a cyan ink containing a binder, a dispersed resin, an aqueous solvent and C.I. pigment blue 15:3 as a pigment, wherein the volume-average particle diameter of the C.I pigment yellow 74 is 80-120nm, the content of the yellow ink relative to the total amount is 4.0-10.0 mass%, the volume-average particle diameter of the C.I. pigment blue 15:3 is 80-100nm, and the content of the cyan ink relative to the total amount is greater than 2.5 mass% and less than 5.5 mass%.

Description

Ink set

[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 saturation, particularly of green.

[0002] Inkjet recording is a recording method in which ink droplets are ejected directly from extremely fine nozzles onto a recording medium, depositing them on the recording medium to produce characters or images. This method has been widely used in offices and homes in recent years for its advantages of low noise and ease of use, as well as its ease of colorization and the ability to use plain paper as the recording medium. Meanwhile, advances in inkjet recording technology have led to expectations for industrial printers as output devices for digital printing, and some printers are replacing analog printers. Furthermore, for inkjet recording inks, demand for water-based inks is increasing, replacing conventional solvent inks and UV inks, due to environmental considerations and other factors (see, for example, Patent Document 1). High saturation is generally required for the print quality of water-based inks. For example, Patent Document 2 discloses an inkjet recording ink set consisting of yellow, magenta, and cyan inks containing a specific pigment and a specific type of dispersant, which is said to improve image saturation and provide excellent ink storage stability.

[0003] JP 2011-12226 A JP 2005-41906 A

[0004] In order to increase the saturation of the primary and secondary colors of an ink, it is necessary to retain the pigment, which is the coloring material, near the paper surface. Reducing the size of ink droplets is considered as a means to achieve this. However, reducing the size of ink droplets tends to reduce image density. While increasing the pigment concentration can suppress the reduction in image density, it also has problems such as reduced ink storage stability and a tendency for saturation to decrease due to aggregation of the pigment components. Furthermore, when inkjet printing is expanded to recording media that are poorly or non-absorbent of ink, such as coated paper, in addition to plain paper, it is necessary to improve the ink fixability and image robustness, specifically abrasion resistance, to prevent the printed image from peeling due to friction, moisture, etc. From this perspective, adding a binder component to the ink is considered, but this reduces the saturation of the printed material, and the ink set disclosed in Patent Document 2 still has room for improvement.

[0005]

[0009] An object of the present invention is to provide an ink set that has excellent saturation of primary and secondary colors, particularly the saturation of green, and that has excellent abrasion resistance of printed images. As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using specific pigments in specific concentration ranges in each of the cyan and yellow inks, and preferably by further incorporating a specific binder into the ink, and have thus completed the present invention.

[0006] The present invention has the following aspects. [1] An ink set comprising 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, wherein 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 mass% relative to the total amount of the yellow ink, and the C.I. Pigment Blue 15:3 has a volume average particle diameter of 80 to 100 nm and is contained in an amount of more than 2.5 mass% and less than 5.5 mass% relative to the total amount of the cyan ink. [2] The minimum film-forming temperature of the binder is 25°C or higher, and the volume average particle diameter of the binder is 4.0 to 10.0 mass% relative to the total amount of the C.I. Pigment Yellow 74 and C.I. The ink set according to [1], further comprising a magenta ink containing a binder, a dispersion resin, an aqueous solvent, and a solid solution pigment, wherein the solid solution pigment is composed of C.I. Pigment Red 122 and C.I. Pigment Violet 19, the mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 in the solid solution pigment is 4 / 1 to 1 / 1, the volume average particle diameter of the solid solution pigment is 90 to 130 nm, and the ratio of the concentration of the solid solution pigment in the magenta ink to the concentration of the pigment in the cyan ink is 1.5 or greater. [4] The ink set according to any of [1] to [3], further comprising a black ink.

[0007] According to the present invention, it is possible to provide an ink set that has excellent saturation of primary and secondary colors, particularly the saturation of green, and that has excellent abrasion resistance of printed images.

[0008] The present invention is an ink set comprising 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, wherein 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 mass% relative to the total amount of the yellow ink, and the C.I. Pigment Blue 15:3 has a volume average particle diameter of 80 to 100 nm and is contained in an amount of more than 2.5 mass% and less than 5.5 mass% relative to the total amount of the cyan ink.

[0009] The ink set of the present invention is excellent in the saturation of primary and secondary colors. In particular, the saturation of green (c ＊ ) can be improved. Preferably, the ink set of the present invention has a minimum film-forming temperature of 25°C or higher and a volume average particle diameter of the binder that is equal to or smaller than the volume average particle diameter of at least one of C.I. Pigment Yellow 74 and C.I. Pigment Blue 15:3, thereby achieving excellent abrasion resistance of printed images. Each component of the ink set of the present invention will be described below.

[0010] [Yellow Ink] 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 4.5 to 9.0% by mass. The volume average particle diameter of C.I. Pigment Yellow 74 is 80 to 120 nm, more preferably 90 to 110 nm. The volume average particle diameter of C.I. Pigment Yellow 74 is determined by dynamic light scattering, laser diffraction, or other methods commonly used to measure pigment dispersed particles. For example, in the case of dynamic light scattering, the pigment particles in the dispersion are measured using a Nanotrac Wave II laser scattering particle size measuring device manufactured by Microtrac Corporation, with the dilution ratio adjusted so that the loading index value is 1, and the measurement time set to 180 seconds and the number of repeated measurements set to 3. The volume average particle size of C.I. Pigment Yellow 74 can be measured.

[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 does not adsorb to the surface of the pigment or the like 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 this depends on the glass transition temperatures of the components that make up the binder, a range of 25°C to 60°C is usually more preferable, and a range of 30°C to 45°C is even more preferable. Having the minimum film-forming temperature of the binder within the above range allows for effective film formation under typical drying conditions, resulting in excellent abrasion resistance.

[0012] The volume average particle diameter of the binder is preferably equal to or less than the volume average particle diameter of C.I. Pigment Yellow 74, a pigment constituting the yellow ink, or the volume average particle diameter of C.I. Pigment Blue 15:3, a pigment constituting the cyan ink, and more preferably equal to or less than both of these. More specifically, the volume average particle diameter of the binder is preferably equal to or less than 100 nm, 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 the pigments in the ink is suppressed, dispersion stability is increased, and the ejection stability and storage stability can be improved, and the abrasion resistance of the printed image can be improved. The volume average particle diameter of the binder can be determined by dynamic light scattering, laser diffraction, or other methods commonly used to measure dispersed particles. For example, in the case of a dynamic light scattering method, the volume average particle diameter of the binder can be measured using a Nanotrac Wave II manufactured by Microtrac, which is a laser scattering type particle size measuring device, by adjusting the dilution ratio so that the loading index value is 1, under the setting conditions of a measurement time of 180 seconds and a number of repeated measurements of 3.

[0013] Examples of binders include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinylpyrrolidone, acrylic resins, urethane resins, olefin resins, modified polyolefin resins (such as acid-modified polypropylene), 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] The binder may be, for example, a vinyl polymer (A) having a structural unit derived from an aromatic vinyl monomer (A1) 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. Examples of the vinyl polymer (A1) include copolymers having structural units derived from an aromatic vinyl monomer and structural units derived from a (meth)acrylic monomer. Examples of aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, and p-methylstyrene, with styrene being preferred. Examples of (meth)acrylic monomers 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 structural units derived from aromatic vinyl monomers relative to the total amount of the vinyl polymer (A1) is preferably in the range of 50 to 99 mass%, more preferably 80 to 99 mass%. Furthermore, the content of structural units derived from (meth)acrylic monomers relative to 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. A vinyl chloride-acrylic polymer having structural units derived from vinyl chloride monomers and structural units derived from (meth)acrylic monomers is preferred. The (meth)acrylic monomer is as described above. The content of the structural units derived from vinyl chloride monomers relative to the total amount of the vinyl halide polymer (A2) is preferably in the range of 30 to 90% by mass, more preferably 50 to 80% by mass. Furthermore, the content of the structural units derived from (meth)acrylic monomers relative to the total amount of the vinyl halide polymer (A2) is preferably in the range of 10 to 70% by mass, more preferably 20 to 50% by mass.

[0016] The vinyl polymer (A) can be produced by emulsion polymerization, solution polymerization, suspension polymerization, bulk polymerization, etc. Vinyl polymers (A) having a core-shell structure are more preferred. For example, vinyl polymers having a core-shell structure in which structural units derived from an aromatic vinyl monomer or structural units derived from a vinyl chloride monomer are localized in the core portion and structural units derived from a (meth)acrylic monomer are 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 products may be used as the vinyl polymer (A). 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.); "Hiros X BE7503" (manufactured by Seiko PMC Corporation), "Viniblan 745," and "Viniblan 747" (manufactured by Nissin Chemical Industry Co., Ltd.).

[0018] Of the binders mentioned above, 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 prints.

[0019] The weight average molecular weight (Mw) of the binder is preferably 100,000 to 1,000,000, 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 body: LC1100 series manufactured by Agilent Technologies Column: SHODEX SB806MHQ manufactured by Showa Denko KK Eluent: N / 3 phosphate buffer (pH 3) containing N / 10 sodium nitrate Flow rate: 1.0 ml / min Detector 1: DAWN multi-angle light scattering detector manufactured by Wyatt Technology Detector 2: RI-101 differential refractive index detector manufactured by Showa Denko KK

[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, and 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 this range, the ejection stability and storage stability of the ink are improved. Furthermore, 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 soaked in water, the ink tends to not peel off, and the abrasion resistance tends to be excellent.

[0022] The dispersing resin contained in the yellow ink acts as a means for stably dispersing the pigment by adsorbing it to the pigment surface and stably dispersing the pigment in water and solvent components other than water through 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 coats part or all of the pigment surface. The dispersing resin corresponds to the solid content of the yellow ink.

[0023] Examples of dispersing resins include polyvinyl alcohols, polyvinylpyrrolidones, acrylic resins such as acrylic acid-acrylic acid ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers, and other styrene-acrylic resins such as styrene-maleic acid copolymers, styrene-maleic anhydride copolymers, and vinylnaphthalene-acrylic acid copolymers, as well as salts of the above aqueous resins. Commercially available dispersing resins can be used, including 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 The Lubrizol Japan Corporation, and the "TEGO (registered trademark) Disperses" series manufactured by Evonik. Furthermore, the dispersing resin may be a compound exemplified as polymer (G) in WO 2018 / 190139. These dispersing resins may be subjected to a crosslinking treatment with a crosslinking agent after dispersing the pigment. Among the above, styrene-acrylic resins are preferred as dispersing resins, and styrene-acrylic random copolymer resins are more preferred.

[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 used to measure 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 80 to 200 mgKOH / g, and even more preferably 90 to 150 mgKOH / g.The content of the dispersing resin is preferably 0.5 to 2.5% by mass, and more preferably 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 saturation index (SAR) of 18 or less. When such an aqueous solvent is contained, the content thereof 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, relative to 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 It is a parameter that 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 VII-698 to 711 of the Polymer Handbook (4th edition). Furthermore, Hansen's solubility parameters for many solvents and resins have been investigated, and these solubility parameters are listed, for example, in the Industrial Solvents Handbook (by Wesley L. Archer). These solubility parameters can also be calculated using Hansen Solubility Parameters in Practice (HSPiP) software.

[0028] The polarity term of the HSP of the above-mentioned aqueous solvent is preferably 3 or more and 9 or less, more preferably 4 or more and 7 or less. The hydrogen bonding term of the HSP of the above-mentioned aqueous solvent is also preferably 3 or more and 18 or less, more preferably 4 or more and 17.5 or less. When the polarity term and hydrogen bonding term of the HSP both satisfy the above-mentioned ranges, it is believed that the wettability of the pigment surface in the yellow ink is further improved, resulting in excellent dispersion stability. The boiling point of the above-mentioned aqueous solvent under atmospheric pressure is preferably 150°C or more, 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. 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).

[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, or distilled water. The water may be sterilized by ultraviolet irradiation or the addition of hydrogen peroxide. 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% by mass, and more preferably in the range of 40 to 80% by mass, based on the total amount of the yellow ink.

[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 inkjet printing, 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] Other aqueous solvents include, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols with 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 these, solvents having a boiling point in the range of 180 to 300°C are preferred, and propylene glycol or glycerin are more preferred. Furthermore, the use of propylene glycol and glycerin as other aqueous solvents in combination makes it difficult for the pigment to aggregate or precipitate in the ink, allows the viscosity to be adjusted to a desired level while maintaining dispersion stability, and is preferable from the viewpoints of improving the ejection stability when printing by inkjet printing and improving the drying properties of the ink after printing. The content of the other aqueous solvents is preferably in the range of 0.1 to 35% by mass, and more preferably in the range of 15 to 35% by mass, based on the total amount of the yellow ink.

[0032] [Cyan Ink] 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 more 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 even more preferably in the range of 3.0 to 4.0% by mass.

[0033] The volume average particle diameter of C.I. Pigment Blue 15:3 is 80 to 100 nm, and more preferably 85 to 95 nm. The volume average particle diameter of C.I. Pigment Blue 15:3 is determined by dynamic light scattering, laser diffraction, or other methods commonly used to measure pigment-dispersed particles. One example of such a measurement method is the same as the method for measuring the volume average particle diameter of C.I. 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 binder content in the cyan ink is preferably in the range of 0.4 to 3.0% by mass, and more preferably in the range of 0.4 to 1.5% by mass, relative to the total amount of the cyan ink. A binder content within this range improves the ejection stability and storage stability of the ink. Furthermore, the image fastness of printed matter can be further improved, and the ink tends to exhibit excellent abrasion resistance, even when water is dropped on the printed matter or when the printed matter is rubbed with a cloth containing water.

[0034] The dispersion resin contained in the cyan ink is the same as the dispersion resin contained in the yellow ink, and the details thereof 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% relative to 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 thereof are as described above. The preferred contents of the aqueous solvent and water are also the same as those for the yellow ink.

[0035] In the ink set of the present invention, when 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 both satisfy the above-mentioned ranges, the pigment dispersion stability, ejection stability, storage stability, and sufficient print density are ensured, while the saturation of the primary and secondary colors of the resulting printed matter is excellent. In particular, the saturation of the secondary colors, blue and red, is not reduced, and the saturation 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 this magenta ink is a solid solution pigment consisting of C.I. Pigment Red 122 and C.I. Pigment Violet 19. Commercially available products can be used for these pigments. In the solid solution pigment, the mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 (C.I. Pigment Red 122 / C.I. Pigment Violet 19) is 4 / 1 to 1 / 1, and more preferably 3.5 / 1 to 2.5 / 1. When the mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 is within the above-mentioned range, the saturation of red color is excellent. The method for producing a 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, a solid solution pigment refers to 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 has been formed can be confirmed by X-ray diffraction analysis. In the case of a mixture of two pigments, the resulting X-ray diffraction pattern corresponds to the superposition of the X-ray diffraction patterns of the individual pigments, and the peak intensity is proportional to the blend ratio. On the other hand, when a solid solution pigment is formed, the formed crystals exhibit a unique 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, more preferably 5.0 to 9.0% by mass. The volume-average particle diameter of the solid solution pigment is 80 to 150 nm, more preferably 90 to 130 nm. The volume-average particle diameter of the solid solution pigment is determined by dynamic light scattering, laser diffraction, or other methods commonly used to measure pigment-dispersed particles. An example of such a measurement method is the same as the method for measuring the volume-average particle diameter of C.I. Pigment Yellow 74 described above. The binder contained in the magenta ink is the same as the binder contained in the yellow ink and cyan ink, and the details are as described above. The binder content in the magenta ink is preferably 0.4 to 3.0% by mass, more preferably 0.4 to 1.5% by mass, relative to the total amount of the magenta ink. A binder content within this range improves the ejection stability and storage stability of the ink. Furthermore, 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.

[0038] The dispersion resin contained in the magenta ink is the same as the dispersion resin contained in the yellow ink and cyan ink, and the details thereof 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% relative to 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 cyan ink, and the details thereof are as described above. Furthermore, the preferred contents of the aqueous solvent and water are also the same as those for the yellow ink and 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 saturation balance of the secondary colors tends to be excellent.

[0040] [Black Ink] The ink set of the present invention may further include a black ink. The coloring material of such black ink is not particularly limited. Examples of inorganic pigments that can be used include iron oxide and carbon black produced by a contact method, furnace method, or thermal method. Examples of black pigments include C.I. 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, and No. 50L manufactured by Mitsubishi Chemical Corporation. 52, MCF88, MA7, MA8, MA100, etc.; Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc., manufactured by Columbia Corporation; Regal 400R, Regal 330R, Regal 660R, Mogul L, Mogul 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc., manufactured by Cabot Corporation; Color Black, manufactured by Degussa FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35, U, V, 1400U, Special Black 6, 5, 4, 4A, etc.; and NIPEX150, NIPEX160, NIPEX170, NIPEX180, etc. manufactured by Orion Engineered Carbons.

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

[0042] Each ink constituting the ink set of the present invention may further contain a surfactant. The inclusion of a surfactant facilitates good wetting and spreading of the ink ejected from the nozzles of the inkjet head on the surface of a substrate after landing, thereby preventing printing defects. The surfactant also reduces the surface tension of the ink, improving leveling. Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, with anionic surfactants and nonionic surfactants being preferred. Examples of anionic surfactants include alkylbenzene sulfonates, alkylphenyl sulfonates, alkylnaphthalene sulfonates, higher fatty acid salts, sulfate ester salts or sulfonates of higher fatty acid esters, sulfate ester salts or sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, sulfates, phosphates, and alkyl phosphates of polyoxyethylene alkyl ethers.

[0043] Examples of nonionic surfactants 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, and polyoxyethylene-polyoxypropylene block copolymers.

[0044] Examples of silicone surfactants include polysiloxane compounds and polyether-modified organosiloxanes. 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 fluorine-based surfactants include perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers, perfluoroalkyl phosphates, perfluoroalkyl betaines, and perfluoroalkyl amine oxides. Commercially available fluorine-based surfactants 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 acetylenic diol (having an acetylene bond and two hydroxyl groups in the same molecule) surfactants and surfactants in which an alkylene oxide such as ethylene oxide or propylene oxide is added to an acetylenic diol. Examples 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 acetylenic diol surfactants include 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 Chemicals Co., Ltd.

[0046] Among the surfactants listed above, acetylene diol surfactants are more preferred from the viewpoint of easily preventing printing defects. Furthermore, 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-mentioned range, the wettability of the pigment surface is enhanced, 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 the surfactant is a value defined by the following calculation formula (Griffin formula) according to the Griffin method: HLB value = 20 × [sum of chemical formula weights of hydrophilic moieties] / 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% by mass, more preferably 0.1 to 2% by mass, relative to 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, preservative, polyolefin wax, antioxidant, viscosity adjuster, humectant (drying inhibitor), penetrating agent, chelating agent, plasticizer, and 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, and 1,2-dibenzisothiazolin-3-one. 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).

[0049] Examples of polyolefin waxes include waxes or copolymers produced from olefins such as ethylene, propylene, and butylene, or derivatives thereof, such as polyethylene waxes, polypropylene waxes, polybutylene waxes, and modified waxes thereof. Among these, oxidized polyethylene wax, which is obtained by subjecting polyethylene wax to an oxidation modification treatment, is preferred from the viewpoint of improving the image fastness of printed materials. Commercially available polyolefin waxes may be used, such as the "AQUACER (registered trademark)" series (manufactured by BYK Japan). Examples of antioxidants 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% by mass, and more preferably 0.02 to 3% by mass, of the total amount of each ink.

[0050] There are no particular limitations on the method for 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 before mixing. The pigment may be dispersed in water or another solvent together with a dispersing resin before 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, or Nanomizer can be used for mixing.

[0051] The viscosity at 25°C of each ink 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 achieving excellent storage stability and ejection stability, and of reducing deviation in landing position on a recording medium caused by deflection of ink flight when used in an inkjet recording system, and 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: Measuring device: TVE-25 type viscometer (TVE-25L, manufactured by Toki Sangyo Co., Ltd.) Calibration standard solution: JS20 Measurement temperature: 25°C Rotation speed: 10 to 100 rpm Injection amount: 1200 μL

[0052] The surface tension at 25°C of each ink constituting the ink set of the present invention is preferably 20 mN / m or more, more preferably 25 mN / m or more. Such a surface tension is preferably 40 mN / m or less, more preferably 35 mN / m or less. When the surface tension is within this range, when used in an inkjet recording system, 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 viewpoint of improving the storage stability and ejection stability of the ink, improving the wetting and spreading, print density, and image fastness when printed on a recording medium, and from the viewpoint of suppressing deterioration of the components 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 inkjet recording methods such as thermal jet, piezo, continuous inkjet, roller application, and spray application, as well as to recording devices that use these recording methods. As recording media to which droplets of the ink set of the present invention are deposited, in addition to 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 can be used.

[0055] Although the ink set of the present invention has been described above, the present invention is not limited to the configurations of the above-described embodiments. For example, the ink set of the present invention may have any other optional components in addition to the configurations of the above-described embodiments, or may be substituted with any other components that exhibit similar functions.

[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 these examples are shown below.

[0057] <Pigments> Yellow: C.I. Pigment Yellow 74 ("Hansa Yellow 5GX01" (trade name, manufactured by CLARIANT, volume average particle diameter: 90 nm) Cyan: C.I. Pigment Blue 15:3 ("FASTOGEN BLUE SBG-SD" (trade name, manufactured by DIC Corporation, volume average particle diameter: 90 nm) Magenta: solid solution pigment of C.I. Pigment Red 122 and C.I. Pigment Violet 19 in a mass ratio of 3 / 1 (manufactured by DIC Corporation, volume average particle diameter: 110 nm) <Aqueous solvent> PG: propylene glycol (δ Ｐ = 10.4, δＨ = 21.3, boiling point 188°C) 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 500,000, acid value 20 mgKOH / g, manufactured by DIC Corporation) <Surfactant> SF420: "Surfynol 420" (trade name, manufactured by Evonik Corporation, HLB value = 4) <Preservative> B20: "ACTICIDE B20" (trade name, manufactured by Thor Japan Co., Ltd.) <Dispersion resin> Styrene-acrylic random copolymer resin (Mw 18,000, acid value 110 mgKOH / g)

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

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

[0061] 1. Preparation of Ink Sets 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. Note that the contents in Table 1 are all based on the total amount of each ink.

[0062] 2. Evaluation of Ink Sets 2-1. Evaluation of Saturation The cyan ink, magenta ink, and yellow ink of the ink sets of each Example and Comparative Example were filled into color ink cartridges of an inkjet printer (PX-S740) manufactured by EPSON Corporation, and printed on plain inkjet paper (product name "NEXT-IJ<70>", manufactured by Nippon Paper Industries Co., Ltd., basis weight 81.4 g / m) in the plain paper standard mode. ２ A full solid image of each of the primary colors cyan, magenta, and yellow, and a full solid image of the secondary colors red, green, and blue, each of which is a combination of these three primary colors, were printed on a paper sheet. The full solid image of each color was measured using a spectrophotometer (trade name "eXact", manufactured by X-rite) under the following measurement conditions, 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 following conditions were used as measurement conditions: Observation illumination / observer viewing angle: D65 / 2° Density status: ISO status T ΔE: CIE ΔE* (1976) The evaluation criteria for c* (chroma) for each of red, green, and blue are as follows: <Red> ×: <50 △: 50 to less than 55 ○: 55 to 60 ◎: >60 <Green> ×: <40 △: 40 to less than 45 ○: 45 to 50 ◎: >50 <Blue> ×: <35 △: 35 to less than 39 ○: 39 to 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 coated paper (product name "SWORD iJET (registered trademark) 4.3 Gloss", manufactured by Mitsubishi Paper Mills, basis weight 104.7 g / m) was used. ２ ) was subjected to full solid printing to obtain a coating film of the ink. 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 dried coating film was rubbed under a load of 100 g / cm. ２The print was rubbed 50 times with a rubbing cloth. The degree of peeling of the coating film was visually observed, and the rub resistance (image fastness) was evaluated according to the following criteria. <Evaluation criteria> ○: No scratches were observed on the print, or only slight scratches were observed. ×: Many scratches were observed on the print, and dark coloring was observed in parts of the paper of the rubber.

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

[0065]

[0066] As shown in the above examples, the ink set satisfying the requirements of the present invention exhibits excellent and well-balanced saturation of the secondary colors red, green, and blue, with particularly improved green saturation. 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 exhibit poor green saturation. Comparative Example 1, in which the cyan ink pigment content is lower than the requirements of the present invention, also exhibits low blue saturation, while Comparative Example 2, in which the cyan ink pigment content is higher than the requirements of the present invention, exhibits low red saturation. Comparative Example 3, which does not contain a binder satisfying the requirements of the present invention, exhibits poor abrasion resistance of printed matter. Furthermore, an ink set satisfying the requirements of the present invention suppresses aggregation of pigments in the inks and enhances dispersion stability, thereby enabling a balance between improved ink density (OD) and improved saturation of printed matter.

[0067] The ink set of the present invention has improved saturation of primary and secondary colors, particularly green saturation, and has 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; An ink set comprising a binder having a weight average molecular weight (Mw) of 300,000 to 1,000,000, a dispersion resin, an aqueous solvent, and a cyan ink containing C.I. Pigment Blue 15:3 as a 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 C.I. Pigment Blue 15:3 has a volume average particle diameter of 85 to 100 nm, and its content 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 minimum film-forming temperature of the binder is 25° C. or higher; 2. The ink set according to claim 1, wherein the volume average particle size of the binder is equal to or smaller than the volume average particle size of at least one of C. I. Pigment Yellow 74 and C. I. 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 C.I. Pigment Red 122 and C.I. Pigment Violet 19; 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; The volume average particle size of the solid solution pigment is 90 to 130 nm; 3. The ink set according to claim 1, wherein a ratio of a concentration of the solid solution pigment contained in the magenta ink to a concentration of the pigment contained in the cyan ink is 1.5 or more.

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