inkjet ink

Abstract

To provide an inkjet ink capable of forming images with excellent gloss. [Solution] An inkjet ink comprising a pigment, a pigment dispersant, a binder resin, water, and an organic solvent S, wherein the amount of water is 3.0 to 10.0% by mass relative to the total amount of ink, the pigment dispersant has an acid value of 5 to 25 mg KOH / g and an amine value of 10 to 30 mg KOH / g, and the pigment dispersant dissolves in water and the organic solvent S.

Description

Technical Field

[0001] Embodiments of the present invention relate to inkjet inks.

Background Art

[0002] The inkjet recording method involves ejecting highly fluid inkjet ink as droplets from a fine nozzle and recording an image on a substrate placed opposite the nozzle. In recent years, it has rapidly spread because it enables low-noise and high-speed printing. As inks used in such inkjet recording methods, there are known aqueous inks containing water as the main solvent, ultraviolet curable inks (UV inks) containing a high content of polymerizable monomers as the main component, hot melt inks (solid inks) containing a high content of wax as the main component, and so-called non-aqueous inks containing a non-aqueous solvent as the main solvent. Non-aqueous inks can be classified into solvent inks (solvent-based inks) whose main solvent is a volatile organic solvent and oil-based inks (oil-based inks) whose main solvent is a low-volatile or non-volatile organic solvent. Solvent inks mainly dry on the substrate by evaporation of the organic solvent, while oil-based inks mainly dry by penetration into the substrate.

[0003] As an ink whose main solvent is an organic solvent, Patent Document 1 describes a non-aqueous inkjet ink composition containing (poly)ethylene glycol dialkyl ether and (poly)alkylene glycol monoalkyl ether monoacetate and / or (poly)alkylene glycol diacetate as an ink capable of obtaining a high-gloss printed matter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of the embodiments of the present invention is to provide an inkjet ink capable of forming images with excellent gloss. [Means for solving the problem]

[0006] One embodiment of the present invention relates to an inkjet ink comprising a pigment, a pigment dispersant, a binder resin, water, and an organic solvent S, wherein the water is 3.0 to 10.0% by mass of the total amount of ink, the pigment dispersant has an acid value of 5 to 25 mg KOH / g and an amine value of 10 to 30 mg KOH / g, and the pigment dispersant is soluble in water and the organic solvent S. [Effects of the Invention]

[0007] According to embodiments of the present invention, it is possible to provide an inkjet ink capable of forming images with excellent gloss. [Modes for carrying out the invention]

[0008] The present invention will be described below using embodiments. The examples in the following embodiments are not intended to limit the present invention. In the following description, inkjet ink may be simply referred to as "ink".

[0009] <Inkjet ink> The inkjet ink according to this embodiment comprises a pigment, a pigment dispersant, a binder resin, water, and an organic solvent S, wherein the amount of water is 3.0 to 10.0% by mass of the total amount of ink, and the pigment dispersant has an acid value of 5 to 25 mg KOH / g and an amine value of 10 to 30 mg KOH / g, and the pigment dispersant is soluble in water and the organic solvent S.

[0010] Although not bound by any particular theory, it is presumed that when using the ink of the embodiment, images with excellent gloss can be obtained for the following reasons.

[0011] Factors contributing to obtaining images with excellent gloss include a fine and stable dispersion of pigments, good ink drying properties, and a large dot size that ensures sufficient solid filling. Poor pigment dispersion can lead to pigment aggregation, reducing image smoothness and potentially decreasing gloss. Poor ink drying properties and slow drying can result in uneven drying and mottled patterns, further reducing gloss. Additionally, excessively high ink viscosity or excessive drying can cause the dot size to become too small, resulting in insufficient solid filling and consequently, reduced gloss.

[0012] When an ink contains an organic solvent S and 3.0 to 10.0% by mass of water relative to the total amount of ink, and has an acid value of 5 to 25 mg KOH / g and an amine value of 10 to 30 mg KOH / g, and also contains a pigment dispersant soluble in water and organic solvent S, it tends to exhibit excellent pigment dispersibility and dispersion stability, as described later, and may be able to form images with high smoothness. Furthermore, this ink also tends to have excellent image drying properties. In addition, because the ink viscosity does not tend to become high, it may be possible to achieve appropriate ink dot sizes and proper solid fill. As a result, it is presumed that images with excellent gloss can be obtained.

[0013] Furthermore, when using a pigment dispersant with an acid value of 5-25 mgKOH / g and an amine value of 10-30 mgKOH / g, and which is soluble in water and organic solvent S, excellent storage stability of the ink can be achieved. Although not bound by any particular theory, the reason is presumed to be as follows.

[0014] When the pigment dispersant has an acid value of 5-25 mgKOH / g and an amine value of 10-30 mgKOH / g, and is soluble in water and also in organic solvent S, excellent pigment dispersion stability can be achieved, and the storage stability of the ink can also be improved.

[0015] Dispersion stabilization generally requires that pigment particles be uniformly dispersed in the solvent and that aggregation or sedimentation of pigment particles does not occur over time. Pigment dispersants generally adsorb to the surface of pigment particles and provide electrostatic or steric repulsion to suppress aggregation of pigment particles and ensure uniform dispersion in the solvent.

[0016] When a pigment dispersant has acid and amine values ​​within the above range, is soluble in organic solvent S, and is also soluble in water, the pigment dispersant readily adsorbs to the pigment surface through acid-base and hydrophobic interactions in the organic solvent containing a small amount of water. Furthermore, the molecular chains of the pigment dispersant spread easily in the ink, thereby providing repulsion due to steric hindrance. In addition, the acidic groups contained in the pigment dispersant interact with water to form electrostatic repulsion and a hydration shell, which act as barriers to more effectively suppress aggregation between pigment particles. It is presumed that these effects combined result in excellent pigment dispersion stability and improved ink storage stability.

[0017] Ink may contain pigments as colorants. In addition to pigments, ink may also contain dyes as colorants.

[0018] As the pigment, organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, and lake pigments obtained by dyeing, and inorganic pigments such as carbon black and metal oxides can be used. Examples of azo pigments include soluble azo lake pigments, insoluble azo pigments, and condensed azo pigments. Examples of phthalocyanine pigments include metal phthalocyanine pigments and metal-free phthalocyanine pigments. Examples of polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments, and diketopyrrolopyrrole (DPP). Examples of carbon black include furnace carbon black, lamp black, acetylene black, and channel black. Examples of metal oxides include titanium oxide and zinc oxide. These pigments may be used alone or in combination of two or more.

[0019] From the viewpoints of ejection stability and storage stability, the average particle diameter of the pigment particles in the ink is preferably 1 μm or less, more preferably 500 nm or less, and still more preferably 300 nm or less as the volume-based average value in the particle size distribution measured by the dynamic light scattering method.

[0020] The pigment may be incorporated into the ink as a pigment dispersion. The pigment dispersion may be any dispersion in which the pigment can be dispersed in a solvent and the pigment is in a dispersed state in the ink. For example, a dispersion obtained by dispersing a pigment in a dispersion medium with a pigment dispersant can be used.

[0021] The dispersion form of the pigment may be a so-called capsule pigment in which the pigment is coated with a non-oil-soluble resin or a dispersion in which colored resin particles are dispersed with a pigment dispersant, but a dispersion in which the pigment dispersant is directly adsorbed on the pigment surface and dispersed is preferred.

[0022] As the dye, any dye generally used in the relevant technical field can be arbitrarily used. Since the dye shows affinity for the non-aqueous solvent of the ink, the storage stability becomes better, so it is preferable to use an oil-soluble dye.

[0023] Examples of the oil-soluble dye include azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, phthalocyanine dyes, metal phthalocyanine dyes, etc. These may be used alone or in combination of multiple kinds.

[0024] From the viewpoints of printing density and ink viscosity, the content of the coloring material is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 5 to 10% by mass based on the total amount of the ink.

[0025] In order to stably disperse the pigment in the ink, a pigment dispersant can be used together with the pigment.

[0026] The pigment dispersant preferably has an acid value of 5 to 25 mgKOH / g, an amine value of 10 to 30 mgKOH / g, and is soluble in water and the organic solvent S.

[0027] From the viewpoint of dispersion stabilization, the acid value of the pigment dispersant is preferably 5 mg KOH / g or higher, more preferably 7 mg KOH / g or higher, even more preferably 9 mg KOH / g or higher, and still more preferably 10 mg KOH / g or higher. On the other hand, from the viewpoint of solubility in the solvent and dispersibility, the acid value of the pigment dispersant is preferably 25 mg KOH / g or lower, more preferably 20 mg KOH / g or lower, even more preferably 17 mg KOH / g or lower, and still more preferably 15 mg KOH / g or lower. When the acid value of the pigment dispersant is 25 mg KOH / g or lower, a decrease in solubility in the solvent due to increased aggregation of dispersants and a decrease in dispersibility due to inhibited adsorption to the surface of pigment particles in the case of pigments with acidic surfaces are less likely to occur. The acid value of the pigment dispersant is preferably 5 to 25 mg KOH / g, more preferably 5 to 20 mg KOH / g, even more preferably 7 to 20 mg KOH / g or more, even more preferably 9 to 17 mg KOH / g or more, and even more preferably 10 to 15 mg KOH / g.

[0028] From the viewpoint of dispersion stability, the amine value of the pigment dispersant is preferably 10 mg KOH / g or higher, and more preferably 15 mg KOH / g or higher. The amine value of the pigment dispersant may be, for example, 19 mg KOH / g or higher or 20 mg KOH / g or higher. On the other hand, from the viewpoint of solubility in the solvent and dispersibility, the amine value of the pigment dispersant is preferably 30 mg KOH / g or lower, more preferably 25 mg KOH / g or lower, and may be, for example, 23 mg KOH / g or lower or 20 mg KOH / g or lower. When the amine value is 10 mg KOH / g or higher, the adsorption force to the surface of the pigment particles is good, and good dispersion stability can be obtained. When the amine value of the pigment dispersant is 30 mg KOH / g or lower, a decrease in solubility in the solvent and a decrease in dispersion due to increased aggregation of dispersants are less likely to occur. The amine value of the pigment dispersant is preferably 10 to 30 mg KOH / g, and more preferably 15 to 25 mg KOH / g. The amine value of the pigment dispersant may be, for example, 15-20 mgKOH / g, 19-23 mgKOH / g, or 20-23 mgKOH.

[0029] The acid value of a pigment dispersant is expressed as the number of milligrams (mg) of water-soluble potassium required to neutralize the acidic components contained in 1 g of the sample. The acid value of a pigment dispersant can be determined by potentiometric titration in accordance with JIS K0070:1992.

[0030] The amine value of a pigment dispersant is expressed as the number of milligrams (mg) of potassium hydroxide equivalent to hydrochloric acid or perchloric acid required to neutralize the basic components contained in 1 g of the sample. The amine value of a pigment dispersant can be determined by potentiometric titration in accordance with JIS K7237:1995.

[0031] From the viewpoint of image glossiness and ink storage stability, it is preferable that the pigment dispersant is soluble in water. A pigment dispersant being soluble in water means that when the pigment dispersant and water are mixed to prepare a mixture of 10% by mass of pigment dispersant and 90% by mass of water relative to the total volume of the mixture, the resulting mixture is a transparent solution at 23°C.

[0032] From the viewpoint of image glossiness and ink storage stability, it is preferable that the pigment dispersant dissolves in the organic solvent S. Dissolving the pigment dispersant in the organic solvent S means that when the pigment dispersant and the organic solvent S are mixed to prepare a mixture containing 10% by mass of the pigment dispersant and 90% by mass of the organic solvent S relative to the total volume of the mixture, the resulting mixture is a transparent solution at 23°C.

[0033] When the pigment dispersant is soluble in water and also soluble in the organic solvent S, the viscosity of the pigment dispersion can be lowered, allowing the ink to be adjusted to a viscosity suitable for inkjet ink, and ensuring sufficient solid coverage of the image, thereby improving gloss. Furthermore, the dispersion stability of the pigment and the storage stability of the ink can also be improved.

[0034] As a pigment dispersant, it is preferable to use a polymeric dispersant. The polymeric dispersant may be synthesized or a commercially available product.

[0035] Examples of commercially available pigment dispersants include "DISPERBYK-2013," "DISPERBYK-2012," "BYKJET-9170," "BYKJET-9152," and "BYKJET-9151" from BIC Chemie Japan Co., Ltd. (all are product names). These may be used individually or in combination of two or more.

[0036] The pigment dispersant is preferably included in a mass ratio of 0.2 to 1.0 per unit of pigment. The pigment dispersant content in the total amount of ink is preferably 0.5 to 15% by mass, and more preferably 1 to 5% by mass.

[0037] The ink may contain a binder resin.

[0038] From the viewpoint of forming a uniform ink film and improving the glossiness of the image, and from the viewpoint of improving the adhesion of the image to the substrate, a binder resin that dissolves in the organic solvent S contained in the ink is preferred. From the viewpoint of giving the image water resistance, the binder resin is preferably water-insoluble (does not dissolve in water).

[0039] Examples of binder resins include (meth)acrylic resin, styrene-(meth)acrylic resin, styrene-maleic acid resin, ethylene-(meth)acrylic resin, urethane resin, vinyl chloride resin, vinyl chloride-vinyl acetate resin, polyester resin, polyvinyl alcohol resin, epoxy resin, and polyvinylpyrrolidone resin.

[0040] From the viewpoint of improving the adhesion of the image to the substrate, (meth)acrylic resin is preferred as the binder resin. More preferably, a (meth)acrylic resin that is soluble in the organic solvent S is preferred as the binder resin. When a (meth)acrylic resin is used, the adhesion of the image to plastic substrates such as olefin resins can be improved. In particular, olefin resins tend to have a low affinity for organic solvents in inks, and it can be difficult to obtain good image adhesion, but when a (meth)acrylic resin is used, it is easier to improve the adhesion of the image to the substrate.

[0041] The (meth)acrylic resin may be a resin comprising, for example, at least one unit selected from the group consisting of units derived from (meth)acrylic acid and units derived from (meth)acrylic acid esters. In this disclosure, (meth)acrylic acid means acrylic acid and methacrylic acid collectively, (meth)acrylic acid ester means acrylic acid ester and methacrylic acid ester collectively, and (meth)acrylate means acrylate and methacrylate collectively.

[0042] Examples of (meth)acrylic acid esters include alkyl (meth)acrylates, benzyl (meth)acrylates, and hydroxyalkyl (meth)acrylates. Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having an alkyl group with 1 to 8, 1 to 6, or 1 to 4 carbon atoms, and specifically, examples of these include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0043] The (meth)acrylic resin may be, for example, a polymer of one or more monomers selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters.

[0044] Examples of (meth)acrylic resins include poly(meth)acrylic acid, poly(meth)acrylic acid esters (e.g., methyl poly(meth)acrylate, ethyl poly(meth)acrylate, butyl poly(meth)acrylate, etc.), (meth)acrylic acid ester copolymer resins, (meth)acrylic acid-(meth)acrylic acid ester copolymer resins, etc.

[0045] The (meth)acrylic resin preferably contains units derived from, for example, alkyl (meth)acrylate. The units derived from alkyl (meth)acrylate may be, for example, 50.0% by mass or more, 70.0% by mass or more, or 90.0% by mass or more, relative to the total units of the (meth)acrylic resin.

[0046] Specific examples of (meth)acrylic resins include, for example, polymers of methyl (meth)acrylate, copolymers of methyl (meth)acrylate with at least one selected from the group consisting of (meth)acrylic acid, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and benzyl (meth)acrylate (for example, copolymers of 100 parts by mass of methyl methacrylate with 0.1 to 200 parts by mass, 1 to 180 parts by mass, or 10 to 150 parts by mass of at least one selected from the group consisting of methacrylic acid, butyl methacrylate, and benzyl methacrylate).

[0047] The glass transition temperature (Tg) of the (meth)acrylic resin may be, for example, 60°C or higher, preferably 80°C or higher, and more preferably 100°C or higher, from the viewpoint of improving the adhesion of the image to the substrate. The glass transition temperature of the (meth)acrylic resin may be, for example, 200°C or lower. The glass transition temperature of the (meth)acrylic resin may be, for example, 60-200°C, 80-200°C, or 100-200°C. In this disclosure, the glass transition temperature is an estimated value according to FOX's formula.

[0048] The weight-average molecular weight of the (meth)acrylic resin is preferably 5,000 to 150,000, and more preferably 10,000 to 100,000. From the viewpoint of water resistance and durability, the weight-average molecular weight of the (meth)acrylic resin is preferably 5,000 or more, and more preferably 10,000 or more. From the viewpoint of ink viscosity and discharge properties, the weight-average molecular weight of the (meth)acrylic resin is preferably 150,000 or less, and more preferably 100,000 or less. In this disclosure, the weight-average molecular weight is the value obtained by the GPC method on a standard polystyrene basis.

[0049] As the (meth)acrylic resin, a synthesized resin may be used, or a commercially available resin may be used.

[0050] The method for synthesizing (meth)acrylic resin is not particularly limited. (Meth)acrylic resin can be obtained, for example, by polymerizing one or more radical polymerizable monomers by solution polymerization or the like. For example, at least one monomer selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters can be polymerized.

[0051] The polymerization solvent (reaction solvent) used in solution polymerization is not particularly limited, but it is preferable that it is capable of dissolving the (meth)acrylic resin obtained by polymerization. From the viewpoint of compatibility between the obtained (meth)acrylic resin and the organic solvent in the ink, and thereby preparing a low-viscosity ink, the polymerization solvent may be the organic solvent S or organic solvent A contained in the ink. For example, if the ink contains two or more organic solvents as organic solvent S or organic solvent A, only one of them may be used as the polymerization solvent.

[0052] Polymerization initiators, such as radical polymerization initiators, may be used during the polymerization reaction. As radical polymerization initiators, known radical polymerization initiators such as azo compounds including 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2,4'-dimethylvaleronitrile), and dimethyl 2,2'-azobisisobutyrate, and organic peroxides such as hydroperoxides, dialkylperoxides, peroxyesters, and diallylperoxides can be used. These may be used individually or in combination of two or more.

[0053] As the (meth)acrylic resin, from the viewpoint of good compatibility between the (meth)acrylic resin and the solvent, and thereby the preparation of a low-viscosity ink, an acrylic resin obtained by solution polymerization of a radically polymerizable monomer with a radical polymerization initiator in an organic solvent S or organic solvent A used in the ink is preferred. The (meth)acrylic resin may be, for example, a resin obtained by solution polymerization using only one of two or more organic solvents as the polymerization solvent when the ink contains two or more organic solvents as organic solvent S or organic solvent A.

[0054] Examples of commercially available (meth)acrylic resins include Covestro's "Neocryl B-728" and "Neocryl B-801," and Mitsubishi Chemical Corporation's "Dianal BR-83," "Dianal BR-87," and "Dianal MB-7333" (all are brand names).

[0055] The binder resin may be, for example, 1.0% by mass or more, or 3.0% by mass or more, relative to the total amount of ink. On the other hand, the binder resin may be, for example, 40.0% by mass or less, 30.0% by mass or less, or 20.0% by mass or less, relative to the total amount of ink. The binder resin may be, for example, 1.0 to 40.0% by mass, 1.0 to 30.0% by mass, or 3.0 to 20.0% by mass, relative to the total amount of ink.

[0056] Ink can contain water. While there are no particular restrictions on the type of water used, it is preferable to use water that contains as few ionic components as possible. In particular, from the viewpoint of the storage stability of the ink, it is preferable to use water with a low content of polyvalent metal ions such as calcium. Suitable water options include, for example, deionized water, distilled water, or ultrapure water.

[0057] From the viewpoint of improving image glossiness and reducing image blurring, the amount of water is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, and even more preferably 4.5% by mass or more, relative to the total amount of ink. When the amount of water is 3.0% by mass or more relative to the total amount of ink, the drying properties of the ink are improved, and for example, when printing on roll paper, image transfer during winding after printing can also be suppressed. On the other hand, from the viewpoint of improving image glossiness, improving the storage stability of the ink, and improving the ink discharge properties, the amount of water is preferably 10.0% by mass or less, more preferably 9.0% by mass or less, and even more preferably 8.0% by mass or less, relative to the total amount of ink. Furthermore, when the amount of water is 10.0% by mass or less relative to the total amount of ink, it is possible to prevent an increase in ink viscosity and excessive drying of the ink.

[0058] The amount of water is preferably 3.0 to 10.0% by mass, more preferably 4.0 to 9.0% by mass, and even more preferably 4.5 to 8.0% by mass, relative to the total amount of ink.

[0059] The amount of water in the ink may be the same as the amount of water actively added to the ink. On the other hand, when an organic solvent that has an affinity for water is added to the ink, such an organic solvent may absorb water vapor or other substances contained in the atmosphere, and in such cases, the amount of water added to the ink may not be the same as the amount of water in the ink. The amount of water in the ink may be measured, for example, using the Karl Fischer method.

[0060] The ink may contain an organic solvent S. Examples of organic solvent S include organic solvents with a boiling point of 150°C or higher and less than 200°C (organic solvent A), and other organic solvents. Examples of other organic solvents include organic solvents with a boiling point of less than 150°C and organic solvents with a boiling point of 200°C or higher. Examples of organic solvents with a boiling point of less than 150°C include ethylene glycol monomethyl ether acetate. Examples of organic solvents with a boiling point of 200°C or higher include γ-butyrolactone, 2-pyrrolidone, and γ-hexanolactone. The ink may contain one or more of these other organic solvents.

[0061] The organic solvent (organic solvent A) having a boiling point of 150°C or higher and less than 200°C may be any of the following: ketone-based organic solvents, alcohol-based organic solvents, glycol ether-based organic solvents, acetate-based organic solvents, etc. Organic solvent A may be used alone or in combination of two or more types.

[0062] From the viewpoint of reducing image blurring, the boiling point of organic solvent A is preferably less than 200°C, and more preferably 195°C or lower. On the other hand, from the viewpoint of reducing ejection failures due to nozzle clogging in the inkjet head and ink adhesion near the nozzles, and thereby improving ink ejection performance, the boiling point of organic solvent A is preferably 150°C or higher, more preferably 160°C or higher, and even more preferably 170°C or higher.

[0063] Organic solvent A may contain a water-soluble organic solvent (water-soluble organic solvent B) with a boiling point of 150°C or higher and less than 200°C, but may further contain a non-water-soluble organic solvent with a boiling point of 150°C or higher and less than 200°C.

[0064] As the water-soluble organic solvent, an organic compound that is liquid at room temperature and soluble in water can be used, and it is preferable to use a water-soluble organic solvent that mixes uniformly with the same volume of water at 1 atmosphere and 20°C. Examples of water-soluble organic solvents among organic solvent A with a boiling point of 150°C or higher and less than 200°C include diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol dimethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, diethylene glycol monoethyl ether acetate, 1,2-propanediol, ethyl lactate, ethylene glycol, ethylene glycol monoacetate, etc. These may be used individually or in combination of two or more.

[0065] Examples of non-water-soluble organic solvents among organic solvent A with a boiling point of 150°C or higher and less than 200°C include, for example, ethylene glycol monobutyl ether acetate, ethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol dimethyl ether, propylene glycol 1-monobutyl ether, butyl lactate, hexyl propionate, ethyl 3-ethoxypropionate, and ethyl acetoethyl. Non-water-soluble organic solvents with a boiling point of 150°C or higher and less than 200°C may be used individually or in combination of two or more.

[0066] From the viewpoint of ink storage stability, organic solvent A is preferably an organic solvent containing an ether bond and having a boiling point of 150°C or higher and less than 200°C. Examples of such organic solvents include alkylene glycol monoalkyl ethers with a boiling point of 150°C or higher and less than 200°C, and alkylene glycol dialkyl ethers with a boiling point of 150°C or higher and less than 200°C. An ether bond is a bond between carbon, which has low electronegativity, and oxygen, which has relatively high electronegativity. When an ether bond is present, the reactivity is reduced, and reactions with water and hydrolysis tend to occur less easily. Therefore, it is possible to improve the long-term storage stability of inks that contain a small amount of water.

[0067] From the viewpoint of image drying properties, it is preferable that the organic solvent S contains 90.0% by mass or more of organic solvent A, which has a moderate boiling point of 150°C or more and less than 200°C, relative to the total amount of organic solvent S in the ink.

[0068] When an ink contains 90.0% by mass or more of organic solvent A, which has a moderate boiling point between 150°C and 200°C, relative to the total amount of organic solvent S in the ink, the initial drying properties of the ink are improved, and image blurring can be suppressed. Although not bound by any specific theory, the reason for the improved initial drying properties of the ink is thought to be due to the azeotropic phenomenon between water and the organic solvent. Furthermore, improved drying properties can further enhance the glossiness of the image.

[0069] From the viewpoint of improving ink ejection performance, improving image glossiness, and suppressing image bleeding, the amount of organic solvent A is preferably 90.0% by mass or more, more preferably 95.0% by mass or more, and even more preferably 99.0% by mass or more, relative to the total amount of organic solvent S in the ink. Organic solvent A may be 100% by mass relative to the total amount of organic solvent S in the ink. Organic solvent A may be, for example, 90.0 to 100% by mass, 95.0 to 100% by mass, or 99.0 to 100% by mass relative to the total amount of organic solvent S in the ink.

[0070] The organic solvent S may be, for example, 60% by mass or more, 65% by mass or more, or 70% by mass or more, relative to the total amount of ink. The organic solvent S may be, for example, 95% by mass or less, 90% by mass or less, or 85% by mass or less, relative to the total amount of ink. The organic solvent S may be, for example, 60-95% by mass, 65-90% by mass, or 70-85% by mass, relative to the total amount of ink.

[0071] Ink preferably contains a surfactant. For example, it is preferable for the ink to contain a surfactant in order to improve the wetting and spreading of the ink even on hydrophobic substrate surfaces, increase the drying speed, and form a good image. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants, and nonionic surfactants such as polyoxyethylene derivatives.

[0072] Examples of silicone-based surfactants include polyester-modified silicones and polyether-modified silicones. Examples of commercially available silicone-based surfactants include "BYK-307," "BYK-313," "BYK-330," "BYK-333," "BYK-342," "BYK-370," "BYK-377," "BYK-378," "BYK-3550," "BYK-3750," "BYK-3761," "BYK-3762," "BYK-3764," and "BYK-SILCLEAN 3700" from BIC Chemie Japan Co., Ltd., and "Sylface SAG005," "Sylface SAG008," and "Sylface SAG503A" from Nisshin Chemical Industry Co., Ltd. (all are product names).

[0073] Examples of commercially available fluorine-based surfactants include "BYK-340" from BIC Chemie Japan Co., Ltd., and "Surflon S-241," "Surflon S-242," "Surflon S-242L," "Surflon S-243," "Surflon S-420," and "Surflon S-431" from AGC Inc. (all are product names).

[0074] As the polyoxyethylene derivative, it is preferable to use an acetylene glycol-based surfactant. Examples of commercially available acetylene glycol-based surfactants include, for example, "Surfinol 420," "Surfinol 440," "Surfinol 465," and "Surfinol 485" from Evonik Industries, and "Orfin E-1004" and "Orfin-1010" from Nisshin Chemical Industry Co., Ltd. (all are trade names).

[0075] From the standpoint of continuous ink ejection during printing and image color reproduction, it is preferable that the ink contains a silicone-based surfactant.

[0076] Surfactants may be used individually or in combination of two or more types. The surfactant is preferably present in an amount of 0.05 to 2% by mass, and more preferably 0.1 to 1% by mass, relative to the total amount of ink.

[0077] Depending on the application, the ink may contain various additives. Examples of additives include UV absorbers, light stabilizers, antioxidants, and plasticizers.

[0078] The method for manufacturing ink is not particularly limited, but one method is to mix and stir each component together or separately to produce ink. Specifically, for example, all components can be put together or separately into a disperser such as a bead mill and dispersed, and if desired, the mixture can be passed through a filter such as a membrane filter to produce the ink.

[0079] In the ink manufacturing method, for example, a pigment dispersion may be prepared by first mixing and stirring the pigment with a pigment dispersant and an organic solvent to disperse the pigment.

[0080] The viscosity of an inkjet ink varies depending on the nozzle diameter of the inkjet recording system's ejection head and the ejection environment, but generally, it is preferably 3 to 30 mPa·s at 23°C, more preferably 3 to 15 mPa·s, and even more preferably 4 to 10 mPa·s. In this disclosure, the ink viscosity is a value measured at 23°C. For example, a rheometer MCR302 manufactured by Anton Paar Japan Co., Ltd. can be used as a viscosity measuring device.

[0081] The printing method using inkjet ink is not particularly limited and may be any method, such as piezo, electrostatic, or thermal. When using an inkjet recording device, it is preferable to eject ink according to one embodiment from the inkjet head based on a digital signal and to adhere the ejected ink droplets to the substrate.

[0082] In this embodiment, the substrate is not particularly limited and can be printing paper such as plain paper, coated paper, or specialty paper, cloth, inorganic sheets, films, OHP sheets, or adhesive sheets with an adhesive layer on the back surface using these as substrates. For example, the ink of this embodiment can also be preferably used on plastic substrates such as polyvinyl chloride resin or olefin resin. Examples of olefin resins include polypropylene resin. Such plastic substrates may be absorbent substrates that can absorb the applied ink, such as substrates having an ink-receiving layer, or they may be non-absorbent substrates that do not have an ink-receiving layer. The ink of this embodiment can also be preferably used on substrates that are difficult for ink to penetrate. Furthermore, olefin resins tend to have low affinity for organic solvents in inks, and it may be difficult to obtain good image adhesion to the substrate, but when using the ink of this embodiment, it is possible to obtain good image adhesion even on substrates made of olefin resin. The ink of this embodiment can also be preferably used on synthetic paper made of olefin resin such as polypropylene resin.

[0083] <Manufacturing methods for printed materials> One embodiment of the method for manufacturing a printed material may include applying ink to a substrate by an inkjet method. The ink described in the above embodiment can be used as the ink. The substrate can be any of the substrates described above as substrates that can use the ink described in the above embodiment.

[0084] In the process of applying ink to the substrate, it is preferable that the ink is applied to the substrate by an inkjet method. The inkjet method is not particularly limited and may be any method such as a piezo method, electrostatic method, or thermal method.

[0085] The amount of ink applied to the substrate is 1 to 500 g / m². 2 Preferably, 3-100 g / m 2 More preferably, 5-50 g / m 2 More preferably, 10-30 g / m 2 Most preferable.

[0086] The method for manufacturing printed materials may include steps such as pretreatment and heating.

[0087] This disclosure includes the following embodiments. <1> It comprises a pigment, a pigment dispersant, a binder resin, water, and an organic solvent S. The amount of water is 3.0 to 10.0% by mass relative to the total amount of ink. The aforementioned pigment dispersant has an acid value of 5 to 25 mg KOH / g and an amine value of 10 to 30 mg KOH / g. The pigment dispersant is an inkjet ink that dissolves in water and the organic solvent S. <2> The organic solvent S contains organic solvent A, which has a boiling point of 150°C or higher and less than 200°C, in an amount of 90.0% by mass or more relative to the total amount of the organic solvent S. <1> The inkjet inks listed above. <3> The aforementioned binder resin includes (meth)acrylic resin, <1> or <2> The inkjet inks listed above. <4> The binder resin includes a (meth)acrylic resin having a glass transition temperature (Tg) of 80°C or higher. <1> or <2> The inkjet inks listed above. [Examples]

[0088] The present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples.

[0089] <Manufacturing of pigment dispersions> Each material listed in Table 1 was measured into a beaker in the proportions shown in Table 1, premixed, and then transferred to a plastic container with a lid. Zirconia beads with a diameter of 0.8 mm were added, and the mixture was dispersed for 60 minutes using a rocking mill RM-05 (manufactured by Seiwa Giken Co., Ltd.). The beads were then separated from the dispersion to produce pigment dispersions 1 to 11 with a pigment concentration of 20% by mass.

[0090] Details of the materials listed in Table 1 will be described later.

[0091] [Table 1]

[0092] <Synthesis of binder resin> Binder resins 1 and 2 were manufactured as described below. In the following, the weight-average molecular weight of the manufactured binder resins 1 and 2 was determined by the GPC method on a standard polystyrene basis. A GPC measuring instrument manufactured by Shimadzu Corporation was used for the measurement. The glass transition temperature (Tg) was calculated using the FOX formula.

[0093] [Synthesis of Binder Resin 1] In a 1 L flask, 317.8 g of diethylene glycol diethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.), maintained at 90°C, was mixed with 340.0 g of methyl methacrylate, a radical polymerizable monomer, and 5.1 g of 2,2'-azobis(isobutyronitrile) (AIBN) (manufactured by Tokyo Chemical Industry Co., Ltd.), a polymerization initiator, dissolved in 85.0 g of diethylene glycol diethyl ether. This mixture was added dropwise over 2 hours. After the dropwise addition was complete, 1.1 g of AIBN was added at 30 minutes and 1 hour while maintaining the liquid temperature at 90°C. The reaction was further allowed to proceed at 90°C for 1 hour. The mixture was then diluted with diethylene glycol diethyl ether to obtain a binder resin solution with an active ingredient concentration of 40.0% by mass. The active ingredient concentration in the obtained binder resin solution was 40% by mass. The Tg of binder resin 1 was 105°C, and the weight-average molecular weight was 20,000.

[0094] [Synthesis of Binder Resin 2] In a 1 L flask, 317.3 g of diethylene glycol diethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.), maintained at 90°C, was mixed with 17.0 g of methacrylic acid, 153.0 g of methyl methacrylate, 170.0 g of butyl methacrylate, and 5.1 g of 2,2'-azobis(isobutyronitrile) (AIBN) (manufactured by Tokyo Chemical Industry Co., Ltd.), all radical polymerizable monomers, dissolved in 85.0 g of diethylene glycol diethyl ether. This mixture was added dropwise over 2 hours. After the dropwise addition was complete, 1.1 g of AIBN was added at 30 minutes and 1 hour while maintaining the liquid temperature at 90°C. The reaction was further allowed to proceed at 90°C for 1 hour. The mixture was then diluted with diethylene glycol diethyl ether to obtain a binder resin solution 2 with an active ingredient concentration of 40.0% by mass. The active ingredient concentration in the obtained binder resin solution 2 was 40.0% by mass. The Tg of binder resin 2 was 60°C, and its weight-average molecular weight was 19,000.

[0095] <Ink Manufacturing> Each material listed in Tables 2-5 was weighed out in the proportions shown in Tables 2-5, mixed and stirred using a three-one motor, and then filtered through a 3 μm pore size membrane filter to obtain inks 1-23. Details of the raw materials listed in Tables 2-5 will be described later. Furthermore, Tables 2-4 show the amount of water in the ink, the amount of organic solvent S in the ink, and the amount of organic solvent A with a boiling point between 150°C and 200°C in the ink. These amounts are expressed as a percentage (mass%) of the total ink volume. The amounts of water in the inks listed in Tables 2-5 were measured using the Karl Fischer method. For the measurement, a KF-31 volumetric titration moisture meter manufactured by Nitto Seiko Analytech Co., Ltd. was used.

[0096] [Table 2]

[0097] [Table 3]

[0098] [Table 4]

[0099] [Table 5]

[0100] <Material> Details of the materials listed in Tables 1-5 are shown below.

[0101] (Pigment) Pigment 1: Carbon black, "MOGUL L" (product name), manufactured by Cabot Corporation. Pigment 2: Copper phthalocyanine, "Fastogen Blue 5435K" (product name), manufactured by DIC Corporation.

[0102] (Pigment dispersant) Polymer Dispersant 1: "DISPERBYK-2013" (product name), manufactured by Bic Chemie Japan Co., Ltd., polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 100% by mass, acid value of pigment dispersant 8 mg KOH / g, amine value of pigment dispersant 18 mg KOH / g Polymer Dispersant 2: "DISPERBYK-2012" (product name), manufactured by Bic Chemie Japan Co., Ltd., aqueous solution of polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 40% by mass, acid value of pigment dispersant 10 mg KOH / g, amine value of pigment dispersant 18 mg KOH / g Polymer Dispersant 3: "BYKJET-9170" (product name), manufactured by Bic Chemie Japan Co., Ltd., aqueous solution of polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 40% by mass, acid value of pigment dispersant 18 mg KOH / g, amine value of pigment dispersant 18 mg KOH / g Polymer Dispersant 4: "BYKJET-9151" (product name), manufactured by Bic Chemie Japan Co., Ltd., polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 100% by mass, acid value of pigment dispersant 8 mg KOH / g, amine value of pigment dispersant 17 mg KOH / g Polymer Dispersant 5: "BYKJET-9152" (product name), manufactured by Bic Chemie Japan Co., Ltd., polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 100% by mass, acid value of pigment dispersant 6 mg KOH / g, amine value of pigment dispersant 24 mg KOH / g Polymer Dispersant 6: "Solspers J200" (product name), manufactured by Lubrizol Japan Co., Ltd., polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 100% by mass, acid value of pigment dispersant 10.5 mg KOH / g, amine value of pigment dispersant 33 mg KOH / g Polymer Dispersant 7: "Disparon DA-325" (product name), manufactured by Kusumoto Kasei Co., Ltd., polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 100% by mass, acid value of pigment dispersant 14 mg KOH / g, amine value of pigment dispersant 20 mg KOH / g Polymer Dispersant 8: "Esream AD-3172M" (product name), manufactured by NOF Corporation, polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 100% by mass, acid value of pigment dispersant <0.1 mgKOH / g, amine value of pigment dispersant 37.1 mgKOH / g Polymer Dispersant 9: "Floren GW-1500" (product name), manufactured by Kyoeisha Chemical Co., Ltd., polymer dispersant (pigment dispersant), active ingredient (pigment dispersant) 100% by mass, acid value of pigment dispersant 55 mgKOH / g, amine value of pigment dispersant <0.1 mgKOH / g

[0103] (Pigment dispersion) Pigment dispersions 1-11: Prepared as described above, containing 20% ​​by mass of pigment, 10% by mass of polymer dispersant (pigment dispersant), and 70% by mass of solvent (including components derived from raw materials).

[0104] (Binder resin) Binder resin 1 solution: Prepared as described above, active ingredient ((meth)acrylic resin) 40% by mass, solvent (diethylene glycol diethyl ether) 60% by mass, resin Tg 105℃, resin weight-average molecular weight 20,000 Binder resin 2 solution: Prepared as described above, active ingredient ((meth)acrylic resin) 40% by mass, solvent (diethylene glycol diethyl ether) 60% by mass, resin Tg 60℃, resin weight-average molecular weight 19,000 Binder resin 3: "Hyros-X RS-1190" (product name), manufactured by Seikou PMC Co., Ltd., active ingredient ((meth)acrylic resin) 100% by mass, Tg 73℃ Binder resin 4: "Hyros-X X-1" (product name), manufactured by Seikou PMC Co., Ltd., active ingredient (styrene-(meth)acrylic resin) 100% by mass, Tg 52℃ Binder resin 5: "XIRAN 1000P" (product name), manufactured by Polyscope Polymers BV, active ingredient (styrene-maleic acid resin) 100% by mass, Tg 150℃

[0105] (Organic solvents) Water-soluble organic solvent 1: Diethylene glycol diethyl ether, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 188℃ Water-soluble organic solvent 2:3-methoxy-3-methyl-1-butanol, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 174℃ Water-soluble organic solvent 3: γ-butyrolactone, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 204℃ Water-soluble organic solvent 4:3-methoxy-1-butanol, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 161℃

[0106] Non-water-soluble organic solvent 1: Ethylene glycol monobutyl ether acetate, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 192℃

[0107] (Surfactants) Surfactant: Silicone-based surfactant, "BYK-333" (product name), manufactured by Bic Chemie Japan Co., Ltd.

[0108] <Solubility of pigment dispersants> For inks 1-22, the solubility of their pigment dispersants in water and in the organic solvent S of the ink was evaluated.

[0109] Regarding solubility in water, specifically, a mixture of pigment dispersant and water was prepared by mixing the pigment dispersant with water to create a mixture of 10% by mass of pigment dispersant and 90% by mass of water relative to the total volume of the mixture. The solubility of the resulting mixture at 23°C was visually evaluated. If the mixture was a clear solution, it was judged to be dissolved; if turbidity occurred, it was judged to be undissolved.

[0110] Regarding the solubility of the ink in the organic solvent S, specifically, a mixture of pigment dispersant and organic solvent S was prepared, with a concentration of 10% by mass of pigment dispersant and 90% by mass of organic solvent S relative to the total volume of the mixture. The solubility of the resulting mixture at 23°C was visually evaluated. If the mixture was a clear solution, it was judged to be dissolved; if turbidity occurred, it was judged to be undissolved.

[0111] The results are shown in Tables 2-5. In Tables 2-5, under "Solubility of Pigment Dispersant in Water" and "Solubility of Pigment Dispersant in Organic Solvent S of Ink," A indicates "dissolved" and B indicates "not dissolved."

[0112] <Rating> Printed materials were prepared using the inks manufactured as described above. Evaluations were conducted using the manufactured inks or printed materials. Tables 6-8 show the inks used in Examples 1-14 and Comparative Examples 1-8, and the evaluation results.

[0113] [Production of printed materials] Using inks 1-22 listed in Tables 2-5, printing was performed as described below to obtain printed materials.

[0114] Ink was introduced into the ink path of a commercially available solvent inkjet printer ("ValueJet VJ-628" manufactured by Mutoh Industries, Ltd.), and colorless ink 23 was introduced into the ink paths of colors other than those where ink had been introduced. Subsequently, a solid color image measuring 10 cm vertically x 10 cm horizontally, and an image with single-color text of size 6 to 12 pt were printed on polypropylene synthetic paper ("Yupo High Gloss GAR110" manufactured by Yupo Corporation). The resulting prints were used to evaluate the glossiness of the image, the blurring of the image, and the adhesion of the image to the substrate.

[0115] [Image glossiness] The glossiness of the solid image areas in the obtained printed materials was visually observed and evaluated according to the following evaluation criteria. (Evaluation Criteria) A: Has gloss equal to or greater than that of the substrate. B: The glossiness is slightly inferior to that of the substrate, but there is no problem. C: The gloss is inferior to that of the substrate, which is a problem. D: The glossiness is significantly inferior to that of the substrate.

[0116] [Ink storage stability] Each ink was placed in a sealed container and left at 50°C for 4 weeks. The viscosity change rate of the ink was calculated using the following formula, based on the initial viscosity and the viscosity after 4 weeks, and evaluated according to the following criteria. The ink viscosity was measured at 23°C using a Rheometer MCR302 manufactured by Anton Paar Japan Co., Ltd. Viscosity change rate = [(Viscosity after 4 weeks × 100) / (Initial viscosity)] - 100 (%) (Evaluation Criteria) A: The absolute value of the viscosity change rate is less than 5%. B: The absolute value of the viscosity change rate is 5% or more but less than 10%. C: The absolute value of the viscosity change rate is 10% or more.

[0117] [Image blurring] The blurring of text images in the obtained printed materials was visually observed and evaluated according to the following evaluation criteria. A: Text of any size is clearly visible without blurring. B: The letters are slightly thicker, but all sizes are clearly legible without blurring. C: The letters are thick, and those smaller than 8pt are illegible. D: The letters appear noticeably thicker, and even at 12pt, blurring is noticeable.

[0118] [Image adhesion to substrate] Tape was applied to the solid image area of ​​the obtained printed material, and the image and tape after the tape was removed were observed. The adhesion of the image to the substrate was evaluated according to the evaluation criteria below. (Evaluation Criteria) A: No peeling on the image. B: There is some color transfer to the tape after removal, but no noticeable peeling in the image. C: Some parts of the image are peeling. D: The image in the area where the tape was applied almost completely peels off.

[0119] [Table 6]

[0120] [Table 7]

[0121] [Table 8]

[0122] Examples 1 to 14 showed excellent results in both the evaluation of image glossiness and storage stability.

[0123] In Comparative Examples 1-8, where inks were used that did not satisfy any of the conditions regarding the amount of water in the ink, the specified acid value and amine value, and the solubility of the pigment dispersant in water and organic solvent S, inferior results were shown in the evaluation of glossiness. Furthermore, Comparative Examples 1-4 and 8 also showed inferior results in the evaluation of storage stability.

[0124] In comparative examples 5-7, where inks 19-21 with a low water content were used, the drying properties of the ink decreased, resulting in mottled patterns and reduced gloss. Image blurring also worsened.

[0125] In Comparative Example 8, where ink 22 with a high water content was used, the increased ink viscosity and excessive drying of the ink resulted in smaller dot sizes and poorer solid filling, which is thought to have led to a decrease in glossiness.

[0126] In Comparative Examples 1-4, where inks 11-14 were used in which the pigment dispersant did not meet the specified conditions, it is thought that the gloss decreased because the ink viscosity increased due to aggregation of pigment particles and poor dispersion, resulting in poor filling of solid areas and reduced uniformity of solid areas.

Claims

1. It comprises a pigment, a pigment dispersant, a binder resin, water, and an organic solvent S. The amount of water is 3.0 to 10.0% by mass relative to the total amount of ink. The aforementioned pigment dispersant has an acid value of 5 to 25 mg KOH / g and an amine value of 10 to 30 mg KOH / g. The pigment dispersant is an inkjet ink that dissolves in water and the organic solvent S.

2. The inkjet ink according to claim 1, wherein the organic solvent S contains an organic solvent A having a boiling point of 150°C or higher and less than 200°C in an amount of 90.0% by mass or more relative to the total amount of the organic solvent S.

3. The inkjet ink according to claim 1 or 2, wherein the binder resin comprises a (meth)acrylic resin.

4. The inkjet ink according to claim 1 or 2, wherein the binder resin includes a (meth)acrylic resin having a glass transition temperature (Tg) of 80°C or higher.

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