Composition for aqueous gravure ink

Abstract

To provide a gravure ink composition which can yield a printed material with excellent appearance in gravure printing, while reducing air pollution and operational environmental impact during printing.SOLUTION: An aqueous gravure ink composition comprises a pigment, a water-insoluble polymer, an organic solvent, and water, wherein the organic solvent comprises an organic solvent (A) that dissolves in 100 ml of water at a level of 5 g or more and 15 g or less (measured at 20°C under atmospheric conditions).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based gravure ink composition, more specifically to an ink composition that has little effect on air pollution and the printing environment during printing and can provide printed matter having excellent appearance in gravure printing. [Background technology]

[0002] Gravure printing is a printing method in which ink is transferred to a printing substrate using a gravure plate with cells that receive the ink. In recent years, in order to reduce air pollution and improve the printing environment, there has been a demand for water-based inks for gravure printing, that is, for replacing most of the volatile components in the ink from organic solvents with water. By making the ink water-based, the amount of organic solvents released into the outside environment during printing can be significantly reduced.

[0003] For example, Patent Document 1 discloses an aqueous gravure ink containing a pigment, a polymer, a water-soluble organic solvent containing a glycol ether having a predetermined boiling point, a surfactant containing an acetylene glycol-based surfactant, and water, and describes that by adjusting the amount of the glycol ether, the amount of the water-soluble organic solvent, and the amount of water in the ink, it is possible to obtain an aqueous gravure ink that has a low environmental impact and excellent leveling properties that enable high-resolution printing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-083938 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the water-based gravure ink described in Patent Document 1 can result in printed matter having many pinholes and cissing, as well as uneven shading, which can cause problems with the appearance of the printed matter. Therefore, an object of the present invention is to provide an ink composition that can produce printed matter having excellent appearance in gravure printing while minimizing the impact on air pollution and the printing work environment during printing. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by an aqueous gravure ink composition comprising a pigment, a water-insoluble polymer, an organic solvent, and water, wherein the organic solvent contains organic solvent (A) in an amount that dissolves in 100 ml of water (measured at a temperature of 20°C and under atmospheric pressure) of 5 g or more and 15 g or less.

[0007] That is, the present invention is as follows. [1] A pigment, a water-insoluble polymer, an organic solvent, and water, The aqueous gravure ink composition comprises an organic solvent (A) whose amount dissolved in 100 ml of water (measurement temperature: 20° C., atmospheric pressure condition) is 5 g or more and 15 g or less. [2] The aqueous gravure ink composition according to [1], wherein the organic solvent (A) is at least one selected from the group consisting of glycol monoalkyl ethers and alcohols. [3] The aqueous gravure ink composition according to [1] or [2], wherein the content of the organic solvent in the composition is from 1% by mass to 12% by mass. [4] The aqueous gravure ink composition according to any one of [1] to [3], wherein the organic solvent (A) accounts for 50 mass % or more of the total amount of the organic solvents. [4] The water-based gravure ink composition according to any one of [1] to [4], wherein the content of organic solvents other than the organic solvent (A) in the composition is 1 mass % or less. Effect of the Invention

[0008] According to the present invention, it is possible to provide an ink composition that gives a printed matter having an excellent appearance in gravure printing while minimizing the impact on air pollution and the printing work environment during printing. In addition, it is possible to provide an ink composition that gives a printed matter having excellent adhesion of the ink coating film to the printing substrate (hereinafter, sometimes simply referred to as adhesion). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present invention will be described below, but the present invention is not limited thereto. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less." In addition, "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acrylate" means acrylate or methacrylate. The same applies to terms such as "(meth)acryloxy" and "(meth)acryloyl."

[0010] [Water-based gravure ink composition] The aqueous gravure ink composition described below is a composition for use as an aqueous gravure ink, and the aqueous gravure ink composition may be used as an aqueous gravure ink as is for gravure printing, or may be a composition containing each component at a high concentration so that it can be diluted with a solvent such as water for use in gravure printing. The content of each component in the aqueous gravure ink composition described below indicates the content in the aqueous gravure ink during gravure printing, unless otherwise specified.

[0011] The aqueous gravure ink composition of the present invention (hereinafter, may be simply referred to as "ink composition") is characterized in that it contains a pigment, a water-insoluble polymer, an organic solvent, and water, and the organic solvent contains an organic solvent (A) in an amount that dissolves in 100 ml of water (measurement temperature: 20°C, atmospheric pressure condition) of 5 g or more and 15 g or less.

[0012] [Pigment] The pigment is not particularly limited, and any pigment used in conventional water-based inks can be used. The pigment may be either an inorganic pigment or an organic pigment, but an inorganic pigment is preferred. The pigment may be used alone or in combination of two or more kinds.

[0013] Preferred examples of inorganic pigments include carbon black, titanium dioxide, zinc oxide, magnesium oxide, calcium carbonate, silica, alumina, red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, and ultramarine blue. Preferred examples of the organic pigment include azo pigments, diazo pigments, azo lake pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The pigment may be appropriately selected depending on the desired color, but for example, when a white pigment is used, titanium dioxide is preferred from the viewpoint of high refractive index and excellent hiding power. As the titanium dioxide, known rutile and / or anatase titanium dioxide can be used, more preferably rutile titanium dioxide. As the titanium dioxide, surface-treated titanium dioxide is preferred, and titanium dioxide surface-treated with silica and / or alumina (preferably silica and alumina) is more preferred.

[0014] From the viewpoints of dispersion stability and color development, the average particle size of the pigment is preferably from 20 to 500 nm, more preferably from 100 to 450 nm, and further preferably from 150 to 400 nm.

[0015] The average particle size of the pigment refers to the average particle size in the ink composition of the present invention. The average particle size of the pigment can be measured by a laser diffraction scattering type particle size distribution analyzer or a dynamic light scattering method. For example, the volume-based cumulant average particle size measured by the dynamic light scattering method can be used. However, in cases where it is difficult to measure by the dynamic light scattering method, such as in the case of black pigments, the 50% particle size in the volume-based particle size distribution measured by a laser diffraction scattering type particle size distribution analyzer can be used as the average particle size.

[0016] The form of the pigment is not particularly limited, but it is preferable that the pigment is added as a pigment dispersion stably dispersed in water by a suitable dispersant, and in particular, it is preferable that the pigment is added as a pigment dispersion sufficiently dispersed in water by using an anionic water-soluble polymer as a dispersant, as described below.

[0017] Regarding the content of the pigment, when the pigment is an inorganic pigment, the content in the ink composition is preferably 5 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 35 mass %. When the pigment is an organic pigment, the content in the ink composition is preferably 3 to 30 mass %, more preferably 5 to 20 mass %, and even more preferably 7 to 10 mass %. The content of the pigment is preferably from 30 to 80% by mass, and more preferably from 45 to 70% by mass, of the solid content of the ink composition.

[0018] In this specification, the solid content (non-volatile content) refers to the components excluding the solvent. A known method can be used to calculate the solid content (non-volatile content), and it may be calculated as the mass of the target sample (if the solid content is the ink composition, it is the ink composition) excluding the mass of the volatile components from the total mass according to the following formula 1, or it may be calculated as the solid content (non-volatile content) by weighing 1 g of the target sample and drying it in a hot air dryer at a temperature of 150°C for 20 hours, and the obtained residue is used as the solid content (non-volatile content) according to the following formula 2. Equation 1: [Solid content in sample (mass%)] = ([Total mass of sample - mass of volatile components] ÷ [Total mass of sample]) x 100 Equation 2: [Solid content in sample (mass%)] = ([mass of residue] ÷ [mass of sample (1 g)]) × 100

[0019] [Water-insoluble polymers] The gravure ink composition of the present disclosure contains a binder resin in order to form a uniform and smooth coating film on a printing substrate and to ensure sufficient fixation. In the present invention, a water-insoluble polymer is used as the binder resin, so that the viscosity of the ink composition can be easily adjusted to a range appropriate for use as an ink for gravure printing.

[0020] In this specification, the term "water-insoluble polymer" refers to a molecule that dissolves in an amount of less than 10 g in 100 mL of water at 25° C. and has a number average molecular weight of at least 1000. The number average molecular weight and the weight average molecular weight described below can be calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC).

[0021] The weight average molecular weight of the water-insoluble polymer is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more, from the viewpoint of further improving the blocking resistance of the ink, adhesion to the substrate, etc. The upper limit of the weight average molecular weight of the polymer is not particularly limited, because when the polymer has a crosslinked structure, it is difficult to measure the weight average molecular weight.

[0022] The water-insoluble polymer is preferably present in a localized state (particularly in a dispersed state) in the ink composition, and more preferably present as emulsion particles. The emulsion particles may be single-layer emulsion particles or may be emulsion particles having multiple layers (e.g., having a core-shell structure). The water-insoluble polymer may be emulsion particles in which a polymer for increasing the dispersion stability of the emulsion particles (hereinafter, sometimes referred to as a particle-affinity polymer) is attached (e.g., oriented) around a single-layer or multiple-layer emulsion particle (hereinafter, sometimes referred to as a core particle) in a state in which it is difficult to separate in the ink composition.

[0023] The average particle size of the emulsion particles is preferably 20 to 400 nm, more preferably 30 to 300 nm, and even more preferably 40 to 200 nm. By adjusting the average particle size of the emulsion particles to the above range, it becomes easy to blend the emulsion particles at a high concentration while maintaining the viscosity of the ink composition in an appropriate range. The average particle size of the emulsion particles may be the volume-based cumulant average particle size measured by a dynamic light scattering method as shown in the examples described later.

[0024] In order to further increase the dispersion stability of the water-insoluble polymer (preferably emulsion particles) in the ink composition, the water-insoluble polymer preferably has an acid group. Examples of the acid group include a carboxy group and a sulfo group, and among these, the carboxy group is preferred.

[0025] From the viewpoint of further enhancing the above-mentioned effect of improving dispersion stability, it is preferable that the acid group is present in the polymer constituting the surface of the water-insoluble polymer. For example, when the water-insoluble polymer is an emulsion particle, if the emulsion particle is a single layer, it is preferable that the polymer constituting the emulsion particle has an acid group. If the emulsion particle has a multilayer structure, it is preferable that the polymer constituting the outermost layer has an acid group. If the emulsion particle is an emulsion particle in which a particle-affinity polymer is oriented around a central particle, it is preferable that the particle-affinity polymer has an acid group.

[0026] The amount of acid groups in the water-insoluble polymer is preferably such that the acid value of the water-insoluble polymer is 10 to 150 mgKOH / g, more preferably 30 to 100 mgKOH / g. By adjusting the acid value to a predetermined value or more, the dispersion stability of the water-insoluble polymer can be further improved, and by adjusting the acid value to a predetermined value or less, the storage stability of the resulting ink composition can be further improved.

[0027] The acid value of a water-insoluble polymer indicates the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of the water-insoluble polymer. It can be calculated by a measurement method conforming to JIS K 5601-2-1 using a dried water-insoluble polymer, or it can be calculated from the charged amounts of the monomer components constituting the water-insoluble polymer, that is, by measuring the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of the monomer components charged to synthesize the water-insoluble polymer.

[0028] The glass transition temperature (Tg) of the water-insoluble polymer is not particularly limited, but is preferably 5 to 80° C., more preferably 10 to 70° C., and even more preferably 15 to 60° C. By adjusting the Tg of the water-insoluble polymer to a predetermined temperature or higher, it is possible to suppress the occurrence of tack in the coating film formed from the ink composition, and by adjusting the Tg of the water-insoluble polymer to a predetermined temperature or lower, it is possible to further improve the film-forming properties of the ink coating film.

[0029] The Tg (°C) can be measured by differential scanning calorimetry (AST D3418-08). When the monomer components used in the synthesis of the water-insoluble polymer are known, the Tg can be calculated from the Fox equation shown in the following formula (1). A It may be calculated from (K).

[0030]

number

[0031] The water-insoluble polymer is not particularly limited as long as it has water-insoluble properties, and examples thereof include acrylic resins, styrene resins, polyurethane resins, polyester resins, polyolefin resins such as polyethylene resins and polypropylene resins, epoxy resins, polyvinyl chloride resins, polyvinylidene chloride resins, polyvinyl fluoride resins, polyvinylidene fluoride resins, and other polyhalogenated vinyl resins. From the viewpoint of improving print density, acrylic resins, polyurethane resins, and polyester resins are preferred. Also, from the viewpoint of improving the appearance of the resulting printed matter, acrylic resins are preferred. The water-insoluble polymers may be used alone or in combination of two or more.

[0032] The acrylic resin is preferably a resin containing structural units derived from (meth)acrylic monomers such as (meth)acrylic acid and (meth)acrylic acid esters as a main component. In this specification, "containing structural units derived from (meth)acrylic monomers as a main component" means containing 50% by mass or more of structural units derived from (meth)acrylic monomers such as (meth)acrylic acid and (meth)acrylic acid esters. The acrylic resin may have one or more structural units derived from (meth)acrylic monomers. The content of structural units derived from (meth)acrylic monomers in the acrylic resin is preferably 50 to 100% by mass, more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0033] Examples of the (meth)acrylic acid ester include a chain alkyl (meth)acrylic acid ester, a (meth)acrylic acid ester having an alicyclic hydrocarbon group, and a (meth)acrylic acid ester having an aromatic hydrocarbon group.

[0034] Examples of the (meth)acrylic acid chain alkyl ester include (meth)acrylic acid C esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, and lauryl (meth)acrylate. 1-18 Linear alkyl ester (preferably (meth)acrylic acid C 1-5 Linear alkyl esters; (meth)acrylic acid C such as isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, neopentyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. 3-18 Branched alkyl ester (preferably (meth)acrylic acid C 3-10 The chain alkyl group constituting the chain alkyl ester of (meth)acrylic acid may be selected from the group consisting of a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, a hydroxyl group, an alkoxy group (preferably C 1-4 The aryl group may have one or more substituents such as an alkoxy group or an amino group.

[0035] Examples of the (meth)acrylic acid ester having an alicyclic hydrocarbon group include (meth)acrylic acid C esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and t-butylcyclohexyl (meth)acrylate. 3-18 Cycloalkyl esters include isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. Among these, (meth)acrylic acid C 5-10 Cycloalkyl esters and isobornyl (meth)acrylate are preferred. The alicyclic hydrocarbon group constituting the (meth)acrylic acid ester having an alicyclic hydrocarbon group is preferably a halogen atom such as a fluorine atom, a chlorine atom or a bromine atom, a hydroxyl group, an alkoxy group (preferably C 1-4 The aryl group may have one or more substituents such as an alkoxy group or an amino group.

[0036] Examples of the (meth)acrylic acid ester having an aromatic hydrocarbon group include (meth)acrylic acid C esters such as phenyl (meth)acrylate, 4-t-butylphenyl (meth)acrylate, and naphthyl (meth)acrylate. 6-18 Aryl; (meth)acrylic acid C such as benzyl (meth)acrylate and phenylethyl (meth)acrylate 7-18 The aromatic hydrocarbon group constituting the (meth)acrylic acid ester having an aromatic hydrocarbon group may be a halogen atom such as a fluorine atom, a chlorine atom, or a bromine atom, a hydroxyl group, an alkoxy group (preferably C 1-4 The aryl group may have one or more substituents such as an alkoxy group or an amino group.

[0037] The acrylic resin preferably contains a structural unit derived from (meth)acrylic acid and a structural unit derived from a (meth)acrylic acid ester, and more preferably contains a structural unit derived from (meth)acrylic acid and a structural unit derived from a (meth)acrylic acid chain alkyl ester and / or a (meth)acrylic acid ester having an alicyclic hydrocarbon group; 1-5 Linear alkyl ester, (meth)acrylic acid C 3-10 Branched alkyl ester, (meth)acrylic acid C 5-10 It is more preferable that the copolymer contains a structural unit derived from at least one (meth)acrylic acid ester selected from the group consisting of cycloalkyl ester and isobornyl (meth)acrylate.

[0038] The acrylic resin may have a structural unit derived from a monomer other than the (meth)acrylic monomer (hereinafter, other monomer (1)). Examples of the other monomer (1) include styrene-based monomers such as styrene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, vinyltoluene, methoxystyrene, and divinylbenzene; vinyl-based monomers such as vinyl acetate, vinyl chloride, and vinyl benzoate; and olefin-based monomers such as ethylene and propylene. Among these, styrene-based monomers are preferred, and styrene is more preferred.

[0039] The acrylic resin may be appropriately synthesized or may be a commercially available product. The method of synthesizing the acrylic resin is not particularly limited, and a conventionally known method can be adopted. For example, when synthesizing emulsion particles made of an acrylic resin, the above-mentioned monomer components can be emulsion-polymerized to obtain the emulsion particles. In addition, when synthesizing emulsion particles made of an acrylic resin in which a particle-affinity polymer is oriented around a central particle, a monomer constituting the particle-affinity polymer is first polymerized by emulsion polymerization or the like to obtain a particle-affinity polymer, and then a basic compound is added to dissolve the obtained particle-affinity polymer, and the monomer constituting the central particle is polymerized in the presence of the dissolved particle-affinity polymer to obtain the emulsion particles. The acid value of the particle-affinity polymer may be appropriately set from the viewpoint of the dispersion stability and viscosity of the entire emulsion particle containing the polymer, and it is preferable to include the polymer in an amount of preferably 30 to 300 mgKOH / g, more preferably 50 to 200 mgKOH / g, as an example.

[0040] Examples of the commercially available products include the Joncryl series (manufactured by BASF), the Boncoat series (manufactured by DIC), the Polysol series (manufactured by Showa Denko KK), the Cybinol series (manufactured by Saiden Co., Ltd.), and the SE series (manufactured by Taisei Fine Chemical Co., Ltd.).

[0041] The styrene-based resin is preferably a resin containing a structural unit derived from a styrene-based monomer as a main component. In this specification, "containing a structural unit derived from a styrene-based monomer as a main component" means containing 50% by mass or more of a structural unit derived from a styrene-based monomer. The content of the structural unit derived from a styrene-based monomer in the styrene-based resin is preferably 50 to 100% by mass, more preferably 60% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more. The styrene-based monomer may be the same monomer as the styrene-based monomer exemplified as the other monomer (1). Among them, styrene and divinylbenzene are preferable, and styrene is more preferable. The styrene-based resin may contain one or more structural units derived from a styrene-based monomer.

[0042] The styrene-based resin may have a structural unit derived from a monomer other than the styrene-based monomer (hereinafter, other monomer (2)). Examples of the other monomer (2) include unsaturated monocarboxylic acids such as cinnamic acid, crotonic acid, and (meth)acrylic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; monoesters of unsaturated dicarboxylic acids such as maleic acid monomethyl ester, maleic acid monobutyl ester, itaconic acid monomethyl ester, and itaconic acid monobutyl ester; anhydrides of unsaturated dicarboxylic acids such as maleic anhydride; (meth)acrylic acid esters; vinyl monomers; and olefin monomers. Examples of (meth)acrylic acid esters, vinyl monomers, and olefin monomers are the same as those of the monomers in the acrylic resin.

[0043] The polyurethane resin is not particularly limited as long as it has a urethane bond in the main chain and is water-insoluble. For example, commercially available products include U-coat series (manufactured by Sanyo Chemical Industries, Ltd.), Permalin series (manufactured by Sanyo Chemical Industries, Ltd.), Superflex series (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), ETERNACOLL UW series (manufactured by UBE Co., Ltd.), etc.

[0044] The polyester resin is not particularly limited as long as it has an ester bond in the main chain and is water-insoluble. For example, commercially available products include Vylonal series (manufactured by Toyobo Co., Ltd.), Nichigo Polyester series (manufactured by Mitsubishi Chemical Corporation), and Elitel series (manufactured by Unitika Co., Ltd.).

[0045] The polyolefin resin includes a resin containing a structural unit derived from an olefin monomer such as ethylene or propylene as a main component, such as a polyethylene resin, a polypropylene resin, or an ethylene-propylene copolymer resin. The polyolefin resin contains a structural unit derived from an olefin monomer in an amount of preferably 50 to 100% by mass, more preferably 60% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more. Examples of commercially available products include the Sumifit series (manufactured by Sumitomo Chemical Co., Ltd.) and the Auroren series (manufactured by Nippon Paper Industries Co., Ltd.).

[0046] Examples of the epoxy resin include homoradical polymers of radically polymerizable monomers containing an epoxy group (e.g., 3,4-epoxycyclohexylmethyl(meth)acrylate, glycidyl(meth)acrylate, etc.), copolymers of the monomers with other radically polymerizable monomers (e.g., (meth)acrylic acid, (meth)acrylic acid esters, styrene-based monomers, vinyl-based monomers, olefin-based monomers, etc.), and conventionally known epoxy resins having at least one epoxy group in one molecule, such as bisphenol-type epoxy resins, novolac-type epoxy resins, ε-caprolactam-modified bisphenol-type epoxy resins, and polyvinylcyclohexene diepoxide. In addition, such epoxy resins may be modified with polycarboxylic acids, such as polycarboxylic acid resins (e.g., the acrylic resins having structural units derived from (meth)acrylic acid, polyester-based resins having multiple carbonyl groups, etc.) and polycarboxylic acid compounds (e.g., adipic acid, sebacic acid, phthalic acid, etc.).

[0047] The polyvinyl halide resin includes polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, etc., which contain 20% by mass or more of structural units derived from vinyl halide monomers such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc. The polyvinyl halide resin preferably contains 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more of structural units derived from vinyl halide monomers.

[0048] The polyvinyl halide resin may have a structural unit derived from a monomer other than the vinyl halide monomer (hereinafter, other monomer (3)). Examples of the other monomer (3) include unsaturated monocarboxylic acids such as cinnamic acid, crotonic acid, and (meth)acrylic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; monoesters of unsaturated dicarboxylic acids such as maleic acid monomethyl ester, maleic acid monobutyl ester, itaconic acid monomethyl ester, and itaconic acid monobutyl ester; anhydrides of unsaturated dicarboxylic acids such as maleic anhydride; (meth)acrylic acid esters; styrene-based monomers; and olefin-based monomers. Examples of (meth)acrylic acid esters, styrene-based monomers, and olefin-based monomers are the same as those of the monomers described in other monomers (1) and (2). In addition, in this specification, a resin containing 50% by mass or more of structural units derived from a (meth)acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester, or a resin containing 50% by mass or more of structural units derived from a styrene monomer, but containing 20% ​​by mass or more of structural units derived from a halogenated vinyl monomer, is treated as a polyhalogenated vinyl resin.

[0049] As the polyvinyl halide resin, a commercially available product may be used, and examples of the commercially available product include the Vinyblan series (manufactured by Nissin Chemical Industry Co., Ltd.).

[0050] The content of the water-insoluble polymer in the ink composition is preferably from 1 to 40% by mass, more preferably from 5 to 30% by mass, and even more preferably from 10 to 20% by mass. The content of the water-insoluble polymer is preferably from 5 to 60% by mass, more preferably from 15 to 50% by mass, and even more preferably from 20 to 40% by mass, based on the solid content of the ink composition.

[0051] [water] The ink composition of the present invention contains water as a solvent. The content of water in the ink composition is not particularly limited, but is, for example, 20 to 80% by mass, preferably 35 to 70% by mass, and more preferably 45 to 60% by mass.

[0052] [Organic solvents] The ink composition contains an organic solvent as well as water as a solvent. In general, in an aqueous ink composition, a pigment in a dispersed state, a water-insoluble polymer, and an organic solvent coexist in water, so it is necessary to select an appropriate type of organic solvent in consideration of the storage stability of the ink composition and the compatibility during printing (film formation) in a comprehensive manner.

[0053] The inventors have focused on the solubility of organic solvents in water and found that an organic solvent (A) having an amount dissolved in 100 ml of water (measured at 20° C. under atmospheric pressure conditions; hereinafter, sometimes referred to as solubility in water) of 5 g to 15 g is suitable for the present invention. The reason is not clear, but is presumed as follows. That is, it is believed that a part of the organic solvent (A) having a solubility in water of 5 to 15 g is miscible with water to reduce the surface tension of the liquid phase components of the ink composition, forming a uniform and smooth coating film without uneven shading on the printing substrate, and suppressing coating defects such as pinholes. In addition, it is believed that an organic solvent with a relatively low solubility dissolves in solid phase components such as water-insoluble polymers and acts like a plasticizer, but by using an organic solvent (A) having a specific solubility in water, the distribution of the organic solvent into solid and liquid is balanced, the solid phase components can be appropriately plasticized during printing (film formation), and the film formability is enhanced, resulting in a good appearance of the resulting printed matter.

[0054] Furthermore, when an aqueous ink is used in gravure printing, the high surface tension of water can result in insufficient transfer of the ink from the gravure plate to the printing substrate. In contrast, the present invention is preferable in that the use of the organic solvent (A) reduces the surface tension of the liquid phase components of the ink composition and adjusts the balance of distribution between solid and liquid, thereby improving the transferability of the ink.

[0055] In addition, the use of an organic solvent (A) having a specific solubility in water is also preferable in that it enables the formation of a uniform coating film with fewer defects for the reasons mentioned above, and therefore improves the adhesion of the ink coating film to the printing substrate.

[0056] As a specific organic solvent (A), an appropriate one may be selected according to the type of pigment, water-insoluble polymer, etc., to be blended, so long as it is an organic solvent having a solubility in water of 5 g or more and 15 g or less. Examples of the organic solvent (A) include glycol monoether solvents (A) such as propylene glycol monobutyl ether and dipropylene glycol monobutyl ether having a solubility in water of 5 to 15 g; alcohol solvents (A) such as 1-butanol and t-amyl alcohol having a solubility in water of 5 to 15 g; ester solvents (A) such as ethyl acetate, dimethyl succinate, and propylene glycol diacetate having a solubility in water of 5 to 15 g; and the like. The organic solvent (A) may be used alone or in combination of two or more kinds.

[0057] From the viewpoint of air pollution and the influence on the printing work environment, the organic solvent (A) is preferably a glycol monoether solvent (A), an alcohol solvent (A), or an ester solvent (A), and more preferably a glycol monoalkyl ether (e.g., propylene glycol monobutyl ether, dipropylene glycol monobutyl ether), an alcohol (e.g., 1-butanol, t-amyl alcohol), an alkyl carboxylate (e.g., ethyl acetate, dimethyl succinate), or a glycol diacetate (e.g., propylene glycol diacetate). Among these, from the viewpoint of further improving the appearance and adhesion, the glycol monoether solvent (A) or the alcohol solvent (A) is preferred, and the glycol monoalkyl ether or the alcohol is more preferred.

[0058] Furthermore, the ink composition may contain an organic solvent other than the organic solvent (A) (hereinafter, may be referred to as organic solvent (B)). Examples of the organic solvent (B) include glycol solvents (B), glycol monoether solvents (B), glycol diether solvents (B), alcohol solvents (B), ester solvents (B), and ketone solvents (B) other than the organic solvent (A). Specifically, glycol solvents (B) such as ethylene glycol, diethylene glycol, and propylene glycol, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monoisobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monoisobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ... Examples of the organic solvent include glycol monoether solvents (B) such as propylene glycol monoethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monopropyl ether, and tripropylene glycol monobutyl ether; glycol diether solvents (B) such as ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether; alcohol solvents (B) such as isopropyl alcohol; ester solvents (B) such as dipropylene glycol methyl ether acetate; ketone solvents (B) such as methyl isobutyl ketone and diacetone alcohol; and the like. The organic solvent (B) may be used alone or in combination of two or more.

[0059] The content of the organic solvent in the ink composition is preferably 1 to 12 mass %, more preferably 3 to 10 mass %, and even more preferably 5 to 8 mass %, from the viewpoint of improving the image quality of printed matter while reducing the impact on air pollution and the printing work environment. The content of the organic solvent in the total amount of water and the organic solvent is preferably from 1 to 30 mass %, more preferably from 3 to 20 mass %, and further preferably from 5 to 15 mass %.

[0060] In order to improve the adhesion, transferability, and appearance of the resulting printed matter, it is preferable that the organic solvent (A) accounts for a certain or higher proportion of the total amount of organic solvents contained in the ink composition. The content of the organic solvent (A) in the organic solvent is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 85% by mass or more, and may be 100% by mass.

[0061] In order to improve the appearance of the resulting printed matter, the content of the organic solvent (B) in the ink composition is preferably 5 mass % or less, more preferably 3 mass % or less, and even more preferably 1 mass % or less, and it is particularly preferable that the ink composition does not contain any organic solvent (B).

[0062] The total content of the pigment, water-insoluble polymer, water, and organic solvent in the ink composition of the present invention (100% by mass) is, for example, 75% by mass or more, preferably 85% by mass or more, and more preferably 93% by mass or more, and may be 100% by mass or 99% by mass or less.

[0063] [Water-soluble polymer] The ink composition of the present invention may further contain a water-soluble polymer. In this specification, the term "water-soluble polymer" refers to a molecule that dissolves in an amount of 10 g or more in 100 mL of water at 25° C. and has a number average molecular weight of 1,000 or more.

[0064] Furthermore, in this specification, the water-soluble polymer does not include a surfactant, the definition of which will be given later.

[0065] Examples of the water-soluble polymer include a nonionic water-soluble polymer, an anionic water-soluble polymer, and a cationic water-soluble polymer. It is preferable that the water-soluble polymer contains at least an anionic water-soluble polymer, and it is more preferable that the water-soluble polymer contains an anionic water-soluble polymer and a nonionic water-soluble polymer. The total content of the anionic water-soluble polymer and the nonionic water-soluble polymer relative to 100 parts by mass of the pigment and the water-insoluble polymer is preferably 1 to 30 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 8 to 15 parts by mass. By adjusting the total content of the anionic water-soluble polymer and the nonionic water-soluble polymer to the above range, the appearance of the obtained printed matter can be made better.

[0066] (Anionic water-soluble polymer) The ink composition preferably contains an anionic water-soluble polymer for stabilizing the dispersion of the pigment.

[0067] An anionic water-soluble polymer refers to a water-soluble polymer obtained by (co)polymerizing a monomer (hereinafter, sometimes referred to as an anionic monomer) having a functional group that ionizes and becomes negatively charged when dissolved in water. That is, an anionic water-soluble polymer is a water-soluble polymer containing a structural unit derived from an anionic monomer. An anionic monomer may be used alone (i.e., an anionic water-soluble polymer may be an anionic homopolymer), or may be used in combination of two or more kinds (i.e., an anionic water-soluble polymer may be an anionic copolymer). When dissolving the anionic water-soluble polymer, a base may be added to neutralize it as necessary, and crushing, stirring, heating, etc. may be performed.

[0068] The content of structural units derived from anionic monomers in the anionic water-soluble polymer is, for example, 30 to 100% by mass, preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0069] Examples of functional groups that ionize and become negatively charged when dissolved in water (hereinafter, anionic groups) include acid groups such as a sulfo group and a carboxy group; salts of these acid groups such as alkali metal salts of these acid groups (e.g., sodium salts and potassium salts), ammonium salts of these acid groups, and amine salts of these acid groups (e.g., triethylamine salts and monomethanolamine salts); and the like, with the carboxy group and salts of the carboxy group being preferred.

[0070] Examples of the anionic monomer include unsaturated monocarboxylic acids such as (meth)acrylic acid, cinnamic acid, and crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; monoesters of unsaturated dicarboxylic acids such as maleic acid monomethyl ester, maleic acid monobutyl ester, itaconic acid monomethyl ester, and itaconic acid monobutyl ester; anhydrides of unsaturated dicarboxylic acids such as maleic anhydride; 2-acryloyloxyethyl succinic acid; 2-acryloyloxyethyl phthalic acid; 2-acryloyloxyethyl hexahydrophthalic acid; and salts thereof such as alkali metal salts, ammonium salts, and amine salts. Among these, unsaturated monocarboxylic acids and salts of unsaturated monocarboxylic acids are preferred, and (meth)acrylic acid and salts of (meth)acrylic acid are more preferred.

[0071] In addition, a monomer that does not have a functional group that ionizes when dissolved in water (hereinafter, sometimes referred to as a nonionic monomer) may be copolymerized together with the anionic monomer. That is, the anionic water-soluble polymer may be a water-soluble polymer that contains a structural unit derived from a nonionic monomer as well as a structural unit derived from an anionic monomer.

[0072] Examples of the nonionic monomer include olefin monomers such as ethylene, propylene, and butadiene; styrene monomers (examples are the same as the above-mentioned styrene monomers); alkylene oxide monomers having 2 to 10 carbon atoms such as ethylene oxide, propylene oxide, and butylene oxide; vinyl lactam monomers such as N-vinylpyrrolidone, N-methylvinylpyrrolidone, N-vinylpiperidone, and N-vinylcaprolactam; (meth)acrylic acid esters (examples are the same as the above-mentioned (meth)acrylic acid esters); vinyl carboxylate monomers such as vinyl acetate, vinyl propionate, and vinyl butyrate; vinyl ether monomers such as methyl vinyl ether; oxazoline monomers such as 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, and 2-propyl-2-oxazoline; and N-vinyl amides such as N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylformamide, and N-vinyl-N-methylacetamide. As the nonionic monomer, a styrene-based monomer is preferable, and styrene is more preferable.

[0073] The polymer obtained by polymerizing the anionic monomer and / or the nonionic monomer used as required may be chemically modified (saponified, acetalized, etc.).

[0074] In order to fully function as a pigment dispersant, the anionic water-soluble polymer preferably has a salt of an acid group, i.e., preferably contains a structural unit derived from a monomer having a salt of an acid group. The structural unit derived from a monomer having a salt of an acid group may be introduced by (co)polymerizing a monomer having a salt of an acid group (e.g., a salt of an unsaturated monocarboxylic acid, a salt of an unsaturated dicarboxylic acid, a salt of a monoester of an unsaturated dicarboxylic acid, etc.), or may be introduced by neutralizing a polymer obtained by (co)polymerizing a monomer having an acid group (e.g., an unsaturated monocarboxylic acid, an unsaturated dicarboxylic acid, a monoester of an unsaturated dicarboxylic acid, etc.) with a base. The base is not particularly limited, but includes ammonia; mono-, di-, or tri-C such as trimethylamine and triethylamine. 1-3 Alkylamines; mono-, di-, or tri-C alkylamines such as monoethanolamine and diethanolamine1-3 Examples of the suitable additives include alcohol amines, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, and alkali metal hydrogen carbonates such as sodium hydrogen carbonate. From the viewpoint of further improving the storage stability of the ink composition and the drying properties after printing, it is preferable to use ammonia, triethylamine, and monomethanolamine, that is, it is preferable that the anionic water-soluble polymer has at least one selected from the group consisting of a structural unit derived from a monomer having an ammonium salt of an acid group, a structural unit derived from a monomer having a triethylamine salt of an acid group, and a structural unit derived from a monomer having a monomethanolamine salt of an acid group.

[0075] Of 100 mol % of anionic groups possessed by the anionic water-soluble polymer, 50 to 100 mol % is preferably a salt of an acid group, more preferably 70 mol % or more is a salt of an acid group, and even more preferably 90 mol % or more is a salt of an acid group.

[0076] When a base is used to introduce a structural unit derived from a monomer having a salt of an acid group, the amount of the base added relative to 100 mol % of acid groups in a polymer obtained by (co)polymerizing a monomer having an acid group is preferably 50 to 150 mol %, more preferably 70 to 130 mol %, and even more preferably 90 to 110 mol %.

[0077] The weight average molecular weight of the anionic water-soluble polymer is preferably 3,000 to 70,000, more preferably 5,000 to 50,000, and even more preferably 10,000 to 30,000, from the viewpoints of providing good pigment dispersibility and stability and an appropriate viscosity for a gravure ink composition.

[0078] From the viewpoint of good pigment dispersibility and prevention of pigment aggregation, the acid value of the anionic water-soluble polymer is preferably 100 to 400 mgKOH / g, more preferably 150 to 350 mgKOH / g, and further preferably 200 to 300 mgKOH / g. The acid value of the anionic water-soluble polymer can be measured in the same manner as the acid value of the water-insoluble polymer.

[0079] The anionic water-soluble polymer may be used alone or in combination of two or more kinds.

[0080] The content of the anionic water-soluble polymer may be appropriately adjusted depending on the type of pigment used. For example, when an inorganic pigment is used as the pigment, the content of the anionic water-soluble polymer is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 16 parts by mass, and even more preferably 0.5 to 13 parts by mass, and may be 0.1 to 10 parts by mass, 0.3 to 7 parts by mass, or 0.5 to 5 parts by mass, relative to 100 parts by mass of the pigment. When an organic pigment is used as the pigment, the content of the anionic water-soluble polymer is preferably 0.5 to 100 parts by mass, more preferably 1 to 50 parts by mass, and even more preferably 2 to 30 parts by mass, relative to 100 parts by mass of the pigment. By setting the content of the anionic water-soluble polymer relative to the pigment to a predetermined value or more, the pigment dispersibility can be further improved, and by setting the content of the anionic water-soluble polymer relative to the pigment to a predetermined value or less, the storage stability of the ink composition can be further improved.

[0081] (Nonionic water-soluble polymer) The ink composition of the present disclosure may contain a nonionic water-soluble polymer. By containing a nonionic water-soluble polymer, a uniform and smooth coating film with less unevenness in shading can be formed on a printing substrate, coating film defects such as pinholes can be further suppressed, and sufficient transferability can be provided in gravure printing. In addition, the storage stability of the ink composition can be improved.

[0082] Here, the nonionic water-soluble polymer refers to a water-soluble polymer obtained by polymerizing a monomer (nonionic monomer) that does not have a functional group that ionizes when dissolved in water. That is, the nonionic water-soluble polymer is a water-soluble polymer consisting of a structural unit derived from a nonionic monomer. The nonionic monomer may be used alone (i.e., the nonionic water-soluble polymer may be a nonionic homopolymer), or may be used in combination of two or more kinds (i.e., the nonionic water-soluble polymer may be a nonionic copolymer). When dissolving, crushing, stirring, heating, etc. may be performed as necessary.

[0083] Examples of the nonionic monomer include the monomers exemplified as the nonionic monomers described above. The polymer obtained by polymerizing the nonionic monomer may be chemically modified (saponified, acetalized, etc.). For example, a vinyl acetate (co)polymer may be saponified to form a polyvinyl alcohol (co)polymer, or the polyvinyl alcohol (co)polymer may be acetalized to form a polyvinyl acetal. Even a polymer derived from a natural product such as a cellulose derivative may be used as the nonionic water-soluble polymer as long as the structure of the monomer constituting the polymer does not have a functional group that ionizes when dissolved in water.

[0084] Specific examples of nonionic water-soluble polymers include polyvinyl lactams such as polyvinylpyrrolidone and polyvinyl caprolactam; vinyl alcohol (co)polymers such as polyvinyl alcohol and polyethylene-vinyl alcohol copolymer; cellulose derivatives; polyvinyl ethers such as poly(methyl vinyl ether); polyoxazolines such as poly(2-methyl-2-oxazoline), poly(2-ethyl-2-oxazoline), and poly(2-propyl-2-oxazoline); polyvinyl acetals such as polyvinyl formal and polyvinyl butyral; and poly-N-vinyl amides such as poly-N-vinyl acetamide. Among these, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene-vinyl alcohol copolymer, cellulose derivatives, polyvinyl ether, polyoxazoline, polyvinyl acetal, and poly N-vinyl acetamide are preferred, and polyvinylpyrrolidone, polyvinyl alcohol, polyoxazoline, polyvinyl ether, and poly N-vinyl acetamide are more preferred. In particular, from the viewpoint of further improving the ink transferability in gravure printing, polyvinyl lactam, polyoxazoline, polyvinyl ether, and poly N-vinyl amide are preferred, and polyvinylpyrrolidone, polyoxazoline, polyvinyl ether, and poly N-vinyl acetamide are more preferred.

[0085] The nonionic water-soluble polymer may be used alone or in combination of two or more kinds.

[0086] The weight average molecular weight of the nonionic water-soluble polymer is preferably 5,000 to 100,000, more preferably 10,000 to 70,000, and even more preferably 15,000 to 50,000, from the viewpoint of improving the ink transferability in gravure printing and the appearance of the resulting printed matter.

[0087] The content of the nonionic water-soluble polymer in the ink composition is preferably from 0.1 to 15% by mass, more preferably from 0.5 to 10% by mass, and even more preferably from 1 to 5% by mass. The content of the nonionic water-soluble polymer is preferably 0.5 to 30 mass %, more preferably 1.0 to 15 mass %, and even more preferably 1.5 to 10 mass %, of the solid content of the ink composition. By adjusting the content of the nonionic water-soluble polymer to a specified value or above, the ink transferability in gravure printing, the appearance of the resulting printed matter, and the storage stability of the ink composition are likely to be improved, and by adjusting the content of the nonionic water-soluble polymer to a specified value or below, the ink viscosity can be maintained within an appropriate range.

[0088] (cationic water-soluble polymer) The ink composition may contain a cationic water-soluble polymer, but the content is preferably small. Here, the cationic water-soluble polymer refers to a water-soluble polymer having a functional group, such as a primary to tertiary amino group, that is ionized and positively charged when dissolved in water.

[0089] Specific examples of the cationic water-soluble polymer include compounds such as polyethyleneimine, polyvinylpyridine, polyvinylamine, polydimethyldiallylammonium chloride, polyallylamine hydrochloride, allylamine hydrochloride-diallylamine hydrochloride copolymer, epichlorohydrin polyamide, and polyepoxyamine, as well as modified compounds thereof.

[0090] The content of the cationic water-soluble polymer in the ink composition is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, and it is particularly preferable that the ink composition does not contain a cationic water-soluble polymer. By adjusting the amount of the cationic water-soluble polymer within the above range, the storage stability of the ink composition can be further improved, and the ink transferability in gravure printing and the appearance of the obtained printed matter tend to be better.

[0091] [Surfactants] From the viewpoint of further improving leveling properties, the ink composition preferably further contains a surfactant.

[0092] Here, the term "surfactant" refers to a substance that has the effect of significantly lowering the surface tension when dissolved in water, and although various definitions are generally known, in the present invention, unless otherwise specified, a surfactant is defined as a compound whose 0.1% by mass aqueous solution has a static surface tension of 45.0 mN / m or less at 25° C. The static surface tension can be measured using a high-performance surface tensiometer DY-500 (manufactured by Kyowa Interface Science Co., Ltd.), and either the plate method or the ring method may be adopted for the measurement.

[0093] As the surfactant, any conventionally known surfactant can be used, but it is preferable to select and use one or more of acetylene glycol-based, acetylene alcohol-based, silicone-based, fluorine-based, Pluronic-based, alcohol alkoxylate-based, etc., and it is more preferable to use an acetylene glycol-based surfactant and / or an acetylene alcohol-based surfactant because they have good compatibility with water-soluble polymers and good wettability on the printing substrate.

[0094] As the acetylene glycol surfactant or acetylene alcohol surfactant, commercially available products may be used, and specific examples thereof include the Surfynol series (manufactured by Evonik), the Olfine series (manufactured by Nissin Chemical Industry Co., Ltd.), and the Acetylenol series (manufactured by Kawaken Fine Chemicals Co., Ltd.).

[0095] Examples of silicone surfactants include polyether-modified siloxane, polyether-modified polydimethylsiloxane, etc. Commercially available products may be used as the silicone surfactant, and specific examples include Silface series (manufactured by Nissin Chemical Industry Co., Ltd.), KF series (manufactured by Nissin Chemical Industry Co., Ltd.), BYK-345, 347, 348, 349, 3450, 3451, 3455 (all manufactured by BYK), etc.

[0096] Examples of fluorosurfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains, etc. As the fluorosurfactant, commercially available products may be used, and specific examples include the Surflon series (manufactured by AGC Seiki Chemical Co., Ltd.) and the Megafac F series (manufactured by DIC Corporation).

[0097] A pluronic surfactant is a nonionic surfactant of block copolymer type of hydrophilic polyoxyethylene and hydrophobic polyoxypropylene. Commercially available products may be used as the pluronic surfactant, and specific examples include Adeka Pluronic series (ADEKA Corporation), polyoxyethylene polyoxypropylene glycol (160E.O.) (30P.O.) (FUJIFILM Wako Pure Chemical Industries, Ltd.), etc.

[0098] As the alcohol alkoxylate surfactant, commercially available products may be used, and specific examples thereof include DYNWET800 (manufactured by BYK) and Adekatall LB series (manufactured by ADEKA).

[0099] The surfactant may be used alone or in combination of two or more kinds.

[0100] The content of the surfactant in the ink composition is preferably 0.01 to 3.0% by mass, more preferably 0.05 to 1.5% by mass, and even more preferably 0.1 to 0.8% by mass.

[0101] [Other additives] The ink composition may contain additives such as defoamers, film-forming assistants, ultraviolet absorbers, ultraviolet protection agents, fillers, dispersants, thickeners, wetting agents, plasticizers, stabilizers, antioxidants, preservatives, etc. in appropriate amounts within the scope of the invention. The additives may be used alone or in combination of two or more.

[0102] [Physical properties of ink composition] The Zahn cup viscosity of the ink composition of the present invention at 25° C. is preferably 5 to 40 seconds, more preferably 10 to 30 seconds, and even more preferably 12 to 20 seconds, as measured using cup #3 manufactured by Rigo Co., Ltd. By adjusting the Zahn cup viscosity to a predetermined value or more, printability such as ink transferability in gravure printing and the appearance of the resulting printed matter can be further improved, and by adjusting the Zahn cup viscosity to a predetermined value or less, printability and storage stability can be further improved.

[0103] In a preferred embodiment, the ink composition of the present invention has excellent storage stability. When the ink composition of the present invention is stored at 50° C. for two weeks and its Zahn cup viscosity is measured at 25° C. before and after storage, the rate of change in Zahn cup viscosity calculated by the following formula is preferably within +10%. Rate of change in Zahn cup viscosity (%) = {(Zahn cup viscosity after storage - Zahn cup viscosity before storage) / Zahn cup viscosity before storage} x 100

[0104] [Method of manufacturing ink composition] The method for producing the ink composition of the present invention is not particularly limited. For example, the ink composition can be produced by mixing the pigment, the water-insoluble polymer, water, and an organic solvent, and a water-soluble polymer, a surfactant, and other additives that are used as necessary. An example of the method for producing the ink composition is shown below, but the method is not limited thereto.

[0105] First, it is preferable to prepare a pigment dispersion in which the pigment is dispersed in water. The pigment dispersion can be produced, for example, by mixing a part of water, the pigment, a part or all of the anionic water-soluble polymer, and a part or all of the surfactant used as necessary, and dispersing the mixture with a bead mill or the like. As described above, a base may be added when introducing a salt of an acid group into the anionic water-soluble polymer. In this case, the base may be added in advance to prepare the anionic water-soluble polymer into which the salt of the acid group has been introduced, and then the above-mentioned mixing may be carried out, or the base may be added during the above-mentioned mixing.

[0106] The content of the pigment in the pigment dispersion is not particularly limited, but is preferably from 20 to 80 mass%, more preferably from 30 to 70 mass%, and even more preferably from 40 to 65 mass%, based on 100 mass% of the pigment dispersion. The content of the anionic water-soluble polymer in the pigment dispersion may be adjusted appropriately depending on the type of pigment used. For example, when an inorganic pigment is used as the pigment, the content of the anionic water-soluble polymer is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 7 parts by mass, and even more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the pigment. When an organic pigment is used as the pigment, the content of the anionic water-soluble polymer is preferably 0.5 to 100 parts by mass, more preferably 1 to 50 parts by mass, and even more preferably 2 to 30 parts by mass, relative to 100 parts by mass of the pigment. By adjusting the content of the anionic water-soluble polymer relative to the pigment within the above range, the pigment dispersibility can be further improved.

[0107] The content of solids in the pigment dispersion is not particularly limited, but is preferably from 25 to 85% by mass, more preferably from 35 to 75% by mass, and even more preferably from 45 to 70% by mass, based on 100% by mass of the pigment dispersion.

[0108] It is also preferable to separately prepare a resin dispersion in which the water-insoluble polymer is dispersed in water. The resin dispersion is preferably an emulsion in which emulsion particles made of a water-insoluble polymer are dispersed in water. The resin dispersion may be a reaction liquid obtained by using water as a solvent in synthesizing a water-insoluble polymer, or a commercially available product.

[0109] Next, it is preferable to mix the pigment dispersion, the resin dispersion, the remainder of the water, the organic solvent, and the water-soluble polymer, the surfactant, and other additives that are used as necessary. When mixing, the water-soluble polymer, the surfactant, and other additives may be added as they are and mixed, or may be added as a solution diluted with a solvent such as water and mixed. The method and order of mixing the above components are not particularly limited. After mixing, centrifugation, filtration, etc. can be performed as necessary.

[0110] [Printed material] A printed matter can be produced by printing the ink composition of the present invention on a printing base material (substrate) by gravure printing. The ink composition may be used as is for gravure printing, or may be prepared and / or stored in a concentrated state and diluted with a solvent before use at the time of printing.

[0111] Examples of the printing substrate include paper; paper (coated paper, etc.) laminated with a resin film such as polyethylene, polypropylene, or polystyrene; metal plates such as aluminum, zinc, or copper; polyolefin films such as polyethylene film and polypropylene film, polyester films such as polyethylene terephthalate film, polyvinyl chloride film, nylon film, cellulose film, polystyrene film, polycarbonate film, polyvinyl acetal film, acrylic resin film, and polyamide film; paper having a metal coating; and resin films having a metal coating. Among these, resin films are preferred, and polyester films and polyolefin films are more preferred, and polyethylene terephthalate films and polypropylene films (particularly biaxially oriented polypropylene films and non-oriented polypropylene films). In addition, it is preferable that the resin film is subjected to a corona surface treatment at least on the printing surface in order to improve the adhesion of the ink composition to the printing substrate.

[0112] Printing by the gravure method may be performed by a conventionally known method, for example, by using a gravure printing machine. The printing speed is not particularly limited, but is, for example, 10 to 150 m / min. After printing, heat drying may be performed as necessary. The heat drying conditions may be appropriately adjusted depending on the printing substrate used, and for example, heat drying may be performed at 50 to 100°C for about 10 seconds to 30 minutes.

[0113] The printed matter can be said to be a laminate having a coating film formed from the ink composition on the printing substrate. The laminate may or may not have a primer layer between the printing substrate and the coating film, but it is preferable that it does not have one from the viewpoint of productivity, and it is preferable to form a coating film directly on the printing substrate (i.e., print the ink composition directly on the printing substrate). The laminate is laminated in the order of the printing substrate and the coating film, and may have a protective film (laminate layer) on the coating film. The laminate of the present disclosure can be suitably used for various printed matters. EXAMPLES

[0114] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples, "parts" means "parts by mass" and "%" means "% by mass".

[0115] The following abbreviations have the following meanings: <Polymerization raw materials> CHMA: Cyclohexyl methacrylate 2-EHA: 2-Ethylhexyl acrylate MMA: Methyl methacrylate MAA: Methacrylic acid TDM: tert-dodecyl mercaptan SR-20: Emulsifier [Manufactured by ADEKA Corporation, Product name: ADEKA REASORB SR-20] APS: Ammonium persulfate <Water-insoluble polymer> Polyurethane resin: U-coat DA-200 [manufactured by Sanyo Chemical Industries, Ltd., non-volatile content 38%] <Nonionic water-soluble polymer> PVP: Polyvinylpyrrolidone K-30 [Nippon Shokubai, powder] <Anionic water-soluble polymer> Joncryl 60J: Water-soluble styrene acrylic resin [BASF, non-volatile content 34%] <Organic solvent> PnB: Propylene glycol monobutyl ether (solubility in water: 5.2 g) DPnB: Dipropylene glycol monobutyl ether (solubility in water: 5g) 1-BuOH: 1-butanol (solubility in water: 7.7g) tert-AmOH: tert-amyl alcohol (solubility in water: 12.0 g) DPMA: Dipropylene glycol methyl ether acetate (solubility in water: 22g) BDG: Diethylene glycol monobutyl ether (solubility in water: ∞g) EH: Ethylene glycol monohexyl ether (solubility in water: 0.9g) IPA: Isopropyl alcohol (solubility in water: ∞g)

[0116] The solubility of an organic solvent in water refers to the amount of each organic solvent that dissolves in 100 ml of water when measured at a measurement temperature of 20° C. and atmospheric pressure.

[0117] The physical properties of each sample prepared in the following Production Examples, Examples, and Comparative Examples were measured as follows.

[0118] <Solid content (non-volatile content)> The solid content (non-volatile content) of each sample was determined by weighing 1 g of the target sample, drying it in a hot air dryer at 150° C. for 20 minutes, and calculating the solid content from the resulting residue using the following formula: [Solid content in sample] = ([mass of residue] ÷ [1 g of sample]) × 100 It was calculated based on the above.

[0119] <Acid value> The acid value of the water-insoluble polymer was obtained by calculating the number of milligrams of potassium hydroxide required to neutralize the acidic functional groups present in 1 g of the monomer component constituting the water-insoluble polymer.

[0120] <Glass transition temperature> The glass transition temperature (Tg) of the water-insoluble polymer was calculated as a temperature based on the Fox equation represented by the following formula (1) using the glass transition temperatures of the homopolymers of the monomers used in the monomer components constituting the water-insoluble polymer.

[0121]

number

[0122] <Average particle size> The measurement temperature was set at 25±0.5°C, and a multi-analyte nanoparticle size measurement system (manufactured by Otsuka Electronics Co., Ltd., product name: nanoSAQLA), a particle size measurement device using the dynamic light scattering method, was used to determine the volume average particle size (hydrodynamic diameter) by calculation (cumulant analysis) using the software provided with the device.

[0123] <Zahn cup viscosity> The sample used was a water-based ink whose internal temperature had reached equilibrium after being conditioned in a thermostatic chamber adjusted to 25°C for 30 minutes or more. Using a Zahn Cup #3 (manufactured by Rigo Co., Ltd.), the time (seconds) until the ink flow was complete was measured, and this value was taken as the Zahn cup viscosity.

[0124] [Production Example 1: Production of Aqueous Dispersion 1 Containing Water-Insoluble Acrylic Resin A] In a flask equipped with a dropping funnel, a stirrer, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 326 parts of deionized water was charged and heated to 72°C under nitrogen gas flow. A first-stage pre-emulsion for dropping consisting of 71 parts of deionized water, 5 parts of SR-20, 82 parts of MMA, 53 parts of EA, 19 parts of MAA and 8 parts of TDM was prepared in the dropping funnel, and 7 parts, which corresponds to 3% of the total amount, was added to the flask, and then 22 parts of a 5% APS aqueous solution was added to start polymerization. Thereafter, the remaining part of the pre-emulsion for dropping was uniformly dropped into the flask over a period of 90 minutes. After the dropwise addition was completed, the contents of the flask were maintained at 75°C for 25 minutes to obtain a first-stage polymer dispersion. Subsequently, 15 parts of ammonia water (25%) was slowly added while thoroughly stirring the polymer dispersion to dissolve the polymer, and the contents of the flask were maintained at 78°C for 15 minutes. Next, a pre-emulsion for the second stage, consisting of 50 parts of deionized water, 1 part of SR-20, 53 parts of CHMA, and 62 parts of 2-EHA, was prepared in the dropping funnel and added dropwise to the flask uniformly over a period of 50 minutes. After the dropping was completed, the contents of the flask were maintained at 78°C for 30 minutes. Next, a pre-emulsion for the third stage dropping consisting of 50 parts of deionized water, 1 part of SR-20, 82 parts of CHMA, and 33 parts of 2-EHA was prepared in a dropping funnel and dropped uniformly into the flask over 50 minutes. After the dropping was completed, 12 parts of a 2% APS aqueous solution was dropped uniformly into the flask over 30 minutes. After the dropping was completed, the contents of the flask were maintained at 78°C for 60 minutes. The resulting reaction liquid was cooled to room temperature and then filtered through a 300-mesh wire screen to obtain an aqueous dispersion 1 containing water-insoluble acrylic resin A as emulsion particles. The solid content in the aqueous dispersion 1 was 40%, the acid value of the acrylic resin A was 32 mgKOH / g, and the glass transition temperature of the acrylic resin A was 17° C. The average particle size of the emulsion particles was 65 nm.

[0125] [Production Example 2: Preparation of white paste] 738 parts of deionized water, 30 parts of anionic water-soluble polymeric pigment dispersant [Nippon Shokubai Co., Ltd., Aqualic HL-415, solids 35%] as solids, 0.9 parts of surfactant [Nissin Chemical Industry Co., Ltd., Olfin D-10PG, active ingredient 50%] as active ingredient, 20 parts of 25% ammonia water, 1000 parts of titanium oxide [Ishihara Sangyo Co., Ltd., JR-403] and 200 parts of glass beads (diameter 1 mm) were mixed in a disperser at a rotation speed of 3000 min -1 After dispersing for 120 minutes, the mixture was filtered through a 300 mesh wire screen to prepare a white paste.

[0126] [Example 1] The aqueous dispersion 1 obtained in Production Example 1 was placed in a container so that the solid content of the water-insoluble acrylic resin A contained therein was 12 parts, and the dispersion was mixed in a homodisper at a rotation speed of 1000 min -1 While stirring at 400°C, an aqueous solution of PVP, a nonionic water-soluble polymer, (40% aqueous solution) was slowly dropped to a solid content of 2.5 parts. Next, 45 parts of the white paste obtained in Production Example 2 (titanium oxide amount 25 parts, anionic water-insoluble polymer 0.75 parts), 3.0 parts of deionized water, and a mixture of 6.0 parts of PnB and 0.5 parts of deionized water were added in that order. Furthermore, a surfactant [Olfine D-10PG, manufactured by Nissin Chemical Industry Co., Ltd.] was added to an active ingredient of 0.5 parts, an antifoaming agent [San Nopco Co., Ltd., trade name: SND-1360] of 0.1 parts, and deionized water to a total of 100 parts were added, and the mixture was stirred for another 20 minutes, followed by filtration through a 300-mesh wire net to prepare water-based ink 1. The Zahn cup viscosity of water-based ink 1 was 16 seconds.

[0127] [Examples 2 to 8, Comparative Examples 1 to 4] Water-based inks 2 to 8 and water-based inks c1 to c4 were obtained in the same manner as in Example 1, except that the types and amounts of each component were as shown in Table 1. In Examples 1 to 8 and Comparative Examples 1 to 4, the blending ratios were adjusted so that the Zahn cup viscosity of the resulting water-based inks was 14 to 19 seconds.

[0128] <Preparation of gravure prints> The aqueous inks produced in the Examples and Comparative Examples were used for printing with a tabletop gravure printing machine (manufactured by RK Print-Coat Instruments Ltd., product name: K Printing Proofer). A solid-colored plate with 150 lines / inch was used as the plate. A corona-treated OPP film (manufactured by Futamura Chemical Co., Ltd., product name: FOR-AQ#30) was used as the printing film, and the film was fixed to a printing impression cylinder roll so that its longitudinal direction and the conveying direction were the same. The printing speed was 40 m / min, and the film was dried for 1 minute in a thermostatic dryer at 70°C immediately after printing to obtain a test sheet with an ink coating formed on the printed film.

[0129] -Evaluation method- <Appearance of ink film> The obtained test sheets were visually inspected to confirm the presence or absence of defects such as pinholes and repelling over the entire solid coating surface, and evaluated as to which of the following categories A to C they fell into. The results are shown in Table 1. If the ink can produce a coating film of category A or B, a printed matter with a uniform coating film (i.e., a printed matter with a good appearance) can be obtained when printed using an actual gravure printing machine. A: There are almost no pinholes or repelling, and the coating film has no unevenness in shade. B: There are a few areas with pinholes and cratering, but a coating film with no unevenness in shading has been obtained. C: The coating has overall uneven shading and many pinholes and repelling marks.

[0130] <Ink film adhesion> The obtained test sheets were prepared by curing in a thermostatic chamber at 50°C for 2 hours. Cellophane tape (manufactured by Nichiban) was applied to the printed surface and pressed with the pad of a finger to adhere it, and then the cellophane tape was quickly pulled straight up and removed. The coating film in the area where the cellophane tape had been applied was observed and evaluated as to whether it fell into any of the following categories A to C. The results are shown in Table 1. In terms of adhesion strength of the ink coating film in actual gravure prints, any ink that can produce a coating film of category A or B is practical. A: The coating hardly peels off. B: More than 80% of the coating remains. C: Less than 80% of the coating remains.

[0131] [Table 1]

[0132] The content of each component in Table 1 indicates the amount of active ingredient (parts by mass). Furthermore, the amount of surfactant in Table 1 indicates the total amount of surfactant contained in the water-based ink, that is, the amount of surfactant derived from the white paste is also included. [Industrial Applicability]

[0133] The ink composition of the present invention can be suitably used as an aqueous gravure ink since it can produce printed matter having excellent appearance (preferably excellent appearance and adhesion) in gravure printing while minimizing the impact on air pollution and the printing work environment during printing.

Claims

1. A pigment, a water-insoluble polymer, an organic solvent, and water, The aqueous gravure ink composition comprises an organic solvent (A) whose amount dissolved in 100 ml of water (measurement temperature: 20° C., atmospheric pressure condition) is 5 g or more and 15 g or less.

2. 2. The aqueous gravure ink composition according to claim 1, wherein the organic solvent (A) is at least one selected from the group consisting of glycol monoalkyl ethers and alcohols.

3. 2. The aqueous gravure ink composition according to claim 1, wherein the content of the organic solvent in the composition is from 1% by mass to 12% by mass.

4. 2. The aqueous gravure ink composition according to claim 1, wherein the organic solvent (A) accounts for 50 mass % or more of the total amount of the organic solvents.

5. 2. The aqueous gravure ink composition according to claim 1, wherein the content of the organic solvent other than the organic solvent (A) in the composition is 1% by mass or less.

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