Water-based ink for plate printing

Abstract

To provide aqueous ink for plate printing which enables production of a printed matter excellent in defoaming property, image density and scratch resistance, and an ink set containing the aqueous ink.SOLUTION: There is provided [1] aqueous ink for plate printing that contains a pigment, a fixing resin, a surface active agent, a water-soluble organic solvent, and water, in which the surface active agent contains a silicone-based surface active agent having a specific structure; a content of the silicone-based surface active agent in the ink is 0.05-4 mass%; and a content of the water-soluble organic solvent in the ink is 12 mass% or less. There is also provided [2] an ink set that contains the aqueous ink and white ink.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based ink for plate printing, and an ink set containing the water-based ink. [Background technology]

[0002] 2. Description of the Related Art Gravure printing, flexographic printing, letterpress printing, and the like, which use printing plates such as intaglio, lithographic, and letterpress plates, are widely used because they allow the quality of printing to be controlled by changing the form of the plate and enable high-definition printing. Conventionally, oil-based inks have been widely used in plate printing such as gravure printing, but there are problems with the use of oil-based inks in terms of the working environment, the global environment, and disaster prevention, and plate printing has problems in that it is difficult to meet the market needs for high-mix, small-lot production. Therefore, plate printing using water-based inks has been attracting attention. However, with water-based inks, there is a problem that it is difficult to obtain high-quality printed matter due to poor drying and poor wetting of the ink onto the plate surface due to surface tension, and various proposals have been made to improve this problem.

[0003] For example, Patent Document 1 discloses an aqueous gravure ink that has a low environmental impact and is excellent in print density and drying properties, the aqueous gravure ink containing a pigment, a water-soluble organic solvent, a surfactant, and water, wherein the water-soluble organic solvent contains a glycol ether having a boiling point of 100 to 260°C, the surfactant contains a silicone-based surfactant having a specific structural unit, the content of the water-soluble organic solvent in the ink is 1 to 10 mass %, and the content of water in the ink is 50 to 80 mass %. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-210433 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, resin films have come to be widely used as printing substrates, but water-based inks have low affinity with highly oleophilic printing substrates such as resin films, which can lead to problems such as poor printing due to ink repellency and scratches or peeling of printed images. Water-based inks are also more prone to bubble formation than oil-based inks, which can adversely affect print quality. The water-based ink described in Patent Document 1 was insufficient in suppressing the generation of bubbles that occurs when plate printing is performed on a low-water-absorbency printing substrate such as a resin film, and in improving the abrasion resistance of the printed image, leaving room for improvement. An object of the present invention is to provide a water-based ink for plate printing which is excellent in defoaming properties and can give printed matter which is excellent in image density and abrasion resistance, and an ink set containing the water-based ink. [Means for solving the problem]

[0006] The present inventors have discovered that the above-mentioned problems can be solved by an aqueous ink for plate printing that contains a pigment, a fixing resin, a surfactant, a water-soluble organic solvent, and water, the aqueous ink containing a specific amount of a specific silicone-based surfactant and having a low content of water-soluble organic solvent. That is, the present invention provides the following [1] and [2]. [1] A water-based ink for plate printing containing a pigment, a fixing resin, a surfactant, a water-soluble organic solvent, and water, wherein the surfactant contains a silicone-based surfactant represented by general formula (1) described below, the content of the silicone-based surfactant in the ink is 0.05% by mass or more and 4% by mass or less, and the content of the water-soluble organic solvent in the ink is 12% by mass or less. [2] An ink set comprising the water-based ink described in [1] above and a white ink. Effect of the Invention

[0007] According to the present invention, it is possible to provide a water-based ink for plate printing which is excellent in defoaming properties and can give printed matter which is excellent in image density and abrasion resistance, and an ink set containing the water-based ink. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Water-based ink for plate printing] The water-based ink for plate printing of the present invention is a water-based ink for plate printing (hereinafter, also referred to as "the ink of the present invention") containing a pigment, a fixing resin, a surfactant, a water-soluble organic solvent, and water, the surfactant comprises a silicone-based surfactant represented by the following general formula (1), and the content of the silicone-based surfactant in the ink is 0.05% by mass or more and 4% by mass or less; The content of the water-soluble organic solvent in the ink is 12% by mass or less. Water-based ink for plate printing.

[0009] [ka]

[0010] [In formula (1), R 1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R 2 represents a group represented by formula (a), and R 3 represents a group represented by formula (b), k is a number of 1 or more and 500 or less, m is a number of 1 or more and 500 or less, and n is a number of 0 or more and 100 or less.

[0011] [ka]

[0012] [In formula (a), R 4 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R 5 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an acyl group having 1 to 4 carbon atoms. a is a number from 1 to 20, b is a number from 0 to 50, and c is a number from 0 to 50. In formula (b), R 6 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, d is a number from 2 to 20, and e is a number from 1 to 20. The term "aqueous" means that water accounts for the majority of the medium. The ink of the present invention can be suitably used for printing using a printing plate, such as gravure printing, flexographic printing, and letterpress printing, but is more preferably used for gravure printing.

[0013] The ink of the present invention has excellent defoaming properties and can give high-quality printed matter having excellent image density and abrasion resistance. The reason for this is not clear, but is thought to be as follows. The ink of the present invention contains 0.05% by mass or more and 4% by mass or less of a specific silicone surfactant and 12% by mass or less of a water-soluble organic solvent, so that the ink can be wetted and spread on the printing substrate without being inhibited, and a uniform ink coating film without surface irregularities can be formed, which is believed to result in excellent image density and abrasion resistance. In addition, the ink contains a specific silicone surfactant and a water-soluble organic solvent, which is believed to improve defoaming properties and suppress defects during production.

[0014] <Pigments> The pigment used in the ink of the present invention is preferably one that can maintain a dispersed state in an aqueous ink with a particle diameter of 250 nm or less. Suitable forms of the pigment include (i) a pigment that can maintain a dispersed state without a dispersant, i.e., a self-dispersing pigment, (ii) a pigment particle form in which the pigment is dispersed with a low-molecular or high-molecular surfactant, and (iii) a polymer particle form containing the pigment. Among these, from the viewpoint of improving the defoaming property and improving the image density and abrasion resistance of the resulting printed matter, the form of the polymer particle containing the pigment is preferred, and the form of the water-insoluble polymer particle containing the pigment is more preferred. In this specification, the polymer particles containing a pigment refer to particles in which the pigment is encapsulated in a polymer, particles in which part of the pigment is exposed on the surface of a particle consisting of a polymer and a pigment, particles in which the polymer is adsorbed on part of the pigment, or mixtures of these. Of these, particles in which the pigment is encapsulated in a polymer are more preferred.

[0015] (Pigments) The pigment used in the present invention may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, channel black, etc. Examples of white inks include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, and other metal oxides. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The hue is not particularly limited, and in the case of chromatic inks, any chromatic pigment such as yellow, magenta, cyan, red, blue, orange, green, etc. can be used. The above pigments can be used alone or in combination of two or more kinds.

[0016] (Pigment-containing polymer particles) The polymer constituting the pigment-containing polymer particles (hereinafter also referred to as "polymer a") is not particularly limited as long as it has at least the ability to disperse the pigment. The pigment-containing polymer particles (hereinafter also referred to as "pigment-containing polymer particles") are more preferably pigment-containing crosslinked polymer particles (hereinafter also referred to as "pigment-containing crosslinked polymer particles") obtained by further crosslinking the pigment-containing polymer particles with a crosslinking agent. The polymer a before crosslinking may be a water-soluble polymer or a water-insoluble polymer, but is preferably a water-insoluble polymer. Even if the polymer used is a water-soluble polymer, the polymer becomes a water-insoluble polymer by crosslinking treatment. In this specification, the term "water-insoluble" of a polymer means that when a polymer that has been dried at 105° C. for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25° C., the amount of dissolution is less than 10 g, and the amount of dissolution of the polymer is preferably 5 g or less, more preferably 1 g or less. When the polymer is an anionic polymer, the amount of dissolution is the amount of dissolution when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

[0017] (Polymer a) Polymer a is a polymer having a pigment dispersing ability to disperse a pigment in an aqueous medium mainly composed of water. Polymer a may have any structure, but from the viewpoint of improving the storage stability of the ink of the present invention, a vinyl-based polymer obtained by addition polymerization of a vinyl monomer such as a vinyl compound, a vinylidene compound, or a vinylene compound is preferred. The vinyl polymer preferably contains a constituent unit derived from (a-1) an ionic monomer (hereinafter also referred to as "(a-1) component"), and more preferably is a vinyl polymer obtained by copolymerizing a monomer mixture A (hereinafter also referred to as "monomer mixture A") containing the (a-1) component and the (a-2) hydrophobic monomer (hereinafter also referred to as "(a-2) component"). The vinyl polymer has a constituent unit derived from the (a-1) component and a constituent unit derived from the (a-2) component.

[0018] [(a-1) Ionic Monomer] From the viewpoint of improving the dispersion stability of the pigment in the ink of the present invention, the ionic monomer (a-1) is preferably used as a monomer component of the polymer a. Examples of the ionic monomer (a-1) include anionic monomers and cationic monomers, and anionic monomers are preferred. Examples of the anionic monomer include a carboxylic acid monomer, a sulfonic acid monomer, a phosphoric acid monomer, etc. Examples of the carboxylic acid monomer include an acrylic acid, a methacrylic acid, a crotonic acid, an itaconic acid, a maleic acid, a fumaric acid, a citraconic acid, etc. Among these, from the same viewpoint as above, carboxylic acid monomers are more preferred, and one or more selected from acrylic acid and methacrylic acid are even more preferred.

[0019] [(a-2) Hydrophobic Monomer] From the viewpoint of improving the dispersion stability of the pigment in the ink of the present invention, it is preferable to use the hydrophobic monomer (a-2) as a further monomer component in addition to the component (a-1). Specific examples of the (a-2) component include those described in paragraphs

[0020] to

[0022] of JP 2018-83938 A. Among these, one or more selected from alkyl (meth)acrylates having an alkyl group having 1 to 22 carbon atoms, styrene, α-methylstyrene, and benzyl (meth)acrylate are preferred.

[0020] [(a-3) Nonionic Monomer] The nonionic monomer (a-3) (hereinafter also referred to as "component (a-3)") can be used from the viewpoint of further improving the dispersion stability of the pigment in the ink of the present invention. The component (a-3) is a monomer that has a high affinity for water or a water-soluble organic solvent, such as a monomer that contains a hydroxyl group or a polyalkylene glycol chain. Specific examples of the (a-3) component include those described in paragraph

[0018] of JP 2018-83938 A. Among these, one or more selected from methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferred. The monomer components contained in each of the above components (a-1) to (a-3) can be used alone or in combination of two or more kinds.

[0021] (Content of each component in monomer mixture A or each structural unit in polymer a) The contents of components (a-1) to (a-3) in monomer mixture A (content as unneutralized amount; the same applies hereinafter) during production of polymer a, or the contents of constitutional units derived from components (a-1) to (a-3) in polymer a, are as follows, from the viewpoint of improving the dispersion stability of the pigment and the storage stability of the ink of the present invention. The content of the (a-1) component is preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 15 mass% or more, and is preferably 40 mass% or less, more preferably 30 mass% or less, even more preferably 20 mass% or less. The content of the (a-2) component is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less. When the component (a-3) is contained, the content thereof is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less. The mass ratio of the component (a-1) to the component (a-2) [(a-1) / (a-2)] is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.25 or more, and is preferably 1.2 or less, more preferably 1.0 or less, even more preferably 0.8 or less. In the present invention, the content of the structural units derived from the components (a-1) to (a-3) in the polymer a can be determined by measurement, or can be substituted by the charging ratio of the raw material monomers including the components (a-1) to (a-3) during the production of the polymer a.

[0022] (Production of polymer a) The polymer a can be produced by copolymerizing the monomer mixture A by a known polymerization method, preferably a solution polymerization method. The solvent used in the solution polymerization method is not limited, but polar solvents such as water, aliphatic alcohols, ketones, ethers, and esters are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone, and the like are more preferred. In the polymerization, a polymerization initiator and a polymerization chain transfer agent can be used. Examples of the polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble azo polymerization initiators, and examples of the polymerization chain transfer agent include mercaptans. The polymerization temperature varies depending on the types of polymerization initiator, monomer, solvent, etc. used, but is preferably 30° C. or higher, more preferably 50° C. or higher, and is preferably 95° C. or lower, more preferably 80° C. or lower. The polymerization atmosphere is preferably a nitrogen gas or inert gas atmosphere. It is preferable that the polymer a is neutralized with a neutralizing agent as described below.

[0023] From the viewpoint of improving the dispersion stability in the ink of the pigment dispersed in the polymer, the weight average molecular weight of polymer a is preferably 10,000 or more, more preferably 15,000 or more, and is preferably 200,000 or less, more preferably 100,000 or less, and even more preferably 50,000 or less. From the same viewpoint as above, the acid value of polymer a is preferably 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, even more preferably 80 mgKOH / g or more, and preferably 300 mgKOH / g or less, more preferably 280 mgKOH / g or less, even more preferably 260 mgKOH / g or less. The weight average molecular weight and the acid value can be measured by the method described in the Examples.

[0024] Polymer a may be a commercially available product as long as it has a structural unit derived from component (a-1) and a structural unit derived from component (a-2). Commercially available examples of vinyl polymers include styrene-acrylic resins such as Joncryl 67, 611, 678, 680, 690, and 819 manufactured by BASF.

[0025] [Preparation of pigment-containing polymer particles] From the viewpoint of efficient production, the pigment-containing polymer particles are preferably produced as pigment dispersion A in which the pigment-containing polymer particles are dispersed in an aqueous medium by a method including the following step I and, if necessary, step II: Step I: A step of dissolving polymer a in a solvent to obtain a solution of polymer a, and then adding and mixing a pigment and, if necessary, a neutralizing agent, a surfactant, etc., to obtain a pigment dispersion A consisting of a pigment mixture. In order to efficiently incorporate the pigment into the polymer particles, it is preferable that the solvent contains an organic solvent in Step I. When the solvent contains an organic solvent, in addition to Step I, the method may further include the following Step II. Step II: A step of removing the organic solvent from the pigment mixture obtained in step I to obtain a pigment dispersion A. In addition to the above steps I and II, it is preferable to further carry out the following step III. Step III: A step of mixing the pigment dispersion A obtained in step I or step II with a crosslinking agent a to obtain crosslinked pigment-containing crosslinked polymer particles. In this specification, pigment dispersion A refers to both a dispersion in which pigment-containing polymer particles are dispersed in an aqueous medium and a dispersion in which pigment-containing crosslinked polymer particles are dispersed in an aqueous medium.

[0026] (Process I) In step I, the solvent in which polymer a is dissolved is not limited, but from the viewpoints of wettability to the pigment, solubility of polymer a, and adsorption to the pigment, it is preferable to use one or more selected from water, aliphatic alcohols having from 1 to 3 carbon atoms, ketones, ethers, esters, etc. When polymer a is synthesized by a solution polymerization method, the solvent used in the polymerization may be used as it is. When the polymer a is an anionic polymer, it is preferable to neutralize the anionic groups using a neutralizing agent so that the pH is 7 or more and 11 or less. Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines. The polymer a may also be neutralized in advance. From the viewpoint of improving the storage stability of the ink of the present invention, the degree of neutralization of the anionic groups of polymer a, expressed as the ratio of the molar equivalent of the neutralizing agent to the molar equivalent of the anionic groups of polymer a, is preferably 30 mol % or more, more preferably 40 mol % or more, even more preferably 50 mol % or more, and is preferably 300 mol % or less, more preferably 200 mol % or less, even more preferably 150 mol % or less.

[0027] In step I, it is preferable to apply mechanical force to the obtained pigment mixture to perform a dispersion treatment. There is no particular limitation on the method of applying mechanical force, but for example, the method described in paragraph

[0032] of JP-A-2018-83938 can be mentioned. As a device for applying mechanical force, a media type dispersing machine is preferable from the viewpoint of efficiently reducing the particle size of the pigment. When carrying out the dispersion treatment, the pigment can be adjusted to have a desired particle size by controlling the dispersion pressure and the like.

[0028] (Process II) Step II is an optional step. The organic solvent in the obtained pigment dispersion A is preferably substantially removed, but may remain as long as it does not impair the object of the present invention. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less. From the viewpoint of improving storage stability and performing high-definition printing, the average particle size of the pigment-containing polymer particles in Pigment Dispersion A is preferably 50 nm or more, more preferably 100 nm or more, even more preferably 120 nm or more, and is preferably 350 nm or less, more preferably 320 nm or less, even more preferably 300 nm or less. Even when crosslinking treatment is carried out in the below-described step III, the average particle size of the pigment-containing crosslinked polymer particles in the resulting pigment dispersion A is the same as the average particle size of the pigment-containing polymer particles. The average particle size is measured by the method described in the Examples.

[0029] (Process III) In step III, a part of the carboxyl groups of the polymer a constituting the pigment-containing polymer particles is crosslinked to form a crosslinked structure in a part or all of the surface layer of the pigment-containing polymer particles, thereby converting the pigment-containing polymer particles into pigment-containing crosslinked polymer particles. This crosslinking treatment is believed to suppress swelling and shrinkage of the polymer a, which adversely affects the dispersion stability of the pigment, and to further improve the storage stability of the ink of the present invention and the abrasion resistance of the resulting printed matter.

[0030] When polymer a is an anionic polymer having an anionic group, crosslinking agent a is preferably a compound having a functional group capable of reacting with the anionic group, and more preferably a compound having 2 to 6 such functional groups in the molecule. Suitable examples of the crosslinking agent a include compounds having two or more epoxy groups, oxazoline groups, or isocyanate groups in the molecule. Among these, compounds that are water-insoluble with a water solubility of 50% by mass or less, preferably 40% by mass or less, and have 2 to 4 epoxy groups in the molecule are preferred, and one or more selected from trimethylolpropane polyglycidyl ether and pentaerythritol polyglycidyl ether are more preferred, and trimethylolpropane polyglycidyl ether (water solubility of 27% by mass) is even more preferred. Here, the "water solubility" refers to the solubility (mass%) when 10 parts by mass of the crosslinking agent are dissolved in 90 parts by mass of ion-exchanged water at 25°C.

[0031] From the viewpoint of improving storage stability and abrasion resistance, the crosslinking rate of the pigment-containing polymer particles in step III is preferably 10 mol % or more, more preferably 20 mol % or more, even more preferably 30 mol % or more, and is preferably 80 mol % or less, more preferably 70 mol % or less, even more preferably 60 mol % or less, in terms of the ratio of the molar equivalent number of the crosslinkable functional groups of the crosslinking agent to the molar equivalent number of the carboxy groups of polymer a, from the viewpoint of improving storage stability and abrasion resistance. From the viewpoints of completion of the crosslinking reaction and economic efficiency, the temperature of the crosslinking treatment is preferably 40° C. or higher, more preferably 55° C. or higher, and is preferably 95° C. or lower, more preferably 80° C. or lower. From the viewpoint of improving the dispersion stability of the pigment dispersion, the solid content concentration of the obtained pigment dispersion A is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less. The solids concentration is measured by the method described in the Examples.

[0032] <Fixing resin> The ink of the present invention contains a fixing resin from the viewpoints of improving defoaming properties and improving the image density and abrasion resistance of the resulting printed matter. It is more preferable that the fixing resin is composed of only resin, that is, the fixing resin is preferably resin particles that do not contain a pigment (hereinafter, also referred to as "resin particles B"). The resin particles B may be subjected to a crosslinking treatment, if necessary. Examples of the polymer constituting the resin particles B (hereinafter also referred to as "polymer b") include urethane polymers, vinyl polymers, polyester polymers, etc. Among these, from the viewpoint of improving the image density and abrasion resistance of the resulting printed matter, urethane polymers are preferred, and water-insoluble polyurethane resins are more preferred. Here, the term "water-insoluble" has the same definition as that for the polymer a.

[0033] [Polyurethane resin] The polyurethane resin used in the present invention can be obtained by subjecting a polyol having two or more alcoholic hydroxyl groups in one molecule to a polyaddition reaction with a polyisocyanate. (Polyol) The polyol is not particularly limited, but is preferably at least one selected from polyether polyols, polycarbonate polyols, and polyester polyols, and more preferably polyether polyols. That is, the polyurethane resin is preferably at least one selected from polyether-based polyurethane resins, polycarbonate-based polyurethane resins, and polyester-based polyurethane resins, and more preferably a polyether-based polyurethane resin.

[0034] Examples of polyether polyols include polymers obtained by ring-opening polymerization of cyclic ether compounds such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, epichlorohydrin, etc., either alone or in combination, using a compound having an active hydrogen atom as a catalyst, etc. Specific examples include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc.

[0035] The polycarbonate polyol can be obtained by reacting a carbonate compound with a diol. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, and diethylene carbonate. Examples of the diol include aliphatic diols which may be substituted with lower alcohols, alicyclic diols such as cyclohexanediol and hydrogenated xylylene glycol, and aromatic diols such as xylylene glycol. Among these, aliphatic diols are preferred, and aliphatic diols having a carbon chain length of 4 to 9, such as 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, heptanediol, octanediol, and nonanediol, are more preferred.

[0036] The polyester polyol can be obtained by condensing a low molecular weight diol and a dicarboxylic acid. Examples of low molecular weight diols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and 1,4-butanediol, with ethylene glycol, propylene glycol, and 1,4-butanediol being preferred. Examples of dicarboxylic acids include aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and brassylic acid, and aromatic dibasic acids such as isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Among these, aliphatic dibasic acids are preferred, and dibasic acids with a methylene chain length of 4 to 8, such as adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, are more preferred.

[0037] (Polyisocyanate) Examples of polyisocyanates include chain aliphatic diisocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; aliphatic diisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate and tetramethylxylylene diisocyanate; aromatic diisocyanates such as tolylene diisocyanate and diphenylmethane diisocyanate; and modified products of these diisocyanates (carbodiimide, uretdione, uretoimine-containing modified products, etc.). Among these, aliphatic diisocyanates and aromatic diisocyanates are preferred.

[0038] Examples of the reaction solvent for the polyaddition reaction include acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, toluene, and xylene. In the polyaddition reaction, a chain extender or a reaction terminator may be used in combination as necessary. The molecular weight can be further increased by using a chain extender. Examples of the chain extender include polyols and polyamines, and examples of the reaction terminator include monoalcohols and monoamines. The polyurethane resin is preferably used as an emulsion, and the emulsion may contain a dispersing agent such as a surfactant, if necessary.

[0039] From the viewpoint of improving fixation and abrasion resistance, the weight average molecular weight of the polyurethane resin is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 300,000 or more, and is preferably 2.5 million or less, more preferably 1 million or less, and even more preferably 600,000 or less. From the viewpoint of improving the storage stability, fixation property and abrasion resistance of the ink of the present invention, the acid value of the polyurethane resin is preferably 1 mgKOH / g or more, more preferably 2 mgKOH / g or more, even more preferably 4 mgKOH / g or more, and is preferably 40 mgKOH / g or less, more preferably 20 mgKOH / g or less, even more preferably 10 mgKOH / g or less.

[0040] From the viewpoint of improving the storage stability, fixation property, and abrasion resistance of the ink of the present invention, the average particle size of the polyurethane resin particles in the emulsion is preferably 20 nm or more, more preferably 40 nm or more, and even more preferably 50 nm or more, and is preferably 300 nm or less, more preferably 200 nm or less, and even more preferably 100 nm or less. The average particle size is measured by the method described in the Examples.

[0041] Examples of commercially available polyurethane resin emulsions include NeoRez R-9660, R-2170 (aliphatic polyester-based urethane resin emulsions), NeoRez R-966, R-967, R-650 (aliphatic polyether-based urethane resin emulsions), and NeoRez Examples include R-986, R-9603 (aliphatic polycarbonate-based urethane resin emulsions); Superflex 460, 420, 470, 460S (carbonate-based urethane resin emulsions), Superflex 150HS (ester-ether-based urethane resin emulsions), Superflex 740, 840 (aromatic isocyanate-based ester-based urethane resin emulsions) manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Takelac WS-5100 (anionic urethane resin emulsion) manufactured by Mitsui Chemicals, Inc., the "WBR" series manufactured by Taisei Fine Chemical Co., Ltd., the Suncure series manufactured by Lubrizol; the Parmarin series manufactured by Sanyo Chemical Industries, Ltd.; and the Adeka Bontitor HUX series manufactured by ADEKA Corporation.

[0042] <Surfactant> The ink of the present invention contains a silicone-based surfactant from the viewpoint of improving the wetting and spreading properties of the ink on a printing substrate and improving image density and abrasion resistance. The silicone-based surfactant means a surfactant having a polysiloxane structure, and may have a hydrophilic group, a hydrophilic polymer chain, or the like, on a side chain, an end, or the like. The silicone surfactant contains a silicone surfactant represented by the following general formula (1), and the content of the silicone surfactant in the ink is 0.05% by mass or more and 4% by mass or less.

[0043] [ka]

[0044] In formula (1), R 1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a methyl group or an ethyl group, and more preferably a methyl group. R2 represents a group represented by formula (a), and R 3 represents a group represented by formula (b). k is a number from 1 to 500, preferably from 5 to 400, and more preferably from 10 to 300. m is a number from 1 to 500, preferably from 1 to 300, and more preferably from 2 to 200. n is a number from 0 to 100, preferably from 0 to 75, and more preferably from 0 to 50.

[0045] [ka]

[0046] In formula (a), R 4 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and is preferably a hydrogen atom. R 5 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an acyl group having 1 to 4 carbon atoms, and is preferably a hydrogen atom. The average number of added moles a is a number of 1 or more and 20 or less, preferably 1 or more and 3 or less, and more preferably 1. The average number of added moles b is a number of 0 or more and 50 or less, preferably 1 or more and 3 or less, and more preferably 1. The average number of added moles c is a number of 0 or more and 50 or less, preferably 0 or more and 3 or less, and more preferably 0.

[0047] In formula (b), R 6 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and is preferably a hydrogen atom. The average number of added moles d is a number of 2 or more and 20 or less, preferably a number of 2 or more and 16 or less, and more preferably 2 to 12. The average number of added moles e is a number of 1 or more and 20 or less, preferably a number of 2 or more and 16 or less, and more preferably 2-12. In the present invention, the silicone surfactant represented by general formula (1) has a ratio of k:m:n of preferably 60-90:40-10:10-0, more preferably 65-85:35-13:0-5, and even more preferably 70-85:30-15:0-2, from the viewpoint of improving abrasion resistance. From the viewpoint of improving abrasion resistance, the silicone surfactant represented by the general formula (1) preferably has n of 0 or more, that is, has a group represented by formula (b).

[0048] The silicone surfactant represented by the general formula (1) may be a commercially available product, such as TEGO twin 4000 and TEGO twin 4100 (gemini surfactants) manufactured by Evonik.

[0049] The ink of the present invention preferably further contains an acetylene glycol surfactant as a surfactant, and may further contain, as necessary, a polyether silicone surfactant other than the silicone surfactant represented by the general formula (1), a known nonionic surfactant, etc. The acetylene glycol surfactant is preferably an acetylene glycol having 8 to 22 carbon atoms and an ethylene adduct of the acetylene glycol, and more preferably an acetylene glycol having 8 to 22 carbon atoms. The number of carbon atoms of the acetylene glycol is preferably 10 or more, more preferably 12 or more, and preferably 20 or less, more preferably 18 or less, and even more preferably 16 or less. More specifically, one or more acetylene glycols selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 2,5-dimethyl-3-hexyne-2,5-diol, and an ethylene oxide adduct of the acetylene glycol may be mentioned. Among these, 2,4,7,9-tetramethyl-5-decyne-4,7-diol is preferable.

[0050] The HLB of the acetylene glycol surfactant is preferably 0 or more, more preferably 1 or more, even more preferably 2 or more, and is preferably 5 or less, more preferably 4.5 or less, even more preferably 4 or less. Here, the HLB (hydrophilic lipophilic balance) value is a value indicating the affinity of a surfactant for water and oil, and can be determined by the Griffin method. Commercially available examples of acetylene glycol surfactants include Air Products & Chemicals' Surfynol 104 (2,4,7,9-tetramethyl-5-decyne-4,7-diol), Surfynol 104E (Surfynol 104 diluted with 50% ethylene glycol), Surfynol 104PG-50 (Surfynol 104 diluted with 50% propylene glycol), Surfynol 420 (Surfynol 104 average number of moles added EO: 1.3), and Acetylenol E13T (average number of moles added EO: 1.3) manufactured by Kawaken Fine Chemicals Co., Ltd. The above surfactants can be used alone or in combination of two or more.

[0051] <Water-soluble organic solvent> The water-soluble organic solvent used in the ink of the present invention may be either liquid or solid at 25°C. When the organic solvent is dissolved in 100 ml of water at 25°C, the amount of the dissolved organic solvent is 10 ml or more. The content of the water-soluble organic solvent is 12% by mass or less, and preferably less than 10% by mass, from the viewpoints of improving defoaming properties and improving the image density and abrasion resistance of the resulting printed matter. From the viewpoint of improving the wetting and spreading properties of the ink, the boiling point of the water-soluble organic solvent is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 140°C or higher, and is preferably 260°C or lower, more preferably 250°C or lower, even more preferably 240°C or lower. Examples of the water-soluble organic solvent include glycol ethers such as alkylene glycol ethers, polyhydric alcohols such as propylene glycol, amide compounds, etc. Among these, alkylene glycol ethers are preferred.

[0052] Examples of the alkylene glycol ether include one or more selected from ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and the like. Among these, from the viewpoints of improving defoaming properties and improving the image density and abrasion resistance of the resulting printed matter, one or more selected from diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether are preferred, and diethylene glycol monoisobutyl ether is more preferred.

[0053] (Content of each component in the ink of the present invention) The contents of pigment, fixing resin, surfactant, water-soluble organic solvent and water in the ink of the present invention are as follows, from the viewpoint of improving defoaming properties and improving image density and abrasion resistance of the resulting printed matter. The content of each component below refers to the content of each component in the ink at the time of printing. The ink of the present invention may be used as is after adjusting the content of each component to the content at the time of printing, or a previously prepared base ink may be diluted with water or the like and adjusted to the content at the time of printing.

[0054] The pigment content in the ink of the present invention is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 18% by mass or less. The content of the pigment-containing polymer particles in the ink of the present invention is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less.

[0055] The content of the fixing resin in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less. The mass ratio of the polymer (total amount of polymer a and polymer b) to the pigment in the ink of the present invention [polymer / pigment] is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, and is preferably 3 or less, more preferably 2 or less, even more preferably 1.5 or less.

[0056] The content of the silicone surfactant represented by general formula (1) in the ink of the present invention is 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and is 4% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less, even more preferably 1.5% by mass or less. When an acetylene glycol surfactant is used, its content in the ink is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, even more preferably 0.3 mass% or more, and preferably 3 mass% or less, more preferably 2 mass% or less, even more preferably 1.5 mass% or less.

[0057] The total content of water-soluble organic solvents in the ink of the present invention is 12% by mass or less, preferably less than 10% by mass, more preferably 9% by mass or less, even more preferably 8% by mass or less, still more preferably 7% by mass or less, and preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more.

[0058] The water content in the ink of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less. The ink of the present invention may contain various additives such as a pH adjuster, a viscosity adjuster, a defoamer, a preservative, and a rust inhibitor as optional components depending on the application. When the ink contains any other optional components other than the pigment, fixing resin, surfactant, water-soluble organic solvent and water, the water content may be partially replaced by the other components.

[0059] The Zahn cup viscosity of the ink of the present invention at 20°C is, from the viewpoints of improving defoaming properties and improving the image density and abrasion resistance of the obtained printed matter, preferably 10 seconds or more, more preferably 12 seconds or more, even more preferably 13 seconds or more, and is preferably 25 seconds or less, more preferably 20 seconds or less, even more preferably 18 seconds or less. The pH of the ink of the present invention at 20°C is preferably 5.5 or more, more preferably 6.0 or more, and even more preferably 6.5 or more, from the viewpoint of improving dispersion stability, and is preferably 11.0 or less, more preferably 10.5 or less, and even more preferably 10.0 or less, from the viewpoints of component resistance and skin irritation.

[0060] [Ink Set] The ink set of the present invention comprises the ink of the present invention and a white ink. In this case, the pigment of the ink of the present invention is a chromatic pigment or a black pigment. The water-based ink for plate printing and the ink set of the present invention can be suitably used in gravure printing using a gravure plate. By printing the ink of the present invention on a printing substrate by a gravure printing method, a high-definition gravure print having excellent image density and abrasion resistance can be obtained. Examples of printing substrates used in gravure printing include papers such as coated paper, art paper, synthetic paper, and processed paper; and resin films such as polyester film, polyethylene film, polypropylene film, polystyrene film, polyvinyl chloride film, and nylon film. As the printing substrate, a resin film is preferred from the viewpoint of the wetting and spreading property of the ink on the printing substrate, and a polyester film or a polypropylene film is preferred from the viewpoint of suitability for post-processing such as punching after the production of the printed matter. These resin films may be biaxially stretched films, uniaxially stretched films, or non-stretched films. From the viewpoint of improving suitability for gravure printing, a resin film that has been subjected to a surface treatment by electrical discharge processing such as corona treatment or plasma treatment may be used. EXAMPLES

[0061] In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

[0062] (1) Measurement of weight average molecular weight of polymer The measurement was performed by gel chromatography (GPC apparatus (HLC-8320GPC) manufactured by Tosoh Corporation, columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolum Super AW-H) manufactured by Tosoh Corporation, flow rate: 0.5mL / min) using a solution of phosphoric acid and lithium bromide dissolved in N,N-dimethylformamide to a concentration of 60mmol / L and 50mmol / L, respectively, as an eluent, and using a monodisperse polystyrene kit with known molecular weight (PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), manufactured by Tosoh Corporation) as a standard substance. The measurement sample was prepared by mixing 0.1 g of resin with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25° C. for 10 hours, and filtering with a syringe filter (DISMIC-13HP PTFE 0.2 μm, manufactured by Advantec Co., Ltd.).

[0063] (2) Measurement of the acid value of the polymer The polymer was dissolved in a titration solvent of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with 0.1N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve as the end point. The acid value was calculated from the titration amount of potassium hydroxide solution up to the end point.

[0064] (3) Measurement of solids concentration of pigment dispersion Using an infrared moisture meter "FD-230" (Kett Electric Laboratory Co., Ltd.), the solid content of 5 g of the measurement sample was measured under conditions of a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / fluctuation range 0.05%).

[0065] (4) Measurement of the average particle size of pigment-containing polymer particles The measurements were performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) and cumulant analysis. The particle concentration to be measured was approximately 5 × 10 -3 A dispersion diluted with water to a weight percent was used. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was entered as the refractive index of the dispersion solvent, and the obtained cumulant average particle size was taken as the average particle size of the pigment-containing polymer particles and polymer particles.

[0066] Production Example 1 (Production of Pigment Dispersion A1) (1) 236 parts of ion-exchanged water was weighed out into a 2 L flask, and 60 parts of a water-insoluble styrene-acrylic polymer (manufactured by BASF, product name: JONCRYL 690, weight average molecular weight: 16500, acid value: 240 mgKOH / g) as a pigment dispersion polymer and 36.5 parts of 5N sodium hydroxide solution (degree of sodium neutralization: 60 mol%) were added. The mixture was stirred for 2 hours at 200 rpm using an anchor impeller, and 332.5 parts of a styrene-acrylic polymer aqueous solution (solid concentration: 19.9%) was obtained. 331.7 parts of the above aqueous solution and 448.3 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper impeller, and stirred at 1400 rpm for 15 minutes using a disper (Ultra Disper: product name, manufactured by Asada Iron Works Co., Ltd.) while cooling in a 0°C water bath. (2) Then, 220 parts of cyan pigment (CI Pigment Blue 15:3) was added and stirred at 6400 rpm for 1 hour. The resulting dispersion was charged into a wet disperser (Hiroshima Metal & Machinery Co., Ltd., product name: Ultra Apex Mill UAM05) filled with 80% by volume of zirconia beads (Nikkato Co., Ltd., product name: XTZ Ball, 0.3 mm diameter), and dispersed five times at a peripheral speed of 8 m / s and a flow rate of 200 g / min while cooling with cooling water at 5°C, and then filtered using a 200 mesh wire screen. (3) To 500 parts of the filtrate obtained above (110 parts of pigment, 33 parts of polymer), 7.3 parts of Denacol EX-321L (manufactured by Nagase ChemteX Corporation, trimethylolpropane polyglycidyl ether, epoxy equivalent: 129) (40 mol % equivalent to the carboxylic acid that becomes the crosslinking reaction point contained in the acrylic acid in the polymer), 1 part of Proxel LV (S) (manufactured by Lonza Japan Co., Ltd., antifungal agent, active ingredient concentration: 20%) were added, and 17.9 parts of ion-exchanged water was added so that the solid concentration became 28.6%, and the mixture was stirred at 70°C for 3 hours, and then filtered through a 200 mesh wire net to obtain 526.2 parts of pigment dispersion A1 of pigment-containing crosslinked polymer particles (content of pigment-containing crosslinked polymer particles: 28.6%, average particle size: 164 nm).

[0067] Example I-1 (Production of Water-Based Ink) To obtain the composition shown in Table 1, 47.5 parts of the pigment dispersion A1 obtained in Production Example 1 (pigment content in the water-based ink: 10.0 parts, pigment dispersion polymer a content: 3.6 parts) was added to a production vessel, and 21.1 parts of a urethane emulsion, NeoRez R-650 (manufactured by DSM Coating Resins, acid value: 5.6 mg KOH / g, average particle size: 60 nm, solids concentration: 38%) was added as a fixing resin (polymer b), and the mixture was stirred at 150 rpm. Further, 5.0 parts of diethylene glycol monoisobutyl ether (iBDG: manufactured by Nippon Nyukazai Co., Ltd., boiling point 220°C), 0.5 parts of a silicone compound represented by general formula (1) as a surfactant (manufactured by Evonik, product name: TEGO Twin 4100), 1.3 parts of a viscosity modifier (manufactured by ADEKA Corporation, nonionic polymer surfactant, product name: ADEKA NOL UH-420, active ingredient concentration 30% aqueous solution), and 23.6 parts of ion-exchanged water were added, and the mixture was stirred at room temperature for 30 minutes, and then filtered through a stainless steel wire mesh (200 mesh) to obtain water-based ink 1. The total amount of each component is 100 parts.

[0068] Examples I-2 to I-13 and Comparative Examples I-1 to I-4 (Production of Water-Based Inks) Water-based inks 2 to 17 were obtained in the same manner as in Example I-1, except that the blending compositions shown in Table 1 were used in Example I-1. Details of the surfactants and water-soluble organic solvents in Table 1 are as follows.

[0069] (Surfactant) Silicone-based surfactant (1): TEGO twin 4100, an organic modified siloxane copolymer represented by the general formula (1) manufactured by Evonik (wherein R 1 = methyl group, k = 1 to 500, m = 1 to 500, n = 1 to 100, k:m:n = 71:27:2, in formula (a), R 4 = hydrogen atom, R 5 = hydrogen atom, a = 1, b = 1, c = 0, in formula (b), R 6 = hydrogen atom, d=3, e=1-20) Silicone-based surfactant (2): TEGO twin 4000, an organic modified siloxane copolymer represented by the general formula (1) manufactured by Evonik (wherein R 1 = methyl group, k = 1 to 500, m = 1 to 500, n = 0, k:m:n = 85:15:0, in formula (a), R 4 = hydrogen atom, R 5 = hydrogen atom, a=1, b=1, c=0) Silicone surfactant (3): TEGO Wet 240, a polyethylene glycol ether-modified siloxane copolymer not represented by general formula (1), manufactured by Evonik Silicone-based surfactant (4): Polyethylene glycol ether-modified siloxane copolymer not represented by general formula (1), KF642, manufactured by Shin-Etsu Chemical Co., Ltd. Acetylene glycol surfactant: Air Products & Chemicals, Surfynol 104PG-50, 50% solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (HLB: 3.0) in propylene glycol

[0070] (Water-soluble organic solvent) iBDG: Diethylene glycol monoisobutyl ether, boiling point 220°C BDG: Diethylene glycol monobutyl ether, boiling point 230℃ MFDG: Dipropylene glycol monomethyl ether, boiling point 187°C The above water-soluble organic solvents are manufactured by Nippon Nyukazai Co., Ltd.

[0071] <Evaluation of antifoaming properties> 30 g of each of the obtained water-based inks was placed in a 50 mL screw tube, and the screw tube was placed horizontally and shaken at 150 rpm for 300 seconds using a multi-shaker (Tokyo Rika Kikai Co., Ltd., product name: MMS-210). Immediately after shaking, the time until the bubbles disappeared was measured by visual inspection, and the defoaming property was evaluated according to the following evaluation criteria. The results are shown in Table 1. (Evaluation Criteria) 5: Time to defoam is less than 5 seconds 4: Time until foam disappears is between 5 and 10 seconds 3: Time until foam disappears is between 10 and 30 seconds 2: Time until foam disappears is between 30 and 60 seconds 1: Time until foam disappears is 60 seconds or more The shorter the time until defoaming, the better the defoaming property and the more excellent the practical use. If the evaluation standard is 3 or higher, the defoaming property is satisfactory for practical use.

[0072] Examples II-1 to II-13, Comparative Examples II-1 to II-4 (gravure printing) (1) Evaluation of image density Using the aqueous inks obtained in Examples I-1 to I-13 and Comparative Examples I-1 to I-4, gravure printing was performed on the corona discharge treated surface of an OPP film (Futamura Chemical Co., Ltd., FOR-AQ#20, laminate grade). Printing was performed using a tabletop gravure printing test machine (Matsuo Sangyo Co., Ltd., K Printing Proofer) and a laser platemaking gravure 250 line, 8 μm plate (Nabe Process Co., Ltd.). The solid printing was performed by printing a solid layer with printing ink 1 (chromatic ink) and drying for 10 minutes in a dryer (Yamato Scientific Co., Ltd., Drying Oven DSV402) set at 60°C. The image density of the printed portion was measured using a spectrophotometer (manufactured by GretagMacbeth, product name: SpectroEye) in the measurement mode (DIN, Abs), and evaluated according to the following evaluation criteria. The results are shown in Table 1. (Evaluation Criteria) A: Image density is 1.7 or more B: Image density is 1.5 or more and less than 1.7 C: Image density is less than 1.5 If the evaluation result is B or above, there is no problem in practical use.

[0073] (2) Evaluation of abrasion resistance Using the aqueous inks obtained in Examples I-1 to I-13 and Comparative Examples I-1 to I-4, the aqueous inks were applied to the corona discharge treated surface of an OPP film (Futamura Chemical Co., Ltd., FOR-AQ#20, laminate grade) using a bar coater (SA-203, ROD No. 4, Tester Sangyo Co., Ltd.) to produce printed matter. The obtained print was placed in a dryer (DVS402, Yamato Scientific Co., Ltd.) set to 60°C, dried for 1 minute, and rubbed 50 times with a white cloth for dye fastness testing (designation number 3-1, Japan Standards Association) using a Gakushin type rub tester (RT-300, Daiei Scientific Precision Machinery Co., Ltd.) with a load of 500g. The peeled area rate was then visually observed and the rub resistance was evaluated according to the following criteria. The results are shown in Table 1. (Evaluation Criteria) A: There are no scratches or peeling on the coated surface. B: There is slight peeling on the coating surface. C: More than 50% of the coating surface is peeled off. A rating of B or higher is considered suitable for practical use.

[0074] [Table 1]

[0075] From Table 1, it can be seen that the water-based inks obtained in the Examples have superior defoaming properties compared to the water-based inks obtained in the Comparative Examples, and the image density and abrasion resistance of the resulting printed matter are well-balanced at a high level.

Claims

1. A water-based ink for plate printing, comprising a pigment, a fixing resin, a surfactant, a water-soluble organic solvent, and water, The fixing resin is a water-insoluble polyurethane resin, the surfactant comprises a silicone-based surfactant represented by the following general formula (1), and the content of the silicone-based surfactant in the ink is 0.05% by mass or more and 4% by mass or less, The content of the water-soluble organic solvent in the ink is 12% by mass or less, The content of the water in the ink is more than 70% by mass. Water-based ink for plate printing. 【Chemistry 1】 [In formula (1), R １ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ２ represents a group represented by formula (a), and R ３ represents a group represented by formula (b), k is a number of 1 or more and 500 or less, m is a number of 1 or more and 500 or less, and n is a number of 0 or more and 100 or less. 【Chemistry 2】 [In formula (a), R ４ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ５ each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an acyl group having 1 to 4 carbon atoms, a is a number from 1 to 20, b is a number from 1 to 3, and c is a number from 0 to 3. In formula (b), R ６ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, d is a number from 2 to 20, and e is a number from 1 to 20.

2. 2. The water-based plate printing ink according to claim 1, wherein the pigment is in the form of pigment-containing polymer particles.

3. 3. The water-based ink for plate printing according to claim 1, wherein the pigment is a chromatic pigment or a black pigment.

4. The water-based ink for plate printing according to any one of claims 1 to 3, wherein the content of the water-soluble organic solvent is less than 10 mass%.

5. 5. The water-based ink for plate printing according to claim 1, wherein the boiling point of the water-soluble organic solvent is 100° C. or higher and 260° C. or lower.

6. The water-based ink for plate printing according to any one of claims 1 to 5, wherein the surfactant further comprises an acetylene glycol surfactant.

7. The water-based ink for plate printing according to any one of claims 1 to 6, which is for gravure printing.

8. An ink set comprising the water-based ink according to any one of claims 3 to 7 and a white ink.

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