Pretreatment liquid for inkjet printing

Abstract

To provide a pretreatment liquid for inkjet printing, an ink set for inkjet printing, and an inkjet printing method capable of obtaining a printed matter excellent in sharpness of a printed image.SOLUTION: The pretreatment liquid for inkjet printing to be applied onto a printing medium contains water, an anionic polymer compound (A), and a water-soluble basic compound (B), wherein the water-soluble basic compound (B) contains one or more selected from the group consisting of ammonia and water-soluble amine compounds.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pretreatment liquid for inkjet printing, an ink set for inkjet printing, and an inkjet printing method. [Background technology]

[0002] Inkjet printing has many advantages, such as not requiring plate making, being easily adaptable to variable printing, and not contacting the printed material, and is therefore gaining popularity in a wide range of fields, including office and home use. In recent years, attempts have been made to expand into commercial printing and industrial printing applications, which require significantly larger print volumes, and inkjet printing is being required to print on a variety of printing media. In response to such demands, a method has been proposed in which a treatment liquid is applied to the printing medium in advance, before the ink is applied to the printing medium, to intentionally aggregate the solid components contained in the ink, such as coloring materials and resins, thereby forming an ink aggregation layer on the printing medium.

[0003] For example, Patent Document 1 discloses a pretreatment liquid for inkjet recording, which is composed of an aqueous solution containing colloidal silica and polyacrylic acid having a weight-average molecular weight of 80,000 or more, for the purpose of obtaining an image that has high gloss, excellent color mixing prevention properties, and excellent water resistance when printed using a pigment-containing water-based ink, in which the average particle size of secondary particles of the colloidal silica in the pretreatment liquid is 60 nm or more and 300 nm or less, and the mass ratio of colloidal silica to polyacrylic acid having a weight-average molecular weight of 80,000 or more [colloidal silica / polyacrylic acid] is 4 or more and 100 or less. Furthermore, for example, Patent Document 2 discloses a recording method and an inkjet recording apparatus that can suppress unevenness in density, provide a recorded matter that is excellent in color development and abrasion resistance, and also aims to improve printing speed, and for example, in Example 1, discloses a treatment liquid that contains a styrene-acrylic resin emulsion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-30370 [Patent Document 2] Japanese Patent Publication No. 2022-101991 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the pretreatment liquid described in Patent Document 1 and the treatment liquid described in Patent Document 2 lacked sharpness in printed images.

[0006] An object of the present invention is to provide a pretreatment liquid for inkjet printing, an ink set for inkjet printing, and an inkjet printing method that can produce printed matter with excellent image clarity. [Means for solving the problem]

[0007] The present inventors have found that the above-mentioned problems can be solved by providing a pretreatment liquid for inkjet printing to be applied to a printing medium that contains water, an anionic polymer compound (A), and a water-soluble base compound (B), wherein the water-soluble base compound (B) contains one or more compounds selected from the group consisting of ammonia and water-soluble amine compounds.

[0008] That is, the present invention provides the following [1] to [3]. [1] A pretreatment liquid for inkjet printing that is applied onto a printing medium, the pretreatment liquid contains water, an anionic polymer compound (A), and a water-soluble basic compound (B); The pretreatment liquid for inkjet printing, wherein the water-soluble basic compound (B) comprises at least one selected from the group consisting of ammonia and water-soluble amine compounds. [2] An ink set for inkjet printing, comprising the pretreatment liquid for inkjet printing according to [1] above, and an ink containing a colorant and water. [3] An inkjet printing method using the pretreatment liquid for inkjet printing according to [1] above, comprising the following steps 1 and 2: Step 1: Applying the inkjet printing pretreatment liquid to a printing medium to obtain a surface-treated printing medium. Step 2: A step of forming an image on the treated surface of the surface-treated printing medium obtained in Step 1 by inkjet printing using an ink containing a colorant and water. [Effects of the Invention]

[0009] The present invention can provide a pretreatment liquid for inkjet printing, an ink set for inkjet printing, and an inkjet printing method that can produce printed matter with excellent print image clarity. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Pretreatment liquid for inkjet printing] The pretreatment liquid for inkjet printing according to the present invention is a pretreatment liquid for inkjet printing to be applied onto a printing medium, the pretreatment liquid containing water, an anionic polymer compound (A), and a water-soluble base compound (B), wherein the water-soluble base compound (B) contains one or more compounds selected from the group consisting of ammonia and water-soluble amine compounds. In the present invention, the term "printing" is a concept that includes printing to record characters or images and printing letters. Hereinafter, the inkjet printing pretreatment liquid may be simply referred to as the "pretreatment liquid."

[0011] By using the pretreatment liquid according to the present invention, it is possible to obtain printed matter with excellent print image clarity. The reason for this is not clear, but is thought to be as follows. Inkjet printing is a printing method in which liquid is ejected as tiny droplets and deposited on the target substrate. As a result, during printing, ultra-fine droplets called mist can sometimes be scattered into the nozzles of a head other than the one that ejected the liquid. When a pretreatment agent containing an acid or cation, which has been widely used in the past, is used together with a water-based ink by inkjet printing, there is a risk that part of the pretreatment liquid will splash as a mist onto the head that ejects the ink during printing, causing the ink in the nozzles to aggregate.

[0012] On the other hand, the pretreatment liquid according to the present invention exhibits anionic properties, in which the acid groups of the polymer compound are neutralized with one or more compounds selected from the group consisting of ammonia and water-soluble amine compounds, and therefore is less likely to cause ink aggregation even if a mist of the pretreatment liquid is scattered onto the ejection head of the aqueous ink during printing. Furthermore, the ammonia and water-soluble amine compound used as neutralizing agents in the pretreatment liquid according to the present invention volatilize after printing with the pretreatment liquid, thereby canceling the neutralization of the polymer compound applied to the printing substrate and exerting the effect of aggregating the components in the ink. For these reasons, it is believed that use of the pretreatment liquid according to the present invention makes it possible to obtain printed matter with excellent print image clarity.

[0013] [Anionic polymer compound (A)] In the present invention, the term "anionic polymer compound" refers to a compound having an anionic group and a repeating structure derived from a monomer. In the present invention, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom; a linear, branched, or cyclic alkyl group; an alkali metal; ammonium, or an organic ammonium. Among these, the anionic resin preferably has a carboxy group (-COOM) as the anionic group. The weight average molecular weight of the anionic polymer compound (A) is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and is preferably 3,000,000 or less, more preferably 1,000,000 or less, even more preferably 200,000 or less. Furthermore, in the present invention, from the viewpoint of improving the continuous ejection stability of the ink and the clarity of the printed image of the obtained printed matter, the anionic polymer compound (A) preferably has an acid value of 50 mgKOH / g or more, more preferably 80 mgKOH / g or more, even more preferably 100 mgKOH / g or more, still more preferably 120 mgKOH / g or more, and preferably 320 mgKOH / g or less, more preferably 280 mgKOH / g or less, even more preferably 240 mgKOH / g or less, and still more preferably 200 mgKOH / g or less.

[0014] The acid value and weight average molecular weight of the anionic polymer compound (A) are measured by the method described in the Examples. The acid value of the anionic polymer compound (A) can also be calculated from the mass ratio of the constituent monomers. When the anionic polymer compound (A) has a crosslinked structure, the acid value of the anionic polymer compound (A) can also be calculated from the mass ratio of the constituent monomers and crosslinking agent.

[0015] Examples of the anionic polymer compound (A) include anionic vinyl resins, anionic urethane resins, and anionic silicone resins. The anionic polymer compound (A) may be used alone or in combination of two or more.

[0016] The anionic vinyl resin is preferably a vinyl resin containing a structural unit derived from a vinyl monomer having an anionic group. The vinyl monomer having an anionic group is preferably one or more selected from the group consisting of (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, more preferably one or more selected from the group consisting of (meth)acrylic acid and maleic acid, and even more preferably (meth)acrylic acid. That is, when the anionic polymer compound is an anionic vinyl resin, the anionic vinyl resin preferably contains structural units derived from one or more selected from the group consisting of (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, more preferably contains structural units derived from one or more selected from the group consisting of (meth)acrylic acid and maleic acid, and even more preferably contains structural units derived from (meth)acrylic acid. In the present invention, "(meth)acrylic acid" refers to at least one selected from the group consisting of acrylic acid and methacrylic acid. The "(meth)acrylic acid" used below has the same meaning.

[0017] The anionic vinyl resin may be either a homopolymer or a copolymer, but may also be a vinyl resin that further contains a structural unit derived from a hydrophobic vinyl monomer in addition to a structural unit derived from a vinyl monomer having an anionic group. Preferred examples of the hydrophobic vinyl monomer include one or more selected from the group consisting of alkyl(meth)acrylates having a linear, branched, or cyclic alkyl group with 1 to 22 carbon atoms, aryl group-containing (meth)acrylates having an aryl group with 6 to 22 carbon atoms, and styrene-based monomers. Preferred examples of alkyl(meth)acrylates having an alkyl group having 1 to 22 carbon atoms include alkyl(meth)acrylates having one or more linear or branched alkyl groups selected from the group consisting of methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, butyl(meth)acrylate, isobutyl(meth)acrylate, hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, dodecyl(meth)acrylate, and stearyl(meth)acrylate; and one or more cycloalkyl(meth)acrylates selected from the group consisting of cyclopentyl(meth)acrylate, cyclohexyl(meth)acrylate, and cycloheptyl(meth)acrylate. Preferred examples of the aryl group-containing (meth)acrylate having an aryl group having 6 to 22 carbon atoms include one or more selected from the group consisting of phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate. The styrene-based monomer is preferably at least one selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene. Among these, the hydrophobic vinyl monomer is more preferably one or more selected from the group consisting of alkyl(meth)acrylates having a linear or branched alkyl group having from 1 to 8 carbon atoms, cycloalkyl(meth)acrylates, and styrene-based monomers, even more preferably one or more selected from the group consisting of methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, isobutyl(meth)acrylate, cyclohexyl(meth)acrylate, styrene, and α-methylstyrene, even more preferably one or more selected from the group consisting of cyclohexyl(meth)acrylate, styrene, and α-methylstyrene, and even more preferably cyclohexyl(meth)acrylate. In the present invention, the term "(meth)acrylate" refers to at least one selected from the group consisting of acrylate and methacrylate. The term "(meth)acrylate" used below has the same meaning.

[0018] The content of vinyl monomers having an anionic group in the raw material monomers constituting the anionic vinyl resin, or the content of structural units derived from vinyl monomers having an anionic group in the anionic vinyl resin, is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 36% by mass or less, even more preferably 32% by mass or less. The content of hydrophobic vinyl monomers in the raw material monomers constituting the anionic vinyl resin, or the content of structural units derived from hydrophobic vinyl monomers in the anionic vinyl resin, is preferably 60% by mass or more, more preferably 64% by mass or more, even more preferably 68% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.

[0019] From the viewpoint of improving the continuous ejection stability of the ink, the anionic vinyl resin preferably has a crosslinked structure. From the same viewpoint, the anionic vinyl resin having a crosslinked structure is preferably one obtained by reacting an anionic vinyl resin containing a structural unit derived from a vinyl monomer having an anionic group and a structural unit derived from a hydrophobic vinyl monomer with a crosslinking agent. In this case, the anionic vinyl resin having a crosslinked structure has a structure derived from the crosslinking agent in addition to the structural unit derived from the vinyl monomer having an anionic group and the structural unit derived from the hydrophobic vinyl monomer. As the crosslinking agent, from the viewpoint of improving the continuous ejection stability of the ink, a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms is preferred, one or more compounds selected from the group consisting of pentaerythritol polyglycidyl ether and trimethylolpropane polyglycidyl ether is more preferred, and trimethylolpropane polyglycidyl ether is even more preferred.

[0020] The crosslinking rate of the anionic vinyl resin having a crosslinked structure is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, even more preferably 60 mol% or less. When the anionic vinyl resin having a crosslinked structure is obtained by reacting an anionic vinyl resin containing a structural unit derived from a vinyl monomer having an anionic group and a structural unit derived from a hydrophobic vinyl monomer with a crosslinking agent, the crosslinking rate is calculated from the equivalent of the anionic group in the anionic vinyl resin before crosslinking and the equivalent of the crosslinkable functional group in the crosslinking agent, and is expressed as "the number of molar equivalents of the crosslinkable functional group in the crosslinking agent / the number of molar equivalents of the anionic group in the anionic vinyl resin before crosslinking."

[0021] The anionic vinyl resin may be a synthesized product or a commercially available product, and may be produced by copolymerizing raw material monomers by a known polymerization method. The anionic vinyl resin is preferably used as a dispersion.

[0022] Anionic urethane resins are resins that contain structural units derived from organic compounds (polyols) that have two or more alcoholic hydroxyl groups per molecule, structural units derived from polyisocyanates, and structural units derived from dialkanolcarboxylic acids. Anionic urethane resins are obtained by polyaddition reaction of polyols, polyisocyanates, and dialkanolcarboxylic acids. The anionic urethane resin is preferably a polycarbonate-based polyurethane or a polyester-based polyurethane. The anionic urethane resin is preferably used as an emulsion, and the emulsion may contain a dispersant such as a surfactant, if necessary.

[0023] An anionic silicone resin is a resin having a silicone structure and an anionic group in the resin structure. The silicone structure may be present in the main chain structure of the resin or as a side chain of the resin. In the present invention, when an anionic resin has a polyurethane structure or a vinyl structure in addition to a silicone structure, it is classified as an anionic silicone resin if it has a silicone structure in the resin structure.

[0024] [Water-soluble basic compound (B)] The pretreatment liquid according to the present invention contains a water-soluble basic compound (B). In the present invention, the term "water-soluble basic compound" means that the solubility in 100 g of water at 25°C (hereinafter simply referred to as "water solubility") is 5 g or more (5 g / 100 g H2O). The water-soluble basic compound (B) contains one or more compounds selected from the group consisting of ammonia and water-soluble amine compounds, but may further contain a water-soluble basic compound other than ammonia and water-soluble amine compounds, as long as the effects of the present invention are not impaired. The water-soluble basic compound (B) suppresses pH fluctuations due to environmental changes, and can maintain the pH of the pretreatment liquid constant, thereby functioning as a pH adjuster. The water-soluble basic compound (B) can be used alone or in combination of two or more.

[0025] Examples of the water-soluble amine compound (B) include alkanolamines such as N,N-dimethylethanolamine, diethanolamine, triethanolamine, and N-methyldiethanolamine; primary amines, secondary amines, tertiary amines, and quaternary ammonium salts. From the viewpoint of improving the continuous ejection stability of the ink and the clarity of the printed image, the water-soluble amine compound (B) is preferably one or more selected from the group consisting of primary alkanolamines, secondary alkanolamines, and tertiary alkanolamines, more preferably a secondary alkanolamine, and even more preferably N,N-dimethylethanolamine (also referred to as N,N-dimethylaminoethanol). Examples of water-soluble basic compounds other than ammonia and water-soluble amine compounds include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; and alkali metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate, and sodium hydrogencarbonate. When the water-soluble basic compound (B) is an alkanolamine, a primary amine, a secondary amine, a tertiary amine, or a quaternary ammonium salt, these amines or quaternary ammonium salts are preferably monovalent.

[0026] The water-soluble base compound (B) may further contain a water-soluble base compound other than ammonia and the water-soluble amine compound. From the viewpoint of improving the continuous ejection stability of the ink and the clarity of the printed image, the content of one or more compounds selected from the group consisting of ammonia and the water-soluble amine compounds in the water-soluble base compound (B) is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 95 mol % or more, and even more preferably 100 mol %. From the viewpoint of improving the continuous ejection stability of the ink and the clarity of the printed image, the boiling point of the water-soluble amine compound (B) is preferably 85°C or higher, more preferably 100°C or higher, and even more preferably 200°C or higher, and is preferably 350°C or lower, more preferably 320°C or lower, and even more preferably 270°C or lower.

[0027] 〔water〕 The pretreatment liquid according to the present invention contains water. The pretreatment liquid according to the present invention is preferably aqueous. The pretreatment liquid according to the present invention being "aqueous" means that water accounts for the largest proportion by mass of the liquid components contained in the pretreatment liquid. The water is preferably pure water or ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, etc., from which ionic impurities have been removed as much as possible.

[0028] (Water-soluble organic solvent) The pretreatment liquid according to the present invention preferably further contains a water-soluble organic solvent from the viewpoints of improving the continuous ejection stability of the ink and the clarity of the printed image of the resulting printed matter. In the present invention, the term "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 10 mL or more. The water-soluble organic solvents can be used alone or in combination of two or more. From the viewpoint of improving the clarity of the printed image of the resulting printed matter, the static surface tension of the water-soluble organic solvent measured at 25°C is preferably 40 mN / m or less, more preferably 38 mN / m or less, and is preferably 18 mN / m or more, more preferably 20 mN / m or more, even more preferably 22 mN / m or more, and still more preferably 24 mN / m or more. The static surface tension of the water-soluble organic solvent at 25°C is measured by the method described in the Examples. When two or more organic solvents are used as the water-soluble organic solvent, the static surface tension of the water-soluble organic solvent is a weighted average value weighted by the content (mass %) of each organic solvent.

[0029] The boiling point of the water-soluble organic solvent under atmospheric pressure is preferably 280°C or lower, more preferably 260°C or lower, and even more preferably 240°C or lower, from the viewpoint of promoting evaporation from the printing medium and improving the clarity of the printed image in the obtained printed matter, and is preferably 140°C or higher, more preferably 160°C or higher, and even more preferably 180°C or higher, from the viewpoint of improving the continuous ejection stability of the ink and suppressing uneven distribution of components that suppress wetting and spreading by suppressing excessive acceleration of the evaporation rate, thereby improving the clarity of the printed image in the obtained printed matter. When two or more organic solvents are used as the water-soluble organic solvent, the boiling point of the water-soluble organic solvent is a weighted average value weighted by the content (mass %) of each organic solvent.

[0030] Examples of the water-soluble organic solvent include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, etc. Among these, one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred.

[0031] Examples of polyhydric alcohols include diols such as ethylene glycol, diethylene glycol, propylene glycol (1,2-propanediol), 1,3-propylene glycol, dipropylene glycol (isomer mixture), 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, triethylene glycol, polyethylene glycol, and polypropylene glycol.

[0032] Examples of polyhydric alcohol alkyl ethers include (poly)alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, and dipropylene glycol dimethyl ether. Examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0033] Examples of the nitrogen-containing heterocyclic compound include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and ε-caprolactam. Examples of amides include formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide. Examples of amines include monoethanolamine, diethanolamine, triethanolamine, and triethylamine. Examples of sulfur-containing compounds include dimethyl sulfoxide, sulfolane, and thiodiethanol.

[0034] The pretreatment liquid according to the present invention may further contain, as necessary, other components such as a pH adjuster other than the water-soluble basic compound (B), a surfactant, a fixing aid, a colorant, an antifoaming agent, an antiseptic / fungal agent, and a rust inhibitor.

[0035] The pretreatment liquid according to the present invention preferably further contains a surfactant. The surfactant is preferably a nonionic surfactant. Examples of nonionic surfactants include polyoxyalkylene alkyl ether surfactants, acetylene glycol surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorine surfactants. Among these, the surfactant is more preferably one or more selected from the group consisting of acetylene glycol surfactants and silicone surfactants, and even more preferably a combination of a silicone surfactant and an acetylene glycol surfactant.

[0036] Examples of acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and ethylene oxide adducts of these diols. The sum (n) of the average number of moles of ethyleneoxy groups (EO) added in the ethylene oxide adduct is preferably 0 or more and preferably 20 or less, more preferably 10 or less. The HLB of the acetylene glycol surfactant is preferably 2 or more, more preferably 3 or more, and preferably 6 or less.

[0037] The silicone surfactant is preferably, for example, one or more selected from the group consisting of polyether-modified silicones and amino-modified silicones, with polyether-modified silicones being more preferred. When the silicone surfactant is a polyether-modified silicone, its HLB is preferably 5 or more, more preferably 6 or more, and preferably 15 or less.

[0038] Examples of commercially available nonionic surfactants include the "Surfynol" series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals, the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd., the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd., "Silface SAG005" manufactured by Nissin Chemical Industry Co., Ltd., and "BYK-348" manufactured by BYK Japan KK. The surfactants can be used alone or in combination of two or more.

[0039] (pH adjusters other than water-soluble basic compounds (B)) Examples of pH adjusters other than the water-soluble basic compound (B) include acidic compounds used to acidify the pretreatment solution, and specific examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and boric acid; organic acids such as acetic acid, citric acid, succinic acid, tartaric acid, malic acid, fumaric acid, malonic acid, ascorbic acid, and glutamic acid; and acetates of alkali metals such as lithium acetate and sodium acetate.

[0040] The pretreatment liquid according to the present invention may contain a colorant as long as the effects of the present invention are not impaired. Examples of such colorants include those used in the colorant-containing inks described below. When the pretreatment liquid according to the present invention contains a colorant, the colorant is preferably a pigment or a hydrophobic dye from the viewpoint of water resistance, and preferably a pigment from the viewpoint of achieving high weather resistance.

[0041] [Composition of pretreatment solution] The content of the anionic polymer compound (A) in the pretreatment liquid according to the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of improving the continuous ejection stability of the ink and the clarity of the printed image of the obtained printed matter, and from the same viewpoints, is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less.

[0042] The content of the water-soluble basic compound (B) in the pretreatment liquid according to the present invention is preferably 0.2% by mass or more, more preferably 4% by mass or more, and even more preferably 0.5% by mass or more, from the viewpoint of improving the continuous ejection stability of the ink and the clarity of the printed image of the obtained printed matter, and from the same viewpoints, is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0043] From the viewpoint of improving the clarity of the printed image of the obtained printed matter, the content of the water-soluble organic solvent in the pretreatment liquid according to the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and still more preferably 25% by mass or more, and from the same viewpoint, is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and still more preferably 35% by mass or less.

[0044] The water content in the pretreatment liquid according to the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, and still more preferably 70% by mass or less. In addition, when the pretreatment liquid contains a polyvalent metal salt and the polyvalent metal salt is used in the form of a hydrate having water of hydration as a raw material form, the content of water in the pretreatment liquid according to the present invention means the amount including the content of water from the hydrate of the polyvalent metal salt.

[0045] When the pre-treatment liquid according to the present invention contains a surfactant, the content of the surfactant in the pre-treatment liquid is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.4% by mass or more, and from the same viewpoint, is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. The content of the colorant in the pretreatment liquid according to the present invention is preferably 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, still more preferably 0.1% by mass or less, and even more preferably 0% by mass.

[0046] From the viewpoint of further improving the continuous ejection stability of the ink and suppressing odor, the pretreatment liquid according to the present invention preferably does not contain a polyvalent metal salt, a cationic polymer compound, or an organic acid. Specifically, the contents of the polyvalent metal salt, the cationic polymer compound, and the organic acid in the pretreatment liquid are each preferably independently 0% by mass.

[0047] In the present invention, the polyvalent metal salt refers to a salt composed of a divalent or higher polyvalent metal ion and an anion (a counter ion of the polyvalent metal ion). Examples of divalent or higher polyvalent metal ions include ions of calcium, magnesium, copper, nickel, zinc, barium, aluminum, titanium, strontium, chromium, cobalt, iron, and the like. The anions constituting the polyvalent metal salt include inorganic ions and organic ions. Examples of inorganic ions include monovalent anions such as nitrate ions and halide ions; and divalent anions such as sulfate ions. The organic ions include organic acid ions such as carboxylate ions. Specific examples of polyvalent metal salts include magnesium nitrate, magnesium sulfate, calcium nitrate, and aluminum nitrate.

[0048] In the present invention, the cationic polymer compound refers to a compound having a cationic group and a repeating structure derived from a monomer. The "cationic group" has the same meaning as the cationic group explained in the section on cationic surfactants, and the cationic polymer compound usually has one or more groups selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, and a quaternary ammonium group. The basic group includes those neutralized with acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, maleic acid, fumaric acid, citric acid, tartaric acid, adipic acid, and lactic acid.

[0049] Examples of organic acids include formic acid, acetic acid, glycolic acid, oxalic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, pyrrolidonecarboxylic acid, pyronecarboxylic acid, pyrrolecarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumaric acid, thiophenecarboxylic acid, nicotinic acid, derivatives of these compounds, and salts thereof.

[0050] The pretreatment liquid according to the present invention is preferably prepared by appropriately mixing an anionic polymer compound (A), a water-soluble base compound (B), water, and, if necessary, a water-soluble organic solvent, a hydrophilic nonionic surfactant, a hydrophobic surfactant, a cationic surfactant, and, if necessary, the other components described above. The pH of the pretreatment liquid can be appropriately adjusted by using the water-soluble base compound (B) and, if necessary, other pH adjusters. The pH of the pretreatment liquid according to the present invention is preferably higher than 7. When the pH of the pretreatment liquid according to the present invention is higher than 7, the anionic polymer compound (A) can be neutralized and dissolved before use. The pH of the pretreatment solution is more preferably 7.3 or higher, even more preferably 7.5 or higher, and even more preferably 8.0 or higher, and is preferably 11.0 or lower, more preferably 10.5 or lower, and even more preferably 10.0 or lower. The pH of the treatment solution of the present invention is measured by the method described in the Examples.

[0051] [Inkjet printing ink set] <Inkjet printing ink> Hereinafter, an ink for inkjet printing that can be applied to a printing medium that has been treated with the treatment liquid of the present invention (hereinafter also referred to as a "surface-treated printing medium") will be described. The ink for inkjet printing preferably contains a colorant and water from the viewpoint of improving the clarity of printed images when a liquid-absorbent printing medium is used. That is, in the present invention, the treatment liquid can be used as an inkjet printing ink set together with an ink containing a colorant and water.

[0052] [Coloring Agent] The colorant used in the inkjet printing ink according to the present invention may be either a dye or a pigment. Among these, it is preferable to use a pigment as the colorant from the viewpoint of water resistance, light resistance, weather resistance, gas resistance, etc. The pigment may be any of known organic pigments and inorganic pigments, and may be used singly or in combination of two or more kinds, or may be a mixed crystal. Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Examples of organic pigments include azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (e.g., basic dye chelates, acid dye chelates, etc.), nitro pigments, nitroso pigments, and aniline black. Specific examples of pigments for black inks include carbons such as lamp black (CI Pigment Black 6), furnace black, acetylene black, channel black, and other carbon blacks (CI Pigment Black 7); metals such as copper-chromium oxide (CI Pigment Black 28), iron oxide (CI Pigment Black 11), and titanium oxide (CI Pigment Black 35); and organic pigments such as aniline black (CI Pigment Black 1). Specific examples of pigments for chromatic inks include one or more product numbers selected from the group consisting of CI Pigment Yellow, CI Pigment Orange, CI Pigment Red, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green.

[0053] The dye is not particularly limited, and examples thereof include acid dyes, basic dyes, direct dyes, reactive dyes, etc. The dyes may be used alone or in combination of two or more. Examples of the dye include product numbers selected from the group consisting of CI Acid Yellow, CI Acid Red, CI Acid Blue, CI Acid Black, CI Food Black, CI Direct Yellow, CI Direct Red, CI Direct Blue, CI Direct Black, CI Reactive Red, and CI Reactive Black.

[0054] When an inkjet printing ink contains a pigment, the pigment is dispersed in a medium in the ink. The form of the pigment in the inkjet printing ink may be a form in which the pigment is dispersed using a resin (hereinafter also referred to as a "pigment dispersion resin") or a surfactant as a dispersant, or a form of a self-dispersed pigment that is dispersed without using a dispersant. Among these, the form in which the pigment in the colorant-containing ink is dispersed using a pigment dispersion resin is preferred. The pigment dispersing resin may be either a water-soluble resin or a water-insoluble resin. Here, with regard to "water-soluble" and "water-insoluble" resins, when a resin that has reached a constant weight after drying at 105°C for 2 hours is dissolved in 100 g of water at 25°C until saturation is reached, if the dissolved amount exceeds 10 g it is judged to be "water-soluble," and if it is 10 g or less it is judged to be "water-insoluble." Furthermore, as will be described later, if the resin has an anionic group, the dissolved amount is the amount measured in the presence of a neutralizer under conditions where the mass ratio of the resin to the neutralizer is the same as that in an inkjet printing ink.

[0055] Specific examples of the form of the pigment in the inkjet printing ink, from the viewpoint of improving the dispersion stability of the pigment, include (a) a form in which a water-soluble resin is adsorbed onto the surface of the pigment, (b) a form in which a water-soluble surfactant or a water-dispersible surfactant is adsorbed onto the surface of the pigment, (c) a form in which a hydrophilic functional group is chemically or physically introduced onto the surface of the pigment and the pigment is dispersed without using a pigment dispersing resin or a surfactant, and (d) a form in which the pigment is coated with a water-insoluble resin.

[0056] The pigments having the above-mentioned forms (a) to (d) are preferably anionic. In form (a), the water-soluble resin preferably has an anionic group, in form (b), the water-soluble surfactant or water-dispersible surfactant preferably has an anionic group, in form (c), the hydrophilic functional group introduced onto the pigment surface preferably has an anionic group, and in form (d), the water-insoluble resin preferably has an anionic group. The anionic group is as defined for the anionic polymer compound (A). Examples of the anionic group include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Among these, the anionic resin preferably has a carboxy group as the anionic group, and M is preferably an alkali metal. As described above, the pretreatment liquid according to the present invention exhibits anionic properties, in which the acid groups of the polymer compound are neutralized with one or more compounds selected from the group consisting of ammonia and water-soluble amine compounds. Therefore, the pretreatment liquid according to the present invention is preferably used together with an aqueous ink containing a pigment dispersed using an anionic dispersant whose acid groups have been neutralized. Even if a mist of the pretreatment liquid is scattered onto the ejection head of the aqueous ink during printing, the ink is less likely to aggregate, and good ejection properties can be maintained more stably even during continuous printing.

[0057] Among these, the form of the pigment in the inkjet printing ink is preferably one or more forms selected from the group consisting of form (c) and form (d), more preferably form (d), from the viewpoint of reducing the dispersibility of dispersoids present in the ink and efficiently exerting an aggregation effect, thereby improving the clarity of the printed image in the resulting printed matter. When the form of the pigment in the inkjet printing ink is form (d), the form in which the pigment is coated with the water-insoluble resin includes a form in which the water-insoluble resin encapsulates the pigment, a form in which the pigment is uniformly dispersed in the water-insoluble resin, a form in which the pigment is exposed from the surface of the water-insoluble resin particles, a form in which the water-insoluble resin is adsorbed to the pigment, and the like. When the pigment in the inkjet printing ink is in the form (d), the pigment is preferably coated with a water-insoluble resin having a crosslinked structure. In the form in which the pigment is coated with a water-insoluble resin having a crosslinked structure, the water-insoluble resin preferably has a structure containing a polymer component having a linear two-dimensional structure, which may have branched chains, and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a polymer having a linear two-dimensional structure, which may have branched chains, being converted into a three-dimensional structure by the component derived from the crosslinking agent.

[0058] [Pigment dispersing resin] When the inkjet printing ink is in the form (d), the type of water-insoluble resin used to disperse the pigment as the pigment dispersing resin of the inkjet printing ink is not particularly limited. Specific examples of water-insoluble resins include (meth)acrylic resins, styrene / (meth)acrylic resins, maleic acid resins, styrene / maleic acid resins, urethane resins, and polyester resins. Furthermore, when the pigment in the colorant-containing ink is in the form (d) and the pigment is coated with a water-insoluble resin having a crosslinked structure, the constituent component of the polymer having a linear two-dimensional structure that may have a branched chain is preferably at least one selected from the group consisting of (meth)acrylic resins, styrene / (meth)acrylic resins, urethane resins, and polyester resins, from the viewpoint of forming high-quality printed images, and more preferably at least one selected from the group consisting of (meth)acrylic resins and styrene / (meth)acrylic resins. The water-insoluble resin may be synthesized by a known method or may be a commercially available product. The water-insoluble resin may be used alone or in combination of two or more.

[0059] The weight average molecular weight of the pigment dispersing resin is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and is preferably 200,000 or less, more preferably 100,000 or less, even more preferably 80,000 or less. The weight average molecular weight of the pigment dispersing resin is measured by the method described in the examples. When the colorant-containing ink is in the form (d) in which the pigment is coated with a water-insoluble resin having a crosslinked structure, the number average molecular weight of the polymer component having a linear two-dimensional structure which may have a branched chain, which is the water-insoluble resin used to disperse the pigment as the pigment dispersing resin, is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. The acid value of the pigment dispersing resin is preferably 5 mgKOH / g or more, more preferably 50 mgKOH / g or more, even more preferably 70 mgKOH / g or more, and still more preferably 90 mgKOH / g or more, and is preferably 800 mgKOH / g or less, more preferably 500 mgKOH / g or less, and even more preferably 300 mgKOH / g or less. The acid value of the pigment dispersing resin can be determined by the method described in the examples, or can be calculated from the mass ratio of the constituent monomers. When the pigment dispersing resin has a crosslinked structure, the acid value of the pigment dispersing resin can also be calculated from the mass ratio of the constituent monomers and crosslinking agent.

[0060] [Fixing resin] From the viewpoint of forming a high-quality printed image, the colorant-containing ink may contain a resin that functions as a fixing aid (hereinafter also referred to as a "fixing resin"). The fixing resin in the colorant-containing ink is preferably in the form of a resin that does not coat the pigment, and more preferably in the form of resin particles that do not contain a pigment. The fixing resin is not particularly limited and can be appropriately selected depending on the purpose. Specific examples of the fixing resin include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene / butadiene resin, vinyl chloride resin, styrene / acrylic resin, and acrylic silicone resin. The ink can be obtained by mixing a particulate fixing resin with a colorant, water, an organic solvent, etc. The fixing resin may be a synthesized one or a commercially available product. The fixing resin may be used alone or in combination of two or more.

[0061] 〔wax〕 The inkjet printing ink may contain wax from the viewpoint of forming a high-quality printed image. As used herein, "wax" refers to an organic substance that is solid or semi-solid at room temperature (25°C) and becomes liquid when heated. Here, "semi-solid wax" means that the wax deforms and flows when force is applied to it, but can maintain a certain shape when no force is applied to it. Furthermore, the temperature at which wax becomes liquid when heated, known as the melting point of wax, is in the temperature range of 45°C or higher. The wax may be either a natural wax or a synthetic wax. Examples of natural waxes include petroleum waxes such as paraffin wax and microcrystalline wax; vegetable waxes such as carnauba wax, candelilla wax and rice wax; and animal waxes such as lanolin and beeswax. Examples of synthetic waxes include synthetic hydrocarbon waxes such as polyolefin wax and Fischer-Tropsch wax; silicone wax; and modified waxes such as paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives. Among these, polyolefin waxes containing an olefin monomer as the main component are preferred. The waxes can be used alone or in combination of two or more.

[0062] The inkjet printing ink preferably contains wax as a dispersion (hereinafter also referred to as "wax dispersion"). The wax dispersion is not particularly limited, and examples thereof include those prepared by emulsifying wax with a known surfactant, such as a nonionic surfactant or an anionic surfactant. Examples of nonionic surfactants include ethylene oxide adducts of higher alcohols and ethylene oxide adducts of alkylated phenols. Examples of anionic surfactants include sulfates and phosphates based on ethylene oxide adducts of higher alcohols; and alkylated benzenesulfonates. Among these, from the viewpoint of improving the ink ejection stability and the image fastness of printed matter, a nonionic wax dispersion obtained by emulsifying wax with a nonionic surfactant is preferred, and a nonionic polyolefin wax dispersion is more preferred. Suitable examples of commercially available wax dispersions include the "Hi-Tec E" series manufactured by Toho Chemical Industry Co., Ltd., the "AQUACER" series manufactured by BYK, the "Cellosol" series manufactured by Chukyo Yushi Co., Ltd., and the "Chemipearl" series manufactured by Mitsui Chemicals, Inc.

[0063] 〔water〕 The ink for inkjet printing is preferably a water-based ink containing water. Here, "water-based" means that water accounts for the largest proportion by mass of the ink-jet printing ink medium. The water contained in the ink for inkjet printing is preferably ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water.

[0064] [Water-soluble organic solvent] The inkjet printing ink may further contain a water-soluble organic solvent as the aqueous medium. Examples of the water-soluble organic solvent contained in the ink include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0065] From the viewpoint of environmental friendliness, the water content in the aqueous medium of the colorant-containing ink is preferably 51% by mass or more, more preferably 53% by mass or more, even more preferably 55% by mass or more, still more preferably 57% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and still more preferably 80% by mass or less.

[0066] The inkjet printing ink may contain surfactants, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, pH adjusters, and the like, as required.

[0067] [Composition of ink for inkjet printing] From the viewpoint of improving the image density of the printed matter, the content of the colorant in the inkjet printing ink is preferably 2% by mass or more, more preferably 3% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When the inkjet printing ink contains a pigment as a colorant, the content of the pigment in the ink is preferably 2% by mass or more, more preferably 3% by mass or more, from the viewpoint of improving the image density of the printed matter, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When the inkjet printing ink contains a pigment dispersing resin, the content of the pigment dispersing resin in the ink is preferably 2% by mass or more, more preferably 3% by mass or more, from the viewpoint of pigment dispersion stability and forming a high-quality printed image, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of improving the image density of the printed matter. When the inkjet printing ink contains a pigment dispersion resin, the mass ratio of the pigment content to the pigment dispersion resin content in the ink [pigment / pigment dispersion resin] is preferably 0.30 or more, more preferably 0.50 or more, and even more preferably 0.60 or more, from the viewpoint of improving the image density of the printed matter, and is preferably 1.00 or less, more preferably 0.90 or less, and even more preferably 0.80 or less, from the viewpoint of pigment dispersion stability and forming a high-quality printed image. When the inkjet printing ink contains a fixing resin, the content of the fixing resin in the ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of forming a high-quality printed image, and is preferably 10% by mass or less, more preferably 7% by mass or less, from the viewpoint of improving the image density of the printed matter. When the inkjet printing ink contains wax, the content of wax in the ink is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.8% by mass or more, from the viewpoint of forming a high-quality printed image, and is preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less. When the inkjet printing ink contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the ink is, from the viewpoint of forming a high-quality printed image, preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 42% by mass or less, even more preferably 38% by mass or less, and still more preferably 35% by mass or less. From the viewpoint of environmental friendliness, the water content in the inkjet printing ink is preferably 30% by mass or more, more preferably 33% by mass or more, even more preferably 35% by mass or more, and still more preferably 37% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0068] [Inkjet printing method] As an inkjet printing method using the pretreatment liquid for inkjet printing of the present invention, a method of forming an image by inkjet printing using an ink for inkjet printing on the treated surface of a surface-treated printing medium that has been treated with the treatment liquid is preferred, and a method including the following steps 1 and 2 is more preferred. Step 1: Applying the inkjet printing pretreatment liquid to a printing medium to obtain a surface-treated printing medium. Step 2: A step of forming an image on the treated surface of the surface-treated printing medium obtained in Step 1 by inkjet printing using an ink containing a colorant and water.

[0069] [Process 1] Step 1 is a step of applying a pretreatment liquid for inkjet printing to a printing medium to obtain a surface-treated printing medium.

[0070] (print media) The printing medium used in the present invention may be either a low-absorbency printing medium or a high-absorbency printing medium, but from the viewpoint of the clarity of the printed image of the resulting printed matter, a low-absorbency printing medium is preferred. In the present invention, whether a printing medium has low or high liquid absorption is determined by the amount of water absorbed by the printing medium when the printing medium is in contact with pure water for 100 ms. The amount of water absorbed can be measured as the amount of water transferred when the printing medium is in contact with pure water for 100 ms using an automatic scanning liquid absorption meter (for example, the "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions of 23°C and 50% relative humidity. In the present invention, the term "low liquid absorption" is a concept that includes low liquid absorption and non-liquid absorption, and the water absorption amount is 0 g / m 2 More than 7g / m 2 "Highly absorbent" means that the water absorption is 7 g / m or less. 2 It means to be super. Examples of low-absorbency print media include low-absorbency coated paper and non-absorbent resin film. Examples of coated paper include general-purpose glossy paper and multicolor foam gloss paper. The resin film is preferably at least one selected from the group consisting of polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film. These resin films may be surface-treated, such as by corona discharge treatment. Highly absorbent print media include highly absorbent plain paper. When a resin film is used as the low-liquid-absorbent printing medium, step 1 may be performed by setting areas to become dark image forming areas and light image forming areas based on a mirror image of the desired printed image, so that the printed image will appear as the desired image when viewed from the opposite side of the printed image forming surface of the non-liquid-absorbent film.

[0071] There are no particular limitations on the method for applying the pretreatment liquid to the print medium, and examples of methods for applying the pretreatment liquid to the print medium include immersion, roller application, spray application, brush application, and application by inkjet printing. Among these, application by a roller is preferred from the viewpoint of being able to apply the pretreatment liquid simply and uniformly. The roller application method refers to (i) a method in which the pretreatment liquid is held in the gap between the print medium and a member that comes into contact with the print medium, and one of the print medium and the member that comes into contact with the print medium is moved to spread the pretreatment liquid applied to a portion of the print medium over the entire print medium, thereby obtaining a surface-treated print medium that has been treated with the pretreatment liquid, or (ii) a method in which the print medium and a member that is in contact with the print medium or is close to the print medium and holds a small gap therebetween are rotated to print the pretreatment liquid onto the print medium or to cause the print medium to absorb the pretreatment liquid held in the small gap. Specific examples of rollers used for roller application include offset gravure coaters, gravure coaters, doctor coaters, bar coaters, blade coaters, flexo coaters, and roll coaters. Among these, one or more types selected from the group consisting of doctor coaters, bar coaters, and roll coaters are preferred. Furthermore, from the viewpoint of being able to perform steps 1 and 2 continuously, the device used to apply the pretreatment liquid to the printing medium is preferably one that integrates a means for applying the pretreatment liquid used in step 1, a heat drying means used in step 1, and a means for applying the inkjet printing ink used in step 2. In this case, for example, a means for applying the pretreatment liquid, such as a roller coater, may be incorporated into the inkjet printing device described below.

[0072] From the viewpoint of improving the clarity of the printed image of the resulting printed matter, the pretreatment liquid according to the present invention is preferably applied to the printing medium in a solid state, that is, so that the printing duty of the pretreatment liquid is 100%.

[0073] The amount of the pretreatment liquid applied to the printing medium is preferably 0.2 g / m from the viewpoint of improving the clarity of the printed image of the resulting print. 2 More preferably, 0.5 g / m 2 More preferably, 1 g / m 2 From the same viewpoint, it is preferably 5 g / m 2Less than 2 g / m, more preferably 2 The following is the result.

[0074] From the viewpoint of step 1, it is preferable that after the pretreatment liquid is applied to the printing medium, the pretreatment liquid on the printing medium is dried. The drying method in step 1 may be static drying, air drying, heat drying, or reduced pressure drying. The temperature during drying in step 1 is preferably 100°C or lower, more preferably 90°C or lower, even more preferably 80°C or lower, and even more preferably 70°C or lower, from the viewpoint of suppressing deformation of the printing medium, and is preferably 20°C or higher, more preferably 25°C or higher, from the viewpoint of drying in a short time. The drying time in step 1 is preferably 0.5 minutes or more, more preferably 1 minute or more, and preferably 30 minutes or less, more preferably 20 minutes or less, and even more preferably 10 minutes or less.

[0075] [Process 2] Step 2 is a step of forming an image on the treated surface of the surface-treated print medium obtained in step 1 by inkjet printing using an ink containing a colorant and water (ink for inkjet printing). The inkjet printing ink is loaded into a known inkjet printing device and adheres as ink dots to the treated surface of the surface-treated printing medium obtained in step 1, thereby forming an image. Any type of inkjet printing device can be used, such as a thermal type or a piezo type.

[0076] In the present invention, examples of the printed image that can be formed include images such as outlined characters, one-dimensional codes such as barcodes, matrix-type or stack-type two-dimensional codes, and extremely small characters. In the present invention, "image of blank characters" means an image in which characters can be recognized by light image forming areas of a color other than the first color against a background of dark image forming areas inkjet printed in a first color. In this case, the first color and the color other than the first color may be primary colors such as yellow, magenta, cyan, and black, respectively, or may be a mixture of these primary colors, that is, a secondary color. Among these print images, from the viewpoint of improving the clarity of the print image on the resulting printed matter, a cut-out character image is preferred as the print image to be formed. [Example]

[0077] 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. The physical properties of the resin and the like were measured by the following methods.

[0078] [Measurement of number average molecular weight and weight average molecular weight of resin] The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: 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)] (Tosoh Corporation) Measurement sample: 0.1 g of resin was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered through a syringe filter "DISMIC-13HP" (PTFE, 0.2 μm, Advantec Co., Ltd.) to calculate the number average molecular weight or weight average molecular weight of the resin.

[0079] [Measurement of resin acid value] Using an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), the resin without a crosslinked structure was dissolved in a titration solvent consisting of a 2:1 mixture of toluene and acetone. Alternatively, the resin with a crosslinked structure was dispersed in the titration solvent and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0080] [Measurement of solid concentration] 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm), and approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed and maintained at 105°C for 2 hours to remove volatiles. The mixture was then left in the desiccator for a further 15 minutes, after which the mass was measured. The mass of the sample after devolatilization was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration (%).

[0081] [Measurement of the average particle size of resin particles containing no pigment and resin particles containing pigment] Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was taken as the average particle size of resin particles containing no pigment or resin particles containing pigment. The measurement sample had a particle concentration of 5 × 10 -3 The dispersion was diluted with water to a concentration of 1.333 (solids content equivalent). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 integrations. The refractive index of water (1.333) was entered as the refractive index of the dispersion medium.

[0082] [Measurement of static surface tension of water-soluble organic solvents at 25°C] A platinum plate was immersed in a cylindrical polyethylene container (3.6 cm diameter x 1.2 cm depth) containing 5 g of sample adjusted to 25°C, and the static surface tension at 25°C was measured by the Wilhelmy method using a surface tensiometer (Kyowa Interface Science Co., Ltd., "CBVP-Z").

[0083] <Production of Anionic Polymer Compound (A)> (1) Preparation of acrylic resin before crosslinking and neutralization (acrylic resin C) Manufacturing Example 1-1: Manufacturing of acrylic resin C-1 A reaction vessel equipped with a stirrer, a reflux condenser, and a dropping tank was initially charged with 2.75 parts of cyclohexyl acrylate, 1.30 parts of acrylic acid, 0.95 parts of butyl acrylate, 4.50 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), and 0.50 parts of water, and the mixture was stirred for 10 minutes while maintaining the temperature of the reaction vessel at 77°C. Next, a mixture of 24.75 parts cyclohexyl acrylate, 11.70 parts acrylic acid, 8.55 parts butyl acrylate, 39.36 parts MEK, 4.36 parts water, 0.56 parts 4,4'-azobis(4-cyanovaleric acid) as a polymerization initiator, and 0.72 parts 3-mercaptopropionic acid as a chain transfer agent was continuously added to the reaction vessel over 5 hours. After the addition was completed, the polymerization reaction was carried out for 1 hour, and then the mixture was cooled to room temperature to terminate the polymerization reaction, yielding a solution of acrylic resin C-1 (solids concentration 50%). The physical properties of acrylic resin C-1 are shown in Table 1.

[0084] Production Examples 1-2 to 1-4: Production of acrylic resins C-2 to C-4 Solutions of acrylic resins C-2 to C-4 (all with a solid content of 50%) were obtained in the same manner as in Production Example 1-1, except that the raw material monomer composition was changed to a composition according to the types and amounts shown in Table 1. In Table 1, blank spaces indicate that the corresponding ingredient is not used (0% in quantity).

[0085] [Table 1]

[0086] (2) Preparation of anionic polymer compound (A) As the anionic polymer compound (A), the following acrylic resins (1) to (9) were produced.

[0087] Manufacture of acrylic resin (1) 20.54 parts of the acrylic resin C-1 solution obtained in Production Example 1-1 was diluted with 8.80 parts of MEK to a solids concentration of 35%. Next, 0.76 parts of 25% aqueous ammonia (Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the solution so that the degree of neutralization of the acrylic resin C-1 was 30 mol%, and the mixture was stirred at 25°C. 69.14 parts of water was then added over 1 hour. After the addition was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of the acrylic resin C-1 (solids concentration 25%).

[0088] To 100 parts of the resulting aqueous dispersion, 4.69 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321L, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 130 g / eq.) as a crosslinking agent and 43.78 parts of ion-exchanged water were added, and the mixture was heated with stirring at 70°C for 3 hours. After cooling to room temperature, the liquid layer was collected and filtered through a Mini Sart Syringe Filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding acrylic resin (1) (solids concentration: 20% by mass).

[0089] Manufacture of acrylic resins (2) to (9) Aqueous dispersions of acrylic resins (2) to (9) (all with a solids concentration of 25%) were obtained in the same manner as in the production of acrylic resin (1), except that in the production of acrylic resin (1), the composition of the acrylic resin before crosslinking and neutralization (acrylic resin C), the neutralizing agent (water-soluble basic compound (B)), and the crosslinking agent were made according to the types and amounts shown in Table 2, and the amount of ion-exchanged water was changed as necessary so that the solids content of the resin was 20%. In Table 2, blanks indicate that the corresponding component was not used (0% in quantity). Acrylic resin (4) does not use a crosslinking agent and is an uncrosslinked resin.

[0090] [Table 2]

[0091] <Ink manufacturing> [Production of pigment dispersion resin] Production Example 2-1 (Production of Water-Insoluble Polymer (a1) Having Carboxy Groups) 16 parts of methacrylic acid, 44 parts of styrene, 30 parts of styrene macromonomer ("AS-6S" manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solid content 50% by mass), and 25 parts of methoxypolyethylene glycol methacrylate ("BLEMMER PME-200" manufactured by NOF Corporation) were mixed to prepare 115 parts of a monomer mixture. In a reaction vessel, 18 parts of MEK, 0.03 parts of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture were placed and mixed, and the inside of the vessel was thoroughly purged with nitrogen gas.

[0092] Separately, a mixture of the remaining 90% (103.5 parts) of the monomer mixture with 0.27 parts of the chain transfer agent, 42 parts of MEK, and 3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was placed in a dropping funnel. Under a nitrogen atmosphere, the mixture in the reaction vessel was heated to 75°C while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 75°C from the end of the dropping, a solution of 3 parts of the polymerization initiator in 5 parts of MEK was added, and the mixture was further aged at 75°C for 2 hours and then at 80°C for 2 hours. An additional 50 parts of MEK was added to obtain a solution of a water-insoluble polymer (a1) having a carboxy group (weight average molecular weight: 50,000). The solids concentration of the solution of the water-insoluble polymer (a1) having a carboxy group was 45% by mass.

[0093] [Preparation of aqueous dispersion of pigment-containing resin particles] Production Example 2-2 (Production of Water Dispersion (D2) of Black Pigment-Containing Resin Particles) 95.2 parts of the solution of the water-insoluble polymer (a1) having carboxy groups obtained in Production Example 2-1 (pigment dispersing resin) were mixed with 53.9 parts of MEK. To this mixture were added 15.0 parts of 5N aqueous sodium hydroxide, 0.5 parts of 25% aqueous ammonia, and 341.3 parts of ion-exchanged water as neutralizing agents. 100 parts of CI Pigment Black 7 (PB7, manufactured by Cabot Corporation) were then added as a black pigment to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The pigment mixture was mixed using a disperser blade at 7,000 rpm and 20°C for 1 hour, and then dispersed using a high-pressure homogenizer "Microfluidizer M-140K" (manufactured by Microfluidics) for 15 passes at 180 MPa to obtain a dispersion.

[0094] The obtained dispersion was heated under reduced pressure at 60°C to remove MEK, and then some of the water was removed. The mixture was centrifuged, and the liquid layer was recovered and filtered through a Mini Sart Syringe Filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of black pigment-containing polymer particles. The solid content was 25% by mass. To 100 parts of the resulting aqueous dispersion of black pigment-containing polymer particles, 0.45 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321L, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 130) as a crosslinker and 15.23 parts of ion-exchanged water were added, followed by heating at 70°C for 3 hours with stirring. After cooling to room temperature, the liquid layer was collected and filtered through a Mini Sart Syringe Filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding aqueous dispersion K of black pigment-containing polymer particles (solids concentration: 22% by mass, mass ratio [pigment / (pigment + pigment dispersion resin with crosslinked structure)]: 0.69). The average particle size of the black pigment-containing polymer particles in the resulting aqueous dispersion K was 100 nm.

[0095] Production Example 2-3 (Production of aqueous dispersion (d1) of pigment-free acrylic resin particles) In a reaction vessel equipped with a dropping funnel, the monomers shown in the "initial charge monomer solution" in Table 3, sodium polyoxyethylene alkyl ether sulfate ("Latemul E-118B" manufactured by Kao Corporation) as an emulsifier (referred to as "Latemul E-118B" in Table 3), potassium persulfate as a polymerization initiator, and ion-exchanged water were mixed and purged with nitrogen gas to obtain an initial charge monomer solution. Separately, the monomer, emulsifier, polymerization initiator, and ion-exchanged water shown in "Monomer solution to be added" in Table 3 were mixed to obtain a monomer solution to be added, and the monomer solution to be added was then placed in a dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the initial monomer solution in the reaction vessel was heated from room temperature to 80°C over 30 minutes while stirring. While maintaining the temperature at 80°C, the monomer solution in the dropping funnel was gradually added dropwise to the reaction vessel over 3 hours. After the addition was completed, the mixture was stirred for 1 hour while maintaining the temperature inside the reaction vessel. The mixture was then filtered through a 200-mesh filter to obtain a pigment-free aqueous dispersion (d1) of acrylic resin particles (solid concentration: 44.1% by mass, acid value: 16 mg KOH / g, weight-average molecular weight of the acrylic resin: 750,000, average particle size: 95 nm).

[0096] [Table 3]

[0097] [Production of Water-Based Ink] Ink manufacturing example (water-based ink manufacturing) 46.27 g of the water dispersion (D2) of black pigment-containing resin particles obtained in Production Example 2-2 (solid content concentration: 22% by mass), 12.81 g of the water dispersion (d1) of pigment-free acrylic resin particles obtained in Production Example 2-3 (solid content concentration: 44.1% by mass), 30.00 g of propylene glycol, 3.00 g of diethylene glycol monoisobutyl ether (manufactured by Nippon Nyukazai Co., Ltd.), acetylene glycol surfactant "Surfynol 440" (manufactured by Nippon Nyukazai Co., Ltd.), 1.00 g of 2,4,7,9-tetramethyl-5-decyne-4,7-diol EO (3.5 mol) adduct (HLB value: 8 (catalog value), active content: 100% by mass) manufactured by Shin-Etsu Chemical Co., Ltd., 1.00 g of polyether-modified silicone surfactant "KF-6011" (PEG-11 methyl ether dimethicone, HLB value: 14.5 (catalog value) manufactured by Shin-Etsu Chemical Co., Ltd.), and 1.00 g of ion-exchanged water were added to a total weight of 100.00 g. The resulting mixture was filtered through a "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain water-based ink W-1 (viscosity: 5.6 mPa·s, pH: 8.2).

[0098] <Production of pretreatment liquid> Each component of the pretreatment solution was added to a container equipped with a stirrer in the composition (%) shown in Table 4, mixed at 25°C for 1 hour, and then filtered using the membrane filter with a pore size of 5 μm and the needleless syringe described above to obtain pretreatment solutions 1 to 8 of the examples and pretreatment solution 101 of the comparative example. In Table 4, blank spaces indicate 0% except for the "Water-soluble basic compound (B)" column; in the "Water-soluble basic compound (B)" column, "○" indicates that the corresponding component was used, and blank spaces indicate that the corresponding component was not used.

[0099] (Water-soluble basic compound (B)) 25% ammonia water: 25% by mass ammonia aqueous solution (aqueous solution containing 25% by mass of the active ingredient) N,N-Dimethylethanolamine: N,N-Dimethylethanolamine (Fujifilm Wako Pure Chemical Industries, Ltd., Reagent) 1N sodium hydroxide: 1 mol / L sodium hydroxide aqueous solution (Fujifilm Wako Pure Chemical Industries, Ltd., reagent)

[0100] (Water-soluble organic solvent) Diethylene glycol monobutyl ether: (Fujifilm Wako Pure Chemical Industries, Ltd., Reagent, static surface tension at 25°C: 26.2 mN / m) Propylene glycol: (Fujifilm Wako Pure Chemical Industries, Ltd., Reagent, static surface tension at 25°C: 36.0 mN / m)

[0101] (acetylene glycol surfactant) Surfynol 104PG50: "Surfynol 104-PG50" manufactured by Nissin Chemical Industry Co., Ltd. (2,4,7,9-tetramethyl-5-decyne-4,7-diol propylene glycol solution, active ingredient 50% by mass, HLB value = 4 (catalog value))

[0102] (Silicone surfactant) KF-6011: Shin-Etsu Chemical Co., Ltd. "KF-6011" (PEG-11 methyl ether dimethicone (side-chain polyether-modified linear silicone), HLB value = 14.5 (catalog value))

[0103] <Inkjet printing method> [Examples 1 to 8, Comparative Example 1] In an environment with a temperature of 25±1°C and a relative humidity of 30±5%, ink was filled into the cartridge of a print evaluation device (Seiko Epson Corporation, inkjet printer, PX105, piezo type), an A4-sized film heater (Kawai Electric Works, Ltd.) was fixed to the print medium outlet section so that the print medium described below could be heated, and a corona discharge-treated polyethylene terephthalate film (Futamura Chemical Co., Ltd.) cut to A4 size was placed in the paper storage area. The cartridges were loaded with black ink and inks containing pretreatment liquids 1 to 8 and 101. The printing order was such that the pretreatment liquid was ejected first, followed by the black ink.

[0104] <Clarity of printed images (sharpness of cut-out characters)> Using the inkjet recording method described above, 5pt and 7pt size cut-out character images were printed. The background area was solid with 100% duty for the pretreatment liquid and black ink. The cut-out characters on the resulting prints were observed, and the clarity of the printed image (sharpness of the cut-out characters) was evaluated visually. The evaluation results are shown in Table 4. (Evaluation criteria) The 5:5pt size cut-out characters are not crushed and can be clearly identified. The 4:5pt cut-out letters are slightly crushed but still clearly identifiable. 3: The 5pt size cut-out characters are crushed and difficult to distinguish, but the 7pt size cut-out characters are clearly distinguishable, and are not at a level that would be a problem in practical use. 2: The 5pt and 7pt cut-out characters are crushed and difficult to read. 1: The 5pt and 7pt cut-out characters are obscured by black ink and cannot be read. In practical use, a rating of 3 or higher on the above evaluation criteria is sufficient. The higher the rating, the better the clarity of the printed image.

[0105] <Evaluation of continuous discharge stability of pretreatment liquid> Using the inkjet printing method described above, 100 B5-sized solid images were printed using black ink and the pretreatment liquid. A nozzle check pattern was then printed, and the number of nozzle clogs in the pretreatment liquid was evaluated. The evaluation results are shown in Table 4. (Evaluation criteria) 5: No missing nozzles or distorted ejection were observed. 4: No nozzle missing is observed, but distorted ejection is observed. 3: The number of nozzles with missing nozzles is 1 or more but less than 5. 2: The number of nozzles with missing nozzles is 5 or more but less than 15. 1: The number of nozzles with missing nozzles is 15 or more. In practical use, a rating of 2 or higher is sufficient. A higher rating indicates better continuous ejection stability.

[0106] [Table 4]

[0107] As can be seen from Table 4, the printed matter obtained in the comparative examples lacked sharpness of the printed image, whereas the printed matter obtained in the examples had excellent sharpness of the printed image and also had excellent continuous ejection stability of the pretreatment liquid. Therefore, it is clear that the use of the pretreatment liquid used in the examples makes it possible to achieve both high clarity of printed images and good continuous ejection stability of the pretreatment liquid. [Industrial Applicability]

[0108] According to the present invention, a printed matter having excellent image clarity can be obtained.

Claims

1. A pretreatment liquid for inkjet printing to be applied onto a printing medium, comprising: the pretreatment liquid contains water, an anionic polymer compound (A), and a water-soluble basic compound (B); The pretreatment liquid for inkjet printing, wherein the water-soluble basic compound (B) comprises at least one selected from the group consisting of ammonia and water-soluble amine compounds.

2. 2. The pretreatment liquid for inkjet printing according to claim 1, wherein the content of the one or more compounds selected from the group consisting of ammonia and the water-soluble amine compounds in the water-soluble base compound (B) is 50 mol % or more.

3. The pretreatment liquid for inkjet printing according to claim 1 or 2, wherein the boiling point of the water-soluble amine compound is 85°C or higher and 350°C or lower.

4. 3. The pretreatment liquid for inkjet printing according to claim 1, wherein the water-soluble amine compound is at least one selected from the group consisting of primary alkanolamines, secondary alkanolamines, and tertiary alkanolamines.

5. The pretreatment liquid for inkjet printing according to claim 1 or 2, wherein the anionic polymer compound (A) has an acid value of 50 mgKOH / g or more.

6. 3. The pretreatment liquid for inkjet printing according to claim 1, wherein the anionic polymer compound (A) is an anionic vinyl resin containing structural units derived from at least one selected from the group consisting of (meth)acrylic acid and maleic acid.

7. The pretreatment liquid for inkjet printing according to claim 6 , wherein the anionic vinyl resin further contains a structural unit derived from cyclohexyl (meth)acrylate.

8. The pretreatment liquid for inkjet printing according to claim 1 or 2, which has a pH of greater than 7.

9. The pretreatment liquid for inkjet printing according to claim 1 or 2, which does not contain a polyvalent metal salt, a cationic polymer compound, or an organic acid.

10. An ink set for inkjet printing, comprising the pretreatment liquid for inkjet printing according to claim 1 or 2, and an ink containing a colorant and water.

11. An inkjet printing method using the pretreatment liquid for inkjet printing according to claim 1 or 2, comprising the following steps 1 and 2: Step 1: Applying the inkjet printing pretreatment liquid to a printing medium to obtain a surface-treated printing medium. Step 2: A step of forming an image on the treated surface of the surface-treated printing medium obtained in Step 1 by inkjet printing using an ink containing a colorant and water.

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