Cleaning liquid for inkjet printing apparatus

Abstract

To provide a cleaning liquid that exhibits excellent removability of aqueous ink adhered to a discharge head of an inkjet printing apparatus, while suppressing damage to the printing apparatus, and a technology utilizing the same.SOLUTION: A cleaning fluid for an inkjet printing apparatus comprises 25 mass% or more of a glycol ether compound with a boiling point of 120°C or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cleaning liquid for an inkjet printing device. [Background technology]

[0002] Inkjet printing is a method of producing printed materials with characters and images by ejecting ink droplets directly from extremely fine nozzles onto a recording medium using an inkjet printing device. When using inkjet printing devices, ink droplets can adhere to the nozzles, resulting in ejection problems. This type of ink adhesion is particularly likely to occur in inkjet printing devices designed for printing on non-absorbent and low-absorbent recording media, such as film, because inks with excellent adhesion and drying properties are used. When nozzle ejection problems occur, excess ink adhering to the nozzle surface and ejection ports is removed by wiping with a nonwoven fabric or similar material soaked in cleaning fluid. Furthermore, when using different types of ink, the ink passages within the printing device must be cleaned with cleaning fluid before and after changing inks. Furthermore, when not using the recording head for an extended period of time, the ink is removed from the recording head, and the recording head is filled with cleaning fluid, capped, and stored. Various cleaning solutions have been explored.

[0003] For example, Patent Document 1 describes a cleaning liquid capable of effectively cleaning ink, which contains water, a predetermined organic solvent, and an acetylene surfactant, the predetermined organic solvent being at least one selected from the group consisting of polyhydric alcohols and polyalkylene glycols, the content of the predetermined organic solvent being 1% by mass or more and 18% by mass or less relative to the mass of the cleaning liquid, and the content of the acetylene surfactant being 0.3% by mass or more and 1.0% by mass or less relative to the mass of the cleaning liquid, and Patent Document 2 describes a cleaning liquid having excellent ink removal properties and preventing corrosion of the ink ejection head and surrounding components. The document describes a cleaning liquid that can prevent this and maintain stable ejection characteristics for a long period of time, the cleaning liquid comprising water and an organic solvent containing a compound having two or more carbon atoms and two or three OH groups, the cleaning liquid having a pH of 7 to 10, a phosphate ion concentration of 100 ppm to 5000 ppm, a proportion of the organic solvent in the total amount of the cleaning liquid of 5% by mass to 20% by mass, and a proportion of the compound having two or three OH groups in the total amount of the organic solvent of 60% by mass to 100% by mass. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-125365 [Patent Document 2] Japanese Patent Application Publication No. 2023-90029 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the cleaning solutions described in Patent Documents 1 and 2 are insufficient in terms of cleaning ability, and in particular in the case of inkjet printing devices intended for printing on non-absorbent recording media such as film and low-absorbent recording media, inks with excellent adhesion and drying properties are used, so the cleaning ability is particularly insufficient.In addition, the inventors' studies have revealed that when a highly soluble solvent such as acetone is used as a cleaning solution, it corrodes the liquid-repellent material of the ejection head, significantly reducing the ejection ability of the head. The object of the present invention has been made in consideration of the above-mentioned problems, and is to provide a cleaning liquid and a technology for using the same that is excellent at removing aqueous ink adhering to the ejection head of an inkjet printing device and that can minimize damage to the printing device. [Means for solving the problem]

[0006] The present inventors have discovered that the above problems can be solved by using a cleaning liquid for an inkjet printing device containing 25% by mass or more of a glycol ether compound having a boiling point of 120°C or higher, and have completed the present invention. [Effects of the Invention]

[0007] According to the present invention, a cleaning liquid that is excellent at removing water-based ink adhering to the ejection head of an inkjet printing device and that can suppress damage to the printing device, and a technology for using the cleaning liquid are provided. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the present invention will be described below, but the present invention is not limited thereto. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less." The cleaning liquid for inkjet printing devices (also referred to as cleaning liquid) of the present disclosure is characterized in that the content of a glycol ether compound having a boiling point of 120° C. or higher is 25 parts by mass or more per 100 parts by mass of the cleaning liquid.

[0009] <Glycol ether> The cleaning liquid of the present disclosure contains a glycol ether compound having a boiling point of 120°C or higher. Glycol ether compounds with a boiling point of 120°C or higher include ethylene glycol monomethyl ether (boiling point 125°C, molecular weight 76.09, SP value 11.6), diethylene glycol monomethyl ether (boiling point 194°C, molecular weight 120.15, SP value 10.7), triethylene glycol monomethyl ether (boiling point 249°C, molecular weight 164.2, SP value 10.5), ethylene glycol isopropyl ether (boiling point 142°C, molecular weight 104.15, SP value 9.2), and diethylene glycol monoisopropyl Ether (boiling point 207°C, molecular weight 148.2, SP value 9.0), ethylene glycol monobutyl ether (boiling point 171°C, molecular weight 118.17, SP value 9.8), diethylene glycol monobutyl ether (boiling point 231°C, molecular weight 162.2, SP value 9.5), triethylene glycol monobutyl ether (boiling point 271°C, molecular weight 206.28, SP value 9.6), ethylene glycol monoisobutyl ether (boiling point 161°C, molecular weight 118.17, SP value 8.9), diethylene glycol monoisobutyl ether ether (boiling point 220°C, molecular weight 162.2, SP value 8.7), ethylene glycol monohexyl ether (boiling point 208°C, molecular weight 146.3, SP value 9.6), diethylene glycol monohexyl ether (boiling point 259°C, molecular weight 190.28, SP value 9.7), ethylene glycol mono-2-ethylhexyl ether (boiling point 229°C, molecular weight 174.3, SP value 9.6), diethylene glycol mono-2-ethylhexyl ether (boiling point 272°C, molecular weight 218.3, SP value 9.7), ethylene glycol Monophenyl ether (boiling point 245°C, molecular weight 138.2, SP value 11.5), diethylene glycol monophenyl ether (boiling point 283°C, molecular weight 182.2, SP value 9.9), ethylene glycol monobenzyl ether (boiling point 256°C, molecular weight 152.2, SP value 10.8), diethylene glycol monobenzyl ether (boiling point 302°C, molecular weight 196.2, SP value 9.6), propylene glycol monomethyl ether (boiling point 121°C, molecular weight 90.12, SP value 10.4), dipropylene glycol monomethyl ether (boiling point 187°C, molecular weight 148.2, SP value 9.6), tripropylene glycol monomethyl ether (boiling point 242°C, molecular weight 206.3, SP value 9.1), propylene glycol monopropyl ether (boiling point 150°C, molecular weight 118.17, SP value 9.4), dipropylene glycol monopropyl ether (boiling point 212°C, molecular weight 176.25, SP value 8.6), propylene glycol mono-n-butyl ether (boiling point 170°C, molecular weight 13.2, SP value 8.9), dipropylene glycol mono-n-butyl ether (boiling point 231°C, molecular weight 190.28, SP value 8.2), propylene glycol mono-phenyl ether (boiling point 243°C, molecular weight 152.19, SP value 10.5), tripropylene glycol mono Examples include n-butyl ether (boiling point 274°C, molecular weight 248.36, SP value 7.6), diethylene glycol dimethyl ether (boiling point 162°C, molecular weight 134.18, SP value 8.6), triethylene glycol dimethyl ether (boiling point 216°C, molecular weight 178.2, SP value 8.4), tetraethylene glycol dimethyl ether (boiling point 275°C, molecular weight 222.28, SP value 8.4), diethylene glycol methyl ethyl ether (boiling point 176°C, molecular weight 148.2, SP value 8.3), diethylene glycol diethyl ether (boiling point 189°C, molecular weight 162.22, SP value 8.6), diethylene glycol dibutyl ether (boiling point 255°C, molecular weight 218.33, SP value 8.3), and dipropylene glycol dimethyl ether (boiling point 171°C, molecular weight 162.23, SP value 8.2).

[0010] As the glycol ether compound having a boiling point of 120° C. or higher, diethylene glycol monobutyl ether, tripropylene glycol methyl ether, and dipropylene glycol methyl ether are preferred, and diethylene glycol monobutyl ether and tripropylene glycol methyl ether are more preferred. The glycol ether compound having a boiling point of 120°C or higher may have a boiling point of 270°C or lower, or 260°C or lower.

[0011] In the cleaning liquid of the present disclosure, the solubility parameter (SP value) of the glycol ether compound having a boiling point of 120°C or higher is preferably 8.0 or higher, more preferably 8.5 or higher, and even more preferably 9.0 or higher, and more preferably 11.0 or lower, more preferably 10.0 or lower, and even more preferably 9.5 or lower. The content of the glycol ether compound having a boiling point of 120°C or higher contained in 100 parts by mass of the cleaning solution of the present disclosure is preferably 25 parts by mass or higher, more preferably 35 parts by mass or higher, even more preferably 40 parts by mass or higher, particularly preferably 45 parts by mass or higher, and may be 50 parts by mass or higher, and the upper limit of the content may be 100 parts by mass, but may be 90 parts by mass or lower, 70 parts by mass or lower, 60 parts by mass or lower, or 55 parts by mass or lower from the viewpoint of safety.

[0012] <Cleaning liquid for inkjet printing equipment> The cleaning liquid of the present disclosure may further contain water. The lower limit of the water content in 100 parts by mass of the cleaning solution of the present disclosure may be 5 parts by mass or less, but from the viewpoint of safety, it is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, particularly preferably 40 parts by mass or more, and may be 45 parts by mass or more. From the viewpoint of cleaning performance, the upper limit is preferably 75 parts by mass or less, more preferably 65 parts by mass or less, even more preferably 60 parts by mass or less, particularly preferably 55 parts by mass or less, and may be 50 parts by mass or less. The total amount of the glycol ether compound having a boiling point of 120°C or higher and water in 100 parts by mass of the cleaning solution of the present disclosure is preferably 90 parts by mass or higher, more preferably 95 parts by mass or higher, and even more preferably 100 parts by mass.

[0013] The cleaning liquid of the present disclosure may contain a glycol ether compound having a boiling point of 120° C. or higher and other compound (A) other than water. Examples of the other compound (A) include glycol ether compounds having a boiling point of 120° C. or higher, water-soluble solvents other than water, surfactants, pH adjusters, viscosity adjusters, surface tension adjusters, and preservatives. The content of the other compound (A) in 100 parts by mass of the cleaning liquid of the present disclosure may be 10 parts by mass or less, 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less from the viewpoint of productivity, or may be substantially free of the other compound (A). Substantially free of the other compound (A) means that it is not intentionally added.

[0014] <Water-based ink> The cleaning liquid of the present disclosure is more effective when used in an inkjet printing device for aqueous inks. The water-based ink of the present disclosure may be a water-based ink that includes a pigment and a water-insoluble polymer. The water-insoluble polymer of the present disclosure may be dissolved in an organic solvent, but from the viewpoint of use in aqueous inks, it is preferably in the form of an aqueous dispersion, and is preferably an aqueous dispersion of resin emulsion particles. The resin emulsion particles of the present disclosure may be single-layered resin emulsion particles or multiple-layered resin emulsion particles. The water-insoluble polymer of the present disclosure is not particularly limited, but examples thereof include acrylic polymers, polyester polymers, urethane polymers, and olefin polymers, and from the viewpoint of washability, acrylic polymers and polyester polymers are more preferred. The acrylic polymer of the present disclosure is a polymer that uses an acrylic monomer as a polymerization component, and the amount of the acrylic monomer used per 100 parts by mass of the total monomer components is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more.

[0015] Monomer components used in the acrylic polymer of the present disclosure include monofunctional and polyfunctional monomers. The monofunctional and polyfunctional monomers may be used alone or in combination. The acrylic polymer of the present disclosure may have structural units derived from an aromatic group-containing monomer, which is preferably a monomer having at least one aromatic hydrocarbon ring and at least one polymerizable unsaturated group in the molecule. Examples of the aromatic hydrocarbon ring include a benzene ring, a naphthalene ring, a phenanthrene ring, and an anthracene ring, and among these, a benzene ring is preferred. Examples of the polymerizable unsaturated group include a (meth)acryloyl group, a vinyl group, and a maleimide group, and among these, a (meth)acryloyl group and a vinyl group are preferred. Examples of the aromatic group-containing monomer include styrene-based monomers, aryl (meth)acrylates, aralkyl (meth)acrylates, aryloxy group-containing alkyl (meth)acrylates, and maleimides having an aryl group.

[0016] Examples of the styrene-based monomer of the present disclosure include styrene optionally having one or more substituents such as a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), an alkyl group (e.g., a C1-4 alkyl group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, or a tert-butyl group), a vinyl group, or an alkoxysilyl group (e.g., a tri-C1-4 alkoxysilyl group such as a trimethoxysilyl group or a triethoxysilyl group). The substituent is preferably at least one selected from a halogen atom and an alkyl group. Specific examples of the styrene-based monomer include styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, chlorostyrene, chloromethylstyrene, divinylbenzene, p-styryltrimethoxysilane, and 2-styrylethyltrimethoxysilane. Examples of the aryl (meth)acrylate of the present disclosure include aryl (meth)acrylates having an aryl group having 6 to 18 carbon atoms, such as phenyl (meth)acrylate, o-tolyl (meth)acrylate, m-tolyl (meth)acrylate, p-tolyl (meth)acrylate, 2,3-xylyl (meth)acrylate, 2,4-xylyl (meth)acrylate, 2,5-xylyl (meth)acrylate, 2,6-xylyl (meth)acrylate, 3,4-xylyl (meth)acrylate, 3,5-xylyl (meth)acrylate, 1-naphthyl (meth)acrylate, and 2-naphthyl (meth)acrylate. Examples of the aralkyl (meth)acrylate of the present disclosure include aralkyl (meth)acrylates having an aralkyl group having 7 to 18 carbon atoms, such as benzyl (meth)acrylate, phenylethyl (meth)acrylate, methylbenzyl (meth)acrylate, and naphthylmethyl (meth)acrylate. Examples of the aryloxy group-containing alkyl(meth)acrylate of the present disclosure include phenoxyethyl(meth)acrylate, phenoxypropyl(meth)acrylate, methylphenoxyethyl(meth)acrylate, and 2-naphthoethyl(meth)acrylate. Examples of maleimides having an aryl group according to the present disclosure include N-phenylmaleimide. Among these, preferred aromatic group-containing monomers are styrene-based monomers, aryl(meth)acrylates, and aralkyl(meth)acrylates, with styrene optionally having at least one substituent selected from halogen atoms and alkyl groups, aryl(meth)acrylates having an aryl group with 6 to 18 carbon atoms, and aralkyl(meth)acrylates having an aralkyl group with 7 to 18 carbon atoms being more preferred, styrene, aryl(meth)acrylates having an aryl group with 6 to 10 carbon atoms, and aralkyl(meth)acrylates having an aralkyl group with 7 to 10 carbon atoms being even more preferred, with styrene and benzyl(meth)acrylate being particularly preferred. When the aromatic group-containing monomer is one of the above compounds, the viscosity stability of the resulting ink can be further improved. The acrylic polymer of the present disclosure may contain one or more structural units derived from aromatic group-containing monomers. The content of the structural unit derived from the aromatic group-containing monomer in 100 parts by mass of the acrylic polymer of the present disclosure is 18 to 42 parts by mass, and preferably 20 to 40 parts by mass. By adjusting this content to 18 parts by mass or more (preferably 20 parts by mass or more), the viscosity stability of the resulting ink can be improved, and by adjusting this content to 42 parts by mass or less (preferably 40 parts by mass or less), the adhesion to the substrate (particularly OPP film) can be improved.

[0017] The acrylic polymer of the present disclosure preferably further contains structural units derived from a hydroxyl group-containing monomer. The hydroxyl group-containing monomer of the present disclosure is preferably a monomer having at least one hydroxyl group and at least one polymerizable unsaturated group in the molecule (but not having an aromatic hydrocarbon ring). Examples of the polymerizable unsaturated group include a (meth)acryloyl group, a vinyl group, and a maleimide group, and among these, a (meth)acryloyl group is preferred. Specific examples of the hydroxyl group-containing monomer of the present disclosure include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; halogen-substituted hydroxyalkyl (meth)acrylates such as 3-chloro-2-hydroxypropyl (meth)acrylate; modified hydroxyalkyl (meth)acrylates such as caprolactone-modified 2-hydroxyethyl (meth)acrylate and 2-(meth)acryloyloxyethyl 2-hydroxyethyl phthalate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and hydroxyl group-containing vinyl monomers such as vinyl alcohol and allyl alcohol. Among these, the hydroxyl group-containing monomer is preferably a hydroxyalkyl(meth)acrylate, more preferably a hydroxyalkyl(meth)acrylate having a hydroxyalkyl group with 1 to 4 carbon atoms, and even more preferably a hydroxyalkyl(meth)acrylate having a hydroxyalkyl group with 2 to 4 carbon atoms. When the hydroxyl group-containing monomer is any of the above compounds, the viscosity stability of the resulting ink can be further improved. The acrylic polymer of the present disclosure may contain one or more structural units derived from hydroxyl group-containing monomers.

[0018] The content of the structural units derived from the hydroxyl group-containing monomer in 100 parts by mass of the acrylic polymer of the present disclosure is, for example, 0 to 60 parts by mass, preferably 10 to 40 parts by mass, and more preferably 15 to 35 parts by mass. By adjusting the content of the structural units derived from the hydroxyl group-containing monomer within the above-mentioned preferred range, the adhesion to substrates (particularly PET films and OPP films) can be further improved. The content of the structural units derived from the hydroxyl group-containing monomer in the acrylic polymer of the present disclosure is preferably 30 to 150 parts by mass, more preferably 50 to 120 parts by mass, and even more preferably 70 to 95 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. By adjusting the content of the structural units derived from the hydroxyl group-containing monomer within the above range, adhesion to substrates (particularly PET films and OPP films) can be further improved. The content of the structural units derived from the hydroxyl group-containing monomer may be 0 to 150 parts by mass per 100 parts by mass of the structural units derived from the aromatic group-containing monomer.

[0019] The acrylic polymer of the present disclosure preferably further contains structural units derived from a cyclic aliphatic group-containing monomer. By containing structural units derived from a cyclic aliphatic group-containing monomer together with structural units derived from an aromatic group-containing monomer, the acrylic polymer of the present disclosure can further improve adhesion to a substrate (particularly an OPP film) without reducing the viscosity stability of the resulting ink. The cycloaliphatic group-containing monomer of the present disclosure is preferably a monomer having at least one alicyclic hydrocarbon ring and at least one polymerizable unsaturated group in the molecule (however, having no aromatic hydrocarbon ring or hydroxyl group). The alicyclic hydrocarbon ring of the present disclosure may be saturated or unsaturated, but is preferably saturated. The alicyclic hydrocarbon ring may be monocyclic or polycyclic, such as bicyclic or tricyclic. In the case of a polycyclic ring, it is preferably a fused ring, and particularly preferably a bridged ring. The alicyclic hydrocarbon ring is preferably a ring having 3 to 10 carbon atoms, such as a cycloalkyl group, an isobornyl group, or an adamantyl group having 3 to 10 carbon atoms, and more preferably a cycloalkyl group or an isobornyl group having 3 to 10 carbon atoms. Examples of the polymerizable unsaturated group include a (meth)acryloyl group, a vinyl group, and a maleimide group, with a (meth)acryloyl group being preferred. Specific examples of the cycloaliphatic group-containing monomer of the present disclosure include cycloalkyl (meth)acrylates such as cyclopropyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; esters of (meth)acrylic acid and polycyclic alcohols such as isobornyl (meth)acrylate and adamantyl (meth)acrylate; and cycloalkyl group-containing maleimides such as N-cyclohexylmaleimide. Among these, as the cycloaliphatic group-containing monomer, cycloalkyl(meth)acrylate and isobornyl(meth)acrylate are preferred, cycloalkyl(meth)acrylate having a cycloalkyl group having 3 to 10 carbon atoms and isobornyl(meth)acrylate are more preferred, and cyclohexyl(meth)acrylate and isobornyl(meth)acrylate are even more preferred. When the cycloaliphatic group-containing monomer is any of the above compounds, adhesion to the substrate can be further improved. The copolymer may contain one or more structural units derived from cycloaliphatic group-containing monomers.

[0020] The content of the structural units derived from the cycloaliphatic group-containing monomer in 100 parts by mass of the acrylic polymer of the present disclosure is, for example, 0 to 60 parts by mass, preferably 20 to 50 parts by mass, and more preferably 25 to 45 parts by mass. By adjusting the content of the structural units derived from the cycloaliphatic group-containing monomer within the above-mentioned preferred range, it is possible to further improve adhesion to substrates (particularly OPP films) without reducing viscosity stability. The content of the structural units derived from the cycloaliphatic group-containing monomer in the acrylic polymer of the present disclosure is preferably 60 to 180 parts by mass, more preferably 80 to 160 parts by mass, and even more preferably 100 to 140 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. By adjusting the content of the structural units derived from the cycloaliphatic group-containing monomer within the above range, adhesion to substrates (particularly OPP films) can be further improved without reducing viscosity stability. The content of the structural units derived from the cycloaliphatic group-containing monomer may be 0 to 180 parts by mass per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. The acrylic polymer of the present disclosure preferably contains structural units derived from the hydroxyl group-containing monomer and structural units derived from the cycloaliphatic group-containing monomer, in addition to structural units derived from the aromatic group-containing monomer. In such polymer (A), the content of structural units derived from the hydroxyl group-containing monomer per 100 parts by mass of structural units derived from the cycloaliphatic group-containing monomer is preferably 20 to 150 parts by mass, more preferably 40 to 100 parts by mass, and even more preferably 60 to 85 parts by mass.

[0021] Furthermore, the content of the structural units derived from the hydroxyl group-containing monomer relative to a total of 100 parts by mass of the structural units derived from the aromatic group-containing monomer and the structural units derived from the cyclic aliphatic group-containing monomer in the acrylic polymer of the present disclosure is, for example, 0 to 150 parts by mass, preferably 15 to 120 parts by mass, and more preferably 25 to 100 parts by mass. The total content of structural units derived from aromatic group-containing monomers, structural units derived from hydroxyl group-containing monomers, and structural units derived from cyclic aliphatic group-containing monomers in 100 parts by mass of the acrylic polymer of the present disclosure is preferably 20 to 100% by mass, more preferably 35 to 99% by mass, even more preferably 50 to 97% by mass, and still more preferably 75 to 95% by mass. The acrylic polymer of the present disclosure may further contain structural units derived from monomers other than aromatic group-containing monomers, hydroxyl group-containing monomers, and cycloaliphatic group-containing monomers (hereinafter also referred to as "other monomers"). The other monomers are monomers other than aromatic group-containing monomers, hydroxyl group-containing monomers, and cycloaliphatic group-containing monomers, which have at least one polymerizable unsaturated group in the molecule. Examples of other monomers include (meth)acrylic acid alkyl esters, nitrogen atom-containing monomers, and acid group-containing monomers.

[0022] Specific examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, 2-pentyl (meth)acrylate, isopentyl (meth)acrylate, and neobutyl (meth)acrylate. Pentyl (meth)acrylate, 3-methyl-2-butyl (meth)acrylate, 3-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-hexyl (meth)acrylate, 3,3-dimethyl-2-butyl (meth)acrylate, 3-methyl-2-pentyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2,4-dimethyl-3-pentyl (meth)acrylate, n-heptyl (meth)acrylate, 2-heptyl (meth)acrylate ) acrylate, 2-methyl-3-hexyl (meth)acrylate, 3-heptyl (meth)acrylate, 5-methyl-2-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2,2-dimethyl-3-hexyl (meth)acrylate, 2,5-dimethyl-3-hexyl (meth)acrylate, 3-octyl (meth)acrylate, 4-octyl (meth)acrylate, Examples of the methacrylate include 5-methyl-2-heptyl (meth)acrylate, 5-methyl-3-heptyl (meth)acrylate, 6-methyl-2-heptyl (meth)acrylate, 6-methyl-3-heptyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, tridecyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, henicosyl (meth)acrylate, and tetracosyl (meth)acrylate. The polymer (A) may contain one or more structural units derived from a (meth)acrylic acid alkyl ester.

[0023] Among these, the (meth)acrylic acid alkyl ester is preferably a (meth)acrylic acid C1-20 alkyl ester. Also preferred is at least one selected from a (meth)acrylic acid alkyl ester having a homopolymer glass transition temperature (Tg) of −20° C. or lower (hereinafter sometimes referred to as a low-Tg (meth)acrylic acid alkyl ester) and a methacrylic acid C1-5 alkyl ester. By appropriately adjusting the content of the structural unit derived from the low-Tg (meth)acrylic acid alkyl ester and / or the structural unit derived from the methacrylic acid C1-5 alkyl ester, it becomes easy to adjust the glass transition temperature of the polymer (A) to the range described below. In this specification, the "glass transition temperature of a homopolymer" may be, for example, the value (if multiple Tg values are listed, the lowest value) described in "POLYMER HANDBOOK THIRD EDITION" (by J. BRANDRUP and EHIMMERGUT, 1989, published by John Wiley & Sons, Inc., pp. VI / 209-VI / 277). For compounds not described in "POLYMER HANDBOOK THIRD EDITION," a value (calculated value) determined by computer using commercially available glass transition temperature calculation software (e.g., "MATERIALS STUDIO" manufactured by Accelrys Software Inc., version 4.0.0.0, module: Synthia, calculation conditions: weight average molecular weight 100,000) may be used.

[0024] The Tg of the low Tg (meth)acrylic acid alkyl ester is −20° C. or lower, preferably −100 to −20° C., and more preferably −80 to −30° C. Examples of the low Tg (meth)acrylic acid alkyl ester include ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate, n-nonyl acrylate, and isononyl acrylate. Of these, n-butyl acrylate, 2-octyl acrylate, and 2-ethylhexyl acrylate are preferred, and 2-octyl acrylate and 2-ethylhexyl acrylate are more preferred. As the methacrylic acid C1-5 alkyl ester, methacrylic acid C1-3 alkyl ester is preferred, and methyl methacrylate is more preferred. The content of the structural units derived from the (meth)acrylic acid alkyl ester (particularly the total content of the structural units derived from the low Tg (meth)acrylic acid alkyl ester and the methacrylic acid C1-5 alkyl ester) may be appropriately adjusted so that the Tg of the polymer (A) falls within the range described below, and is, for example, 0 to 600 parts by mass, and preferably 10 to 420 parts by mass, relative to 100 parts by mass of the structural units derived from the aromatic group-containing monomer. The total content of the structural units derived from aromatic group-containing monomers, the structural units derived from hydroxyl group-containing monomers, the structural units derived from alicyclic group-containing monomers, and the structural units derived from alkyl (meth)acrylate esters in the polymer (A) is preferably 60 to 100% by mass, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0025] The nitrogen atom-containing monomer is a monomer having at least a substituent containing a nitrogen atom as a constituent and a polymerizable unsaturated group in the molecule (however, it does not have an aromatic hydrocarbon ring, a hydroxyl group, or an alicyclic hydrocarbon ring). Examples of the nitrogen atom-containing monomer include a nitrogen-based heterocycle-containing monomer, an amino group-containing monomer, and an amide group-containing monomer. Note that, in this specification, a monomer that is an amino group-containing monomer or an amide group-containing monomer but contains a nitrogen-based heterocycle is referred to as a nitrogen-based heterocycle-containing monomer. Specific examples of the nitrogen-based heterocycle-containing monomer include vinyl lactam monomers such as N-methylvinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinylpyrrolidone, N-vinyl-2-pyrrolidone, and N-(meth)acryloylpyrrolidone; maleimide monomers such as maleimide; piperidyl(meth)acrylic monomers such as 2,2,6,6-tetramethyl-4-piperidyl(meth)acrylate and 1,2,2,6,6-pentamethyl-4-piperidyl(meth)acrylate; (meth)acrylic aziridinyl group-containing (meth)acrylic monomers such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline; and the like.

[0026] Specific examples of the amino group-containing monomer include amino group-containing (meth)acrylic monomers such as N,N-dimethylaminomethyl (meth)acrylate and N,N-dimethylaminoethyl (meth)acrylate. Examples of the amide group-containing monomer include (meth)acrylamide-based monomers such as (meth)acrylamide, N-monomethyl(meth)acrylamide, N-monoethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, Nn-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, methylenebis(meth)acrylamide, N-butoxymethyl(meth)acrylamide, dimethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropylacrylamide, and diacetone acrylamide. As the nitrogen atom-containing monomer, a nitrogen-based heterocycle-containing monomer is preferred, a vinyl lactam-based monomer and a piperidyl(meth)acrylic monomer are more preferred, and N-vinyl-2-pyrrolidone, 2,2,6,6-tetramethyl-4-piperidyl(meth)acrylate, and 1,2,2,6,6-pentamethyl-4-piperidyl(meth)acrylate are even more preferred. From the viewpoint of improving light stability, a nitrogen atom-containing monomer having a hindered amine structure is preferred. As such a monomer, a monomer having a 2,2,6,6-tetraalkylpiperidine ring structure and a polymerizable unsaturated group (e.g., (meth)acryloyl group, vinyl group, etc.) in the molecule is preferred, a monomer having a 2,2,6,6-tetramethylpiperidine ring structure and a polymerizable unsaturated group (e.g., (meth)acryloyl group, vinyl group, etc.) is more preferred, and 2,2,6,6-tetramethyl-4-piperidyl(meth)acrylate and 1,2,2,6,6-pentamethyl-4-piperidyl(meth)acrylate are even more preferred. The content of the structural units derived from the nitrogen atom-containing monomer is preferably 0 to 40 parts by mass, more preferably 2 to 30 parts by mass, and even more preferably 5 to 25 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. The acid group-containing monomer has at least one acid group and at least one polymerizable unsaturated group in the molecule. Monomers having a hydroxyl group (however, aromatic hydrocarbon rings, hydroxyl groups, alicyclic hydrocarbon rings, and nitrogen atoms The acid group is a sulfo group, a carboxylic acid group, or a carboxylic acid group. Examples of the polymerizable unsaturated group include a (meth)oxy group, and a carboxy group is preferred. ) acryloyl group, vinyl group, etc.

[0027] Specific examples of the acid group-containing monomer include unsaturated monocarboxylic acids such as (meth)acrylic acid, cinnamic acid, and crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; monoesters of unsaturated dicarboxylic acids such as maleic acid monomethyl ester, maleic acid monobutyl ester, itaconic acid monomethyl ester, and itaconic acid monobutyl ester; anhydrides of unsaturated dicarboxylic acids such as maleic anhydride; 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, and 2-acryloyloxyethyl hexahydrophthalic acid. Among these, unsaturated monocarboxylic acids are preferred, and (meth)acrylic acid is more preferred. The content of the structural units derived from the acid group-containing monomer in the acrylic polymer of the present disclosure is preferably 0 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. By adjusting the content of the structural units derived from the acid group-containing monomer to the above-mentioned predetermined value or less, the sedimentation stability of the resulting ink can be improved, and by adjusting the content of the structural units derived from the acid group-containing monomer to the above-mentioned predetermined value or more, the viscosity stability of the resulting ink can be further improved.

[0028] Further, examples of other monomers in the acrylic polymer of the present disclosure include di(meth)acrylates of alkanediols having 1 to 10 carbon atoms, such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate; diethylene glycol di(meth)acrylate, and dipropylene glycol di(meth)acrylate. di-C2-4 alkylene glycol di(meth)acrylates such as polyethylene glycol di(meth)acrylates having an added mole number of ethylene oxide of 2 to 50, polypropylene glycol di(meth)acrylates having an added mole number of propylene oxide of 2 to 50, and the like; ethoxylated glycerin tri(meth)acrylate, propylene oxide-modified glycerol tri(meth)acrylate, ethylene oxide-modified tri(meth)acrylate, Tri(meth)acrylates of trihydric alcohols having 1 to 10 carbon atoms, such as trimethylolpropane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and trimethylolpropane triethoxytri(meth)acrylate; tetra(meth)acrylates of tetrahydric alcohols having 1 to 10 carbon atoms, such as pentaerythritol tetra(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate; hexa(meth)acrylates of hexahydric alcohols having 1 to 10 carbon atoms, such as dipentaerythritol hexa(meth)acrylate. acrylate; 2-(2'-vinyloxyethoxyethyl) (meth)acrylate; (meth)acryloyl group-containing silane coupling agents such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, and 3-(meth)acryloxyethoxypropyltrimethoxysilane; vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane;Epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate, α-methylglycidyl (meth)acrylate, and 2-glycidyloxyethyl (meth)acrylate; epoxy group-containing vinyl monomers such as allyl glycidyl ether; fluoroalkyl (meth)acrylates such as trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, and octafluoropentyl (meth)acrylate; methoxyethyl (meth)acrylate Examples of the monomers include alkoxyalkyl group-containing (meth)acrylates such as acrylate, methoxybutyl (meth)acrylate, ethoxybutyl (meth)acrylate, and trimethylolpropane tripropoxy (meth)acrylate; carbonyl group-containing (meth)acrylates such as (meth)acryloxyalkylpropenal, acetonyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate acetylacetate, butanediol-1,4-acrylate acetylacetate, and 2-(acetoacetoxy)ethyl (meth)acrylate; vinyl monomers such as vinyl acetate, vinyl chloride, and vinyl benzoate; and olefin monomers such as ethylene and propylene.

[0029] The acrylic polymer of the present disclosure may contain one or more structural units derived from other monomers. From the viewpoint of adhesion to substrates (particularly PET films and OPP films), the weight-average molecular weight (Mw) of the acrylic polymer of the present disclosure is preferably 50,000 or more, more preferably 60,000 or more, and even more preferably 70,000 or more, and is preferably 100,000 or less, and more preferably 90,000 or less. The weight-average molecular weight of the acrylic polymer of the present disclosure can be measured using a known method, but the method described in the Examples can also be adopted.

[0030] The polyester-based polymer of the present disclosure may be any polymeric material having an ester bond in the main chain, and may be, for example, an unmodified polyester or a modified polyester. Examples of the polyester-based polymer of the present disclosure include polycarboxylic acids such as dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, sodium sulfoisophthalate, succinic acid, adipic acid, azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, and dimer acid, and tricarboxylic or higher carboxylic acids such as trimellitic acid and pyrrolimetic acid, and polycarboxylic acids such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, polytetraethylene glycol, The polyester may be a polymer formed by an ester bond of a dihydric alcohol such as 1,4-cyclohexanedimethanol or an ethylene oxide adduct of bisphenol A, or a polyhydric alcohol such as trihydric or higher alcohol such as trimethylolpropane or pentaerythritol, or a block copolymer, random copolymer, graft copolymer, or the like thereof. Examples of commercially available polyesters include Polyester manufactured by Nippon Synthetic Chemical Industry Co., Ltd., PLASCOAT (registered trademark) manufactured by GOO Chemical Industry Co., Ltd., ARONMELT (registered trademark) manufactured by Toagosei Co., Ltd., ELITEL (registered trademark) manufactured by Unitika Ltd., PESRESIN (registered trademark) manufactured by Takamatsu Oil & Fats Co., Ltd., Vylonal (registered trademark) manufactured by Toyobo Co., Ltd., and Nipporan (registered trademark), a polyester polyol manufactured by Tosoh Corporation. From the viewpoint of adhesion to substrates (particularly PET films and OPP films), the weight-average molecular weight (Mw) of the resin emulsion of the present disclosure is preferably 50,000 or more, more preferably 60,000 or more, and even more preferably 70,000 or more, and is preferably 100,000 or less, and more preferably 90,000 or less. The weight-average molecular weight of the resin emulsion of the present disclosure can be measured using a known method, but the method described in the examples can also be adopted. The resin emulsion particles of the present disclosure may contain an emulsifier together with the water-insoluble polymer.

[0031] The emulsifier contained in the resin emulsion particles of the present disclosure may be a conventionally known emulsifier, such as a nonionic emulsifier, an anionic emulsifier, a cationic emulsifier, or an amphoteric emulsifier. These emulsifiers may be used alone or in combination of two or more. Furthermore, an emulsifier containing a polymerizable unsaturated group in the molecule may also be used. Examples of the polymerizable unsaturated group include a group having an ethylenically unsaturated double bond. Incidentally, an emulsifier containing a polymerizable unsaturated group is also referred to as a reactive emulsifier. Furthermore, a polymeric emulsifier may also be used as the emulsifier. Among the above emulsifiers, nonionic emulsifiers or anionic emulsifiers are preferred, anionic emulsifiers having a polymerizable unsaturated group or nonionic emulsifiers having a polymerizable unsaturated group are more preferred, and anionic emulsifiers having a polymerizable unsaturated group are even more preferred. Examples of the anionic emulsifier include alkyl sulfate salts such as ammonium dodecyl sulfate and sodium dodecyl sulfate; alkyl sulfonate salts such as ammonium dodecyl sulfonate, sodium dodecyl sulfonate and sodium alkyl diphenyl ether disulfonate; alkyl aryl sulfonate salts such as ammonium dodecyl benzene sulfonate, sodium dodecyl benzene sulfonate and sodium dodecyl naphthalene sulfonate; polyoxyethylene alkyl sulfonate salts; polyoxyethylene alkyl ether sulfate salts; polyoxyethylene alkyl aryl ether sulfate salts; polyoxyethylene polycyclic phenyl ether sulfate; ester salts; dialkyl sulfosuccinate salts; arylsulfonic acid-formalin condensates; fatty acid salts such as ammonium laurate and sodium stearylate; sulfates or salts thereof having an allyl group such as bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfonate salts, propenyl-alkyl sulfosuccinate ester salts, (meth)acrylic acid polyoxyethylene sulfonate salts, (meth)acrylic acid polyoxyethylene phosphonate salts, and sulfonate salts of allyloxymethyl alkyloxy polyoxyethylene; sulfate ester salts of allyloxymethyl alkoxyethyl polyoxyethylene, and polyoxyalkylene alkenyl ether ammonium sulfate salts. Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, condensates of polyethylene glycol and polypropylene glycol, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid monoglycerides, condensates of ethylene oxide and aliphatic amines, and polyoxyalkylene alkenyl ethers. Examples of polymeric emulsifiers include poly(meth)acrylates such as sodium polyacrylate; polyvinyl alcohol; polyvinylpyrrolidone; polyhydroxyalkyl(meth)acrylates such as polyhydroxyethyl acrylate; and copolymers containing one or more of the monomers that make up these polymers as copolymerization components. Examples of reactive emulsifiers include propenyl-alkyl sulfosuccinate salts, (meth)acrylic acid polyoxyethylene sulfonate salts, (meth)acrylic acid polyoxyethylene phosphonate salts (e.g., Sanyo Chemical Industries, Ltd., trade name: Eleminol RS-30, etc.), polyoxyethylene alkylpropenylphenyl ether sulfonate salts (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon HS-10, etc.), sulfonate salts of allyloxymethyl alkyloxy polyoxyethylene (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon KH-10, etc.), polyoxyethylene styrenated propenyl phenyl ether sulfate ester ammonium (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon AR-10, etc.), sulfonate salts of allyloxymethyl nonylphenoxyethyl hydroxy polyoxyethylene (e.g., ADEKA Corporation, trade name: Adeka Reasoap SE-10, etc.), and allyloxymethyl alkoxyethyl hydroxy polyoxyethylene sulfate. Examples of the emulsifier include anionic emulsifiers having a polymerizable unsaturated group, such as ester salts (e.g., ADEKA CORPORATION, trade names: ADEKA REASOAP SR-10, SR-30, etc.) and bis(polyoxyethylene polycyclic phenyl ether) methacrylated sulfonate salts (e.g., Nippon Nyukazai Co., Ltd., trade name: ANTOX MS-60, etc.); and nonionic emulsifiers having a polymerizable unsaturated group, such as polyoxyethylene styrenated propenyl phenyl ether (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon AN-10, etc.), allyloxymethylalkoxyethylhydroxypolyoxyethylene (e.g., ADEKA CORPORATION, trade name: ADEKA REASOAP ER-20, etc.), polyoxyethylene alkylpropenyl phenyl ether (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon RN-20, etc.), and allyloxymethylnonylphenoxyethylhydroxypolyoxyethylene (e.g., ADEKA CORPORATION, trade name: ADEKA REASOAP NE-10, etc.). The amount of emulsifier used in the resin emulsion particles of the present disclosure is, for example, preferably 0.5 to 10 parts by mass, more preferably 1.0 to 8 parts by mass, and even more preferably 1.5 to 6 parts by mass, relative to 100 parts by mass of the water-insoluble polymer. If necessary, protective colloids can be used alone or together with the emulsifier.

[0032] Pigments used in the aqueous inks of the present disclosure include organic pigments and inorganic pigments. Examples of organic pigments of the present disclosure include azo pigments such as benzidine and Hansa Yellow, azomethine pigments, methine pigments, anthraquinone pigments, phthalocyanine pigments such as phthalocyanine blue, perinone pigments, perylene pigments, diketopyrrolopyrrole pigments, thioindigo pigments, iminoisoindoline pigments, iminoisoindolinone pigments, quinacridone pigments such as quinacridone red and quinacridone violet, flavanthrone pigments, indanthrone pigments, anthrapyrimidine pigments, carbazole pigments, monoarylide yellow, diarylide yellow, benzimidazolone yellow, tolyl orange, naphthol orange, and quinophthalone pigments, but the present invention is not limited to these examples. These organic pigments may be used alone or in combination of two or more. Preferred organic pigments include, for example, CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of inorganic pigments of the present disclosure include titanium dioxide, antimony trioxide, zinc oxide, lithopone, white lead, red iron oxide, black iron oxide, iron oxide, chromium oxide green, carbon black, yellow lead, molybdenum red, ferric ferrocyanide (Prussian blue), ultramarine, and lead chromate; flat-shaped pigments such as mica, clay, aluminum powder, talc, and aluminum silicate; and extender pigments such as calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, and magnesium carbonate; but the present invention is not limited to these examples. These inorganic pigments may be used alone or in combination of two or more.

[0033] When used in a white ink, the content of the water-insoluble polymer in 100 parts by mass of the aqueous ink of the present disclosure may be 1 part by mass or more, preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and may be 50 parts by mass or less, preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. On the other hand, when used in a color ink other than the white ink, the content may be 1 part by mass or more, preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and may be 40 parts by mass or less, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less. For the aqueous ink of the present disclosure, the pigment content per 100 parts by mass of the non-volatile content of the aqueous ink is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, from the viewpoint of sufficiently coloring the print or image formed with the aqueous ink, and is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, from the viewpoint of forming a uniform coating film. The aqueous ink of the present disclosure may contain water as well as a water-soluble organic solvent from the viewpoints of ink viscosity, control of wetting and spreading on a recording medium to be printed, improvement of image quality, and ejection stability.

[0034] The water content per 100 parts by mass of the aqueous ink of the present disclosure may be 35 parts by mass or more, preferably 40 parts by mass or more, and more preferably 45 parts by mass or more, and may be 70 parts by mass or less, preferably 65 parts by mass or less, and more preferably 60 parts by mass or less. The content of the water-soluble organic solvent in 100 parts by mass of the aqueous ink of the present disclosure may be 5 parts by mass or more, preferably 8 parts by mass or more, and more preferably 10 parts by mass or more, and may be 50 parts by mass or less, preferably 45 parts by mass or less, and more preferably 40 parts by mass or less. The water-based ink of the present disclosure may contain a compound (B) other than the pigment and the water-insoluble polymer. Examples of the other compound (B) of the present disclosure include a water-soluble resin, a surfactant, a film-forming aid, an ultraviolet absorber, an ultraviolet inhibitor, a filler, a leveling agent, a dispersant, a thickener, a wetting agent, a plasticizer, a stabilizer, and an antioxidant.

[0035] <Ink set> In a preferred embodiment, the cleaning liquid of the present disclosure is used together with an aqueous ink as an ink set for inkjet printing. The ink set of the present disclosure is not particularly limited as long as it is used for the purpose of cleaning with the cleaning liquid of the present disclosure after printing with the aqueous ink, but the cleaning liquid may be contained in an ink tank together with the aqueous ink, or the cleaning liquid may not be contained in an ink tank together with the aqueous ink.

[0036] <Inkjet printing device> The ink set for inkjet printing of the present disclosure is excellent at preventing adhesion of aqueous ink to the ejection head portion, and is expected to contribute to improving printing efficiency. In other words, an inkjet printing apparatus using the ink set of the present disclosure is an inkjet printing apparatus in which adhesion of ink to the ejection head portion is suppressed by using a cleaning liquid that is excellent at removing ink. The inkjet printing apparatus of the present disclosure may be an inkjet printing apparatus including an ink storage container that stores ink, an ink ejection head that ejects the ink, an ink supply path that connects the ink ejection head and the ink storage container, a cleaning liquid storage container that stores cleaning liquid for replacing the ink in the ink ejection head and the ink supply path, and cleaning liquid supply means that supplies the cleaning liquid in the cleaning liquid storage container to the ink supply path and the ink ejection head, and may also include other means as necessary.

[0037] <Discharge head> The ejection head in the inkjet printing device of the present disclosure is not particularly limited, but is preferably an ejection head having nozzles for ejecting ink and further having a liquid-repellent layer on at least the surface on the ink ejection surface side, and may have a step structure on the ink ejection surface side. Although an ejection head having a step structure on the ink ejection surface side is prone to accumulation of dirt, it is expected that the use of the cleaning liquid of the present disclosure will improve its cleanability. When using ink with improved drying properties and adhesion from the perspective of printability, dirt tends to be more difficult to remove from the ejection head, but it is expected that the use of the cleaning liquid of the present disclosure will improve its cleanability.

[0038] <Discharge head and discharge head cleaning method> The cleaning liquid of the present disclosure is used as a cleaning liquid for inkjet printing devices. The cleaning liquid of the present disclosure is effective when used to clean the ejection head of an inkjet printing device. The method for cleaning the ejection head may be such that a cleaning liquid is set in the printing device and discharged from the ejection head through piping, or such that the cleaning liquid is sprayed directly onto the liquid-repellent surface of the ejection head or wiped directly with a cloth impregnated with the cleaning liquid, or such that the ejection head is removed and immersed in the cleaning liquid; however, from the viewpoint of workability, it is more preferable to adopt the method of removing the ejection head and immersing it in the cleaning liquid or the method of discharging the cleaning liquid from the ejection head through piping. [Example]

[0039] The present invention will now be described in more detail based on examples, but the present invention is not limited to these examples. In the following examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." <Glass transition temperature of polymer> The glass transition temperature (Tg) of the polymer constituting the polymer particles contained in the aqueous dispersion was calculated based on the glass transition temperature of the homopolymer of each monomer used in the monomer component constituting the polymer, according to the Fox equation shown below.

[0040] 1 / Tg A =Σ(Wm / Tgm) / 100 [In the formula, Tg A indicates the glass transition temperature (absolute temperature: K) of the polymer, Wm indicates the content (mass%) of monomer m in all the monomer components constituting the polymer, and Tgm indicates the glass transition temperature (absolute temperature: K) of a homopolymer of monomer m.] <Acid value of polymer> The acid value of the polymer constituting the polymer particles contained in the aqueous dispersion was obtained by approximating the acid value as the number of mg of potassium hydroxide required to neutralize the acid groups present in 1 g of the monomer component constituting the polymer.

[0041] <Non-volatile content (NV value) of aqueous dispersion> The nonvolatile content of the aqueous dispersion was calculated based on the following formula by weighing 1 g of the aqueous dispersion, drying it in a hot air dryer at 110°C for 1 hour, and using the resulting residue as the nonvolatile content. Formula: [Non-volatile content in aqueous dispersion (mass%)] = ([mass of residue] ÷ [mass of aqueous dispersion (1 g)]) × 100 <Weight average molecular weight of polymer> The weight-average molecular weight of the polymer constituting the polymer particles contained in the aqueous dispersion was determined from a gel permeation chromatography chart prepared using a gel permeation chromatography equipped with an RI detector (Tosoh Corporation, product number: HLC-8120GPC, columns: TSKgel G-5000HXL and TSKgel GMHXL-L used in series, developing solvent: tetrahydrofuran (THF)) and a calibration curve prepared using standard polystyrenes F-450, A-5000, A-1000, and A-300, all of which are also manufactured by Tosoh Corporation.

[0042] <Production Example 1: Production of titanium oxide aqueous dispersion> A 250 mL plastic container was charged with 40.77 parts of pure water, 4.13 parts of DISPERBYK-190 (manufactured by BYK Japan, polyalkylene glycol group-containing acrylic water-soluble polymer, acid value 10 mg KOH / g, active ingredient concentration 40%) as a dispersant, and 55.00 parts of JR-403 (manufactured by Teika Corporation, rutile-type titanium dioxide, primary particle diameter 250 nm) as titanium dioxide. Subsequently, 100 parts of 0.1 mm diameter zirconia beads were added as dispersion media. The plastic container was sealed and subjected to a paint shaker treatment for 300 minutes. The zirconia beads were then suction filtered through a 7 μm mesh paper filter to obtain Titanium Dioxide Dispersion 1, with a rutile-type titanium dioxide concentration of 55%.

[0043] <Production Example 2: Production of aqueous resin dispersion> A flask equipped with a dropping funnel, stirrer, nitrogen gas inlet tube, thermometer, and reflux condenser was charged with 1,050 parts of deionized water. A pre-emulsion for dropping, consisting of 381 parts of deionized water, 80 parts of a 25% aqueous solution of emulsifier (ADEKA Corporation, trade name: ADEKA REASOAP SR-10), 300 parts of styrene, 100 parts of 2-ethylhexyl acrylate, 350 parts of cyclohexyl methacrylate, 250 parts of 2-hydroxyethyl methacrylate, and 10 parts of tert-dodecyl mercaptan, was prepared. 74 parts (5% of the total amount) of the pre-emulsion for dropping was added to the dropping funnel. The temperature was raised to 80°C while slowly blowing in nitrogen gas. Next, 30 parts of a 5% aqueous solution of ammonium persulfate was added to initiate polymerization. The remainder of the pre-emulsion for dropping and 30 parts of a 5% aqueous solution of ammonium persulfate were then added dropwise uniformly to the flask over 180 minutes. After the dropwise addition was completed, the contents of the flask were maintained at 80°C for 120 minutes, and the pH was adjusted to 8 by adding 25% aqueous ammonia to terminate the polymerization. The resulting reaction solution was cooled to room temperature and filtered through a 300-mesh wire screen to obtain aqueous resin dispersion A, in which emulsion particles composed of resin A were dispersed. The nonvolatile content of this aqueous resin dispersion was 40%. Furthermore, resin A had an acid value of 0 mgKOH / g, a glass transition temperature of 56°C, and a weight-average molecular weight of 80,000.

[0044] <Production Example 3: Preparation of titanium oxide dispersion> A 250 mL plastic container was charged with 40.77 parts of pure water, 4.13 parts of DISPERBYK-190 (manufactured by BYK Japan, polyalkylene glycol group-containing acrylic water-soluble polymer, acid value 10 mg KOH / g, active ingredient concentration 40%) as a dispersant, and 55.00 parts of JR-403 (manufactured by Teika Corporation, rutile-type titanium dioxide, primary particle diameter 250 nm) as titanium dioxide. Subsequently, 100 parts of 0.1 mm diameter zirconia beads were added as dispersion media. The plastic container was sealed and subjected to a paint shaker treatment for 300 minutes. The zirconia beads were then suction filtered through a 7 μm mesh paper filter to obtain Titanium Dioxide Dispersion 1, with a rutile-type titanium dioxide concentration of 55%.

[0045] <Production Example 4: Production of Water-Based White Inkjet (IJ) Ink A> 8.2 parts of pure water, 15.0 parts of propylene glycol, 12.0 parts of dipropylene glycol monomethyl ether, and 3.0 parts of diethylene glycol monobutyl ether as water-soluble organic solvents, 27.3 parts of the titanium oxide dispersion 1 described above, 33.2 parts of the aqueous resin dispersion obtained in Production Example 2 as a binder resin, 0.8 parts of BYK-3480 (a silicone-based surfactant manufactured by BYK Japan KK) and 0.5 parts of Olfine E1004 (an acetylene glycol-based surfactant manufactured by Nissin Chemical Industry Co., Ltd.) as surfactants were mixed in a homodisper at 1000 rpm, and the mixture was filtered through a 3 μm filter [MCP-3-C10S manufactured by Advantec Co., Ltd.] to obtain aqueous white ink A. This white ink was loaded into a jetXpert print evaluation device (manufactured by imageXpert) equipped with an SII Printec RC1536 inkjet head, which has a stepped structure due to a stainless steel shield attached to the ejection surface. A solid white image was printed on corona-treated OPP film (manufactured by Futamura Chemical Co., Ltd., trade name: FOR-AQ) and corona-treated PET film (manufactured by Futamura Chemical Co., Ltd., trade name: FE-2001) at a dot density of 360 DPI with a droplet size of 50 pL. The solid white image was then dried at 100°C for 5 minutes, yielding a printed product. A cellophane tape peel test of the white coating was then performed, and no coating peeling was observed in either the PET or OPP films, even when quickly peeled at a 90° angle.

[0046] <Production Example 5: Production of Water-Based White Inkjet Ink B> Aqueous white ink B was obtained in the same manner as in Production Example 4, except that 53.1 parts of Vylonal MD-1480, a water-dispersible polyester resin manufactured by Toyobo MC Co., Ltd., was used as the binder resin instead of 33.2 parts of the aqueous resin dispersion obtained in Production Example 2. When this white ink was subjected to a cellophane tape peeling test on PET and OPP in the same manner as in Production Example 4, no coating peeling was observed in either the PET or OPP cases, even when quickly peeled at a 90° angle.

[0047] <Production Example 6: Production of cleaning solution A> 88.9 parts of pure water, 10 parts of glycerin, 1.0 part of Olfine EXP4300 (an acetylene surfactant manufactured by Nissin Chemical Industry Co., Ltd.) as an acetylene surfactant, and 0.1 parts of a 1 N aqueous sodium hydroxide solution were mixed at 1000 rpm in a Homodisper, and the mixture was filtered through a 3 μm filter [MCP-3-C10S manufactured by Advantec Co., Ltd.] to obtain cleaning solution A, which is described as cleaning solution C-1 in Patent Document 1.

[0048] <Production Example 7: Production of cleaning solution B> 89.7 parts of pure water, 5.0 parts of propylene glycol, 2.0 parts of glycerin, 1.0 part of 1,2-ethanediol, 1.0 part of 2-pyrrolidone, 1.0 part of ε-caprolactam, 0.03 parts of 1,2,3-benzotriazole as a preservative, 0.02 parts of Proxel LV (manufactured by Avecia) as a preservative, 0.06 parts of Emulgen LS-106 (manufactured by Kao Corporation) as a surfactant, 0.15 parts of 2-amino-2-ethyl-1,3-propanediol as a pH adjuster, and 0.05 parts of N-cyclohexyl-2-aminoethanesulfonic acid as a pH buffer were mixed in a Homodisper at 1000 rpm, and the mixture was filtered through a 3 μm filter [MCP-3-C10S, manufactured by Advantec Co., Ltd.] to obtain cleaning solution B, which is described as cleaning solution No. 1 in Patent Document 2.

[0049] Example 1 The acrylic binder water-based white inkjet ink prepared in Production Example 3 was filled into a stainless steel tray to a depth of 10 mm, and an inkjet head RC1536 manufactured by SII Printec, Inc. was immersed in the ink with the ink ejection surface facing downward for 10 minutes. The inkjet head was then removed from the tray and dried in a 30°C fan dryer for 12 hours, yielding an inkjet head with accumulated white ink stains on the ejection surface. The tray was then filled with a 50% by weight aqueous solution of MFTG (methyl tripropylene glycol, boiling point 241°C) as a cleaning solution to a depth of 10 mm. The inkjet head with accumulated white ink stains on the ejection surface was then immersed at room temperature for 12 hours, and the ease of removal of the accumulated white ink stains was evaluated as cleanability. The inkjet ejection performance after the cleaning process was evaluated by filling the prepared water-based white ink into a print evaluation device, jetXpert (manufactured by imageXpert). The results are shown in Table 1.

[0050] <Cleaning performance evaluation criteria> A: After soaking in the cleaning solution for 12 hours, ink stains can be removed by washing with pure water. B: After immersion in the cleaning solution for 12 hours, it is impossible to remove the ink stains by washing with pure water, but the ink stains can be removed by wiping with a Kimwipe moistened with water. C: After immersion in the cleaning solution for 12 hours, the ink stains cannot be removed by washing with pure water, nor can they be removed by wiping with a Kimwipe moistened with water. <Inkjet ejection properties after cleaning treatment> 〇: 0 non-discharge nozzles out of 100 nozzles ×: One or more non-ejecting nozzles out of 100 nozzles <Examples 2 to 9 and Comparative Examples 1 to 6> Using the inks shown in Table 1, the cleaning properties and ink jet ejection properties after cleaning treatment were evaluated in the same manner as in Example 1, except that the cleaning solution was changed to one having the composition shown in Table 1. The results are shown in Table 1.

[0051] [Table 1]

[0052] MFTG: Tripropylene glycol methyl ether, boiling point 242°C, SP value 9.1 BDG: Diethylene glycol monobutyl ether, boiling point 230°C, SP value 9.5 MFDG: Dipropylene glycol methyl ether, boiling point 188°C, SP value 9.6 H2O: Water

Claims

1. A cleaning liquid for an inkjet printing device, wherein the content of a glycol ether compound having a boiling point of 120°C or higher per 100 parts by mass of the cleaning liquid is 25 parts by mass or more.

2. The cleaning solution of claim 1 , wherein the cleaning solution further comprises water.

3. 3. The cleaning solution according to claim 2, wherein the total amount of the glycol ether compound having a boiling point of 120° C. or higher and water is 90 parts by mass or more per 100 parts by mass of the cleaning solution.

4. 2. The cleaning solution of claim 1, wherein the inkjet printing device is an inkjet printing device for aqueous inks.

5. The cleaning liquid according to claim 4 , wherein the water-based ink contains a pigment and a water-insoluble polymer, and the water-insoluble polymer contains an acrylic polymer and / or a polyester polymer.

6. The cleaning solution according to claim 1, which is used to clean a discharge head in an inkjet printing device.

7. An ink set for ink-jet printing, comprising the cleaning liquid according to claim 1 and a water-based ink.

8. 8. The ink set according to claim 7, wherein the water-based ink contains a pigment and a water-insoluble polymer, and the water-insoluble polymer contains an acrylic polymer and / or a polyester polymer.

9. An inkjet printing device using the ink set according to claim 7.

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