Aqueous emulsion and method for producing the same, and aqueous ink

Abstract

This invention provides a water-based emulsion useful as a binder component for water-based inks, capable of forming a coating film with excellent abrasion resistance, alcohol resistance, hot water resistance (shrink resistance), and adhesion to various substrates. [Solution] The emulsion contains polymer-formed emulsion particles, the polymer comprising 20-40% by mass of constituent units (1) derived from a polymer-type monomer represented by general formula (1), 57-79.9% by mass of constituent units (2) derived from a water-insoluble first monomer having one vinyl group, and 0.1-3% by mass of constituent units (3) derived from a water-insoluble second monomer having two or more vinyl groups, wherein constituent units (1) are neutralized with alkali. TIFF2026054283000014.tif51170

Description

Technical Field

[0001] The present invention relates to an aqueous emulsion, a method for producing an aqueous emulsion, and an aqueous ink.

Background Art

[0002] In recent years, the development of environmentally friendly products has been demanded, and aqueous inks have attracted attention. In fields such as gravure printing, flexographic printing, and inkjet printing, the water-based conversion of inks has been demanded, and many studies have been made on the transition from oil-based inks to aqueous inks. Aqueous inks such as aqueous gravure ink, aqueous flexographic ink, and aqueous inkjet ink are used for printing on plastic containers, packaging films such as labels and packaging. Furthermore, these aqueous inks are used as overcoat agents and transparent varnishes for overcoating and protecting printed materials.

[0003] For the images recorded on printed materials and the films formed by transparent varnishes (hereinafter also referred to as "ink coatings" or "coatings"), in addition to the adhesion to the substrate, durability such as abrasion resistance, water resistance, chemical resistance, and solvent resistance is required. In order to improve the durability of the coating film, for example, various binders for film formation and aqueous inks containing such binders have been proposed (Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] While water-based inks have a lower environmental impact, the resulting coating often lacks sufficient abrasion resistance, particularly in wet conditions (moisture abrasion resistance) and in heat (hot water resistance, shrink resistance). Therefore, transporting printed materials with water-based ink in wet conditions or immersing them in hot water can lead to problems such as cracking or peeling of the coating.

[0006] Furthermore, in recent years, high-concentration ethanol aqueous solutions have been used as disinfectants to remove viruses such as COVID-19. However, wiping a coating formed with water-based ink with an ethanol aqueous solution has sometimes resulted in problems such as the coating dissolving or peeling off from the substrate.

[0007] This invention has been made in view of the problems of the prior art, and its objective is to provide a water-based emulsion that is useful as a binder component material for water-based inks that can form a coating film with excellent abrasion resistance, alcohol resistance, hot water resistance (shrink resistance), and adhesion to various substrates.

[0008] Furthermore, an object of the present invention is to provide a cost-effective and simple method for producing the above-mentioned aqueous emulsion, which has good storage stability. Moreover, an object of the present invention is to provide an aqueous ink that can form a coating film with excellent abrasion resistance, alcohol resistance, hot water resistance, and adhesion to various substrates, using the above-mentioned aqueous emulsion. [Means for solving the problem]

[0009] In other words, the present invention provides the following aqueous emulsion. [1] An aqueous emulsion used for preparing an aqueous ink, comprising an aqueous liquid medium and emulsion particles formed of an internally crosslinked polymer dispersed and emulsified in the liquid medium, wherein the polymer comprises 20-40% by mass of constituent units (1) derived from a polymer-type monomer represented by the following general formula (1), having a number average molecular weight of 1,000-10,000 and a content of 10-35% by mass of constituent units derived from methacrylic acid; 57-79.9% by mass of constituent units (2) derived from a water-insoluble first monomer having one vinyl group; and 0.1-3% by mass of constituent units (3) derived from a water-insoluble second monomer having two or more vinyl groups, wherein the constituent units (1) are neutralized with at least one alkali selected from the group consisting of ammonia, dimethylaminoethanol, sodium hydroxide, and 2-amino-2-methyl-1-propanol, and the number average particle diameter of the emulsion particles is 50-200 nm.

[0010] TIFF2026054283000001.tif51170 (In the above general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, R2 represents an alkyl group having 8 to 18 carbon atoms, and R3 represents at least one group selected from the group consisting of alkyl groups having 1 to 7 carbon atoms, cycloalkyl groups, arylmethyl groups, hydroxyalkyl groups, and polyalkylene glycol monomethyl ether groups.)

[0011] [2] The aqueous emulsion according to [1], wherein the constituent unit (2) comprises 20 to 40% by mass of constituent units derived from styrene and 15 to 59.9% by mass of constituent units derived from at least one selected from the group consisting of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate. [3] The aqueous emulsion according to [1] or [2], wherein in the general formula (1), R2 is at least one group selected from the group consisting of a 2-ethylhexyl group, a dodecyl group, and a tridecyl group, and the content of constituent units derived from a methacrylic acid ester having an alkyl group having 8 to 18 carbon atoms in the polymer-type monomer is 15 to 40% by mass. [4] The aqueous emulsion according to any one of [1] to [3], wherein the liquid medium contains at least one water-soluble organic solvent selected from the group consisting of isopropanol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and 3-methoxy-N,N-dimethylpropanamide, and the content of the water-soluble organic solvent is 3 to 10% by mass.

[0012] Furthermore, the present invention provides a method for producing the following aqueous emulsion. [5] A method for producing an aqueous emulsion according to any of [1] to [4] above, comprising the steps of (a) heating a monomer mixture having a solid content of 55 to 70% by mass, containing 100 parts by mass of monomer, 1 to 10 parts by mass of a compound represented by the following general formula (2), and a water-soluble organic solvent in the presence of a radical generator to radically polymerize it and obtain a solution containing the polymer-type monomer; (b) adding the alkali and water to the solution to obtain an aqueous solution of the polymer-type monomer; and adding to the aqueous solution an amount of water such that the water-soluble organic solvent content is 3 to 10% by mass, the first monomer, A method for producing an aqueous emulsion, comprising the steps of (c) adding the second monomer and heating in the presence of a radical generator to perform radical polymerization, wherein the monomer comprises methacrylic acid, a methacrylic acid ester having an alkyl group having 8 to 18 carbon atoms, and at least one selected from the group consisting of methacrylic acid ester having an alkyl group having 1 to 7 carbon atoms, cycloalkyl methacrylate, arylmethyl methacrylate, hydroxyalkyl methacrylate, and polyalkylene glycol monomethyl ether methacrylate.

[0013] TIFF2026054283000002.tif28170 (In the above general formula (2), R1 represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms)

[0014] Furthermore, the present invention provides the following aqueous inks. [6] An aqueous ink containing the aqueous emulsion described in any of [1] to [4] above. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an aqueous emulsion that is useful as a constituent material for a binder component of aqueous ink, capable of forming a coating film with excellent abrasion resistance, alcohol resistance, hot water resistance (shrink resistance), and adhesion to various substrates.

[0016] Furthermore, the present invention provides a cost-effective and simple method for producing the above-mentioned aqueous emulsion, which has good storage stability. Moreover, the present invention provides an aqueous ink that can form a coating film with excellent abrasion resistance, alcohol resistance, hot water resistance, and adhesion to various substrates, using the above-mentioned aqueous emulsion. [Modes for carrying out the invention]

[0017] <Water-based emulsion> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the aqueous emulsion of the present invention is an aqueous emulsion used for preparing an aqueous ink. The aqueous emulsion of this embodiment contains an aqueous liquid medium and emulsion particles formed of a polymer having internal crosslinking and dispersed and emulsified in the liquid medium. The polymer is a structural unit (1) derived from a polymer-type monomer having a number average molecular weight of 1,000 to 10,000, represented by the following general formula (1), and having a content of structural units derived from methacrylic acid of 10 to 35% by mass, 20 to 40% by mass, a structural unit (2) derived from a water-insoluble first monomer having one vinyl group, 57 to 79.9% by mass, and a structural unit (3) derived from a water-insoluble second monomer having two or more vinyl groups, 0.1 to 3% by mass. The structural unit (1) is neutralized with at least one alkali selected from the group consisting of ammonia, dimethylaminoethanol, sodium hydroxide, and 2-amino-2-methyl-1-propanol. And the number average particle diameter of the emulsion particles is 50 to 200 nm. Hereinafter, the details of the aqueous emulsion of this embodiment will be described.

[0018] TIFF2026054283000003.tif51170(In the general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, R2 represents an alkyl group having 8 to 18 carbon atoms, and R3 represents at least one group selected from the group consisting of an alkyl group having 1 to 7 carbon atoms, a cycloalkyl group, an arylmethyl group, a hydroxyalkyl group, and a polyalkylene glycol monomethyl ether group)

[0019] The polymer forming the emulsion particles is a graft-type polymer. The structural unit (1) is a structural unit derived from a polymer-type monomer and having an unsaturated bond at its terminal. This terminal unsaturated bond reacts with the structural unit (2) and the structural unit (3) and is linked, resulting in a branched structure of the structural unit (1). Further, the unsaturated bond of the structural unit (1), the structural unit (2), and the structural unit (3) polymerize to form the polymer chain of the backbone. One of the important features of the polymer forming the emulsion particles in the aqueous emulsion of the present embodiment is that it contains the structural unit (3) derived from a water-insoluble second monomer having two or more radically polymerizable vinyl groups, so that the polymer chain of the backbone forms a three-dimensional network structure. For this reason, a polymer having a three-dimensional network structure in which the polymer chains serving as the backbone are crosslinked forms emulsion particles insoluble in water and organic solvents, and has a structure in which the structural unit (1) is grafted to the formed emulsion particles. Note that the polymer constitutes a very large molecule having a three-dimensional network structure, is insoluble in solvents, and it is difficult to measure its molecular weight. The grafted structural unit (1) has a carboxy group, and when this carboxy group is neutralized with an alkali and ionized, the structural unit (1) dissolves in water. That is, the aqueous emulsion of the present embodiment is an aqueous emulsion in which emulsion particles formed by a polymer having a graft chain (structural unit (1)) soluble in water and a water-insoluble part are stably dispersed and emulsified in an aqueous liquid medium.

[0020] (Structural unit (1)) The structural unit (1) is a structural unit derived from a polymer-type monomer represented by the following general formula (1).

[0021] TIFF2026054283000004.tif51170(In the general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, R2 represents an alkyl group having 8 to 18 carbon atoms, and R3 represents at least one group selected from the group consisting of an alkyl group having 1 to 7 carbon atoms, a cycloalkyl group, an arylmethyl group, a hydroxyalkyl group, and a polyalkylene glycol monomethyl ether group)

[0022] Polymer monomers have unsaturated bonds at their ends. A carboxyl group or alkyl ester group is bonded to the polymer chain at the α-position of this unsaturated bond. Because this unsaturated bond is bulky, it does not react with methacrylates that generate tertiary radicals, but instead reacts with vinyl groups and acryloyloxy groups. In general formula (1), the hydrogen atom represented by R1 and the alkyl group with 1 to 2 carbon atoms have small molecular weights and are not bulky, so they do not inhibit polymerization reactions at the ends.

[0023] The monomer constituting the polymer-type monomer includes methacrylic acid, a methacrylic acid ester having an alkyl group with 8 to 18 carbon atoms, and at least one selected from the group consisting of methacrylic acid esters having an alkyl group with 1 to 7 carbon atoms, cycloalkyl methacrylate, arylmethyl methacrylate, hydroxyalkyl methacrylate, and polyalkylene glycol monomethyl ether methacrylate. By using methacrylic acid, a carboxyl group can be introduced into the polymer chain of the polymer-type monomer. This carboxyl group can be neutralized with an alkali to ionize, allowing the polymer chain to dissolve in water. The content of constituent units derived from methacrylic acid in the polymer-type monomer is 10 to 35% by mass, preferably 15 to 25% by mass. If the content of constituent units derived from methacrylic acid is less than 10% by mass, the polymer chain may not be able to dissolve in water even after neutralization and ionization. On the other hand, if the content of constituent units derived from methacrylic acid exceeds 35% by mass, the proportion of hydrophilic carboxyl groups is too high, which tends to reduce the water resistance and heat resistance of the coating film (image).

[0024] Polymer-type monomers contain structural units derived from methacrylic acid esters having alkyl groups with 8 to 18 carbon atoms. The inclusion of these structural units makes the polymer more flexible and improves its film-forming properties. Furthermore, its high hydrophobicity contributes to improved water resistance. Additionally, the inclusion of these structural units lowers the glass transition temperature (Tg) of the polymer, making it more flexible and reducing solution viscosity even at high solid content levels, thus facilitating easy stirring during polymerization.

[0025] Examples of methacrylic acid esters having an alkyl group with 8 to 18 carbon atoms include octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, isodecyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, hexadecyl methacrylate, octadecyl methacrylate, and isodecyl methacrylate. In general formula (1), the alkyl group with 8 to 18 carbon atoms represented by R2 is preferably a 2-ethylhexyl group, a dodecyl group, and a tridecyl group. That is, as methacrylic acid esters having an alkyl group with 8 to 18 carbon atoms, 2-ethylhexyl methacrylate, dodecyl methacrylate, and tridecyl methacrylate are preferred.

[0026] In the polymer-type monomer, the content of constituent units derived from methacrylic acid esters having C8-C18 alkyl groups is preferably 15-40% by mass, and more preferably 20-35% by mass. If the content of constituent units derived from methacrylic acid esters having C8-C18 alkyl groups is less than 15% by mass, it may be difficult to soften the polymer, and the fluidity may decrease during high-solids polymerization, as well as the film-forming ability may decrease. On the other hand, if the content of constituent units derived from methacrylic acid esters having C8-C18 alkyl groups exceeds 40% by mass, the polymer may become too soft, which may cause tackiness in the coating film or a decrease in solvent resistance.

[0027] The polymer monomer includes constituent units derived from methacrylic acid esters having at least one group selected from the group consisting of C1-C7 alkyl groups, cycloalkyl groups, arylmethyl groups, hydroxyalkyl groups, and polyalkylene glycol monomethyl ether groups. Examples of methacrylic acid esters having C1-C7 alkyl groups include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and hexyl methacrylate. Examples of cycloalkyl methacrylate esters include cyclohexyl methacrylate and tricyclodecyl methacrylate, and also include methacrylic acid esters having alkyl-substituted cyclohexyl groups such as t-butylcyclohexyl methacrylate and trimethylcyclohexyl methacrylate. Examples of arylmethyl methacrylate esters include benzyl methacrylate and naphthylmethyl methacrylate. Examples of hydroxyalkyl methacrylates include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 3-hydroxybutyl methacrylate, and 4-hydroxybutyl methacrylate. Examples of polyalkylene glycol monomethyl ether methacrylates include methacrylate esters of polyethylene glycol monomethyl ether with molecular weights of 200, 400, and 1,000.

[0028] The number-average molecular weight (Mn) of the polymer monomer is 1,000 to 10,000, preferably 3,000 to 8,000. If the number-average molecular weight of the polymer monomer is less than 1,000, the resulting emulsion particles may not be sufficiently dispersed and emulsified, potentially reducing storage stability. On the other hand, if the number-average molecular weight of the polymer monomer is greater than 10,000, the viscosity increases due to polymerization with a high solid content, and because the molecular weight of the water-soluble portion is large, the viscosity of the aqueous emulsion tends to become excessively high, potentially resulting in a gel-like state. The number-average molecular weight (Mn) used herein is a polystyrene-converted value measured by gel permeation chromatography (GPC) using tetrahydrofuran as the developing solvent.

[0029] The content of constituent unit (1) in the polymer forming the emulsion particles is 20 to 40% by mass, preferably 25 to 35% by mass. If the content of constituent unit (1) in the polymer is less than 20% by mass, the water solubility of the polymer will be insufficient, resulting in inadequate dispersion and emulsification stability of the emulsion particles. On the other hand, if the content of constituent unit (1) in the polymer exceeds 40% by mass, the hydrophilicity will be excessively high, which will easily reduce the water resistance and heat resistance of the coating film.

[0030] The constituent unit (1) is neutralized with at least one alkali selected from the group consisting of ammonia, dimethylaminoethanol, sodium hydroxide, and 2-amino-2-methyl-1-propanol. When neutralized with ammonia, it can be made into a fast-drying ink that can be dried at room temperature. When neutralized with organic amines such as dimethylaminoethanol or 2-amino-2-methyl-1-propanol, it can be made into an ink that can form an insoluble film by controlling the heating and drying conditions. Furthermore, when neutralized with sodium hydroxide, the carboxyl group does not deionize even after drying and remains as an ion (-COO - Because they remain in that state, the ink can be made to exhibit resolubility. Therefore, for example, even if clogging occurs in the recording head of an inkjet system, the ink can be made to easily resolve the clogging by redissolving it with a cleaning solution or the like. All of the carboxyl groups in the constituent unit (1) may be neutralized, or some of the carboxyl groups in the constituent component (1) that can dissolve in water may be neutralized.

[0031] (Constituent unit (2)) Constituent unit (2) is derived from a water-insoluble first monomer having one radically polymerizable vinyl group. Constituent unit (2) is a component that makes up the main backbone of the polymer, and is the stem part to which constituent unit (1) is grafted. The content of constituent unit (2) in the polymer that forms emulsion particles is 57 to 79.9% by mass. The first monomer is also a water-insoluble monomer. If a water-soluble monomer is used, emulsification during polymer production becomes difficult, making it difficult to form emulsion particles, and the resulting polymer may become water-soluble. In addition, gelation may occur when combined with constituent unit (3) to form a three-dimensional network structure.

[0032] Examples of first monomers include aromatic vinyl monomers such as styrene, vinyltoluene, and chloromethylstyrene; acrylic acid esters having alkyl groups, cycloalkyl groups, and arylmethyl groups with 1 to 18 carbon atoms; methacrylic acid esters having alkyl groups, cycloalkyl groups, and arylmethyl groups with 1 to 18 carbon atoms; vinyl monomers such as vinyl acetate, vinylcarbazole, and vinylpyrrolidone; and the like.

[0033] The constituent unit (2) preferably contains constituent units derived from styrene, and the content of styrene-derived constituent units in constituent unit (2) is preferably 20 to 40% by mass. By using constituent unit (2) containing styrene-derived constituent units, the adhesion of the coating film (image) can be further improved by ππ stacking, especially to resin substrates having aromatic rings such as polyethylene terephthalate. Furthermore, the constituent unit (2) preferably contains 15 to 59.9% by mass of constituent units selected from the group consisting of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate. These monomers are highly versatile and can be copolymerized with styrene to adjust the softness, hardness, or glass transition temperature (Tg) of the stem portion, and to make it rubbery.

[0034] (Constituent unit (3)) The constituent unit (3) is derived from a water-insoluble second monomer having two or more radically polymerizable vinyl groups. By using a second monomer having two or more radically polymerizable vinyl groups, the stem portion forms a three-dimensional network structure (internal crosslinking structure), making it possible to produce a polymer insoluble in organic solvents. Furthermore, since emulsion particles form a film to create a coating film with a crosslinking structure, physical properties such as water resistance, hot water resistance, solvent resistance, abrasion resistance, and ethanol resistance can be significantly improved. The second monomer is a so-called polyfunctional monomer having two or more radically polymerizable vinyl groups, and is a water-insoluble monomer. If a water-soluble monomer is used, emulsification is difficult during polymer production, making it difficult to form emulsion particles, and the resulting polymer may become water-soluble, potentially leading to gelation when forming a three-dimensional network structure.

[0035] Examples of second monomers include relatively low molecular weight polyfunctional monomers such as divinylbenzene, trivinylbenzene, divinylnaphthalene, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, dimethylolpropane tri(meth)acrylate, dimethylolbutane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol(meth)acrylate. If a second monomer with a large molecular weight is used, it may be ejected from the particles during polymerization, resulting in the formation of foreign substances such as precipitates or the precipitation of emulsion particles. Preferred second monomers are divinylbenzene, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate.

[0036] Polymers incorporating constituent unit (3) undergo internal crosslinking and become insoluble in organic solvents. However, the polymer functions as a film-forming component in the ink. Therefore, in order to form a film while undergoing internal crosslinking, the content of constituent unit (3) in the polymer forming emulsion particles is 0.1 to 3% by mass, preferably 0.5 to 1.5% by mass. If the content of constituent unit (3) in the polymer is less than 0.1% by mass, internal crosslinking becomes insufficient, making it difficult to form a three-dimensional network structure, and the polymer becomes easily soluble in organic solvents. On the other hand, if the content of constituent unit (3) in the polymer exceeds 3% by mass, internal crosslinking may become too dense. As a result, hard emulsion particles may be formed, making film formation difficult.

[0037] The emulsion particles are dispersed and emulsified in an aqueous liquid medium. The number-average particle size of the emulsion particles is 50 to 200 nm, preferably 80 to 120 nm. If the number-average particle size of the emulsion particles is less than 50 nm, the particles become too fine, which may result in high viscosity or gelation. On the other hand, if the number-average particle size of the emulsion particles exceeds 200 nm, the filter is more likely to clog, and when applied to aqueous flexographic printing, plate fogging is more likely to occur. Also, when applied to inkjet printing, the recording head is more likely to clog. The number-average particle size of the emulsion particles in this specification is a value measured and calculated using a dynamic light scattering particle size distribution analyzer.

[0038] The aqueous liquid medium constituting the aqueous emulsion of this embodiment may be water alone, or it may be an aqueous mixed liquid medium containing water and a water-soluble organic solvent. That is, it is preferable that the aqueous liquid medium contains water and a water-soluble organic solvent. By using a liquid medium containing a water-soluble organic solvent, the wettability and film-forming properties of the ink can be further improved. The water-soluble organic solvent is preferably at least one selected from the group consisting of isopropanol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and 3-methoxy-N,N-dimethylpropanamide.

[0039] Water-soluble organic solvents can be added after the polymer has been emulsion-polymerized in water. However, it is preferable not to add the water-soluble organic solvent after the polymer has been emulsion-polymerized, even when manufacturing the constituent unit (1). Even in the presence of a water-soluble organic solvent, the polymer can be emulsion-polymerized (emulsified polymerized) without substantially precipitation. Normally, in emulsion polymerization carried out in the presence of a surfactant, if a water-soluble organic solvent is also present, some of the monomer may dissolve, resulting in the formation of an unemulsified polymer, or particles may precipitate, or the particle size may become too large. However, the aqueous emulsion of this embodiment can be obtained in a state where the emulsion is stably maintained even when emulsion polymerization is carried out in the presence of the above-mentioned water-soluble organic solvent.

[0040] The content of water-soluble organic solvent in the aqueous emulsion is preferably 3 to 10% by mass, and more preferably 5 to 8% by mass, based on the total aqueous emulsion. If the content of water-soluble organic solvent is less than 3% by mass, the effect of improving wettability and film-forming properties may be insufficient. On the other hand, if the content of water-soluble organic solvent exceeds 10% by mass, particles may precipitate during emulsion polymerization or emulsion stability may be insufficient.

[0041] The content of the polymer that forms the emulsion particles in the aqueous emulsion is preferably 10 to 50% by mass, and more preferably 15 to 40% by mass. The pH of the aqueous emulsion at 25°C is preferably 7.5 to 11, and more preferably 8.5 to 10. If the pH of the aqueous emulsion is less than 7.5, the particles may become unstable and precipitate. On the other hand, if the pH of the aqueous emulsion is greater than 11, it is too alkaline, which may cause the acrylic acid ester used as a monomer to be easily hydrolyzed.

[0042] (Other additives) The aqueous emulsion may further contain various additives. Examples of additives include surfactants, leveling agents, wax components, preservatives, antibacterial agents, UV absorbers, light stabilizers, antioxidants, thickeners, and water-soluble polymers. Examples of water-soluble polymers include polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, and polyacrylic acid.

[0043] <Method for producing aqueous emulsion> One embodiment of the present invention for producing an aqueous emulsion is a method for producing the aforementioned aqueous emulsion, comprising the steps of: (a) obtaining a solution containing a polymer-type monomer; (b) obtaining an aqueous solution of the polymer-type monomer; and (c) adding water, a first monomer, and a second monomer in an amount such that the water-soluble organic solvent content is 3 to 10% by mass to the aqueous solution obtained in step (b), and heating in the presence of a radical generator to perform radical polymerization. Step (a) is a step of heating a monomer mixture containing 100 parts by mass of monomer, 1 to 10 parts by mass of a compound represented by the following general formula (2), and a water-soluble organic solvent, with a solid content of 55 to 70% by mass, in the presence of a radical generator to perform radical polymerization and obtain a solution containing a polymer-type monomer. Step (b) is a step of adding alkali and water to the solution obtained in step (a) to obtain an aqueous solution of the polymer-type monomer. The monomer used in step (a) includes methacrylic acid, a methacrylic acid ester having an alkyl group with 8 to 18 carbon atoms, and at least one selected from the group consisting of methacrylic acid esters having an alkyl group with 1 to 7 carbon atoms, cycloalkyl methacrylate, arylmethyl methacrylate, hydroxyalkyl methacrylate, and polyalkylene glycol monomethyl ether methacrylate. The details of the method for producing the aqueous emulsion of this embodiment will be described below.

[0044] TIFF2026054283000005.tif28170 (In the above general formula (2), R1 represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms)

[0045] (Step (a)) In step (a), a monomer mixture containing a predetermined monomer, a compound represented by general formula (2), and a water-soluble organic solvent is heated in the presence of a radical generator to undergo radical polymerization and obtain a solution containing a polymer-type monomer. As the monomer, monomers constituting the polymer-type monomer are used. Specifically, the monomer includes methacrylic acid, a methacrylic acid ester having an alkyl group having 8 to 18 carbon atoms, and at least one selected from the group consisting of methacrylic acid esters having an alkyl group having 1 to 7 carbon atoms, cycloalkyl methacrylate, arylmethyl methacrylate, hydroxyalkyl methacrylate, and polyalkylene glycol monomethyl ether methacrylate.

[0046] The compound represented by general formula (2) is a chain transfer agent (hereinafter, "the compound represented by general formula (2)" will also be simply referred to as "the chain transfer agent"). During radical polymerization, polymer terminal radicals generated attack the unsaturated bonds of the chain transfer agent, electron transfer occurs, a bromine atom radical is eliminated, and an unsaturated bond derived from the chain transfer agent can be introduced to the polymer terminal. The eliminated bromine atom radical is used in the polymerization of the monomer to produce a polymer, and the terminal radical of that polymer reacts with the chain transfer agent to introduce an unsaturated bond to the polymer terminal. This repeated reaction allows polymerization to proceed.

[0047] From the viewpoint of availability and polymerizability, bromomethylacrylic acid, methyl bromomethylacrylate, and ethyl bromomethylacrylate are preferred as chain transfer agents. The amount of the compound represented by general formula (2) (chain transfer agent) is 1 to 10 parts by mass, preferably 1.5 to 8 parts by mass, per 100 parts by mass of monomer. By using a chain transfer agent within the above range, the molecular weight of the formed polymer-type monomer can be easily adjusted.

[0048] The solid content (total amount of monomers) of the monomer mixture undergoing radical polymerization is 55-70% by mass, preferably 60-65% by mass. If the solid content of the monomer mixture is less than 55% by mass, the amount of water-soluble organic solvent in the final aqueous emulsion becomes too high, which may affect the stability of the emulsion particles. On the other hand, if the solid content of the monomer mixture exceeds 70% by mass, stirring during polymerization may become difficult.

[0049] As radical generators, azo initiators such as azobisisobutyronitrile and peroxides such as benzoyl peroxide can be used. The amount of radical generator is preferably 0.01 to 0.5 parts by mass, and more preferably 0.075 to 0.2 parts by mass, per 100 parts by mass of monomer solids. If the amount of radical generator is too high, a large amount of components that do not form the desired graft chain may be generated.

[0050] (Step (b)) In step (b), alkali and water are added to the solution obtained in step (a) to obtain an aqueous solution of the polymer-type monomer. The carboxyl group in constituent unit (1) is neutralized by the alkali, and the polymer-type monomer dissolves in water to form an aqueous solution of the polymer-type monomer. Neutralization with alkali may be carried out at room temperature or around 50°C with stirring, or it may be heated after neutralization. The polymer-type monomer content (solids) in the neutralization reaction system is easy to handle if it is, for example, 40-50% by mass, as it exhibits fluidity.

[0051] (Process (c)) In step (c), water, a first monomer, and a second monomer are added to the aqueous solution obtained in step (b) in an amount such that the final water-soluble organic solvent content is 3 to 10% by mass, and radical polymerization is carried out by heating in the presence of a radical generator. This allows the desired aqueous emulsion to be obtained. In step (c), emulsion polymerization is carried out in a large excess of water. In contrast, if solution polymerization is carried out in the presence of an organic solvent in which the monomer dissolves, gelation occurs due to the crosslinking reaction of the second monomer. In contrast, in step (c), by polymerization in the presence of a small amount of water-soluble organic solvent and a large excess of water, the polymer-type monomer becomes a protective colloid of the water-insoluble first and second monomers, enabling emulsion polymerization, and the desired aqueous emulsion can be obtained without problems such as gelation.

[0052] A radically polymerizable unsaturated bond exists at one end of the polymer-type monomer. Due to steric hindrance, this unsaturated bond is known to be less copolymerizable with tertiary radicals derived from methacrylates, but more copolymerizable with secondary radicals derived from vinyl monomers, acrylates, etc. By copolymerizing a polymer-type monomer having such an unsaturated bond at one end with a first monomer and a second monomer, a graft-type polymer can be formed, and the desired aqueous emulsion can be obtained.

[0053] It is preferable to use a water-soluble radical generator. Examples of radical generators include peroxides such as hydrogen peroxide, ammonia persulfate, sodium persulfate, and potassium persulfate; and water-soluble azo initiators such as azobiscyanopropionic acid. The amount of radical generator is preferably 1 to 5 parts by mass per 100 parts by mass of monomer solids.

[0054] <Use of aqueous emulsions> The aqueous emulsion of this embodiment is suitable as an additive to aqueous ink. That is, the aqueous emulsion of this embodiment is useful as a film-forming component, such as a binder component, used to prepare aqueous ink.

[0055] Furthermore, one embodiment of the aqueous ink of the present invention contains the aforementioned aqueous emulsion. The content of the binder component (polymer solids) in the aqueous ink is appropriately set according to the thickness of the coating film to be formed using the aqueous ink, and is preferably about 5 to 20% by mass.

[0056] Water-based inks may further contain various additives. Examples of additives include dyes, pigments, pigment dispersants, defoamers, leveling agents, surfactants, wax components, crosslinking agents, fillers, UV absorbers, antioxidants, light stabilizers, preservatives, antibacterial agents, viscosity modifiers, scratch inhibitors, surface tension modifiers, pH adjusters, water-soluble organic solvents, and thickeners. In addition, water-based inks may also contain water-soluble polymers other than those that form emulsion particles in water-based emulsions.

[0057] Examples of water-based inks include water-based inkjet inks, water-based gravure inks, water-based flexographic inks, and water-based stationery inks. They are also useful as water-based paints and water-based coating agents. The coating film formed by water-based paints, etc., may be a clear coating film, or it may be a colored or achromatic coating film using pigments or dyes as coloring agents. Among these, water-based inkjet inks and water-based flexographic inks are particularly suitable due to their properties.

[0058] The physical properties of water-based inks are designed according to their intended use. For water-based flexographic inks, the viscosity at 25°C, measured using a Zahn cup #3 or #4, is preferably 5 to 30 seconds. Furthermore, the surface tension of the water-based flexographic ink at 25°C is preferably 20 to 50 mN / m.

[0059] The physical properties of the aqueous inkjet ink are preferably adjusted according to the ejection characteristics of the recording head. The viscosity of the aqueous inkjet ink at 25°C is preferably 2 to 5 mPa·s. When using a recording head that can handle high viscosity inks, the viscosity of the aqueous inkjet ink at 25°C is preferably 3 to 50 mPa·s. Furthermore, the surface tension of the aqueous inkjet ink at 25°C is preferably 15 to 45 mN / m, and more preferably 20 to 40 mN / m.

[0060] The pH of water-based ink at 25°C is preferably 7.0 to 10.0, and more preferably 7.5 to 9.5. If the pH of water-based ink is below 7.0, the binder component is more likely to precipitate. On the other hand, if the pH of water-based ink is above 10.0, it becomes too alkaline, which can lead to hydrolysis of the acrylic ester monomer component or deterioration of the printing press and recording head.

[0061] Water-based inks can be manufactured according to conventional methods. For example, first, each component is blended and then stirred and mixed using a disperser or similar device to obtain a mill base. Then, if necessary, the obtained mill base is filtered to remove impurities, foreign matter, and debris, thereby obtaining the desired water-based ink.

[0062] The aqueous ink of this embodiment contains the aforementioned graft-type polymer that is internally crosslinked. Therefore, by using the aqueous ink, a coating film that adheres highly to plastic media (recording media) can be formed. Suitable plastic recording media include polyolefin films, polyethylene terephthalate films, and vinyl chloride films. Examples of polyolefins that form polyolefin films include polyethylene, polypropylene, ethylene-propylene copolymer, propylene-butene copolymer, cycloolefin, polyethylene polyvinyl alcohol, and polyethylene ethyl acrylate. A multilayer film formed from these polyolefins may also be used. The film may be a stretched film or an unstretched film. The surface of the film may be untreated, or it may be subjected to surface treatments such as corona discharge treatment, plasma treatment, flame treatment, chemical treatment, and matte finish. The vinyl chloride film may contain conventionally known plasticizers. [Examples]

[0063] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0064] <Manufacturing of aqueous emulsions> (Example 1) [Polymer-type monomer M-1] 56.1 parts of propylene glycol monomethyl ether (MPG), 55 parts of methyl methacrylate (MMA), 11 parts of dodecyl methacrylate (DMA), 9 parts of tridecyl methacrylate (TDMA), 10 parts of 2-hydroxyethyl methacrylate (HEMA), 15 parts of methacrylic acid (MAA), and 4 parts of ethyl α-bromomethylacrylate (EBMA) were placed in a reaction vessel and heated to 80°C while bubbling nitrogen. At 72°C, 0.3 parts of dimethyl 2,2'-azobis(2-methylpropionate) (V-601) (trade name "V-601", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added, and polymerization was carried out for 8 hours while bubbling nitrogen to form a polymer and obtain a polymer solution. The polymer solids content of the reaction solution was 65%.

[0065] A portion of the polymer solution was sampled and dried at 150°C. The solid content, calculated from the mass at which constant weight was reached, was 65%, confirming that polymerization had almost completely occurred. The number-average molecular weight (Mn) of the polymer, measured by gel permeation chromatography (GPC) with tetrahydrofuran (THF) as the developing solvent, was 5,300, and the molecular weight distribution (PDI = weight-average molecular weight (Mw) / number-average molecular weight (Mn)) was 1.69. Furthermore, a portion of the sampled polymer solution was added to methanol, a poor solvent, and the precipitated material was washed and dried to obtain a solid. A portion of the obtained solid was dissolved in a toluene / ethanol = 1 / 1 (volume ratio) mixture, and the acid value of the polymer was measured by titration with a 0.1N potassium hydroxide ethanol solution using phenolphthalein ethanol solution as an indicator. The measured acid value of the polymer was 93.0 mgKOH / g. 1 ¹H-NMR was measured to confirm that EBMA acts as a chain transfer agent, and that the polymer has constituent units derived from MMA, EHMA, HEMA, and MAA, respectively. Furthermore, the presence of peaks at 5.54 ppm and 6.10 ppm confirmed that a polymer-type monomer with unsaturated bonds derived from EBMA, the chain transfer agent, introduced at its terminals was obtained.

[0066] To the obtained polymer solution, a mixture of 16.3 parts dimethylaminoethanol (DMAE) and 120.7 parts water was added to neutralize the polymer monomer, yielding an aqueous solution of polymer monomer M-1. The obtained aqueous solution had a solid content of 35.0%, a pH of 8.8, and a water-soluble organic solvent (MPG) content of 18.8%.

[0067] [Water-based emulsion E-1] An aqueous solution of polymer monomer M-1 (30 parts solids) and 135.6 parts water were placed in a reaction vessel and stirred. The mixture was heated to 78°C while bubbling nitrogen, and 3.0 parts potassium persulfate (KPS) were added. A mixture of 29.72 parts styrene (St), 15 parts methyl methacrylate (MMA), 25 parts butyl acrylate (BA), and 0.28 parts divinylbenzene (DVB) was added dropwise to the reaction vessel over 2 hours. No precipitate formed, and a translucent emulsion was obtained. Polymerization was carried out at 78°C for 5 hours to obtain aqueous emulsion E-1. The water-soluble organic solvent content of the obtained aqueous emulsion E-1 was 5.5%. The number-average particle size of the emulsion particles, measured using a dynamic light scattering particle size distribution analyzer (product name "nanoSAQRA", manufactured by Otsuka Electronics Co., Ltd.), was 85.1 nm. Furthermore, the pH of aqueous emulsion E-1 was 8.9, the solid content was 34.9%, and the viscosity, measured using a B-type viscometer, was 13.5 mPa·s.

[0068] (Examples 2-10, Comparative Examples 1-7) Aqueous solutions of polymer monomers M-2 to M-5 and aqueous emulsions E-2 to M-10 were obtained in the same manner as in Example 1 described above, except that the formulations were as shown in Tables 1 and 2. Furthermore, aqueous solutions of polymer monomers HM-1 to M-3 and aqueous emulsions HE-1 to M-7 were obtained in the same manner as in Example 1 described above, except that the formulations were as shown in Tables 3 and 4. The meanings of the abbreviations in Tables 2 to 4 are shown below. BzMA: Benzyl methacrylate • 2EHMA: 2-ethylhexyl methacrylate PMEMA: Polyethylene glycol monomethyl ether methacrylate (molecular weight 200) EHA: 2-ethylhexyl acrylate DA: Dodecyl acrylate • ED: Ethylene glycol dimethacrylate TPGDA: Tripropylene glycol diacrylate PPG: Propylene glycol monopropyl ether IPA: Isopropanol • BDG: Diethylene glycol monobutyl ether • DEDG: Diethylene glycol diethyl ether

[0069] (Comparative Example 8) An aqueous solution of polymer monomer HM-4 was obtained in the same manner as in Example 1 described above. The number-average molecular weight (Mn) of polymer monomer HM-4 was 5,400, and the molecular weight distribution (PDI) was 1.65. The solid content of the obtained aqueous solution was 64.3%. 46.2 parts of the aqueous solution of polymer monomer HM-4, 70 parts of MPG, 29.72 parts of St, 15 parts of MMA, 25 parts of BA, 0.28 parts of DVB, and 2 parts of 1,1,3,3-tetramethylbutyl peroxyethyl hexanoate were placed in a reaction vessel and stirred to homogenize. Polymerization was carried out by heating to 70°C while bubbling nitrogen. After about 1 hour, the solution wrapped around the stirring shaft and then gelled. It is thought that the DVB acted as a crosslinking agent, causing gelation, because solution polymerization was performed.

[0070] <Evaluation of aqueous emulsions> (Appearance after polymerization) The appearance of the aqueous emulsion was visually observed, and the appearance after polymerization was evaluated according to the evaluation criteria shown below ("○" and "△" are considered pass). The results are shown in Tables 1 to 4. ○: No precipitates or sediments were found. △: Although there was little or no precipitate formation, precipitates were found adhering to the walls and wings. ×: Precipitates had formed.

[0071] (Filtration properties) 100 mL of aqueous emulsion was placed in a syringe fitted with a 10 μm filter and passed through the filter. The filterability of the aqueous emulsion was evaluated according to the evaluation criteria shown below ("○" and "△" are considered pass). The results are shown in Tables 1-4. ○: Fluid flowed smoothly throughout without any blockages. △: No blockage occurs in the initial stages, but it gradually becomes more difficult for the liquid to pass through, although the entire volume can still be passed through. ×: A blockage occurred.

[0072] (Solvent resistance) A water-based emulsion was placed on an aluminum plate and dried at 120°C to form a thin film. Methyl ethyl ketone (MEK) and THF were then dropped onto the thin film. The thin film was then observed, and the solvent resistance of the water-based emulsion was evaluated according to the evaluation criteria shown below ("◎" and "○" are considered pass). The results are shown in Tables 1-4. ◎: The thin film did not dissolve, and the film state was maintained. ○: The thin film did not dissolve, but whitening or wrinkling occurred. △: The thin film dissolved into pieces. ×: The thin film dissolved uniformly.

[0073] TIFF2026054283000006.tif141170

[0074] TIFF2026054283000007.tif255159

[0075] TIFF2026054283000008.tif140170

[0076] TIFF2026054283000009.tif234170

[0077] <Application Example 1: Preparation of Water-Based Inkjet Ink> (Application Example 1) 150 parts of copper phthalocyanine pigment (PB-15:3, trade name "Cyanine Blue A220JC", manufactured by Dainichi Seika Kogyo Co., Ltd.), 93.8 parts of pigment dispersant solution (isobornyl methacrylate / tetrahydrofurfuryl methacrylate / DMA / MAA=15 / 60 / 30 / 15 (mass ratio), Mn19,800, PDI2.01, dimethylaminoethanol neutralized, polymer content 40.0%, BDG 40%, water 20%, pH 8.8), and 356.2 parts of deionized water were mixed and stirred with a disperser to obtain a mill base. The obtained mill base was dispersed using a horizontal media disperser (trade name "DinoMill 0.6 liter ECM type", manufactured by Shinmaru Enterprises, Ltd., zirconia bead diameter: 0.5 mm) at a peripheral speed of 7 m / s to thoroughly disperse the pigment. After centrifugal separation (7,500 rpm, 20 minutes), the mixture was filtered through a 10 μm membrane filter to remove coarse particles. Deionized water was added to adjust the concentration, yielding a blue pigment dispersion with a pigment concentration of 14%. The number-average particle size of the pigment in the dispersion was 105.9 nm, confirming that the pigment was finely dispersed. Using an E-type viscometer, the viscosity of the pigment dispersion (25°C) measured at 60 rpm was 3.58 mPa·s, and the pH was 8.8.

[0078] A mixture of 4 parts pigment, 4 parts aqueous emulsion E-1 (as solid content), 0.1 parts acetylene surfactant (product name "Surfinol S465", manufactured by Nisshin Chemical Industry Co., Ltd.), 0.7 parts wax dispersion (ethylene-acrylic acid ionomer, product name "Chemipearl W300", manufactured by Mitsui Chemicals, Inc.), 12 parts propylene glycol, and water (the remainder totaling 100 parts) was prepared. After thorough stirring, the mixture was filtered through a 10 μm pore size membrane filter to obtain aqueous inkjet ink I-1. No clogging occurred during filtration with the membrane filter. The number-average particle size of the pigment in the obtained aqueous inkjet ink I-1 was 103.3 nm. The viscosity of aqueous inkjet ink I-1 was 3.40 mPa·s, and the pH was 8.64.

[0079] (Application Examples 2-10, Comparative Examples 1 and 2) Aqueous inkjet inks I-2 to 10 and aqueous inkjet inks HI-1 and HI-2 were obtained in the same manner as in Application Example 1 described above, except that the types of aqueous emulsions shown in Table 5 were used as binder components.

[0080] <Evaluation of water-based inkjet inks> The obtained water-based inkjet inks were each filled into cartridges and mounted in an inkjet printer equipped with a plate heater (product name "MMP825H," manufactured by Mastermind Co., Ltd.). Then, images were printed onto a printing substrate heated to a surface temperature of 50°C by the plate heater to obtain printed materials. The printing substrates used are shown below. • OPP film: Polypropylene film, manufactured by Futamura Chemical Co., Ltd., 50 μm • PET film: Polyethylene terephthalate film, manufactured by Futamura Chemical Co., Ltd., 60 μm

[0081] (Adhesion) After thoroughly drying the printout using a hairdryer, cellophane tape was applied to the image, pressed firmly, and then peeled off. The degree to which the image peeled off the film was visually observed, and the adhesion of the image was evaluated according to the evaluation criteria shown below. The results are shown in Table 5. Of the evaluation criteria shown below, "◎" and "○" were considered to be at a usable level (pass). ◎: The image did not peel off at all. ○: The image has peeled off slightly. △: The area of ​​the peeled-off image was smaller than the area of ​​the image that remained intact. ×: The area of ​​the peeled-off image was larger than the area of ​​the image that remained intact.

[0082] (Dry abrasion resistance and wet abrasion resistance) Using a JSPS-type friction fastness tester (product name "RT-300", manufactured by Daiei Kagaku Co., Ltd.), the surface of the image was moved back and forth 20 times under a load of 500g using both a dry white cloth and a water-dampened white cloth. After 200 back-and-forth movements, the condition of the image was visually observed, and the dry friction resistance and wet friction resistance of the image were evaluated according to the evaluation criteria shown below. The results are shown in Table 5. Among the evaluation criteria shown below, "◎" and "○" were considered to be at a usable level (pass). ◎: The image did not peel off at all. ○: The image has peeled off slightly. △: The area of ​​the peeled-off image was smaller than the area of ​​the image that remained intact. ×: The area of ​​the peeled-off image was larger than the area of ​​the image that remained intact.

[0083] (Alcohol-resistant) A 70% ethanol aqueous solution was dropped onto the recorded image. After standing for 10 seconds, a cotton swab was swab back and forth multiple times over the image. The number of back-and-forth strokes required for the image to peel off was counted, and the alcohol resistance of the image was evaluated according to the evaluation criteria shown below. The results are shown in Table 5. Of the evaluation criteria shown below, "◎" and "○" were considered to be at a usable level (pass). ◎: 20 times or more ○: Less than 10-20 times △: Less than 5-10 times ×: Less than 5 times

[0084] TIFF2026054283000010.tif94170

[0085] <Application Example 2: Preparation of Water-Based Flexo OP Varnish> (Application Examples 11-20, Comparative Application Examples 3, 4) 231.4 parts of the aqueous emulsion of the type shown in Table 6, 61.1 parts of water, 6 parts of polyethylene wax dispersion (product name "Chemipearl W500", manufactured by Mitsui Chemicals, Inc.), 0.6 parts of defoaming agent (product name "Tegoformex 805N", manufactured by Evonik Corporation), 0.3 parts of surfactant (product name "Tegowet 500", manufactured by Evonik Corporation), and 0.6 parts of thickener (product name "SN Thickener 623N", manufactured by Sunopco Corporation) were mixed. The mixture was thoroughly stirred using a disperser to obtain aqueous flexo OP varnishes F-1 to 10, HF-1, and HF-2. The viscosity of the aqueous flexo OP varnish at 25°C, measured using a Zahn cup #4, was 14 sec and the pH was 8.3.

[0086] <Evaluation of water-based flexo-OP varnish> (Manufacturing of shrink labels (formation of coating)) A heat-shrinkable film (product name "HST", manufactured by Gunze Corporation) made of laminated polystyrene and polyethylene terephthalate was prepared and its surface was corona-treated. Additionally, a water-based ink (product name "Hydric FCF series", manufactured by Dainichi Seika Kogyo Co., Ltd.) was diluted with deionized water to prepare a color ink with a viscosity of 14 seconds at 25°C, as measured using a Zahn cup #4. Cell volume: 4.5 cm 3 / m 2 A flexographic hand proofer equipped with an anilox roll was used as an applicator to coat the corona-treated surface of the film with color ink. Additionally, a prepared aqueous flexographic OP varnish was applied to a cell volume of 8.5 cm². 3 / m 2 A flexographic hand proofer equipped with an anilox roll was used as an applicator to coat the color ink. The coating was dried at 25°C for 48 hours to form a film and obtain shrink labels.

[0087] (Adhesion) Cellophane tape was applied to the coated surface (coating) of the shrink label and pressed firmly before being peeled off. The degree of peeling of the coating was then visually observed, and the adhesion of the coating was evaluated according to the evaluation criteria shown below. The results are shown in Table 6. Of the evaluation criteria shown below, "◎" and "○" were considered to be at an acceptable level (pass). ◎: The paint film did not peel off at all. ○: The paint film has peeled off slightly. △: The area of ​​the peeled paint film was smaller than the area of ​​the paint film that remained intact. ×: The area of ​​the peeled paint film was larger than the area of ​​the paint film that remained intact.

[0088] (Blocking resistance) Untreated film and shrink labels were laminated so that the untreated surface of the film and the coating of the shrink labels were in contact. 7 kg / cm² 2 The samples were left in a 40°C constant temperature chamber for 24 hours under the applied load. The peel resistance was then checked when the untreated film and shrink label were separated, and the appearance of the coating was observed. The blocking resistance of the coating was evaluated according to the following evaluation criteria. The results are shown in Table 6. Of the evaluation criteria shown below, "◎" and "○" were considered usable levels (pass). ◎: There was no transfer of the coating to the untreated surface, and there was no resistance to peeling. ○: There was almost no transfer of the coating to the untreated surface, and a slight resistance to peeling was felt. △: Some transfer of the coating to the untreated surface was observed, and some peeling resistance was felt. ×: Severe transfer of the coating to the untreated surface was observed, and strong resistance to peeling was felt.

[0089] (Moisture-resistant and abrasion-resistant) Using a JSPS-type friction fastness tester (product name "RT-300", manufactured by Daiei Kagaku Co., Ltd.), the surface of the coating was moved back and forth 100 times with a water-moistened white cloth under a load of 200g. The condition of the coating after 100 back-and-forth movements was visually observed, and the moisture friction resistance of the coating was evaluated according to the evaluation criteria shown below. The results are shown in Table 6. Among the evaluation criteria shown below, "◎" and "○" were considered to be at an acceptable level (pass). ◎: The paint film did not peel off at all. ○: The paint film has peeled off slightly. △: The area of ​​the peeled paint film was smaller than the area of ​​the paint film that remained intact. ×: The area of ​​the peeled paint film was larger than the area of ​​the paint film that remained intact.

[0090] (Shrink resistance) Except for not forming a color ink layer, test coated materials (shrink labels) were manufactured in the same manner as described in "Manufacturing of Shrink Labels". The manufactured shrink labels were immersed in 85°C hot water for 5 seconds to obtain a 50% shrunk film. The haze value of the shrunk film (the ratio of diffuse light transmission to total light transmission (%)) was measured using an integrating sphere haze meter, and the presence or absence of cracks in the coating was checked. The shrink resistance of the coating was then evaluated according to the evaluation criteria shown below. The results are shown in Table 6. Of the evaluation criteria shown below, "◎" and "○" were considered to be at a usable level (pass). ◎: The haze value was less than 30%, and no cracks occurred. ○: The haze value was between 30% and 40%, and no cracks occurred. △: The haze value was between 30% and 40%, but cracking was occurring. ×: The haze level was 40% or higher, and cracks were also present.

[0091] TIFF2026054283000011.tif100170 [Industrial applicability]

[0092] The aqueous emulsion of the present invention is useful as a component for preparing an aqueous ink that can form an image, which is a film (coating) with excellent abrasion resistance, alcohol resistance, hot water resistance (shrink resistance), and adhesion to various substrates.

Claims

1. A water-based emulsion used for preparing water-based inks, It contains an aqueous liquid medium and emulsion particles formed of a polymer having internal crosslinking, dispersed and emulsified in the liquid medium. The polymer comprises 20 to 40% by mass of a polymer-type monomer (1) which is represented by the following general formula (1), has a number average molecular weight of 1,000 to 10,000, and contains 10 to 35% by mass of constituent units derived from methacrylic acid, Constituent units (2) derived from a water-insoluble first monomer having one vinyl group, 57 to 79.9% by mass, It contains 0.1 to 3% by mass of a constituent unit (3) derived from a water-insoluble second monomer having two or more vinyl groups, The aforementioned constituent unit (1) is neutralized with at least one alkali selected from the group consisting of ammonia, dimethylaminoethanol, sodium hydroxide, and 2-amino-2-methyl-1-propanol. An aqueous emulsion having a number-average particle size of 50 to 200 nm. (In the above general formula (1), R １ R represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms. ２ R represents an alkyl group having 8 to 18 carbon atoms. ３ (This refers to at least one group selected from the group consisting of alkyl groups having 1 to 7 carbon atoms, cycloalkyl groups, arylmethyl groups, hydroxyalkyl groups, and polyalkylene glycol monomethyl ether groups.)

2. The aforementioned constituent unit (2) consists of 20 to 40% by mass of constituent units derived from styrene, The aqueous emulsion according to claim 1, comprising 15 to 59.9% by mass of a constituent unit derived from at least one selected from the group consisting of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate.

3. In the above general formula (1), R ２ However, it is at least one group selected from the group consisting of a 2-ethylhexyl group, a dodecyl group, and a tridecyl group. The aqueous emulsion according to claim 1, wherein the polymer-type monomer contains 15 to 40% by mass of a constituent unit derived from a methacrylic acid ester having an alkyl group having 8 to 18 carbon atoms.

4. The liquid medium comprises at least one water-soluble organic solvent selected from the group consisting of isopropanol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and 3-methoxy-N,N-dimethylpropanamide. The aqueous emulsion according to claim 1, wherein the content of the water-soluble organic solvent is 3 to 10% by mass.

5. A method for producing an aqueous emulsion according to any one of claims 1 to 4, Step (a) involves heating a monomer mixture containing 100 parts by mass of monomer, 1 to 10 parts by mass of a compound represented by the following general formula (2), and a water-soluble organic solvent, with a solid content of 55 to 70% by mass, in the presence of a radical generator to undergo radical polymerization, thereby obtaining a solution containing the polymer-type monomer. (b) A step of adding the alkali and water to the solution to obtain an aqueous solution of the polymer-type monomer, The process includes (c) adding water, the first monomer, and the second monomer to the aqueous solution in an amount such that the water-soluble organic solvent content is 3 to 10% by mass, and heating in the presence of a radical generator to perform radical polymerization. A method for producing an aqueous emulsion, wherein the monomer comprises methacrylic acid, a methacrylic acid ester having an alkyl group having 8 to 18 carbon atoms, and at least one selected from the group consisting of methacrylic acid esters having an alkyl group having 1 to 7 carbon atoms, cycloalkyl methacrylate, arylmethyl methacrylate, hydroxyalkyl methacrylate, and polyalkylene glycol monomethyl ether methacrylate. (In the above general formula (2), R １ (This represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms.)

6. A water-based ink containing the aqueous emulsion described in any one of claims 1 to 4.

Images