Aqueous dispersion of resin particles having a crosslinked structure

Abstract

To provide an aqueous dispersion of resin particles having a crosslinked structure which can provide a printed matter that is excellent in storage stability by being used in aqueous ink, and is excellent in adhesion and scratch resistance of an ink coating film when being printed on a resin printing medium.SOLUTION: There is provided an aqueous dispersion of resin particles having a crosslinked structure in which resin particles having a core-shell structure containing (a) a component derived from a (meth)acrylic acid and (b) a component derived from butyl (meth)acrylate are crosslinked by (c) a component derived from polyglycidyl ether of polyhydric alcohol, wherein a glass transition temperature of a core part resin constituting the core-shell structure is different from a glass transition temperature of a shell part resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous dispersion of resin particles having a crosslinked structure, and an aqueous ink containing the aqueous dispersion. [Background technology]

[0002] In the fields of commercial and industrial printing, such as product packaging printing and label printing for advertising, printing has traditionally been done using solvent-based inks or UV-curable inks on resin printing media such as polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), and nylon (NY). In response to this, there is a demand for the use of inkjet printing and flexographic printing methods from the perspectives of reducing environmental impact, energy conservation, safety, etc. Inkjet printing, in particular, is a printing method in which ink droplets are ejected directly from extremely fine nozzles onto a printing medium and deposited thereon to obtain a printed matter on which characters and images are recorded, and therefore has many advantages, such as ease of full color production, low cost, and non-contact with the printed material, and is therefore becoming increasingly popular. Various inks containing pigments, aqueous media, and polymers have been proposed as inkjet printing inks. However, because resin printing media are non-absorbent, aqueous inks do not penetrate into the interior of the printing media. This has resulted in insufficient adhesion between the printed ink coating and the resin printing media. Therefore, attempts to incorporate aqueous resin dispersions have been investigated as a method for improving the performance of the ink coating.

[0003] For example, Patent Document 1 discloses an aqueous inkjet binder resin composition that aims to provide an aqueous inkjet binder resin composition that is excellent in printability of printed matter, abrasion resistance, and ink storage stability, and that contains core-shell type resin particles obtained by stepwise emulsion polymerization of ethylenically unsaturated monomers including an aromatic ethylenically unsaturated monomer that does not have an ionic group and an ethylenically unsaturated monomer that contains an alkyl group having 1 to 4 carbon atoms. Patent Document 2 discloses a resin emulsion having polymer particles containing structural units derived from itaconic acid and structural units derived from a hydrophobic monomer, with some of the acid groups neutralized, and a water-based ink containing the resin emulsion and a colorant, with the aim of providing an aqueous resin dispersion that has excellent fixability to resin printing media and excellent document offset resistance under high humidity conditions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-201692 [Patent Document 2] Japanese Patent Application Publication No. 2019-19292 Summary of the Invention [Problem to be solved by the invention]

[0005] Resin printing media such as PP, PET, PVC, PE, and NY have low surface free energy, so water-based inks in particular are required to have high wetting and spreading properties on these media. Therefore, compared to water-based inks used on absorbent substrates such as plain paper, they often use hydrophobic water-soluble or poorly water-soluble solvents and surfactants, and there is also a demand for further improvements in the storage stability of water-based inks that use water-based dispersions. Furthermore, measures to improve the wetting and spreading properties of water-based inks are commonly used, such as by increasing the surface free energy of the printing medium surface through corona treatment, plasma treatment, etc., and therefore there is a demand for a balance between the adhesion and abrasion resistance of the ink coating to the resin printing medium after surface modification and the storage stability of the water-based ink. The present invention relates to an aqueous dispersion and an aqueous ink that, when used in an aqueous ink, can provide a printed item that has excellent storage stability and excellent adhesion and abrasion resistance of the ink coating when printed on a resin printing medium that has not been surface-modified or has been surface-modified. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by using an aqueous dispersion of resin particles in an aqueous ink, the resin particles having a core-shell structure, in which the glass transition temperature of the core resin is different from the glass transition temperature of the shell resin, and the resin particles have a crosslinked structure in which the core resin and the shell resin are crosslinked with a component derived from a polyglycidyl ether of a polyhydric alcohol.

[0007] That is, the present invention relates to [1] and [2]. [1] An aqueous dispersion of resin particles having a crosslinked structure in which resin particles having a core-shell structure containing (a) a component derived from (meth)acrylic acid and (b) a component derived from butyl (meth)acrylate are crosslinked with (c) a component derived from a polyglycidyl ether of a polyhydric alcohol, wherein the glass transition temperature of the core resin constituting the core-shell structure is different from the glass transition temperature of the shell resin. [2] A water-based ink containing a pigment and an aqueous dispersion of resin particles having a crosslinked structure according to [1] above. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an aqueous dispersion of resin particles having a crosslinked structure, which, when used in an aqueous ink, can provide a printed item having excellent storage stability and excellent adhesion and abrasion resistance of the ink coating when printed on a resin print medium, and an aqueous ink. DETAILED DESCRIPTION OF THE INVENTION

[0009] The reason why the aqueous dispersion and aqueous ink of the present invention have excellent storage stability, adhesion and abrasion resistance is not clear, but is thought to be as follows. The crosslinked resin particles contained in the aqueous dispersion of the present invention are core-shell resin particles containing a component derived from (meth)acrylic acid and a component derived from butyl (meth)acrylate, and the core-shell resin particles are crosslinked with a component derived from a polyglycidyl ether of a polyhydric alcohol. The resin coating film (hereinafter simply referred to as "resin coating film") obtained by printing with an aqueous ink containing the aqueous dispersion of the crosslinked resin particles of the present invention is believed to have a particularly high affinity with PP film compared to cases using other alkyl (meth)acrylates due to the inclusion of butyl (meth)acrylate in the resin particles, thereby achieving high adhesion to the resin printing medium. Furthermore, when the resin printing medium has been surface-treated by corona treatment, plasma treatment, or the like, the ester bonds in the polymer constituting the resin particles interact with the hydrophilic groups of the surface-hydrophilized resin printing medium, resulting in high adhesion of the resin coating film to the resin printing medium after the surface modification treatment. Furthermore, since the resin particles have a crosslinked structure crosslinked by a component derived from a polyglycidyl ether of a polyhydric alcohol, dissolution of the resin particles in the water-based ink can be suppressed, even when the water-based ink contains a hydrophobic solvent and an activator, and high storage stability can be obtained, and the resin coating film can obtain high adhesion to the resin printing medium and abrasion resistance. In addition, since the resin particles have a core-shell structure made of resins with different glass transition temperatures, it is thought that the resin coating film will have excellent stress relaxation when an external force such as abrasion is applied, and will have excellent abrasion resistance.

[0010] [Water-based dispersion of resin particles having a crosslinked structure] The resin particles having a crosslinked structure contained in the aqueous dispersion of the present invention function as a fixing resin (fixing aid) that improves the adhesion and abrasion resistance of the resin coating film to the resin print medium when used in the aqueous ink. The principle behind the improvement in the adhesion and abrasion resistance of the resin coating film to the resin print medium by containing the resin particles having a crosslinked structure in the aqueous ink is as described above. The resin particles having a crosslinked structure have a core-shell structure containing (a) a component derived from (meth)acrylic acid (hereinafter also referred to as "component (a)") and (b) a component derived from butyl (meth)acrylate (hereinafter also referred to as "component (b)"), and are crosslinked with (c) a component derived from a polyglycidyl ether of a polyhydric alcohol (hereinafter also referred to as "component (c)").

[0011] [Resin particles having a core-shell structure] The resin particles having a core-shell structure contain component (a) and component (b). The core resin and shell resin in the resin particles having a core-shell structure are preferably (meth)acrylic resins composed of component (a), component (b), and, if necessary, components derived from a (meth)acrylic acid ester excluding component (b). By including components derived from a (meth)acrylic acid ester excluding component (b) in the core resin and / or shell resin, it is possible to adjust the properties of the core resin and shell resin, including the glass transition temperature. The component (a) constituting the core resin and the shell resin is at least one selected from acrylic acid and methacrylic acid. In the present invention, excellent effects can be obtained whether the component (a) is acrylic acid or methacrylic acid, and either can be used suitably. Of these, from the viewpoint of improving the adhesion and abrasion resistance of water-based inks, it is preferable that the component (a) contains acrylic acid. From the viewpoint of improving adhesion and abrasion resistance, the mass ratio of acrylic acid in component (a) constituting the core resin and the shell resin is preferably 50 mass% or more, more preferably 80 mass% or more, even more preferably 95 mass% or more, and even more preferably 100 mass%. It is also preferred that both the core and shell contain acrylic acid as component (a), and it is more preferred that both the core and shell contain only acrylic acid as component (a).

[0012] The butyl group of the (meth)butyl acrylate (b), whether n-butyl, s-butyl, t-butyl, or isobutyl, has a high affinity with the surface of the resin printing medium, and the resin coating film exhibits high adhesion. Of these, n-butyl is preferred from the viewpoint of achieving high adhesion between the surface-treated resin printing medium and the resin coating film. In the present invention, component (b) can be either butyl acrylate or butyl methacrylate, as both provide excellent effects and can be suitably used. Of these, from the viewpoint of improving the adhesion and abrasion resistance of water-based inks, component (b) constituting the core preferably contains butyl acrylate, and component (b) constituting the shell preferably contains butyl methacrylate. From the viewpoint of improving adhesion and abrasion resistance, the mass ratio of butyl acrylate in the component (b) constituting the core portion is preferably 50 mass% or more, more preferably 80 mass% or more, even more preferably 95 mass% or more, and even more preferably 100 mass%. Furthermore, from the viewpoint of improving adhesion and abrasion resistance, the mass ratio of butyl methacrylate in component (b) constituting the shell portion is preferably 50 mass% or more, more preferably 80 mass% or more, even more preferably 95 mass% or more, and even more preferably 100 mass%.

[0013] The (meth)acrylic acid ester-derived components excluding component (b) are not limited as long as the aqueous dispersion of resin particles having a crosslinked structure of the present invention exhibits the desired effect, but are preferably components derived from esters of (meth)acrylic acid with linear or branched alkyl alcohols (excluding butanol) having 1 to 10 carbon atoms, and more preferably components derived from (meth)acrylic acid esters selected from methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. The resin particles having a core-shell structure may contain one or more types of (meth)acrylic acid ester-derived components excluding component (b). Of these, methyl (meth)acrylate is preferred, and methyl methacrylate is more preferred.

[0014] When the glass transition temperatures of the core resin and shell resin of resin particles having a core-shell structure are different, a resin coating film that is excellent in stress relaxation when an external force is applied to a resin printing medium and has excellent abrasion resistance can be formed. Furthermore, from the viewpoint of further improving the abrasion resistance of the resin coating film and from the viewpoint of increasing the dispersion stability of the resin particles and improving the storage stability of inks containing them, the glass transition temperature of the core resin is preferably lower than that of the shell resin, more preferably 25°C or more lower than that of the shell resin, even more preferably 30°C or more lower than that of the shell resin, and still more preferably 60°C or more lower than that of the shell resin. The glass transition temperatures of the core resin and the shell resin can be determined from the monomer compositions of the core resin and the shell resin. The glass transition temperatures of the core resin and the shell resin can be calculated from the glass transition temperatures of the respective homopolymers of all the monomers constituting the core and shell using the following Fox formula. 1 / Tg=(W1 / Tg1)+(W2 / Tg2)+···+(W m / Tg m ) W1+W2+W m =1 In the Fox formula, Tg is the glass transition temperature of the polymer, and Tg1, Tg2, ..., Tg m is the glass transition temperature of the homopolymer of each polymerization monomer. The unit of temperature is K. Also, W1, W2, ..., W m represents the mass ratio of each polymerized monomer. As the glass transition temperature of the homopolymer of each polymerizable monomer in the Fox equation, for example, the value described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

[0015] From the viewpoint of improving the scratch resistance of the resin coating film, the glass transition temperature of the core resin is preferably −40° C. or higher, more preferably −35° C. or higher, even more preferably −30° C. or higher, and 50° C. or lower, more preferably 45° C. or lower, and even more preferably 40° C. or lower. From the viewpoint of improving the scratch resistance of the resin coating film, the glass transition temperature of the shell resin is preferably 25° C. or higher, more preferably 30° C. or higher, even more preferably 35° C. or higher, and 90° C. or lower, more preferably 85° C. or lower, and even more preferably 80° C. or lower.

[0016] From the viewpoint of improving the adhesion and abrasion resistance of the resin coating film to the resin printing medium, the acid value of the core resin is preferably 25 mgKOH / g or more, more preferably 30 mgKOH / g or more, even more preferably 35 mgKOH / g or more, and is preferably 200 mgKOH / g or less, more preferably 160 mgKOH / g or less, even more preferably 100 mgKOH / g or less, and still more preferably 80 mgKOH / g or less. When the acid value of the core resin is within the above range, the resin particles having a core-shell structure are appropriately crosslinked by component (c), improving the adhesion and abrasion resistance of the resin coating film to the resin printing medium. From the viewpoint of enhancing storage stability, the acid value of the shell resin is preferably 35 mgKOH / g or more, more preferably 50 mgKOH / g or more, even more preferably 70 mgKOH / g or more, and is preferably 200 mgKOH / g or less, more preferably 170 mgKOH / g or less, even more preferably 150 mgKOH / g or less, and still more preferably 120 mgKOH / g or less. When the acid value of the shell resin is within the above range, sufficient dispersion stability can be exhibited even after the resin particles having a core-shell structure are crosslinked with component (c). Among these, it is preferable that the acid value of the core resin is 35 mgKOH / g or more and 100 mgKOH / g or less, and preferably the acid value of the core resin is 50 mgKOH / g or more and 85 mgKOH / g or less, and the acid value of the shell resin is 70 mgKOH / g or more and 120 mgKOH / g or less.

[0017] In the present invention, the acid values ​​of the core resin and shell resin in the resin particles having a core-shell structure can be calculated from the charge ratio when preparing the resin, and the acid value of the core resin can be calculated from the acid values ​​of the core resin, the acid values ​​of the shell resin, and the mass ratio of the core resin to the shell resin.

[0018] The mass ratio of the core resin to the resin particles having a core-shell structure (core resin / resin particles having a core-shell structure) is preferably 0.50 or more, more preferably 0.60 or more, even more preferably 0.65 or more, from the viewpoint of improving the scratch resistance of the resin coating film, and is preferably 0.90 or less, more preferably 0.80 or less, even more preferably 0.75 or less.

[0019] The mass ratio of component (b) to component (a) in the resin particles having a core-shell structure [component (b) / component (a)] is preferably 1 or more, more preferably 1.2 or more, even more preferably 1.5 or more, from the viewpoint of improving the adhesion of the resin coating film to the resin printing medium, and is preferably 18 or less, more preferably 15 or less, even more preferably 10 or less. Furthermore, the mass ratio of the total content of component (a) and component (b) to all monomer components constituting the resin particles having a core-shell structure [[component (a) + component (b)] / total monomer components] is preferably 0.2 or more, more preferably 0.23 or more, even more preferably 0.27 or more, from the viewpoint of improving the adhesion of the resin coating film to the resin printing medium, and is preferably 1 or less, more preferably 0.95 or less, even more preferably 0.90 or less.

[0020] [Resin particles having a crosslinked structure] The aqueous dispersion of resin particles having a crosslinked structure of the present invention contains resin particles having a crosslinked structure in which the resin particles having the above-mentioned core-shell structure are crosslinked with component (c). That is, the aqueous dispersion of resin particles having a crosslinked structure of the present invention contains component (a), component (b), and component (c), and is preferably composed of component (a), component (b), and component (c). The number of carbon atoms in the polyhydric alcohol portion of component (c) is preferably 2 or more, more preferably 3 or more, even more preferably 5 or more, from the viewpoint of improving the storage stability of the aqueous dispersion and aqueous ink, and the adhesion and abrasion resistance of the resin coating film to the resin printing medium, and is preferably 25 or less, more preferably 20 or less, even more preferably 15 or less.

[0021] The number of glycidyl ether groups in the polyglycidyl ether of polyhydric alcohol constituting component (c) is 2 or more per molecule from the viewpoint of efficiently reacting with acid groups and improving the storage stability of the aqueous dispersion and aqueous ink, and preferably 6 or less per molecule, and from the viewpoint of commercial availability, more preferably 4 or less, and even more preferably 3 or less. Here, the polyglycidyl ether of polyhydric alcohol constituting component (c) refers to the polyglycidyl ether of polyhydric alcohol before the crosslinking reaction.

[0022] The epoxy equivalent of the polyglycidyl ether of a polyhydric alcohol is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, even more preferably 160 or less.

[0023] The polyglycidyl ether of a polyhydric alcohol is preferably at least one selected from polyglycidyl ethers such as 1,6-hexanediol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, and pentaerythritol polyglycidyl ether, more preferably at least one selected from ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether, and even more preferably at least one selected from 1,6-hexanediol diglycidyl ether and trimethylolpropane polyglycidyl ether. Of these, 1,6-hexanediol diglycidyl ether is even more preferred.

[0024] From the viewpoint of improving the storage stability of the aqueous dispersion and aqueous ink, and the adhesion and abrasion resistance of the resin coating film to the resin printing medium, the degree of crosslinking of the resin particles having a crosslinked structure is preferably 3 mol% or more, more preferably 3.5 mol% or more, even more preferably 4 mol% or more, and is preferably 100 mol% or less, more preferably 80 mol% or less, even more preferably 60 mol% or less. Here, the degree of crosslinking is an apparent degree of crosslinking calculated from the acid value of the resin particles having a core-shell structure and the equivalent weight of the glycidyl group of the polyglycidyl ether of a polyhydric alcohol.

[0025] The molar ratio of component (c) to component (a) in the resin particles having a crosslinked structure [component (c) / component (a)] is preferably 0.05 or more, more preferably 0.10 or more, even more preferably 0.20 or more, and is preferably 1 or less, more preferably 0.80 or less, even more preferably 0.60 or less, from the viewpoint of improving the storage stability of the aqueous dispersion and aqueous ink, and the adhesion and abrasion resistance of the resin coating film to the resin printing medium.

[0026] From the viewpoint of improving the ejection stability of the water-based ink, the average particle size of the resin particles having a crosslinked structure is preferably 70 nm or more, more preferably 80 nm or more, even more preferably 90 nm or more, and is preferably 150 nm or less, more preferably 140 nm or less, even more preferably 130 nm or less. The average particle size of the resin particles having a crosslinked structure is measured by the method described in the Examples.

[0027] The acid value of the resin particles having a crosslinked structure is preferably 10 mgKOH / g or more, more preferably 20 mgKOH / g or more, even more preferably 30 mgKOH / g or more, and even more preferably 35 mgKOH / g or more, from the viewpoint of improving the adhesion and abrasion resistance of the ink coating film, and is preferably 100 mgKOH / g or less, more preferably 70 mgKOH / g or less, and even more preferably 50 mgKOH / g or less, from the viewpoint of improving storage stability.

[0028] The acid value of the resin particles having a crosslinked structure can be calculated by multiplying the acid value of the resin particles having a core-shell structure calculated from the acid value of the core resin and the acid value of the shell resin of the resin particles having the above-mentioned core-shell structure and the mass ratio of the core resin to the shell resin, by the above-mentioned degree of crosslinking.

[0029] [Aqueous dispersion] The aqueous dispersion of resin particles having a crosslinked structure of the present invention is prepared by dispersing resin particles having a crosslinked structure in an aqueous medium. In the present invention, the term "aqueous medium" means that water accounts for the largest proportion of the medium. As the water for the aqueous medium, deionized water, ion-exchanged water, or distilled water is preferably used. The aqueous medium may further contain an organic solvent, such as aliphatic alcohols having from 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol, ketones having from 3 to 8 carbon atoms, such as acetone and methyl ethyl ketone, and ethers, such as tetrahydrofuran, which are water-soluble. From the viewpoint of environmental friendliness, the water content in the aqueous medium is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and still more preferably 95% by mass or more.

[0030] [Method for producing aqueous dispersion of resin particles having a crosslinked structure] The method of the present invention for producing an aqueous dispersion of resin particles having a crosslinked structure includes a step of producing resin particles having a core-shell structure and a step of crosslinking the resin particles having a core-shell structure.

[0031] (Step for producing resin particles having a core-shell structure) Resin particles having a core-shell structure can be produced by polymerizing a monomer mixture of components (a) and (b), and optionally components derived from (meth)acrylic acid esters excluding component (b), to produce a core resin, and further polymerizing the monomer mixture of components (a) and (b), and optionally components derived from (meth)acrylic acid esters excluding component (b), in the presence of the core resin, to form a shell resin on the surface of the core resin. In the resin particles having a core-shell structure, the core resin and the shell resin may be formed continuously, or the core resin may be isolated and purified, and then the shell resin may be formed on the surface of the core resin.

[0032] Specifically, the core resin is formed by mixing a monomer mixture for forming the core resin with an aqueous medium and heating the mixture while stirring in the presence of a water-soluble polymerization initiator. The monomer mixture for forming the core resin may be added dropwise directly to a reaction vessel or may be added dropwise after being previously emulsified with an aqueous medium. The monomer mixture may also contain a water-soluble polymerization initiator.

[0033] Next, the monomer mixture for forming the shell resin is mixed with an aqueous medium in the presence of the core resin, and the mixture is heated with stirring in the presence of a water-soluble polymerization initiator, thereby forming the shell resin on the surface of the core resin. Like the monomer mixture for the core resin, the monomer mixture for forming the shell resin may be added dropwise directly to a reaction vessel or may be added dropwise after being previously emulsified with an aqueous medium, and may also contain a water-soluble polymerization initiator.

[0034] The aqueous medium used in the production of resin particles having a core-shell structure means a medium in which water accounts for the largest proportion. Known water-soluble polymerization initiators can be used, including inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide, azo initiators such as 2,2′-azobis(2-amidinopropane) dihydrochloride, and redox initiators in which a peroxide compound is combined with a reducing agent such as sodium sulfite. That is, the aqueous dispersion of resin particles having a crosslinked structure of the present invention preferably contains structural units derived from these water-soluble polymerization initiators in the resin. During polymerization, surfactants such as nonionic surfactants, anionic surfactants, and cationic surfactants can be used, and it is preferable to use anionic surfactants. Examples of the anionic surfactant include fatty acid salts, alkylbenzenesulfonates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene aralkylaryl ether sulfates, and polyoxyethylene alkyl ether sulfates, and polyoxyethylene alkyl ether sulfates are more preferable. Although preferred polymerization conditions vary depending on the type of polymerization initiator, the polymerization temperature is preferably 50° C. to 95° C., and the polymerization time is preferably 1 hour to 20 hours. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.

[0035] (Step of crosslinking resin particles having a core-shell structure) By reacting the polyglycidyl ether of polyhydric alcohol, which is the component (c), with the acid groups of the resin particles having a core-shell structure, resin particles having a crosslinked structure are obtained. The reaction between the resin particles having a core-shell structure and the polyglycidyl ether of a polyhydric alcohol is carried out by adding the polyglycidyl ether of a polyhydric alcohol to an aqueous dispersion of the resin particles having a core-shell structure, followed by heat treatment. The aqueous dispersion of core-shell resin particles may be prepared in an aqueous medium and used as is. However, if the aqueous dispersion contains an organic solvent, it is preferable to remove the organic solvent before heat treatment. It is preferable that the organic solvent is substantially removed, but it may remain as long as it does not impair the objectives of the present invention. If the organic solvent remains, its amount is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.

[0036] The preferred heat treatment conditions vary depending on the type of polyglycidyl ether of polyhydric alcohol, but the heat treatment temperature is preferably 70° C. to 95° C., and the polymerization time is preferably 1 hour to 5 hours. The heat treatment atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.

[0037] Furthermore, before the reaction with the polyglycidyl ether of a polyhydric alcohol, the resin particles having a core-shell structure are preferably neutralized with a neutralizing agent to neutralize the carboxyl groups derived from component (a). The degree of neutralization of the resin particles having a core-shell structure is preferably 30 mol% or more, more preferably 35 mol% or more, and even more preferably 40 mol% or more, from the viewpoint of setting the molar ratio of component (c) to component (a) in the resin particles having a crosslinked structure within a predetermined range, and is preferably 99 mol% or less, more preferably 98 mol% or less, and even more preferably 96 mol% or less.

[0038] Examples of the neutralizing agent include alkali metal hydroxides, ammonia, and organic amines. Examples of the alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide. Examples of the organic amines include trimethylamine, ethylamine, diethylamine, triethylamine, and triethanolamine. From the viewpoint of improving the storage stability of the aqueous dispersion of resin particles having a crosslinked structure and the aqueous ink, as well as the adhesion and abrasion resistance of the resin coating film to a resin printing medium, the neutralizing agent is preferably an alkali metal hydroxide such as sodium hydroxide or ammonia, and more preferably ammonia.

[0039] [Water-based ink] The aqueous dispersion of resin particles having a crosslinked structure of the present invention can be mixed with a pigment to form an aqueous ink. Alternatively, it can be used as an aqueous clear ink without a pigment. The aqueous ink can also contain a pigment-dispersing polymer, an organic solvent, a surfactant, etc.

[0040] [Pigments] The pigment used in the present invention is not particularly limited, and may be either an inorganic pigment or an organic pigment. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, thermal black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. The hue is not particularly limited, and achromatic pigments such as white, black, and gray, and chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can all be used. The pigments can be used alone or in combination of two or more.

[0041] From the viewpoint of improving the print density of the water-based ink, the content of the pigment in the water-based ink of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and is preferably 8% by mass or less, more preferably 6% by mass or less, even more preferably 5% by mass or less.

[0042] Furthermore, in the water-based ink of the present invention, the mass ratio of the resin particles having a crosslinked structure to the pigment (resin particles having a crosslinked structure / pigment) is preferably 0.5 or more, more preferably 0.7 or more, even more preferably 1 or more, from the viewpoint of improving the adhesion of the resin coating film to the resin printing medium and the abrasion resistance, and is preferably 8 or less, more preferably 6 or less, even more preferably 5 or less.

[0043] [Pigment Dispersion Polymer] The pigment dispersing polymer is a polymer for dispersing pigments, and from the viewpoint of improving the dispersion stability of the pigment, it preferably has acid groups, and it is preferable that at least a portion of the acid groups be neutralized with a neutralizing agent. This is thought to increase the charge repulsion force that occurs after neutralization, suppress the aggregation of pigment particles in the water-based ink, suppress thickening, and improve storage stability. Examples of the acid group include a group that exhibits acidity by dissociating and releasing a hydrogen ion, such as a carboxy group (-COOM), a sulfonic acid group (-SO3M), or a phosphate group (-OPO3M2), or a dissociated ionic form thereof. Of these, the carboxy group (-COOM) is preferred from the viewpoint of improving the storage stability and ejection stability of the water-based ink.

[0044] From the viewpoint of improving the jetting stability of the aqueous ink, the acid value of the pigment dispersion polymer is preferably 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, even more preferably 90 mgKOH / g or more, and is preferably 300 mgKOH / g or less, more preferably 270 mgKOH / g or less, even more preferably 250 mgKOH / g or less. When the acid value is within the above range, the amount of acid groups and their neutralized acid groups is sufficient, ensuring the dispersion stability of the pigment and, as a result, the jetting stability of the aqueous ink. This is also preferable in terms of the affinity between the pigment dispersion polymer and the aqueous medium. The acid value of the pigment dispersing polymer can be calculated from the mass ratio of the constituent monomers.

[0045] From the viewpoint of improving the storage stability and ejection stability of the water-based ink, the number-average molecular weight of the pigment-dispersing polymer is preferably 3,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more, and from the viewpoint of improving the dispersion stability of the pigment, it is preferably 100,000 or less, more preferably 70,000 or less, and even more preferably 60,000 or less. If the number-average molecular weight of the pigment-dispersing polymer is within the above range, the adsorption force to the pigment is sufficient, and dispersion stability can be achieved.

[0046] From the viewpoint of improving the dispersion stability of pigment molecules in ink, the pigment dispersion polymer preferably contains a structural unit derived from (a-1) an ionic monomer (hereinafter also referred to as "component (a-1)") and a structural unit derived from (a-2) a hydrophobic monomer (hereinafter also referred to as "component (a-2)"). The pigment dispersion polymer may further contain a structural unit derived from (a-3) a nonionic monomer (hereinafter also referred to as "component (a-3)").

[0047] <(a-1) Ionic Monomer> (a-1) The ionic monomer includes anionic monomers and cationic monomers, with anionic monomers being preferred. Specific examples of the (a-1) ionic monomer include those described in paragraph

[0017] of JP 2018-83938 A. Among these, carboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid are preferred, and acrylic acid and methacrylic acid are more preferred.

[0048] <(a-2) Hydrophobic Monomer> (a-2) The term "hydrophobic" in the hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the dissolved monomer is less than 10 g. Specific examples of the (a-2) hydrophobic monomer include those described in paragraphs

[0020] to

[0022] of JP 2018-83938 A. Among these, alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms, particularly 6 to 18 carbon atoms, vinyl monomers having an aromatic group with 6 to 22 carbon atoms, and macromonomers having a polymerizable functional group at one end are preferred, with one or more selected from styrene and α-methylstyrene being more preferred.

[0049] Examples of the macromonomer having a polymerizable functional group at one end include compounds having a number average molecular weight of 500 or more and 100,000 or less, preferably 1,000 or more and 10,000 or less, and in which the polymerizable functional group is an acryloyloxy group or a methacryloyloxy group. The macromonomer is preferably an aromatic group-containing monomer-based macromonomer, and examples of the aromatic group-containing monomer constituting the macromonomer include the aromatic group-containing monomers described above. Specific examples of commercially available styrene-based macromonomers include AS-6(S), AN-6(S), and HS-6(S) manufactured by Toagosei Co., Ltd.

[0050] <(a-3) Nonionic Monomer> (a-3) Nonionic monomers are monomers that have high affinity with water and organic solvents, and are, for example, monomers that contain a hydroxyl group or a polyalkylene glycol chain. Specific examples of the component (a-3) include those described in paragraph

[0018] of JP-A No. 2018-83938. Among these, methoxypolyethylene glycol (n=1 to 30) (meth)acrylate is preferred. The monomer components contained in each of the above components (a-1) to (a-3) can be used alone or in combination of two or more.

[0051] The content of the structural units derived from components (a-1) to (a-3) in the pigment dispersion polymer is as follows, from the viewpoint of improving the storage stability and ejection stability of the water-based ink. The content of component (a-1) in the pigment dispersion polymer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less. The content of the component (a-2) in the pigment dispersion polymer is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 88% by mass or less. When the component (a-3) is contained, its content in the pigment-dispersing polymer is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 0% by mass.

[0052] Furthermore, from the viewpoint of improving the storage stability and ejection stability of the water-based ink, the mass ratio of the component (a-1) to the component (a-2) [component (a-1) / component (a-2)] is preferably 0.1 or more, more preferably 0.15 or more, even more preferably 0.2 or more, and is preferably 3 or less, more preferably 2 or less, even more preferably 1 or less, and still more preferably 0.5 or less. Furthermore, when the (a-3) component is contained, the mass ratio of the (a-1) component to the total of the (a-2) component and the (a-3) component [(a-1) component / [(a-2) component+(a-3) component]] is preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and is preferably 1 or less, more preferably 0.8 or less, even more preferably 0.6 or less.

[0053] <Production of pigment dispersing polymers> The pigment dispersing polymer can be produced by copolymerizing a mixture of the above monomer components (a-1) to (a-3) by a known polymerization method, preferably a solution polymerization method. There are no limitations on the solvent used in the solution polymerization method, but polar solvents such as water, aliphatic alcohols, ketones, ethers, and esters are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone, and the like are more preferred.

[0054] During the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. As the polymerization initiator, known radical polymerization initiators can be used, such as inorganic peroxides such as potassium persulfate, azo compounds such as 2,2'-azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile), and organic peroxides such as t-butyl peroxyoctoate and benzoyl peroxide. The amount of the radical polymerization initiator is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.15 parts by mass or more, per 100 parts by mass of the monomer mixture, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less. As the polymerization chain transfer agent, known chain transfer agents such as mercaptans such as octyl mercaptan and 2-mercaptoethanol, and thiuram disulfides can be used.

[0055] There is no limitation on the chain mode of the polymerized monomers, and any of the polymerization modes such as random, block, and graft may be used. Preferred polymerization conditions vary depending on the types of polymerization initiator, monomer, and solvent used, but typically the polymerization temperature is preferably 40° C. or higher, more preferably 45° C. or higher, and preferably 90° C. or lower, more preferably 85° C. or lower. The polymerization time is preferably 1 hour or longer, more preferably 5 hours or longer, and preferably 20 hours or shorter, more preferably 10 hours or shorter. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.

[0056] After the polymerization reaction is completed, the pigment dispersion polymer is preferably used as an aqueous dispersion of the pigment dispersion polymer in which water is the main dispersion medium, without removing the solvent used in the polymerization reaction, from the viewpoint of compatibility with inks. Furthermore, if necessary, the produced pigment dispersion polymer can be isolated from the reaction solution by known methods such as reprecipitation or solvent distillation. Furthermore, the obtained pigment dispersion polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatography, extraction, or the like.

[0057] <Method for producing water-based pigment dispersion> The pigment can be dispersed in a water-based pigment dispersion by a known method using a pigment dispersing polymer. Examples of the dispersion method include the following methods. First, the pigment and the pigment-dispersing polymer are mixed in water. At this time, a neutralizing agent may be added to neutralize the pigment-dispersing polymer. There are no particular restrictions on the order in which the pigment and the pigment-dispersing polymer are mixed in water, but when adding the neutralizing agent, it is preferable to add the pigment-dispersing polymer to water, and then mix the neutralizing agent and the pigment in this order. The pigment and the pigment dispersing polymer can be mixed by a conventional method such as using an ultrasonic homogenizer.

[0058] When performing the dispersion treatment, an organic solvent for dispersion treatment may be used. There are no particular restrictions on the organic solvent for dispersion treatment, as long as it can be removed from the aqueous dispersion after the dispersion treatment. As the organic solvent for dispersion treatment, aliphatic alcohols, ketones, ethers, esters, etc. having 1 to 3 carbon atoms are preferred, and from the viewpoint of improving the wettability to the pigment, the solubility of the polymer dispersant, and the adsorption of the polymer dispersant to the pigment, ketones having 4 to 8 carbon atoms are more preferred, methyl ethyl ketone and methyl isobutyl ketone are even more preferred, and methyl ethyl ketone is even more preferred.

[0059] In the dispersion treatment, pigment particles can be atomized to a desired particle size by main dispersion using shear stress alone, but from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture and then further carry out main dispersion.

[0060] When pre-dispersing the pigment mixture, a commonly used mixing and stirring device such as an anchor blade or a disper blade can be used, but among these, a high-speed stirring and mixing device is preferred. The pre-dispersion temperature is preferably 0° C. or higher, and preferably 40° C. or lower, more preferably 30° C. or lower, and even more preferably 25° C. or lower. The pre-dispersion time is preferably 0.5 hours or higher, more preferably 0.8 hours or higher, and preferably 30 hours or lower, more preferably 10 hours or lower, and even more preferably 5 hours or lower.

[0061] Examples of means for applying shear stress for this dispersion include kneading machines such as roll mills and kneaders, high-pressure homogenizers such as Microfluidizer (manufactured by Microfluidics), and media-type dispersers such as paint shakers and bead mills. Commercially available media-type dispersers include Ultra Apex Mill (manufactured by Kotobuki Industries Co., Ltd.) and Picomill (manufactured by Asada Iron Works Co., Ltd.). A combination of these devices can also be used. Of these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment. When the main dispersion is carried out using a high-pressure homogenizer, the pigment particle size can be controlled to a desired size by controlling the processing pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more, more preferably 100 MPa or more, even more preferably 130 MPa or more, and is preferably 250 MPa or less, more preferably 230 MPa or less. The number of passes is preferably 3 or more, more preferably 8 or more, and is preferably 20 or less, more preferably 16 or less.

[0062] The pigment dispersion obtained above may be crosslinked with a crosslinking agent. From the viewpoint of efficient reaction with the pigment dispersion in a water-based medium, as well as the storage stability and ejection stability of the water-based ink, the water solubility (mass ratio) of the crosslinking agent is preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less. Here, the water solubility (mass ratio) refers to the solubility (%) when 10 parts by mass of the crosslinking agent is dissolved in 90 parts by mass of water at room temperature (25°C).

[0063] The crosslinking treatment is carried out by heating a mixture of the pigment dispersion and the crosslinking agent. The heating temperature is preferably 50° C. or higher and 90° C. or lower. From the viewpoints of completion of the crosslinking reaction and economic efficiency, the heating time is preferably 0.5 hours or longer, more preferably 1 hour or longer, and even more preferably 1.5 hours or longer, and is preferably 12 hours or shorter, more preferably 8 hours or shorter, and even more preferably 6 hours or shorter. The progress of the crosslinking reaction can be confirmed by measuring the change in pH of the pigment dispersion during the crosslinking treatment, and the crosslinking reaction can be considered complete when no further change in pH occurs. It is desirable to continue the heat treatment until the crosslinking reaction is completely completed.

[0064] Examples of crosslinking agents for crosslinking the pigment dispersion include compounds similar to the polyglycidyl ether of polyhydric alcohol as component (c) above. Suitable examples of crosslinking agents for crosslinking the pigment dispersion include one or more selected from polyglycidyl ethers such as 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether, with trimethylolpropane polyglycidyl ether being more preferred.

[0065] [Organic solvent] The water-based ink of the present invention may contain an organic solvent to improve wetting and spreading properties on a substrate. The organic solvent is not particularly limited, and examples thereof include glycols and glycol ethers having a boiling point of 100° C. or higher and 260° C. or lower. The glycols and glycol ethers having a boiling point of 100° C. or higher and 260° C. or lower may be used alone or in combination of two or more.

[0066] Specific examples of glycols having a boiling point of 100°C or higher and 260°C or lower include those described in paragraph

[0054] of JP 2018-83938 A. Specific examples of glycol ethers having a boiling point of 100°C or higher and 300°C or lower include those described in paragraphs

[0051] and

[0052] of JP 2018-83938 A. Among these, ethylene glycol, propylene glycol, and diethylene glycol monoalkyl ether are preferred, and propylene glycol and diethylene glycol monoisobutyl ether are more preferred.

[0067] From the viewpoint of improving wetting and spreading properties on a substrate, the total amount of organic solvents in the ink is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less.

[0068] [Surfactant] The water-based ink of the present invention may contain a surfactant to improve wetting and spreading properties on a substrate. Preferred surfactants are acetylene glycol surfactants and polyether-modified silicone surfactants. The acetylene glycol surfactants and polyether-modified silicone surfactants may be used alone or in combination.

[0069] Specific examples of acetylene glycol surfactants include those described in paragraphs

[0056] and

[0057] of JP 2018-83938 A. Specific examples of polyether-modified silicone surfactants include those described in paragraph

[0061] of JP 2018-83938 A. Among these, 2,4,7,9-tetramethyl-5-decyne-4,7-diol and PEG-11 methyl ether dimethicone are preferred.

[0070] From the viewpoint of improving wettability to the printing substrate, the content of the surfactant in the ink is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less. [Content of Resin Particles Having a Crosslinked Structure in Water-Based Ink] When the resin particles having a crosslinked structure of the present invention are used to prepare a water-based ink, in an ink that does not contain a pigment, i.e., a so-called clear ink, the content of the resin particles having a crosslinked structure of the present invention relative to the total amount of the clear ink is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, from the viewpoint of improving adhesion to the printing substrate and abrasion resistance. Furthermore, in a pigment-containing ink, the content of the resin particles having a crosslinked structure of the present invention relative to the entire ink is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, from the viewpoint of improving adhesion to a printing substrate and abrasion resistance, particularly abrasion resistance, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less.

[0071] [Method for preparing water-based ink] The aqueous ink of the present invention can be prepared by mixing a pigment or an aqueous pigment dispersion with an aqueous dispersion of resin particles having a crosslinked structure. When preparing the aqueous ink, the above-mentioned organic solvent and surfactant may be further added, as well as various additives commonly used in aqueous inks, such as humectants, wetting agents, penetrants, viscosity adjusters, pH adjusters, antifoaming agents, preservatives, antifungals, and anticorrosives, if necessary. Furthermore, after mixing, filtration treatment using a filter or the like can be carried out.

[0072] [Resin printing media] Resin printing media for printing using the water-based ink of the present invention include, for example, resin films made of polypropylene, polyethylene terephthalate, polyvinyl chloride, polyethylene, nylon, polymethyl methacrylate, polybutylene terephthalate, polystyrene, polyamide, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer, polycarbonate (PC), polymer alloys of PC and ABS, etc. Among these, resin printing media are preferably made of polyester resins such as polyvinyl chloride and polyethylene terephthalate, or resin films made of polypropylene. The surface of the non-liquid-absorbent resin printing medium may be subjected to surface treatment such as corona treatment or plasma treatment. As a non-liquid-absorbing resin printing medium for printing with the water-based ink of the present invention, a resin film made of polypropylene is preferred, and a resin film made of polypropylene that has been surface-treated by corona treatment is more preferred. The water-based ink of the present invention can also be used for printing on processed paper, synthetic paper, art paper, low-liquid-absorbency coated paper, etc. Examples of low-liquid-absorbency coated paper include general-purpose glossy paper and multicolor foam gloss paper. [Example]

[0073] In the following Production Examples, Synthesis Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. In the following examples, the physical properties were measured by the following methods.

[0074] [measurement] [Measurement of average particle size] The cumulant average particle size measured using Otsuka Electronics Co., Ltd.'s laser particle analysis system "ELS-8000" (cumulant analysis) was used as the average particle size. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 integrations. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measured concentration was usually 5 x 10 -3 The results were calculated in mass %.

[0075] [Measurement of solids concentration] 10.0 parts of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (Φ=40 mm, height=30 mm), and approximately 1.0 part of the sample was added thereto and mixed. The mixture was then accurately weighed, maintained at 105°C for 2 hours to remove volatiles, and then left in the desiccator for 15 minutes, after which the mass was measured. The mass of the sample after devolatilization was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration.

[0076] <Production of Resin Dispersion> Manufacturing Example 1-1 Resin Composition 1 and Resin Composition 2 shown in Table 1 were mixed and stirred to prepare emulsions of Resin Compositions 1 and 2. A 1-liter three-neck flask equipped with a thermometer, a stainless steel stirring rod, a dropping funnel, a downflow condenser, and a nitrogen inlet tube was charged with 163.8 parts of ion-exchanged water, 14.5 parts of a surfactant (Kao Corporation, product name: Latemul E-118B), 25.2 parts of a 1% aqueous ammonium persulfate solution, and 10% of Resin Composition 1. The temperature of the reaction system was raised to 90°C while stirring. The remaining amount of Resin Composition 1 was then added dropwise over 50 minutes, and the mixture in the reaction vessel was stirred at 90°C for 15 minutes. The entire amount of Resin Composition 2 was then added dropwise over 30 minutes, and the mixture was stirred and maintained at 90°C for 90 minutes. Next, 20 parts of a 1% aqueous ammonium persulfate solution was added dropwise, and the mixture was stirred and maintained at 90°C for another 30 minutes, after which it was cooled to room temperature to obtain Resin Dispersion A (solids concentration: 40%).

[0077] Production Examples 1-2 to 1-5 and Comparative Production Examples 1-2 and 1-3 Resin dispersions B to E, G and H (solid content: 40%) were obtained in the same manner as in Production Example 1-1, except that Resin Compositions 1 and 2 were changed as shown in Table 1.

[0078] Comparative Manufacturing Example 1-1 Resin composition 1 shown in Table 1 was mixed and stirred to prepare an emulsion. 234.0 parts of ion-exchanged water, 20.8 parts of a surfactant (manufactured by Kao Corporation, product name: Latemul E-118B), 25.2 parts of a 1% aqueous ammonium persulfate solution, and 10% of resin composition 1 were added to a 1-liter three-neck flask equipped with a thermometer, a stainless steel stirring rod, a dropping funnel, a downflow condenser, and a nitrogen inlet tube. The temperature of the reaction system was raised to 90°C while stirring. Next, the remaining amount of resin composition 1 was added dropwise over 50 minutes, and the mixture in the reaction vessel was stirred at 90°C for 15 minutes. Next, 20 parts of a 1% aqueous ammonium persulfate solution was added dropwise, and the mixture was stirred at 90°C for an additional 30 minutes, after which it was cooled to room temperature to obtain resin dispersion F (solids concentration: 40%).

[0079] [Table 1-1]

[0080] [Table 1-2]

[0081] Manufacturing Example 2-1 100 parts of Resin Dispersion A were filled into a pressure-resistant glass bottle, and 1.89 parts of 25% aqueous ammonia was slowly added dropwise to a neutralization degree of 50 mol%. Next, 4.2 parts of a polyglycidyl ether of a polyhydric alcohol (Nagase ChemteX Corporation, product name: Denacol EX-212 1,6-hexanediol diglycidyl ether, epoxy equivalent 151) as a crosslinking agent, 70.6 parts of ion-exchanged water, and a stirrer bar were added, the bottle was capped, and the mixture was stirred in a 90°C water bath for 90 minutes. After cooling to room temperature, the mixture was filtered through a 5 μm pore size membrane filter (Sartorius, product name: Minisart) to obtain an aqueous dispersion 1 (solids concentration: 25%) of resin particles having a crosslinked structure with an average particle size of 116 nm.

[0082] Manufacturing Examples 2-2 to 2-7, Comparative Manufacturing Examples 2-1 to 2-4 Aqueous dispersions 2 to 7 and 11 to 14 of resin particles having a crosslinked structure were obtained in the same manner as in Production Example 2-1, except that the resin dispersion, 25% ammonia water, and polyglycidyl ether of polyhydric alcohol as a crosslinking agent were changed as shown in Table 2. In Table 2, Denacol EX321 used in Production Example 2-2 is a trade name of Nagase ChemteX Corporation, and the compound name is trimethylolpropane polyglycidyl ether, with an epoxy equivalent of 141. However, since no polyglycidyl ether of a polyhydric alcohol was used in the production of the aqueous dispersion of resin particles in Comparative Production Example 2-1, the resin particles in Comparative Production Example 2-1 do not have a crosslinked structure. Furthermore, the resin particles contained in the aqueous dispersion of Comparative Production Example 2-3 have a crosslinked structure derived from 1,6-hexanediol diacrylate, since 1,6-hexanediol diacrylate was used in the production of Resin Particle G, as shown in Table 1-2. Table 2 shows the physical properties of the resin particles having a crosslinked structure.

[0083] [Table 2]

[0084] <Preparation of clear ink> Examples I-1 to I-7, Comparative Examples I-1 to I-4 As shown in Table 3, 20 parts of an aqueous dispersion 1 of resin particles having a crosslinked structure (solids concentration: 25%), 10 parts of propylene glycol, 15 parts of diethylene glycol monoisobutyl ether, 2 parts of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., product name: Surfynol 104PG50, propylene glycol solution: active content 50%), 1 part of a polyether-modified silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., PEG-11 methyl ether dimethicone, product name: KF-6011, active content 100%), and ion-exchange water were mixed to make a total of 100 parts, and the mixture was stirred using a magnetic stirrer at room temperature for 15 minutes to obtain clear ink 1. Clear inks 2 to 7 and 11 to 14 were obtained in the same manner as in Example I-1, except that the aqueous dispersion of resin particles having a crosslinked structure was changed as shown in Table 3. Using each of the obtained clear inks, the storage stability, and the adhesion and abrasion resistance of the ink coating to a resin print medium after corona treatment were evaluated by the following methods. The results are shown in Table 3.

[0085] [Evaluation of storage stability of clear ink] The clear ink was stored in a sealed container in a constant temperature room at 70°C for 28 days, and then removed and the average particle size was measured. The rate of change in average particle size after 28 days of storage at 70°C was calculated using the following formula (rounded down to the nearest whole number), and the storage stability was evaluated according to the following criteria. Average particle size change rate (%) = [(average particle size after storage / average particle size before storage) - 1] x 100 (Evaluation criteria) A: The absolute value of the rate of change in average particle size is less than 5%. B: The absolute value of the rate of change in average particle size is 5% or more and less than 10%. C: The absolute value of the rate of change in average particle size is 10% or more and less than 15%. D: The absolute value of the rate of change in average particle size is 15% or more. If the evaluation result is C or higher, there is no problem in practical use.

[0086] [Evaluation of Adhesion] Using a Corona Master (manufactured by Shinko Electric Instrumentation Co., Ltd., product name: PS-10S), a polypropylene (PP) film (manufactured by Futamura Chemical Co., Ltd.) was subjected to corona treatment three times under conditions of a treatment voltage of 14 kV and a treatment speed of 50 mm / s. Clear inks 1 to 7 and 11 to 14 were each applied to the surface-treated PP film using a No. 6 bar coater and a tabletop coater (manufactured by Mitsui Electric Seiki Co., Ltd., product name: TC-1) at a speed of 6 m / min, and then dried in a dryer at 50°C for 10 minutes to form a coating film. Next, 11 vertical and horizontal cuts (1 mm apart) were made on the formed coating surface using a cutter knife, reaching down to the PP film base, creating a grid of 100 squares. Cellotape (registered trademark) (manufactured by Nichiban Co., Ltd., product name: CT15) was then applied to the grid areas, and the tape was peeled off at an angle of 90° at a rate of 10 cm / sec. The number of squares that did not peel off was visually confirmed, and the adhesion of the ink coating was evaluated according to the following evaluation criteria. The greater the number of squares that did not peel off, the better the adhesion to the surface-treated PP film. (Evaluation criteria) A: There are 90 or more squares without peeling. B: The number of squares without peeling is 80 or more but less than 90. C: The number of squares without peeling is 60 or more but less than 80. D: There are less than 60 squares without peeling. If the evaluation result is B or above, there is no problem in practical use.

[0087] [Evaluation of Scratch Resistance] A coating film was formed in the same manner as in the "Evaluation of Adhesion" above. Cotton (manufactured by Asahi Kasei Corporation, product name: BEMCOT) and a 200 g weight were placed on the resulting coating film, and the film was rubbed back and forth over a distance of 10 cm 100 times. After rubbing, the coating film was observed under an optical microscope, the remaining area of ​​the coating film was calculated, and the rub resistance was evaluated according to the following evaluation criteria. (Evaluation criteria) A: The remaining area of ​​the coating after rubbing is 90% or more. B: The remaining area of ​​the coating film after rubbing is 80% or more and less than 90%. C: The remaining area of ​​the coating film after rubbing is 60% or more and less than 80%. D: The remaining area of ​​the coating film after rubbing is less than 60%. If the evaluation result is B or above, there is no problem in practical use.

[0088] [Table 3]

[0089] Table 3 shows that the clear inks 1 to 7 obtained in Examples I-1 to I-7 have superior storage stability and / or adhesion of the ink coating to the PP film after corona treatment compared to the clear inks 11 to 14 obtained in Comparative Examples I-1 to I-4. It can be seen that the clear ink 11 has poor storage stability and poor adhesion of the ink coating to the resin printing medium after corona treatment because the resin particles do not have a crosslinked structure. It can be seen that the clear ink 12 has poor abrasion resistance on resin print media because the resin particles do not have a core-shell structure. Clear ink 13 does not have a crosslinked structure in which resin particles are crosslinked by a component derived from polyglycidyl ether of a polyhydric alcohol, and therefore it is clear that the ink coating has poor adhesion to resin printing media. It can be seen that the resin particles of clear ink 14 do not have a structure derived from butyl (meth)acrylate, and therefore have poor adhesion to resin print media and poor abrasion resistance.

[0090] (Production of pigment aqueous dispersion) A monomer mixture was prepared by mixing 60 parts of acrylic acid, 130 parts of styrene, and 10 parts of α-methylstyrene. A reaction vessel was charged with 20 parts of methyl ethyl ketone (MEK), 0.3 parts of 2-mercaptoethanol as a chain transfer agent, and 10% of the monomer mixture, and the mixture was thoroughly purged with nitrogen gas. A mixture of the remaining 90% of the monomer mixture, 0.27 parts of the chain transfer agent, 60 parts of MEK, and 2.5 parts of an azo radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), product name: V-65, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was placed in a dropping funnel. Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours had passed at 65°C from the end of the dropwise addition, a solution of 0.3 parts of the polymerization initiator dissolved in 5 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours, thereby obtaining an MEK solution of a pigment dispersing polymer with an acid value of 233 mgKOH / g. The obtained MEK solution of the pigment dispersion polymer was dried under reduced pressure, and 37 parts of the obtained polymer was dissolved in 148 parts MEK. 7.7 parts of a 48% by mass aqueous solution of sodium hydroxide as a neutralizing agent and 372 parts of ion-exchanged water were added, and 100 parts of a cyan pigment (CI Pigment Blue 15:3, manufactured by DIC Corporation, product name: TGR-SD) were further added to obtain a pigment mixed liquid (neutralization degree: 60 mol%). The resulting pigment mixture was mixed for 1 hour using a Disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) at 7,000 rpm and 20°C, and then further dispersed using a high-pressure homogenizer (manufactured by Microfluidics, product name: Microfluidizer M-140K) at a pressure of 180 MPa for 15 passes. The obtained aqueous dispersion of pigment-containing polymer particles was subjected to vacuum treatment at 60°C to remove MEK, and then some of the water was removed. The mixture was then centrifuged, and the liquid layer was filtered through a Minisart syringe filter (pore size: 5 μm) to remove coarse particles. The solid content was then adjusted to 22% with ion-exchanged water to obtain a pigment dispersion. 100 parts of the resulting pigment dispersion was placed in a screw-cap glass bottle, 1.5 parts of a crosslinker (Denacol EX-321L) was added, the bottle was sealed, and the bottle was heated at 70°C for 5 hours while stirring with a stirrer. After cooling to room temperature, the solids content was adjusted with ion-exchanged water, and the resulting pigment dispersion was filtered through a 25 mL syringe (manufactured by Terumo Corporation) equipped with a 5 μm pore filter (acetyl cellulose membrane, outer diameter: 2.5 cm) to obtain a pigment aqueous dispersion (solids concentration: 20%, pigment content: 14.6%, pigment dispersing polymer content: 5.6%, average particle size: 103 nm).

[0091] <Preparation of Water-Based Ink> Examples II-1 to II-7, Comparative Examples II-1 to II-4 A 100 mL screw tube was charged with 10 parts of propylene glycol, 15 parts of diethylene glycol monoisobutyl ether, 2 parts of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol 104PG50 propylene glycol solution: active content 50%), 1 part of a polyether-modified silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., PEG-11 methyl ether dimethicone, trade name: KF-6011), and 25.6 parts of ion-exchanged water, and the mixture was stirred using a magnetic stirrer at room temperature for 15 minutes to obtain a mixed solution. Next, 27.4 parts of the pigment aqueous dispersion prepared above (corresponding to a 4.0% pigment content in the aqueous ink) was added to the mixed solution while stirring using a magnetic stirrer. 20 parts of the aqueous dispersion 1 of resin particles having a crosslinked structure shown in Table 4 (corresponding to a 5.0% resin content in the aqueous ink) were then added dropwise with a dropper while stirring and mixing (total 100 parts). The mixture was then filtered through a 5.0 μm pore size filter (manufactured by Sartorius Stedim Biotech, trade name: Minisart) to obtain aqueous ink 1 (solids concentration: 10.5%, pigment content: 4%, polymer dispersant content: 1.5%). Water-based inks 2 to 7 and 11 to 14 were obtained in the same manner as in Example II-1, except that the aqueous dispersion of resin particles having a crosslinked structure was changed as shown in Table 4.

[0092] Example II-8 Water-based ink 8 was obtained in the same manner as in Example II-1, except that the amounts of the pigment water dispersion and the water-based dispersion 1 of resin particles having a crosslinked structure were changed as shown in Table 4.

[0093] [Evaluation of storage stability of water-based ink] The water-based ink was stored in a sealed container in a constant temperature room at 70°C for 28 days, and then removed and the average particle size was measured. The rate of change in average particle size after 28 days of storage at 70°C was calculated using the following formula (rounded down to the nearest whole number), and the storage stability was evaluated according to the following criteria. Average particle size change rate (%) = [(average particle size after storage / average particle size before storage) - 1] x 100 (Evaluation criteria) A: The absolute value of the rate of change in average particle size is less than 5%. B: The absolute value of the rate of change in average particle size is 5% or more and less than 10%. C: The absolute value of the rate of change in average particle size is 10% or more and less than 15%. D: The absolute value of the rate of change in average particle size is 15% or more. If the evaluation result is C or higher, there is no problem in practical use.

[0094] [Evaluation of Adhesion] Using a Corona Master (Shinko Electric Instrumentation Co., Ltd., product name: PS-10S), a polypropylene (PP) film (Futamura Chemical Co., Ltd.) was subjected to corona treatment three times under conditions of treatment voltage: 14 kV, treatment speed: 50 mm / s. The aqueous ink obtained above was filled into an inkjet printer (Ricoh Co., Ltd., product name: IPSiO GX 2500, piezoelectric type), and an A4 solid image was printed on the surface-treated PP film. The print was then dried for 5 minutes in a 50°C dryer and left to stand for 1 day in an environmental chamber at room temperature of 25°C and relative humidity of 50%, to obtain a print for evaluation. A cutter knife was used to make 11 vertical and horizontal cuts (1 mm apart) on the printed surface of the evaluation print, reaching down to the PVC film substrate, creating a grid of 100 squares. Cellotape (registered trademark) (product name: CT15) was then applied to the grid areas, and the tape was peeled off at a 90° angle at a speed of 10 cm / sec. The number of squares that did not peel off was visually confirmed, and the adhesion of the ink coating film was evaluated according to the following evaluation criteria. The greater the number of squares that did not peel off, the better the adhesion to the surface-treated PP film. (Evaluation criteria) A: There are 90 or more squares without peeling. B: The number of squares without peeling is 80 or more but less than 90. C: The number of squares without peeling is 60 or more but less than 80. D: There are less than 60 squares without peeling. If the evaluation result is B or above, there is no problem in practical use.

[0095] [Evaluation of Scratch Resistance] A cotton ball (product name: BEMCOT, manufactured by Asahi Kasei Corporation) and a 200 g weight were placed on the coating film obtained in the same manner as in the "Adhesion Evaluation" above, and the coating film was rubbed back and forth over a distance of 10 cm 100 times. After rubbing, the coating film was observed under an optical microscope, the remaining area of ​​the coating film was calculated, and the rub resistance was evaluated according to the following evaluation criteria. (Evaluation criteria) A: The remaining area of ​​the coating after rubbing is 90% or more. B: The remaining area of ​​the coating film after rubbing is 80% or more and less than 90%. C: The remaining area of ​​the coating film after rubbing is 60% or more and less than 80%. D: The remaining area of ​​the coating film after rubbing is less than 60%. If the evaluation result is B or above, there is no problem in practical use.

[0096] [Table 4]

[0097] Table 4 shows that the water-based inks 1 to 7 obtained in Examples II-1 to II-8 have superior storage stability compared to the water-based inks 11 to 14 obtained in Comparative Examples II-1 to II-4, and can produce printed matter with excellent adhesion of the ink coating to the PP film after corona treatment and excellent abrasion resistance. It can be seen that the resin particles of water-based ink 11 do not have a crosslinked structure, and therefore the storage stability, adhesion of the ink coating to the resin printing medium after corona treatment, and abrasion resistance are poor. The water-based ink 12 has resin particles that do not have a core-shell structure, and therefore has poor adhesion and abrasion resistance on resin print media. It can be seen that water-based ink 13 has poor adhesion of the ink coating to the resin printing medium after corona treatment because the resin particles do not have a crosslinked structure formed by crosslinking with a constituent derived from polyglycidyl ether of a polyhydric alcohol. It can be seen that the resin particles of water-based ink 14 do not have a structure derived from butyl (meth)acrylate, and therefore have poor adhesion to resin print media and poor abrasion resistance.

Claims

1. An aqueous dispersion of resin particles having a crosslinked structure in which (a) resin particles having a core-shell structure containing a component derived from (meth)acrylic acid and (b) a component derived from butyl (meth)acrylate are crosslinked with (c) a component derived from a polyglycidyl ether of a polyhydric alcohol, An aqueous dispersion of resin particles having a crosslinked structure, wherein the glass transition temperature of a core resin constituting the core-shell structure is different from the glass transition temperature of a shell resin, and the mass ratio of the core resin to the resin particles having a core-shell structure (core resin / resin particles having a core-shell structure) is 0.50 or more and 0.90 or less.

2. 2. The aqueous dispersion according to claim 1, wherein the glass transition temperature of the core resin is lower than the glass transition temperature of the shell resin.

3. 3. The aqueous dispersion according to claim 1, wherein the components constituting the resin particles having a crosslinked structure satisfy the following conditions 1 and 2: Condition 1: The mass ratio of component (b) to component (a) [component (b) / component (a)] is 1 or more and 18 or less Condition 2: the molar ratio of component (c) to component (a) [component (c) / component (a)] is 0.05 or more and 1 or less

4. 4. The aqueous dispersion according to claim 1, wherein the mass ratio of the total content of the component (a) and the component (b) to the total content of all monomer components constituting the resin particles having a core-shell structure [[component (a) + component (b)] / total monomer components] is 0.2 or more and 1 or less.

5. 5. The aqueous dispersion according to claim 1, wherein the polyhydric alcohol moiety of component (c) has 2 or more and 25 or less carbon atoms.

6. 6. The aqueous dispersion according to claim 1, wherein the component (c) is at least one selected from the group consisting of 1,6-hexanediol diglycidyl ether and trimethylolpropane polyglycidyl ether.

7. 7. The aqueous dispersion according to claim 1, wherein the resin particles having a core-shell structure further contain a constituent derived from a (meth)acrylic acid ester other than butyl (meth)acrylate.

8. 8. A water-based clear ink comprising an aqueous dispersion of resin particles having a crosslinked structure according to claim 1 and an organic solvent.

9. 8. A water-based ink comprising a water-based dispersion of resin particles having a crosslinked structure according to claim 1 and a pigment.

10. The water-based ink according to claim 9 , wherein the mass ratio of the resin particles having a crosslinked structure to the pigment (resin particles / pigment) is 0.5 or more and 8 or less.

11. Resin particles having a core-shell structure containing (a) a component derived from (meth)acrylic acid and (b) a component derived from butyl (meth)acrylate, and (c) a crosslinked structure formed by crosslinking with a component derived from a polyglycidyl ether of a polyhydric alcohol, Resin particles having a crosslinked structure, wherein the glass transition temperature of the core resin constituting the core-shell structure is different from the glass transition temperature of the shell resin, and the mass ratio of the core resin to the resin particles having a core-shell structure (core resin / resin particles having a core-shell structure) is 0.50 or more and 0.90 or less.

12. A water-based clear ink containing resin particles having the cross-linked structure described in claim 11 and an organic solvent.

13. A water-based ink containing resin particles having the cross-linked structure described in claim 11 and a pigment.

14. A method for producing an aqueous dispersion of resin particles having a crosslinked structure, which satisfies the following conditions 1 and 2 and includes the following steps 1 to 3. Condition 1: The glass transition temperature of the resin obtained from the monomer mixture in step 1 is different from the glass transition temperature of the resin obtained from the monomer mixture in step 2. Condition 2: The mass ratio of the monomer mixture in step 1 to the total of the monomer mixture in step 1 and the monomer mixture in step 2 (monomer mixture in step 1 / total of the monomer mixture in step 1 and the monomer mixture in step 2) is 0.50 or more and 0.90 or less. Step 1: A monomer mixture containing at least (meth)acrylic acid and butyl (meth)acrylate is polymerized in an aqueous medium to obtain resin particles 1. Step 2: A monomer mixture containing at least (meth)acrylic acid and butyl (meth)acrylate, which is different from the monomer mixture of Step 1, is polymerized in an aqueous medium in the presence of resin particles 1 to obtain a polymer. Step 3: React the polyglycidyl ether of polyhydric alcohol with the polymer obtained in step 2 to obtain resin particles having a crosslinked structure.

15. A manufacturing method described in claim 14, wherein the following step 4 is carried out after step 2 and before step 3. Step 4: Neutralizing 30 mol % or more of the acid groups of the polymer obtained in step 2 using a neutralizing agent.

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