Aqueous resin dispersion and aqueous coating material

Abstract

To provide an aqueous resin dispersion and an aqueous coating material which have excellent storage stability and, when formed into a coating film, have both water resistance and solvent resistance. [Solution] An aqueous resin dispersion containing a resin (A) and a crosslinking agent (B), wherein the resin (A) contains a polyurethane resin (A1) having an acid value of 0.5 to 60.0 mgKOH / g, the crosslinking agent (B) contains a metal-based crosslinking agent (B1), and the content of the metal-based crosslinking agent (B1) is 0.05 to 10.0 parts by mass per 100 parts by mass of the resin (A).

Description

[Technical Field]

[0001] The present invention relates to an aqueous resin dispersion and an aqueous coating material. [Background technology]

[0002] In the field of coating materials such as paints, inks, and adhesives, efforts have been made to switch from organic solvent-based coating materials to water-based coating materials from the perspectives of environmental conservation and safety and health. However, water-based coating materials have the problem of being inferior to organic solvent-based coating materials in terms of storage stability, coating film appearance, coating film strength, weather resistance, heat resistance, water resistance, solvent resistance, and contamination resistance. In particular, in recent years, there has been a demand for excellent durability (weather resistance, heat resistance, water resistance, and solvent resistance) that is less affected by the usage environment and duration of use.

[0003] As a material for aqueous coating materials to solve these various problems, aqueous dispersions of composite resins containing resins with different properties have been proposed. For example, Patent Document 1 describes an aqueous resin dispersion of polymer particles containing a urethane polymer and an acrylic polymer. A coating film applied with an aqueous paint containing the aqueous resin dispersion described in Patent Document 1 has excellent adhesion to resin substrates such as ABS and metal substrates such as aluminum, and when formed into a film, it has excellent tensile strength and hardness. However, it has a problem with solvent resistance.

[0004] Therefore, Patent Document 2 proposes a composite resin of a polyurethane resin and a (meth)acrylate resin, which can provide a coating film that is excellent not only in solvent resistance but also in coating film strength, heat resistance, and water resistance. As such a composite resin, a composite resin of a polyurethane resin having a structure derived from a linear diol having 8 to 11 carbon atoms and a (meth)acrylate resin is disclosed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-209656 [Patent Document 2] International Publication No. 2024 / 122493 Summary of the Invention [Problem to be solved by the invention]

[0006] The prior art (Patent Document 2) had a problem of insufficient storage stability in some cases. The present invention aims to solve this problem and provide an aqueous resin dispersion and an aqueous coating material that have excellent storage stability and, when formed into a coating film, have both water resistance and solvent resistance. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that an aqueous resin dispersion containing a polyurethane resin having a specific acid value and a specific amount of a metal-based crosslinking agent can solve the above problems, and have completed the present invention.

[0008] That is, the gist of the present invention is as follows. [1] An aqueous resin dispersion containing a resin (A) and a crosslinking agent (B), the resin (A) contains a polyurethane resin (A1) having an acid value of 0.5 to 60.0 mgKOH / g, the crosslinking agent (B) contains a metal-based crosslinking agent (B1), The aqueous resin dispersion contains the metal crosslinking agent (B1) in an amount of 0.05 to 10.0 parts by mass relative to 100 parts by mass of the resin (A). [2] The aqueous resin dispersion according to [1] above, wherein the polyurethane resin (A1) has an acid value of 35.0 to 60.0 mgKOH / g. [3] The aqueous resin dispersion according to [1] or [2] above, wherein the resin (A) contains a (meth)acrylate resin (A2). [4] The aqueous resin dispersion according to [3] above, wherein the resin (A) contains a composite resin consisting of the polyurethane resin (A1) and the (meth)acrylate resin (A2). [5] The aqueous resin dispersion according to any one of the above [1] to [4], wherein the polyurethane resin (A1) has a structure derived from a polycarbonate polyol. [6] The aqueous resin dispersion according to any one of [1] to [5] above, wherein the content of the metal crosslinking agent (B1) is 0.05 to 6.0 parts by mass per 100 parts by mass of the polyurethane resin (A1). [7] The aqueous resin dispersion according to any one of the above [1] to [6], wherein the metal-based crosslinking agent (B1) is at least one selected from the group consisting of titanium-based crosslinking agents, aluminum-based crosslinking agents, bismuth-based crosslinking agents, iron-based crosslinking agents, zirconium-based crosslinking agents, tin-based crosslinking agents, zinc-based crosslinking agents, copper-based crosslinking agents, and lead-based crosslinking agents. [8] An aqueous coating material containing the aqueous resin dispersion according to any one of [1] to [7] above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an aqueous resin dispersion and an aqueous coating material which have excellent storage stability and which, when formed into a coating film, have both water resistance and solvent resistance. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this specification, a numerical range indicated by "to" means a range including the numerical values ​​before and after it. The upper and lower limits of a numerical range can be combined in any way. "(Meth)acrylate" is a general term for acrylate and methacrylate.

[0011] <Resin (A)> The resin (A) preferably contains a polyurethane resin (A1) and a (meth)acrylate resin (A2). Furthermore, the polyurethane resin (A1) and the (meth)acrylate resin (A2) may form a composite resin, which will be described later, and the resin (A) more preferably contains a composite resin. The resin (A) may contain a resin other than the polyurethane resin (A1) and the (meth)acrylate resin (A2). Examples of such other resins include polyester resins, polyolefin resins, epoxy resins, polyvinyl alcohol resins, and polyvinylpyrrolidone resins. Emulsions and water-soluble resins of these resins are particularly preferred. Furthermore, the total content of the polyurethane resin (A1) and the (meth)acrylate resin (A2) is preferably from 10 to 99 mass %, more preferably from 50 to 98 mass %, particularly preferably from 80 to 97 mass %, based on the total mass of the resin (A). The total content of the polyurethane resin (A1) and the (meth)acrylate resin (A2) refers to the sum of the contents of the polyurethane resin (A1) and the (meth)acrylate resin (A2) that do not form a complex, and the contents of the polyurethane resin (A1) and the (meth)acrylate resin (A2) that form a complex resin.

[0012] [Polyurethane resin (A1)] In the present invention, the polyurethane resin (A1) is a resin obtained by reacting a polyol (a1-1) with a polyisocyanate (a1-2). The polyol is an organic compound having at least two hydroxyl groups per molecule. The polyisocyanate is an organic compound having at least two isocyanate groups per molecule. Each component will be explained in turn.

[0013] [Polyol (a1-1)] Examples of the polyol (a1-1) used in the present invention include linear diols (a1-1-1) having 8 to 11 carbon atoms; linear diols (a1-1-2) having 7 or less carbon atoms or 12 or more carbon atoms; branched diols (a1-1-3); reaction products (a1-1-4) obtained by reacting diols (a1-1-1), diols (a1-1-2), or diols (a1-1-3) with other compounds; high-molecular-weight polyols (a1-1-5) (excluding reaction product (a1-1-4)); and carboxyl group-containing diols (a1-1-6). These may be used alone or in combination of two or more. As the polyol (a1-1), from the viewpoint of improving the stability of the resulting aqueous resin dispersion and the coating film strength, heat resistance, water resistance, and solvent resistance of the resulting coating film, it is preferable to use at least one of the diol (a1-1-1) and the reactant (a1-1-4), and it is more preferable to use the reactant (a1-1-4). It is also preferred to use diol (a1-1-6) from the viewpoint of improving the stability of the aqueous resin dispersion and the coating strength, heat resistance, water resistance and solvent resistance of the resulting coating film.

[0014] The linear diol (a1-1-1) having 8 to 11 carbon atoms refers to a diol in which hydroxyl groups are substituted on both terminal carbon atoms of a linear alkane having 8 to 11 carbon atoms. Examples thereof include 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,11-undecanediol. These may be used alone or in combination of two or more. 1,10-Decanediol is more preferred from the viewpoint of improving the coating film strength, heat resistance, water resistance and solvent resistance of the resulting coating film.

[0015] The content of the component derived from diol (a1-1-1) is preferably 20 to 90 mass %, more preferably 35 to 80 mass %, and even more preferably 45 to 75 mass %, relative to the total mass of polyurethane resin (A1). By adjusting the content within the above range, the coating film obtained will have improved coating strength, heat resistance, water resistance, and solvent resistance. The content of the constituent derived from the diol (a1-1-1) is preferably from 30 to 95 mass %, more preferably from 50 to 95 mass %, and even more preferably from 65 to 95 mass %, based on the total mass of the polyol (a1-1).

[0016] The linear diol (a1-1-2) having 7 or less or 12 or more carbon atoms refers to a diol in which a hydroxyl group is substituted on the terminal carbon atom of a linear alkane having 7 or less or 12 or more carbon atoms. Examples include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,7-heptanediol, and 1,12-dodecanediol. These may be used alone or in combination of two or more.

[0017] Examples of the branched diol (a1-1-3) include 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,8-octanediol, 2,4-dimethyl-1,5-pentanediol, 2,3-dimethyl-1,5-pentanediol, 2-ethyl-1,5-pentanediol, 2-methyl-1,6-hexanediol, 3-methyl-1,6-hexanediol, 2-ethyl-1,6-hexanediol, and 2-methyl-1,7-heptanediol. Examples of suitable methyl alcohols include methyl methyl 1,7-heptanediol, 4-methyl-1,7-heptanediol, 2-methyl-1,9-nonanediol, 3-methyl-1,9-nonanediol, 4-methyl-1,9-nonanediol, 2-methyl-1,10-decanediol, 3-methyl-1,10-decanediol, 4-methyl-1,10-decanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, trimethylolpropane, trimethylolethane, glycerin, and ε-caprolactone. These may be used alone or in combination of two or more.

[0018] The reactant (a1-1-4) is a polyol obtained by reacting the diol (a1-1-1), the diol (a1-1-2), or the diol (a1-1-3) with the following compound: Examples of the reactant (a1-1-4) include polycarbonate polyols obtained by reacting a carbonate ester, such as dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, or propylene carbonate, with phosgene; polyether diols obtained by addition polymerization with ethylene oxide, propylene oxide, tetrahydrofuran, or the like; and polyester polyols obtained by polycondensation with a dicarboxylic acid, such as adipic acid, sebacic acid, itaconic acid, maleic anhydride, terephthalic acid, or isophthalic acid. These may be used alone or in combination of two or more.

[0019] As the reactant (a1-1-4), polycarbonate polyols and polyether polyols are preferred, and polycarbonate polyols are more preferred, from the viewpoint of improving the stability of the resulting aqueous resin dispersion and the coating film strength, heat resistance, water resistance, and solvent resistance of the resulting coating film. In particular, polycarbonate polyols having a structure derived from a linear diol (a1-1-1) having 8 to 11 carbon atoms are preferred, and polycarbonate polyols having a structure derived from 1,10-decanediol are more preferred. Examples of the polycarbonate polyol include products manufactured by Mitsubishi Chemical Corporation under the trade names "BENEBiOL (registered trademark; the same applies hereinafter) NL1010DB," "BENEBiOL NL1030DB," "BENEBiOL NL2010DB," "BENEBiOL NL2030DB," "BENEBiOL NL2070DB," "BENEBiOL NL2000D," and "BENEBiOL NL3010DB." The number average molecular weight of the polycarbonate polyol is preferably 500 to 3500, more preferably 500 to 2500, and even more preferably 1000 to 2500, since the heat resistance, water resistance, and solvent resistance of the resulting coating film are improved.

[0020] The content of the component derived from the reaction product (a1-1-4) is preferably 15 to 85 mass %, more preferably 30 to 75 mass %, and even more preferably 40 to 70 mass %, based on the total mass of the polyurethane resin (A1). By adjusting the content within the above range, the coating film obtained will have improved coating strength, heat resistance, water resistance, and solvent resistance. The content of the constituent derived from the reactant (a1-1-4) is preferably from 25 to 95 mass %, more preferably from 45 to 95 mass %, and even more preferably from 60 to 95 mass %, based on the total mass of the polyol (a1-1).

[0021] The high molecular weight polyol (a1-1-5) (excluding a1-1-4) is a polyol having a repeating unit, and examples thereof include polyether polyols such as polyethylene glycol, polypropylene glycol, polycaprolactone polyol, and polytetramethylene ether polyol; polybutadiene polyol; hydrogenated polybutadiene polyol; and poly(meth)acrylic acid ester polyol. These may be used alone or in combination of two or more.

[0022] Examples of the diol (a1-1-6) include dimethylolalkanoic acids such as dimethylolpropionic acid and dimethylolbutanoic acid. Use of the diol (a1-1-6) improves the stability of the resulting aqueous resin dispersion and the coating strength, heat resistance, water resistance, and solvent resistance of the resulting coating film.

[0023] [Polyisocyanate (a1-2)] Examples of the polyisocyanate (a1-2) used in the present invention include 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1-methyl-2,4-phenylene diisocyanate, 1-methyl-2,6-phenylene diisocyanate, 1-methyl-2,5-phenylene diisocyanate, 1-methyl-2,6-phenylene diisocyanate, 1-methyl-3,5-phenylene diisocyanate, 1-ethyl-2,4-phenylene diisocyanate, 1-isopropyl-2,4-phenylene diisocyanate, 1,3-dimethyl-2,4-phenylene diisocyanate, 1,3-dimethyl-4,6-phenylene diisocyanate, 1,4-dimethyl-2,5-phenylene diisocyanate, diethylbenzene diisocyanate, diisopropylbenzene diisocyanate, 1- Methyl-3,5-diethylbenzene diisocyanate, 3-methyl-1,5-diethylbenzene-2,4-diisocyanate, 1,3,5-triethylbenzene-2,4-diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, 1-methyl-naphthalene-1,5-diisocyanate, naphthalene-2,6-diisocyanate, naphthalene-2,7-diisocyanate aromatic polyisocyanates such as isocyanate, 1,1-dinaphthyl-2,2'-diisocyanate, biphenyl-2,4'-diisocyanate, biphenyl-4,4'-diisocyanate, 3-3'-dimethylbiphenyl-4,4'-diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, diphenylmethane-2,4-diisocyanate;Examples of the polyisocyanates include aliphatic or alicyclic polyisocyanates such as tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, 1,3-cyclopentylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,3-di(isocyanatemethyl)cyclohexane, 1,4-di(isocyanatemethyl)cyclohexane, lysine diisocyanate, isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, 2,2'-dicyclohexylmethane diisocyanate, and 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate; These may be used alone or in combination of two or more.

[0024] As the polyisocyanate (a1-2), from the viewpoint of the physical properties and polymerizability of the resulting coating film, an aliphatic or alicyclic polyisocyanate is preferred, and among these, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and trimethylhexamethylene diisocyanate are more preferred, and isophorone diisocyanate is even more preferred.

[0025] From the viewpoint of the strength of the resulting coating film, the proportions of the polyol (a1-1) and the polyisocyanate (a1-2) used are preferably in an equivalent ratio of polyol (a1-1):polyisocyanate (a2-1)=1.0:1.0 to 1.0:2.0, more preferably 1.0:1.2 to 1.0:1.8, and even more preferably 1.0:1.3 to 1.0:1.7.

[0026] [Biologically derived (biomass-derived) raw materials] The polyurethane resin (A1) used in the present invention may be produced using biological (biomass-derived) raw materials, such as sugars, typically from corn, sugarcane, and sugar beet, and oils and fats obtained from crops, such as oil palm, soybean (Glycine max), rapeseed, and castor bean. For example, among the components described above, those derived from living organisms can be used, such as biomass diols such as ethylene glycol, 1,4-butanediol, 1,3-propanediol, and 1,10-decanediol, which are derived from living organisms; biomass polyols having biomass dibasic acids and biomass diols as constituent units; and biomass polyols such as glycerin and castor oil polyol, which are derived from living organisms. Examples of bio-derived diisocyanates include dimer acid diisocyanate (DDI), pentamethylene diisocyanate, octamethylene diisocyanate, and decamethylene diisocyanate.

[0027] Examples of biologically derived raw materials include products manufactured by Mitsubishi Chemical Corporation under the trade names "BENEBiOL NL1010DB," "BENEBiOL NL1030DB," "BENEBiOL NL2010DB," "BENEBiOL NL2030DB," "BENEBiOL NL2070DB," "BENEBiOL NL2000D," and "BENEBiOL NL3010DB."

[0028] [Manufacturing method] The polyurethane resin (A1) used in the present invention is produced by mixing the polyol (a1-1) and polyisocyanate (a1-2) described above and reacting them (urethane-forming reaction). When a chain extension reaction is carried out, the polyurethane resin before the chain extension reaction is sometimes called a urethane prepolymer to distinguish it from the polyurethane resin obtained by the chain extension reaction. The polyol (a1-1) and the polyisocyanate (a1-2) can be mixed without a solvent, but an organic solvent may be used to ensure a uniform reaction. Examples of the organic solvent include ethers such as dioxane, ketones such as acetone and methyl ethyl ketone, amides such as dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone, and other organic solvents that are inactive to isocyanate groups and have a high affinity for water. Among the polymerization components used for the (meth)acrylate resin (A2), a (meth)acrylate monomer that is not reactive with isocyanate groups, i.e., that does not contain an active hydrogen group, and other radically polymerizable monomers may be present during the production of the polyurethane resin (A1). In this case, the reaction system is diluted by the monomer, allowing the reaction to proceed more uniformly.

[0029] The temperature of the reaction system during the urethane-forming reaction is about 50 to 100° C., and the reaction time is about 0.5 to 20 hours. This makes it possible to obtain a urethane prepolymer having an isocyanate group at its terminal.

[0030] The catalyst used in the urethane-forming reaction of the polyurethane resin (A1) may be any catalyst generally used in urethane-forming reactions. For example, dibutyltin dilaurate may be used. From an environmental perspective, it is preferable not to use a catalyst.

[0031] When the polyurethane resin (A1) has carboxyl groups, it is preferable that some or all of the carboxyl groups are neutralized with at least one selected from ammonia and primary to tertiary amine compounds (hereinafter, "ammonia and primary to tertiary amine compounds" are collectively referred to as "amine compounds.") This can improve the dispersibility of the polyurethane resin (A1) in an aqueous medium and can also improve the physical properties of the resulting coating film. This neutralization reaction can be carried out at any step after the production of the urethane prepolymer and before dispersing it in an aqueous medium, and is preferably carried out in the first neutralization step described below and, if necessary, in the second neutralization step described below.

[0032] Examples of primary amine compounds include primary amine compounds such as methylamine, ethylamine, butylamine, methanolamine, ethanolamine, propanolamine, and butanolamine; and primary aminoalkanol compounds such as aminomethylpropanol, aminoethylpropanol, aminopropylpropanol, aminomethylbutanol, aminomethylpentanol, and aminoethylbutanol. Examples of the secondary amine compounds include dimethylamine, diethylamine, methylethylamine, dibutylamine, and diethanolamine. Examples of the tertiary amine compound include trimethylamine, triethylamine, tributylamine, triethanolamine, and the like. Tertiary amine compounds are preferred from the viewpoint of improving the physical properties of the resulting coating film.

[0033] From the viewpoint of the dispersion stability of the resulting polyurethane resin (A1), the total amount of the amine-based compound used, as the combined amount used in the first and second neutralization steps described below, is preferably 0.7 equivalents or more, more preferably 0.8 equivalents or more, and even more preferably 1 equivalent or more, relative to the amount of carboxyl groups in the polyurethane resin (A1). That is, the carboxyl groups in the polyurethane resin (A1) are preferably neutralized by the amine-based compound at least 70%, more preferably at least 90%, and even more preferably at least 100%. If the amount is 0.7 equivalents or more, the dispersion stability of the resulting polyurethane resin (A1) tends to be good. On the other hand, if the amount is 2.0 equivalents or less, 2.0 equivalents or less is preferred, and 1.8 equivalents or less is more preferred. If the amount is 2.0 equivalents or less, a small amount of the amine-based compound remains in the emulsion, and the resulting coating film tends to have good water resistance. The upper and lower limits can be combined in any manner, for example, 0.7 to 2.0 equivalents, 0.8 to 2.0 equivalents, or 1 to 1.8 equivalents.

[0034] The polyurethane resin (A1) can be subjected to a chain extension reaction as needed. Examples of the chain extender used in this reaction include a compound having a plurality of active hydrogens capable of reacting with an isocyanate group and water (including water as an aqueous medium for dispersing the polyurethane resin (A1)).

[0035] Examples of compounds having a plurality of active hydrogens capable of reacting with an isocyanate group include polyols having 1 to 8 carbon atoms and polyamine compounds having 1 to 8 carbon atoms. Examples of polyols having 1 to 8 carbon atoms include ethylene glycol and diethylene glycol. Examples of polyamine compounds having 1 to 8 carbon atoms include diamines such as ethylenediamine, hexamethylenediamine, and isophoronediamine.

[0036] Regarding the chain extension reaction of polyurethane resin (A1), when a mixed liquid containing a urethane prepolymer and at least one of a (meth)acrylate monomer not containing an active hydrogen group and other radically polymerizable monomers is emulsified and dispersed in the aqueous medium to obtain an emulsion, if water is used as the aqueous medium, a partial chain extension reaction of the urethane prepolymer may occur during the polymerization step of at least one of the (meth)acrylate monomer not containing an active hydrogen group and other radically polymerizable monomers. Furthermore, when the chain extension reaction is actively carried out, a chain extender can be added after the emulsification and dispersion to carry out the chain extension reaction.

[0037] [Physical properties of polyurethane resin (A1)] The acid value of the polyurethane resin (A1) is from 0.5 to 60.0 mgKOH / g, preferably 37.0 mgKOH / g or more, more preferably 39.0 mgKOH / g or more, and preferably 50.0 mgKOH / g or less, from the viewpoints of stability with the resulting aqueous resin dispersion and the water resistance and solvent resistance of the resulting coating film. The upper and lower limits can be combined in any manner, for example, 37.0 to 60.0 mgKOH / g, 39.0 to 60.0 mgKOH / g, or 39.0 to 50.0 mgKOH / g.

[0038] The acid value can be measured according to the potentiometric titration method (JIS K 0070:1992) using potassium hydroxide. The mass of the sample is the "amount of polyurethane resin." Furthermore, for example, when potassium hydroxide is used for neutralization during the production of polyurethane resin, salt exchange is less likely to occur, making measurement according to the JIS method difficult. In such cases, the "theoretical acid value" per gram of polyurethane resin can be calculated and used according to the following formula (1): Theoretical acid value (mgKOH / g) = (number of moles of acid-containing raw material charged × 56.1 (molecular weight of KOH) / amount of polyurethane resin (g)) × 1000 (1)

[0039] [(Meth)acrylate resin (A2)] The resin (A) of the present invention preferably further contains a (meth)acrylate resin (A2). The (meth)acrylate resin (A2) may exist as particles separate from the polyurethane resin (A1), but it is more preferable that it exists as a composite resin together with the polyurethane resin (A1).

[0040] The (meth)acrylate resin (A2) is a resin obtained by polymerizing a polymerization component (a2) containing a (meth)acrylate monomer (a2-1). The polymerization component (a2) may further contain another radically polymerizable monomer (a2-2) as long as it contains 50 mass % or more of the (meth)acrylate monomer (a2-1).

[0041] [(Meth)acrylate monomer (a2-1)] Examples of the (meth)acrylate monomer (a2-1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate. Alkyl (meth)acrylates having an alkyl group having 1 to 22 carbon atoms; (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and polypropylene glycol (meth)acrylate; ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, trimethylsilyl acrylate, methyl ... Multifunctional (meth)acrylates such as methylolpropane tri(meth)acrylate; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, and t-butylcyclohexyl (meth)acrylate; (meth)acrylates having a hydrolyzable silyl group such as γ-(meth)acryloyloxypropylmethyldimethoxysilane and γ-(meth)acryloyloxypropyltrimethoxysilane; alkyl group-terminated polyalkylene oxides such as methoxypolyethyleneoxide mono(meth)acrylate. (Meth)acrylates having an amide group; (meth)acrylates having an oxirane group such as glycidyl (meth)acrylate; (meth)acrylates having a carbonyl group such as diacetone acrylamide; (meth)acrylates having a light stabilizing effect such as 1,2,2,6,6-pentamethyl-4-piperidyl (meth)acrylate and 2,2,6,6-pentamethyl-4-piperidyl (meth)acrylate; (meth)acrylates having ultraviolet absorbing properties such as 2-[2'-hydroxy-5'-(meth)acryloyloxyethylphenyl]-2H-benzotriazole;Examples include aminoalkyl (meth)acrylates such as 2-aminoethyl (meth)acrylate; (meth)acrylates having an amide group such as (meth)acrylamide; (meth)acrylates having a metal such as zinc di(meth)acrylate; and other (meth)acrylates such as benzyl (meth)acrylate, isobornyl (meth)acrylate, and methoxyethyl (meth)acrylate. As the (meth)acrylate monomer (a2-1), from the viewpoint of the polymerizability of the composite resin described later, an alkyl (meth)acrylate having an alkyl group of 1 to 22 carbon atoms is preferred, an alkyl (meth)acrylate having an alkyl group of 1 to 6 carbon atoms is more preferred, and methyl (meth)acrylate is even more preferred.

[0042] From the viewpoint of the polymerizability of the composite resin, the content of the structural unit derived from the (meth)acrylate monomer (a2-1) is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 100% by mass or less, based on the total mass of the (meth)acrylate resin (A2). The upper and lower limits can be combined arbitrarily, for example, 10 to 100 mass % or 20 to 100 mass %.

[0043] [Other radical polymerizable monomers (a2-2)] Examples of other radically polymerizable monomers (a2-2) include radically polymerizable monomers having a carboxyl group, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; radically polymerizable monomers having a phosphoric acid group, such as 2-methacryloyloxyethyl acid phosphate; radically polymerizable monomers having a sulfonate, such as styrene sulfonate; aromatic vinyl monomers, such as styrene and methylstyrene; conjugated diene monomers, such as 1,3-butadiene and isoprene; and other radically polymerizable monomers, such as vinyl acetate, vinyl chloride, ethylene, and (meth)acrylonitrile.

[0044] The (meth)acrylate resin (A2), like the polyurethane resin (A1), may be produced using raw materials of biological origin. For example, examples of biologically derived (meth)acrylates include lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, isobornyl (meth)acrylate, and octyl (meth)acrylate.

[0045] [Composite resin] In the present invention, the composite resin refers to a resin having a polyurethane resin (A1) and a (meth)acrylate resin (A2). Specifically, the composite resin contains the polyurethane resin (A1) and the (meth)acrylate resin (A2) in the same particle. The particle shape of the composite resin is preferably a core-shell type particle, and more preferably the shell portion is the polyurethane resin (A1) and the core portion is the (meth)acrylate resin (A2). The composite resin of the present invention can be produced by polymerizing a polymerization component (a2) containing a (meth)acrylate monomer (a2-1) in the presence of the polyurethane resin (A1) (or urethane prepolymer). From the viewpoint of the coating film strength, heat resistance, water resistance, and solvent resistance of the resulting coating film, the proportions of the polyurethane resin (A1) and the (meth)acrylate resin (A2) in the composite resin are preferably 10 to 90 mass %, more preferably 20 to 80 mass %, and even more preferably 30 to 70 mass %, of each of the polyurethane resin (A1) and the (meth)acrylate resin (A2) relative to the total mass of the composite resin.

[0046] [Manufacturing method] In the production method described below, a urethane prepolymer can be used in place of the polyurethane resin (A1). The composite resin can be obtained by, for example, preparing a mixture containing a polyurethane resin (A1) or a urethane prepolymer and a polymerization component (a2) (hereinafter simply referred to as "polymerization component (a2)") containing a (meth)acrylate monomer (a2-1), emulsifying and dispersing the mixture in an aqueous medium, and polymerizing the polymerization component (a2) containing the (meth)acrylate monomer (a2-1) in the emulsion to obtain a composite resin-containing aqueous resin dispersion. When a urethane prepolymer is used, a chain extension reaction of the urethane prepolymer can be carried out as necessary during the process.

[0047] When the polyurethane resin (A1) has carboxyl groups, the mixed liquid containing the polyurethane resin (A1) and the polymerization component (a2) may be prepared by a method that allows the polyurethane resin (A1), which has been rendered water-dispersible by neutralizing at least a portion of the carboxyl groups, and the polymerization component (a2) to be uniformly dispersed in an aqueous medium, and the timing of adding the polymerization component (a2) is not particularly limited.

[0048] For example, the polymerization component (a2) may be added before at least a portion of the carboxyl groups of the polyurethane resin (A1) is neutralized, or the polymerization component (a2) may be added after at least a portion of the carboxyl groups of the polyurethane resin (A1) is neutralized. Alternatively, the polyurethane resin (A1) may be produced by mixing a part or all of the polymerization component (a2) with a mixture containing the raw materials of the polyurethane resin (A1), polyol (a1-1) and polyisocyanate (a1-2), and reacting the polyol (a1-1) with the polyisocyanate (a1-2) in the presence of the polymerization component (a2). When the remaining amount of the polymerization component (a2) is added after the production of the polyurethane resin (A1), the timing of adding the polymerization component (a2) may be any time before, simultaneously with, or after the neutralization of the carboxyl groups of the polyurethane resin (A1).

[0049] A method in which a polyol (a1-1) is reacted with a polyisocyanate (a1-2) in the presence of a polymerization component (a2) to obtain a polyurethane resin (A1) or a urethane prepolymer is preferred, since this method allows the polyurethane resin (A1) or the urethane prepolymer and the polymerization component (a2) to be mixed more uniformly.

[0050] The concentration of the mixture of polyurethane resin (A1) or urethane prepolymer and polymerization component (a2) is not particularly limited, but is preferably adjusted so that the amount of nonvolatile components in the final aqueous dispersion composition is 20% by mass or more, more preferably 30% by mass or more. A concentration of 20% by mass or more can shorten the drying time. On the other hand, the amount of nonvolatile components in the final aqueous dispersion composition is preferably adjusted so that the amount is 70% by mass or less, more preferably 60% by mass or less. A concentration of 70% by mass or less facilitates preparation of aqueous dispersibility, and dispersion stability tends to be improved. The concentration of the mixture of the polyurethane resin (A1) or urethane prepolymer and the polymerization component (a2) corresponds to the absolute concentration of the polyurethane resin (A1), the (meth)acrylic resin (A2), and their composite resin in the aqueous resin dispersion and aqueous coating material of the present invention.

[0051] When all of the carboxyl groups of the polyurethane resin (A1) or urethane prepolymer are not neutralized, it is preferable, from the viewpoint of dispersion stability, to add the above-mentioned amine compound to a mixed liquid of the polyurethane resin (A1) or urethane prepolymer and the polymerization component (a2) to neutralize at least a portion of the carboxyl groups of the polyurethane resin (A1) or urethane prepolymer, thereby obtaining a neutralized product of the polyurethane resin (A1) or urethane prepolymer (hereinafter, this step will be referred to as the "first neutralization step").

[0052] From the viewpoint of dispersion stability, the amount of carboxyl groups neutralized in the first neutralization step is preferably 0.5 equivalents or more, more preferably 0.55 equivalents or more, based on the total carboxyl groups in the polyurethane resin (A1) or urethane prepolymer. If the amount of carboxyl groups neutralized in the first neutralization step is 0.7 equivalents or more, the second neutralization step described below does not need to be carried out. On the other hand, if the amount is less than 0.7 equivalents, the second neutralization step described below is carried out as needed.

[0053] Next, the mixture of the polyurethane resin (A1) or the neutralized urethane prepolymer and the polymerization component (a2) is emulsified and dispersed in an aqueous medium to obtain an emulsified dispersion (hereinafter, this step is referred to as the "emulsification step"). The addition of an aqueous medium to the mixed liquid of the polyurethane resin (A1) or the neutralized product of a urethane prepolymer and the polymerization component (a2) is not particularly limited. The aqueous medium may be added dropwise to the mixed liquid of the polyurethane resin (A1) or the neutralized product of a urethane prepolymer and the polymerization component (a2) to disperse the mixture, or the mixed liquid of the polyurethane resin (A1) or the neutralized product of a urethane prepolymer and the polymerization component (a2) may be added dropwise to the aqueous medium to disperse the mixture.

[0054] The temperature in the emulsification step is preferably 0°C or higher, more preferably 10°C or higher, while it is preferably 80°C or lower, more preferably 60°C or lower. The upper and lower limits can be combined arbitrarily. For example, the temperature may be 0 to 80°C, or 10 to 60°C. When the temperature in the emulsification step is within the above range, the denaturation of the polyurethane resin (A1) or the urethane prepolymer can be suppressed.

[0055] Next, the polymerization component (a2) is polymerized in the resulting emulsion dispersion to obtain a composite resin-containing aqueous resin dispersion (hereinafter, this step is referred to as the "polymerization step"). The polymerization step can be carried out by a general polymerization method depending on the polymerization component (a2) used, for example, by adding a radical polymerization initiator to the resulting emulsion dispersion.

[0056] As the radical polymerization initiator, a conventional radical polymerization initiator can be used, for example, an azo initiator such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, or azobiscyanovaleric acid; a persulfate initiator such as sodium persulfate, potassium persulfate, or ammonium persulfate; or an organic peroxide initiator such as t-butyl hydroperoxide, dilauroyl peroxide, t-butylperoxy-2-ethylhexanoate, or t-butylperoxypivalate. A redox polymerization initiator may be used, which is a combination of an organic peroxide initiator or a persulfate initiator with a reducing agent such as ascorbic acid, Rongalite, or a metal sulfite. From the viewpoint of the polymerizability of the polymerization component (a2), the amount of the radical polymerization initiator used is preferably 0.1 to 5 mass %, more preferably 0.5 to 2 mass %, based on the polymerization component (a2).

[0057] From the viewpoint of polymerization rate, the polymerization temperature in the polymerization step is preferably 10 to 80°C, more preferably 30 to 60°C. After the end of heat generation, the polymerization is completed by maintaining the temperature at about 40 to 90°C for about 30 minutes to 3 hours. This gives a composite resin-containing aqueous resin dispersion.

[0058] At least a portion of the urethane prepolymer (including a neutralized urethane prepolymer; the same applies hereinafter) may be chain-elongated between the emulsification step and the polymerization step and after the polymerization step. Alternatively, a portion of the urethane prepolymer may be chain-elongated between the emulsification step and the polymerization step, and the remaining urethane prepolymer that has not been chain-elongated in the chain-elongation step may be chain-elongated after the polymerization step. The chain extension reaction of the urethane prepolymer occurs gradually in the emulsion dispersion due to the presence of water as the dispersion medium, and therefore the chain extension reaction may also occur during the polymerization process. Between the emulsification step and the polymerization step, or after the polymerization step, at least a portion of the carboxyl groups of the polyurethane resin (A1) or the urethane prepolymer may be further neutralized with the aforementioned amine compound (hereinafter, this step is referred to as the "second neutralization step"). By achieving a degree of neutralization within a predetermined range, the storage stability of the resulting composite resin-containing aqueous resin dispersion is improved.

[0059] From the viewpoint of the storage stability of the resulting composite resin-containing aqueous resin dispersion, the amount of the amine compound used in the second neutralization step is preferably 0.7 equivalents or more, calculated as the total amount of the amine compound used in the first neutralization step and the amount used in the first neutralization step, relative to all carboxyl groups of the polyurethane resin (A1) or the urethane prepolymer. If 0.7 equivalents or more of the amine compound have already been used in the first neutralization step, the second neutralization step may be omitted.

[0060] The amine compound used in the first and second neutralization steps is preferably used as an aqueous solution or aqueous dispersion from the viewpoint of ease of addition and mixing. The neutralized mixed resin is dissolved or dispersed in water alone, a mixed solvent of a polar organic solvent and water, or an organic solvent. Examples of polar organic solvents include alcohols, ketones, and other organic solvents. Examples of alcohols include alcohols having 1 to 8 carbon atoms such as ethanol, propanol, isopropanol, butanol, benzyl alcohol, and phenylethyl alcohol; and dihydric or higher alcohols such as alkylene glycols such as glycerin, ethylene glycol, and propylene glycol. Examples of ketones include acetone and methyl ethyl ketone. Other organic solvents include, for example, low-boiling hydrocarbons such as pentane; ethers such as diethyl ether and dimethoxymethane; glycol ethers such as mono-, di-, or tri-ethylene glycol monoalkyl ether; and esters such as methyl acetate.

[0061] In the process of producing the composite resin, an emulsifier is used as needed. Examples of the emulsifier include ionic surfactants such as anionic, cationic, and amphoteric surfactants, and nonionic surfactants. The use of an emulsifier can suppress the formation of aggregates during the production process, and may also improve the storage stability of the resulting composite resin-containing aqueous resin dispersion.

[0062] [Physical properties of composite resin] The biomass ratio of the composite resin of the present invention is preferably 20% or more, more preferably 25% or more. A high biomass content makes it possible to produce an environmentally friendly composite resin.

[0063] In the present invention, the "biomass degree" is an index that indicates the mixing ratio of biologically-derived raw materials to non-biologically-derived raw materials, and is determined by the mass ratio of biologically-derived raw materials in a composite resin, and is expressed by the following formula (2). A high biomass degree can result in an environmentally friendly resin. Biomass content (%) = dry mass of biological raw material (g) / dry mass of composite resin (g) × 100 (2)

[0064] [Physical properties of resin (A)] The acid value of the resin (A) can be 0.5 to 60.0 mgKOH / g, and from the viewpoint of stability with the resulting aqueous resin dispersion and the water resistance and solvent resistance of the resulting coating film, it is preferably 37.0 mgKOH / g or more, more preferably 39.0 mgKOH / g or more, and further preferably 50.0 mgKOH / g or less. The upper and lower limits can be combined in any manner, for example, 37.0 to 60.0 mgKOH / g, 39.0 to 60.0 mgKOH / g, or 39.0 to 50.0 mgKOH / g.

[0065] <Crosslinking agent (B)> The aqueous resin dispersion of the present invention contains a resin (A) and a crosslinking agent (B), and the crosslinking agent (B) contains a metal crosslinking agent (B1). The crosslinking agent (B) may contain another crosslinking agent (B2) in addition to the metal crosslinking agent (B1), as needed.

[0066] [Metal-based crosslinking agent (B1)] Examples of the metal-based crosslinking agent (B1) used in the present invention include titanium-based crosslinking agents, aluminum-based crosslinking agents, bismuth-based crosslinking agents, iron-based crosslinking agents, zirconium-based crosslinking agents, tin-based crosslinking agents, zinc-based crosslinking agents, copper-based crosslinking agents, and lead-based crosslinking agents. Among these, titanium-based crosslinking agents and zirconium-based crosslinking agents are preferred, and titanium-based crosslinking agents are more preferred.

[0067] As the titanium-based crosslinking agent, for example, an organic titanium compound such as a chelate complex containing a titanium atom is preferred, and specifically, titanium triethanolaminate, titanium diethanolaminate, titanium aminoethylaminoethanolate, titanium lactate ammonium salt, titanium lactate, and titanium ethylacetoacetate are preferred. Among these, titanium triethanolaminate is more preferred from the viewpoints of the stability of the resulting aqueous resin dispersion and the coating film strength, heat resistance, water resistance, and solvent resistance of the resulting coating film. As the zirconium-based crosslinking agent, for example, an organic zirconium compound such as a chelate complex containing a zirconium atom is preferred, and specifically, a zirconyl chloride compound or zirconium lactate ammonium salt is preferred.

[0068] The content of the metal crosslinking agent (B1) is 0.05 to 10.0 parts by mass, preferably 0.1 to 6.0 parts by mass, and more preferably 0.5 to 4.0 parts by mass, per 100 parts by mass of the resin (A). When the content is within the above range, the stability of the resulting aqueous resin dispersion and the resulting coating film do not change significantly in elongation or strength, and exhibit excellent water resistance and solvent resistance. Furthermore, the content of the metal crosslinking agent (B1) is preferably 0.05 to 10.0 parts by mass, more preferably 0.5 to 5.0 parts by mass, per 100 parts by mass of the polyurethane resin (A1). The content of the metal crosslinking agent (B1) is preferably from 0.01 to 5.0 parts by mass, more preferably from 0.1 to 3.0 parts by mass, relative to 100 parts by mass of the aqueous resin dispersion described below.

[0069] [Other crosslinkers (B2)] As the other crosslinking agent (B2), known crosslinking agents other than the metal-based crosslinking agent (B1) can be used, and examples thereof include melamine compounds, isocyanate compounds, oxazoline compounds, epoxy compounds, oxazoline compounds, carbodiimide compounds, silane coupling compounds, hydrazide compounds, and aziridine compounds. Among these, from the viewpoint of improving the adhesion and durability of the coating film formed by the aqueous coating material described below, melamine compounds, oxazoline compounds, isocyanate compounds, and epoxy compounds are preferred, and melamine compounds, oxazoline compounds, and isocyanate compounds are more preferred. These crosslinking agents may be used alone or in combination of two or more. Using two or more types in combination may further improve adhesion and durability.

[0070] A melamine compound is a compound having a melamine skeleton within the compound, and examples thereof include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohols to partially or completely etherify them, and mixtures thereof. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. The melamine compound may be either a monomer or a dimer or higher polymer, or a mixture thereof. Furthermore, melamine partially co-condensed with urea or the like can also be used, and a catalyst can also be used to increase the reactivity of the melamine compound. Considering the reactivity with various compounds, melamine compounds having a hydroxyl group are preferred.

[0071] The isocyanate compound is an isocyanate compound or a compound having an isocyanate derivative structure, such as a blocked isocyanate compound. Examples of the isocyanate compound include aromatic isocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanate compounds having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanate compounds such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanate compounds such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexyl isocyanate), and isopropylidenedicyclohexyl diisocyanate. Further examples include polymers and derivatives of these isocyanate compounds, such as biuretized products, isocyanurated products, urethodionated products, and carbodiimide-modified products. These may be used alone or in combination of two or more. Among the above isocyanate compounds, aliphatic isocyanate compounds or alicyclic isocyanate compounds are preferred over aromatic isocyanate compounds, from the viewpoint of preventing yellowing of the coating film of the aqueous coating material described below due to ultraviolet rays. The blocked isocyanate compound can be the one that the isocyanate group of the above-mentioned isocyanate compound is blocked with a blocking agent.The blocking agent can be, for example, bisulfites, phenol, cresol, ethylphenol and other phenolic compounds, propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, ethanol and other alcoholic compounds, dimethyl malonate, diethyl malonate, isobutanoyl methyl acetate, methyl acetoacetate, ethyl acetoacetate, acetylacetone and other active methylene compounds, butyl mercaptan, dodecyl mercaptan and other mercaptan compounds, ε-caprolactam, δ-valerolactam and other lactam compounds, diphenylaniline, aniline, ethyleneimine and other amine compounds, acetanilide, acetic acid amide and other acid amide compounds, formaldehyde, acetaldoxime, acetoneoxime, methyl ethyl ketoneoxime, cyclohexanoneoxime and other oxime compounds. These may be used alone or in combination of two or more. As the blocked isocyanate compound, an isocyanate compound blocked with an active methylene compound is preferred from the viewpoint of improving the durability of the coating film formed by the aqueous coating material described below. The isocyanate compound may be used alone or as a mixture or bond with various polymers. In order to improve the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or bond with a polyester resin or a urethane resin.

[0072] The oxazoline compound is a compound having an oxazoline group in the molecule. The oxazoline compound is preferably a polymer containing an oxazoline group. The polymer containing an oxazoline group can be obtained by polymerizing an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of addition-polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. These may be used alone or in combination of two or more. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer is not particularly limited as long as it is a monomer copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include (meth)acrylates such as alkyl(meth)acrylates (the alkyl group is a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, and a cyclohexyl group); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylates Examples of suitable monomers include unsaturated amides such as acrylamide, N-alkyl(meth)acrylamide, and N,N-dialkyl(meth)acrylamide (the alkyl group can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, or a cyclohexyl group); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride, vinylidene chloride, and vinyl fluoride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene. These may be used alone or in combination of two or more. The amount of oxazoline groups per 1 g of the oxazoline compound is preferably in the range of 0.5 to 10 mmol / g, more preferably 1 to 9 mmol / g, even more preferably 3 to 8 mmol / g, and particularly preferably 4 to 6 mmol / g. When the amount of oxazoline groups is within the above range, the durability of the coating film formed by the aqueous coating material described below is improved, and the adhesion can be easily adjusted.

[0073] An epoxy compound is a compound having an epoxy group in the molecule. Examples of epoxy compounds include condensates of epichlorohydrin with compounds having a hydroxyl group or an amino group (ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc.), such as polyepoxy compounds, diepoxy compounds, monoepoxy compounds, and glycidylamine compounds. Examples of polyepoxy compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl)isocyanate, glycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Examples of diepoxy compounds include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether. Examples of monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether. Examples of glycidylamine compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylamino)cyclohexane.

[0074] The carbodiimide compound is a compound having one or more carbodiimide structures or carbodiimide derivative structures in the molecule. From the viewpoint of the strength of the coating film formed by the aqueous coating material described below, the carbodiimide compound is preferably a polycarbodiimide compound having two or more carbodiimide structures or carbodiimide derivative structures in the molecule. Carbodiimide compounds can be synthesized by known methods, and generally involve the condensation reaction of a diisocyanate compound. The diisocyanate compound is not particularly limited, and either an aromatic or aliphatic diisocyanate can be used, such as tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate. In order to improve the water solubility or water dispersibility of the polycarbodiimide-based compound, a surfactant may be added, or a hydrophilic monomer such as a polyalkylene oxide, a quaternary ammonium salt of a dialkylamino alcohol, or a hydroxyalkyl sulfonate may be added, within a range that does not impair the effects of the present invention.

[0075] A silane coupling compound is an organosilicon compound that has an organic functional group and a hydrolyzable group such as an alkoxy group in one molecule. Examples of silane coupling compounds include epoxy group-containing compounds such as 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; vinyl group-containing compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing compounds such as p-styryltrimethoxysilane and p-styryltriethoxysilane; (meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; (meth)acryloyl group-containing compounds such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane; Examples of such compounds include amino group-containing compounds such as N-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane; isocyanurate group-containing compounds such as tris(trimethoxysilylpropyl)isocyanurate and tris(triethoxysilylpropyl)isocyanurate; and mercapto group-containing compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane. Among the above-mentioned compounds, epoxy group-containing silane coupling compounds, double bond-containing silane coupling compounds such as vinyl group and (meth)acrylic group silane coupling compounds, and amino group-containing silane coupling compounds are preferred as the silane coupling compounds from the viewpoint of the strength of the coating film formed by the aqueous coating material described below.

[0076] The aqueous coating material of the present invention contains the aqueous resin dispersion of the present invention. A coating film obtained from the aqueous resin dispersion or the aqueous coating material of the present invention has both water resistance and solvent resistance.

[0077] <Aqueous resin dispersion> The aqueous resin dispersion of the present invention is a dispersion of a resin (A) and a crosslinking agent (B) in an aqueous medium, and examples of such an aqueous medium include water and a mixed solution of water and an organic solvent compatible with water, such as ethanol. Among these, water is preferred from an environmental viewpoint.

[0078] The solids concentration of the aqueous resin dispersion is preferably 10 to 70% by mass, more preferably 20 to 50% by mass, and even more preferably 30 to 50% by mass. If the solids concentration is equal to or greater than the lower limit, it is easy to adjust the viscosity when preparing an aqueous coating material and to adjust the final solids content. If the solids concentration is equal to or less than the upper limit, the resulting coating film has improved density and excellent water resistance and solvent resistance. Furthermore, the particle size of the resin (A) in the aqueous resin dispersion is preferably 10 to 300 nm, more preferably 30 to 200 nm, and even more preferably 50 to 150 nm. If the particle size is equal to or greater than the above lower limit, it is easy to adjust the viscosity and final solid content when preparing an aqueous coating material. If the particle size is equal to or less than the above upper limit, the resulting coating film will have improved density and excellent water resistance and solvent resistance.

[0079] <Water-based coating material> When used as an aqueous coating material, the aqueous resin dispersion of the present invention is contained. The aqueous medium is preferably water. The aqueous coating material of the present invention may contain, in addition to the components contained in the aqueous resin dispersion, components generally contained in aqueous coating materials as necessary. For example, it may contain resins other than the polyurethane resin (A1) and the (meth)acrylate resin (A2), viscosity modifiers, film-forming aids, curing agents, plasticizers, preservatives, antifungal agents, antialgae agents, antibacterial agents, antifoaming agents, leveling agents, coupling agents, surfactants, pigment dispersants, antisettling agents, anti-sagging agents, wetting agents, catalysts, curing accelerators, dehydrating agents, antifoaming agents, matting agents, antifreezing agents, UV absorbers, antioxidants, light stabilizers, water, and solvents. An aqueous coating material may also be prepared by adding a resin to the aqueous resin dispersion.

[0080] <Base material> There are no particular restrictions on the substrate (subject to be coated) to which the coating composition or aqueous coating material of the present invention is applied, and a coating film can be formed by coating on a variety of substrates.

[0081] Examples of substrates include outer panels of automobile bodies and parts, automobile interior substrates, outer panels of household electrical appliances, cement mortar, slate boards, gypsum boards, extruded molded boards, foam concrete, metals, glass, porcelain tiles, asphalt, wood, waterproof rubber materials, plastics, calcium silicate substrates, PVC sheets, FRP (Fiber Reinforced Plastics), natural leather, synthetic leather, and fibers.

[0082] Specific examples include the interior and exterior of passenger cars, trucks, motorcycles and buses, building materials, interior and exterior of buildings, window frames, window glass, structural members, plate materials, exteriors of machinery and goods, bridges, guardrails, tents, greenhouses, blinds, roofing materials, housing equipment, refrigerators, air conditioners, televisions, lighting equipment, kitchen utensils, and functional fibers.

[0083] <Coating film formation method> Methods for applying the aqueous resin dispersion, paint composition, and aqueous coating material of the present invention to the surface of a substrate include various coating methods, such as air spray coating, airless spray coating, rotary atomization coating, curtain coating, roller coating, bar coating, air knife coating, brush coating, dipping coating, etc. The amount of coating is preferably an amount that results in a coating film thickness after drying of 0.1 to 200 μm, more preferably an amount that results in a coating film thickness of 10 to 100 μm, and particularly preferably an amount that results in a coating film thickness of 20 to 70 μm.

[0084] A coating film is formed when the applied aqueous resin dispersion, paint composition, or aqueous coating material is dried. Drying may be performed at room temperature, such as 0 to 40°C, or by heating to a higher temperature. From the viewpoint of film-forming properties, the drying temperature is preferably 20 to 100°C.

[0085] By heat drying, the coating film can be formed by heating the coating film by a known means. As the heating means, for example, a heating furnace such as a hot air furnace, an electric furnace, or an infrared induction heating furnace can be used. Furthermore, a different type of paint may be further applied as a topcoat on the coating film, and a solvent-based paint is preferred as the topcoat, as the coating film tends to prevent phase mixing. [Example]

[0086] EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. In the examples, "parts" means "parts by mass". The physical property tests of the aqueous resin dispersions in the examples were carried out by the methods described below.

[0087] <Ingredients> [Polyol (a1-1)] NL2000D: Polycarbonate diol containing 87.2% by mass of a structure derived from 1,10-decanediol with a number average molecular weight of 2,000 (manufactured by Mitsubishi Chemical Corporation, product name "BENEBiOL NL2000D") 1,10-DD: 1,10-decanediol (Toyokuni Oil Mills) Bis-MPA: Dimethylolpropionic acid, a diol containing a carboxylic acid (manufactured by Perstorp Japan Co., Ltd.)

[0088] [Polyisocyanate (a1-2)] IPDI: Isophorone diisocyanate (manufactured by Evonik Japan Co., Ltd., product name "VESTANAT IPDI")

[0089] [(Meth)acrylate (a2-1)] MMA: Methyl methacrylate (Mitsubishi Chemical Corporation) BA: n-butyl acrylate (Mitsubishi Chemical Corporation)

[0090] [Metal-based crosslinking agent (B1)] TC-400: Titanium diisopropoxybis(triethanolaminate) (manufactured by Matsumoto Fine Chemical Co., Ltd., trade name "Orgatics TC-400")

[0091] [Preparation of coated panels for evaluating water resistance and solvent resistance] The aqueous resin dispersion obtained in the examples was applied to a black acrylic plate (manufactured by TP Giken Co., Ltd., plate thickness 2 mm, length 150 mm, width 70 mm) using a bar coater so that the film thickness after drying would be 30 μm, and the plate was dried at 60°C for 30 minutes to prepare a coated plate for evaluating water resistance and solvent resistance.

[0092] [Preparation of film for evaluating film strength] The aqueous resin dispersion obtained in each example was applied to a polypropylene plate so that the film thickness after drying would be 200 μm, and the coating was dried at room temperature for 12 hours or more, and then dried at 60°C for 30 minutes. The coating was then peeled off from the polypropylene plate and punched out with a No. 3 dumbbell to prepare a film for evaluating film strength and elongation.

[0093] <Evaluation method> (1) Acid value The acid value of the resulting urethane resin was calculated as follows. The "theoretical acid value" per 1 g of polyurethane resin can be calculated according to the following formula. *Theoretical acid value (mgKOH / g) = (number of moles of acid-containing raw material charged x 56.1 (molecular weight of KOH) / amount of polyurethane resin (g)) x 1000

[0094] (2) Water resistance The obtained coated plates for evaluation were immersed in warm water at 40°C for 16 hours, and the whitening degree ΔL of the coating film 24 hours after being removed from the water compared to the coating film before immersion was measured using a color difference meter (manufactured by Konica Minolta Japan, Inc., product name "CR-300") and evaluated according to the following evaluation criteria. (Evaluation criteria) A: ΔL is greater than -2.0 and less than or equal to 2.0. B: ΔL is greater than −4.0 and equal to or less than −2.0, or greater than 2.0 and equal to or less than 3.0. C: ΔL is −4.0 or less or greater than 3.0.

[0095] (3) Solvent resistance The obtained coated evaluation plate was manually rubbed 10 times with a cotton cloth soaked in butyl acetate, and then the appearance was visually evaluated according to the following evaluation criteria. (Evaluation criteria) A: No change in appearance or slight scratches B: Scratched C: Peeling

[0096] (4) Film strength and elongation The resulting films for evaluation of film strength and elongation were measured for breaking elongation and breaking stress using a tensile tester (Shimadzu Corporation, product name "Autograph AG-X·plus") at a chuck distance of 20 mm and a pulling speed of 200 mm / min, and evaluated according to the following evaluation criteria. (Evaluation criteria) A: Breaking elongation of 100% or more and breaking stress of 20 MPa or more B: Breaking elongation of 100% or more and breaking stress of less than 20 MPa C: Breaking elongation less than 100% and breaking stress less than 20 MPa

[0097] (5) Storage stability The obtained aqueous resin dispersion was stored at 50°C for 4 days, and the viscosity (rotation speed 60 rpm, 23°C) before and after storage was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., product name "TVB-10 Viscometer"), and the viscosity change rate calculated using the following formula was evaluated according to the following evaluation criteria. (Evaluation criteria) A: Viscosity change rate is 0-100% B: Viscosity change rate is 100-500% C: Viscosity change rate is 500% or more D: Viscosity measurement after storage is not possible due to solidification or separation * Viscosity change rate (%) = (viscosity after storage - viscosity before storage) / viscosity before storage

[0098] [Method for producing resin (A)] Resin (A) includes the composite resin in the composite resin-containing aqueous resin dispersion obtained by the following production example. (Production Example 1) Into a four-neck flask equipped with a thermometer, a stirrer, and a reflux condenser, 118.84 parts of MMA, 50.93 parts of BA, 91.62 parts of NL2000D, 16.90 parts of Bis-MPA, 1.25 parts of 1,10-decanediol, 60 parts of IPDI, and 0.03 parts of hydroquinone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization inhibitor were added, and the mixture was mixed at an internal temperature of 50°C. The mixture was then heated to 90°C and reacted at this temperature for 3 hours to obtain a polyurethane resin having isocyanate groups and carboxyl groups. Next, while maintaining the liquid temperature at 50° C., triethylamine was added as a neutralizing agent in an amount equivalent to 1 equivalent of the carboxyl groups of the polyurethane resin to neutralize it. Next, 553.2 parts of ion-exchanged water was added dropwise to this solution at 40° C. over 15 minutes to obtain a milky white, transparent dispersion. The obtained dispersion was kept at 50°C, and at this temperature, 1.21 parts of t-butyl hydroperoxide (manufactured by Arkema Yoshitomi Co., Ltd., trade name "Luperox TBH") as a polymerization initiator and 0.42 parts of L-ascorbic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a reducing agent were added to initiate polymerization of the (meth)acrylate. After the heat generation had ceased, the temperature was further raised to 70°C and maintained at this temperature for 3 hours to obtain an aqueous resin dispersion containing a composite resin of polyurethane resin and (meth)acrylate resin.

[0099] (Production Example 2) A four-neck flask equipped with a thermometer, a stirrer, and a reflux condenser was charged with 84.23 parts of MMA, 36.1 parts of BA, 98.43 parts of NL2000D, 17.74 parts of Bis-MPA, 1.32 parts of 1,10-decanediol, 63 parts of IPDI, and 0.02 parts of hydroquinone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization inhibitor. The mixture was mixed at an internal temperature of 50°C, then heated to 90°C, and reacted at this temperature for 3 hours to obtain a polyurethane resin having isocyanate groups and carboxyl groups. Next, while maintaining the liquid temperature at 50° C., triethylamine was added as a neutralizing agent in an amount equivalent to 1% of the carboxyl group equivalent of the polyurethane resin to neutralize it. Next, 488.02 parts of ion-exchanged water was added dropwise to this solution at 40° C. over 15 minutes to obtain a milky white, transparent dispersion. The obtained dispersion was kept at 50°C, and at this temperature, 0.86 parts of t-butyl hydroperoxide (manufactured by Arkema Yoshitomi Co., Ltd., trade name "Luperox TBH") as a polymerization initiator and 0.30 parts of L-ascorbic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a reducing agent were added to initiate polymerization of the (meth)acrylate. After the heat generation had ceased, the temperature was further raised to 70°C and maintained at this temperature for 3 hours to obtain an aqueous resin dispersion containing a composite resin of polyurethane resin and (meth)acrylate resin.

[0100] The composition of the raw materials used for Resin A produced in Production Example 1 or Production Example 2 is shown in Table 1.

[0101] [Table 1]

[0102] The composition shown in Table 1 is the content of each raw material when the total mass of the raw materials used in the production of Resin A is taken as 100 parts by mass.

[0103] [Method for producing aqueous resin dispersion] (Examples 1 to 4, Comparative Examples 1 and 2) To 100 parts of the composite resin-containing aqueous resin dispersion produced by the production example shown in Table 2, TC-400 was added in the amount shown in Table 2, and the resulting aqueous resin dispersion was subjected to various evaluations. The results are shown in Table 3.

[0104] [Table 2]

[0105] In Table 2, the content (parts by mass) refers to the mass of the metal-based crosslinking agent (B1) added per 100 parts by mass of the composite resin-containing aqueous resin dispersion of each example. (B1) / (A) refers to the content of the metal-based crosslinking agent (B1) per 100 parts by mass of the resin (A) in the aqueous resin dispersion. (B1) / (A1) refers to the content of the metal-based crosslinking agent (B1) per 100 parts by mass of the resin (A1) in the aqueous resin dispersion. The masses of the metal-based crosslinking agent (B1), resin (A), and polyurethane resin (A1) used to calculate the content of the metal-based crosslinking agent (B1), (B1) / (A), and (B1) / (A1) are calculated as pure contents.

[0106] [Table 3]

[0107] As is clear from Table 3, the aqueous resin dispersions of Examples 1 to 4 had excellent storage stability. The coated plates obtained from the aqueous resin dispersions of Examples 1 to 4 had excellent water resistance and solvent resistance 24 hours after being pulled out. The films obtained from the aqueous resin dispersions of Examples 1 to 4 had excellent film strength and elongation. On the other hand, the aqueous resin dispersion of Comparative Example 1, in which the content of the metal crosslinking agent (B1) was more than 10.0 parts by mass per 100 parts by mass of the resin (A), was poor in storage stability. The coated plate obtained from the aqueous resin dispersion of Comparative Example 2, which did not contain the metal crosslinking agent (B1), was poor in water resistance 24 hours after being pulled out.

Claims

1. An aqueous resin dispersion containing a resin (A) and a crosslinking agent (B), the resin (A) contains a polyurethane resin (A1) having an acid value of 0.5 to 60.0 mgKOH / g, the crosslinking agent (B) contains a metal-based crosslinking agent (B1), The aqueous resin dispersion has a content of the metal-based crosslinking agent (B1) of 0.05 to 10.0 parts by mass relative to 100 parts by mass of the resin (A).

2. 2. The aqueous resin dispersion according to claim 1, wherein the polyurethane resin (A1) has an acid value of 35.0 to 60.0 mgKOH / g.

3. The aqueous resin dispersion according to claim 1 or 2, wherein the resin (A) contains a (meth)acrylate resin (A2).

4. The aqueous resin dispersion according to claim 3 , wherein the resin (A) contains a composite resin consisting of the polyurethane resin (A1) and the (meth)acrylate resin (A2).

5. The aqueous resin dispersion according to claim 1 or 2, wherein the polyurethane resin (A1) has a structure derived from a polycarbonate polyol.

6. 3. The aqueous resin dispersion according to claim 1, wherein the content of the metal crosslinking agent (B1) is 0.05 to 6.0 parts by mass per 100 parts by mass of the polyurethane resin (A1).

7. 3. The aqueous resin dispersion according to claim 1, wherein the metal-based crosslinking agent (B1) is at least one selected from the group consisting of a titanium-based crosslinking agent, an aluminum-based crosslinking agent, a bismuth-based crosslinking agent, an iron-based crosslinking agent, a zirconium-based crosslinking agent, a tin-based crosslinking agent, a zinc-based crosslinking agent, a copper-based crosslinking agent, and a lead-based crosslinking agent.

8. An aqueous coating material comprising the aqueous resin dispersion according to claim 1 or 2.

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