Water-dispersible resin and aqueous coating composition

Abstract

To provide a water-dispersible resin which enables formation of a coating film that uses a non-nonylphenol-based emulsifier, has reduced environmental loads, and is excellent in hot water whitening resistance and weather resistance, and an aqueous coating composition using the same.SOLUTION: A water-dispersible resin, which uses a non-nonylphenol-based emulsifier (A) and a polymerizable unsaturated monomer (B) and is obtained by an emulsification polymerization method, has at least one of the following items (1) to (3) that specify the invention. (1) The water-dispersible resin contains a crosslinking agent (C). (2) The water-dispersible resin has a hetero-phase structure. (3) In the polymerizable unsaturated monomer (B), 70 to 100 mass% of an acrylic monomer is contained.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-dispersible resin and an aqueous coating composition. [Background technology]

[0002] Conventionally, acrylic emulsions, which have been widely used as binder resins for water-based paints, have excellent properties such as water resistance and recoatability, and are widely used for building materials, construction, etc. In the production of such acrylic emulsions, nonylphenol-based emulsifiers are widely used because of their excellent polymerizability, stability, and durability of the resulting coating film.

[0003] Patent Document 1 is an invention relating to a resin composition for water-based paints that contains almost no volatile organic compounds such as organic solvents, has excellent stability, and forms a coating film that is excellent in blocking resistance, water resistance, etc. The examples in Patent Document 1 show that a resin for water-based paints that is excellent in all tests of base powder mixing stability, blocking resistance, and warm water resistance can be obtained, but the emulsifiers used all contain nonylphenol-based emulsifiers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-256202 A Summary of the Invention [Problem to be solved by the invention]

[0005] As shown in Patent Document 1, nonylphenol-based emulsifiers are suitable for providing resins for water-based paints that are excellent in both stability and coating film performance, but they have issues such as environmental impact. In response to this, various non-nonylphenol-based emulsifiers that do not contain nonylphenol have been developed, but when used in place of conventional nonylphenol-based emulsifiers, they sometimes result in inferior water whitening resistance (especially warm water whitening resistance) and weather resistance of the coating film.

[0006] Therefore, an object of the present invention is to provide a water-dispersible resin which uses a non-nonylphenol emulsifier and is capable of forming a coating film which has low environmental impact and is excellent in resistance to water-whitening (especially resistance to hot water-whitening) and weather resistance, and an aqueous coating composition to which this water-dispersible resin is applied. [Means for solving the problem]

[0007] (I) A water-dispersible resin obtained by an emulsion polymerization method using a non-nonylphenol emulsifier (A) and a polymerizable unsaturated monomer (B), A water-dispersible resin having at least one of the following invention-specific features (1) to (3): Note (1) The water-dispersible resin contains a crosslinking agent (C). (2) The water-dispersible resin has a heterophase structure. (3) The polymerizable unsaturated monomer (B) contains 70 to 100% by mass of an acrylic monomer.

[0008] (II) An aqueous coating composition comprising the water-dispersible resin described in (I) above, the aqueous coating composition further comprising a pigment (D). (III) The aqueous coating composition according to the above (II), wherein the pigment (D) is a surface-coated pigment that is surface-coated with a metal or a metal oxide. Effect of the Invention

[0009] According to the present invention, it is possible to provide a water-dispersible resin which uses a non-nonylphenol emulsifier and is capable of forming a coating film which has low environmental impact and is excellent in resistance to hot water whitening and weather resistance, and an aqueous coating composition to which this water-dispersible resin is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The water-dispersible resin and the aqueous coating composition of the present invention will be described in detail below. Note that the water-dispersible resin and the aqueous coating composition of the present invention can be embodied in various ways from the following description, and are not limited to the description.

[0011] The present invention relates to a water-dispersible resin obtained by emulsion polymerization using a non-nonylphenol emulsifier (A) and a polymerizable unsaturated monomer (B), the water-dispersible resin having at least one of the following invention-specific features (1) to (3): (1) The water-dispersible resin contains a crosslinking agent (C). (2) The water-dispersible resin has a heterophase structure. (3) The polymerizable unsaturated monomer (B) contains 70 to 100 mass % of an acrylic monomer.

[0012] <Emulsion polymerization method> The water-dispersible resin of the present invention can be produced by emulsion polymerization using a non-nonylphenol emulsifier (A) and a polymerizable unsaturated monomer (B) in an aqueous solvent. Methods for making the water-dispersible resin have a heterophase structure include known polymerization methods such as seed polymerization and multi-stage emulsion polymerization.

[0013] <Water-based solvent> The water-based solvent is not particularly limited to water, but preferably includes pure water such as tap water, ion-exchanged water, and distilled water. A small amount of organic solvent may be blended into the water-based solvent. The organic solvent is not particularly limited, and organic solvents commonly used in the paint industry can be used. As the solvent, organic solvents having polarity that can be mixed with water are preferred, and examples thereof include alcohol-based solvents, ketone-based solvents, ester-based solvents, ether-based solvents, and hydrocarbon-based solvents. In the water-dispersible resin of the present invention, the amount of the organic solvent is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass. The organic solvent may be used alone or in combination of two or more kinds. When the water-dispersible resin is to be stored for a long period of time, water that has been sterilized by ultraviolet irradiation or the like may be used to prevent the growth of mold or bacteria. In the aqueous coating composition of the present invention, the amount of water is preferably 20 to 90 mass %.

[0014] The water-dispersible resin of the present invention has at least one of the features (1) to (3) specific to the invention, which will be described below. <Crosslinking agent (C)> The water-dispersible resin of the present invention contains a crosslinking agent as one of the features specifying the invention, that is, feature (1). By including a crosslinking agent, the crosslinked structure between the polymers when the coating is formed makes the polymer network dense, preventing the intrusion of moisture into the coating and improving the hot water whitening resistance of the coating. In addition, even if the polymer chain is cut by ultraviolet rays or the like, the dense polymer network is less likely to collapse, improving weather resistance.

[0015] <Heterogeneous Phase Structure> The water-dispersible resin of the present invention has a heterophase structure as one of the features specific to the invention, which is feature (2). The heterogeneous phase structure includes a core-shell structure in which an emulsion is formed from a structure having an outermost phase and one or more internal phases, a sea-island structure containing heterogeneous phases within a particle, and a power-feed structure containing a composition gradient within a particle. By making the particle structure a heterogeneous phase structure, each phase can take on conflicting functions, thereby improving performance compared to a homogeneous structure. For example, in a core-shell two-phase structure, the hardness of the coating film can be increased by hardening the shell phase, which can prevent damage to the coating film and improve the hot water whitening resistance and weather resistance. The flexibility of the coating film can be increased by softening the core phase, which can prevent damage due to deformation of the coating film and improve the hot water whitening resistance and weather resistance.

[0016] <Acrylic monomer> The water-dispersible resin of the present invention contains, as one of the invention-specifying features (3), 70 to 100 mass % of an acrylic monomer in the polymerizable unsaturated monomer (B). The water-dispersible resin of the present invention has a polymer chain composed of 70 to 100% acrylic monomer, which reduces absorption of ultraviolet rays and makes the polymer chain less susceptible to scission due to ultraviolet rays, thereby improving weather resistance.

[0017] The emulsion in the water-dispersible resin of the present invention preferably has a volume average particle diameter of 30 to 300 nm, more preferably 50 to 200 nm. By adjusting the volume average particle diameter of the water-dispersible resin of the present invention to 30 to 300 nm, the dispersion stability in an aqueous medium can be improved, and the hot water whitening resistance and weather resistance of the formed coating film can be improved.

[0018] <Non-nonylphenol emulsifier (A)> The water-dispersible resin of the present invention can use a reactive emulsifier having one or more radically polymerizable unsaturated groups of a non-nonylphenol structure and a non-reactive emulsifier that does not have polymerizability. By using a reactive emulsifier having one or more polymerizable unsaturated groups, the emulsifier contributes to the dispersion stability of the water-dispersible resin, and it becomes easier to obtain a coating film that is excellent in hot water whitening resistance, weather resistance, etc. Furthermore, by using a non-reactive emulsifier, the water-dispersible resin is more likely to fuse during the formation of a coating film. In the emulsion polymerization method, one or more of these non-nonylphenol emulsifiers (A) are used in combination. Examples of the non-nonylphenol emulsifier include anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, amphoteric emulsifiers, and polymeric emulsifiers.

[0019] Examples of anionic emulsifiers include alkyl sulfonate salts such as sodium alkyl diphenol ether disulfonate, ammonium dodecyl sulfonate, and sodium dodecyl sulfonate; alkyl aryl sulfonate salts such as ammonium dodecyl benzene sulfonate and sodium dodecyl naphthalene sulfonate; polyoxyethylene alkyl sulfonate salts; dialkyl sulfosuccinate salts; aryl sulfonic acid formalin condensates; fatty acid salts such as ammonium laurate and sodium stearylate; bis(polyoxyethylene polycyclic phenol ether) methacrylate sulfonate salts, and propenyl- Preferred examples of the sulfuric acid ester (salt) having an allyl group include alkyl sulfosuccinate salts, polyoxyethylene sulfonate (meth)acrylate salts, polyoxyethylene phosphonate (meth)acrylate salts, sulfonate salts of allyloxymethyl alkyloxy polyoxyethylene, sulfate salts of allyloxymethyl alkoxyethyl polyoxyethylene, ammonium polyoxyalkylene alkenyl ether sulfate, sodium alkyl allyl sulfosuccinate, sodium methacryloyl polyoxyalkylene sulfate, and 2-dimethylaminoethyl methacrylate salts of polyoxyethylene polycyclic phenyl ether sulfate.

[0020] Suitable examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, condensates of polyethylene glycol and polypropylene glycol; sorbitan fatty acid esters; polyoxyethylene sorbitan fatty acid esters; fatty acid monoglycerides; polyoxyalkylene decyl ethers, polyoxyethylene styrenated phenol ethers; condensation products of ethylene oxide and aliphatic amines; allyloxymethylalkoxyethylhydroxypolyoxyethylene, polyoxyalkylene alkenyl ethers, and the like.

[0021] As the cationic emulsifier, an alkyl ammonium salt such as dodecyl ammonium chloride is preferable. As the amphoteric emulsifier, a betaine ester type emulsifier or the like is preferable. Suitable polymer emulsifiers include poly(meth)acrylates such as sodium polyacrylate; polyvinyl alcohol; polyvinylpyrrolidone; polyhydroxyalkyl(meth)acrylates such as polyhydroxyethyl acrylate; and copolymers containing one or more of the polymerizable monomers that constitute these polymers as copolymerization components.

[0022] As the non-nonylphenol emulsifier, it is preferable to use an emulsifier having a polymerizable group such as a vinyl group, an allyl group, a (meth)acryloyl group, or a propenyl group, particularly when hot water whitening resistance and weather resistance are important. Suitable anionic emulsifiers include, for example, bis(polyoxyethylene polycyclic phenol ether) methacrylated sulfonate salts, propenyl-alkyl sulfosuccinate salts, polyoxyethylene (meth)acrylate sulfonate salts, polyoxyethylene (meth)acrylate phosphonate salts, sulfate salts having an allyl group such as sulfonate salts of allyloxymethyl alkyloxy polyoxyethylene, sulfate salts of allyloxymethyl alkoxyethyl polyoxyethylene, polyoxyalkylene alkenyl ether ammonium sulfate, sodium alkyl allyl sulfosuccinate methacryloyl polyoxyalkylene sulfate sodium salt, and 2-dimethylaminoethyl methacrylate salts of polyoxyethylene polycyclic phenyl ether sulfate esters. Suitable nonionic emulsifiers include allyloxymethylalkoxyethylhydroxypolyoxyethylene, polyoxyalkylene alkenyl ether, and the like.

[0023] The amount of the non-nonylphenol emulsifier added is preferably 0.1% by mass or more based on the total amount of polymerizable unsaturated monomers. It is preferably 0.5% by mass or more, and more preferably 1% by mass or more. On the other hand, it is preferably 10% by mass or less based on the total amount of polymerizable unsaturated monomers. If it exceeds 10% by mass, it may lead to a decrease in hot water whitening resistance and weather resistance.

[0024] <Polymerizable unsaturated monomer (B)> The "polymerizable unsaturated monomer" is a monomer having an unsaturated group that undergoes a polymerization reaction, and examples of the polymerizable unsaturated group include a carbon-carbon double bond that constitutes an acryloyl group, a methacryloyl group, a vinyl group, or an allyl group. The "monomer having a polymerizable unsaturated group" is a monomer that undergoes a polymerization reaction via the polymerizable unsaturated group.

[0025] Examples of the polymerizable unsaturated monomer (B) include (meth)acrylic acid alkyl esters, (meth)acrylates having a hydroxyl group, (meth)acrylates having an acidic functional group, vinyl compounds, polymerizable monomers having an epoxy group, ultraviolet absorbing polymerizable monomers, etc. These polymerizable unsaturated monomers (B) may be used alone or in combination of two or more kinds.

[0026] Specific examples include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tridecyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, n-lauryl (meth)acrylate, benzyl (meth)acrylate, and 2-(acetoacetoxy)ethyl (meth)acrylate; (meth)acrylic acid alkyl esters having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and (meth)acrylic acid alkyl esters having a hydroxyl group and (meth)acrylates having an acidic functional group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. meth)acrylates, ethylene glycol (meth)acrylate, ethylene glycol methoxy (meth)acrylate, diethylene glycol (meth)acrylate, diethylene glycol methoxy (meth)acrylate, and other polymerizable monomers having an oxo group; styrene, α-methylstyrene, vinyl toluene, divinyl benzene, and other vinyl compounds; vinyl esters, such as vinyl acetate; trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, and other fluorine-containing polymerizable monomers; (meth)acrylamide, N,N-dimethylaminopropylacrylamide, N-vinylpyrrolidone, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, diacetone acrylamide, 2-isopropenyl-2-oxazoline, and other nitrogen-containing polymerizable monomers; and glycidyl (meth)acrylate, and other polymerizable monomers having an epoxy group.2-[2'-hydroxy-5'-(meth)acryloyloxyethylphenol]-2H-benzotriazole, 2-[2'-hydroxy-3'-tert-butyl-5'-(meth)acryloyloxyethylphenol]-2H-benzotriazole, 2-hydroxy-4-(2-hydroxy-3-methacryloyloxypropoxy)benzophenone, 2-hydroxy-4-(2-(meth)acryloyloxyethoxy)benzyl UV-absorbing polymerizable monomers such as benzophenone; UV-stable polymerizable monomers such as 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, and 4-(meth)acryloylamino-1,2,2,6,6-pentamethylpiperidine; and the like.

[0027] <Crosslinking agent (C)> The water-dispersible resin of the present invention may contain one or more crosslinking agents (C). As the crosslinking agent (C), it is preferable to use at least one selected from a glycidyl group-containing compound, a hydrazide group-containing compound, a semicarbazide group-containing compound, a carbodiimide compound, an oxazoline compound, and an isocyanate compound. It is preferable to contain the crosslinking agent (C) in an amount of 0.1 to 10 mass% based on the total amount of the polymerizable unsaturated monomer (B).

[0028] Examples of the glycidyl group-containing compound include glycidyl ether compounds such as diglycidyl ether, 2-glycidylphenol glycidyl ether, and 2,6-diglycidylphenol glycidyl ether; epoxy resins having a glycidyl ether group or a glycidyl ester group, such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, cresol novolac type epoxy resin, and phenol novolac type epoxy resin; and glycidyl group-containing polymerizable unsaturated monomers such as glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether. Examples of the hydrazide group-containing compound include dihydrazides of saturated aliphatic carboxylic acids having 2 to 18 carbon atoms, such as oxalic acid dihydrazide, malonic acid dihydrazide, adipic acid dihydrazide, and sebacic acid dihydrazide; dihydrazides of monoolefinically unsaturated dicarboxylic acids, such as maleic acid dihydrazide and itaconic acid dihydrazide; dihydrazides of phthalic acid, terephthalic acid, or isophthalic acid; and polyhydrazides obtained by reacting a low polymer having a carboxylic acid lower alkyl ester group with hydrazine or hydrazine hydrate. The semicarbazide compound is a compound derived from hydrazine and an isocyanate compound, i.e., a reaction product between hydrazine and an isocyanate compound. The semicarbazide group-containing compound may have two or more amino groups or two or more semicarbazide groups.

[0029] Examples of the carbodiimide compound include carbodiimide compounds such as N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimide, N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimide methiodide, N-tert-butyl-N'-ethylcarbodiimide, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide meso-p-toluenesulfonate, N,N'-di-tert-butylcarbodiimide, and N,N'-di-p-tolylcarbodiimide; carbodiimide compounds obtained by a known condensation reaction of polyisocyanate in the presence of a carbodiimidization catalyst; and carbodiimide compounds using polyisocyanate and polyalkylene oxide as raw materials. The carbodiimide compound is desirably water-soluble or water-dispersible, but is not particularly limited. Examples of the oxazoline compound include low molecular weight poly(1,3-oxazoline) compounds such as 2,2'-p-phenylene-bis-(1,3-oxazoline) and 2,2'-tetramethylene-bis-(1,3-oxazoline); and homopolymers of 1,3-oxazoline group-containing vinyl monomers such as 2-isopropenyl-1,3-oxazoline. Examples of the isocyanate compound include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates.

[0030] <Reaction initiator> A reaction initiator can be used for the water-dispersible resin of the present invention. Examples of the reaction initiator to be used include organic reaction initiators such as hydroperoxides such as hydrogen peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, and paramenthane hydroperoxide, peroxides such as benzoyl peroxide and lauroyl peroxide, and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile) and azobisisobutyronitrile, as well as inorganic reaction initiators such as persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate. In addition, so-called redox reaction initiators can be used in which a reducing agent such as sodium bisulfite, ascorbic acid, and its salts are used in combination with a reaction initiator. Among them, reaction initiators that have the effect of reducing the ionic strength of the emulsion polymerization reaction system (aqueous phase of the emulsion) are preferred. For example, persulfates such as ammonium persulfate and potassium persulfate are preferably used. In particular, ammonium persulfate is preferably used.

[0031] <Chain transfer agent> A chain transfer agent can be used for the water-dispersible resin of the present invention. Examples of the chain transfer agent include long-chain alkyl mercaptans such as n-dodecyl mercaptan, aromatic mercaptans, halogenated hydrocarbons, etc. Examples of the emulsion stabilizer include polyvinyl alcohol, hydroxyethyl cellulose, polyvinylpyrrolidone, etc.

[0032] The water-dispersible resin of the present invention may contain known additives, such as an antifoaming agent, a preservative, an antifungal agent, a pH adjuster, a thickener, a freeze stabilizer, a wetting agent, an ultraviolet absorber, a light stabilizer, a dispersant, and an anti-settling agent, if necessary.

[0033] <Water-based paint composition> The water-dispersible resin of the present invention can be applied to an aqueous coating composition. The "aqueous coating composition" in the present invention is a water-based coating containing water as a main solvent. The aqueous coating composition of the present invention is excellent in hot water whitening resistance and weather resistance. The water used in the aqueous coating composition of the present invention is not particularly limited, and preferred examples include tap water, ion-exchanged water, distilled water, and other pure water. Water sterilized by ultraviolet irradiation or the like may also be used. In the aqueous coating composition of the present invention, the amount of the aqueous solvent is preferably 20 to 90% by mass, and more preferably 30 to 80% by mass.

[0034] The aqueous coating composition of the present invention can be used as a clear coating, and also as a normal colored coating containing a pigment or the like. The aqueous coating composition of the present invention can be applied to either an undercoat layer or a topcoat layer on a substrate. Furthermore, the aqueous coating composition of the present invention can be applied to various substrates such as inorganic, metal, wood, plastic, etc. By natural or forced drying, it is possible to form a coating film having excellent resistance to hot water whitening and weather resistance.

[0035] In addition, in order to impart various functions as a paint, if necessary, known additives such as an antifoaming agent, a preservative, an antifungal agent, a thickener, a freeze stabilizer, a wetting agent, an ultraviolet absorber, a light stabilizer, and further, when a pigment is blended, a dispersant, an anti-settling agent, etc. can be blended to use the composition as an aqueous paint composition.

[0036] <Pigment (D)> The aqueous coating composition of the present invention may contain a pigment (D). The pigment (D) may include an extender pigment, a coloring pigment, an anti-rust pigment, a luster pigment, etc., depending on the application.

[0037] <Extender pigment> The extender pigment is a white or colorless pigment. Since the refractive index is low, even if it is mixed with a vehicle, it hardly affects the hiding power, and therefore it can be used as an extender, and is also used to reduce costs and adjust coloring power, gloss, strength, usability, coating film performance, etc. Known materials can be used as the extender pigment, and examples of such materials include precipitated barium sulfate, silica, cristobalite, calcium carbonate, alumina, alum, white clay, magnesium hydroxide, and magnesium oxide. The extender pigment may also be a pigment having a thin, flat shape like a foil (a scale-like pigment), and specific examples of such materials include glass flake, talc, mica, and kaolin clay.

[0038] <Coloring pigments> The color pigments in the aqueous coating composition of the present invention are roughly classified into inorganic pigments and organic pigments based on their composition. Examples of inorganic pigments include titanium oxide, red iron oxide, yellow iron oxide, and carbon black, while examples of organic pigments include phthalocyanine blue, phthalocyanine green, naphthol red, quinacridone red, benzimidazolone yellow, Hansa yellow, benzimidazolone orange, and dioxazine violet.

[0039] <Brilliant Pigments> The luster pigment in the aqueous coating composition of the present invention includes scaly metal pigments of metals such as zinc, nickel, chromium, tin, copper, silver, platinum, gold, and aluminum, which are thin and flat like foil, and pearl pigments in which talc or mica is surface-treated with a metal oxide such as titanium oxide. The scaly metal pigments also include alloy pigments such as stainless steel. These luster pigments may be used alone or in combination of two or more.

[0040] <Surface coating pigment> When titanium oxide is used as the color pigment in the present invention, it is preferable to use a surface-coated pigment that has been surface-treated (surface-coated) with a metal oxide. The metal oxide that is used to surface-treat (surface-coat) titanium oxide is alumina, silica, zirconia, etc. From the viewpoint of improving the weather resistance of the paint, alumina and silica are preferred.

[0041] <Other resins> The aqueous coating composition of the present invention can be used by mixing with other resins. The resin to be mixed can be any resin that is commonly used, such as acrylic resin, silicone resin, acrylic silicone resin, styrene-acrylic copolymer resin, polyester resin, fluororesin, rosin resin, petroleum resin, coumarone resin, phenolic resin, urethane resin, melamine resin, urea resin, epoxy resin, cellulose resin, xylene resin, alkyd resin, aliphatic hydrocarbon resin, butyral resin, maleic acid resin, fumaric acid resin, vinyl resin, amine resin, ketimine resin, etc. These resins can be used alone or in combination of two or more.

[0042] <Other ingredients> Furthermore, the aqueous coating composition of the present invention can appropriately contain other components such as pigments, other resins (including water-soluble resins), organic solvents, surface conditioners, wetting agents, dispersants, emulsifiers, thickeners, anti-settling agents, anti-skinning agents, anti-sagging agents, defoamers, color separation inhibitors, viscosity adjusters, rheology control agents, leveling agents, drying agents, plasticizers, preservatives, anti-fungal agents, antibacterial agents, insecticides, antiviral agents, neutralizing agents, pH adjusters, ultraviolet absorbers, flash rust inhibitors, radical scavengers, antistatic agents, and conductivity imparting agents depending on the purpose.

[0043] (Painting method) The present invention is a coating method for coating a substrate with the above-described aqueous coating composition. The coating method for the aqueous coating composition in the present invention is not particularly limited, and includes known coating methods such as brush, roller, air spray, airless spray, dipping, spin coating, flow coating, roll coating, blade coating, and air knife coating. The amount of the aqueous coating composition of the present invention to be applied can be varied depending on the type of substrate to be coated and the intended use.

[0044] <Painted body> The aqueous coating composition of the present invention can be applied to a substrate to form a coated body. The coating material forming the coated body may be one layer or two or more layers, and the aqueous coating composition of the present invention can be suitably used as an undercoat coating, an intermediate coating, or a topcoat coating. In the coated body of the present invention, examples of the substrate include plastic substrates such as epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, acrylic resin, such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyolefin, such as polypropylene (PP), steel, zinc-plated steel, tin-plated steel, stainless steel, magnesium alloy, aluminum, aluminum alloy, titanium, titanium alloy, and other metal substrates, such as cement, mortar, concrete, slate, gypsum, calcium silicate, glass, ceramic, calcium carbonate, marble, and artificial marble, and other inorganic substrates other than metals, such as wood substrates, and composite substrates such as a combination of two or more of these substrates. Examples of the composite substrate include composite substrates such as wood fiber reinforced cement boards, fiber reinforced cement boards, and fiber reinforced cement-calcium silicate boards, metal substrates that have been subjected to various surface treatments, such as oxidation treatments, and plastic substrates whose surfaces are coated with an inorganic substance (for example, plastic substrates coated with glass). EXAMPLES

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. The aqueous resins shown in Examples 1 to 44 and Comparative Example 1 were prepared by the methods described below. In the examples, "parts" and "%" are by mass unless otherwise specified. Furthermore, "monomer" is referred to as "monomer".

[0046] <Example> Into a reactor equipped with a stirrer, a thermometer, a heating / cooling device, a nitrogen inlet tube and a dropping device, the first solvent was added, then the first emulsifier was added, and stirring was started while replacing the inside of the reactor with nitrogen. The first monomer was added to the reaction vessel as required, and the contents of the reaction vessel were stirred until an o / w type emulsion was formed. In a first dropping container equipped with a stirrer, a second solvent was added, then a second emulsifier was added, stirring was started, and stirring was continued until the contents of the first dropping container became uniform, after which the stirring was stopped. The second monomer was added to the first dropping vessel and stirred until the contents of the first dropping vessel formed an o / w type emulsion, after which the stirring was stopped. If necessary, a third solvent was added to a second dropping vessel equipped with a stirring device, followed by the addition of a third emulsifier, stirring was started, and stirring was continued until the contents of the second dropping vessel became uniform, after which the stirring was stopped. Into the second dropping vessel, the third monomer was added and stirred until the contents of the second dropping vessel formed an o / w type emulsion, after which the stirring was stopped. After the content of the reaction vessel was heated to 80°C, a reaction initiator was added to the reaction vessel while maintaining the temperature at 80°C, and the content of the first dropping vessel previously prepared was continuously dropped into the reaction vessel over a period of 2 hours, and then, if necessary, the content of the second dropping vessel was continuously dropped into the reaction vessel over a period of 2 hours. The contents of the reaction vessel were maintained at 80°C for 2 hours after addition was complete and then cooled to 40°C. 28% ammonia water was added so that the pH of the contents of the reaction vessel became 8.5 to 9.0. Furthermore, when diacetone acrylamide was used as the first, second, and third monomers, 33% adipic dihydrazide was added relative to the amount of diacetone acrylamide added, and then ion-exchanged water was added so that the active ingredient became 40%, thereby obtaining the desired resin emulsion for paint.

[0047] Tables 1A and 1B through 5A and 5B show Examples 1 to 44 and Comparative Example 1 prepared according to the formulations. In the tables, the first solvent, the first emulsifier, the first monomer, the reaction initiator, the second solvent, the second emulsifier, and the second monomer are shown in Tables 1A through 5A, respectively, and the third solvent, the third emulsifier, and the third monomer are shown in Tables 1B through 5B, respectively. Also, the methods for preparing and evaluating samples for hot water whitening resistance and weather resistance using the aqueous dispersion resins of Examples 1 to 44 and Comparative Example 1 are described, and the evaluation results are shown in Tables 1B to 5B.

[0048] [Table 1A]

[0049] [Table 1B]

[0050] [Table 2A]

[0051] [Table 2B]

[0052] [Table 3A]

[0053] [Table 3B]

[0054] [Table 4A]

[0055] [Table 4B]

[0056] [Table 5A]

[0057] [Table 5B]

[0058] <Solvent> 1) Water (ion-exchanged water)

[0059] <Emulsifier> 2) Hitenol N0820 (Polyoxyethylene nonylphenol ether sulfate ammonium salt, nonylphenol type, non-reactive, anionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 3) ADEKA REASOAP NE-30 (α-[1-(allyloxymethyl)2-(nonylphenoxy)ethyl-ω-hydroxypoly(n=1-100)oxyethylene], nonylphenol type, non-reactive, nonionic, manufactured by ADEKA Corporation) 4) Hitenol NF0825 (Polyoxyethylene styrenated phenol ether sulfate ammonium salt, non-nonylphenol type, non-reactive, anionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 5) Teika Power BN2060 (sodium branched alkylbenzene sulfonate, non-nonylphenol type, non-reactive, anionic, manufactured by Teika Co., Ltd.) 6) SP185FN-40 (Polyoxyethylene styrenated phenol ether sulfate ammonium salt, non-nonylphenol type, non-reactive, anionic, manufactured by Toho Chemical Industry Co., Ltd.) 7) Newcol N714SF (Polyoxyethylene styrenated phenol ether sulfate ammonium salt, non-nonylphenol type, non-reactive, anionic, manufactured by Nippon Nyukazai Co., Ltd.) 8) ADEKA REASOAP SR1025 (Polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, non-nonylphenol type, reactive, anionic, manufactured by ADEKA Corporation) 9) ADEKA REASOAP SR2025 (Polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, non-nonylphenol type, reactive, anionic, manufactured by ADEKA Corporation) 10) Aqualon KH05 (Polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, non-nonylphenol type, reactive, anionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 11) Aqualon KH10 (Polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, non-nonylphenol type, reactive, anionic, Daiichi Kogyo Seiyaku Co., Ltd.) 12) Aqualon AR1025 (Polyoxyethylene styrenated propenylphenol ether sulfate ammonium salt, non-nonylphenol type, reactive, anionic, Daiichi Kogyo Seiyaku Co., Ltd.) 13) Aqualon AR20 (Polyoxyethylene styrenated propenylphenol ether sulfate ester ammonium salt, non-nonylphenol type, reactive, anionic, Daiichi Kogyo Seiyaku Co., Ltd.) 14) Emulgen 147 (polyoxyethylene lauryl ether, non-nonylphenol type, non-reactive, non-ionic, manufactured by Kao Corporation) 15) Noigen ET-170D (polyoxyalkylene alkyl ether, non-nonylphenol type, non-reactive, non-ionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 16) ADEKA REASOAP ER10 (Polyoxyethylene-1-(allyloxymethyl) alkyl ether, non-nonylphenol type, reactive, nonionic, manufactured by ADEKA Corporation) 17) ADEKA REASOAP ER20 (Polyoxyethylene-1-(allyloxymethyl) alkyl ether, non-nonylphenol type, reactive, nonionic, manufactured by ADEKA Corporation) 18) ADEKA REASOAP ER30 (Polyoxyethylene-1-(allyloxymethyl) alkyl ether, non-nonylphenol type, reactive, nonionic, manufactured by ADEKA Corporation) 19) Aqualon AN10 (polyoxyethylene styrenated propenylphenol ether, non-nonylphenol type, reactive, nonionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 20) Aqualon AN20 (polyoxyethylene styrenated propenylphenol ether, non-nonylphenol type, reactive, nonionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 21) Aqualon AN30 (polyoxyethylene styrenated propenylphenol ether, non-nonylphenol type, reactive, nonionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0060] <Monomer> 22) Styrene (molecular formula: C6H5CH=CH2) 23) Methyl methacrylate (molecular formula: C5H8O2) 24) 2-Ethylhexyl acrylate (molecular formula: C2H5-CH2=CHCOOCH2CH(C4H9, ester double bond) 25) Acrylic acid (molecular formula: C3H4O2) 26) Methacrylic acid (molecular formula: C4H6O2) 27) α-Methylstyrene dimer (molecular formula: C 18 -H 20 ) 28) n-Butyl acrylate (molecular formula: CH2=CHCOO(CH2)3CH3) 29) n-Butyl methacrylate (molecular formula: CH2=C(CH3)C02(CH2)3CH3C8H 14 O2) 30) Cyclohexyl methacrylate (molecular formula: CH2=C(CH3)COOC6H 11 ) 31) 2-Hydroxyethyl methacrylate (molecular formula: CH2=C(CH3)COOCH2CH2OHC6H 10 O3) 32) Acrylamide (molecular formula: CH2=CHCONH2C3H5NO) 33) Diacetone acrylamide (molecular formula: CH2=CHCONHC(CH3)2CH2COCH3, crosslinking agent) 34) Divinylbenzene (molecular formula: C6H4(CH=CH2)2, crosslinking agent) 35) Glycidyl methacrylate (molecular formula: C7H 10 O3, crosslinker) 36) RUVA-93 (2-(2'-hydroxy-5'-methacryloxyethylphenyl)-2H-benzotriazole, molecular formula: C 18 H 17 N3O3, UV-absorbing vinyl monomer: manufactured by Otsuka Chemical Co., Ltd. 37) KBM-503 (γ-methacryloyloxypropyltrimethoxysilane, molecular formula: C 10 H 20 O5Si, coupling agent, manufactured by Shin-Etsu Chemical Co., Ltd. 38) Ethylene glycol dimethacrylate (molecular formula: CH3(CH2)3OCH2CH2OH) 39) ADK STAB LA-82 (1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, molecular formula: C 13 H 23 NO2, manufactured by ADEKA)

[0061] <Reaction initiator> 40) Ammonium persulfate ((NH4)2SO4) 41) Potassium persulfate (K2(SO4)2)

[0062] <How to prepare and evaluate samples for hot water whitening resistance> Each aqueous resin composition was applied to a glass plate using a 6-mil applicator and forced dried at 80° C. for 5 minutes, and then allowed to cool to room temperature to prepare a sample.

[0063] <Evaluation criteria> Next, the glass plate was immersed in 50° C. hot water for 24 hours, and the appearance of the coating film was visually evaluated immediately after removal from the hot water. After that, the plate was left at room temperature for 24 hours and dried, and the appearance of the coating film was visually evaluated. The evaluation criteria are as follows: ◎: There is little whitening of the coating film, and after drying, the original clear coating film is completely restored. ○+: Some whitening of the coating film is observed, but after drying, it returns to almost its original clear coating within about 2 to 3 hours. ◯: Some whitening of the coating film was observed, and the coating film remained slightly cloudy after 24 hours of drying, but recovered to a clear coating after 48 hours. ×: The coating film was whitened and remained white even after drying, and did not completely return to the original clear coating film.

[0064] <Weatherability test sample preparation and evaluation method> The prepared aqueous resin composition was adjusted to a white paint having the following composition, which was then applied to a flexible board coated with a cationic emulsion sealer so that the dry film thickness was 60 μm. The paint was then forcibly dried for 10 minutes in a hot air drying oven set at 80° C. to obtain a test piece.

[0065] <Paint formulation> Water 10.0 parts Hydroxyethyl cellulose thickener 0.1 parts Special carboxylic acid surfactant 0.5 parts (Product name: Tamor 731, manufactured by R&H) Modified silicon defoamer 0.2 parts (Product name: Deformer 777, manufactured by San Nopco Ltd.) Rutile titanium dioxide 25.0 parts Resin composition 70.0 parts

[0066] Next, this test piece was subjected to an accelerated weather resistance test using a Sunshine Weatherometer, and the change in the coating film after 1500 hours was evaluated according to the evaluation conditions for chalkiness in JIS K-5600-8-6. At the same time, the 60° specular gloss was measured and compared with the initial gloss value to obtain the gloss retention. However, ethylene glycol monobutyl ether was gradually added with stirring so that the MFT was 20°C or less.

[0067] <60° specular gloss measurement> The gloss value of the test piece of the flexiboard coated with the paint is measured using a specular gloss meter specified in JIS K5600-4-7, with the measurement angle being 60°.

[0068] The evaluation criteria are as follows: <Evaluation criteria> ◎: Chalking degree 1 and gloss retention rate 80% or more. ○+: Chalking level 1 or 2, and gloss retention rate 75% or more. ○: Chalking degree 1 or 2, and gloss retention rate 60% or more. ×: Chalking degree less than 3, or gloss retention less than 60%.

[0069] As described above, it is apparent that the water-dispersible resin of the present invention has excellent resistance to whitening in hot water and weather resistance when used as an aqueous coating composition.

Claims

1. A water-dispersible resin obtained by an emulsion polymerization method using a non-nonylphenol emulsifier (A) and a polymerizable unsaturated monomer (B), A water-dispersible resin characterized by having at least one of the following invention-specific features (1) to (3): Note (1) The water-dispersible resin contains a crosslinking agent (C). (2) The water-dispersible resin has a heterophase structure. (3) The polymerizable unsaturated monomer (B) contains 70 to 100% by mass of an acrylic monomer.

2. 2. An aqueous coating composition comprising the water-dispersible resin according to claim 1, the aqueous coating composition further comprising a pigment (D).

3. 3. The aqueous coating composition according to claim 2, wherein the pigment (D) is a surface-coated pigment that is surface-coated with a metal or a metal oxide.

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