Water-based coating composition

Abstract

An aqueous coating composition including: an aqueous dispersion (A) of a polyolefin resin that includes a polypropylene (A1); a crosslinking agent (B) that has a carboxyl group-reactive functional group; an aminosilane (C); and an organic solvent (D) with a water solubility of 0.01-5.0 g / 100 g and a boiling point of 120-250°C.

Description

[Technical Field]

[0001] The present invention relates to an aqueous coating composition which is excellent in corrosion resistance, processability and coating workability and is particularly suitable for can applications. [Background technology]

[0002] As paints for cans, various paint compositions such as epoxy-based, polyvinyl chloride-based and polyester-based paints have been used from the viewpoints of coating film performance such as corrosion resistance and coating workability. In particular, coating compositions containing, as a base resin, an epoxy resin produced using raw materials containing bisphenol A and the like have been widely and generally used.

[0003] However, from the viewpoint of environmental impact, there is a demand for can coating compositions that do not use raw materials containing bisphenol A (BPA) (including raw materials that may contain residual levels of BPA). For example, Patent Documents 1, 2, and 3 disclose coating compositions that use vinyl or acrylic resins as the base resin.

[0004] In recent years, regulations have been enacted, particularly in Europe and the United States, to expand the scope of regulated substances beyond BPA to also include styrene, formaldehyde, isocyanates, etc., and regulations are becoming stricter.

[0005] In this situation where the number of regulated substances is increasing and the freedom of choice of raw materials that can be used in coating compositions is limited, polyolefin resin is one of the most promising resins, particularly as a base resin for coating compositions for the inside of cans.

[0006] Furthermore, in the field of can paints, water-based paints using, for example, acrylic-modified epoxy resins as the base resin have been developed from the viewpoint of reducing organic solvents.

[0007] Patent Document 4 discloses a coating composition for can applications that uses a polyolefin resin as the base resin and that contains as its constituents an aqueous dispersion containing a polyolefin and a stabilizing solvent composition containing an alcohol.

[0008] However, although the coating composition described in Patent Document 4 has excellent storage stability, the resulting coating film has insufficient corrosion resistance and processability, and the coating workability may also be insufficient. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2005-120306 [Patent Document 2] Japanese Patent Publication No. 2005-179491 [Patent Document 3] Japanese Patent Application Publication No. 2016-113561 [Patent Document 4] Japan Special Publication No. 2016-501291 Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved by the present invention is to provide an aqueous coating composition suitable for can applications, which has excellent corrosion resistance, processability and coating workability, and does not use raw materials containing legally restricted substances such as bisphenol A. [Means for solving the problem]

[0011] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by an aqueous coating composition containing (A) a polyolefin resin aqueous dispersion containing polypropylene, (B) a crosslinking agent having a functional group reactive with a carboxyl group, an aminosilane (C) and (D) an organic solvent having a water solubility and boiling point within a specific range, and have thus completed the present invention.

[0012] That is, the present invention relates to the following. 1. An aqueous coating composition comprising: a polyolefin resin aqueous dispersion (A) containing polypropylene (A1); a crosslinking agent (B) having a functional group reactive with a carboxyl group; an aminosilane (C); and an organic solvent (D) having a water solubility of 0.01 to 5.0 g / 100 g and a boiling point of 120 to 250°C. 2. An aqueous coating composition according to item 1, wherein the solid content of the polypropylene (A1) is 40 mass % or more relative to the total solid content of the polyolefin resin water dispersion (A). 3. The aqueous coating composition according to item 1 or 2, wherein the solid content of the crosslinking agent (B) is 0.1 to 20.0 mass%, the solid content of the aminosilane (C) is 0.1 to 10.0 mass%, and the content of the organic solvent (D) is 0.1 to 10.0 mass%, relative to the total solid content of the polyolefin resin water dispersion (A). 4. A coated metal can having a cured coating film made from the aqueous coating composition according to any one of items 1 to 3 on at least a part of the can body. [Effects of the Invention]

[0013] The aqueous coating composition of the present invention contains polypropylene as the base resin of polyolefin, and further contains aminosilane, so that a coating film with excellent corrosion resistance and processability can be obtained. Furthermore, since it also contains a crosslinking agent having a functional group that reacts with a carboxyl group, the curing property is excellent, and the resulting coating film also has excellent coating film properties such as water resistance. Furthermore, since it also contains an organic solvent having a specific range of water solubility and boiling point, it also has excellent coating workability.

[0014] As described above, according to the present invention, it is possible to provide an aqueous coating composition that can provide a coating film that is excellent in corrosion resistance and workability, particularly when used for cans, and that also has excellent coating workability, and that does not contain raw materials that contain legally restricted substances such as bisphenol A. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to an aqueous coating composition (hereinafter sometimes simply referred to as the present coating) containing a polyolefin resin aqueous dispersion (A) containing polypropylene (A1), a crosslinking agent (B) having a functional group reactive with a carboxyl group, an aminosilane (C), and an organic solvent (D) having a water solubility of 0.01 to 5.0 g / 100 g and a boiling point of 120 to 250°C. Hereinafter, embodiments of the present invention will be described in detail. In this specification, proportions (percentages, parts, etc.) based on "mass" are the same as proportions (percentages, parts, etc.) based on "weight".

[0016] <Water-based paint composition> [Polyolefin resin water dispersion (A)] The polyolefin resin water dispersion (A) in the aqueous coating composition according to this embodiment is a dispersion in which the polyolefin resin is present in a dispersed state in a medium whose main component is water.

[0017] The polyolefin resin is not particularly limited, and examples thereof include homopolymers and copolymers (including elastomers) of one or more α-olefins such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene, and 1-dodecene, as represented by polypropylene, polyethylene, poly-1-butene, poly-3-methyl-1-butene, poly-3-methyl-1-pentene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, and propylene-1-butene copolymer; and copolymers of one or more α-olefins such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene, and 1-dodecene, as represented by ethylene-butadiene copolymer and ethylene-ethylidenenorbornene copolymer. Examples of the copolymer include copolymers (including elastomers) of one α-olefin having a conjugated or non-conjugated diene, and polyolefins (including elastomers) such as copolymers of two or more α-olefins having a conjugated or non-conjugated diene, which can be represented by ethylene-propylene-butadiene copolymer, ethylene-propylene-dicyclopentadiene copolymer, ethylene-propylene-1,5-hexadiene copolymer, and ethylene-propylene-ethylidenenorbornene copolymer; ethylene-vinyl compound copolymers such as ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-vinyl chloride copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and ethylene-(meth)acrylate copolymer.

[0018] The polyolefin resin may have a functional group such as a hydroxyl group, an amino group, an aldehyde group, an epoxy group, an ethoxy group, a carboxyl group, an ester group, an anhydride group, or the like, or two or more of these functional groups. Of the above functional groups, the polyolefin resin preferably has a carboxyl group.

[0019] In this specification, "(meth)acrylate" means "acrylate or methacrylate", and "(meth)acrylamide" means "acrylamide or methacrylamide".

[0020] In the present coating material, the polyolefin resin water dispersion (A) contains polypropylene (A1) as an essential component.

[0021] From the viewpoint of corrosion resistance, the solid content of the polypropylene (A1) is preferably 40% by mass or more, more preferably 50% by mass or more, based on the total solid content of the polyolefin resin water dispersion (A).

[0022] In the present coating material, the polyolefin resin aqueous dispersion (A) may contain a polyolefin resin (A2) other than the essential component polypropylene (A1). The polyolefin resin (A2) preferably has a carboxyl group. As the polyolefin resin (A2), one type may be used alone, or two or more types may be used in combination.

[0023] The polyolefin resin water dispersion (A) may contain a stabilizer from the viewpoint of stability, for example, promotion of the formation of the water dispersion. Examples of the stabilizer include surfactants, polymers, etc. The stabilizers can be used alone or in combination of two or more.

[0024] Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. Anionic surfactants include, for example, sulfonates, carboxylates, and phosphates. Examples of cationic surfactants include quaternary amine salts. Examples of nonionic surfactants include polymers containing a nonionic group such as polyoxyalkylene, and silicone surfactants. As the surfactant, a reactive surfactant that is reactive with polyolefin resin can also be used.

[0025] The polymer may be, for example, a polar polymer having a polar group. Examples of polar polymers include those based on resins such as acrylic resins, polyester resins, epoxy resins, polyamide resins, acrylic-modified polyester resins, and acrylic-modified epoxy resins. The polar polymer may also be a polyolefin resin having a polar group. Examples of the polar functional group (polar group) include a hydroxyl group, an amino group, an aldehyde group, an epoxy group, an ethoxy group, a carboxyl group, an ester group, and an anhydride group.

[0026] Furthermore, as the stabilizer, for example, a long-chain fatty acid having 12 to 60 carbon atoms, a fatty acid salt, a fatty acid alkyl ester, an ethylene-acrylic acid resin, etc. can also be used.

[0027] When a stabilizer is used, the solid content of the stabilizer varies depending on the type of stabilizer, but from the viewpoint of storage stability, it is preferably 5 to 35 mass % relative to the total solid content of the polyolefin resin, and particularly preferably in the range of 10 to 30 mass %.

[0028] The polyolefin resin water dispersion (A) can be obtained by dispersing in water, optionally adding a basic compound as a neutralizing agent.

[0029] Examples of basic compounds include hydroxides, carbonates, and amines. Examples of hydroxides include ammonium hydroxide, potassium hydroxide, lithium hydroxide, and sodium hydroxide. Examples of carbonates include sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and calcium carbonate. Examples of amines include monoethanolamine, diethanolamine, triethanolamine, ammonia, monomethylamine, dimethylamine, trimethylamine, 2-amino-2-methyl-1-propanol, triisopropanolamine, diisopropanolamine, N,N-dimethylethanolamine, mono-n-propylamine, dimethyl-n-propylamine, N-methanolamine, N-aminoethylethanolamine, N-methyldiethanolamine, monoisopropanolamine, N,N-dimethylpropanolamine, 2-amino-2-methyl-1-propanol, tris(hydroxymethyl)aminomethane, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine, 1,2-diaminopropane, 2-amino-2-hydroxymethyl-1,3-propanediol, and N,N'-ethylenebis[bis(2-hydroxypropyl)amine]toluene-p-sulfonate. As the basic compound, amines are preferred from the viewpoint of water resistance.

[0030] The polyolefin resin water dispersion (A) can be produced by a known method, for example, by adding polypropylene (A1), an optional polyolefin resin (A2), water, and, if necessary, a stabilizer, a neutralizer (basic compound), etc., and melt-kneading the mixture.

[0031] A specific production procedure includes, for example, melt-mixing polypropylene (A1), an optional polyolefin resin (A2), and, if necessary, one or more stabilizers in the presence of water and one or more neutralizing agents to form an emulsified mixture, and then contacting the emulsified mixture with additional dilution water while removing heat as necessary to form particles dispersed in water, thereby producing an aqueous dispersion.

[0032] The average particle size of the solid content of the polyolefin resin water dispersion (A) is preferably 100 to 1000 nm, particularly preferably 110 to 900 nm, and even more preferably 120 to 800 nm, from the viewpoint of coating workability. The average particle size can be measured using a particle size measuring device, such as a Coulter Model N4MD (trade name, manufactured by Beckman Coulter, Inc.).

[0033] [Crosslinking agent (B)] The crosslinking agent (B) is a compound having a functional group that reacts with a carboxyl group. The crosslinking agent (B) usually has two or more functional groups that react with a carboxyl group in the molecule. Such a crosslinking agent (B) can enhance the curability of the aqueous coating composition according to this embodiment and improve the coating film performance such as corrosion resistance and water resistance, particularly water resistance, of the resulting coating film.

[0034] Examples of functional groups that react with a carboxyl group include a hydroxyalkylamide group, an oxazoline group, an aziridine group, an imide group (particularly a carbodiimide group), an epoxy group, a hydroxyl group, and a methylol group. Of the above functional groups, a hydroxyalkylamide group is preferred from the viewpoint of storage stability.

[0035] Specific examples of the crosslinking agent (B) include hydroxyalkylamide crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, imide crosslinking agents (particularly, crosslinking agents having a carbodiimide group), and epoxy crosslinking agents.

[0036] Examples of hydroxyalkylamide crosslinking agents include bis(N,N'-dihydroxyethyl)adipamide, etc. Specific examples include PRIMID (trademark, trade name of crosslinking resin), such as PRIMID (trademark) XL-522 and PRIMID (trademark) SF-4510, commercially available from EMS-GRILTECH GmbH of Switzerland.

[0037] Examples of oxazoline crosslinking agents include components containing a vinyl monomer containing an oxazoline group, such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline, as well as vinyl resins or acrylic resins obtained by copolymerizing a vinyl monomer containing an oxazoline group with another monomer. Commercially available products include EPOCROS® WS-300, WS-500, and WS-700, and EPOCROS® K-2010, K-2020, and K-2030, manufactured by Nippon Shokubai Co., Ltd.

[0038] Examples of the aziridine crosslinking agent include glycerol-tris(1-aziridinylpropionate), glycerol-tris[2-methyl-(1-aziridinyl)]propionate, glycerol-tris[2-ethyl-(1-aziridinyl)]propionate, glycerol-tris[2-butyl-(1-aziridinyl)]propionate), glycerol-tris[2-propyl-(1-aziridinyl)]propionate, glycerol-tris[2-pentyl-(1-aziridinyl)]propionate, and glycerol-tris[2-hexyl-(1-aziridinyl)]propionate. glycerol-tris[2,3-dimethyl-(1-aziridinyl)]propionate, glycerol-tris[2,3-diethyl-(1-aziridinyl)]propionate, glycerol-tris[2,3-dibutyl-(1-aziridinyl)]propionate, glycerol-tris[2,3-dipropyl-(1-aziridinyl)]propionate, glycerol-tris[2,3-dipentyl-(1-aziridinyl)]propionate, glycerol-tris[2,3-dihexyl-(1-aziridinyl)]propionate, Trimethylolpropane-tris(1-aziridinylpropionate), trimethylolpropane-tris[2-methyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2-ethyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2-butyl-(1-aziridinyl)]propionate), trimethylolpropane-tris[2-propyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2-pentyl-(1-aziridinyl)]propionate , trimethylolpropane-tris[2-hexyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2,3-dimethyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2,3-diethyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2,3-dibutyl-(1-aziridinyl)]propionate), trimethylolpropane-tris[2,3-dipropyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2,3-dipentyl-(1-aziridinyl)]propionate, trimethylolpropane-tris[2,3-dihexyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris(1-aziridinylpropionate), tetramethylolmethane-tris[2-methyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2-ethyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2-butyl-(1-aziridinyl)]propionate, tetramethylolmeth Tetramethylolmethane-tris[2-propyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2-pentyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2-hexyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2,3-dimethyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2,3-diethyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2,3-dibutyl-(1-aziridinyl)] propionate), tetramethylolmethane-tris[2,3-dipropyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2,3-dipentyl-(1-aziridinyl)]propionate, tetramethylolmethane-tris[2,3-dihexyl-(1-aziridinyl)]propionate, pentaerythritol-tetra(1-aziridinylpropionate), pentaerythritol-tetra[2-methyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2-ethyl-(1- aziridinyl)]propionate, pentaerythritol-tetra[2-butyl-(1-aziridinyl)]propionate), pentaerythritol-tetra[2-propyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2-pentyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2-hexyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2,3-dimethyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2,3-diethyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2,3-dibutyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2,3-dipropyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2,3-dipentyl-(1-aziridinyl)]propionate, pentaerythritol-tetra[2,3-dihexyl-(1-aziridinyl)]propionate, tetraaziridin Examples of suitable alkyl ethers include tetramethylpropane, tetraaziridinylmethylparaxylenediamine, tetramethylpropanetetraaziridinylpropionate, neopentyl glycol di(β-aziridinylpropionate), 4,4'-isopropylidenediphenol di(β-aziridinylpropionate), 4,4'-methylenediphenol di(β-aziridinylpropionate), and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

[0039] Examples of imide-based crosslinking agents (particularly crosslinking agents having a carbodiimide group) include 1,3-diisopropylcarbodiimide (i.e., N,N-diisopropylcarbodiimide), N,N-dicyclohexylcarbodiimide, N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide, and carbodiimide derivatives such as hydrochlorides of these.

[0040] A commercially available example of a crosslinking agent having a carbodiimide group is Carbodilite (trade name, registered trademark) manufactured by Nisshinbo Chemical Inc. Examples of Carbodilite include water-soluble types such as "V-02," "V-02-L2," "SV-02," "V-04," "V-10," and "SW-12G" (all product names), and emulsion types such as "E-02," "E-03A," and "E-05" (all product names).

[0041] As the epoxy-based crosslinking agent, any known epoxy resin (compound) having at least two epoxy groups (glycidyl groups) in the molecule can be used without any particular limitation, and alicyclic epoxy compounds can be particularly preferably used.

[0042] As the alicyclic epoxy compound, commercially available products can be used, and a specific example is Denacol (trade name, registered trademark) manufactured by Nagase ChemteX Corporation. Examples of Denacol include bifunctional types such as "EX-211", "EX-212", "EX-252", "EX-810", "EX-811", "EX-850", "EX-851", "EX-821", "EX-830", "EX-832", "EX-841", "EX-861", "EX-911", "EX-941", "EX-920", and "EX-931" (all product names), and multifunctional types such as "EX-313", "EX-314", "EX-321", "EX-411", "EX-421", "EX-512", "EX-521", "EX-612", "EX-614", and "EX-614B" (all product names).

[0043] Examples of crosslinking agents having a hydroxyl group include aliphatic alcohols such as glycerin, ethylene glycol pentaerythritol, pentaglycerol, and polyvinyl alcohol; alicyclic alcohols such as phloroglucitol, quercitol, and inositol; aromatic alcohols such as tris(hydroxy)benzene; sugars such as starch, D-erythrose, L-arabinose, D-mannose, D-galactose, D-fructose, L-rhamnose, saccharose, maltose, and lactose; and sugar alcohols such as erythritol, L-arabitol, adonit, and xylitol; and other polyhydric alcohols having two or more functional groups, preferably three or more functional groups.

[0044] The crosslinking agent (B) can be used alone or in combination of two or more. The solids content of the crosslinking agent (B) varies depending on the type of crosslinking agent, but from the viewpoint of improving corrosion resistance in particular, it is preferably 0.1 to 20.0 mass%, particularly 0.2 to 18.0 mass%, and even more particularly 0.3 to 16.0 mass%, based on the total solids content of the polyolefin resin water dispersion (A). The solids content of the crosslinking agent (B) is preferably 0.1 mass% or more, particularly 0.2 mass% or more, and even more particularly 0.3 mass% or more, based on the total solids content of the polyolefin resin water dispersion (A). Furthermore, the solids content of the crosslinking agent (B) is preferably 20.0 mass% or less, particularly 18.0 mass% or less, and even more particularly 16.0 mass% or less, based on the total solids content of the polyolefin resin water dispersion (A).

[0045] [Aminosilane (C)] The aminosilane (C) can improve the corrosion resistance and processability of the coating film obtained from the aqueous coating composition according to this embodiment.

[0046] The aminosilane (C) is a silane compound having an amino group, and specific examples thereof include aminosilanes such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-benzyl-γ-aminopropyltrimethoxysilane, and γ-ureidopropyltrimethoxysilane; and bisalkoxysilyl amines such as bis(trimethoxysilylpropyl)amine and bis(triethoxysilylpropyl)amine.

[0047] As the aminosilane (C), from the viewpoint of storage stability, γ-aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, and γ-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane can be suitably used.

[0048] The aminosilane (C) preferably has a molecular weight of 100 to 1,000, and in particular, a molecular weight within the range of 100 to 500 is preferred from the viewpoint of reactivity.

[0049] The solid content of the aminosilane (C) varies depending on the type of aminosilane, but from the viewpoint of improving corrosion resistance and processability in particular, it is preferably 0.1 to 10.0 mass% and more preferably 0.2 to 6.0 mass% based on the total solid content of the polyolefin resin water dispersion (A). The solid content of the aminosilane (C) is preferably 0.1 mass% or more and more preferably 0.2 mass% or more based on the total solid content of the polyolefin resin water dispersion (A). Furthermore, the solid content of the aminosilane (C) is preferably 10.0 mass% or less and more preferably 6.0 mass% or less based on the total solid content of the polyolefin resin water dispersion (A).

[0050] [Organic solvent (D)] The organic solvent (D) is an organic solvent having a water solubility of 0.01 to 5.0 g / 100 g and a boiling point of 120 to 250°C.

[0051] The organic solvent (D) improves the defoaming properties of the aqueous coating composition according to this embodiment, thereby improving coating workability.

[0052] From the viewpoint of defoaming property and storage stability, the water solubility of the organic solvent (D) is 0.01 to 5.0 g / 100 g, preferably 0.02 to 4.0 g / 100 g, and particularly preferably 0.03 to 2.0 g / 100 g. The water solubility is 0.01 g / 100 g or more, preferably 0.02 g / 100 g or more, and particularly preferably 0.03 g / 100 g or more. The water solubility is 5.0 g / 100 g or less, preferably 4.0 g / 100 g or less, and particularly preferably 2.0 g / 100 g or less.

[0053] Water solubility is a measure of a substance's affinity for water. It is expressed as the maximum number of grams that can dissolve in 100 g of water at 20°C.

[0054] From the viewpoints of defoaming properties and coating workability, the boiling point of the organic solvent (D) is within the range of 120 to 250°C, and preferably 130 to 240°C, at 1 atmosphere (760 mmHg). The boiling point of the organic solvent (D) is 120°C or higher, and preferably 130°C or higher. In addition, the boiling point of the organic solvent (D) is 250°C or lower, and preferably 240°C or lower.

[0055] Specific examples of the organic solvent (D) include n-hexanol (water solubility 0.6 g / 100 g, boiling point 157° C.), 2-ethyl-1-hexanol (water solubility 0.1 g / 100 g, boiling point 195° C.), 2-hexyloxyethanol (water solubility 1.0 g / 100 g, boiling point 208° C.), butyl acetate (water solubility 0.7 g / 100 g, boiling point 126° C.), butyl propionate (water solubility 0.2 g / 100 g, boiling point 145° C.), and ethylene glycol monobutyl ether acetate. Examples include acetate (water solubility 1.1 g / 100 g, boiling point 191°C), isophorone (water solubility 1.2 g / 100 g, boiling point 215°C), ethylene glycol mono-2-ethylhexyl ether (water solubility 0.2 g / 100 g, boiling point 229°C), dipropylene glycol n-butyl ether (water solubility 4.0 g / 100 g, boiling point 230°C), and propylene glycol monophenyl ether (water solubility 2.0 g / 100 g, boiling point 243°C).

[0056] The content of the organic solvent (D) varies depending on the type of organic solvent (D), but from the viewpoint of improving defoaming properties in particular, it is preferably 0.1 to 10.0 mass% and more preferably 0.2 to 6.0 mass% based on the total solid content of the polyolefin resin water dispersion (A). The content of the organic solvent (D) is preferably 0.1 mass% or more and more preferably 0.2 mass% or more based on the total solid content of the polyolefin resin water dispersion (A). Furthermore, the content of the organic solvent (D) is preferably 10 mass% or less and more preferably 6.0 mass% or less based on the total solid content of the polyolefin resin water dispersion (A).

[0057] The aqueous coating composition according to this embodiment contains a medium whose main component is water. From the viewpoints of coating workability and storage stability, the solids concentration of the aqueous coating composition according to this embodiment is preferably 10 to 50 mass %, and more preferably in the range of 15 to 40 mass %.

[0058] The aqueous coating composition according to this embodiment can further contain conventionally known raw materials such as organic solvents other than the organic solvent (D), antifoaming agents, silane compounds other than aminosilanes, surfactants, lubricants, waxes, viscosity modifiers, pigments, etc., as needed.

[0059] Examples of organic solvents other than the organic solvent (D) that can be used in the present embodiment include methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, isobutanol, amyl alcohol, octanol, alkyl alcohols; glycol ethers such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, methyl carbitol, ethyl carbitol, and butyl carbitol; glycol ether esters such as methyl cellosolve acetate and ethyl cellosolve acetate; dioxane, dimethylformamide, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, and diacetone alcohol, and these can also be used in combination of two or more types.

[0060] Examples of the antifoaming agent include acrylic compounds, vinyl ether compounds, and dimethylpolysiloxane compounds, and two or more of these can be used in combination.

[0061] Examples of silane compounds other than the above aminosilanes include silane coupling agents having an organic functional group such as a vinyl group, a methacryl group, an acryloxy group, or a methacryloxy group, and two or more of these can also be used in combination.

[0062] The aqueous coating composition according to this embodiment can be applied to various substrates, such as untreated or surface-treated metal plates such as aluminum plates, steel plates, and tin plates, as well as metal plates coated with an epoxy or vinyl primer, and cans or other products made from these metal plates.

[0063] Examples of cans to which the aqueous coating composition according to this embodiment can be applied include two-piece cans consisting of two parts, a lid and a bottom, and a body part integrated with the lid, three-piece cans consisting of three parts, a lid, a bottom, and a body, bottle cans, and other cans of various shapes. The aqueous coating composition of the present invention can be applied to each part of each of the above cans.

[0064] The coating film obtained from the aqueous coating composition according to this embodiment has excellent corrosion resistance and workability, and can therefore be suitably used for coating cans such as beverage cans, particularly the inner surfaces of cans. The aqueous coating composition according to this embodiment can also be used for repair painting of seams (joints) on the inside of cans, and for painting the outer surface of cans such as the outer surface of can lids and tabs.

[0065] The aqueous coating composition according to this embodiment can be applied to a substrate by any of a variety of known methods, such as spray coating, roll coater coating, dip coating, electrodeposition coating, etc. Of these, spray coating or roll coater coating is preferred.

[0066] The coating amount may be appropriately selected depending on the application, but a dry coating thickness of, for example, about 1 to 30 μm is preferred, and about 2 to 20 μm is particularly preferred. Drying conditions for the coating film are, for example, preferably a maximum temperature of the material reached of 120 to 300°C for 10 seconds to 30 minutes, and particularly preferably 200 to 280°C for 15 seconds to 10 minutes.

[0067] <Coated metal cans> The coated metal can according to this embodiment has a cured coating film of the above-mentioned aqueous coating composition on at least a portion of the can body.

[0068] The aqueous coating composition used for the coated metal can is the same as the aqueous coating composition in the above-mentioned <Aqueous Coating Composition>, and preferred embodiments are also the same. Furthermore, the method for applying the aqueous coating composition to the coated metal can is not particularly limited, and the application method for the aqueous coating composition in the above-mentioned <Aqueous Coating Composition> can be appropriately adopted. As with the above-mentioned <Aqueous Coating Composition>, cans of various shapes are suitably used, and at least a portion of the can body has a cured coating film made of the above-mentioned aqueous coating composition. [Example]

[0069] The present invention will be explained in more detail below with reference to examples. Here, "parts" and "%" mean "parts by mass" and "% by mass," respectively. Note that the "parts by mass" of raw materials in the following production examples, examples, and comparative examples represent the parts by mass of the solid content (sometimes referred to as active ingredients) of the raw materials.

[0070] <Production Example 1: Production of Polyolefin Resin Water Dispersion (A-1)> Polypropylene (6D43 (trade name), manufactured by Braskem America) added at 60 g / min, and polyolefin resin (A2) PRIMACOR 5980i (trade name, ethylene-acrylic acid copolymer, manufactured by Dow) added at 180 g / min and LICOCENE 6452 (trade name, propylene-maleic anhydride graft copolymer, manufactured by Clariant) added at 60 g / min were fed into a twin-screw extruder heated to 160°C. Deionized water was fed to the extruder at 70 g / min and dimethylethanolamine at 30 g / min, and dilution water was fed to two positions in the dilution section of the extruder so that the final solids content was 47%. The extruder temperature profile was reduced to below 100°C by the end of the extruder. The mixture was extruded at 1200 rpm with back pressure adjustment to obtain a polyolefin resin water dispersion (A-1) with a solids content of 47% by mass. In the polyolefin resin water dispersion (A-1), the solid content of polypropylene (A1) is 20 mass % of the total solid content.

[0071] <Production Example 2: Production of Polyolefin Resin Water Dispersion (A-2)> Polypropylene (6D43 (trade name), manufactured by Braskem America) added at 150 g / min, PRIMACOR 5980i added at 108 g / min as polyolefin resin (A2), and LICOCENE 6452 added at 45 g / min were fed into a twin-screw extruder heated to 160°C. Deionized water was fed to the extruder at 70 g / min and dimethylethanolamine at 30 g / min, and dilution water was fed to two positions in the dilution section of the extruder so that the final solids content was 47%. The extruder temperature profile was reduced to a temperature below 100°C by the end of the extruder. The mixture was extruded at 1200 rpm with back pressure adjustment to obtain a polyolefin resin water dispersion (A-2) with a solids content of 47% by mass. In the polyolefin resin water dispersion (A-2), the solid content of polypropylene (A1) in the total solid content is 49.5 mass %.

[0072] <Production Example 3: Production of Polyolefin Resin Water Dispersion (A-3)> Polypropylene (6D43 (trade name), manufactured by Braskem America) added at a rate of 212 g / min, and polyolefin resin (A2) PRIMACOR 5980i (trade name, ethylene-acrylic acid copolymer, manufactured by Dow) added at a rate of 68 g / min and LICOCENE 6452 (trade name, propylene-maleic anhydride graft copolymer, manufactured by Clariant) added at a rate of 23 g / min were fed into a twin-screw extruder heated to 160°C. Deionized water was fed to the extruder at 70 g / min and dimethylethanolamine at 30 g / min, and dilution water was fed to two positions in the dilution section of the extruder so that the final solids content was 47%. The extruder temperature profile was reduced to a temperature below 100°C by the end of the extruder. The mixture was extruded at 1200 rpm with back pressure adjustment to obtain a polyolefin resin water dispersion (A-3) with a solids content of 47% by mass. In the polyolefin resin water dispersion (A-3), the solid content of polypropylene is 70 mass % of the total solid content.

[0073] Example 1: Preparation of Water-Based Coating Composition No. 1 The raw materials listed in Table 1 were mixed in the composition ratio (mass solids ratio, actual amount of organic solvent (D)) listed in Table 1, and while diluting with deionized water, ethylene glycol monobutyl ether was added so that the total amount of the aqueous coating composition had a mass solids concentration of 20% after dilution adjustment, and the pH was adjusted to 8.0 with dimethylethanolamine to obtain aqueous coating composition No. 1 with a mass solids concentration of 20%. The amount of each raw material in Tables 1 and 2 represents the mass ratio of the solid content (or active ingredient) of each raw material, except for the organic solvent (D), which represents the mass ratio of the actual amount blended.

[0074] In the table, "KBM-1003" shown in the row for aminosilane (C) is a component used for comparison with aminosilane (C). Also, "toluene," "di(ethylene glycol) 2-ethylhexyl ether," "normal decane," "dipropylene glycol methyl ether acetate," and "diethylene glycol monoethyl ether" shown in the row for organic solvent (D) are components used for comparison with organic solvent (D).

[0075] In addition, Notes 1 to 16 in Tables 1 and 2 are as follows: (Note 1) PRIMID XL-522: Hydroxyalkylamide crosslinking agent, manufactured by EMS-GRILTECH (Note 2) Epocross WS-700: Oxazoline-based crosslinking agent, oxazoline-containing polymer, manufactured by Nippon Shokubai Co., Ltd. (Note 3) Carbodilite E-02: Imide-based crosslinking agent, carbodiimide resin, manufactured by Nisshinbo Chemical Inc. (Note 4) KBM-903: γ-aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd. (Note 5) KBM-602: N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd. (Note 6) KBM-1003: Vinyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd. (Note 7) n-Hexanol (water solubility 0.6g / 100g, boiling point 157°C) (Note 8) Butyl acetate (water solubility 0.7g / 100g, boiling point 126°C) (Note 9) 2-Ethyl-1-hexanol (water solubility 0.1 / 100g, boiling point 195°C) (Note 10) Ethylene glycol mono-2-ethylhexyl ether (water solubility 0.2g / 100g, boiling point 229°C) (Note 11) Propylene glycol monophenyl ether (water solubility 2.0 g / 100 g, boiling point 243°C) (Note 12) Toluene (boiling point 111°C) (Note 13) Di(ethylene glycol) 2-ethylhexyl ether (boiling point 272°C) (Note 14) Normal decane (water solubility 0g / 100g) (Note 15) Dipropylene glycol methyl ether acetate (water solubility 19.0 g / 100 g) (Note 16) Diethylene glycol monoethyl ether (water solubility ∞)

[0076] <Examples 2 to 18 and Comparative Examples 1 to 9: Production of Water-Based Coating Compositions Nos. 2 to 27> Water-based coating compositions Nos. 2 to 27 were prepared in the same manner as in Example 1. Water-based coating compositions Nos. 19 to 27 were used as comparative examples.

[0077] <Preparation of test coated panels> Each of the aqueous coating compositions obtained in the above Examples and Comparative Examples was applied to a 0.26 mm thick #5052 aluminum plate (aluminum alloy with alloy number 5052 specified in JIS H4000:2014) using a bar coater so that the thickness of the cured coating film was 5 μm, and the plate was heated at 200°C for 1 minute to obtain each coated test plate. The resulting coated test panels were subjected to the following tests, and the test results are shown in Tables 1 and 2.

[0078] [T-bend workability] The coated test plate was cut into a 5 cm length in the rolling direction and a 4 cm length in the vertical direction, and then the bottom was folded in half parallel to the short edge. In a room at 20°C, two 0.26 mm thick aluminum plates were sandwiched between the folded portions of the coated test plate specimen, and the specimen was placed in a special fold-type DuPont impact tester. A 1 kg iron weight with a flat contact surface was dropped from a height of 50 cm to impact the folded portion. A voltage of 6.5 V was then applied to the folded tip for 6 seconds, and the current value (mA) over a 20 mm width at the folded tip was measured and evaluated according to the following criteria. I: The current value was less than 10 mA. II: The current value was 10 mA or more and less than 40 mA. III: The current value was 40 mA or more and less than 80 mA. IV: The current value was 80 mA or more.

[0079] Furthermore, the coating adhesion of the processed area was evaluated using Cellotape (registered trademark) manufactured by Nichiban Co., Ltd., and was evaluated according to the following criteria. I: The peeled area of ​​the coating film was less than 10%. II: The peeled area of ​​the coating film was 10% or more and less than 20%. III: The peeled area of ​​the coating film was 20% or more and less than 40%. IV: The peeled area of ​​the coating was 40% or more.

[0080] [Retort resistance] The test coated plate was immersed in water and treated at 125°C for 30 minutes, after which the whitening state of the coating was visually observed and evaluated according to the following criteria. I: No whitening was observed. II: Slight partial bleaching was observed. III: Considerable bleaching was observed. IV: Significant whitening was observed.

[0081] [Corrosion resistance] The test coated panels were immersed in a mixed aqueous solution containing 3% each of citric acid and sodium chloride, and stored at 40°C for 2 weeks. The condition of the coating surface was then visually inspected and evaluated according to the following criteria. Each test coated panel was tested using the following test aqueous solutions 1 and 2, and evaluated according to the following criteria. I: No gloss loss or corrosion was observed. II: There was some gloss loss, but no corrosion was observed. III: Slight corrosion was observed. IV: Considerable corrosion was observed. Test aqueous solution 1: Aqueous solution in which citric acid and sodium chloride are dissolved to a mass concentration of 3% each Test aqueous solution 2: A solution in which citric acid and sodium chloride are dissolved at 3% by mass, and ethanol is dissolved at 7% by mass.

[0082] [Painting workability] The paint was applied to the inside of a two-piece can using an airless spray and then cured in a conveyor oven where the can temperature was maintained at 200°C for 1 minute. The resulting coated cans were cut open with metal scissors, and the state of the paint dripping onto the bottom of the can and the state of boiling were evaluated according to the following criteria. I: There was little dripping and no boiling was observed. II: Slight dripping and boiling were observed. III: Dripping and boiling were observed considerably. IV: Dripping and boiling were noticeable.

[0083] <Paint stability> Each aqueous coating composition was allowed to stand at room temperature for one week and then visually evaluated according to the following criteria. I: No precipitation was observed. II: Almost no precipitation was observed. III: A slight amount of precipitation was observed. IV: A considerable amount of precipitate was observed.

[0084] [Table 1]

[0085] [Table 2]

[0086] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-099469) filed on June 8, 2020, the contents of which are incorporated herein by reference. [Industrial Applicability]

[0087] It is possible to provide coated cans that are excellent in corrosion resistance and processability, and to provide an aqueous coating composition that is excellent in coating workability and does not contain legally restricted substances such as bisphenol A.

Claims

1. The present invention comprises a polyolefin resin aqueous dispersion (A) containing polypropylene (A1) and a polyolefin resin (A2) having a carboxyl group, a crosslinking agent (B) having a functional group reactive with a carboxyl group, an aminosilane (C), and an organic solvent (D) having a water solubility of 0.01 to 5.0 g / 100 g and a boiling point of 120 to 250°C, The aqueous coating composition has a solid content of the aminosilane (C) of 0.1 to 10.0 mass% and a content of the organic solvent (D) of 0.1 to 10.0 mass% relative to the total solid content of the polyolefin resin water dispersion (A).

2. 2. The aqueous coating composition according to claim 1, wherein the solid content of the polypropylene (A1) is 40 mass% or more relative to the total solid content of the polyolefin resin water dispersion (A).

3. 3. The aqueous coating composition according to claim 1, wherein the solid content of the crosslinking agent (B) is 0.1 to 20.0 mass% relative to the total solid content of the polyolefin resin water dispersion (A).

4. A coated metal can having a cured coating film of the aqueous coating composition according to any one of claims 1 to 3 on at least a part of the can body.

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