Water-based coating composition

Abstract

The present disclosure aims to provide an aqueous coating composition that has good workability and, preferably, can achieve a coating film with good workability, pencil hardness, and scratch resistance. [Solution] An aqueous paint composition comprising a film-forming resin (A), a crosslinking agent (B), a phosphoric acid-modified epoxy resin (C), and an organic solvent (D), The hydroxyl value of the coating resin (A) is 150 mg KOH / g or less, the acid value of the coating resin (A) is 100 mg KOH / g or less, and the glass transition temperature of the coating resin (A) is 100°C or less. The aforementioned organic solvent (D) has a solubility parameter of 8.3 (cal / cm³). 3 ) 1 / 2 More than 9.6(cal / cm 3 ) 1 / 2 The following applies, and the organic solvent (D1) has a solubility in water of 10 g / L or less at 25°C: An aqueous coating composition in which the content of the organic solvent (D1) is 0.5 parts by mass or more and 35 parts by mass or less, based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B).

Description

[Technical Field]

[0001] This disclosure relates to an aqueous coating composition. [Background technology]

[0002] Painted steel sheets, which are made by applying paint to metal substrates such as cold-rolled steel sheets and plated steel sheets and then using them for forming processes, are also called pre-coated metal (hereinafter also referred to as "PCM") and are used for building components such as shutters, lids, doors, roofs and siding; exterior materials for electrical equipment such as air conditioner outdoor units; and interior materials.

[0003] In recent years, awareness of reducing environmental impact has increased, and there is a growing demand for the replacement of products with environmentally friendly alternatives. In the paint sector, for example, there is a requirement to reduce the amount of volatile organic compounds (VOCs) used, and this requirement can be met by using water-based paint compositions. In other words, there is a very high demand in the market for one-component water-based paint compositions.

[0004] For example, Patent Document 1 describes an aqueous coating composition containing 10 to 50% by weight of an acrylic copolymer (a) obtained by copolymerizing predetermined monomers and having a glass transition temperature of -5 to 5°C, 5 to 40% by weight of an acrylic copolymer (b) obtained by copolymerizing predetermined monomers and having a glass transition temperature of -20 to -10°C, 15 to 50% by weight of an imino-group type benzoguanamine resin (c) having 0.5 to 2.0 imino groups per benzoguanamine nucleus, 5 to 20% by weight of a phosphoric acid-modified epoxy resin (d), and 1 to 10% by weight of an amine-modified epoxy resin (e), wherein at least a portion of the acrylic copolymers (a) and (b) are neutralized with a basic compound and dissolved or dispersed in water.

[0005] Patent Document 2 describes an aqueous coating composition comprising a film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C), and an amine compound (D), wherein the film-forming resin (A) comprises an acrylic resin (A1) having hydroxyl groups, the hydroxyl value of the film-forming resin (A) is 5 mg KOH / g or more and 35 mg KOH / g or less, the crosslinking agent (B) comprises a full alkyl type melamine resin (B1), and the molar neutralization rate of the acid groups of the sulfonic acid compound (C) by the amine compound (D) is 100% or more and 1,300% or less.

[0006] Patent Document 3 describes an aqueous coating composition comprising a nonionic water-dispersible resin (a), a phosphate-modified epoxy resin (b), a melamine compound (c), a silane coupling agent (d), silica particles (e) exchanged with divalent metal ions, and water, wherein, per 100 parts by mass of the total of the nonionic water-dispersible resin (a), the phosphate-modified epoxy resin (b), and the melamine compound (c), the content of the nonionic water-dispersible resin (a) is 60 to 94.5 parts by mass, the content of the phosphate-modified epoxy resin (b) is 5 to 39.5 parts by mass, the content of the melamine compound (c) is 0.5 to 10 parts by mass, and the content of the silane coupling agent (d) is 0.3 to 5 parts by mass. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2004-307540 [Patent Document 2] Japanese Patent Publication No. 2022-189126 [Patent Document 3] Japanese Patent Publication No. 2020-158670 [Overview of the project] [Problems that the invention aims to solve]

[0008] The aforementioned pre-coated steel sheet is typically manufactured by applying an aqueous coating composition to the surface of a metal substrate and forming a coating film by heating (baking) it at, for example, 200-270°C for 30-60 seconds, after which it is subjected to molding. For this reason, the coating film of the pre-coated steel sheet is required to have sufficient workability to prevent cracking or peeling during processing, and sufficient hardness to prevent scratches or dents.

[0009] However, the aqueous coating compositions described in Patent Documents 1 to 3 may not always provide satisfactory workability. The present disclosure aims to provide an aqueous coating composition that has good workability, and preferably a coating film with good workability, pencil hardness, and scratch resistance. [Means for solving the problem]

[0010] This disclosure includes the following aspects: [1] A water-based paint composition comprising a film-forming resin (A), a crosslinking agent (B), a phosphate-modified epoxy resin (C), and an organic solvent (D), The hydroxyl value of the coating resin (A) is 150 mg KOH / g or less, the acid value of the coating resin (A) is 100 mg KOH / g or less, and the glass transition temperature of the coating resin (A) is 100°C or less. The aforementioned organic solvent (D) has a solubility parameter of 8.3 (cal / cm³). 3 ) 1 / 2 More than 9.6(cal / cm 3 ) 1 / 2 The following applies, and the organic solvent (D1) has a solubility in water of 10 g / L or less at 25°C: An aqueous coating composition in which the content of the organic solvent (D1) is 0.5 parts by mass or more and 35 parts by mass or less, based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B). [2] The aqueous paint composition according to [1], wherein the film-forming resin (A) comprises one or more selected from acrylic resin (A1), polyester resin (A2), and polyurethane resin (A3). [3] The aforementioned crosslinking agent (B) comprises an amino resin, as described in [1] or [2]. [4] The aqueous paint composition according to any one of [1] to [3], wherein the crosslinking agent (B) comprises a melamine resin. [5] The aqueous paint composition according to any one of [1] to [4], wherein the number average molecular weight of the phosphate-modified epoxy resin (C) is 400 or more and 10,000 or less. [6] The aqueous paint composition according to any one of [1] to [5], wherein the solid content of the phosphate-modified epoxy resin (C) is 1 part by mass or more and 15 parts by mass or less based on 100 parts by mass of the total solid content of the film-forming resin (A) and the crosslinking agent (B). [7] It further contains sulfonic acid compound (E), The aqueous paint composition according to any one of [1] to [6], wherein the content of the sulfonic acid compound (E) is 0.5 parts by mass or more and 15 parts by mass or less based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B). [8] An aqueous paint composition according to any one of [1] to [7], further comprising an amine compound (F). [9] The aqueous paint composition according to [8], wherein the boiling point of the amine compound (F) is 50°C or higher and 250°C or lower.

[10] It further comprises a sulfonic acid compound (E) and an amine compound (F), The aqueous paint composition according to any one of [1] to [9], wherein the neutralization rate of the sulfonic acid group of the sulfonic acid compound (E) by the amine compound (F) is 100% or more and 1,300% or less.

[11] A water-based paint composition for pre-coated metal, as described in any one of [1] to

[10] .

[12] A step of applying an aqueous paint composition described in any one of [1] to

[11] to an object to be coated to form a paint film, and A step of drying and / or curing the aforementioned coating film under conditions where the temperature reached by the object to be coated is 180°C to 270°C and the drying and / or curing time is 1 to 120 seconds or less. A method for manufacturing a coating film, including the method described above. [Effects of the Invention]

[0011] This disclosure provides an aqueous coating composition that can achieve a coating film with good workability, preferably with good workability, pencil hardness, and scratch resistance. [Modes for carrying out the invention]

[0012] The aqueous coating composition of this disclosure comprises a film-forming resin (A), a crosslinking agent (B), a phosphate-modified epoxy resin (C), and an organic solvent (D), wherein the hydroxyl value of the film-forming resin (A) is 150 mg KOH / g or less, the acid value of the film-forming resin (A) is 100 mg KOH / g or less, and the glass transition temperature of the film-forming resin (A) is 100°C or less, and the solubility parameter of the organic solvent (D) is 8.3 (cal / cm³). 3 ) 1 / 2 More than 9.6(cal / cm 3 ) 1 / 2 The following is true, and it includes an organic solvent (D1) whose solubility in water is 10 g / L or less at 25°C.

[0013] The aqueous coating compositions of this disclosure provide good workability, and preferably enable the realization of coating films with good workability, pencil hardness, and scratch resistance. While this disclosure should not be construed as limiting to any particular theory, the reasons why the aqueous coating compositions of this disclosure may achieve such effects are thought to be as follows.

[0014] In other words, the aqueous coating composition of this disclosure includes a film-forming resin and a crosslinking agent, as well as a phosphate-modified epoxy resin and a specific organic solvent. Simply adding a phosphate-modified epoxy resin may not result in sufficient workability, but by using a specific organic solvent, the film-forming resin and the phosphate-modified epoxy resin become more compatible, and even after film formation, they remain in close proximity, resulting in improved workability, preferably improved workability, pencil hardness, and scratch resistance.

[0015] (A) Film-forming resin The aforementioned film-forming resin (A) refers to a resin that can react with a crosslinking agent (B) to form a coating film. The aforementioned film-forming resin (A) preferably includes one or more selected from acrylic resin (A1), polyester resin (A2), and polyurethane resin (A3). The aforementioned film-forming resin (A) preferably has hydroxyl groups.

[0016] (Acrylic resin (A1)) The acrylic resin (A1) refers to a polymer having units derived from monomers having (meth)acryloyl groups, and can be prepared by polymerizing a monomer mixture containing monomers having ethylenically unsaturated bonds. In this specification, (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0017] The monomers having the ethylenically unsaturated bond include unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, isocrotonic acid, 2-propenoic acid, ethacrylic acid, propylacrylic acid, and isopropylacrylic acid; unsaturated polycarboxylic acids such as maleic acid, fumaric acid, and itaconic acid (including their anhydrides); monoalkyl esters of unsaturated polycarboxylic acids such as ethyl maleate, butyl maleate, ethyl fumarate, butyl fumarate, ethyl itaconate, and butyl itaconate; methyl (meth)acrylate, ethyl (meth)acrylate, (methyl (Meth)Propyl acrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-pentyl methacrylate, neopentyl methacrylate, isopentyl methacrylate, sec-pentyl methacrylate, 3-pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate Alkyl (meth)acrylate esters such as syl, dodecyl (meth)acrylate, and stearyl (meth)acrylate; (meth)acrylate esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecyl (meth)acrylate, and adamantyl (meth)acrylate; hydroxy (meth)acrylate esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Lukil; (meth)acrylic acid esters having hydroxyl groups, such as these lactone adducts (e.g., ε-caprolactone); monomers having organosilyl groups, such as γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, γ-(meth)acryloxypropylmethyldiethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, and vinylmethyldithoxysilane;Monomers having sulfonic acid groups such as α-vinylbenzenesulfonic acid, p-(meth)acrylamidepropanesulfonic acid, t-butyl(meth)acrylamidesulfonic acid; monomers having phosphate groups such as (meth)acrylic acid ester nophosphate monoesters having the hydroxyl group; (meth)acrylamide monomers such as (meth)acrylamide, N-methylol(meth)acrylamide, methoxybutyl(meth)acrylamide, diacetone(meth)acrylamide; aminoethyl(meth)acrylamide, dimethylaminoethyl(meth)acrylamide, methylaminopropyl(meth) Examples include (meth)acrylamide monomers having an amino group such as acrylamide; (meth)acrylic acid esters having an epoxy group (oxyranyl group) such as glycidyl (meth)acrylate; (meth)acrylonitrile monomers such as (meth)acrylonitrile and α-chloro(meth)acrylonitrile; vinyl carboxylate esters such as vinyl acetate and vinyl propionate; styrene monomers such as styrene, α-methylstyrene, α-methylstyrene dimer, vinyltoluene, and divinylbenzene; carbonyl group monomers; and crosslinkable monomers such as polyfunctional vinyl monomers other than those mentioned above. The monomer having an ethylenically unsaturated bond may be used alone or in combination of two or more types.

[0018] The acrylic resin (A1) preferably has at least one of a hydroxyl group and an acid group. Having at least one of a hydroxyl group and an acid group in the acrylic resin (A1) allows for a crosslinking reaction between at least one of the hydroxyl group and acid group and the reactive group of the crosslinking agent, thereby curing the coating film. To obtain at least one of a hydroxyl group and an acid group in the acrylic resin (A1), when forming the polymer, a (meth)acrylic acid ester having at least one of a hydroxyl group and an acid group can be used as the monomer having the ethylenically unsaturated bond. Furthermore, having an acid group in the acrylic resin (A1) can improve its curability.

[0019] The hydroxyl value of the acrylic resin (A1) is preferably 0 mg KOH / g or more and 150 mg KOH / g or less, more preferably 0 mg KOH / g or more and 130 mg KOH / g or less, and even more preferably 0 mg KOH / g or more and 120 mg KOH / g or less. If both hydroxyl groups and acidic groups are present, it is preferably 1 mg KOH / g or more and 150 mg KOH / g or less, more preferably 10 mg KOH / g or more and 130 mg KOH / g or less, and even more preferably 20 mg KOH / g or more and 120 mg KOH / g or less. If only hydroxyl groups are present, it is preferably 5 mg KOH / g or more and 150 mg KOH / g or less, more preferably 10 mg KOH / g or more and 130 mg KOH / g or less, and even more preferably 20 mg KOH / g or more and 120 mg KOH / g or less. When the hydroxyl value of the acrylic resin (A1) is within the above range, good workability is obtained, and preferably a coating film with good workability, pencil hardness and scratch resistance can be obtained.

[0020] The (meth)acrylic acid ester having a hydroxyl group preferably has 1 to 3 carbon atoms in the group that bonds to the (meth)acryloyl group, and more preferably has 2 carbon atoms. Including a (meth)acrylic acid ester having a hydroxyl group and having 1 to 3 carbon atoms in the group that bonds to the (meth)acryloyl group facilitates the formation of hydrogen bonds with the phosphoric acid-modified epoxy resin.

[0021] The weight-average molecular weight of the acrylic resin (A1) is preferably 2,000,000 or less, more preferably 10,000 to 1,000,000, and even more preferably 50,000 to 500,000. The smaller the weight-average molecular weight of the acrylic resin (A1), the better the storage stability of the aqueous coating composition may be. In this disclosure, the weight-average molecular weight is the value converted to polystyrene equivalent by gel permeation chromatography (GPC).

[0022] In order for the acrylic resin (A1) to have an acidic group, when forming the polymer, an acidic monomer such as an unsaturated monocarboxylic acid, an unsaturated polycarboxylic acid, a monoalkyl ester of an unsaturated polycarboxylic acid, a monomer having a sulfonic acid group, or a monomer having a phosphate group may be used as the monomer having the ethylenically unsaturated bond.

[0023] The monomer having the acid group is preferably an unsaturated monocarboxylic acid, an unsaturated polycarboxylic acid, or a monoalkyl ester of an unsaturated polycarboxylic acid, more preferably an unsaturated monocarboxylic acid or an unsaturated polycarboxylic acid, even more preferably an unsaturated monocarboxylic acid, and particularly preferably (meth)acrylic acid.

[0024] The acid value of the acrylic resin (A1) is preferably 1 mg KOH / g or more and 100 mg KOH / g or less, more preferably 5 mg KOH / g or more and 50 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 20 mg KOH / g or less. If both hydroxyl groups and acidic groups are present, it is preferably 1 mg KOH / g or more and 100 mg KOH / g or less, more preferably 5 mg KOH / g or more and 50 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 20 mg KOH / g or less. If only acidic groups are present, it is preferably 5 mg KOH / g or more and 100 mg KOH / g or less, more preferably 5 mg KOH / g or more and 50 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 20 mg KOH / g or less. Being within the above range allows for stable dispersion of the acrylic resin (A1). In this disclosure, the acid value and hydroxyl value represent the solids acid value and solids hydroxyl value, respectively, and can be measured in accordance with JIS K 0070:1999.

[0025] The glass transition temperature (Tg) of the acrylic resin (A1) is preferably 100°C or lower, more preferably 0°C to 95°C, and even more preferably 20°C to 90°C. Being within this range allows for the acquisition of a coating film with excellent coating processability.

[0026] The glass transition temperature can be calculated as the reciprocal of the sum of the respective quotients obtained by dividing the mass fraction of each monomer constituting the acrylic resin (A1) by the Tg (K: Kelvin) value of the homopolymer derived from each monomer.

[0027] More specifically, in this specification, the glass transition temperature (Tg) can be calculated by Fox's equation (T.G. Fox; Bull. Am. Phys. Soc., 1(3), 123 (1956)).

[0028] For example, when the resin is a polymer of a plurality of monomers (monomer A, monomer B,... monomer N), the following general formula: 1 / Tg = w a / Tg a + w b / Tg b + ··· + w n / Tg n Let the Tg represented by this be the Tg of the resin.

[0029] Here, Tg a : The glass transition temperature (K) of the homopolymer of monomer A, w a : The mass fraction of monomer A, Tg b : The glass transition temperature (K) of the homopolymer of monomer B, w b : The mass fraction of monomer B, Tg n : The glass transition temperature (K) of the homopolymer of monomer N, w n : The mass fraction of monomer N, means, w a + w b + ··· + w n = 1.

[0030] In the monomers forming (A1) in the acrylic resin, the monomer having an ethylenically unsaturated bond preferably contains an alkyl (meth)acrylate, and more preferably contains an alkyl (meth)acrylate having 1 to 6 carbon atoms in the alkyl group, more preferably 1 to 4 carbon atoms. Using monomers within the above range results in excellent scratch resistance of the resulting coating film. The content of the alkyl (meth)acrylate having 1 to 6 carbon atoms in the alkyl group is preferably 20% by mass or more and 100% by mass or less, more preferably 30% by mass or more and 90% by mass or less, and even more preferably 40% by mass or more and 85% by mass or less, in the alkyl (meth)acrylate.

[0031] In the monomers contained in the acrylic resin (A1), from the viewpoint of weather resistance, the content of styrene monomers is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, with a lower limit of 0% by mass or more.

[0032] If the acrylic resin (A1) has acidic groups, the aqueous coating composition may contain a basic compound. The inclusion of a basic compound in the aqueous coating composition neutralizes some or all of the acidic groups, thereby providing good water dispersibility to the acrylic resin. Examples of the basic compound include ammonia, amine compounds, alkali metals, etc. Furthermore, a portion of the amine compound (F) described later may also be the basic compound.

[0033] Furthermore, known anionic and / or nonionic surfactants may be used to impart water dispersibility to the acrylic resin.

[0034] In one embodiment, the solid content of the acrylic resin (A1) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, out of 100% by mass of the total solid content of the coating resin (A), with an upper limit of 100% by mass. In another embodiment, the solid content of the acrylic resin (A1) is 0% by mass, out of 100% by mass of the total solid content of the coating resin (A).

[0035] In this disclosure, the solid content of a component means the residue after heating the component at 150°C for 1 hour.

[0036] The acrylic resin (A1) is preferably an aqueous resin, may be a water-soluble resin, or may be a water-dispersible resin such as a colloidal dispersion type or an emulsion type (emulsion polymerization type, forced emulsion type). The acrylic resin (A1) is preferably a water-dispersible resin, more preferably an emulsion-type water-dispersible resin, and particularly preferably an emulsion-type water-dispersible resin produced by emulsion polymerization. The acrylic resin (A1) can be an aqueous resin by having acid groups and / or hydroxyl groups, and / or coexisting with an emulsifier.

[0037] When the acrylic resin (A1) is an emulsion-type water-dispersible resin, the average particle diameter of the emulsion particles is preferably 500 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less, and may be, for example, 10 nm or more, 30 nm or more, or 50 nm or more. Being within this range ensures good storage stability of the emulsion particles and the aqueous coating composition containing the emulsion particles. In this specification, the average particle diameter is the average particle diameter determined by dynamic light scattering, and can specifically be measured using an electrophoretic light scattering photometer ELSZ series (manufactured by Otsuka Electronics Co., Ltd.) or the like.

[0038] The minimum film-forming temperature (MFT) of the acrylic resin (A1) is preferably 120°C or lower. Being within this range helps to suppress blocking between the resulting coating films. In this specification, the minimum film-forming temperature refers to the lowest temperature at which a uniform, crack-free coating is formed when the emulsion-type water-dispersible resin is dried, and can be measured in accordance with JIS K 6828-2:2003.

[0039] If the acrylic resin (A1) is an emulsion-type water-dispersible resin, the emulsion may be an emulsion in which multilayer structure particles consisting of a core portion and a shell portion are dispersed.

[0040] The multilayer particles can be prepared, for example, by the method described in Japanese Patent Application Publication No. 2002-12816.

[0041] The acrylic resin (A1) can be produced by polymerizing the monomer having an ethylenically unsaturated bond, and the polymerization reaction can be carried out, for example, by heating the monomer having an ethylenically unsaturated bond in part or all of an aqueous medium (E) while stirring. The polymerization reaction is preferably an emulsion polymerization reaction. It is preferable to include a polymerization initiator in the polymerization reaction, and if necessary, an emulsifier. The reaction temperature is preferably, for example, 30 to 100°C, and the reaction time is preferably, for example, 1 to 10 hours.

[0042] As the polymerization initiator, a radical polymerization initiator is preferred. As a water-soluble free radical polymerization initiator, persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate can be used. In addition, redox initiators can be used, which are combinations of an oxidizing agent such as potassium persulfate, sodium persulfate, ammonium persulfate, or hydrogen peroxide, and a reducing agent such as sodium bisulfite, sodium thiosulfate, longalit, or ascorbic acid. These radical polymerization initiators may be dissolved in part or all of the aqueous medium (E) and used as an aqueous solution.

[0043] As the emulsifier, an anionic or nonionic emulsifier having a hydrophobic portion such as a hydrocarbon group with 6 or more carbon atoms and a hydrophilic portion such as a carboxylate, sulfonate, or sulfate partial ester in the same molecule can be used. As the anionic emulsifier, alkali metal salts or ammonium salts of sulfate partial esters of alkylphenols or higher alcohols; alkali metal salts or ammonium salts of alkyl or allyl sulfonates; polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, or polio Examples include alkali metal salts or ammonium salts of sulfuric acid hemiesters of xyethylene allyl ether; and various anionic reactive emulsifiers having acrylic, methacrylic, propenyl, allyl, allyl ether, maleic acid, and other groups with ethylenically unsaturated bonds.

[0044] Examples of nonionic emulsifiers include polyoxyalkylene ethers such as polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, or polyoxyethylene allyl ethers; and nonionic reactive emulsifiers having ethylenically unsaturated bonds with groups such as acrylic, methacrylic, propenyl, allyl, allyl ether, and maleic acid.

[0045] Furthermore, during polymerization (preferably emulsion polymerization), the use of molecular weight adjustment aids (chain transfer agents) such as mercaptan compounds and lower alcohols is often preferable from the viewpoint of promoting polymerization (preferably emulsion polymerization), and from the viewpoint of promoting the smooth and uniform formation of the coating film and improving adhesion to the substrate, and is carried out as appropriate depending on the situation.

[0046] When carrying out emulsion polymerization, any emulsion polymerization method can be used, including the conventional single-stage continuous monomer uniform dropping method, the core-shell polymerization method which is a multi-stage monomer feed method, and the power-feed polymerization method which continuously changes the monomer composition fed during polymerization.

[0047] The acrylic resin (A1) may be used in the preparation of the aqueous coating composition as an aqueous solution or aqueous dispersion containing the acrylic resin (A1) and a portion of the aqueous medium (E) described later. The aqueous solution or aqueous dispersion may further contain the emulsifier.

[0048] The acrylic resin (A1) may be a commercially available product. Alternatively, only one type may be used, or two or more types may be used in combination.

[0049] (Polyester resin (A2)) The polyester resin (A2) refers to a polymer having ester bonds within its molecule. Typically, the polyester resin (A2) may be a condensate of a polyol and a polybasic acid, and / or a modified product of said condensate.

[0050] Examples of the polyols include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol or 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, and 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl Examples include methyl-3-hydroxypropionate (BASHPN), N,N-bis-(2-hydroxyethyl)dimethylhydantoin, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, tris-(hydroxyethyl)isocyanate, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvaleric acid. One polyol may be used alone, or two or more may be used in combination.

[0051] Examples of the polybasic acids include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetraphthalic acid, methyltetrahydrophthalic anhydride, hymic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, lactic acid, dodecenyl succinic acid, dodecenyl succinic anhydride, cyclohexane-1,4-dicarboxylic acid, endo anhydride, and the like. Only one basic acid may be used, or two or more may be used in combination.

[0052] Examples of the modified material include modified polyester resins such as urethane-modified polyester resin, epoxy-modified polyester resin, acrylic-modified polyester resin, and silicone-modified polyester resin.

[0053] The polyester resin (A2) preferably has at least one of a hydroxyl group and an acid group. Having at least one of a hydroxyl group and an acid group in the polyester resin (A2) allows for a crosslinking reaction between at least one of these groups and the reactive group of the crosslinking agent, thereby curing the coating film. Furthermore, having an acid group in the polyester resin (A2) allows for stable dispersion in water.

[0054] The hydroxyl value of the polyester resin (A2) is preferably 1 mg KOH / g or more and 160 mg KOH / g or less, more preferably 1 mg KOH / g or more and 155 mg KOH / g or less, and even more preferably 1 mg KOH / g or more and 150 mg KOH / g or less. If both hydroxyl groups and acidic groups are present, it is preferably 1 mg KOH / g or more and 160 mg KOH / g or less, more preferably 1 mg KOH / g or more and 155 mg KOH / g or less, and even more preferably 1 mg KOH / g or more and 150 mg KOH / g or less. If only hydroxyl groups are present, it is preferably 1 mg KOH / g or more and 160 mg KOH / g or less, more preferably 5 mg KOH / g or more and 155 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 150 mg KOH / g or less. By having the hydroxyl value of the polyester resin (A2) within the above range, the resulting coating film can have good corrosion resistance and weather resistance.

[0055] The weight-average molecular weight of the polyester resin (A2) is preferably 150,000 or less, more preferably 1,000 to 120,000, and even more preferably 5,000 to 100,000. The smaller the weight-average molecular weight of the polyester resin (A2), the better the storage stability of the aqueous coating composition.

[0056] The acid value of the polyester resin (A2) is preferably 1 mg KOH / g or more and 100 mg KOH / g or less, more preferably 1 mg KOH / g or more and 80 mg KOH / g or less, and even more preferably 1 mg KOH / g or more and 60 mg KOH / g or less. If both hydroxyl groups and acidic groups are present, it is preferably 1 mg KOH / g or more and 100 mg KOH / g or less, more preferably 1 mg KOH / g or more and 80 mg KOH / g or less, and even more preferably 1 mg KOH / g or more and 60 mg KOH / g or less. If only acidic groups are present, it is preferably 5 mg KOH / g or more and 100 mg KOH / g or less, more preferably 5 mg KOH / g or more and 80 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 60 mg KOH / g or less.

[0057] The glass transition temperature (Tg) of the polyester resin (A2) is preferably 80°C or lower, more preferably -40°C to 60°C, and -30°C to 50°C. Being within this range allows for the acquisition of a coating film with excellent coating processability. In this disclosure, the glass transition temperature of resins other than acrylic resins can be measured by differential thermal scanning calorimetry (DSC).

[0058] In one embodiment, the solid content of the polyester resin (A2) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, out of 100% by mass of the total solid content of the coating resin (A), with an upper limit of 100% by mass. In another embodiment, the solid content of the polyester resin (A2) is 0% by mass, out of 100% by mass of the total solid content of the coating resin (A).

[0059] (Polyurethane resin (A3)) The polyurethane resin (A3) refers to a polymer having urethane bonds. Typically, the polyurethane resin (A3) may be a reaction product of a polyol, a polyisocyanate, and a chain extender and / or end-terminating agent used as needed.

[0060] Examples of the polyol include polymer polyols such as polyether polyols, polyester polyols, polycarbonate polyols, and glycerin polycaprolactone triols; and low molecular weight polyols. The number-average molecular weight of such polymer polyols may be, for example, 300 to 5,000, and moreover, 500 to 3,000. The number of hydroxyl groups contained in the polymer polyol may be 2 to 3.

[0061] Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; examples of the polyester polyol include polybutylene adipate, polyhexamethylene adipate, and polyneopentyl adipate; and examples of the polycarbonate polyol include polycaprolactone diol, poly-3-methylvalerolactone diol, and polyhexamethylene carbonate.

[0062] Examples of the low molecular weight polyols include aliphatic polyols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, pentanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, cyclohexanediol, hexanediol, dicyclohexanediol, dicyclohexanedimethanol, hydrogenated bisphenol A, and cyclohexanetriol; aromatic polyols such as bisphenol compounds such as bisphenol A, bisphenol F, and bisphenol AD, and ethylene oxide adducts or propylene oxide adducts of such bisphenol compounds; triols such as trimethylolpropane and trimethylolethane; and polyols having carboxyl groups such as dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutyric acid. The polyol may be a single type or a combination of two or more types.

[0063] The polyisocyanate refers to a compound having two or more isocyanate groups in one molecule. The polyisocyanate compound preferably includes one or more selected from aliphatic polyisocyanate compounds, aromatic polyisocyanate compounds; alicyclic polyisocyanate compounds; aromatic polyisocyanates; polymers of aliphatic polyisocyanate compounds, aromatic polyisocyanate compounds, or alicyclic polyisocyanate compounds; and modified products of aliphatic polyisocyanate compounds, aromatic polyisocyanate compounds, or alicyclic polyisocyanate compounds.

[0064] Examples of the aliphatic polyisocyanate compounds include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, undecane diisocyanate-(1,11), lysine ester diisocyanate, diethylene glycol diisocyanate, dipropylene glycol diisocyanate, triethylene glycol diisocyanate, and thiodipropyl diisocyanate.

[0065] Examples of the aromatic polyisocyanates include 1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene, 1,5-trimethyl-2,4-bis(ω-isocyanatoethyl)benzene, 1,3,5-trimethyl-2,4-bis(isocyanatomethyl)benzene, 1,3,5-triethyl-2,4-bis(isocyanatomethyl)benzene, 2,4- and / or 2,6-toluenediisocyanate, 4,4'-diphenylmethanediisocyanate, and 1,4-diisocyanatoisopropylbenzene.

[0066] Examples of the alicyclic polyisocyanate compounds include cyclohexane diisocyanate, isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate. The polyisocyanate may be used as a single type, or as a combination of two or more types.

[0067] Examples of the aforementioned polymers include allophanates, uretdiones, biuretes, isocyanurates, and trimethylolpropane (TMP) adducts of the aliphatic polyisocyanate compound, the aromatic polyisocyanate compound, and the alicyclic polyisocyanate compound.

[0068] Examples of the chain extender include the low molecular weight polyols; polyamine compounds such as ethylenediamine, propanediamine, butanediamine, hexamethylenediamine, cyclohexanediamine, isophoronediamine, dicyclohexylmethanediamine, bis(aminomethyl)cyclohexane, hydrazine, tolylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0069] Examples of the end-stopping agents include methanol, ethanol, propanol, butanol, ammonia, dibutylamine, and aminosilane. The chain extender and terminal arrester may each be used individually, or two or more may be used in combination.

[0070] The polyurethane resin (A3) preferably has at least one of a hydroxyl group and an acid group. Having at least one of a hydroxyl group and an acid group in the polyurethane resin (A3) allows the hydroxyl group to crosslink with the reactive group of the crosslinking agent, thereby curing the coating film. By using the polyol in excess of the polyisocyanate, or by using a monomer having an acid group (for example, a polyol having an acid group), a polyurethane resin (A3) having at least one of a hydroxyl group and an acid group can be obtained. Furthermore, having an acid group in the polyurethane resin (A3) allows for stable dispersion in water.

[0071] The hydroxyl value of the polyurethane resin (A3) is preferably 1 mg KOH or more and 80 mg KOH / g or less, more preferably 5 mg KOH or more and 70 mg KOH / g or less, and even more preferably 5 mg KOH / g or more and 60 mg KOH / g or less. If both hydroxyl groups and acidic groups are present, it is preferably 1 mg KOH or more and 80 mg KOH / g or less, more preferably 5 mg KOH or more and 70 mg KOH / g or less, and even more preferably 5 mg KOH / g or more and 60 mg KOH / g or less. If only hydroxyl groups are present, it is preferably 5 mg KOH / g or more and 80 mg KOH / g or less, more preferably 5 mg KOH or more and 70 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 60 mg KOH / g or less. By having a hydroxyl value within the aforementioned range, the resulting coating film may exhibit good corrosion resistance and weather resistance.

[0072] The weight-average molecular weight of the polyurethane resin (A3) is preferably 100,000 or less, more preferably 1,000 to 80,000, and even more preferably 3,000 to 60,000. The smaller the weight-average molecular weight of the polyurethane resin (A3), the better the storage stability of the aqueous coating composition.

[0073] The acid value of the polyurethane resin (A3) is preferably 1 mg KOH / g or more and 70 mg KOH / g or less, more preferably 5 mg KOH / g or more and 65 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 60 mg KOH / g or less. If both hydroxyl groups and acidic groups are present, it is preferably 1 mg KOH / g or more and 70 mg KOH / g or less, more preferably 5 mg KOH / g or more and 60 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 60 mg KOH / g or less. If only acidic groups are present, it is preferably 5 mg KOH / g or more and 70 mg KOH / g or less, more preferably 5 mg KOH / g or more and 50 mg KOH / g or less, and even more preferably 10 mg KOH / g or more and 30 mg KOH / g or less.

[0074] The glass transition temperature (Tg) of the polyurethane resin (A3) is preferably 80°C or lower, more preferably -50°C to 75°C, and even more preferably -40°C to 70°C. Being within this range allows for the acquisition of a coating film with excellent coating processability. The glass transition temperature can be measured by differential scanning calorimetry (DSC) or the like.

[0075] In one embodiment, the solid content of the polyurethane resin (A3) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, out of 100% by mass of the total solid content of the coating resin (A), with an upper limit of 100% by mass. The solid content of the polyurethane resin (A3) is 0% by mass out of 100% by mass of the total solid content of the coating resin (A).

[0076] The total content of the acrylic resin (A1), polyester resin (A2), and polyurethane resin (A3) is preferably 80% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass, of the total amount of the coating resin (A) by mass.

[0077] (Other resins) The coating-forming resin (A) may also contain other resins (A4) in addition to the acrylic resin (A1), polyester resin (A2), and polyurethane resin (A3).

[0078] Examples of the aforementioned other resins include acrylic resins, vinyl acetate resins, fluororesins, and vinyl chloride resins that do not have hydroxyl groups or acid groups. Each of these is preferably an aqueous resin, more preferably a water-dispersible resin, and even more preferably an emulsion-type water-dispersible resin. The other resin (A4) may be used in the preparation of the aqueous coating composition as an aqueous solution or aqueous dispersion containing a portion of the other resin (A4) beforehand. The aqueous solution or aqueous dispersion may contain an emulsifier.

[0079] The aforementioned acrylic resin without hydroxyl groups and acid groups represents a polymer having units derived from monomers having (meth)acryloyl groups, and can be prepared by polymerizing a mixture of monomers having ethylenically unsaturated bonds that do not have hydroxyl groups.

[0080] The weight-average molecular weight of the acrylic resin without hydroxyl and acid groups is preferably 2,000,000 or less, more preferably 10,000 to 1,000,000, and even more preferably 50,000 to 500,000. Having the weight-average molecular weight of the acrylic resin without hydroxyl and acid groups within this range can result in good storage stability of the resulting coating film.

[0081] The glass transition temperature of the acrylic resin without hydroxyl groups and acid groups is preferably 100°C or lower, more preferably 0°C to 95°C, and even more preferably 20°C to 90°C. Having the glass transition temperature of the acrylic resin without hydroxyl groups and acid groups within this range can result in good processability.

[0082] The minimum film-forming temperature (MFT) of the acrylic resin without hydroxyl and acidic groups is preferably 200°C or lower, more preferably 50°C to 150°C, and even more preferably 40°C to 120°C. By having the glass transition temperature of the acrylic resin without hydroxyl and acidic groups within this range, blocking between coating films can be suppressed.

[0083] The acrylic resin lacking hydroxyl groups and acidic groups is preferably one that has acidic groups. The acid value of the acrylic resin lacking hydroxyl groups and acidic groups is preferably 100 mg KOH / g or less, more preferably 5 mg KOH / g to 50 mg KOH / g, and even more preferably 10 mg KOH / g to 20 mg KOH / g.

[0084] When the acrylic resin without hydroxyl groups and acid groups is included, its content is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 90% by mass or less, and more preferably 85% by mass or less, of the total of the acrylic resin (A1) and the acrylic resin without hydroxyl groups and acid groups.

[0085] The hydroxyl value of the coating-forming resin (A) is 150 mg KOH / g or less, preferably 130 mg KOH / g or less, and more preferably 120 mg KOH / g or less. Having the hydroxyl value of the coating-forming resin (A) within this range provides a coating with good processability and scratch resistance.

[0086] The weight-average molecular weight of the coating-forming resin (A) is preferably 2,000,000 or less, more preferably 10,000 to 1,000,000, and even more preferably 50,000 to 500,000. Having the weight-average molecular weight of the coating-forming resin (A) within this range ensures that a coating with good processability can be obtained.

[0087] The acid value of the coating resin (A) is 100 mg KOH / g or less, preferably 5 mg KOH / g to 50 mg KOH / g, and more preferably 10 mg KOH / g to 20 mg KOH / g. The acid value of the coating resin (A) being within this range allows for stable dispersion of the coating resin (A) in the aqueous medium (E).

[0088] The glass transition temperature (Tg) of the coating-forming resin (A) is 100°C or less, preferably 0°C to 95°C, and more preferably 20°C to 90°C. By having the glass transition temperature of the coating-forming resin (A) within this range, a coating with excellent workability and scratch resistance can be obtained.

[0089] The coating-forming resin (A) may be of one type only, or two or more types may be used in combination. When two or more types of coating-forming resin (A) are included, each parameter of the coating-forming resin (A), except for the glass transition temperature, may be calculated as a weighted average value based on the parameters and content of each resin. The glass transition temperature may also be calculated by summing the values ​​obtained by dividing the mass-based content of each coating-forming resin by the glass transition temperature (K: Kelvin value), and taking the reciprocal of the result.

[0090] The content of the film-forming resin (A) is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, preferably 100 parts by mass or less, more preferably 95 parts by mass or less, and even more preferably 90 parts by mass or less, per 100 parts by mass of solids of the aqueous paint composition. In this specification, the content of the film-forming resin (A) refers to the content of solids only.

[0091] (B) Crosslinking agent The crosslinking agent (B) refers to a compound that reacts with the coating resin (A) to form a coating film. In a preferred embodiment, the crosslinking agent is a compound having two or more groups in one molecule that can react with hydroxyl groups.

[0092] The crosslinking agent (B) preferably contains an amino resin. Examples of the amino resin include melamine resin, urea resin, and benzoguanamine. From the viewpoint of storage stability of the resulting aqueous coating composition and various physical properties of the resulting coating film (processability, scratch resistance), the crosslinking agent (B) preferably contains a melamine resin (B1).

[0093] Melamine resin (B1) is a thermosetting resin synthesized from melamine and an aldehyde, and is preferably a compound or polycondensate thereof having three reactive functional groups represented by the following formula in one triazine core molecule. -NX 1 X 2 [X 1 , X 2Each of these independently consists of a hydrogen atom, a methylol group, or a -CH2-OR group. 1 It represents. R 1 C 1-8 Alkyl alkyl groups, preferably linear or branched C 1-8 Represents an alkyl group. Multiple -CH2-OR groups within the same molecule 1 If it includes multiple R 1 They may be the same or different.

[0094] As for melamine resin (B1), the reactive functional group is -N(CH2OR 2 )2 only, full alkyl type; reactive functional group -N(CH2OR 2 Methylol group containing (CH2OH); reactive functional group -N(CH2OH) 2 Imino group type containing )(H); reactive functional group: -N(CH2OR 2 )(CH2OH) and -N(CH2OR 2 Four types of methylol / imino group forms can be exemplified, including )(H) or -N(CH2OH)(H). 2 C 1-4 Represents an alkyl group or a hydrogen atom.

[0095] The melamine resin (B1) preferably contains a full alkyl type melamine resin, and examples of full alkyl type melamine resins include methylated melamine resin, butylated melamine resin, isobutylated melamine resin, etc. The content of the full alkyl type melamine resin in the melamine resin (B1) is preferably 80% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass, out of 100% by mass of the total amount of melamine resin (B1). Being within this range can result in good storage stability of the resulting coating composition.

[0096] The degree of polymerization of the melamine resin (B1) is 1 or higher, preferably 1.2 or higher, more preferably 1.5 or higher, preferably 10 or lower, more preferably 5 or lower, and even more preferably 3 or lower.

[0097] The number-average molecular weight of the melamine resin (B1) is preferably 300 or more, preferably 2,000 or less, more preferably 1,300 or less, even more preferably 1,000 or less, and particularly preferably 800 or less.

[0098] In this specification, the number-average molecular weight is the value converted to polystyrene equivalent by gel permeation chromatography (GPC).

[0099] As the melamine resin (B1), commercially available products can be used, for example, Cymel 303, Cymel 325, Cymel 350, Cymel 370, Mycoat 715 (all methylated melamine resins, manufactured by Ornex Japan Co., Ltd.), Cymel 202, Cymel 235, Cymel 254, Cymel 1123, Cymel 1128, Cymel 1170, Mycoat 212 (all methyl-butylated mixed melamine resins, manufactured by Ornex Japan Co., Ltd.), Sumimar M-40S (methylated melamine resin, manufactured by Sumitomo Chemical Co., Ltd.), Amidia J-820-60, Amidia L-127-60 (both butylated melamine resins, manufactured by DIC Corporation), etc. These may be used individually or in combination of two or more.

[0100] The content of the melamine resin (B1) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, out of 100% by mass of the total amount of the crosslinking agent (B), with an upper limit of 100% by mass.

[0101] The crosslinking agent (B) may contain other crosslinking agents (B2) in addition to the melamine resin (B1). Examples of other crosslinking agents (B2) include melamine resins other than the melamine resin (B1), urea resins, benzoguanamine resins, and other amino resins. The amino resin has high reactivity with the film-forming resin (A), resulting in a good appearance and moisture resistance of the resulting coating film. The crosslinking agent (B) may be of one type only, or two or more types may be used in combination.

[0102] The ratio of the crosslinking agent (B) to the content of the coating resin (A) ((B) / (A)) is preferably 3 / 97 to 35 / 65 by mass, more preferably 5 / 95 to 30 / 70, and even more preferably 10 / 90 to 20 / 80. Being within this range results in good processability and scratch resistance of the resulting coating film.

[0103] (C) Phosphate-modified epoxy resin Phosphate-modified epoxy resin (C) is a phosphate group [-OPO(OH)(OR 3 )](R here 3 is a hydrogen atom, a phenyl group, or C 1-20 It has an alkyl group, preferably a hydrogen atom.

[0104] The phosphate-modified epoxy resin (C) refers to an epoxy resin into which phosphate groups have been introduced. The phosphate-modified epoxy resin (C) is preferably one with high affinity for organic solvents (D), particularly organic solvent (D1), and especially preferably one that is compatible with them. As a result, the compatibility between the phosphate-modified epoxy resin (C) and the film-forming resin (A) and / or crosslinking agent (B) in the aqueous coating composition is good, and because they are in close proximity within the coating film, good workability is expected.

[0105] Phosphate-modified epoxy resin (C) can be obtained, for example, by adding a phosphate compound to an epoxy resin. Specifically, it can be obtained by mixing the epoxy resin and the phosphate compound in a mass such that the molar ratio of the glycidyl groups of the epoxy resin to the phosphate groups of the phosphate compound is 1:1 to 1:2, and reacting them at 80°C for 120 minutes, for example.

[0106] The epoxy resin is preferably an epoxy resin having glycidyl groups only at both ends. In one embodiment, the phosphate-modified epoxy resin (C) does not contain a phosphate-modified epoxy resin that has reacted with sulfonic acid.

[0107] Examples of the epoxy resin include bisphenol-type epoxy resins, novolac-type epoxy resins, and modified epoxy resins obtained by reacting various modifying agents with glycidyl groups or hydroxyl groups in these epoxy resins. Among these, bisphenol-type epoxy resins are preferred, and bisphenol A-type epoxy resins are more preferred.

[0108] Commercially available epoxy resins may be used as the aforementioned epoxy resins, for example, jER825, jER828, jER834, jER1004, jER1007, jER1009, jER1010, jER1255HX30 (all bisphenol A type, manufactured by Mitsubishi Chemical Corporation), jER 1009F (bisphenol F type, manufactured by Mitsubishi Chemical Corporation), etc., with jER828, jER834, jER1004, jER1007, and jER1009 being preferred.

[0109] The number-average molecular weight of the epoxy resin is preferably 300 to 10,000, for example, when the modified phosphate compound is phosphoric acid.

[0110] As the epoxy resin, acrylic-modified epoxy resin, polyester-modified epoxy resin, and the like may be used.

[0111] The aforementioned phosphate-based compound is not particularly limited as long as it can introduce a phosphate group into the epoxy resin, but examples include orthophosphoric acid and acidic phosphate esters.

[0112] The aforementioned acidic phosphate ester refers to a compound in which one or two of the three hydrogen atoms of phosphoric acid (O=P(OH)3) are replaced by an organic group. Here, the organic group is an alkyl group (for example, having 1 to 24 carbon atoms) or an alkyl ether group (for example, R 4 -OR 5 Represented by O-, R 4 is C 1-5 It is an alkyl group, R 5 C 1-3 Alkylene group, preferably C 2-3 Examples of acidic phosphate esters include alkylene groups and aromatic groups. Examples of the acidic phosphate esters include methyl acid phosphate, butyl acid phosphate, 2-ethylhexyl acid phosphate, isodecyl acid phosphate, lauryl acid phosphate, isotridecyl acid phosphate, oleyl acid phosphate, tetracosyl acid phosphate, and phenyl acid phosphate.

[0113] The molecular weight of the phosphate compound is preferably 98 to 1,200.

[0114] The number-average molecular weight of the phosphate-modified epoxy resin (C) is preferably 400 to 10,000, more preferably 460 to 8,000. Having the number-average molecular weight of the phosphate-modified epoxy resin (C) within this range contributes to the formation of a coating film that has high solvent resistance, sufficient bendability, workability, and chemical resistance, and preferably further good pencil hardness and scratch resistance.

[0115] The solid content of the phosphate-modified epoxy resin (C) is preferably 0.5 parts by mass to 15 parts by mass, more preferably 1 part by mass to 10 parts by mass, and even more preferably 1 part by mass to 5 parts by mass, based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B). By including the phosphate-modified epoxy resin (C) within the above range, a coating film with sufficient workability, preferably workability, pencil hardness, and scratch resistance can be formed.

[0116] (D) Organic solvents Organic solvents refer to organic compounds that exist as liquids at room temperature (25°C, 1,013 hPa). Organic solvent (D) has a solubility parameter of 8.3 (cal / cm³). 3 ) 1 / 2 More than 9.6(cal / cm 3 ) 1 / 2 It contains an organic solvent (D1) which has the following characteristics and a solubility in water of 10 g / L or less at 25°C.

[0117] The solubility parameter (hereinafter also referred to as the "SP value") of the organic solvent (D1) is 8.3 (cal / cm³). 3 ) 1 / 2 More than 9.6(cal / cm 3 ) 1 / 2 The following is true: Because the solubility parameter of the organic solvent (D1) is within the aforementioned range, the compatibility between the phosphoric acid-modified epoxy resin (C) and the film-forming resin (A) and / or crosslinking agent (B) in the aqueous paint composition is good, and since both are located in close proximity within the paint film, it is believed that high workability can be obtained.

[0118] The solubility parameter of the organic solvent (D1) is preferably 8.3 (cal / cm³). 3 ) 1 / 2 More than 9.6(cal / cm 3 ) 1 / 2 More preferably 8.5 (cal / cm 3 ) 1 / 2 More than 9.4(cal / cm 3 ) 1 / 2 More preferably, 8.7 (cal / cm³) 3 )1 / 2 More than 9.2(cal / cm 3 ) 1 / 2 The following applies:

[0119] The aforementioned solubility parameter (unit: (cal / cm) 3 ) 1 / 2 SP value is an indicator of polarity; a larger SP value indicates higher polarity, and a smaller SP value indicates lower polarity. In this disclosure, the SP value can be measured by the following method (Reference: SUH, CLARKE, JPSA-1, 5, 1671-1681 (1967)).

[0120] [Method for measuring solubility parameters] As a sample, 0.5 g of organic solvent is weighed into a 100 ml beaker, 10 ml of acetone is added using a volumetric pipette, and the solvent is dissolved using a magnetic stirrer. A poor solvent is added dropwise to this sample using a 50 ml burette at a measurement temperature of 20°C, and the point at which turbidity occurs is recorded as the volume added. Deionized water is used as the high-SP poor solvent, and n-hexane is used as the low-SP poor solvent, and turbidity is measured for each. The SP value δ of the organic solvent is given by the following formula. δ=(V ml 1 / 2 δ ml +V mh 1 / 2 δ mh ) / (V ml 1 / 2 +V mh 1 / 2 ) V i : Molecular volume of solvent i (ml / mol) φ i : Volume fraction of each solvent i at the diacritic point δ i SP value of solvent i ml: Low SP poor solvent mixed system mh: High SP poor solvent mixed system

[0121] Furthermore, the molecular volume and SP value of the solvent mixture system containing solvent 1 and solvent 2 are given by the following calculation formula. V m =V1V2 / (φ1V2+φ2V1) δ m = φ1δ1 + φ2δ2

[0122] At 25°C, the solubility of the organic solvent (D1) in water (hereinafter also referred to as "water solubility") is 10 g / L or less. When the solubility of the organic solvent (D1) in water is within the above range, the organic solvent (D1) does not mix with water and is appropriately present in the vicinity of the film-forming resin (A), the crosslinking agent (B), and the phosphate-modified epoxy resin (C), and it is considered that the homogeneity of the resulting coating film is improved.

[0123] At 25°C, the solubility of the organic solvent (D1) in water is preferably 0 g / L or more and 10 g / L or less, more preferably 0 g / L or more and 5 g / L or less, still more preferably 0 g / L or more and 3 g / L or less.

[0124] Specific examples of the organic solvent (D1) include aromatic hydrocarbons such as xylene (SP value: 8.8 (cal / cm 3 ), water solubility: 0.2 g / L), toluene (SP value: 8.9 (cal / cm 1 / 2 ), water solubility: 0.005 g / L), benzene (SP value: 9.2 (cal / cm 3 ), water solubility: 1.8 g / L); glycol diethers such as dibutyl diglycol (SP value: 8.3 (cal / cm 1 / 2 ), water solubility: 3.0 g / L); and alcohols such as texanol (SP value: 9.6 (cal / cm 3 ), water solubility: 0.9 g / L). These may be used alone or in combination of two or more. 1 / 2 、水溶解度:1.8g / L)等の芳香族炭化水素;ジブチルジグリコール(SP値:8.3(cal / cm 3 ) 1 / 2 、水溶解度:3.0g / L)等のグリコールジエーテル;テキサノール(SP値:9.6(cal / cm 3 ) 1 / 2 、水溶解度:0.9g / L)等のアルコールが挙げられる。これらは、単独で用いてもよく、2種以上を併用してもよい。

[0125] The content of the organic solvent (D1) in the organic solvent (D) is preferably 60% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, still more preferably 80% by mass or more and 100% by mass or less in 100% by mass of the total amount of the organic solvent (D).

[0126] The content of the organic solvent (D1) is preferably 0.5 parts by mass or more and 35 parts by mass or more preferably 1 part by mass or more and 30 parts by mass, and even more preferably 5 parts by mass or more and 25 parts by mass or 5 parts by mass or more and 10 parts by mass, based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B).

[0127] The organic solvent (D) may include other organic solvents (D2) in addition to the organic solvent (D1). Examples of other organic solvents (D2) include hydrocarbon solvents such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane; glycol solvents such as ethylene glycol, propylene glycol, butanediol, pentanediol, diethylene glycol, dipropylene glycol, and triethylene glycol; ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol Examples of organic solvents (D2) include glycol ether solvents such as glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate; alcohol solvents such as methanol, ethanol, isopropyl alcohol, and benzyl alcohol; cyclic ether solvents such as dioxane and tetrahydrofuran; alcohol ester solvents such as 2,2,4-trimethylpentane-1,3-diol monoisobutyrate; ketone solvents such as acetone; and N-methyl-2-pyrrolidone. Using such organic solvents (D2) results in a water-based paint composition with good wettability with the substrate. However, organic solvent (D1) and organic solvent (D2) are different.

[0128] The organic solvent (D2) is preferably a hydrophilic organic solvent, and the solubility of the organic solvent (D2) in water at 25°C is preferably 1 g / L or more, 3 g / L or more, greater than 3 g / L, 5 g / L or more, greater than 5 g / L, 10 g / L or more, greater than 10 g / L, 15 g / L or more, 30 g / L or more, or 50 g / L or more. The organic solvent (D2) may be miscible with water as desired.

[0129] The boiling point of the organic solvent (D2) is preferably 150°C to 300°C, more preferably 180°C to 250°C. Examples of such organic solvents (D2) include glycol-based solvents such as propylene glycol (1,2-propanediol), 1,4-butanediol, 1,5-pentanediol, diethylene glycol, and dipropylene glycol. These may be used individually or in combination of two or more types.

[0130] The content of the organic solvent (D2) is 0 parts by mass or more and 20 parts by mass or less, more preferably 0 parts by mass or more and 10 parts by mass or less, and even more preferably 0 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B). Being within this range results in good wettability to the substrate and, furthermore, good coating processability.

[0131] In particular, the SP value of the organic solvent (D2) is 8.3 (cal / m³). 3 ) 1 / 2 If less than the specified value, the content of organic solvent (D1) and organic solvent (D2) per 100 parts by mass of the total solid content of the coating resin (A) and crosslinking agent (B) is preferably 0.5 parts by mass or more and 30 parts by mass or less for organic solvent (D1) and 0 parts by mass or more and 5 parts by mass or less for organic solvent (D2), more preferably 1 part by mass or more and 25 parts by mass or less for organic solvent (D1) and 0 parts by mass or more and 3 parts by mass or less for organic solvent (D2), and even more preferably 5 parts by mass or more and 10 parts by mass or less for organic solvent (D1) and 0 parts by mass or more and 2 parts by mass or less for organic solvent (D2).

[0132] In the aqueous coating composition of the present disclosure, the content of the organic solvent (D) in the total of the aqueous medium and the organic solvent (D) described later is preferably 3% by mass or more and 30% by mass or less, more preferably 4% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less. Being within this range reduces the burden on the environment and improves the storage stability of the aqueous coating composition, the wettability to the substrate, and the appearance of the resulting coating film.

[0133] The content of the organic solvent (D) is preferably 0.5 parts by mass or more and 35 parts by mass or less, more preferably 1 part by mass or more and 25 parts by mass or less, and even more preferably 5 parts by mass or more and 10 parts by mass or less, based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B).

[0134] The aqueous coating compositions of this disclosure may further contain a sulfonic acid compound (E) and / or an amine compound (F).

[0135] (E) Sulfonic acid compounds The sulfonic acid compound (E) acts as a catalyst to promote the reaction between the film-forming resin (A) and the crosslinking agent (B), which can result in a paint composition with good curability.

[0136] The sulfonic acid compound (E) may be a monosulfonic acid compound or a polysulfonic acid compound. Examples of the sulfonic acid compound include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid; and the like. The sulfonic acid compound (E) may be used alone or in combination of two or more.

[0137] The content of the sulfonic acid compound (E) is preferably 0.5 parts by mass to 15 parts by mass, more preferably 1 part by mass to 10 parts by mass, and even more preferably 1 part by mass to 5 parts by mass, based on 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B). Having the content of the sulfonic acid compound (E) within this range can result in better processability and adhesion of the resulting coating film.

[0138] (F) Amine compound The amine compound (F) has the effect of neutralizing the sulfonic acid compound (E), and by coexisting with the sulfonic acid compound (E) to achieve a specific neutralization rate, it becomes easier to achieve both storage stability and high reactivity during heat drying and curing after painting. A portion of the amine compound (F) may exist in the form of a salt with the sulfonic acid compound (E).

[0139] The amine compound (F) refers to a compound having one or more amino groups. Examples of the amino groups include primary amino groups, secondary amino groups, and tertiary amino groups, with one or more selected from secondary and tertiary amino groups being preferred.

[0140] The substituents on the nitrogen atom of the amine compound (F) are preferably saturated or unsaturated aliphatic hydrocarbon groups, and the hydrogen atoms contained in the saturated or unsaturated aliphatic hydrocarbon group may be independently substituted with -COOH, -OH, etc., and the -CH2- contained in the saturated or unsaturated aliphatic hydrocarbon group may be replaced with -O-. Furthermore, the substituents on the nitrogen atom of the amine compound may be bonded to each other to form a ring containing the nitrogen atom.

[0141] Examples of the amine compound (F) include secondary aliphatic amine compounds such as diethylamine, di-n-propylamine, diisopropylamine, diisobutylamine, di-n-butylamine, di-sec-butylamine, diamylamine, N-ethyl-1,2-dimethylpropylamine, N-methylhexylamine, di-n-octylamine, and diallylamine; tertiary aliphatic amine compounds such as triethylamine, tributylamine, triallylamine, N,N-dimethylethanolamine, N-methyldiallylamine, and N,N-dimethylallylamine; secondary cyclic amine compounds such as piperidine, 2-pipecolin, 3-pipecolin, 4-pipecolin, 2,4-lupetidine, 2,6-lupetidine, 3,5-lupetidine, and 3-piperidinemethanol; tertiary cyclic amine compounds such as N-methylpiperidine, N-methylpiperazine, and N-methylmorpholine; and aromatic amine compounds such as pyridine and 4-ethylpyridine.

[0142] The boiling point of the amine compound (F) is preferably 50°C to 250°C, more preferably 70°C to 220°C, and even more preferably 100°C to 220°C. Having the boiling point of the amine compound (F) within this range further enhances the storage stability of the aqueous coating composition.

[0143] The content of the amine compound (F) is preferably in a range such that the neutralization rate of the sulfonic acid compound (E) by the amine compound (F) is 100% or more and 1,300% or less, more preferably 120% or more and 1,100%, and even more preferably 140% or more and 1,000% or less. The neutralization rate may be 900% or less, and even more preferably 800% or less.

[0144] The aforementioned neutralization rate is a molar-based neutralization rate and can be calculated using the following formula. Neutralization rate (%) = [(Base value of amine compound (F) × Number of moles of amine compound (F)) / (Acid value of sulfonic acid compound (E) × Number of moles of sulfonic acid compound (E)] × 100

[0145] The sulfonic acid compound (E) and the amine compound (F) may be used directly in the preparation of the aqueous paint composition, or they may be used as a mixture prepared in advance. In this case, in the mixture, some or all of the sulfonic acid compound (E) and the amine compound (F) may form a salt (for example, a salt in which the sulfonic acid group in the sulfonic acid compound (E) is blocked by the amino group in the amine compound (F)), or a salt may be formed of some or all of the sulfonic acid compound (E) and the amine compound (F) before being incorporated into the paint composition. Examples of salts of some or all of the sulfonic acid compound (E) and the amine compound (F) include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as dinonylnaphthalenesulfonic acid and dinonylnaphthalenesulfonic acid, and their amine block bodies. Commercial products may also be used as salts of some or all of the sulfonic acid compound (E) and the amine compound (F).

[0146] The aqueous paint composition may, if necessary, contain water as an aqueous medium in addition to the organic solvent (D).

[0147] The content of the aqueous medium is preferably 20% to 90% by mass, more preferably 25% to 85% by mass, and even more preferably 30% to 60% by mass, out of 100% by mass of the total amount of the aqueous coating composition.

[0148] (others) The aqueous paint composition may further contain other additives as needed. Examples of these other additives include extender pigments; colorants such as coloring pigments and dyes; rust-preventive pigments; heat-shielding pigments; lustrous pigments; aggregates (resin particles, silica particles, etc.); waxes; solvents other than those mentioned above; ultraviolet absorbers (benzophenone-based ultraviolet absorbers, etc.); antioxidants (phenol-based, sulfoid-based, hindered amine-based antioxidants, etc.); plasticizers; coupling agents (silane-based, titanium-based, zirconium-based coupling agents, etc.); anti-sagging agents; viscosity modifiers; pigment dispersants; pigment wetting agents; surface modifiers (silicone-based, organic polymer-based, etc.); leveling agents; color separation inhibitors; sedimentation inhibitors; settling inhibitors; defoaming agents; surfactants; antifreeze agents; emulsifiers; rust inhibitors; preservatives; fungicides; antibacterial agents; stabilizers, etc. These additives may be used individually or in combination of two or more.

[0149] Examples of the aforementioned extender pigments include calcium carbonate, barium sulfate, clay, talc, mica, and glass fiber. These may be used individually or in combination of two or more.

[0150] In one embodiment, the amount of extender pigment is preferably 1 to 40 parts by mass, more preferably 10 to 30 parts by mass, based on 100 parts by mass of the total solid content of the coating resin (A) and curing agent (B). Having the amount of extender pigment within this range makes it easier to improve the scratch resistance of the coating film.

[0151] Examples of the aforementioned coloring pigments include inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and cold dust; organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo yellow, induthrone blue, dibromanzathrone red, perylene red, azo red, and anthraquinone red; and aluminum powder, alumina powder, bronze powder, copper powder, tin powder, zinc powder, iron phosphide, and finely atomized titanium. These may be used individually or in combination of two or more.

[0152] In this disclosure, the term "rust-preventive pigment" refers to a pigment that exhibits rust-preventive properties and can function as an inhibitor. Examples of rust-preventive pigments include basic rust-preventive pigments such as lead-based rust-preventive pigments, boric acid-based rust-preventive pigments, silica-based rust-preventive pigments, and alkaline earth metal composite oxide-based rust-preventive pigments; passive film-forming rust-preventive pigments such as chromic acid-based rust-preventive pigments, molybdic acid and / or tungstic acid-based rust-preventive pigments, phosphoric acid-based rust-preventive pigments, and organometallic salt-based rust-preventive pigments; reducing rust-preventive pigments such as metallic rust-preventive pigments, phosphite-based rust-preventive pigments, and hypophosphorous acid-based rust-preventive pigments; and pigments that utilize the form of mica-like iron oxide, leafing aluminum, etc.

[0153] As the rust-preventive pigment, a passive film-forming rust-preventive pigment is preferred, and a phosphate-based rust-preventive pigment is more preferred. Examples of the phosphate-based rust-preventive pigment include metal salts of phosphates. Examples of phosphates include orthophosphate, pyrophosphate, tripolyphosphate, tetrapolyphosphate, metaphosphate, etc., and examples of metals that may be included in the metal salt include iron, aluminum, magnesium, calcium, molybdenum, zinc, etc. Specific examples of the phosphate-based rust-preventive pigment include zinc phosphate, aluminum phosphate, magnesium phosphate, calcium phosphate, aluminum tripolyphosphate, and aluminum phosphate molybdate, aluminum phosphate zinc, etc.

[0154] Commercially available products may be used as the rust-preventive pigment. Examples of such commercially available products include LF-Bousei ZP-DL, LF-Bousei PM-303W, LF-Bousei MZP-500, LF-Bousei MGM-200, LF-Bousei CP-Z, and LF-Bousei AP-200 (manufactured by Kikuchi Color Co., Ltd.).

[0155] The heat-shielding pigment refers to a pigment that does not absorb light in the near-infrared wavelength range (wavelength: 780nm to 2,500nm) or has a low absorption rate of light in the near-infrared wavelength range (wavelength: 780nm to 2,500nm). The heat-shielding pigment is not particularly limited, and the following inorganic and organic heat-shielding pigments can be used.

[0156] Examples of inorganic heat-shielding pigments include metal oxide pigments such as titanium dioxide, magnesium oxide, barium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, indium oxide, sodium titanate, silicon oxide, nickel oxide, manganese oxide, chromium oxide, iron oxide, copper oxide, cerium oxide, and aluminum oxide; iron oxide-manganese oxide, iron oxide-chromium oxide (for example, Dainichi Seika's Dipyroxide Color Black #9595, Asahi Kasei Kogyo's Black 6350), and iron oxide-cobalt oxide-chromium oxide (for example, Dainichi Seika's Dipyroxide Color Brown). Examples include composite oxide pigments such as #9290, dipyroxide color black #9590), copper oxide-magnesium oxide (e.g., dipyroxide color black #9598 from Dainichi Seika Co., Ltd.), manganese oxide-bismuth oxide (e.g., Black 6301 from Asahi Kasei Kogyo Co., Ltd.), and manganese oxide-yttrium oxide (e.g., Black 6303 from Asahi Kasei Kogyo Co., Ltd.); metallic pigments such as silicon, aluminum, iron, magnesium, manganese, nickel, titanium, chromium, and calcium; and alloy pigments such as iron-chromium, bismuth-manganese, iron-manganese, and manganese-yttrium. These may be used individually or in combination of two or more.

[0157] Examples of organic heat-shielding pigments include azo pigments, azomethine pigments, lake pigments, thioindigo pigments, anthraquinone pigments (anthanthrone pigment, diaminoanthraquinonyl pigment, indanthrone pigment, flavanthrone pigment, anthrapyrimidine pigment, etc.), perylene pigments, perinone pigments, diketopyrrolopyrrole pigments, dioxazine pigments, phthalocyanine pigments, quiniphthalone pigments, quinacridone pigments, isoindoline pigments, isoindolinone pigments, etc. These may be used individually or in combination of two or more.

[0158] Examples of the aforementioned luminous pigments include foil pigments such as aluminum foil, bronze foil, tin foil, gold foil, silver foil, titanium metal foil, stainless steel foil, nickel-copper alloy foil, and foil-like phthalocyanine blue. These may be used individually or in combination of two or more.

[0159] As the wax, waxes known to those skilled in the art for use in paints can be used, such as microcrystalline, polyethylene, polypropylene, paraffin, carnauba, and modified versions thereof. These may be used individually or in combination of two or more.

[0160] The aqueous coating composition disclosed herein is a one-component aqueous coating composition. The aqueous coating composition disclosed herein is preferably used for pre-coated metals.

[0161] <Method for preparing a water-based paint composition> The method for preparing the aqueous paint composition of this disclosure is not particularly limited and can be carried out by mixing the components. For example, mixing can be done using a mixer, disperser, and / or kneader such as a roller mill, ball mill, bead mill, pebble mill, sand grind mill, pot mill, paint shaker, or disperser. A coating film formed from the aqueous coating composition and a method for manufacturing the coating film are also included within the technical scope of this disclosure.

[0162] <Object to be coated> Examples of substrates to be coated with the aqueous coating composition of this disclosure include galvanized steel sheets, zinc-aluminum alloy coated steel sheets, aluminum alloy coated steel sheets, hot-dip zinc-aluminum-magnesium alloy coated steel sheets, stainless steel sheets, cold-rolled steel sheets, etc., manufactured by melting or electrolytic methods. In addition to these steel sheets or coated steel sheets, metal sheets such as aluminum sheets (including aluminum alloy sheets) can also be coated.

[0163] The workpiece to be coated is preferably surface-treated. Specifically, the workpiece to be coated is preferably subjected to a chemical conversion treatment after undergoing a pretreatment such as alkaline degreasing, hot water washing, or water washing. The chemical conversion treatment may be carried out by known methods, and includes, for example, non-chromate treatments such as chromate treatment and zinc phosphate treatment. The surface treatment can be appropriately selected depending on the steel sheet used, but treatments that do not contain heavy metals are preferred. By applying the aqueous coating composition of this disclosure onto the workpiece that has undergone such chemical conversion treatment, the adhesion of the coating film to the metal sheet surface is improved, as is the corrosion resistance. Alternatively, an undercoat coating (primer coating) can be formed on the metal sheet surface that has undergone chemical conversion treatment, and the coating can be applied on top of that. The thickness of the undercoat coating is preferably 3 μm or more, more preferably 5 μm or more, preferably 15 μm or less, and more preferably 10 μm or less.

[0164] <Method for manufacturing coating film> The method for manufacturing the coating film disclosed herein is: A step of applying the aqueous coating composition of the present disclosure to an object to be coated to form a coating film, and The process includes a step of drying and / or curing the aforementioned coating film under conditions where the maximum temperature attainable is 180°C to 270°C and the drying and / or curing time is 1 to 120 seconds, in order to obtain a coating film.

[0165] The method for applying the aqueous coating composition to the object to be coated is not particularly limited, but conventionally known methods such as the roll coater method, airless spray method, electrostatic spray method, and curtain flow coater method can be used. Preferably, the roll coater method and the curtain flow coater method are used, and more preferably, the roll coater method.

[0166] The maximum temperature reached is 180 to 270°C, preferably 190 to 260°C, and more preferably 200 to 250°C.

[0167] The drying and / or curing time is 1 to 120 seconds, preferably 1 to 60 seconds, more preferably 1 to 60 seconds, even more preferably 1 to 30 seconds, and may be 1 to 10 seconds, or even more preferably 1 to 6 seconds.

[0168] The method for drying and / or curing the aforementioned coating film is not particularly limited, but heating means such as hot air heating, infrared heating, and induction heating can be used.

[0169] The film thickness of the coating after drying and / or curing (dry film thickness) is preferably 1 μm or more, more preferably 5 μm or more, preferably 30 μm or less, and more preferably 25 μm or less.

[0170] A laminate having the aforementioned object to be coated and the coating film formed on the object to be coated is also included in the technical scope of this disclosure.

[0171] If the object to be coated has the coating film on one surface, it may also have a coating film formed from a known aqueous coating composition, such as an aqueous coating composition containing an epoxy resin, on the other surface.

[0172] The aqueous coating composition of this disclosure can be used to obtain a coating film that has high curability and good coating film properties (adhesion, crack resistance, and other workability, scratch resistance), particularly good work adhesion, preferably high work adhesion, pencil hardness, and scratch resistance, even when coating is performed under conditions that are higher and shorter than those typically used for coating metal substrates (for example, drying / curing temperature of 60-80°C, drying / curing time of 30 minutes to 1 hour).

[0173] The coating obtained from the aqueous coating composition of this disclosure is less likely to peel off from the coated object even when processed such as bending, exhibits good workability, and preferably also has excellent pencil hardness and scratch resistance. Therefore, the aqueous coating composition of this disclosure can be suitably used for coating metals, particularly as a precoat. [Examples]

[0174] The present invention will be further described in detail by the following examples, but the present invention is not limited thereto. The components used in the preparation of the aqueous paint composition are as follows:

[0175] Preparation of coating resin (A1) (Preparation example A1-1) 0.6 parts by mass of Perex SS-H (surfactant, manufactured by Kao Corporation) was dissolved in 60.0 parts by mass of deionized water. A monomer mixture consisting of 69.5 parts by mass of methyl methacrylate, 23.5 parts by mass of n-butyl acrylate, 5.0 parts by mass of 2-hydroxyethyl methacrylate, and 2.0 parts by mass of methacrylic acid was added to this mixture and stirred to prepare 160.6 parts by mass of monomer preemulsification. Separately, 1.0 part by mass of ammonium persulfate was dissolved in 20.0 parts by mass of deionized water as an initiator to prepare an initiator aqueous solution.

[0176] In a reaction vessel equipped with a thermometer, condenser, and stirrer, 40.0 parts by mass of deionized water and 0.4 parts by mass of Perex SS-H were charged and heated to 80°C under a nitrogen atmosphere. While maintaining the temperature at 80°C, the initiator aqueous solution was added dropwise over 180 minutes, and 10 minutes after the start of the dropwise addition, the monomer preemulsion was added dropwise from another opening of the reaction vessel over 150 minutes to carry out emulsion polymerization. After the dropwise addition of the initiator aqueous solution was completed, the mixture was heated and stirred at 80°C for another 60 minutes, then cooled to room temperature, and 2.1 parts by mass of dimethylethanolamine was added to prepare an acrylic resin emulsion (solid content concentration: 45% by mass) in which the film-forming resin (A1-1) was dispersed in an aqueous medium.

[0177] (Preparation examples A1-2 to A1-6) The film-forming resins (A1-2) to (A1-6) were prepared in the same manner as described above, except that the monomer type, amount, and initiator amount were changed as shown in Table 1. The characteristic values ​​such as hydroxyl value for each film-forming resin are shown in Table 1.

[0178] [Table 1]

[0179] Preparation of coating resin (A2) (Preparation example A2-2) In a reaction vessel equipped with a thermometer, condenser, and stirrer, 26.5 parts by mass of isophthalic acid, 37.3 parts by mass of neopentyl glycol, 22.3 parts by mass of phthalic anhydride, 9.4 parts by mass of trimethylolpropane, and 0.1 parts by mass of dibutyltin oxide as a catalyst were charged. The temperature was raised from 150°C to 230°C over 3 hours and held at 230°C for about 5 hours. After that, it was cooled to 130°C, 4.4 parts by mass of trimellitic anhydride was added, and the mixture was stirred for 1 hour. To this, 7.0 parts by mass of diethanolamine and 150.0 parts by mass of deionized water were added to prepare a polyester resin dispersion (solid content concentration: 40% by mass) in which the film-forming resin (A2-2) was dispersed in an aqueous medium.

[0180] (Preparation examples A2-3 to A2-7) The film-forming resins (A2-3) to (A2-7) were prepared in the same manner as described above, except that the monomer species and quantities were changed as shown in Table 2. The characteristic values ​​such as hydroxyl value for each film-forming resin are shown in Table 2.

[0181] [Table 2]

[0182] Preparation of coating resin (A3) (Preparation example A3-3) In a reaction vessel equipped with a thermometer, condenser, and stirrer, 19.0 parts by mass of adipic acid, 23.0 parts by mass of neopentyl glycol, 37.0 parts by mass of isophthalic acid, 20.2 parts by mass of 1,6-hexanediol, and 0.1 parts by mass of dibutyltin oxide as a catalyst were charged. The temperature was raised from 150°C to 230°C over 3 hours, and the mixture was held at 230°C for about 5 hours to obtain a polyester resin. After cooling to 70°C, 20.0 parts by mass of dimethylolpropionic acid, 6.0 parts by mass of trimethylolpropane, and 56.0 parts by mass of isophorone diisocyanate were added, and the mixture was heated to 95°C and reacted for 1 hour. After cooling to 50°C, 335.0 parts by mass of deionized water and 8.8 parts by mass of diethanolamine were added to prepare a polyurethane resin dispersion (solid content concentration: 35% by mass) in which the coating resin (A3-3) was dispersed in an aqueous medium.

[0183] (Preparation examples A3-4 to A3-6) The film-forming resins (A3-4) to (A3-6) were prepared in the same manner as described above, except that the monomer species and quantities were changed as shown in Table 3. The amount of deionized water added was adjusted so that the solid content concentration of each film-forming resin was 35% by mass. The characteristic values ​​such as hydroxyl value for each film-forming resin are shown in Table 3.

[0184] [Table 3]

[0185] Details of the other film-forming resins (A) used in the examples and comparative examples are as follows. (A1-7) NeoCryl XK-103 (manufactured by Covestro, acrylic resin emulsion); Hydroxyl value: 106 mg KOH / g, Acid value: 16 mg KOH / g, Weight-average molecular weight: 430,000, Glass transition temperature: 50°C, Solids content: 45% by mass (A2-1) Byronal MD-1985 (manufactured by Toyobo Co., Ltd., polyester resin dispersion); hydroxyl value: 4 mg KOH / g, acid value: 3 mg KOH / g, weight-average molecular weight: 30,000, glass transition temperature: -20℃, solid content concentration: 27% by mass (A3-1) Hydran HW-163 (manufactured by DIC Corporation, polyurethane resin dispersion); hydroxyl value: 0 mg KOH / g, acid value: 25 mg KOH / g, weight-average molecular weight: 5,000, glass transition temperature: 65°C, solid content concentration: 33% by mass (A3-2) Hydran WLS-210 (manufactured by DIC Corporation, polyurethane resin dispersion); Hydroxyl value: 0 mg KOH / g, Acid value: 15 mg KOH / g, Weight-average molecular weight: 55,000, Glass transition temperature: -32°C, Solid content concentration: 35% by mass

[0186] Preparation of phosphoric acid-modified epoxy resin (C) (Preparation example C-1) In a reaction vessel equipped with a thermometer, condenser, dropping funnel, and stirrer, 43.0 parts by mass of 85% phosphoric acid aqueous solution and 22.0 parts by mass of butyl cellosolve were charged, and the temperature was raised to 80°C under a nitrogen atmosphere. To this, a mixed solution of 130.0 parts by mass of jER 825 epoxy resin pre-dissolved in 23.0 parts by mass of butyl cellosolve was added dropwise at a constant rate through the dropping funnel over 60 minutes. The reaction temperature was then maintained at 80°C for 60 minutes to prepare phosphoric acid-modified epoxy resin (C-1).

[0187] (Preparation examples C-2 to C-4) Phosphate-modified epoxy resins (C-2) to (C-4) were prepared in the same manner as described above, except that the epoxy resin type and quantity were changed as shown in Table 1. The characteristic values ​​such as hydroxyl value for each film-forming resin are shown in Table 4.

[0188] [Table 4]

[0189] The details of each component listed in Table 4 are as follows: [phosphoric acid] • 85% phosphoric acid (manufactured by Kishida Chemical Co., Ltd.) [Epoxy resin] jER825: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation); number average molecular weight 340, solids content concentration: 100% by mass jER1009: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation); number average molecular weight 3,800, solids content concentration: 100% by mass jER1010: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation); number average molecular weight 5,500, solids content concentration: 100% by mass • Epotote YD-020H: Bisphenol A type epoxy resin (manufactured by Toto Chemical Co., Ltd.); number average molecular weight 8,000, solid content concentration: 100% by mass

[0190] Preparation of aqueous paint composition 1 (Example 1) In the above preparation example, 82.6 parts by mass of the film-forming resin (A1-1), 6.5 parts by mass of Cymel 303 as a crosslinking agent (B-1), and 14.0 parts by mass of ECO100 OXIDE RED (manufactured by Chromaflo) as a coloring pigment were mixed. Then, 3.0 parts by mass of phosphoric acid-modified epoxy resin (C-1) and 0.5 parts by mass of dibutyl diglycol as an organic solvent (D1) were mixed and stirred. Next, 3.3 parts by mass of dodecylbenzenesulfonic acid as a sulfonic acid compound (E-1) and 0.5 parts by mass of amine compound (F-1) were mixed while stirring to obtain aqueous paint composition 1.

[0191] (Examples 2-39, Comparative Examples 1-17) An aqueous paint composition was prepared in the same manner as in Example 1, except that the film-forming resin (A), crosslinking agent (B), phosphate-modified epoxy resin (C), organic solvent (D1), sulfonic acid compound (E), amine compound (F), and organic solvent (D2) were changed as shown in Tables 5 to 10. Note that the amounts of each component refer to the amount in its natural state, including volatile components such as solvents.

[0192] The details of each component shown in the table below, which was used in the examples and comparative examples, are as follows. Crosslinking agent (B) (B-1) Cymel 303 (manufactured by Ornex Japan, full alkyl type methylated melamine resin); solid content concentration: 100% by mass (B-2) Cymel 370 (manufactured by Ornex Japan, methylol-type melamine resin); solid content concentration: 88% by mass (B-3) Cymel 327 (manufactured by Ornex Japan, imino-based methylated melamine resin); solid content concentration: 90% by mass Organic solvent (D) (D1-1) Dibutyl diglycol (manufactured by Nippon Emulsifier Co., Ltd.); solubility in water: 3 g / L, SP value: 8.3 (cal / cm³) 3 ) 1 / 2 (D1-2) Xylene (manufactured by ENEOS Corporation); solubility in water: 0.2 g / L, SP value: 8.8 (cal / cm³) 3 ) 1 / 2 (D1-3) CS-12 (manufactured by JNC, Texanol); Solubility in water: 0.9 g / L, SP value: 9.6 (cal / cm³) 3 ) 1 / 2 (D2-1)N-Hexane (manufactured by Fuji Oil Co., Ltd.); Solubility in water: 0.01 g / L, SP value: 7.3 (cal / cm³) 3 ) 1 / 2 (D2-2) Diethylene glycol (manufactured by Okura Chemitech Co., Ltd.); mixed with water in any proportion; SP value: 12.2 (cal / cm³) 3 ) 1 / 2 (D2-3) Propylene glycol (manufactured by Okura Chemitech Co., Ltd.); mix with water in any proportion; SP value: 12.6 (cal / cm³)3 ) 1 / 2 (D2-4) Ethylene glycol monobutyl ether (manufactured by Shoei Chemical Co., Ltd.); dissolves in water in any proportion; SP value: 9.5 (cal / cm³) 3 ) 1 / 2 (D2-5) Methyl isobutyl ketone (manufactured by Mitsubishi Chemical Corporation); solubility in water: 19 g / L, SP value: 9.6 (cal / cm³) 3 ) 1 / 2 Sulfonic acid compounds (E) (E-1) AC400S (manufactured by Teika Co., Ltd., dodecylbenzenesulfonic acid); solid content concentration: 40% by mass (E-2) AC700 (manufactured by Teika Co., Ltd., p-toluenesulfonic acid); solid content concentration: 25% by mass (E-3) Nacure-1051 (manufactured by Kusumoto Chemical Co., Ltd., dinonylnaphthalene sulfonic acid); solid content concentration: 51% by mass

[0193] Preparation of test plates After alkaline degreasing of an aluminum-zinc plated steel sheet (29.7 x 21.0 x 0.4 mm), Surfcoat EC2310 (phosphate-based surface treatment agent: manufactured by Nippon Paint Surf Chemicals Co., Ltd.) was applied to both the front and back surfaces of the steel sheet as a surface treatment agent, and then dried. The aqueous paint composition obtained above was applied to the surface of the treated steel plate using a bar coater so that the dry coating film was 11 μm thick, and the coating film was formed by baking at a maximum temperature of 230°C for 30 seconds, thereby obtaining test plates.

[0194] The following evaluations were performed on the aforementioned paint composition and test board.

[0195] (Paint condition) The paint composition was visually observed and evaluated immediately after preparation. The evaluation criteria were as follows: ○ or higher was considered acceptable. ○: No abnormalities were found. ×: Abnormalities such as clumping, gelation, or separation are observed.

[0196] (Storage stability) For the paint compositions obtained in the examples and comparative examples, evaluation was carried out in accordance with the method specified in JIS K 5600 2-2 (Ford cup method) using a Ford cup No. 4 (manufactured by Ueshima Seisakusho). That is, ion-exchanged water was added to each paint composition, and the viscosity was adjusted to 30 ± 10 seconds (initial viscosity (seconds)). Specifically, the initial viscosity was the viscosity measured immediately after diluting with the ion-exchanged water, stirring at 1,000 rpm for 3 minutes using a disperser. The paint composition adjusted to the initial viscosity was put into a 1 / 5 can at the 8th to 9th minute, sealed, and then left standing in a constant temperature room at 40°C. Then, it was taken out after 14 days (2 weeks), and the viscosity was measured in the same manner as above (viscosity over time (seconds)). The measurement temperature was 25°C in all cases. The change rate of the viscosity over time with respect to the initial viscosity was calculated by the following formula, and the storage stability was evaluated according to the following criteria. Those with ○ or above were considered qualified. Viscosity change rate (%) = Viscosity over time (seconds) / Initial viscosity (seconds) × 100 ◎: The viscosity change rate is 0% or more and less than 30%. 〇: The viscosity change rate is 30% or more and less than 100%. △: The viscosity change rate is 100% or more and less than 150%. ×: The viscosity change rate is 150% or more.

[0197] (Pencil hardness) The hardness of the paint film of each test panel obtained in the examples and comparative examples was evaluated in accordance with JIS K 5600-5-4 (scratch hardness (pencil method)). The hardness of the hardest pencil without scratches was taken as the pencil hardness of the paint film. Those with H or above were considered qualified.

[0198] (Scratch resistance) The scratch resistance of the paint film of each test panel obtained in the examples and comparative examples was evaluated using a continuous load scratching strength tester TYPE: 18 / 18L (manufactured by Shin-Toyo Kagaku Co., Ltd.). That is, a diamond needle (a conical scratch needle with R-processed, 0.4 mm in diameter) with R = 0.4 mm was applied to the coating film surface of each test plate obtained in the examples and comparative examples, and a load was applied and rubbed once at a speed of 300 mm / min and a moving width of 10 cm. The weight of the load when the coating film surface was damaged and the exposure of the substrate was confirmed was defined as the scratch resistance, and evaluated according to the following criteria. Pass was defined as ○ or above. The load was applied in increments of 500 gf. The test conditions were a temperature of 23 °C and a humidity of 60 RH%. ◎: The substrate is not exposed even when the load exceeds 2,000 gf ○: The substrate is exposed when the load exceeds 1,500 gf and is 2,000 gf or less △: The substrate is exposed when the load exceeds 1,000 gf and is 1,500 gf or less ×: The substrate is exposed when the load is 1,000 gf or less

[0199] (Processing adhesion) Each test plate obtained in the examples and comparative examples was cut into 5 cm × 3 cm, and pre-bent using a creasing machine (manufactured by Ueshima Seisakusho) so that the coating film surface was on the front side. Two steel plates with the same thickness (0.4 mm) as that were sandwiched between the painted steel plates, and bending was performed using a press machine (manufactured by Kyoritsu Kogyo). A cellophane tape (registered trademark) (LP-24, manufactured by Nichiban) was adhered to the processed part of the painted steel plate and peeled off at once, and the adhesion of the coating film of the processed part was evaluated. The appearance of the part peeled off with the tape was evaluated according to the following criteria (2TT). In addition, except that the number of steel plates sandwiched between the test pieces was 0 (no steel plate was sandwiched) during the bending process, the same tests and evaluations as above were performed (0TT). Pass was defined as ○ or above for both 0TT and 2TT. ◎: No metal substrate is observed in the part peeled off by the tape. ○: A metal substrate part is observed in an area of the part peeled off by the tape that exceeds 0% and is less than 20%. △: A metal substrate part is observed in an area of the part peeled off by the tape that is 20% or more and less than 50%. ×: A metal substrate part is observed in an area of the part peeled off by the tape that is 50% or more.

[0200] [Table 5]

[0201] [Table 6]

[0202] [Table 7]

[0203] [Table 8]

[0204] Examples 1 to 39 are embodiments of the present disclosure, and it was confirmed that the condition and storage stability of the obtained coatings, as well as the hardness, scratch resistance, and workability of the obtained coating films, were good. Comparative Example 1 was an example that did not include the phosphate-modified epoxy resin (C) and the organic solvent (D), and the workability of the resulting coating film was not sufficiently satisfactory. Comparative Example 2 was an example that did not include organic solvent (D), and the resulting coating film did not exhibit sufficiently satisfactory workability. Comparative Example 3 was an example that did not include the phosphate-modified epoxy resin (C), and the resulting coating film did not exhibit sufficiently satisfactory workability. Comparative Examples 4, 8, and 11 were examples where the acid value of the coating-forming resin (A) exceeded 100 mg KOH / g, and the workability of the resulting coating films was not sufficiently satisfactory. Comparative Examples 5, 7, and 10 were examples in which the hydroxyl value of the coating-forming resin (A) exceeded 150 mgKOH / g, and the hardness, scratch resistance, and work adhesion of the resulting coatings were not sufficiently satisfactory. Comparative Examples 6, 9, and 12 were cases where the glass transition temperature of the film-forming resin (A) exceeded 100°C, and the resulting paint state was not entirely satisfactory (gelation). Comparative Examples 13 and 14 were examples where the solubility parameter of the organic solvent (D) was less than 8.3, and the properties of the resulting paints were not sufficiently satisfactory (separation). Comparative Example 16 was an example where the solubility parameter of the organic solvent (D) exceeded 9.6, and the process adhesion of the resulting coating film was not sufficiently satisfactory. Comparative Example 15 was an example where the water solubility of the organic solvent (D) exceeded 10 g / L, and the resulting coating film did not exhibit sufficiently satisfactory workability. Comparative Example 17 is an example in which the content of the organic solvent (D1) exceeds 30 parts by mass relative to 100 parts by mass of the total solid content of the coating resin (A) and crosslinking agent (B), and the properties of the resulting paint were not sufficiently satisfactory (gelation). [Industrial applicability]

[0205] The coating obtained from the aqueous coating composition of this disclosure is less likely to peel off from the coated object even when processed such as bending, exhibits good workability, and preferably also has excellent pencil hardness and scratch resistance. Therefore, the aqueous coating composition of this disclosure can be suitably used for coating metals, particularly as a precoat.

Claims

1. A water-based paint composition comprising a film-forming resin (A), a crosslinking agent (B), a phosphate-modified epoxy resin (C), and an organic solvent (D), The hydroxyl value of the coating resin (A) is 150 mg KOH / g or less, the acid value of the coating resin (A) is 100 mg KOH / g or less, and the glass transition temperature of the coating resin (A) is 100°C or less. The organic solvent (D) has a solubility parameter of 8.3 (cal / cm³). ３ ) １／２ More than 9.6 (cal / cm ３ ) １／２ The following applies, and the organic solvent (D1) has a solubility in water of 10 g / L or less at 25°C: An aqueous coating composition in which the content of the organic solvent (D1) is 0.5 parts by mass or more and 35 parts by mass or less, based on 100 parts by mass of the total solid content of the coating film-forming resin (A) and the crosslinking agent (B).

2. The aqueous paint composition according to claim 1, wherein the film-forming resin (A) comprises one or more selected from acrylic resin (A1), polyester resin (A2), and polyurethane resin (A3).

3. The aqueous paint composition according to claim 1, wherein the crosslinking agent (B) comprises an amino resin.

4. The aqueous coating composition according to claim 1, wherein the crosslinking agent (B) comprises a melamine resin.

5. The aqueous coating composition according to claim 1, wherein the number average molecular weight of the phosphate-modified epoxy resin (C) is 400 or more and 10,000 or less.

6. The aqueous coating composition according to claim 1, wherein the solid content of the phosphate-modified epoxy resin (C) is 1 part by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the total solid content of the coating film-forming resin (A) and the crosslinking agent (B).

7. It further contains a sulfonic acid compound (E), The aqueous coating composition according to claim 1, wherein the content of the sulfonic acid compound (E) is 0.5 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the total solid content of the coating resin (A) and the crosslinking agent (B).

8. The aqueous paint composition according to claim 1, further comprising an amine compound (F).

9. The aqueous paint composition according to claim 8, wherein the boiling point of the amine compound (F) is 50°C or higher and 250°C or lower.

10. It further comprises a sulfonic acid compound (E) and an amine compound (F), The aqueous paint composition according to claim 1, wherein the neutralization rate of the sulfonic acid group of the sulfonic acid compound (E) by the amine compound (F) is 100% or more and 1,300% or less.

11. The aqueous coating composition according to claim 1, for use with pre-coated metal.

12. A step of applying the aqueous coating composition according to any one of claims 1 to 11 to an object to be coated to form a coating film, and A step of drying and / or curing the aforementioned coating film under conditions where the temperature reached by the object to be coated is 180°C to 270°C and the drying and / or curing time is 1 to 120 seconds or less. A method for manufacturing a coating film, including the method described above.

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