Water-based paint composition and method for manufacturing paint film

Abstract

To provide a water-based coating material composition capable of forming a coating film by one time of coating, excellent in dryness to the touch when dried at normal temperature, excellent in appearance, corrosion resistance and blocking resistance of a coating film to be obtained.SOLUTION: A water-based coating material composition includes a coating film formation resin (A), a rust preventive pigment (B) and resin beads (C). The coating film formation resin (A) includes acrylic resin emulsion (A1) and acrylic resin emulsion (A2); the acrylic resin emulsion (A1) includes core shell type acrylic resin emulsion including a core part and a shell part; the acrylic resin emulsion (A2) includes monolayer type acrylic resin emulsion; the glass transition temperature of the entire acrylic resin in the acrylic resin emulsion (A1) is 30°C or more and 50°C or less; and the glass transition temperature of the entire acrylic resin in the acrylic resin emulsion (A2) is -20°C or more and 0°C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to an aqueous paint composition and a method for producing a coating film. [Background technology]

[0002] In various fields such as building exteriors, building materials, bridges, ships, vehicles, industrial machinery, construction machinery, and automobiles, a coating is formed on the surface of the material being coated using a coating composition for protection and aesthetic purposes.

[0003] In recent years, with the worsening of environmental problems, there has been a growing demand for reducing the environmental impact of paints and coatings, and various studies are being conducted. A key challenge in the paint sector is reducing the amount of organic solvents used. From this perspective, water-based paints, which contain reduced organic solvents, are being used, and their use is expanding in various fields. Among these, steel materials are used in building materials, civil engineering materials, and machinery applications, and a coating with good corrosion resistance is required to withstand long-term use in outdoor environments.

[0004] In the manufacturing lines for lightweight steel sections and other steel materials, a common procedure involves degreasing the formed steel sections, preheating them to a temperature of approximately 60-110°C, and then airlessly applying a water-based paint composition to the preheated steel sections. Furthermore, the painted steel sections are bundled, stacked, and transported.

[0005] Since the aforementioned series of processes are carried out in a short time of about 5 minutes, the water-based paint composition is required to be fast-drying. Furthermore, the resulting coating film is required to have a good finish appearance, as well as resistance to blocking and cracking. In particular, in order to satisfy the standard of JIS K 5674 (lead- and chromium-free rust-preventive paint), a film thickness of 30 μm or more is required, and resistance to blocking and cracking becomes a significant challenge. In addition, for industrially produced goods, low cost is extremely important for expanding the market for application of the product.

[0006] As an example of a water-based paint, Patent Document 1 describes a water-based paint that contains 1 to 5% by mass of an acrylic resin emulsion and an acrylic resin dispersion as solid components, with a glass transition temperature (Tg) of 28 to 50°C, a film-forming aid content of 1 to 5% by mass, and a minimum film-forming temperature of 25 to 45°C. Patent Document 2 describes an aqueous coating composition containing urethane resin particles having a weight-average molecular weight of 100,000 to 5,000,000 and a glass transition temperature of 30 to 100°C, and acrylic resin particles having a glass transition temperature of -20 to 30°C, wherein the solid content relative to the total solid content of the urethane resin particles and acrylic resin particles is 40 to 80% by mass for the urethane resin particles and 20 to 60% by mass for the acrylic resin particles. Patent Document 3 describes a resin composition for aqueous coatings containing a binder made of two types of heterosynthetic emulsion particles. One of the heterosynthetic emulsion particles has a glass transition temperature of -50 to 10°C for the emulsion polymer forming the outermost phase and a glass transition temperature of 30 to 110°C for the emulsion polymer forming at least one phase inside the outermost phase. The other has a glass transition temperature of 60 to 80°C for the emulsion polymer forming the outermost phase and a glass transition temperature of -50 to 0°C for the emulsion polymer forming at least one phase inside the outermost phase. Patent Document 4 describes an emulsion coating for a bituminous vibration damping sheet, in which the main component is a synthetic resin emulsion containing a styrene / acrylic copolymer synthetic resin emulsion with a minimum film-forming temperature of 80 to 100°C and an acrylic acid ester copolymer synthetic resin emulsion with a minimum film-forming temperature of 20°C or less, in a mass ratio of 2 to 4:8 to 6. Patent Document 5 describes an aqueous resin dispersion comprising a high-Tg resin component with a glass transition temperature (Tg) of 50°C or higher, polymerized using two or more polymerizable monomers with different glass transition temperatures (Tg), and a low-Tg resin component with a glass transition temperature of 40°C or lower. It also states that the minimum film-forming temperature (MFT) of the aqueous resin dispersion is 10°C or more lower than the glass transition temperature (Tg) of the entire aqueous resin dispersion. Patent Document 6 describes a paint composition comprising water, an organic solvent, a pigment, and a resin, wherein the pigment volume concentration (PVC) is in the range of 0.1 to 35%, and the resin has at least one loss tangent (tanδ) peak that is between 45°C and 180°C. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-002330 [Patent Document 2] Japanese Patent Publication No. 2020-002327 [Patent Document 3] Japanese Patent Publication No. 2003-128981 [Patent Document 4] Japanese Patent Application Publication No. 09-087572 [Patent Document 5] Japanese Patent Publication No. 2008-063567 [Patent Document 6] Japanese Patent Publication No. 2022-154462 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, conventionally known water-based paint compositions, when applied in a single coat and dried at room temperature, did not adequately satisfy the requirements for touch-drying properties, the resulting paint film, appearance, corrosion resistance, and blocking resistance.

[0009] The present disclosure aims to provide an aqueous coating composition that forms a coating film in a single application, exhibits good touch-dry properties even when dried at room temperature, and provides a coating film with good appearance, corrosion resistance, and blocking resistance. [Means for solving the problem]

[0010] [1] It comprises a film-forming resin (A), a rust-preventive pigment (B), and resin beads (C), The coating film-forming resin (A) contains an acrylic resin emulsion (A1) and an acrylic resin emulsion (A2). The acrylic resin emulsion (A1) contains a core-shell type acrylic resin emulsion having a core part and a shell part. The acrylic resin emulsion (A2) contains a single-layer type acrylic resin emulsion. The glass transition temperature of the entire acrylic resin of the acrylic resin emulsion (A1) is 30°C or higher and 50°C or lower. The glass transition temperature of the entire acrylic resin of the acrylic resin emulsion (A2) is -20°C or higher and 0°C or lower. A water-based paint composition. [2] The water-based paint composition according to [1], wherein the glass transition temperature of the shell part of the core-shell type acrylic resin emulsion is higher than the glass transition temperature of the core part of the core-shell type acrylic resin emulsion. [3] The water-based paint composition according to [1] or [2], wherein the ratio of the solid content of the acrylic resin emulsion (A1) to the solid content of the acrylic resin emulsion (A2) is 90:10 to 50:50. [4] The water-based paint composition according to any one of [1] to [3], wherein the content of the rust preventive pigment (B) is 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the solid content of the coating film-forming resin (A). [5] The water-based paint composition according to any one of [1] to [4], wherein the average particle diameter of the resin beads (C) is 1 μm or more. [6] The water-based paint composition according to any one of [1] to [5], wherein the content of the resin beads (C) is 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the solid content of the coating film-forming resin (A). [7] The water-based paint composition according to any one of [1] to [6], further comprising a film-forming auxiliary agent (D), wherein the content of the film-forming auxiliary agent (D) is 1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the solid content of the coating film-forming resin (A). [8] Preheat the object to be coated to 60°C or higher and 110°C or lower, and A method for producing a coating film, comprising applying an aqueous coating composition described in any one of [1] to [7] to the surface of the object to be coated after preheating, and forming a film to obtain a coating film. [Effects of the Invention]

[0011] The aqueous coating composition of this disclosure forms a coating film in a single application, exhibits good touch-dry properties even when dried at room temperature, and provides a good appearance, corrosion resistance, and blocking resistance of the resulting coating film. [Modes for carrying out the invention]

[0012] The aqueous coating compositions disclosed herein are It comprises a film-forming resin (A), a rust-preventive pigment (B), and resin beads (C), The aforementioned coating-forming resin (A) comprises an acrylic resin emulsion (A1) and an acrylic resin emulsion (A2). The acrylic resin emulsion (A1) includes a core-shell type acrylic resin emulsion having a core portion and a shell portion. The acrylic resin emulsion (A2) comprises a single-layer acrylic resin emulsion. The glass transition temperature of the entire acrylic resin in the aforementioned acrylic resin emulsion (A1) is between 30°C and 50°C. The glass transition temperature of the entire acrylic resin in the aforementioned acrylic resin emulsion (A2) is between -20°C and 0°C.

[0013] The aqueous coating composition of this disclosure forms a coating film in a single application, exhibits good touch-dry properties even when dried at room temperature, and provides a good appearance, corrosion resistance, and blocking resistance of the resulting coating film.

[0014] This disclosure should not be interpreted as being limited to any particular theory, but the reason why the aqueous coating composition of this disclosure exhibits such effects is thought to be as follows. Specifically, the aqueous coating composition of this disclosure contains two types of acrylic resin emulsions as film-forming resins, one of which is a core-shell type acrylic resin emulsion (A1), and the glass transition temperature of the entire acrylic resin in acrylic resin emulsion (A1) is between 30°C and 50°C. As a result, the film-forming properties when the aqueous coating composition is applied are good, and the resulting coating film may have good blocking resistance. The glass transition temperature of the entire acrylic resin in the other acrylic resin emulsion (A2) is between -20°C and 0°C. Therefore, even when a coating film is formed from the aqueous coating composition in a single application and dried at room temperature, it is thought that good touch-drying properties and good film-forming properties can be obtained. Furthermore, since the aqueous coating composition of this disclosure contains both the acrylic resin emulsion (A1) and the acrylic resin emulsion (A2), even if it contains rust-preventive pigments and resin beads, it can suppress cracking in the resulting coating film and has a good appearance. Therefore, it is considered that it can exhibit the effect of improving blocking resistance due to the resin beads and the effect of improving corrosion resistance due to the rust-preventive pigments. As a result, it is considered that an aqueous coating composition can be provided that has good touch-drying properties even when a coating film is formed in a single application and dried at room temperature, and the resulting coating film has good appearance, corrosion resistance, and blocking resistance.

[0015] (A) Film-forming resin The aforementioned coating-forming resin (A) includes acrylic resin emulsion (A1) and acrylic resin emulsion (A2) from the viewpoint of obtaining a coating film with excellent touch-drying properties, coating appearance, and corrosion resistance, as described later. Acrylic resin emulsion (A1) and acrylic resin emulsion (A2) also have advantages from a cost standpoint.

[0016] Acrylic resin emulsion (A1) The acrylic resin emulsion (A1) is an aqueous dispersion containing an acrylic resin, and more specifically, it means an acrylic resin dispersed in a medium in particulate form. The acrylic resin may be, for example, a polymer of a monomer mixture containing an ethylenic monomer.

[0017] As the ethylenic monomer, hydroxyl group-containing monomers; ε-caprolactone-modified (meth)acrylic monomers; esters of polyhydric alcohols such as ethylene glycol and propylene glycol with (meth)acrylic acid; esters of polyhydric alcohols such as ethylene glycol and propylene glycol with (meth)acrylic acid modified with ε-caprolactone; carboxyl group-containing monomers and mixtures of other monomers can be used.

[0018] Examples of the hydroxyl group-containing monomers include hydroxyalkyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2,3-dihydroxybutyl (meth)acrylate, and hydroxymethylcyclohexyl (meth)acrylate; and monomers obtained by modifying the hydroxyalkyl group-containing monomers with ε-caprolactone. Specific examples of ε-caprolactone-modified (meth)acrylic monomers include Praxel FA-1, Praxel FA-2, Praxel FA-3, Praxel FA-4, Praxel FA-5, Praxel FM-1, Praxel FM-2, Praxel FM-3, Praxel FM-4, and Praxel FM-5, all manufactured by Daicel Corporation. In this disclosure, (meth)acrylic acid means acrylic acid and methacrylic acid.

[0019] Examples of carboxyl group-containing monomers include carboxylic acid monomers such as (meth)acrylic acid, 2-ethylpropenoic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, or dicarboxylic acid monoester monomers thereof. Acrylic acid and methacrylic acid are preferred as carboxyl group-containing monomers. These may be used alone, or two or more may be used in combination.

[0020] Other ethylenic monomers include, for example, styrene monomers such as styrene, α-methylstyrene, and vinyltoluene; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n, i and t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; amino group-containing monomers such as aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and butylaminoethyl (meth)acrylate; ethyl maleate, maleate Dicarboxylic acid monoester monomers such as butyl iodide, ethyl itaconate, and butyl itaconate; cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, cyclodecyl (meth)acrylate, cyclododecyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and adamantyl (meth)acrylate; aminoethyl (meth)acrylate and dimethylaminoethyl (meth)acrylate. (meth)acrylamide monomers such as butylaminoethyl (meth)acrylate; aminoalkyl (meth)acrylamide monomers such as aminoethyl (meth)acrylamide, dimethylaminomethyl (meth)acrylamide, and methylaminopropyl (meth)acrylamide; other N-substituted (meth)acrylamide monomers such as acrylamide and methacrylamide; vinyl cyanide monomers such as (meth)acrylonitrile and α-chloroacrylonitrile; saturated aliphatic carboxylic acid vinyl ester monomers such as vinyl acetate and vinyl propionate; (meth)acrylamide monomers such as (meth)acrylamide, N-hydroxy(meth)acrylamide, methoxybutyl (meth)acrylamide, N-alkoxy(meth)acrylamide, N-alkylol (meth)acrylamide (e.g., N-methylol (meth)acrylamide), and diacetone (meth)acrylamide; amino group-containing (meth)acrylamide monomers such as aminoethyl (meth)acrylamide, dimethylaminomethyl (meth)acrylamide, and methylaminopropyl (meth)acrylamide;Examples include glycidyl monomers such as (meth)glycidyl acrylate; vinyl cyanide monomers such as (meth)acrylonitrile and α-chloroacrylonitrile; alkoxysilyl group-containing monomers such as (meth)trimethoxysilylpropyl acrylate and (meth)triethoxysilylpropyl acrylate, difunctional monomers such as divinylbenzene and ethylene glycol methacrylate; and others. The ethylenic monomer may be used alone or in combination of two or more types.

[0021] The glass transition temperature of the acrylic resin aqueous dispersion (A1) is preferably 30°C to 50°C, more preferably 35°C to 45°C. Having the glass transition temperature of the acrylic resin within this range results in a good appearance and blocking resistance of the resulting coating film. In this disclosure, when referring to the entire acrylic resin in an acrylic resin aqueous dispersion, it means the entire acrylic resin contained in the acrylic resin aqueous dispersion.

[0022] In this disclosure, the glass transition temperature (Tg) of an acrylic resin (polymer) in an acrylic resin emulsion can be calculated as the reciprocal of the sum of the quotients obtained by dividing the mass fraction of each monomer constituting the acrylic resin (polymer) by the Tg (expressed in K: Kelvin) value of the homopolymer derived from each monomer.

[0023] More specifically, in this disclosure, the glass transition temperature (Tg) of the acrylic resin in the acrylic resin emulsion can be calculated by Fox's equation (TGFox; Bull. Am. Phys. Soc., 1(3), 123 (1956)).

[0024] For example, if the fine particles are a polymer of multiple acrylic monomers, the following general formula 1 / Tg = w1 / Tg1 + w2 / Tg2 + ... + w n / Tg n The Tg expressed as is defined as the Tg of the fine particles. Tg a : Glass transition temperature (K) of the homopolymer of monomer A, W a : Mass fraction of monomer A Tg b : Glass transition temperature (K) of the homopolymer of monomer B, W b : Mass fraction of monomer B Tg n : Glass transition temperature (K) of the homopolymer of monomer N, W n : Mass fraction of monomer N (W a + W b + ··· + W n = 1)

[0025] The acid value of the entire acrylic resin of the acrylic resin emulsion (A1) is preferably 10 mgKOH / g or more and 150 mgKOH / g or less, more preferably 10 mgKOH / g or more and 120 mgKOH / g or less. When the acid value of the acrylic resin is within the above range, there are advantages such as better appearance and corrosion resistance of the resulting coating film. In the present disclosure, both the acid value and the hydroxyl value indicate values in terms of solid content and are values measured by a method conforming to JIS K 0070.

[0026] The weight average molecular weight of the acrylic resin of the acrylic resin emulsion (A1) can be preferably more than 50,000 and 10,000,000 or less, more preferably more than 100,000 and 2,000,000 or less. When the weight average molecular weight of the acrylic resin is within the above range, the strength of the resulting coating film can be good. In the present disclosure, the weight average molecular weight is a polystyrene conversion value measured by gel permeation chromatography.

[0027] The average particle diameter of the acrylic resin of the acrylic resin emulsion (A1) can be preferably 50 nm or more and 200 nm or less, more preferably 75 nm or more and 180 nm or less, still more preferably 80 nm or more and 150 nm or less. When the average particle diameter of the acrylic resin is within the above range, there are advantages such as better appearance and corrosion resistance of the resulting coating film. In this disclosure, the average particle diameter is the average particle diameter determined by dynamic light scattering, which can be measured using an electrophoretic light scattering photometer ELSZ series (manufactured by Otsuka Electronics Co., Ltd.) or the like.

[0028] The overall solubility parameter (SP value) of the acrylic resin in the acrylic resin emulsion (A1) is preferably 9.5 to 10.9, more preferably 9.8 to 10.7, and even more preferably 10.0 to 10.7. Having the SP value of the acrylic resin within this range has the advantage of improving the appearance of the resulting coating film. In this disclosure, the unit of the solubility parameter (SP value) is [(cal / cm³)]. 3 ) 1 / 2 ]

[0029] The aforementioned SP value is an abbreviation for solubility parameter and serves as a measure of solubility. A higher SP value indicates higher polarity, while a lower SP value indicates lower polarity.

[0030] The SP value can be measured by the following method [Reference: SUH, CLARKE, JPSA-1, 5, 1671~1681 (1967)]. As a sample, 0.5 g of the monomer is weighed into a 100 mL beaker, 10 mL of acetone is added using a volumetric pipette, and the mixture 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 of the monomer δ[(cal / cm²)] 3 ) 1 / 2 ] is given by the following formula. δ=(Vml 1 / 2 δml+Vmh 1 / 2 δmh) / (Vml 1 / 2 +Vmh 1 / 2 ) Vm = V1V2 / (φ1V2 + φ2V1) δm = φ1δ1 + φ2δ2 V i : Molecular volume of solvent (mL / mol) φ i : Volume fraction of each solvent at the turbidity point δ i : SP value of the solvent ml: Low SP poor solvent mixed system mh: High SP poor solvent mixed system

[0031] Furthermore, if the acrylic resin emulsion (A1) contains two or more types of acrylic resins, the SP value of the entire acrylic resin in the acrylic resin aqueous dispersion (A1) can be determined by using the SP values ​​of each monomer and calculating the average value based on the solid content mass ratio in the acrylic resin aqueous dispersion (A1) components. Furthermore, in this disclosure, the solid content of the resin can be determined by measuring the heat residue (mass of the residue after heating at 105°C for 180 minutes) in accordance with JIS K 5601-1-2 (2008).

[0032] The acrylic resin emulsion (A1) includes a core-shell type acrylic resin emulsion. The core-shell type acrylic resin emulsion is in particulate form and has a core portion inside the particle and a shell portion covering at least a part of the core portion.

[0033] Preferably, the glass transition temperature of the shell portion (hereinafter also simply referred to as the "shell portion") of the core-shell type acrylic resin emulsion is higher than the glass transition temperature of the core portion (hereinafter also simply referred to as the "core portion") of the core-shell type acrylic resin emulsion. This has the advantage of potentially improving the blocking resistance of the resulting coating film.

[0034] The glass transition temperature (Tgc) of the core portion is preferably 80°C or lower, more preferably 30°C or lower, even more preferably 0°C to 30°C, and even more preferably 5°C to 30°C. Having the glass transition temperature of the core portion within this range allows for good film-forming properties and can result in a better appearance of the resulting coating.

[0035] The glass transition temperature (Tgs) of the shell portion is preferably 10°C or higher, more preferably 60°C or higher, even more preferably 60°C to 150°C, and even more preferably 60°C to 100°C. Having the glass transition temperature of the shell portion within this range can result in better blocking resistance of the resulting coating film.

[0036] The difference (Tgs-Tgc) between the glass transition temperature (Tgs) of the shell portion and the glass transition temperature (Tgc) of the core portion is preferably -60°C or higher, more preferably 40°C or higher, even more preferably 40°C to 130°C, even more preferably 45°C to 70°C, and even more preferably 50°C to 60°C. Having the difference (Tgs-Tgc) within this range can result in better appearance and blocking resistance of the resulting coating film.

[0037] Furthermore, the glass transition temperature of the entire acrylic resin in a core-shell type acrylic resin emulsion can be calculated as the reciprocal of the sum of the quotients obtained by dividing the mass fractions of the core and shell constituting the acrylic resin in the core-shell type acrylic resin emulsion by the Tg (expressed in Kelvin) values ​​of the core and shell, respectively.

[0038] The solid content of the core-shell type acrylic resin emulsion 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 solid content of the acrylic resin emulsion (A1).

[0039] Acrylic resin emulsion (A1) can be prepared by polymerizing a monomer mixture containing the ethylenic monomer in an aqueous medium. The polymerization reaction is preferably carried out by emulsion polymerization, and specifically, by batch polymerization, monomer dropwise polymerization, emulsion monomer dropwise polymerization, etc.

[0040] Emulsion polymerization can be carried out by heating the monomer mixture in an aqueous solution with stirring in the presence of a radical polymerization initiator and an emulsifier. The reaction temperature is preferably about 30 to 100°C, and the reaction time is preferably about 1 to 10 hours. The reaction temperature can be adjusted, for example, by adding the monomer mixture or monomer pre-emulsifier to a reaction vessel containing water and an emulsifier all at once or by adding it dropwise.

[0041] As the radical polymerization initiator, known initiators commonly used in emulsion polymerization of acrylic resins can be used. Specifically, as water-soluble free radical polymerization initiators, persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate can be used in aqueous solution form. In addition, so-called redox initiators, which are combinations of oxidizing agents such as potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide, and reducing agents such as sodium bisulfite, sodium thiosulfate, rongalit, and ascorbic acid, can be used in aqueous solution form.

[0042] As the emulsifier, an anionic or nonionic emulsifier can be selected from micellar compounds having 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. Examples of anionic emulsifiers include alkali metal salts or ammonium salts of sulfate semi-esters of alkylphenols or higher alcohols; alkali metal salts or ammonium salts of alkyl or allyl sulfonates; alkali metal salts or ammonium salts of sulfate semi-esters of polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, or polyoxyethylene allyl ethers. Examples of nonionic emulsifiers include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, or polyoxyethylene allyl ethers. In addition to these general-purpose anionic and nonionic emulsifiers, various anionic and nonionic reactive emulsifiers having radically polymerizable unsaturated double bonds in their molecules, i.e., groups such as acrylic, methacrylic, propenyl, allyl, allyl ether, and maleic acid groups, can also be used individually or in combination of two or more as appropriate.

[0043] Furthermore, during 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 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.

[0044] 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.

[0045] In polymerization, the monomer mixture may be supplied continuously, sequentially, or in stages. For example, a core-shell type acrylic resin emulsion having a core and a shell can be prepared by supplying two or more monomer mixtures in stages.

[0046] To maintain the stability of the acrylic resin emulsion, a basic compound may be added to the obtained acrylic resin emulsion to neutralize some or all of the acidic groups as needed. Examples of basic compounds that can be used include ammonia, various amines, alkali metals, etc.

[0047] The solid content of the acrylic resin emulsion (A1) is preferably 30% to 99% by mass, more preferably 40% to 90% by mass, and even more preferably 50% to 80% by mass, based on 100 parts by mass of the solid content of the coating resin (A).

[0048] Acrylic resin emulsion (A2) The acrylic resin emulsion (A2) is an aqueous dispersion containing an acrylic resin, and more specifically, it means an acrylic resin dispersed in a medium in particulate form. The acrylic resin may be, for example, a polymer of a monomer mixture containing an ethylenic monomer.

[0049] As the ethylenic monomer used in the acrylic resin emulsion (A2), the monomers exemplified as ethylenic monomers used in the acrylic resin emulsion (A2) can be used. Acrylic resin emulsion (A2) can be produced by polymerizing such ethylenic monomers in the same manner as for acrylic resin emulsion (A1). The glass transition temperature of the acrylic resin in the acrylic resin aqueous dispersion (A2) is preferably between -20°C and 0°C, and more preferably between -18°C and -5°C. Having the glass transition temperature of the acrylic resin within this range improves film-forming properties and results in a good appearance and touch-dry properties of the resulting coating film.

[0050] The acid value of the acrylic resin in the acrylic resin emulsion (A2) is preferably 5 mg KOH / g or more and 150 mg KOH / g or less, more preferably 5 mg KOH / g or more and 120 mg KOH / g or less. Having the acid value of the acrylic resin within this range has advantages such as better appearance and corrosion resistance of the resulting coating film.

[0051] The weight-average molecular weight of the acrylic resin in the acrylic resin emulsion (A2) is preferably more than 50,000 and 10,000,000 or less, and more preferably more than 100,000 and 2,000,000 or less. Having the weight-average molecular weight of the acrylic resin within this range can result in a coating with good strength.

[0052] The average particle size of the acrylic resin in the acrylic resin emulsion (A2) is preferably 50 nm to 250 nm, more preferably 75 nm to 230 nm, and even more preferably 100 nm to 200 nm. Having the average particle size of the acrylic resin within this range has the advantage of resulting in better appearance and corrosion resistance of the resulting coating film.

[0053] The overall solubility parameter (SP value) of the acrylic resin in the acrylic resin emulsion (A2) is preferably 9.0 to 10.3, more preferably 9.3 to 10.0, and even more preferably 9.3 to 9.7. Having the SP value of the acrylic resin within this range has the advantage of improving the appearance of the resulting coating film.

[0054] The acrylic resin emulsion (A2) comprises a single-layer acrylic resin emulsion, preferably a single-layer acrylic emulsion. This has the advantage of providing good film-forming properties for the aqueous coating composition, as well as good touch-drying properties and appearance of the resulting coating film.

[0055] The ratio of the solid content of the acrylic resin emulsion (A1) to the solid content of the acrylic resin emulsion (A2) ((A1):(A2)) is preferably 97:3 to 50:50, more preferably 90:10 to 50:50, even more preferably 80:20 to 50:50, and even more preferably 75:25 to 55:45. Having the ratio ((A1):(A2)) within this range has the advantage of resulting in a better appearance, blocking resistance, and touch-dry properties of the resulting coating film.

[0056] In 100 parts by mass of the total amount of solids in the coating resin (A), the combined content of the solids of the acrylic resin emulsion (A1) and the acrylic resin emulsion (A2) is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 70% by mass or more and 100% by mass or less.

[0057] The coating-forming resin (A) may contain resins other than acrylic resin emulsion (A1) and acrylic resin emulsion (A2). Examples of such resins include polyester resin emulsion, urethane resin emulsion, and fluororesin emulsion.

[0058] In the aqueous coating composition, the solid content of the film-forming resin (A) is preferably 40% by mass or more and 90% by mass or less, more preferably 45% by mass or more and 80% by mass or less, and even more preferably 50% by mass or more and 75% by mass or less, out of 100 parts by mass of the total solid content of the aqueous coating composition.

[0059] (B) Anti-corrosion pigment The rust-preventive pigment (B) is typically present in the coating film and can exert an effect of suppressing the occurrence of rust on the coated object. Including the rust-preventive pigment (B) can improve the corrosion resistance of the resulting coating film. The rust-preventive pigment (B) typically contains a metal with a higher ionization tendency than the coated object, and can suppress the occurrence of rust on the coated object; it can form a film on the coated object, thereby suppressing contact between the coated object and rust-causing substances, and can suppress the occurrence of rust on the coated object; and it can release basic substances, among other properties, one or more of which are selected.

[0060] Examples of such rust-preventive pigments (B) include inorganic rust-preventive pigments. Examples of the inorganic rust-preventive pigments include phosphoric acid-based rust-preventive pigments, zinc oxide-based rust-preventive pigments, molybdenum-based rust-preventive pigments, boric acid-based rust-preventive pigments, silicate-based rust-preventive pigments, vanadic acid-based rust-preventive pigments, tungstic acid-based rust-preventive pigments, and the like. These rust-preventive pigments may be used individually, or two or more may be used in combination.

[0061] Examples of the phosphate-based rust-preventive pigments include oxymetallic salts of phosphorus. The metals include one or more metals selected from Mg, Ca, Ba, Sr, Zn, or Al. Examples of phosphorus oxyacids include phosphite, phosphate, and / or polyphosphate. Specific examples of phosphate-based rust-preventive pigments include, as phosphite metal salts, magnesium phosphite, calcium phosphite, barium phosphite, strontium phosphite, zinc phosphite, aluminum phosphite, zinc calcium phosphite, zinc potassium phosphite, etc. Examples of phosphate metal salts include magnesium phosphate, calcium phosphate, barium phosphate, strontium phosphate, zinc phosphate, aluminum phosphate, magnesium zinc phosphate, calcium zinc phosphate, zinc potassium phosphate, zinc potassium phosphate, etc. Examples of polyphosphate metal salts include aluminum pyrophosphate, calcium polyphosphate, magnesium polyphosphate, zinc polyphosphate, and aluminum polyphosphate. These compounds may be modified with silica or the like as needed.

[0062] Examples of the zinc oxide-based rust-preventive pigments include zinc oxide and modified zinc oxide. Examples of modified zinc oxide include zinc oxide modified with a metal salt such as a metal nitrite.

[0063] Examples of the molybdenum-based rust-preventive pigments include metal molybdate salts. Examples of metal molybdate salts include zinc molybdate, calcium molybdate, barium molybdate, aluminum molybdate, magnesium molybdate, strontium molybdate, zinc calcium molybdate, and zinc potassium molybdate. Examples of phosphomolybdate salts include zinc molybdate, calcium molybdate, barium molybdate, aluminum molybdate, magnesium molybdate, strontium molybdate, and zinc potassium molybdate.

[0064] Examples of the boric acid-based rust-preventive pigments include metal borate salts and metal metaborate salts. Examples of metal borate salts include zinc borate, calcium borate, barium borate, aluminum borate, magnesium borate, strontium borate, zinc calcium borate, and zinc potassium borate. Examples of metal metaborate salts include barium metaborate.

[0065] Examples of the aforementioned silicate-based rust-preventive pigments include metal borosilicate salts. Examples of metal borosilicate salts include silica, zinc borosilicate, calcium borosilicate, barium borosilicate, aluminum borosilicate, magnesium borosilicate, strontium borosilicate, potassium zinc borosilicate, calcium zinc borosilicate, and calcium strontium zinc borosilicate, zinc phosphatesilicate, calcium phosphatesilicate, barium phosphatesilicate, aluminum phosphatesilicate, magnesium phosphatesilicate, strontium phosphatesilicate, potassium zinc phosphatesilicate, calcium zinc phosphatesilicate, and calcium strontium zinc phosphatesilicate.

[0066] The metal salt may be a normal salt, a basic salt, or a complex salt, and may be hydrated or anhydrous.

[0067] In addition to the above, other examples of inorganic rust-preventive pigments include vanadic acid-based rust-preventive pigments and tungstic acid-based rust-preventive pigments. Other examples include cyanamide zinc calcium-based rust-preventive pigments and modified silica-based rust-preventive pigments in which metal cations such as calcium, zinc, cobalt, lead, strontium, and barium are bonded to porous silica particles.

[0068] Commercially available products may be used as the rust-preventive pigment (B). Examples of commercially available products include phosphate-based rust-preventive pigments such as LF-Bousei PM-300C, LF-Bousei PW-2 (manufactured by Kikuchi Color Co., Ltd.), and K-White #140W (manufactured by Teika Co., Ltd.), silicic acid-based rust-preventive pigments such as SHIELDEX CS-311 (manufactured by GRACE Co., Ltd.), molybdenum-based rust-preventive pigments such as LF-Bousei M-PSN (manufactured by Kikuchi Color Co., Ltd.), and zinc oxide-based rust-preventive pigments such as two types of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd.).

[0069] The rust-preventive pigment (B) may be used alone, or two or more may be used in combination. Preferably, the rust-preventive pigment (B) includes at least one selected from the group consisting of phosphate-based rust-preventive pigments, zinc oxide-based rust-preventive pigments, and molybdenum-based rust-preventive pigments, and more preferably at least one selected from the group consisting of phosphate-based rust-preventive pigments and zinc oxide-based rust-preventive pigments. It may also include a silicate-based rust-preventive pigment.

[0070] The content of the rust-preventive pigment (B) in the aqueous paint composition is preferably 1 to 50 parts by mass, more preferably 5 to 30 parts by mass, based on 100 parts by mass of the total amount of solids of the film-forming resin (A) contained in the aqueous paint composition. Having the content of the rust-preventive pigment (B) within the above range has the advantage of resulting in good corrosion resistance of the resulting coating film.

[0071] (C) Resin Beads Resin beads (C) are fine resin particles. Including resin beads (C) can improve the blocking resistance of the resulting coating film.

[0072] Examples of resins constituting the resin beads (C) include acrylic resin, urethane resin, polyester resin, polyamide resin, polystyrene resin, polyethylene resin, melamine resin, urea resin, fluororesin, and polyacrylonitrile resin, with acrylic resin being preferred from the viewpoint of hardness and cost. Furthermore, the term "particulate" refers to particulate, spherical, or hollow spherical. The resin beads are preferably spherical. Note that the spherical shape is not limited to a perfect sphere, but may also include shapes such as a roughly spherical shape.

[0073] The average particle size of the resin beads (C) is preferably 1 μm or more, more preferably 10 μm to 150 μm, even more preferably 20 μm to 100 μm, and even more preferably 40 μm to 80 μm.

[0074] In this specification, the average particle size of the resin beads (C) refers to the volume-average particle size (D50), which can be measured using a laser Doppler particle size analyzer (for example, the Microtrac UPA150 manufactured by Nikkiso Co., Ltd.).

[0075] As for the resin beads (C), commercially available acrylic resin particles may be used. Examples of commercially available products include Gantz Pearl GM-0801, GM-4003 (manufactured by Aica Kogyo Co., Ltd.), Toughtick AM, AR750MXQ, AR750MLQ2 (manufactured by Nippon Exlan Kogyo Co., Ltd.), Techpolymer MBX-40, MBX-80 (manufactured by Sekisui Kasei Kogyo Co., Ltd.), etc. Examples of urethane resin particles include ART PEARL C-80T, C-100T (manufactured by Negami Kogyo Co., Ltd.).

[0076] The content of resin beads (C) in the aqueous paint composition is preferably 1 to 30 parts by mass, more preferably 5 to 25 parts by mass, based on 100 parts by mass of the total amount of resin solids contained in the aqueous paint composition.

[0077] (D) Film-forming aid The aqueous coating compositions of this disclosure may optionally contain a film-forming aid (D). By incorporating a film-forming aid, the flowability of the coating film is improved when water evaporates and emulsion resin particles fuse to form a coating film, and as a result, the finished appearance of the coating film is improved.

[0078] The film-forming aid (D) is not particularly limited, but at least one of the following can be used: alcohol-based (e.g., benzyl alcohol); cellosolve-based (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether); propylene glycol ether-based (e.g., propylene glycol monomethyl ether, propylene glycol monoethyl ether); carbitol-based (e.g., diethylene glycol monoethyl ether, diethylene glycol monobutyl ether); triglycol ether-based (e.g., triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether); ketone-based (e.g., acetylacetone); amine-based (e.g., triethylamine, diethanolamine); or 2,2,4-trimethylpentanediol-1,3-monoisobutyrate (trade name "Texanol," manufactured by Eastman Chemical Japan). Two or more film-forming aids may be used in combination.

[0079] The content of film-forming aid (D) is preferably 1 to 40 parts by mass, more preferably 4 to 30 parts by mass, and even more preferably 8 to 20 parts by mass, based on 100 parts by mass of the total solid content of the aqueous coating composition. Having the content of film-forming aid (D) within this range can result in a better appearance of the resulting coating film.

[0080] (Other ingredients) In addition to the components described above, the aqueous coating composition may contain other components as needed, depending on the purpose and application. Examples of other components include curing agents, extender pigments, coloring pigments, resin particles, curing catalysts, viscosity modifiers, pH adjusters, film-forming aids, and additives commonly used in aqueous coating compositions (e.g., dispersion stabilizers, UV absorbers, light stabilizers, antioxidants, defoamers, surface modifiers, pinhole inhibitors, organic rust inhibitors, etc.). These components can be added as appropriate in a manner that does not impair the various physical properties of the aqueous coating composition of this disclosure.

[0081] Examples of the aforementioned pigments include coloring pigments and extender pigments. Examples of coloring pigments include inorganic coloring pigments and organic coloring pigments. Examples of the aforementioned inorganic coloring pigments include titanium dioxide, carbon black, iron oxide, and yellow iron oxide. Examples of the aforementioned organic coloring pigments include phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green; azo pigments such as azo red, azo yellow, and azo orange; quinacridone pigments such as quinacridone red, syncasha red, and syncasha magenta; perylene pigments such as perylene red and perylene maroon; and carbazole violet, anthrapyridine, flavanthrone yellow, isoindoline yellow, induthrone blue, dibromoanzathrone red, anthraquinone red, and diketopyrrolopyrrole. Examples of the aforementioned extender pigments include calcium carbonate, precipitated barium sulfate, clay, and talc.

[0082] When using the aforementioned coloring pigment, the pigment mass concentration of the coloring pigment relative to the resin solid content of the aqueous paint composition is preferably 5% by mass or more and 60% by mass or less.

[0083] When using the aforementioned extender pigment, the pigment mass concentration of the extender pigment relative to the resin solids content of the aqueous paint composition is preferably 0% by mass or more and 60% by mass or less, more preferably 0% by mass or more and 40% by mass or less. Having the amount of extender pigment within this range has the advantage of improving the water resistance of the resulting coating film.

[0084] (Method for preparing a water-based paint composition) A water-based paint composition can be prepared by mixing the film-forming resin (A), rust-preventive pigment (B), resin beads (C), and other components as needed, by a method known to those skilled in the art. The method for preparing the water-based paint composition can be one commonly used by those skilled in the art. For example, a kneading and mixing method using a kneader or roll, or a dispersion and mixing method using a sand grind mill or disperser, can be used, as commonly used by those skilled in the art.

[0085] (subject to be coated) Examples of the substrates to be coated include metal substrates such as iron, zinc, tin, copper, titanium, and tinplate. These metal substrates may be plated with zinc, copper, chromium, etc., or they may be surface-treated using surface treatment agents such as chromic acid, zinc phosphate, or zirconium salts.

[0086] The aqueous paint compositions of this disclosure are suitable for painting metal substrates, particularly steel materials such as steel bars, steel plates, and steel pipes, as well as steel towers, steel columns, steel doors, and vehicle bodies. More specifically, the steel materials include C-shaped steel such as lip channel steel, light channel steel, and deformed light channel steel, L-angles such as equal-sided light angle steel and unequal-sided light angle steel, lightweight steel shapes such as square steel pipes and deck plates, cast iron pipes, etc., and steel materials that have been subjected to chemical treatment such as phosphate treatment and / or metal spraying treatment.

[0087] (Method for forming a coating film) A coating film can be manufactured by applying the aqueous coating composition to the surface of an object to be coated and forming a film to obtain a coating film.

[0088] The method for applying the aqueous coating composition is not particularly limited, and examples include commonly used coating methods such as dipping, brushing, rolling, roll coater, air spray, airless spray, curtain flow coater, roller curtain coater, and die coater. These can be appropriately selected depending on the type of building material. The aqueous coating composition is preferably applied to a dry film thickness of 30 to 100 μm, and more preferably to 40 to 80 μm.

[0089] In the drying process, the coating film is dried. This forms the coating film. In one embodiment, the drying temperature may be 5 to 35°C, and the drying time may be 1 to 10 days. In another embodiment, the drying temperature may be, for example, 50 to 100°C, and moreover, 60 to 80°C, and in this case, the drying time may be 15 to 60 minutes.

[0090] In a preferred embodiment, the object to be coated may be preheated before painting. The preheating temperature may be set so that the temperature of the object to be coated is 60 to 110°C at the time of painting. When such preheating is performed, for example, the method for manufacturing the coating film may include preheating the object to be coated to 60°C to 110°C, and applying the aqueous coating composition to the surface of the object after preheating to form a coating film.

[0091] The heating method is not particularly limited and can be carried out using a heating furnace such as a gas furnace or an electric furnace. The heating temperature of the object to be coated is not particularly limited, and it is necessary to set it within a range that can maintain the object's temperature, taking into account the amount of heat stored due to the shape and thickness of the object and the interval from preheating to painting. Generally, it is often set about 10 to 30°C higher than the painting temperature, preferably 90°C or higher. [Examples]

[0092] The present disclosure will be further illustrated by the following embodiments, but will not be limited thereto.

[0093] Manufacturing example (A1-1) Preparation example of acrylic resin emulsion (A1-1) In a stainless steel container, 61.5 parts by mass of methyl methacrylate, 1.8 parts by mass of methacrylic acid, and 36.7 parts by mass of 2-ethylhexyl acrylate were stirred and mixed. Then, 2.5 parts by mass of diammonium sulfosuccinate (Latemul S-180A, manufactured by Kao Corporation) and 60.0 parts by mass of water were added as emulsifiers, and the mixture was stirred at room temperature for 15 minutes using a homomixer to obtain the first reaction emulsified mixture.

[0094] In a reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, and thermometer, 60.0 parts by mass of water were added, and the temperature in the reaction vessel was raised to 80°C. Then, 91.8 parts by mass of the first pre-reaction emulsion mixture and 5.5 parts by mass of a 1.5% by mass aqueous solution of ammonium persulfate as a reaction initiator were simultaneously added dropwise from separate dropping funnels over a period of 2 hours. After the addition was complete, the temperature in the reaction vessel was maintained at 80°C for 30 minutes to obtain an acrylic resin emulsion. In a separate container, 85.9 parts by mass of methyl methacrylate, 1.8 parts by mass of methacrylic acid, and 12.3 parts by mass of 2-ethylhexyl acrylate were stirred and mixed. Then, 2.5 parts by mass of diammonium sulfosuccinate (Latemul S-180A, manufactured by Kao Corporation) and 60.0 parts by mass of water were added as emulsifiers, and the mixture was stirred at room temperature for 15 minutes using a homomixer to obtain the emulsified mixture before the second reaction.

[0095] To a container containing the previously obtained acrylic resin emulsion, 91.8 parts by mass of the second pre-reaction emulsification mixture and 5.5 parts by mass of a 1.5% by mass aqueous solution of ammonium persulfate as a reaction initiator were simultaneously added dropwise from separate dropping funnels over a period of 2 hours. After the addition was complete, the temperature in the reaction vessel was maintained at 80°C for 1 hour, and then cooled to 30°C to obtain a core-shell type acrylic resin emulsion (A1-1) (solid content concentration: 45% by mass).

[0096] Manufacturing examples (A1-2) to (A1-5), (a1-1), (a1-2) The film-forming resins (A1-2) to (A1-5), (a1-1), and (a1-2) were prepared in the same manner as described above, except that the monomer species and amounts were changed as shown in Table 1. The characteristic values ​​such as the glass transition temperature for each film-forming resin are shown in Table 1.

[0097] [Table 1]

[0098] Manufacturing example (A2-1) Preparation example of acrylic resin emulsion (A2-1) In a stainless steel container, 34.0 parts by mass of methyl methacrylate, 1.0 part by mass of acrylic acid, 5.0 parts by mass of styrene, and 60.0 parts by mass of 2-ethylhexyl acrylate were stirred and mixed. Then, 2.5 parts by mass of diammonium sulfosuccinate (Latemul S-180A, manufactured by Kao Corporation) and 60.0 parts by mass of water were added as emulsifiers, and the mixture was stirred at room temperature for 15 minutes using a homomixer to obtain the first reaction emulsified mixture.

[0099] In a reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, and thermometer, 30.0 parts by mass of water were added, and the temperature in the reaction vessel was raised to 80°C. Then, 91.8 parts by mass of the first pre-reaction emulsified mixture and 5.5 parts by mass of a 1.5% by mass aqueous solution of ammonium persulfate as a reaction initiator were simultaneously added dropwise from separate dropping funnels over a period of 2 hours. After the addition was complete, the temperature in the reaction vessel was maintained at 80°C for 30 minutes to obtain acrylic resin emulsion (A2-1) (solid content concentration: 45% by mass).

[0100] Manufacturing example (A2-2), (A2-3), (a2-1)~(a2-3) The film-forming resins (A2-2), (A2-3), and (a2-1) to (a2-3) were prepared in the same manner as described above, except that the monomer species and amounts were changed as shown in Table 1. The characteristic values ​​such as the glass transition temperature for each film-forming resin are shown in Table 2.

[0101] [Table 2]

[0102] <Example of Pigment Dispersion Paste 1 Production> After pre-mixing 1.63 parts by mass of Disperbyk190 as a dispersant, 0.05 parts by mass of SN-477T as an antifoaming agent, 32.9 parts by mass of ion-exchanged water, 31.4 parts by mass of Ti-Pure R-706 as a pigment, and 33.8 parts by mass of LF Bowsei PW-2 as a rust-preventive pigment (B-1), the mixture was dispersed using an SG mill (dispersion medium: glass beads) at 1,600 rpm until the maximum particle size of the pigment coarse particles was 5 μm, thereby obtaining pigment dispersion paste 1.

[0103] <Example of Pigment Dispersion Paste 2 Production> After pre-mixing 1.63 parts by mass of Disperbyk190 as a dispersant, 0.05 parts by mass of SN-477T as an antifoaming agent, 32.9 parts by mass of ion-exchanged water, 31.4 parts by mass of Ti-Pure R-706 as a pigment, 16.9 parts by mass of LF Bowsei PW-2 as a rust-preventive pigment (B-1), and 16.9 parts by mass of SHIELDEX CS-311 as a rust-preventive pigment (B-2), the mixture was dispersed at 1,600 rpm using an SG mill (dispersion medium: glass beads) until the maximum particle size of the coarse pigment particles was 5 μm, thereby obtaining pigment dispersion paste 1.

[0104] <Example of Pigment Dispersion Paste 3 Production> After pre-mixing 1.63 parts by mass of Disperbyk190 as a dispersant, 0.05 parts by mass of SN-477T as an antifoaming agent, 32.9 parts by mass of ion-exchanged water, 31.4 parts by mass of Ti-Pure R-706 as a pigment, 16.9 parts by mass of LF Bowsei PW-2 as a rust-preventive pigment (B-1), and 16.9 parts by mass of two types of zinc oxide as rust-preventive pigments (B-3), the mixture was dispersed at 1,600 rpm using an SG mill (dispersion medium: glass beads) until the maximum particle size of the coarse pigment particles was 5 μm, thereby obtaining pigment dispersion paste 1.

[0105] <Example of Pigment Dispersion Paste 4 Production> After pre-mixing 1.63 parts by mass of Disperbyk190 as a dispersant, 0.05 parts by mass of SN-477T as an antifoaming agent, 32.9 parts by mass of ion-exchanged water, and 64.7 parts by mass of Ti-Pure R-706 as a pigment, the mixture was dispersed using an SG mill (dispersion medium: glass beads) at 1,600 rpm until the maximum particle size of the pigment coarse particles was 5 μm, thereby obtaining pigment dispersion paste 1.

[0106] <Example of Pigment Dispersion Paste 5 Production> After pre-mixing 1.63 parts by mass of Disperbyk190 as a dispersant, 0.05 parts by mass of SN-477T as an antifoaming agent, 32.9 parts by mass of ion-exchanged water, 31.4 parts by mass of Ti-Pure R-706 as a pigment, and 7.7 parts by mass of LF Bowsei PW-2 as a rust-preventive pigment (B-1), the mixture was dispersed using an SG mill (dispersion medium: glass beads) at 1,600 rpm until the maximum particle size of the coarse pigment particles was 5 μm, thereby obtaining pigment dispersion paste 1.

[0107] <Example of manufacturing pigment dispersion paste 6> After pre-mixing 1.63 parts by mass of Disperbyk190 as a dispersant, 0.05 parts by mass of SN-477T as an antifoaming agent, 32.9 parts by mass of ion-exchanged water, 31.4 parts by mass of Ti-Pure R-706 as a pigment, and 61.3 parts by mass of LF Bowsei PW-2 as a rust-preventive pigment (B-1), the mixture was dispersed using an SG mill (dispersion medium: glass beads) at 1,600 rpm until the maximum particle size of the coarse pigment particles was 5 μm, thereby obtaining pigment dispersion paste 1.

[0108] (Example 1) Preparation of aqueous paint composition 1 To 20.8 parts by mass of pigment dispersion paste 1, 46.0 parts by mass of acrylic resin aqueous dispersion (A1-1), 25.0 parts by mass of acrylic resin aqueous dispersion (A2-1), 7.0 parts by mass of resin beads (C-1), and 6.0 parts by mass of film-forming aid (D-1) were added, and the mixture was stirred and mixed with a disperser to obtain aqueous paint composition 1.

[0109] (Examples 2-23, Comparative Examples 1-7) The paint composition was prepared in the same manner as water-based paint composition 1, except that the types and amounts of each component were changed as shown in Tables 3 to 5. The amounts of rust-preventive pigment (B) shown in Tables 3 to 5 represent the amount of rust-preventive pigment (B) contained in the pigment dispersion paste. In the example where (a) was used instead of the film-forming resin (A), the amount of (A) is read as the amount of (a). Note that the amounts of each component refer to the amount in its natural state, including volatile components such as solvents.

[0110] The components used in the preparation of the aqueous paint composition are as follows: (1) Materials to be used (B) Anti-corrosion pigments; (B-1) LF Bousei PW-2 (Phosphoric acid-based rust-preventive pigment, manufactured by Kikuchi Color Co., Ltd.) (B-2) SHIELDEX CS-311 (Silicate-based rust-preventive pigment, manufactured by GRACE Co., Ltd.) (B-3) Two types of zinc oxide (zinc oxide-based rust-preventive pigments, manufactured by Sakai Chemical Industry Co., Ltd.) (C) Resin beads; (C-1) ToughTic AR750MXQ (acrylic resin beads, manufactured by Nippon Exlan Industries Co., Ltd.), particle size: 40 μm (C-2) Techpolymer MBX-80 (acrylic resin beads, manufactured by Sekisui Chemical Co., Ltd.), particle size: 80 μm (C-3) ART PEARL C-100T (urethane resin beads, manufactured by Negami Kogyo), particle size: 50 μm (D) Film-forming aid; (D-1) Benzyl alcohol (manufactured by Lanxess) (D-2) Diethylene glycol monobutyl ether (manufactured by Nippon Emulsifier Co., Ltd.) others; • Coloring pigment: Ti-Pure R-706 (titanium dioxide, manufactured by DuPont) • Dispersant: Disperbyk190 (manufactured by Bic Chemie), Active ingredient concentration: 40% by mass • Antifoaming agent: SN-477T (mineral oil-based antifoaming agent, manufactured by Sunopco), active ingredient concentration: 100% by mass

[0111] Preparation of test plates The aqueous coating compositions obtained in the examples or comparative examples were diluted with water to a temperature of 30 seconds (25°C) using an NK2 cup manufactured by Anest Iwata. Then, the coatings were air-sprayed onto JIS G 3141 (SPCC-SD) cold-rolled steel sheets (0.8 × 70 × 150 mm) that had been degreased with a solvent and preheated to 60°C, to a dry film thickness of 80 μm. The sheets were then cured at room temperature for 7 days to obtain test plates.

[0112] 1) Dry to the touch The aqueous paint compositions obtained in the examples or comparative examples were diluted with water to a temperature of 30 seconds (25°C) using an NK2 cup manufactured by Anest Iwata, and then painted onto JIS G 3141 (SPCC-SD) cold-rolled steel sheets (0.8 × 70 × 150 mm) that had been degreased with a solvent and preheated to 60°C, using an 8 MIL doctor blade. The time required for the coating obtained by painting to reach a "touch-dry" state according to JIS K 5600-1-1 under conditions of 23 degrees Celsius and 50% humidity was measured and evaluated according to the following criteria. A score of △ or higher was considered acceptable. ○: Touch-dry time is within 90 seconds. △: Touch-dry time is between 90 and 120 seconds. ×: Touch-dry time is 120 seconds or longer.

[0113] 2) Crack resistance The appearance of the coatings on the test plates obtained in the examples and comparative examples was visually observed and evaluated according to the following criteria. A score of △ or higher was considered acceptable. ○: No visible abnormalities such as cracks are observed in the paint film. △: Cracks are visible in part of the paint film. ×: Cracks are visible across the entire surface of the coating.

[0114] 3) Blocking resistance The test plates obtained in the examples and comparative examples were evaluated for blocking resistance using a blocking tester (manufactured by Kami Kiko Co., Ltd.) according to the following procedure. Two test panels were placed with their painted surfaces overlapping, at a panel temperature of 50°C and a load of 3 kg / cm². 2A 10-minute test was conducted, and the appearance of the coating film was visually observed after removing the test plate. The following criteria were used for evaluation. A score of △ or higher was considered a pass. ○: No change in the coating surface. △: Damage is observed in a portion of the paint film. ×: Damage is observed across the entire surface of the coating.

[0115] 4) Corrosion resistance Cross-cut scratches 10 cm long were made in the coating of the test plates obtained in the examples and comparative examples using a utility knife, so as to reach the substrate. A salt spray test (SST) was then performed for 120 hours using a salt spray tester ST-11L (manufactured by Suga Test Instruments Co., Ltd.) according to the neutral salt spray resistance test method described in JIS K 5600-7-1 (JIS Z 2371). After the test, the corrosion resistance of the coating was visually evaluated based on the rust and blistering that occurred from the cross-cut areas, according to the following criteria. A score of △ or higher was considered a pass. ○: The maximum width of the rust or blister that has occurred is less than 2 mm from the cross-cut area. △: The maximum width of the rust or blister that has occurred is 2 mm or more but less than 3 mm from the cross-cut area. ×: The maximum width of the rust or blister that has occurred is 3 mm or more from the cross-cut area.

[0116] [Table 3]

[0117] [Table 4]

[0118] [Table 5]

[0119] Examples 1 to 23 are embodiments of the present disclosure, in which a coating film was formed in a single application and dried at room temperature, exhibiting good touch-dry properties, as well as good appearance, corrosion resistance, and blocking resistance of the resulting coating film.

[0120] Comparative Example 1 is an example in which a core-shell type acrylic resin emulsion, one of the coating film-forming resins, was used, and the overall glass transition temperature of the resin was less than 30°C. As a result, the blocking resistance of the resulting coating film was not sufficiently satisfactory. Comparative Example 2 is an example in which a core-shell type acrylic resin emulsion, which is a type of coating film-forming resin, was used, and the glass transition temperature of the entire resin exceeded 50°C. As a result, the crack resistance and corrosion resistance of the resulting coating film were not sufficiently satisfactory. Comparative Example 3 is an example in which a single-layer acrylic resin emulsion, one of the coating-forming resins, was used, and the overall glass transition temperature of the resin was less than -20°C. As a result, the blocking resistance and corrosion resistance of the resulting coating film were not sufficiently satisfactory. Comparative Example 4 is an example in which a single-layer acrylic resin emulsion, a type of coating-forming resin, was used, and the glass transition temperature of the entire resin exceeded 0°C. As a result, the crack resistance of the resulting coating film was not sufficiently satisfactory. Comparative Example 5 is an example that does not include a core-shell type acrylic resin emulsion (A1) as the coating film-forming resin, and the crack resistance and blocking resistance of the resulting coating film were not sufficiently satisfactory. Comparative Example 6 was an example that did not include rust-preventive pigment (B), and the corrosion resistance of the resulting coating film was not sufficiently satisfactory. Comparative Example 7 was an example that did not include resin beads (C), and the blocking resistance of the resulting coating film was not sufficiently satisfactory. [Industrial applicability]

[0121] The aqueous coating composition of this disclosure forms a coating film in a single application, has good touch-dry properties even when dried at room temperature, and the resulting coating film has good appearance, corrosion resistance, and blocking resistance. It can be suitably used in various fields such as building exteriors, building materials, bridges, ships, vehicles, industrial machinery, construction machinery, and automobiles.

Claims

1. It comprises a film-forming resin (A), a rust-preventive pigment (B), and resin beads (C), The aforementioned coating film-forming resin (A) comprises an acrylic resin emulsion (A1) and an acrylic resin emulsion (A2). The acrylic resin emulsion (A1) includes a core-shell type acrylic resin emulsion having a core portion and a shell portion. The acrylic resin emulsion (A2) comprises a single-layer acrylic resin emulsion. The glass transition temperature of the entire acrylic resin in the aforementioned acrylic resin emulsion (A1) is 30°C or higher and 50°C or lower. The glass transition temperature of the entire acrylic resin in the aforementioned acrylic resin emulsion (A2) is between -20°C and 0°C. Water-based paint composition.

2. The aqueous paint composition according to claim 1, wherein the glass transition temperature of the shell portion of the core-shell type acrylic resin emulsion is higher than the glass transition temperature of the core portion of the core-shell type acrylic resin emulsion.

3. The aqueous paint composition according to claim 1, wherein the ratio of the solid content of the acrylic resin emulsion (A1) to the solid content of the acrylic resin emulsion (A2) is 90:10 to 50:

50.

4. The aqueous paint composition according to claim 1, wherein the content of the rust-preventive pigment (B) is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of the solid content of the coating film-forming resin (A).

5. The aqueous paint composition according to claim 1, wherein the average particle size of the resin beads (C) is 1 μm or more.

6. The aqueous paint composition according to claim 1, wherein the content of the resin beads (C) is 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the solid content of the coating film forming resin (A).

7. The aqueous coating composition according to claim 1, further comprising a film-forming aid (D), wherein the content of the film-forming aid (D) is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the solid content of the coating resin (A).

8. Preheat the object to be coated to 60°C or higher and 110°C or lower, and A method for producing a coating film, comprising applying the aqueous coating composition according to any one of claims 1 to 7 to the surface of the object to be coated after preheating, and forming a film to obtain a coating film.

Images