Water-based coating composition and anticorrosion coating method

Abstract

Provided is an aqueous coating composition that is capable of forming a coating film that has excellent environmental barrier properties and adhesion and long-term corrosion prevention properties. [Solution] An aqueous paint composition comprising at least (A) a scaly pigment and (B) a water-dispersible resin, wherein the scaly pigment (A) comprises (A-1) a scaly pigment having an average particle size of 1 to 13 μm and an aspect ratio of less than 10, and (A-2) a scaly pigment having an average particle size of 14 to 150 μm and an aspect ratio of 10 to 100, wherein the mass ratio of (A-1):(A-2) is 95:5 to 50:50, the pigment volume concentration (PVC) is 20 to 35%, and the volume content of (A-2) is 3 to 20 volume% relative to the total amount of pigment contained in the aqueous paint composition.

Description

[Technical Field]

[0001] The present invention relates to an aqueous coating composition and a corrosion-protective coating method using the aqueous coating composition. [Background technology]

[0002] In the field of coatings for architectural and civil engineering structures, there has been a shift from solvent-based to water-based coatings in order to reduce the health hazards to painters and residents and to reduce odors.

[0003] JP 2010-90325 A (Patent Document 1) describes a two-component aqueous organic / inorganic coating composition consisting of a base agent and a curing agent, in which the base agent contains an emulsion containing an acrylic-urethane composite resin having a carboxyl group and an organosilane compound having an alkoxy group. Patent Document 1 also describes that the coating composition, while water-based, can provide a coating film with high elasticity and durability, and that by combining the acrylic-urethane composite resin and the organosilane compound, a two-component aqueous organic / inorganic coating composition with excellent stability can be obtained, and that a coating film with excellent appearance can be formed even after long-term storage.

[0004] Furthermore, two-component water-based paint compositions that cure at room temperature using epoxy resins have been developed because of their excellent corrosion resistance and ease of application.

[0005] Japanese Patent Application Laid-Open Publication No. 2013-199621 (Patent Document 2) describes an aqueous epoxy resin coating composition that contains a base agent containing an epoxy resin emulsion and a curing agent containing an amine resin emulsion, and that has a viscosity of 1.0 to 500 (Pa·s, 23°C) at a shear rate of 0.1 (1 / s) and a viscosity of 0.010 to 1 (Pa·s, 23°C) at a shear rate of 1000 (1 / s), and that this makes it possible to provide an aqueous epoxy resin coating composition that is excellent in workability and corrosion resistance.

[0006] JP 2016-186021 A (Patent Document 3) describes a two-component waterborne epoxy resin coating composition that contains at least (A) an epoxy resin, (B) a curing agent, (C) a viscosity modifier, (D) a pigment, and (E) water, and that is used by mixing the (A) epoxy resin and the (B) curing agent immediately before application, wherein the content of film-forming components in the waterborne epoxy resin coating composition is 55 to 75 mass %, and the (C) viscosity modifier is at least one selected from the group consisting of polyacrylic acid-based viscosity modifiers and polyurethane-based viscosity modifiers. The patent document also describes a waterborne epoxy resin coating composition that can form a coating film with a dry film thickness of 100 μm or more in a single application and that has high corrosion resistance. Furthermore, Patent Document 3 describes a scaly pigment as the (D) pigment, and states that if the aspect ratio of the scaly pigment is less than 1.2, it becomes difficult to obtain a shielding effect, and on the other hand, if the aspect ratio exceeds 100, coating workability may deteriorate or the scaly pigment may not be properly arranged during film formation.

[0007] Japanese Patent Publication No. 2018-53028 (Patent Document 4) describes a two-component, reactively curable aqueous coating composition for primer paint, containing an epoxy resin and an amine resin, where the epoxy resins have an epoxy equivalent weight of 400-1000 g / eq and an epoxy resin with an epoxy equivalent weight of 150-300 g / eq in a weight ratio of 90:10 to 60:40. This coating composition provides a two-component, reactively curable aqueous coating composition for primer paint that provides a primer paint film with excellent chemical resistance. Patent Document 4 also describes that the aqueous coating composition may contain scale-shaped inorganic powder with an aspect ratio of 2-1000. It notes that an aspect ratio of less than 2 results in poor shielding effect and poor chemical resistance of the resulting primer paint film, while an aspect ratio of more than 1000 can lead to poor coating workability or improper alignment of the inorganic powder during film formation.

[0008] In addition, although the coating composition is solvent-based, by adjusting the flake pigment, coating compositions have been developed that can block water vapor in the external environment, thereby exhibiting excellent corrosion prevention properties.

[0009] JP 2019-196417 A (Patent Document 5) describes a coating composition containing a resin component and a pigment, in which the coefficient of linear expansion at a temperature equal to or lower than the glass transition temperature of the nonvolatile content contained in the coating composition is 2.5 × 10 -5 / K~5.4×10 -5 / K, and when a coating film having a thickness of 200 μm is formed from the coating composition, the water vapor permeability of the coating film is 0.1 to 1.4 g / m 2 Patent Document 5 describes a coating composition characterized by the above-mentioned coefficient of linear expansion being within the above-mentioned specified range, and states that it is possible to provide a coating composition capable of forming a coating film with excellent corrosion resistance and peeling resistance. Patent Document 5 also describes a scaly pigment as a pigment, and states that by using the scaly pigment or adjusting the ratio of the scaly pigment and resin component, it is possible to reduce the water vapor permeability while maintaining the coefficient of linear expansion within the above-mentioned specified range.

[0010] JP 2021-195500 A (Patent Document 6) describes a paint composition containing a resin, a flake-like aluminum pigment or stainless steel flakes, and a flake-like pigment other than the aluminum pigment or stainless steel flakes, wherein the flake-like aluminum pigment or stainless steel flakes are non-leafing aluminum pigments or stainless steel flakes with an average particle diameter of 20 to 60 μm, and the flake-like pigment other than the aluminum pigment or stainless steel flakes has an average particle diameter of 5 to 50 μm and an aspect ratio of 10 to 100, and the mass ratio (A / B) of the flake-like aluminum pigment or stainless steel flakes (A) to the flake-like pigment other than the aluminum pigment or stainless steel flakes (B) is 1 / 2 to 1 / 18. The paint composition describes that this can provide a paint composition that is capable of forming a coating film that has excellent environmental barrier properties and good corrosion resistance. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-90325 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-199621 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-186021 [Patent Document 4] Japanese Patent Application Publication No. 2018-53028 [Patent Document 5] Japanese Patent Application Publication No. 2019-196417 [Patent Document 6] Patent Publication No. 2021-195500 Summary of the Invention [Problem to be solved by the invention]

[0012] Although Patent Document 6 describes an invention relating to a coating composition capable of forming a coating film that has excellent environmental barrier properties and good corrosion prevention properties, the coating composition described in Patent Document 6 has the problem that when it is a water-based paint, it is more difficult to orient the scale-like pigments regularly in the coating film than when it is a solvent-based paint. If the scale-like pigments are not regularly oriented in the coating film, sufficient environmental barrier properties cannot be obtained, and adhesion to the substrate is also reduced, making it difficult to achieve long-term corrosion prevention.

[0013] Therefore, an object of the present invention is to provide an aqueous coating composition capable of forming a coating film having excellent environmental barrier properties and adhesion and long-term corrosion protection. Another object of the present invention is to provide a corrosion protection coating method using such an aqueous coating composition. [Means for solving the problem]

[0014] As a result of extensive research into achieving the above-mentioned object, the present inventors have discovered that, for an aqueous paint composition containing at least a scale-like pigment and a water-dispersible resin, by using two types of scale-like pigments with different average particle sizes and aspect ratios in specific proportions, adjusting the pigment volume concentration (PVC), and adjusting the proportion of the scale-like pigment with the larger average particle size and aspect ratio among the two types of scale-like pigments in the total pigment, it is possible to form a coating film with excellent environmental barrier properties and adhesion, as well as long-term corrosion protection, and have completed the present invention.

[0015] Therefore, the aqueous coating composition of the present invention is an aqueous coating composition containing at least (A) a scaly pigment and (B) a water-dispersible resin, (A) the scaly pigment includes (A-1) a scaly pigment having an average particle size of 1 to 13 μm and an aspect ratio of less than 10, and (A-2) a scaly pigment having an average particle size of 14 to 150 μm and an aspect ratio of 10 to 100, The mass ratio of (A-1):(A-2) is 95:5 to 50:50, The pigment volume concentration (PVC) is 20 to 35%. The aqueous coating composition is characterized in that the volume content of (A-2) is 3 to 20% by volume relative to the total amount of pigments contained in the aqueous coating composition.

[0016] In a preferred embodiment of the aqueous coating composition of the present invention, the water-dispersible resin (B) is an epoxy resin.

[0017] In another preferred embodiment of the aqueous coating composition of the present invention, the aqueous coating composition contains an amine curing agent (C).

[0018] In another preferred embodiment of the aqueous coating composition of the present invention, the amine curing agent (C) contains a polyamine resin having a cyclic structure.

[0019] The corrosion-resistant coating method of the present invention is characterized in that the aqueous coating composition of the present invention described above is applied to a surface to be coated to form a coating film on the surface to be coated, and then a coating material other than the aqueous coating composition is applied onto the coating film. [Effects of the Invention]

[0020] The aqueous coating composition of the present invention can provide an aqueous coating composition capable of forming a coating film having excellent environmental barrier properties and adhesion and long-term corrosion protection. Furthermore, the corrosion-protective coating method of the present invention can provide a corrosion-protective coating method using such an aqueous coating composition. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below. The present invention relates to an aqueous coating composition and a corrosion-protective coating method.

[0022] In this specification, an aqueous coating composition refers to a coating composition containing water as the main solvent (the solvent with the highest content in the coating). The water that can be used in the aqueous coating composition is not particularly limited, but examples include tap water, ion-exchanged water, distilled water, and other pure water. Furthermore, when storing the coating composition for a long period of time, water that has been sterilized by ultraviolet irradiation or the like may be used to prevent the growth of mold and bacteria. The amount of water contained in the aqueous coating composition of the present invention is preferably 30 to 90% by mass, and more preferably 40 to 80% by mass. In this specification, the aqueous coating composition of the present invention is also referred to as the "coating composition of the present invention."

[0023] In this specification, the anticorrosion coating method refers to a coating method carried out for the purpose of preventing corrosion on the surface of a substrate, and in particular, a coating method carried out for the purpose of applying a coating to the surface of a metal substrate such as iron or steel to protect the substrate from rust and corrosion.

[0024] The aqueous coating composition of the present invention is an aqueous coating composition containing at least a scaly pigment and a water-dispersible resin. In this specification, the scaly pigment is referred to as component (A) and is also referred to as "(A) scaly pigment." The water-dispersible resin is referred to as component (B) and is also referred to as "(B) water-dispersible resin."

[0025] (A) Flake pigments are pigments with a thin, flat, foil-like shape. Specific examples include metal pigments such as zinc, nickel, chromium, tin, copper, silver, platinum, gold, and aluminum, as well as glass flakes, talc, mica, kaolin clay, and micaceous iron oxide. Metal pigments also include alloy pigments such as stainless steel. Furthermore, flake pigments, such as talc and mica, may be surface-treated with inorganic metal oxides such as titanium oxide and silica, or organic substances such as silicone resins. (A) Flake pigments contribute to the environmental barrier properties of the coating film.

[0026] In this specification, the (A) scaly pigment has an aspect ratio of 2 or more.

[0027] In the coating composition of the present invention, the amount of (A) scaly pigment is preferably 30 to 65 mass %, more preferably 40 to 60 mass %, based on the total amount of the coating film-forming components. When the coating composition contains multiple (A) scaly pigments, the amount of (A) scaly pigment is the total amount of (A) scaly pigments.

[0028] In the aqueous coating composition of the present invention, the (A) scaly pigment comprises two types of scaly pigments corresponding to the following (A-1) and (A-2). (A-1) A scaly pigment having an average particle size of 1 to 13 μm and an aspect ratio of less than 10 (A-2) A scaly pigment having an average particle size of 14 to 150 μm and an aspect ratio of 10 to 100

[0029] In this specification, a scaly pigment that falls under (A-1) is also referred to as (A-1), (A-1) scaly pigment, etc. A scaly pigment that falls under (A-2) is also referred to as (A-2), (A-2) scaly pigment, etc. A scaly pigment that does not fall under (A-1) or (A-2) is also referred to as (A-3), (A-3) scaly pigment, (A-3) other scaly pigment, etc.

[0030] In addition, in the aqueous coating composition of the present invention, the mass ratio of the (A-1) scaly pigment to the (A-2) scaly pigment [i.e., the mass ratio of (A-1):(A-2)] is 95:5 to 50:50, preferably 95:5 to 70:30, and more preferably 90:10 to 75:25.

[0031] The (A-2) scaly pigment has a high aspect ratio and is a preferred pigment from the viewpoint of improving the environmental barrier properties of the coating film, and increasing the content of the (A-2) scaly pigment can also improve the environmental barrier properties. On the other hand, because the (A-2) scaly pigment has a high aspect ratio, it is difficult to orient it regularly in the coating film, which may result in a decrease in the adhesion of the coating film to the substrate. According to the aqueous coating composition of the present invention, by combining the (A-2) scaly pigment with the (A-1) scaly pigment having a small average particle size and aspect ratio in a specific mass ratio, it is possible to orient the (A) scaly pigment regularly in the coating film, thereby ensuring adhesion while improving the environmental barrier properties and ultimately achieving long-term corrosion protection of the coating film.

[0032] The average particle size of the (A-1) scaly pigment is 1 to 13 μm, preferably 5 to 13 μm, and more preferably 8 to 13 μm. The aspect ratio of the (A-1) scaly pigment is less than 10, preferably 8 or less, and more preferably 6 or less. The aspect ratio of the (A-1) scaly pigment is 2 or more. Suitable examples of the (A-1) scaly pigment include talc and kaolin.

[0033] The average particle size of the (A-2) scaly pigment is 14 to 150 μm, preferably 14 to 100 μm, and more preferably 14 to 80 μm. The aspect ratio of the (A-2) scaly pigment is 10 to 100, preferably 10 to 80, and more preferably 14 to 80. The larger the average particle size of a scaly pigment with a high aspect ratio, the more improved its environmental barrier properties can be. However, if the average particle size is too large, excessive amounts may lead to deterioration of the coating film appearance and storage stability. For this reason, the average particle size of the (A-2) scaly pigment is set within the above-specified range. Suitable examples of the (A-2) scaly pigment include aluminum flakes, mica, and glass flakes.

[0034] In this specification, the aspect ratio of a scaly pigment refers to the ratio (D / T) of the average particle diameter (D) to the average thickness (T) of the scaly pigment. The average particle diameter of a scaly pigment refers to the 50% particle diameter (D50) of the volume-based particle size distribution, and is determined from the particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer. The particle diameter of a scaly pigment is expressed as the spherical equivalent diameter measured by the laser diffraction / scattering method. The average thickness refers to the average value of the thicknesses measured for 100 or more scaly pigment particles using an SEM (scanning electron microscope).

[0035] In the aqueous coating composition of the present invention, the pigment volume concentration (PVC) is 20 to 35%, preferably 21 to 33%, and more preferably 23 to 31%. In the coating composition of the present invention, the scaly pigment (A-1) and the scaly pigment (A-2) are used in combination, so the PVC is set relatively high. However, if the PVC is too high, the resin component tends to become relatively small, and the dispersibility of the pigment tends to decrease, which may result in a decrease in the storage stability of the coating composition or a decrease in the corrosion resistance of the coating film.

[0036] In this specification, pigment volume concentration (PVC) refers to the ratio of the total volume of the pigment to the total volume of the film-forming components, and can be calculated from the composition and specific gravity of the components that make up the film-forming components.

[0037] In the aqueous coating composition of the present invention, the volume content of the (A-2) scaly pigment is 3 to 20 volume %, preferably 7 to 19 volume %, and more preferably 10 to 16 volume %, based on the total amount of pigment contained in the coating composition. When a coating composition contains multiple (A-2) scaly pigments, the volume content of the (A-2) scaly pigments is the total amount of the (A-2) scaly pigments. According to the coating composition of the present invention, by having the pigment volume concentration and the volume content of the (A-2) scaly pigment within the above-specified ranges, it is possible to improve environmental barrier properties while ensuring adhesion, and to suppress the occurrence of unevenness due to the (A-2) scaly pigment during coating film formation, thereby preventing deterioration of the appearance of the coating film.

[0038] In the aqueous coating composition of the present invention, the volume content of the (A-1) scaly pigment is preferably 35 to 65% by volume, more preferably 45 to 55% by volume, based on the total amount of pigment contained in the coating composition.

[0039] The aqueous coating composition of the present invention may contain, as pigments, not only scaly pigments but also non-scaly pigments such as spherical, chunky, rod-like, angular, needle-like, fibrous, etc. Pigments include anti-rust pigments, extender pigments, coloring pigments, etc. Some of these pigments fall under the category of scaly pigments, while others fall under the category of non-scaly pigments. In this specification, pigments that do not fall under the category of scaly pigments are referred to as component (D), and are also referred to as (D) pigments that do not fall under the category of scaly pigments, (D) pigments, etc.

[0040] Examples of anti-rust pigments include zinc powder, zinc oxide, barium metaborate, calcium silicate, aluminum phosphate, condensed aluminum phosphate, aluminum tripolyphosphate, zinc phosphate, zinc phosphite, potassium phosphite, calcium phosphite, aluminum phosphite, calcium zinc phosphate, zinc aluminum phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, magnesium phosphate, and vanadate / phosphate mixed pigments.

[0041] Examples of extender pigments include silica, talc, mica, calcium carbonate, and barium sulfate.

[0042] Examples of color pigments include titanium oxide, iron oxide (e.g., red iron oxide), carbon black, yellow lead, molybdate orange, ultramarine, Prussian blue, phthalocyanine blue, phthalocyanine green, quinacridone red, naphthol red, benzimidazolone yellow, Hansa yellow, benzimidazolone orange, and dioxazine violet.

[0043] The water-dispersible resin (B) is a resin that can be dispersed in water to form a heterogeneous system (e.g., an emulsion or suspension). The water-dispersible resin (B) is present in a dispersed state in the aqueous coating composition of the present invention.

[0044] The (B) water-dispersible resin can be prepared, for example, by emulsifying the water-dispersible resin in water, or by emulsion polymerization of the monomer components, using a surfactant as needed, while applying forced shear force using a high-speed agitator or the like. Alternatively, a water-dispersible resin dispersion can be prepared by adding a surfactant as needed to a water-dispersible resin polymerized in an organic solvent and then subjecting the polymer to phase inversion into water, and the organic solvent contained in the water-dispersible resin dispersion can be removed as needed by distillation or the like. Alternatively, a water-dispersible resin dispersion can be prepared by polymerization in water using water as the medium.

[0045] Water-dispersible resins can be classified into emulsion resins and dispersion resins. Emulsion resins refer to water-dispersible resins obtained by emulsion polymerization. Dispersion resins refer to self-water-dispersible resins, but emulsion resins are excluded in the present invention. Resins that dissolve in water are water-soluble resins.

[0046] In the coating composition of the present invention, the amount of (B) water-dispersible resin is preferably 30 to 70 mass %, more preferably 40 to 60 mass %, based on the total amount of the coating film-forming components. When the coating composition contains multiple (B) water-dispersible resins, the amount of (B) water-dispersible resins is the total amount of the (B) water-dispersible resins.

[0047] In the aqueous coating composition of the present invention, the (B) water-dispersible resin preferably contains an epoxy resin (ie, a water-dispersible epoxy resin).

[0048] Epoxy resins are resins that contain epoxy groups in their molecules and can be cured by reaction of the epoxy groups. Epoxy resins generally have high adhesion to substrates, particularly metal substrates, and also have the effect of shielding the substrate from environmental factors (e.g., water, oxygen, etc.) that affect corrosion of substrates, particularly metal substrates, and are therefore known as resins with excellent corrosion resistance.

[0049] The epoxy resin is preferably a resin having at least two epoxy groups in one molecule, and is, for example, one obtained by reacting a polyhydric alcohol or a polyhydric phenol with a halohydrin. Specific examples include bisphenol A type epoxy resins, halogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyglycol type epoxy resins, bisphenol F type epoxy resins, epoxidized oil, 1,6-hexanediol diglycidyl ether, and neopentyl glycol diglycidyl ether.

[0050] The epoxy resin is preferably present in the form of an epoxy resin emulsion or epoxy resin dispersion. In this specification, "resin emulsion" refers to an emulsion in which a resin is dispersed in an aqueous medium primarily composed of water, and "resin dispersion" refers to a dispersion in which a resin is dispersed in an aqueous medium primarily composed of water. The epoxy resin emulsion is prepared by emulsifying an epoxy resin in an aqueous medium primarily composed of water using a conventional forced emulsification method (a method using an emulsifier and a high-speed stirrer, etc.), without any particular limitation. Examples of emulsifiers include polyethers such as polyoxyethylene alkylphenol ether-based nonionic surfactants and polyoxyethylene-polyoxypropylene block copolymers; and adducts of at least one of these nonionic surfactants and polyethers with a diisocyanate compound. The emulsifiers may be used alone or as a blend of two or more. Commercially available epoxy resin emulsions include Epolsion EA-1, 2, 3, 7, 12, 20, 55, and HD2 (manufactured by Henkel Japan Co., Ltd.); Yuka Resin RE-1050, KE-002, KE-116, KE-307, E-1022, KE-301C, and NE-320 (manufactured by Yoshimura Oil Chemical Co., Ltd.); Adeka Resin EM-101-50 (manufactured by Adeka Corporation); jER W1155R55, jER W3435R67, and jER W2821R70 (manufactured by Mitsubishi Chemical Corporation). Commercially available epoxy resin dispersions include Beckpox EP2381 (manufactured by Allnex Corporation) and EPI-REZ6530-WH-53 (manufactured by Momentive Corporation).

[0051] The epoxy resin may be a modified epoxy resin, such as a urethane-modified epoxy resin, an amine-modified epoxy resin, an isocyanate-modified epoxy resin, an acrylic-modified epoxy resin, a polyester-modified epoxy resin, or a dimer acid-modified epoxy resin.

[0052] The epoxy equivalent of the epoxy resin is preferably 100 to 1,000 g / eq, more preferably 200 to 700 g / eq, and even more preferably 300 to 600 g / eq. When the epoxy equivalent is 100 g / eq or more, sufficient coating film properties are easily obtained. On the other hand, when the epoxy equivalent is 1,000 g / eq or less, leveling properties are less likely to decrease and a uniform coating film is easily obtained. The epoxy resin may be used alone or as a blend of two or more types. The epoxy equivalent of the epoxy resin can be determined according to JIS K 7236:2001, "Determination of the epoxy equivalent of epoxy resins." When multiple epoxy resins are used, the epoxy equivalent is determined from the total epoxy resins used.

[0053] In the coating composition of the present invention, the amount of water-dispersible epoxy resin is preferably 20 to 65 mass %, more preferably 40 to 55 mass %, based on the total amount of coating film-forming components. When the coating composition contains multiple water-dispersible epoxy resins, the amount of water-dispersible epoxy resins is the total amount of the water-dispersible epoxy resins.

[0054] The aqueous coating composition of the present invention may contain a curing agent. When the (B) water-dispersible resin contains an epoxy resin, the aqueous coating composition of the present invention preferably contains an amine curing agent. In this specification, the amine curing agent is referred to as component (C) and is also referred to as "(C) amine curing agent."

[0055] (C) Amine curing agents are amines used to react with epoxy resins, particularly their epoxy groups, to promote or control the curing reaction. Resins containing active hydrogen atoms that react with epoxy groups are preferred as amine curing agents, with polyamine resins being more preferred. Polyamine resins are resins containing at least two amino groups per molecule. Examples of polyamine resins include those produced by condensation polymerization of amines and aldehydes, etherification of amines with alcohols, ring-opening polymerization of amines with heterocyclic structures (e.g., ethyleneimine), condensation of amines with carboxylic acids, or the Mannich reaction of amines with formaldehyde and ketones or phenols. Polyamine resins containing amide bonds in the molecule, such as those produced by condensation of amines and carboxylic acids, are also referred to as "polyamidoamine resins" or "polyamidoamines." Furthermore, ring-opening polymerization of alkylene oxides, such as ethylene oxide and propylene oxide, can be used to etherify amines with alcohols.

[0056] Examples of amines that can be used in producing the polyamine resin include aliphatic polyamines such as ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, triaminopropane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, isophoronediamine, and 1,3-bisaminomethylcyclohexane; aromatic polyamines such as phenylenediamine, metaxylylenediamine, paraxylylenediamine, and diaminodiphenylmethane; and amines having a heterocyclic structure such as ethyleneimine.

[0057] The polyamine resin may also be a modified polyamine resin. The modified polyamine resin is a polyamine resin in which some of the amino groups have been modified. The amino groups can be modified by known methods, such as amidation of the amino groups, the Mannich reaction of the amino groups with a carbonyl compound, or the addition reaction of the amino groups with an epoxy group.

[0058] The (C) amine curing agent preferably contains a polyamine resin having a cyclic structure, and more preferably contains a polyamidoamine having a cyclic structure. By using a polyamine resin having a cyclic structure as the (C) amine curing agent, it is possible to further improve the adhesion of the coating film to the substrate and to a layer containing zinc dust (zinc layer) that may be formed on the substrate.

[0059] The amount of the polyamine resin having a cyclic structure is preferably 40 to 100% by mass, more preferably 60 to 90% by mass, based on the total amount of the amine curing agent (C). When the coating composition contains polyamine resins having multiple cyclic structures, the amount of the polyamine resins having a cyclic structure is the total amount of the polyamine resins having cyclic structures.

[0060] Polyamine resins having a cyclic structure can be obtained by using a substance having a cyclic structure during their production. Examples of amines having a cyclic structure that can be used to produce polyamine resins include piperazines such as N-aminoethylpiperazine, 1,3-bisaminoethylcyclohexane, isophoronediamine, 1-cyclohexylamino-3-aminopropane, 1,4-diaminocyclohexane, di(aminocyclohexyl)methane, 1,3-di-(aminocyclohexyl)propane, 2,4-diaminocyclohexane, N,N'-diethyl-1,4-diaminocyclohexane, and 3,3'-dimethyl-4,4'-diaminocyclohexylmethane; and aromatic polyamines such as phenylenediamine, metaxylylenediamine, paraxylylenediamine, and diaminodiphenylmethane. Aliphatic polyamines having a cyclic structure are sometimes referred to as alicyclic polyamines. Examples of alcohols having a cyclic structure that can be used to produce polyamine resins include phenol and its derivatives. Examples of phenol derivatives include phenols in which the benzene ring is substituted with a hydrocarbon group, particularly phenols substituted with a linear or branched hydrocarbon group which may have one or more unsaturated bonds. Here, the hydrocarbon group is preferably a long-chain hydrocarbon group having 10 to 20 carbon atoms, particularly an alkyl group. A specific example of a phenol derivative is cardanol.

[0061] The polyamine resin having a cyclic structure is also preferably a polyamine resin obtained by the Mannich reaction of amines, formaldehyde, and a phenol derivative. Here, the cyclic structure is derived from a phenol derivative, and the amines are preferably chain compounds (or acyclic compounds) such as ethylenediamine. The phenol derivative is as described above, and cardanol is particularly preferred. Such polyamine resins are also called phenalkamine-based curing agents.

[0062] Polyamine resins having a cyclic structure may have low reactivity with epoxy resins. Therefore, it is preferable that the (C) amine curing agent contains a polyamine resin having a cyclic structure and a polyamine resin that does not fall under the category of polyamine resins having a cyclic structure. This ensures the reactivity of the (C) amine curing agent. Here, the polyamine resin that can be used in combination with the polyamine resin having a cyclic structure is not particularly limited, and for example, polyoxyethylene amines (also called polyether amines) such as polyoxyethylene diamine and polyoxypropylene diamine can be used.

[0063] When a polyamine resin having a cyclic structure is used in combination with a polyamine resin other than the polyamine resin having a cyclic structure, the amount of the polyamine resin having a cyclic structure is preferably 50 to 99 mass% relative to the total amount of the amine curing agent (C), and the amount of the polyamine resin other than the polyamine resin having a cyclic structure is preferably 1 to 50 mass% relative to the total amount of the amine curing agent (C).

[0064] The amine curing agent (C) is preferably blended in the form of an emulsion, a dispersion, or an aqueous solution.

[0065] The active hydrogen equivalent of the (C) amine curing agent is preferably 80 to 350 g / eq, more preferably 100 to 250 g / eq. The active hydrogen equivalent of the amine curing agent is the number of grams [g / eq] of the amine curing agent containing 1 equivalent of active hydrogen, and is the value obtained by dividing the molecular weight of the amine curing agent by the number of hydrogen atoms in the amino group per molecule.

[0066] In the coating composition of the present invention, the amount of (C) amine curing agent is preferably 3 to 30 mass %, more preferably 10 to 20 mass %, based on the total amount of the coating film-forming components. When the coating composition contains multiple (C) amine curing agents, the amount of (C) amine curing agent is the total amount of the (C) amine curing agents.

[0067] The aqueous coating composition of the present invention is preferably a two-component coating composition. A two-component coating composition is a coating composition consisting of a base agent and a curing agent. A two-component coating composition can be prepared by mixing the base agent, curing agent, and additives selected as necessary at the time of application. For example, (B) an agent containing an epoxy resin as a water-dispersible resin is the base agent, and (C) an agent containing an amine curing agent is the curing agent. (A) The scaly pigment may be contained in either the base agent or the curing agent, but is usually contained in the base agent. Water is usually contained in the base agent and the curing agent, but may also be used only in the base agent. Furthermore, part of the water may also be used as an additive when mixing the base agent and curing agent.

[0068] Other components that can be appropriately blended into the coating composition of the present invention depending on the purpose include resins other than component (B), dispersants, silane coupling agents, film-forming aids, antifreeze agents, viscosity modifiers, antifoaming agents, thickeners, rust inhibitors that do not fall under the category of anti-rust pigments, surface conditioners, anti-settling agents, anti-skinning agents, anti-sagging agents, anti-color separation agents, matting agents, adhesion imparting agents, leveling agents, drying agents, catalysts, plasticizers, anti-mold agents, antibacterial agents, antiviral agents, preservatives, insecticides, antistatic agents, and conductivity imparting agents.

[0069] The amount of the film-forming component contained in the aqueous coating composition of the present invention is preferably 10 to 70 mass %, more preferably 30 to 60 mass %.

[0070] In this specification, the term "film-forming components" refers to the components excluding volatile components such as water and organic solvents, and are the components that ultimately form a coating film. In this specification, the components that remain when the coating composition is dried at 130°C for 60 minutes are considered to be the film-forming components. The mass fraction of the components (film-forming components) that remain when the coating composition is dried at 130°C for 60 minutes is sometimes referred to as the heating residue (or non-volatile content NV).

[0071] The aqueous coating composition of the present invention can be prepared by mixing various components appropriately selected as needed. When the coating composition of the present invention is a two-component coating composition, the base agent and curing agent are prepared in advance, and the base agent, curing agent, and optional additives can be mixed at the time of application to prepare the coating composition. The base agent and curing agent can be prepared by mixing various components appropriately selected as needed. The viscosity of the base agent, as measured with a digital Stormer viscometer, is preferably 80 to 140 (KU, 23°C), more preferably 80 to 120 (KU, 23°C).

[0072] The aqueous coating composition of the present invention preferably has a viscosity of 1 to 1000 (Pa·s, 23°C) at a shear rate of 0.1 (1 / s), and a viscosity of 0.05 to 10 (Pa·s, 23°C) at a shear rate of 1000 (1 / s).

[0073] In this specification, viscosity is measured using a rheometer (for example, Anton Paar MCR302e rheometer) after adjusting the liquid temperature to 23°C.

[0074] The means for applying the aqueous coating composition of the present invention is not particularly limited, and known coating means such as brush coating, roller coating, trowel coating, spatula coating, flow coater coating, and spray coating (e.g., air spray coating, airless spray coating) can be used.

[0075] The drying method for the aqueous coating composition of the present invention is not particularly limited and may be either natural drying at ambient temperature or forced drying using a dryer or the like, but the aqueous coating composition of the present invention is preferably a coating composition that is to be natural dried at ambient temperature, which is assumed to be a temperature of about 5 to 40°C.

[0076] The aqueous coating composition of the present invention is capable of forming a coating film that has excellent environmental barrier properties and adhesion and has long-term corrosion protection, making the coating composition of the present invention suitable as an undercoat coating.

[0077] The substrate to be coated with the aqueous coating composition of the present invention has various shapes, for example, two-dimensional substrates such as film-like, sheet-like, and plate-like, and three-dimensional substrates which are complex three-dimensional objects. The surface of the substrate may be smooth or may have irregularities. Specific examples of the substrate include steel materials such as steel plates, steel pipes, and steel bars, and steel structures such as steel towers, bridge facilities, and plants.

[0078] The surface of the substrate may be subjected to pretreatment such as degreasing, chemical conversion treatment, or polishing, or may be coated with a sealer, primer, zinc-rich paint, or the like, or plated or metal sprayed.

[0079] The substrate may have an old paint film on its surface. The old paint film may cover a part or the whole of the surface of the substrate. In this specification, the old paint film means a paint film that is already present on the substrate when painting, particularly repair, is performed.

[0080] When a substrate has an old coating film on its surface, the substrate surface, including the old coating film, can be coated with the coating composition of the present invention. If the old coating film is sound, the coating composition of the present invention can be applied to the old coating film without peeling or removing the old coating film from the substrate surface. Since contaminants such as dust and dirt adhere to the old coating film, removing the contaminants can improve the adhesion of a new coating film to the old coating film. Methods for removing contaminants include high-pressure water washing, alkaline washing with caustic soda or the like, acid washing with inorganic or organic acids, washing with bleaching agents such as perchloric acid, and washing by scraping and wiping with a cloth.

[0081] The old paint film preferably contains a resin, for example, acrylic resin, silicone resin, acrylic silicone resin, styrene acrylic copolymer resin, polyester resin, fluororesin, rosin resin, petroleum resin, coumarone resin, phenolic resin, urethane resin, melamine resin, urea resin, epoxy resin, cellulose resin, xylene resin, alkyd resin, aliphatic hydrocarbon resin, butyral resin, maleic acid resin, fumaric acid resin, vinyl resin, amine resin, ketimine resin, and resins obtained by modifying these resins (modified resins), etc. The resins may be used alone or in combination of two or more.

[0082] The old paint film may contain various additives as other components, such as pigments, dispersants, curing catalysts, surface conditioners, antioxidants, plasticizers, rust inhibitors, solvents, antibacterial agents, antiviral agents, viscosity adjusters, fillers, antifoaming agents, thickeners, charge control agents, stress relaxation agents, penetrating agents, light-guiding materials, lustrous materials, magnetic materials, phosphors, ultraviolet absorbers, and radical scavengers.

[0083] Next, the anticorrosion coating method of the present invention will be described.

[0084] The corrosion-resistant coating method of the present invention is a corrosion-resistant coating method characterized by applying the above-mentioned aqueous coating composition of the present invention to a surface to be coated to form a coating film on the surface to be coated, and then applying a coating material other than the aqueous coating composition on top of the coating film.

[0085] The aqueous coating composition of the present invention is suitable as an undercoat coating because it is capable of forming a coating film that has excellent environmental barrier properties and adhesion and has long-term corrosion protection.

[0086] The dry film thickness formed by the aqueous coating composition of the present invention is preferably 50 to 300 μm. In this specification, the dry film thickness means the thickness of the coating film after coating is completed and dried. The coating composition of the present invention may be applied multiple times to the surface to be coated. When multiple coatings are performed, the dry film thickness formed by the coating composition of the present invention means the thickness of the coating film finally formed after multiple coatings are completed.

[0087] In the corrosion-protective coating method of the present invention, the surface to be coated can be the surface of the above-mentioned substrate. The substrate may have a layer containing zinc dust (zinc layer) formed on its surface by painting with a zinc-rich paint or the like.

[0088] In the corrosion-resistant coating method of the present invention, the paint applied on the coating film formed from the coating composition of the present invention is a paint different from the coating composition of the present invention, and a paint suitable for forming an intermediate coating film or a topcoat coating film can be appropriately used.Therefore, the multilayer film formed on the substrate by the corrosion-resistant coating method of the present invention includes, for example, a multilayer film comprising an undercoat coating film and a topcoat coating film, a multilayer film comprising an undercoat coating film, an intermediate coating film and a topcoat coating film, etc.By forming an additional coating film on the coating film (undercoat coating film) formed by the coating composition of the present invention, the environmental barrier properties of the undercoat coating film can be strengthened and better corrosion protection can be achieved.

[0089] The coating material for forming the intermediate coating film or the top coating film is preferably an aqueous coating material composition, similar to the coating material composition of the present invention.These coating materials can be appropriately blended with resins, curing agents, curing catalysts, solvents, dispersants, silane coupling agents, film-forming aids, antifreeze agents, viscosity adjusters, antifoaming agents, thickeners, rust inhibitors, surface conditioners, antisettling agents, antiskinning agents, antisagging agents, color-fade inhibitors, matting agents, adhesion imparting agents, leveling agents, drying agents, catalysts, plasticizers, antifungal agents, antibacterial agents, antiviral agents, antiseptics, insecticides, antistatic agents, and conductivity imparting agents, etc., according to the purpose. [Example]

[0090] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0091] <Example of preparation of coating composition> The raw materials were mixed according to the formulations shown in Tables 1 to 3 to prepare the base agent and curing agent. The obtained base agent and curing agent were mixed in the mixing ratios shown in Tables 4 to 5 to prepare the coating compositions. The formulations shown in Tables 1 to 3 and the mixing ratios shown in Tables 4 and 5 are based on mass. The "Non-volatile content" column in Tables 1 to 3 shows the mass percentage of the non-volatile content when the mass of the raw materials is taken as 1.

[0092] Details of the raw materials used in preparing the coating compositions are given below. (1) (A-1) A scaly pigment having an average particle size of 1 to 13 μm and an aspect ratio of less than 10 Scaly pigment 1: Talc (average particle size 13 μm, aspect ratio less than 10, non-volatile content 100% by mass) Scaly pigment 2: Kaolin (average particle size 4 μm, aspect ratio less than 10, non-volatile content 100% by mass) (2) (A-2) A scale-like pigment having an average particle size of 14 to 150 μm and an aspect ratio of 10 to 100 Scaly pigment 3: Aluminum paste A (average particle size 14 μm, aspect ratio 14, non-volatile content 60% by mass) Scaly pigment 4: Aluminum paste B (average particle size 50 μm, aspect ratio 50, non-volatile content 60% by mass) Scaly pigment 5: Mica (average particle size 23 μm, aspect ratio 70, non-volatile content 100% by mass) Scaly pigment 6: Glass flake (average particle size 15 μm, aspect ratio 25, non-volatile content 100% by mass) (3) (A-3) Other scale-like pigments Scaly pigment 7: Glass flake (average particle size 160 μm, aspect ratio 32, non-volatile content 100% by mass) (4)(B) Water-dispersible resin Epoxy resin 1: ADEKA Resin EM101-50 (Epoxy resin emulsion manufactured by ADEKA Corporation: Non-volatile content 47% by mass, epoxy equivalent weight 465-540 g / eq) Epoxy resin 2: jER W2821R70 (epoxy resin emulsion manufactured by Mitsubishi Chemical Corporation: non-volatile content 70% by mass, epoxy equivalent weight 220-240 g / eq) (5)(C) Amine curing agent Polyamine resin 1: Cardolite NX-8401 (amine resin emulsion manufactured by Cardolite; non-volatile content 57% by mass, active hydrogen equivalent 165 g / eq) Polyamine resin 2: Daitoclar X-7024 (amine resin emulsion manufactured by Daito Sangyo Co., Ltd.: non-volatile content 50%, active hydrogen equivalent 196g / eq) Polyamine resin 3: JEFFAMINE T-403 (polyetheramine manufactured by HUNTSUMAN; non-volatile content 100% by mass, active hydrogen equivalent 81 g / eq) (6)(D) Pigments not classified as flake pigments Extender pigment: calcium carbonate (average particle size 6 μm, aspect ratio less than 2, specific gravity 2.7, non-volatile content 100% by mass) Color pigment: titanium dioxide (white pigment, aspect ratio less than 2, non-volatile content 100% by mass) Anti-rust pigment: Aluminum tripolyphosphate K-WHITE #84S (manufactured by Teika Co., Ltd., aspect ratio less than 2, non-volatile content 100% by mass) (7)(E)Water Ion-exchanged water In this specification, the water mixed with the raw materials such as epoxy resin emulsion when preparing the coating composition, rather than the water used as a solvent in the raw materials such as epoxy resin emulsion, is referred to as component (E), and is also referred to as (E) water, etc. (8) Other additives Dispersant 1: FLORENE GW-1640 (Kyoeisha Chemical Co., Ltd., non-volatile content 40% by mass) Dispersant 2: BYK-190 (manufactured by BYK Japan, non-volatile content 30% by mass) Film-forming agent: Dipropylene glycol n-butyl ether Antifoaming agent: SN Deformer 1312 (manufactured by San Nopco, non-volatile content 50% by mass) Thickener: SN Thickener 665T (manufactured by San Nopco, urethane-modified polyether compound, non-volatile content 30% by mass) Rust inhibitor 1: HALOX 650 (IPL (benzothiazol-2-ylthio) succinic acid, non-volatile content 100% by mass) Rust inhibitor 2: Sodium nitrite (non-volatile content 100% by mass)

[0093] <Painting method: Single layer> The coating compositions prepared in the above <Coating Composition Preparation Examples> were further diluted with water as needed. The dilution ratios were in the range of 0 to 20% by mass. The dilution ratios are shown in Tables 4 and 5. The coating was applied by spray coating or applicator coating, and test panels were prepared so that the dry film thickness was 55 to 65 μm. The substrates used were grit-blasted steel plates measuring 70 × 150 × 3.2 mm or polypropylene plates measuring 300 × 300 × 2 mm. The coating composition was mixed and applied in an environment with a temperature of 5 to 30°C and a relative humidity of 85% or less.

[0094] <Painting method: multi-layer film> A first coating was prepared as described above in <Coating Method: Single Layer>, and after aging for one day in an environment of 23°C and 50% relative humidity, a topcoat was applied to prepare a second coating. For the topcoat, Dai Nippon Toryo Co., Ltd.'s Water-Based V-Flon #100H Topcoat IG was used, diluted further with water as necessary. The dilution ratio was 10% by mass. The dilution ratios are shown in Tables 4 and 5. The topcoat was applied by spray coating or applicator coating, and test panels were prepared by applying multiple coats to a dry film thickness of 15 to 25 μm. The substrates used were grid-blasted steel plates measuring 70 × 150 × 3.2 mm or polypropylene plates measuring 300 × 300 × 2 mm. The coating compositions were mixed and applied in an environment with a temperature of 5 to 30°C and a relative humidity of 85% or less.

[0095] <Paint evaluation> 1. Viscosity (initial) The viscosity of the base resin prepared in the above <Preparation Example of Paint Composition> was measured immediately after preparation. The measurement was carried out at a liquid temperature of 23°C using a digital Stormer viscometer. The initial viscosity was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (standard) ○: 80KU or more, less than 120KU △: 120KU or more, less than 140KU ×: Unmeasurable

[0096] 2.Storage stability The base material prepared in the above <Preparation Example of Coating Composition> was placed in a sealed container and left to stand at 50°C for 4 weeks. Changes in properties were observed during this time, and storage stability was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (standard) ○: No change or almost no change △: Slight change in properties observed ×: Viscosity changes significantly or solidification occurs

[0097] <Evaluation of single-layer and multi-layer films> 3.Environmental isolation Using polypropylene plates as the substrate, the test plates prepared by the above-mentioned <Coating Method: Single Layer Film> and <Coating Method: Multi-Layer Film> were dried for two weeks in an environment of 23°C and 50% relative humidity. Then, an isolated film was taken from the test plate and the water vapor permeability (g / m) of the film was measured using a water vapor permeability measuring device. 2 The water vapor permeability (g·μm / m) was measured. Since the water vapor permeability value varies depending on the film thickness, the product of the film thickness (μm) and the water vapor permeability was calculated, and the water vapor permeability (g·μm / m) was calculated taking the film thickness into account. 2 The environmental barrier properties were evaluated using the test pieces according to the following criteria. The results are shown in Tables 4 and 5. (standard) ○: Water vapor permeability is 600g μm / m 2 Less than d △: Water vapor permeability is 600g·μm / m 2 ·d or more 800g·μm / m 2 Less than d ×: Water vapor permeability is 800g μm / m 2 ·d or more

[0098] 4. Appearance Test panels were prepared according to the above <Painting Method: Single Layer> and <Painting Method: Multi-Layer> methods and then left for 48 hours. After 48 hours, the appearance of the single layer and multi-layer films was visually inspected. JIS K 5551:2018 "Rust-Preventive Paints for Structures" section "7.8 Appearance of Paint Film" was used as a reference. The evaluation was carried out visually under diffused daylight to confirm the absence of irregularities, dents, wrinkles, unevenness, cracks, bulges, holes, peeling, etc. For multi-layer films, changes in gloss were also checked. The appearance was evaluated according to the following criteria, and the results are shown in Tables 4 and 5. (Standard: Single layer film) ○: No abnormalities △: Partially deformed ×: Deformation on the entire surface (Standard: multi-layer membrane) ○: No abnormalities △: Partial deformation or loss of gloss ×: Deformation on the entire surface

[0099] 5. Monolayer adhesion The coating composition diluted in the above <Coating method: single layer> was applied to a grid-blasted steel plate measuring 70 × 150 × 3.2 mm using an air spray so that the dry film thickness was 55 to 65 μm, and the plate was then cured for one week in an environment of 23°C and 50% relative humidity to prepare a test plate. The test plate was subjected to an adhesion test in accordance with the adhesion (pull-off method) described in JIS K 5600-5-7, and the adhesive strength was measured. The adhesion was evaluated according to the following criteria, and the results are shown in Tables 4 and 5. (Standard: Single layer film) ○: Adhesion strength is 6 MPa or more △: Adhesion strength is 4MPa or more but less than 6MPa ×: Adhesion strength is less than 4 MPa

[0100] 6. Adhesion of multi-layer film A first coating was applied to a grid-blasted 70 x 150 x 3.2 mm steel plate using an air spray to a total dry film thickness of 70-90 μm as described above for <Coating Method: Multi-Layer Film>, and the plate was left to cure for one day at 23°C and 50% relative humidity. A second coating was then applied over the first coating, and the plate was then left to cure for one week at 23°C and 50% relative humidity to prepare a test plate. The test plate was subjected to an adhesion test in accordance with the adhesion (pull-off method) described in JIS K 5600-5-7, and the adhesive strength was measured. The adhesion was evaluated according to the following criteria, and the results are shown in Tables 4 and 5. (Standard: multi-layer membrane) ○: Adhesion strength is 6 MPa or more, and no delamination occurs between the first and second coatings △: Adhesion strength is between 4 MPa and 6 MPa, or partial delamination occurs between the first and second coatings ×: Adhesion strength is less than 4 MPa, or delamination occurs between the first and second coatings

[0101] 7. Long-term corrosion protection of single layer film Sandblasted steel plates measuring 70 × 150 × 3.2 mm were painted with an air spray as described above for <Painting method: Single layer> so that the dry film thickness was 55 to 65 μm, and the test plates were then cured for one week in an environment of 23°C and 50% relative humidity to prepare test panels. The test was conducted in accordance with JIS K 5600-7-1:1999 "General Test Methods for Paints - Part 7: Long-Term Durability of Coating Films - Section 1: Neutral Salt Spray Resistance." The test was conducted for 3000 hours, after which the single-layer film was observed for the degree of rust, blisters, etc., and the long-term corrosion resistance of the single-layer film was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (Standard: Single layer film) ○: No abnormality △: Only swelling occurs ×: Not only blisters but also rust occurs

[0102] 8. Long-term corrosion protection of multi-layer film A first coating was applied to a grid-blasted 70 x 150 x 3.2 mm steel plate using an air spray, as described above for <Coating Method: Multi-Layer Coating>, to a total dry film thickness of 70-90 μm, and then cured for one day at 23°C and 50% relative humidity. A second coating was then applied over the first coating, and the resulting plate was then cured for one week at 23°C and 50% relative humidity to prepare a test plate. The test was conducted in accordance with JIS K 5600-7-1:1999 "General Test Methods for Paints - Part 7: Long-Term Durability of Coatings - Section 1: Neutral Salt Spray Resistance." The test was conducted for 3,000 hours, after which the multi-layer film was observed for the degree of rust, blisters, etc., and the long-term corrosion resistance of the multi-layer film was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (Standard: multi-layer membrane) ○: No abnormality △: Only swelling occurs ×: Not only blisters but also rust occurs

[0103] The results in Tables 4 and 5 show that the coating compositions of Examples 1 to 13 were capable of forming coating films with excellent environmental barrier properties and adhesion, as well as long-term corrosion protection. Furthermore, the coating compositions of Comparative Examples 1 to 4, 6, and 7 failed to produce coating films with long-term corrosion protection. The coating composition of Comparative Example 5 used a scaly pigment with a high aspect ratio as the (A-3) scaly pigment, which allowed for the formation of a coating film with long-term corrosion protection. However, the average particle size of the scaly pigment was too large, resulting in poor appearance of the coating film and poor storage stability of the paint.

[0104] [Table 1]

[0105] [Table 2]

[0106] [Table 3]

[0107] [Table 4]

[0108] [Table 5]

Claims

1. An aqueous coating composition comprising at least (A) a scaly pigment and (B) a water-dispersible resin, (A) The scaly pigment includes (A-1) a scaly pigment having an average particle size of 1 to 13 μm and an aspect ratio of 2 or more and less than 10, and (A-2) a scaly pigment having an average particle size of 14 to 150 μm and an aspect ratio of 10 to 100, the mass ratio of (A-1):(A-2) is 95:5 to 50:50; The pigment volume concentration (PVC) is 20 to 35%, An aqueous coating composition characterized in that the volume content of (A-2) is 3 to 20% by volume based on the total amount of pigments contained in the aqueous coating composition.

2. 2. The aqueous coating composition according to claim 1, wherein the water-dispersible resin (B) is an epoxy resin.

3. 3. The aqueous coating composition according to claim 2, further comprising an amine curing agent (C).

4. 4. The aqueous coating composition according to claim 3, wherein the amine curing agent (C) comprises a polyamine resin having a cyclic structure.

5. A corrosion-resistant coating method comprising applying the aqueous coating composition according to any one of claims 1 to 4 to a surface to be coated to form a coating film on the surface to be coated, and further applying a coating material other than the aqueous coating composition on the coating film.

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