Water-based paint composition and corrosion-preventive coating method

Abstract

The present invention provides an aqueous coating composition capable of forming a coating film with excellent environmental barrier properties and adhesion, and long-term corrosion resistance. [Solution] An aqueous paint composition comprising at least (A) flake pigment and (B) water-dispersible resin, wherein (A) flake pigment comprises (A-1) flake pigment having an average particle diameter of 1 to 13 μm and an aspect ratio of less than 10, and (A-2) flake pigment having an average particle diameter 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%, and the volume content of (A-2) is 3 to 20 volume% of 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-preventive coating method using the aqueous coating composition. [Background technology]

[0002] Traditionally, in the field of coatings for buildings and civil engineering structures, there has been a shift from solvent-based to water-based coatings from the perspective of reducing health hazards to painters and residents, as well as odor.

[0003] Japanese Patent Publication No. 2010-90325 (Patent Document 1) describes a two-component aqueous paint composition comprising a main component and a curing agent, wherein the main component contains an emulsion comprising an acrylic-urethane composite resin having carboxyl groups and an organic silane compound having alkoxy groups. Patent Document 1 describes that this paint composition, while being water-based, can provide a highly elastic and highly durable coating film, and that by compounding the acrylic-urethane composite resin with the organic silane compound, a two-component aqueous organic inorganic paint composition with excellent stability can be obtained, and a coating film with excellent appearance can be formed even after long-term storage.

[0004] Furthermore, due to its excellent corrosion resistance and ease of application, a room-temperature curing, two-component, water-based paint composition using epoxy resin has been developed.

[0005] Japanese Patent Publication No. 2013-199621 (Patent Document 2) describes an aqueous epoxy resin coating composition comprising a main component containing an epoxy resin emulsion and a curing agent containing an amine resin emulsion, characterized in that the viscosity at a shear rate of 0.1 (1 / s) is 1.0 to 500 (Pa·s, 23℃) and the viscosity at a shear rate of 1000 (1 / s) is 0.010 to 1 (Pa·s, 23℃), and states that this provides an aqueous epoxy resin coating composition with excellent workability and corrosion resistance.

[0006] Japanese Patent Publication No. 2016-186021 (Patent Document 3) describes a two-component water-based epoxy resin coating composition comprising at least (A) epoxy resin, (B) curing agent, (C) viscosity modifier, (D) pigment, and (E) water, wherein (A) epoxy resin and (B) curing agent are mixed immediately before painting, and the content of film-forming components in the water-based epoxy resin coating composition is 55 to 75% by 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, and describes that this provides a water-based 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 flake-shaped pigment as (D) pigment, stating that if the aspect ratio of the flake-shaped pigment is less than 1.2, it becomes difficult to obtain a shielding effect, while if the aspect ratio exceeds 100, the paintability may deteriorate, or the flake-shaped pigment may not be properly arranged during film formation.

[0007] Japanese Patent Publication No. 2018-53028 (Patent Document 4) describes a two-component reaction-curing aqueous paint composition for primers, comprising an epoxy resin and an amine resin, wherein the weight ratio of the epoxy resin to the epoxy resin with an epoxy equivalent of 400 to 1000 g / eq is 90:10 to 60:40, and states that this provides a two-component reaction-curing aqueous paint composition for primers that gives a primer film with excellent chemical resistance. Furthermore, Patent Document 4 states that the aqueous paint composition may also contain scale-shaped inorganic powder with an aspect ratio of 2 to 1000, and states that if the aspect ratio is less than 2, it becomes difficult to obtain a shielding effect and the chemical resistance of the resulting primer film does not improve easily, on the other hand, if the aspect ratio exceeds 1000, the paint workability may deteriorate or the inorganic powder may not be properly arranged during film formation.

[0008] In addition, although it is a solvent-based paint composition, a paint composition has been developed that, by adjusting the flake-like pigment, can block water vapor from the external environment and, as a result, exhibit excellent corrosion resistance.

[0009] Japanese Patent Publication No. 2019-196417 (Patent Document 5) describes a paint composition comprising a resin component and a pigment, wherein the coefficient of linear expansion of the nonvolatile component contained in the paint composition at a temperature below the glass transition temperature is 2.5 × 10⁻⁶. -5 / K~5.4×10 -5 The coating composition is / K, and when a coating film with 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 / m². 2 This document describes a paint composition characterized by being day-based, and states that this provides a paint composition capable of forming a coating film with excellent corrosion resistance and peel resistance. Furthermore, Patent Document 5 describes a flake-shaped pigment as a pigment, and states that by using a flake-shaped pigment or by adjusting the ratio of the flake-shaped pigment and resin components, it is possible to reduce the water vapor transmission rate while maintaining a coefficient of linear expansion that satisfies the specified range.

[0010] Japanese Patent Publication No. 2021-195500 (Patent Document 6) describes a paint composition containing a resin, flake-shaped aluminum pigment or stainless steel flakes, and flake-shaped pigments other than aluminum pigment or stainless steel flakes, wherein the flake-shaped aluminum pigment or stainless steel flakes are non-leafing type aluminum pigment or stainless steel flakes with an average particle size of 20 to 60 μm, the flake-shaped pigments other than aluminum pigment or stainless steel flakes have an average particle size of 5 to 50 μm and an aspect ratio of 10 to 100, and the mass ratio (A / B) of the flake-shaped aluminum pigment or stainless steel flakes (A) to the flake-shaped pigments other than aluminum pigment or stainless steel flakes (B) is 1 / 2 to 1 / 18. The publication states that this provides a paint composition capable of forming a coating film that exhibits excellent environmental barrier properties and good corrosion resistance. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2010-90325 [Patent Document 2] Japanese Patent Publication No. 2013-199621 [Patent Document 3] Japanese Patent Publication No. 2016-186021 [Patent Document 4] Japanese Patent Publication No. 2018-53028 [Patent Document 5] Japanese Patent Publication No. 2019-196417 [Patent Document 6] Japanese Patent Publication No. 2021-195500 [Overview of the project] [Problems that the invention aims to solve]

[0012] Patent Document 6 describes an invention relating to a coating composition capable of forming a coating film that exhibits excellent environmental barrier properties and good corrosion resistance. However, the coating composition described in Patent Document 6, when it is a water-based coating, has the problem that the flake-like pigments are less likely to be regularly oriented in the coating film compared to solvent-based coatings. When the flake-like pigments are not regularly oriented in the coating film, sufficient environmental barrier properties cannot be obtained, and adhesion to the substrate also decreases, making it difficult to achieve long-term corrosion resistance.

[0013] Therefore, an object of the present invention is to provide an aqueous coating composition that has excellent environmental barrier properties and adhesion, and can form a coating film with 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 intensive studies to achieve the above object, the present inventor has found that, for an aqueous paint composition containing at least a flaky pigment and a water-dispersible resin, by using two types of flaky pigments having different average particle diameters and aspect ratios at a specific ratio, adjusting the pigment volume concentration (PVC), and adjusting the ratio of the flaky pigment having a larger average particle diameter and aspect ratio among the two types of flaky pigments to the total pigment, it is possible to form a coating film having excellent environmental barrier properties and adhesion and having long-term corrosion protection properties, and thus the present invention has been completed.

[0015] Therefore, the aqueous paint composition of the present invention is an aqueous paint composition containing at least (A) a flaky pigment and (B) a water-dispersible resin, (A) The flaky pigment includes (A-1) a flaky pigment having an average particle diameter of 1 to 13 μm and an aspect ratio of less than 10, and (A-2) a flaky pigment having an average particle diameter 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 volume content of (A-2) is 3 to 20 volume % with respect to the total amount of pigments contained in the aqueous paint composition, and it is an aqueous paint composition characterized by this. <​​​​​​​​​​​​​​​

Advantages of the Invention

[0020] According to the aqueous coating composition of the present invention, an aqueous coating composition capable of forming a coating film excellent in environmental barrier properties and adhesion and having long-term corrosion protection can be provided. Further, according to the corrosion protection coating method of the present invention, a corrosion protection coating method using such an aqueous coating composition can be provided.

Embodiments for Carrying Out the Invention

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

[0022] In this specification, an aqueous coating composition is a coating composition containing water as a main solvent (the solvent having the highest content in the coating). The water that can be used in the aqueous coating composition is not particularly limited, and examples include pure water such as tap water, ion-exchanged water, and distilled water. Further, when the coating composition is stored for a long time, water sterilized by ultraviolet irradiation or the like may be used to prevent the generation 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, a corrosion protection coating method is a coating method carried out for the purpose of corrosion protection of the surface of a substrate, and in particular, it is a coating method carried out for the purpose of applying a coating to the surface of a metal substrate such as iron or steel and protecting the substrate from rust and corrosion.

[0024] The aqueous coating composition of the present invention is an aqueous coating composition containing at least a flaky pigment and a water-dispersible resin. In this specification, the flaky pigment is referred to as component (A), and is also referred to as "(A) flaky pigment". Further, 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 that have a thin, flat shape like foil. Specific examples include metallic pigments such as zinc, nickel, chromium, tin, copper, silver, platinum, gold, and aluminum, as well as glass flakes, talc, mica, kaolin clay, and mica-like iron oxide. Metallic 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 dioxide and silica, or organic materials such as silicone resin. (A) Flake pigments are pigments that contribute to the environmental barrier properties of the coating film.

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

[0027] In the paint composition of the present invention, the amount of (A) flake-like pigment is preferably 30 to 65% by mass, and more preferably 40 to 60% by mass, relative to the total amount of film-forming components. If the paint composition contains multiple (A) flake-like pigments, the amount of (A) flake-like pigment is the total amount of (A) flake-like pigments.

[0028] In the aqueous paint composition of the present invention, (A) flake pigment includes two types of flake pigments corresponding to (A-1) and (A-2) below. (A-1) Flecked pigments with an average particle size of 1 to 13 μm and an aspect ratio of less than 10 (A-2) Flecked pigment with an average particle size of 14-150 μm and an aspect ratio of 10-100

[0029] In this specification, flake-like pigments corresponding to (A-1) are also referred to as (A-1), (A-1) flake-like pigments, etc. Also, flake-like pigments corresponding to (A-2) are also referred to as (A-2), (A-2) flake-like pigments, etc. Also, flake-like pigments that do not fall under (A-1) or (A-2) are also referred to as (A-3), (A-3) flake-like pigments, (A-3) other flake-like pigments, etc.

[0030] Furthermore, in the aqueous coating composition of the present invention, the mass ratio of (A-1) flake pigment to (A-2) flake 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] (A-2) flake pigments have a high aspect ratio and are preferred from the viewpoint of improving the environmental barrier properties of the coating film, and the environmental barrier properties can be improved by increasing the content of (A-2) flake pigments. On the other hand, because (A-2) flake pigments have a high aspect ratio, they are difficult to orient regularly in the coating film, which may reduce the adhesion of the coating film to the substrate. According to the aqueous coating composition of the present invention, by using (A-2) flake pigments and (A-1) flake pigments with a low average particle size and aspect ratio in a specific mass ratio, it becomes possible to orient (A) flake pigments regularly in the coating film, thereby improving environmental barrier properties while ensuring adhesion, and ultimately achieving long-term corrosion protection of the coating film.

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

[0033] (A-2) The average particle size of the flake pigment is 14 to 150 μm, preferably 14 to 100 μm, and more preferably 14 to 80 μm. (A-2) The aspect ratio of the flake pigment is 10 to 100, preferably 10 to 80, and more preferably 14 to 80. While a larger average particle size can improve the environmental barrier properties of flake pigments with a high aspect ratio, if the average particle size is too large, it can lead to deterioration of the appearance of the coating film and storage stability if the amount used is excessive. For this reason, (A-2) the average particle size of the flake pigment is set within the range specified above. (A-2) Suitable flake pigments include, for example, aluminum flakes, mica, and glass flakes.

[0034] In this specification, the aspect ratio of a flake pigment refers to the ratio (D / T) of the average particle diameter (D) to the average thickness (T) of the flake pigment. The average particle diameter of a flake 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 flake pigment is expressed as the equivalent spherical diameter by the laser diffraction / scattering method. The average thickness refers to the average value of the thicknesses measured for 100 or more flake pigments using a scanning electron microscope (SEM).

[0035] In the aqueous coating composition of the present invention, the pigment volume concentration (PVC) is 20-35%, preferably 21-33%, and more preferably 23-31%. In the coating composition of the present invention, since (A-1) flake pigment and (A-2) flake pigment are used in combination, the PVC is set relatively high. However, if the PVC is too high, the resin component becomes relatively low, and the dispersibility of the pigment tends to decrease, which may lead to 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) is the ratio of the total volume of pigment to the total volume of the film-forming components, and can be calculated from the composition and specific gravity of the components constituting the film-forming components.

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

[0038] In the aqueous paint composition of the present invention, the volume content of (A-1) flake-like pigment is preferably 35 to 65% by volume, and more preferably 45 to 55% by volume, relative to the total amount of pigment contained in the paint composition.

[0039] The aqueous coating composition of the present invention may contain, as a pigment, non-flaking pigments such as spherical, lumpy, rod-shaped, horn-shaped, needle-shaped, or fibrous pigments, in addition to flake-shaped pigments. Pigments include rust-preventive pigments, extender pigments, and coloring pigments. Some of these pigments fall under the category of flake-shaped pigments, while others fall under the category of non-flaking pigments. In this specification, pigments that do not fall under the category of flake-shaped pigments are referred to as component (D), and are also referred to as (D) pigments that do not fall under the category of flake-shaped pigments, or (D) pigments, etc.

[0040] Examples of rust-preventive 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, aluminum zinc phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, magnesium phosphate, and vanadic acid / phosphate mixed pigments.

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

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

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

[0044] (B) Water-dispersible resins can be prepared, for example, by emulsifying the water-dispersible resin in water or by emulsion polymerization of monomer components, using a surfactant as needed while applying a forced shear force by using a high-speed stirrer or the like. Alternatively, a dispersion of the water-dispersible resin can be prepared by adding a surfactant as needed to a water-dispersible resin polymerized in an organic solvent and performing a phase change into water, and the organic solvent contained in the dispersion of the water-dispersible resin may be removed by distillation or the like as needed. Furthermore, a dispersion of the water-dispersible resin can also be prepared by polymerizing it in water using water as a medium.

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

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

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

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

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

[0050] The epoxy resin is preferably in the form of an epoxy resin emulsion or an epoxy resin dispersion. In this specification, a resin emulsion means an emulsion obtained by dispersing a resin in an aqueous medium mainly composed of water, and a resin dispersion means a dispersion obtained by dispersing a resin in an aqueous medium mainly composed of water. The epoxy resin emulsion is not particularly limited, but is prepared by emulsifying the epoxy resin in an aqueous medium mainly composed of water using a conventional forced emulsification method (a method using an emulsifier and a high-speed stirrer, etc.). Examples of emulsifiers include polyoxyethylene alkylphenol ether-based nonionic surfactants, polyethers such as polyoxyethylene-polyoxypropylene block copolymers, and adducts of at least one of the nonionic surfactant and the polyethers with a diisocyanate compound. The emulsifier may be used alone or as a blend of two or more. Commercially available epoxy resin emulsions include, for example, Epulsion EA-1, 2, 3, 7, 12, 20, 55, and HD2 (manufactured by Henkel Japan); Yukaresin RE-1050, KE-002, KE-116, KE-307, E-1022, KE-301C, NE-320 (manufactured by Yoshimura Oil & Chemical Co., Ltd.); Adekaresin EM-101-50 (manufactured by Adeka Corporation); jER W1155R55, jER W3435R67, jER W2821R70 (manufactured by Mitsubishi Chemical Corporation). On the other hand, commercially available epoxy resin dispersions include, for example, Beckpox EP2381 (manufactured by Ornex Corporation); EPI-REZ6530-WH-53 (manufactured by Momentive Corporation).

[0051] The epoxy resin may be a modified epoxy resin. Examples of modified epoxy resins include urethane-modified epoxy resins, amine-modified epoxy resins, isocyanate-modified epoxy resins, acrylic-modified epoxy resins, polyester-modified epoxy resins, and dimer acid-modified epoxy resins.

[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 higher, sufficient coating film properties are easily obtained. On the other hand, when the epoxy equivalent is 1,000 g / eq or lower, leveling properties are less likely to decrease, and a uniform coating film is easily obtained. Note that 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 "Method for determining the epoxy equivalent of epoxy resin". When using multiple epoxy resins, the epoxy equivalent is determined from the total epoxy resin used.

[0053] In the paint composition of the present invention, the amount of water-dispersible epoxy resin is preferably 20 to 65% by mass, and more preferably 40 to 55% by mass, relative to the total amount of film-forming components. If the paint composition contains multiple water-dispersible epoxy resins, the amount of water-dispersible epoxy resin is the total amount of water-dispersible epoxy resins.

[0054] The aqueous coating composition of the present invention may contain a curing agent. Here, if (B) the water-dispersible resin includes 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 also as "(C) amine curing agent".

[0055] (C) The amine curing agent is an amine used to react with epoxy resins, particularly their epoxy groups, to promote or control the curing reaction. As the amine curing agent, resins having active hydrogen that reacts with epoxy groups are preferred, and polyamine resins are more preferred. Polyamine resins are resins having at least two amino groups in one molecule. Examples of polyamine resins include resins produced by condensation polymerization of amines and aldehydes, etherification of amines with alcohols, ring-opening polymerization of heterocyclic amines (such as ethyleneimine), condensation of amines and carboxylic acids, or Mannich reactions of amines, formaldehyde, and ketones or phenols. Here, polyamine resins that also have amide bonds in their molecules, such as resins produced by condensation of amines and carboxylic acids, are also called "polyamideamine resins" or "polyamideamines." Furthermore, ring-opening polymerization of alkylene oxides such as ethylene oxide and propylene oxide can be used for etherification of amines with alcohols.

[0056] Examples of amines that can be used in the production of polyamine resins 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 with heterocyclic structures such as ethyleneimines.

[0057] Furthermore, the polyamine resin may be a modified polyamine resin. A modified polyamine resin is a polyamine resin in which some of the amino groups have been modified. Known methods can be used to modify the amino groups, such as amidation of the amino group, the Mannich reaction between the amino group and a carbonyl compound, and the addition reaction between the amino group and an epoxy group.

[0058] (C) The amine curing agent preferably contains a polyamine resin having a cyclic structure, and more preferably contains a polyamideamine having a cyclic structure. (C) By using a polyamine resin having a cyclic structure as the amine curing agent, the adhesion of the coating film to the substrate or to a zinc powder-containing layer (zinc layer) that may be formed on the substrate can be further improved.

[0059] The amount of polyamine resin having a cyclic structure is preferably 40 to 100% by mass, and more preferably 60 to 90% by mass, relative to the total amount of (C) amine curing agent. If the paint composition contains multiple polyamine resins having cyclic structures, the amount of polyamine resin having a cyclic structure is the total amount of 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 manufacture. Examples of amines having a cyclic structure that can be used in the manufacture of polyamine resins include piperazines such as N-aminoethylpiperazine, aliphatic polyamines such as 1,3-bisaminoethylcyclohexane, isophoronediamine, 1-cyclohexylamino-3-aminopropane, 1,4-diaminocyclohexane, di(aminocyclohexyl)methane, 1,3-di-(aminocyclohexyl)propane, 2,4-diamino-cyclohexaneN,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 in the manufacture of polyamine resins include phenol and its derivatives. Examples of phenol derivatives include phenols in which a benzene ring is substituted with a hydrocarbon group, and in particular, phenols substituted with linear or branched hydrocarbon groups 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, and especially preferably an alkyl group. A specific example of a phenol derivative is cardanol.

[0061] Furthermore, the polyamine resin having a cyclic structure is preferably a polyamine resin obtained by the Mannich reaction of amines, formaldehyde, and a phenol derivative. Here, the cyclic structure is derived from the phenol derivative, and the amines are preferably chain compounds (or acyclic compounds) such as ethylenediamine. The phenol derivatives are as described above, with cardanol being 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 both a polyamine resin having a cyclic structure and a polyamine resin that does not have a cyclic structure. This ensures the reactivity of the (C) amine curing agent. 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 polyetheramines) such as polyoxyethylenediamine and polyoxypropylenediamine can be used.

[0063] When a polyamine resin having a cyclic structure and a polyamine resin not having a cyclic structure are used in combination, the amount of the polyamine resin having a cyclic structure is preferably 50 to 99% by mass of the total amount of (C) amine curing agent, and the amount of the polyamine resin not having a cyclic structure is preferably 1 to 50% by mass of the total amount of (C) amine curing agent.

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

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

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

[0067] The aqueous paint composition of the present invention is preferably a two-component paint composition. A two-component paint composition is a paint composition consisting of a main component and a curing agent. A two-component paint composition can be prepared by mixing the main component, the curing agent, and additives selected as needed during painting. For example, (B) an agent containing epoxy resin as a water-dispersible resin is the main component, and (C) an agent containing an amine curing agent is the curing agent. (A) A flake-like pigment may be contained in either the main component or the curing agent, but is usually contained in the main component. Water is usually contained in both the main component and the curing agent, but may also be used only in the main component. In addition, some of the water may be used as an additive when mixing the main component and the curing agent.

[0068] The paint composition of the present invention may contain, as appropriate for the purpose, other components such as resins not corresponding to component (B), dispersants, silane coupling agents, film-forming aids, antifreeze agents, viscosity modifiers, defoaming agents, thickeners, rust inhibitors not corresponding to rust-inhibiting pigments, surface modifiers, anti-settling agents, anti-skinning agents, anti-sagging agents, anti-color separation agents, matting agents, adhesion promoters, leveling agents, drying agents, catalysts, plasticizers, antifungal agents, antibacterial agents, antiviral agents, preservatives, insecticides, antistatic agents, and conductivity promoters.

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

[0070] In this specification, the term "film-forming component" refers to the component excluding volatile components such as water and organic solvents, and is the component that ultimately forms a paint film. In this specification, the component remaining after drying the paint composition at 130°C for 60 minutes is treated as the film-forming component. The mass fraction of the component remaining after drying the paint composition at 130°C for 60 minutes (film-forming component) may be 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 as appropriate. If the coating composition of the present invention is a two-component coating composition, the main component and the hardener can be prepared in advance, and the main component, hardener, and any additives can be mixed at the time of application. The main component and the hardener can be prepared by mixing various components as appropriate. The viscosity of the main component, when measured with a digital stommer viscometer, is preferably 80 to 140 (KU, 23°C), and 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℃) at a shear rate of 0.1 (1 / s), and a viscosity of 0.05 to 10 (Pa·s, 23℃) at a shear rate of 1000 (1 / s).

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

[0074] The means of coating the aqueous coating composition of the present invention are not particularly limited, and known coating methods 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 drying machine, etc. However, the aqueous coating composition of the present invention is preferably a coating composition that is intended to be naturally dried at ambient temperature. An ambient temperature of about 5 to 40°C is assumed.

[0076] The aqueous coating composition of the present invention has excellent environmental barrier properties and adhesion, and can form a coating film with long-term corrosion resistance. For this reason, the coating composition of the present invention is suitable as a primer.

[0077] The substrates coated with the aqueous coating composition of the present invention can be of various shapes, such as two-dimensional substrates such as films, sheets, and plates, or three-dimensional substrates with complex shapes. The surface of the substrate may be smooth or may have irregularities. Specific examples of substrates include steel materials such as steel plates, steel pipes, and steel bars, as well as steel structures such as steel towers, bridges, and plants.

[0078] The substrate may have its surface pretreated with degreasing, chemical treatment, polishing, etc., or it may have been coated with sealer, primer, zinc-rich paint, plating, or thermal spraying.

[0079] The substrate may have a prior coating on its surface. The prior coating may cover part or all of the surface of the substrate. In this specification, "prior coating" means a coating that is already present on the substrate when painting, in particular repair, is performed.

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

[0081] The existing coating preferably contains a resin, such as acrylic resin, silicone resin, acrylic silicone resin, styrene-acrylic copolymer resin, polyester resin, fluororesin, rosin resin, petroleum resin, coumarone resin, phenolic resin, urethane resin, melamine resin, urea resin, epoxy resin, cellulose resin, xylene resin, alkyd resin, aliphatic hydrocarbon resin, butyral resin, maleic acid resin, fumaric acid resin, vinyl resin, amine resin, ketimine resin, and modified resins of these resins (modified resins). The resin may be used alone or in combination of two or more types.

[0082] The existing paint film may also contain various additives as other components, such as pigments, dispersants, curing catalysts, surface modifiers, antioxidants, plasticizers, rust inhibitors, solvents, antibacterial agents, antiviral agents, viscosity modifiers, fillers, defoamers, thickeners, charge control agents, stress relievers, penetrating agents, light guides, brightening agents, magnetic materials, phosphors, ultraviolet absorbers, and radical scavengers.

[0083] Next, the corrosion-preventive coating method of the present invention will be described.

[0084] The corrosion-preventive coating method of the present invention is characterized by applying the above-described aqueous paint composition of the present invention to a surface to be coated to form a coating film on the surface to be coated, and further applying a paint other than the aqueous paint composition on the coating film.

[0085] The aqueous coating composition of the present invention is suitable as a primer because it can form a coating film with excellent environmental barrier properties and adhesion, and long-term corrosion resistance.

[0086] The dry film thickness formed by the aqueous coating composition of the present invention is preferably 50 to 300 μm. In this specification, dry film thickness refers to the thickness of the coating film after painting is complete and the coating has dried. The coating composition of the present invention may be applied to the surface to be coated multiple times. When multiple coats are applied, the dry film thickness formed by the coating composition of the present invention refers to the thickness of the coating film that is finally formed after multiple coats have been applied.

[0087] In the corrosion-preventive coating method of the present invention, the surface to be coated is the surface of the substrate as described above. The substrate may have a layer containing zinc powder (zinc layer) formed on its surface by coating with zinc-rich paint or the like.

[0088] In the corrosion-preventive coating method of the present invention, the paint applied on the coating film formed from the paint composition of the present invention is a different paint from the paint composition of the present invention, and a paint suitable for forming an intermediate coating film or a top coating film can be used as appropriate. For this reason, the multilayer film formed on the substrate by the corrosion-preventive coating method of the present invention may be, for example, a multilayer film comprising an undercoat film and a topcoat film, or a multilayer film comprising an undercoat film, an intermediate coating film and a topcoat film. By forming an additional coating film on the coating film (undercoat film) formed from the paint composition of the present invention, the environmental barrier properties of the undercoat film can be enhanced, and better corrosion protection can be achieved.

[0089] The paint used to form the intermediate or topcoat film is preferably an aqueous paint composition, similar to the paint composition of the present invention. These paint compositions may contain, as appropriate, resins, curing agents, curing catalysts, solvents, dispersants, silane coupling agents, film-forming aids, antifreeze agents, viscosity modifiers, defoaming agents, thickeners, rust inhibitors, surface modifiers, settling inhibitors, anti-skinning agents, anti-sagging agents, anti-color separation agents, matting agents, adhesion promoters, leveling agents, drying agents, catalysts, plasticizers, antifungal agents, antibacterial agents, antiviral agents, preservatives, insecticides, antistatic agents, and conductivity promoters, etc., depending on the purpose. [Examples]

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

[0091] <Examples of paint composition preparation> The main component and hardener were prepared by mixing the raw materials according to the formulations shown in Tables 1-3. The obtained main component and hardener were mixed in the mixing ratios shown in Tables 4-5 to prepare the paint composition. The formulations shown in Tables 1-3 and the mixing ratios shown in Tables 4-5 are based on mass. The "Non-volatile content" column in Tables 1-3 shows the mass percentage of non-volatile content when the mass of the raw materials is set to 1.

[0092] The details of the raw materials used in the preparation of the paint composition are shown below. (1)(A-1) Flecked pigments with an average particle size of 1 to 13 μm and an aspect ratio of less than 10 Scale-like pigment 1: Talc (average particle size 13 μm, aspect ratio less than 10, non-volatile content 100% by mass) Scale-like pigment 2: Kaolin (average particle size 4 μm, aspect ratio less than 10, non-volatile content 100% by mass) (2)(A-2) Fleck-like pigment with an average particle size of 14-150 μm and an aspect ratio of 10-100. Scale-like pigment 3: Aluminum paste A (average particle size 14 μm, aspect ratio 14, non-volatile content 60% by mass) Scale-like pigment 4: Aluminum paste B (average particle size 50 μm, aspect ratio 50, non-volatile content 60% by mass) Scale-like pigment 5: Mica (average particle size 23 μm, aspect ratio 70, non-volatile content 100% by mass) Scale-like pigment 6: Glass flakes (average particle size 15 μm, aspect ratio 25, non-volatile content 100% by mass) (3)(A-3) Other flake pigments Scale-like pigment 7: Glass flakes (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 (ADEKA epoxy resin emulsion: non-volatile content 47% by mass, epoxy equivalent 465-540 g / eq) Epoxy resin 2: jER W2821R70 (Mitsubishi Chemical's epoxy resin emulsion: 70% by mass of non-volatile content, epoxy equivalent 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: Daitokral X-7024 (Amine resin emulsion manufactured by Daito Sangyo Co., Ltd.: 50% non-volatile content, 196 g / eq of active hydrogen equivalent) 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 that do not fall under the category of 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) Coloring pigment: Titanium dioxide (white pigment, aspect ratio less than 2, non-volatile content 100% by mass) Rust-preventive 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, water that is mixed together with the raw materials such as epoxy resin emulsions during the preparation of a paint composition, rather than water used as a solvent in the raw materials such as epoxy resin emulsions, is referred to as component (E) and is also called (E) water, etc. (8) Other additives Dispersant 1: Floren GW-1640 (manufactured by Kyoeisha Chemical Co., Ltd., non-volatile content 40% by mass) Dispersant 2: BYK-190 (manufactured by Bic Chemie Japan, non-volatile content 30% by mass) Film-forming aid: Dipropylene glycol n-butyl ether Defoaming agent: SN Deformer 1312 (manufactured by Sunopco, 50% by mass of non-volatile content) Thickener: SN Thickener 665T (manufactured by Sunopco, urethane-modified polyether compound, 30% by mass of non-volatile content) Rust inhibitor 1: HALOX 650 (manufactured by IPL (benzothiazole-2-ylthio) succinic acid, 100% by mass of non-volatile content) Rust inhibitor 2: Sodium nitrite (100% by mass of non-volatile content)

[0093] <Painting method: Single layer> The paint compositions prepared in the above <Example of Paint Composition Preparation> were further diluted with water as needed. The dilution ratio was in the range of 0 to 20% by mass. The dilution ratios are shown in Tables 4 and 5. Painting was performed by spray painting or applicator painting, and test plates were prepared so that the dry film thickness was 55-65 μm. The substrate used was a grid-blasted 70 × 150 × 3.2 mm steel plate or a 300 × 300 × 2 mm polypropylene plate. The mixing and application of the paint composition were carried out under conditions of 5-30°C and relative humidity of 85% or less.

[0094] <Painting method: Multi-layer film> As described above under <Painting Method: Single Layer>, the first coating was prepared, cured for one day at 23°C and 50% relative humidity, and then the topcoat was applied to prepare the second coating. For the topcoat, "Water-based V-Flon #100H Topcoat IG" manufactured by Dainippon Paint Co., Ltd. was used and further diluted with water as needed. The dilution ratio was 10% by mass. The dilution ratios are shown in Tables 4 and 5. The topcoat was applied by spray painting or applicator painting, and test plates were prepared by applying multiple coats to achieve a dry film thickness of 15-25 μm. The substrate used was a grid-blasted 70 x 150 x 3.2 mm steel plate or a 300 x 300 x 2 mm polypropylene steel plate. The mixing of the paint composition and painting were carried out in an environment with a temperature of 5-30°C and a relative humidity of 85% or less.

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

[0096] 2. Storage Stability The main agent prepared in the above <Preparation Example of Coating Composition> was placed in a sealed container and allowed to stand at 50 °C for 4 weeks. The change in properties at that time was observed, and the storage stability was evaluated according to the following criteria. The results are shown in Tables 4 to 5. (Criteria) ○: No change or almost no change △: A slight change in properties is observed ×: Significant change in viscosity or solidification

[0097] <Evaluation of Single-Layer Film and Multilayer Film> 3. Environmental Barrier Property Using a polypropylene plate as the substrate, each test plate prepared by the above <Coating Method: Single-Layer Film> and <Coating Method: Multilayer Film> was dried in an environment of 23 °C and 50% relative humidity for 2 weeks. Then, an isolation film was collected from the test plate, and the water vapor transmission rate of the film (g / m 2 ·d) was measured using a water vapor transmission rate measuring device. Since the value of the water vapor transmission rate varies depending on the film thickness, the product of the film thickness (μm) and the water vapor transmission rate was obtained, and the water vapor transmission rate (g·μm / m 2 ·d) was used to evaluate the environmental barrier property according to the following criteria. The results are shown in Tables 4 to 5. (Criteria) ○: Water vapor transmission rate is less than 600 g·μm / m 2 ·d △: Water vapor transmission rate is 600 g·μm / m or more and less than 800 g·μm / m 2 ·d 2 ·d ×: Water vapor transmission rate is 800 g·μm / m or more 2 ·d

[0098] 4. Appearance After preparing the test plates according to the above <Coating Method: Single-Layer Film> and <Coating Method: Multilayer Film>, they were left standing for 48 hours. The appearance of the single-layer film and the multilayer film after 48 hours was visually observed. JIS K 5551:2018 "Rust Preventive Paint for Structures" "7.8 Appearance of Coating Film" was referred to. The evaluation was performed visually under diffused daylight to confirm the absence of irregularities, dents, wrinkles, unevenness, cracks, blisters, holes, and peeling. For multilayer films, changes in gloss were also checked. The appearance was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (Reference: Monolayer film) ○: No abnormalities △: Partially deformed ×: Deformed throughout (Reference: multilayer film) ○: No abnormalities △: Partially discolored or showing reduced gloss. ×: Deformed throughout

[0099] 5. Adhesion of the single-layer film A 70 x 150 x 3.2 mm steel plate that had been grid-blasted was coated with the paint composition diluted according to the above <coating method: single layer film> using an air spray so that the dry film thickness was 55-65 μm, and a test plate was prepared by curing it for one week in an environment of 23°C and 50% relative humidity. Adhesion tests were performed on the test plates according to the adhesion method (pull-off method) described in JIS K 5600-5-7, and the adhesion strength was measured. Adhesion was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (Reference: Monolayer film) ○: Adhesion strength of 6 MPa or higher △: Adhesion strength between 4 MPa and less than 6 MPa ×: Adhesion strength is less than 4 MPa

[0100] 6. Adhesion of the multilayer film A 70 x 150 x 3.2 mm steel plate that had been grid-blasted was coated with a first coating using an air spray according to the <Coating Method: Multi-layer Film> described above, so that the total dry film thickness would be 70-90 μm. After curing for one day at 23°C and 50% relative humidity, a second coating was formed on top of the first coating. Subsequently, the test plate was prepared by curing for one week at 23°C and 50% relative humidity. Adhesion tests were performed on the test plates according to the adhesion method (pull-off method) described in JIS K 5600-5-7, and the adhesion strength was measured. Adhesion was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (Reference: multilayer film) ○: Adhesion strength of 6 MPa or higher, and no delamination occurs between the first and second coating layers. △: Adhesion strength is between 4 MPa and 6 MPa, or partial delamination occurs between the first and second coating layers. ×: Adhesion strength is less than 4 MPa, or delamination occurs between the first and second coating layers.

[0101] 7. Long-term corrosion protection of single-layer films A 70 x 150 x 3.2 mm steel plate that had been sandblasted was painted using an air spray according to the above <Painting Method: Single Layer> to achieve a dry film thickness of 55-65 μm, and a test plate was prepared by curing it for one week at 23°C and 50% relative humidity. The tests were conducted in accordance with JIS K 5600-7-1:1999 "General test methods for paints - Part 7: Long-term durability of coatings - Section 1: Resistance to neutral salt spray". The tests were carried out for 3000 hours, and the degree of rust, blistering, etc., was observed on the single-layer film after the test. The long-term corrosion protection of the single-layer film was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (Reference: Monolayer film) ○: No abnormalities △: Only swelling occurs ×: Not only does it swell, but rust also occurs.

[0102] 8. Long-term corrosion protection of multilayer films A 70 x 150 x 3.2 mm steel plate that had been grid-blasted was coated with a first coating using an air spray as described in <Coating Method: Multi-layer Film> above, so that the total dry film thickness would be 70-90 μm. The coating was then cured for one day at 23°C and 50% relative humidity, and a second coating was then applied on top of the first coating. After that, the test plate was prepared by curing it for one week at 23°C and 50% relative humidity. The tests were conducted in accordance with JIS K 5600-7-1:1999 "General test methods for paints - Part 7: Long-term durability of coatings - Section 1: Resistance to neutral salt spray". The tests were carried out for 3000 hours, and the degree of rust, blistering, etc., was observed on the multilayer film after the tests. The long-term corrosion protection of the multilayer film was evaluated according to the following criteria. The results are shown in Tables 4 and 5. (Reference: multilayer film) ○: No abnormalities △: Only swelling occurs ×: Not only does it swell, but rust also occurs.

[0103] The results in Tables 4-5 show that the coating compositions of Examples 1-13 can form coating films with excellent environmental barrier properties and adhesion, as well as long-term corrosion resistance. In contrast, the coating compositions of Comparative Examples 1-4, 6, and 7 did not yield coating films with long-term corrosion resistance. In the coating composition of Comparative Example 5, a coating film with long-term corrosion resistance was formed because a flake pigment with a high aspect ratio was used as the (A-3) flake pigment. However, the average particle size of the flake pigment was too large, resulting in a 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 flake-like pigment and (B) a water-dispersible resin, (A) The flake pigment comprises (A-1) a flake pigment with an average particle size of 1 to 13 μm and an aspect ratio of less than 10, and (A-2) a flake pigment with 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 20-35%. An aqueous paint composition characterized in that the volume content of (A-2) is 3 to 20% by volume relative to the total amount of pigment contained in the aqueous paint composition.

2. The aqueous paint composition according to claim 1, characterized in that the (B) water-dispersible resin is an epoxy resin.

3. The aqueous paint composition according to claim 2, characterized in that the aqueous paint composition contains (C) an amine curing agent.

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

5. A corrosion-preventive coating method characterized by applying an 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 other than the aqueous coating composition on the coating film.

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