Method for forming a multilayer film

Abstract

This invention provides a method for forming a multilayer film that has excellent adhesion and long-term corrosion resistance. [Solution] A water-based paint composition (P) containing (A1) epoxy resin, (B1) extender pigment and (B2) coloring pigment, and (C1) a curing agent that reacts with the epoxy resin is applied to a substrate, thereby achieving an elastic modulus (X) of 800 to 2500 N / mm 2 The process involves (1) forming a first coating film with a dry film thickness of 20 to 300 μm, and then applying an aqueous coating composition (Q) containing (A2) acrylic resin and (B2) coloring pigment to the first coating film, thereby achieving an elastic modulus (Y) of 80 to 500 N / mm². 2 The method for forming a multilayer film comprises a step (2) of forming a second coating film with a dry film thickness of 10 to 200 μm, characterized in that the PVC in the aqueous coating composition (P) is greater than the PVC in the aqueous coating composition (Q).

Description

[Technical Field]

[0001] The present invention relates to a method for forming a multilayer film. [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 to reduce health hazards to painters and occupants, as well as to minimize odor. Furthermore, due to its superior corrosion resistance, a corrosion-preventive coating method has been proposed that uses a two-component, room-temperature curing, water-based paint composition made with epoxy resin to form the primer film.

[0003] Japanese Patent Publication No. 2013-202488 (Patent Document 1) describes a water-based corrosion-preventive coating method in which a water-based epoxy resin primer is applied to a surface to be coated to form a primer film, and then a water-based topcoat is applied on the primer film to form a topcoat film, characterized in that it satisfies the following requirements a) to c), and states that this provides a water-based corrosion-preventive coating method that can impart excellent weather resistance and corrosion resistance. a) Both the water-based epoxy resin primer and the water-based topcoat are multi-component reaction-curing types. b) The water-based topcoat paint has a lower pigment volume concentration than the water-based epoxy resin undercoat paint. c) The topcoat film has an ultraviolet transmittance of 0.2% or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-202488 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] According to the aqueous anticorrosive coating method described in Patent Document 1, a multilayer film including an undercoat film and a topcoat film is formed on a substrate, but there were problems with the adhesion of the multilayer film. Epoxy resin is generally known as a resin with excellent adhesion. However, when used in aqueous paints, compared to when used in organic solvent-based paints, it was considered that the adhesion of the epoxy resin was not fully exhibited, which was one of the factors contributing to the reduction in the adhesion of the multilayer film. If the adhesion of the multilayer film is low, it becomes difficult to achieve long-term anticorrosive properties.

[0006] Therefore, an object of the present invention is to provide a method capable of forming a multilayer film having excellent adhesion and long-term anticorrosive properties.

Means for Solving the Problems

[0007] As a result of intensive studies to achieve the above object, the present inventor has found that in a method for forming a multilayer film in which a first coating film is formed from an epoxy resin-based aqueous paint composition on a substrate and then a second coating film is formed from an acrylic resin-based aqueous paint composition, by adjusting the elastic modulus of the first coating film and the elastic modulus of the second coating film, it is possible to form a multilayer film having excellent adhesion and long-term anticorrosive properties, and thus the present invention has been completed.

[0008] Therefore, the method for forming a multilayer film of the present invention includes a step (1) of coating a substrate with an aqueous paint composition (P) to form a first coating film having a dry film thickness of 20 to 300 μm, a step (2) of coating the first coating film with an aqueous paint composition (Q) to form a second coating film having a dry film thickness of 10 to 200 μm and is a method for forming a multilayer film, where the aqueous paint composition (P) contains (A1) an epoxy resin, one or more pigments selected from (B1) extender pigments and (B2) coloring pigments, and (C1) a curing agent that reacts with the epoxy resin, the aqueous paint composition (Q) contains (A2) an acrylic resin and (B2) a coloring pigment, the pigment volume concentration (PVC) of the aqueous paint composition (P) is greater than the pigment volume concentration (PVC) of the aqueous paint composition (Q), The elastic modulus (X) of the first coating film is 800 to 2500 N / mm ,

[0012] ,

[0014] , , , , , , , , , ,

[0015] ,

[0013] , , and the elastic modulus (Y) of the second coating film is 80 to 500 N / mm 2 and Here, the elastic modulus of the coating film is calculated from the slope (proportionality constant) within the range where stress and strain are proportional in the stress-strain curve obtained from a tensile test conducted on a strip-shaped test piece of 50 mm × 10 mm × 20 to 100 μm at 23°C and 50% humidity at a speed of 5 mm / min and a gripping distance of 30 mm. This is a method for forming a multilayer film.

[0009] In a preferred example of the method for forming a multilayer film of the present invention, the curing agent that reacts with the (C1) epoxy resin contains a polyamine resin having a cyclic structure.

[0010] In another preferred example of the method for forming a multilayer film of the present invention, the aqueous paint composition (P) contains a (B3) flaky pigment as the (B1) extender pigment and / or the (B2) coloring pigment.

[0011] In another preferred example of the method for forming a multilayer film of the present invention, the second coating film has a crosslinked structure.

[0012] In another preferred example of the method for forming a multilayer film of the present invention, the aqueous paint composition (Q) contains a (C2) carbodiimide curing agent.

[0013] In another preferred example of the method for forming a multilayer film of the present invention, the (A2) acrylic resin has silicon.

Advantages of the Invention

[0014] According to the method for forming a multilayer film of the present invention, a multilayer film excellent in adhesion and having long-term corrosion resistance can be formed.

Embodiments for Carrying Out the Invention

[0015] The present invention will be described in detail below. The present invention relates to a method for forming a multilayer film. This method is referred to as a "method for forming a multilayer film".

[0016] In this specification, a multilayer film is a film comprising at least two types of coating films (i.e., a first coating film and a second coating film) formed from a specific coating composition described later. In addition, the multilayer film may include further films in addition to the first and second coating films.

[0017] The present invention provides a method for forming a multilayer film, which involves forming a first coating film and a second coating film on a substrate in that order. Furthermore, the present invention also provides a method for forming additional films before the formation of the first coating film, between the formation of the first and second coating films, and / or after the formation of the second coating film.

[0018] In this specification, the first coating is a film that constitutes a multilayer film, is located closer to the substrate than the second coating (in other words, inside the second coating), and has a higher elastic modulus than the second coating. The first coating may also be referred to as the undercoat coating. A multilayer film may have one or more first coatings. If a multilayer film has multiple first coatings, the first coating located closest to the substrate may be referred to as the undercoat coating, and the other first coatings may be referred to as the intermediate coatings. The second coating is a film that constitutes a multilayer film, is located further from the substrate than the first coating (in other words, outside the first coating), and has a lower elastic modulus than the first coating. The second coating may also be referred to as the topcoat coating. A multilayer film may have one or more second coatings. If a multilayer film has multiple second coatings, the second coating located furthest from the substrate may be referred to as the topcoat coating, and the other second coatings may be referred to as the intermediate coatings.

[0019] The first coating film is formed from an aqueous coating composition comprising an epoxy resin, one or more pigments selected from extender pigments and coloring pigments, and a curing agent that reacts with the epoxy resin. In this specification, the aqueous coating composition used to form the first coating film may be referred to as "aqueous coating composition (P)". The epoxy resin may be referred to as "(A1) epoxy resin" with component (A1). The extender pigment may be referred to as "(B1) extender pigment" with component (B1). The coloring pigment may be referred to as "(B2) coloring pigment" with component (B2). The curing agent that reacts with the epoxy resin may be referred to as "(C1) curing agent that reacts with epoxy resin" with component (C1).

[0020] In this specification, an aqueous paint composition is a paint composition that contains water as the main solvent (the solvent with the highest content in the paint). While there are no particular restrictions on the type of water that can be used in an aqueous paint composition, examples include tap water, deionized water, distilled water, and other pure water. Furthermore, when storing the paint composition for a long period, water sterilized by ultraviolet irradiation or other means may be used to prevent the growth of mold and bacteria.

[0021] The second coating film is formed from an aqueous coating composition containing an acrylic resin and a coloring pigment. In this specification, the aqueous coating composition used to form the second coating film may be referred to as "aqueous coating composition (Q)". In addition, the acrylic resin may be referred to as component (A2) and referred to as "(A2) acrylic resin".

[0022] The pigment volume concentration (PVC) of the aqueous paint composition (P) is greater than the pigment volume concentration (PVC) of the aqueous paint composition (Q), and the difference is preferably 1 to 23%, and more preferably 6 to 19%.

[0023] In this specification, Pigment Volume Concentration (PVC) is the ratio of the total volume of pigment to the total volume of film-forming components or the paint film in the paint composition, and can be calculated from the composition and specific gravity of the components constituting the film-forming components or the paint film.

[0024] In this specification, the coating film-forming component refers to the component excluding volatile components such as water and organic solvents, and is the component that finally forms the coating film. In this specification, the component remaining when the coating composition is dried at 130 °C for 60 minutes is treated as the coating film-forming component. The mass fraction of the component (coating film-forming component) remaining when the coating composition is dried at 130 °C for 60 minutes may be referred to as the heat residue (or non-volatile content NV).

[0025] The elastic modulus of the first coating film is 800 to 2500 N / mm 2 and preferably 1000 to 2300 N / mm [[ID=?]] 2 and more preferably 1200 to 2100 N / mm 2 The coating film with an elastic modulus of 800 to 2500 N / mm 2 has high adhesion to the substrate and a low water absorption rate. Placing such a coating film at a position close to the substrate can contribute to forming a multi-layer film with excellent adhesion and long-term corrosion resistance. There is a correlation trend between the elastic modulus and the water absorption rate. As the elastic modulus increases, the water absorption rate decreases, and as the elastic modulus decreases, the water absorption rate increases. A coating film with a low elastic modulus and a high water absorption rate has a large amount of water absorption and a large strain of the coating film, which leads to a decrease in adhesion and corrosion resistance. In this specification, the elastic modulus of the first coating film may be referred to as "the elastic modulus (X) of the first coating film", "the elastic modulus (X)", etc.

[0026] When the multi-layer film has a plurality of first coating films, the elastic modulus of each first coating film is 800 to 2500 N / mm 2 and preferably 1000 to 2300 N / mm 2 and more preferably 1200 to 2100 N / mm 2 and more preferably so.

[0027] The elastic modulus of the second coating film is 80 to 500 N / mm 2 and preferably 120 to 450 N / mm 2 and more preferably 200 to 450 N / mm 2 and more preferably so. The coating film with an elastic modulus of 80 to 500 N / mm 2A coating film with this characteristic has lower hardness than a coating film with a higher modulus of elasticity, and also maintains a certain degree of elasticity, resulting in high stain resistance. Placing such a coating film on the outer surface contributes to the formation of a multilayer film with good appearance and weather resistance. Furthermore, by combining a first coating film and a second coating film with such controlled elasticity, it is possible to form a multilayer film with excellent adhesion, long-term corrosion protection, and high resistance to environments with large temperature fluctuations and extreme temperature differences. In this specification, the elasticity of the second coating film may be referred to as "elasticity of the second coating film (Y)," "elasticity (Y)," etc.

[0028] When a multilayer film has multiple second coatings, the elastic modulus of each second coating is 80 to 500 N / mm². 2 The force is 120-450 N / mm². 2 Preferably, it is 200-450 N / mm 2 It is even more preferable that this be the case.

[0029] In this specification, the elastic modulus of the first and second coating films refers to the elastic modulus of the coating film after curing and drying has progressed. A coating film that has progressed in curing and drying means a state in which the entire thickness of the coating film is dry, rather than a state in which most of the coating film is still soft, as defined in JIS K 5600-3-3. Furthermore, if the curing of the coating film occurs through the reaction of components (resins, etc.) contained in the paint composition, it refers to a coating film in a state in which the reaction has progressed. For example, a coating film formed from an aqueous paint composition (P) or an aqueous paint composition (Q) can be expected to be dried by drying for about 7 days under conditions of 23°C and 50% humidity. Needless to say, the drying period will be shorter under higher temperature conditions.

[0030] In this specification, the elastic modulus of a coating film can be determined as follows: After applying the coating composition to a dry film thickness of 20 to 100 μm, a strip-shaped test piece measuring 50 mm × 10 mm × 20 to 100 μm is cut out to prepare a sample for measurement. Next, a tensile test is performed on the test piece under the conditions of 23°C and 50% humidity, a speed of 5 mm / min, and a grip distance of 30 mm. The elastic modulus of the coating film is calculated from the slope (proportionality constant) within the range in which stress and strain are proportional in the stress-strain curve obtained from the tensile test. The stress-strain curve is plotted on a graph with stress on the vertical axis and strain on the horizontal axis.

[0031] There is a correlation between the elastic modulus of a coating film and its water absorption. A higher elastic modulus results in less water absorption, while a lower elastic modulus results in more water absorption. Considering this relationship, high water absorption in a coating film leads to increased strain, resulting in reduced adhesion and corrosion resistance. Furthermore, a lower elastic modulus reduces the strength of the coating film. Furthermore, to form a coating film with a high modulus of elasticity, it is conceivable to use a resin with a high modulus of elasticity or to use a pigment as a filler. Since the modulus of elasticity of a resin is greatly influenced by the rigidity of the molecular chains and the interactions between molecular chains, it is thought that strong interactions occur in resins with a high modulus of elasticity, and it is presumed that this makes it easier to inhibit water permeability.

[0032] The second coating film preferably has a cross-linked structure. The cross-linked structure in the second coating film may be a cross-linked structure present in a component (e.g., resin) in the paint composition used to form the second coating film, or a cross-linked structure formed by the reaction of components (e.g., resin and curing agent) in the paint composition during the formation of the second coating film. A second coating film having a cross-linked structure can improve weather resistance.

[0033] The second coating preferably has an ultraviolet transmittance of 2.0% or less.

[0034] In this specification, ultraviolet transmittance refers to the transmittance of light in the wavelength range from 280 nm to 400 nm, and can be measured using a spectrophotometer (for example, Shimadzu UV-2450).

[0035] In one embodiment of the multilayer film formation method of the present invention, the elastic modulus is 800 to 2500 N / mm 2 From the viewpoint of adjusting it to a certain range, the glass transition temperature (Tg) of the first coating film is preferably 20 to 70°C, and more preferably 40 to 65°C.

[0036] In one embodiment of the multilayer film formation method of the present invention, the elastic modulus is set to 80-500 N / mm². 2 From the viewpoint of adjusting it to a certain range, the glass transition temperature (Tg) of the second coating film is preferably 10 to 70°C, and more preferably 20 to 60°C.

[0037] In this specification, the glass transition temperature of the coating film was measured using a DSC (Differential Scanning Calorimeter) in accordance with JIS K 7121:2012 (Method for Measuring Transition Temperature of Plastics). For the measurement, approximately 10 mg of the coating film was taken into an aluminum pan for measurement, and DSC measurement was performed under the following measurement conditions. (Measurement temperature conditions) -80℃ to 220℃ (20℃ / min)

[0038] The present invention provides a method for forming a multilayer film, which includes the step of applying an aqueous coating composition (P) to a substrate to form a first coating film with a dry film thickness of 20 to 300 μm. In this specification, the step of forming the first coating film may be referred to as step (1). In step (1), it is also possible to apply the aqueous coating composition (P) multiple times to form multiple first coating films.

[0039] The dry film thickness of the first coating is 20 to 300 μm, and more preferably 30 to 250 μm. When a multilayer film has multiple first coatings, the film thickness of the first coating described here refers to the total film thickness of the first coatings. Dry film thickness is the thickness of the dried coating, and the dried coating is as described above.

[0040] The aqueous paint composition (P) comprises one or more pigments selected from epoxy resin, extender pigments, and coloring pigments, as well as a curing agent that reacts with the epoxy resin.

[0041] The amount of water contained in the aqueous paint composition (P) is preferably 20 to 80% by mass, and more preferably 30 to 70% by mass.

[0042] 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 corrosion of the substrate. However, in water-based paint compositions, the effects of epoxy resins in improving adhesion and corrosion resistance have not been fully realized. However, according to the present invention, by adjusting the elastic modulus of the coating film, adhesion and corrosion resistance can be sufficiently improved even in water-based paint compositions.

[0043] 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. Furthermore, from the viewpoint of increasing the elastic modulus of the resulting coating film, the epoxy resin is preferably one that has a rigid structure such as an aromatic ring.

[0044] The epoxy resin is preferably a water-dispersible epoxy resin. A water-dispersible epoxy resin is an epoxy resin that can be distributed in water to form a heterogeneous system (e.g., an emulsion or suspension). The water-dispersible epoxy resin is dispersed in the aqueous paint composition.

[0045] 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 KE-002, KE-116, E-1022, KE-301C (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).

[0046] 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.

[0047] 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. 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".

[0048] In the aqueous paint composition (P), the amount of epoxy 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 epoxy resins, the amount of epoxy resin described herein refers to the total amount of epoxy resins.

[0049] A curing agent that reacts with epoxy resin is a curing agent used to react with epoxy resin, particularly its epoxy groups, to promote or control the curing reaction. Preferably, the curing agent that reacts with epoxy resin is a curing agent having active hydrogen that reacts with epoxy groups, and more preferably, an amine curing agent. Amine curing agents are preferred from the viewpoint of imparting corrosion resistance to coating films containing epoxy resin. Preferably, the amine curing agent is a polyamine resin. A polyamine resin is a resin having at least two amino groups in one molecule. Examples of polyamine resins include those 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 the Mannich reaction of amines, formaldehyde, and ketones or phenols. Here, polyamine resins that also have amide bonds in their molecules, such as those produced by condensation of amines and carboxylic acids, are sometimes referred to as "polyamideamine resins" or "polyamideamines." Furthermore, ring-opening polymerization of alkylene oxides such as ethylene oxide and propylene oxide can be used for the etherification of amines with alcohols.

[0050] 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.

[0051] 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.

[0052] The curing agent that reacts with the epoxy resin preferably contains a polyamine resin having a cyclic structure. By using a polyamine resin having a cyclic structure as the curing agent that reacts with the epoxy resin, the elastic modulus of the coating film can be increased. The polyamine resin having a cyclic structure is preferably a modified polyamine resin having a cyclic structure, and more preferably a Mannich-modified polyamidoamine. Furthermore, by using a modified polyamine resin having a cyclic structure, preferably a polyamidoamine having a cyclic structure, the adhesion of the coating film to the substrate or the zinc layer that may be formed on the substrate can be further improved, and a coating film with high elastic modulus and excellent adhesion can be formed.

[0053] The amount of polyamine resin having a cyclic structure as a curing agent is preferably 50 to 100% by mass, and more preferably 60 to 90% by mass, relative to the total amount of curing agent that reacts with the epoxy resin. If the paint composition contains multiple polyamine resins having cyclic structures, the amount of polyamine resin having a cyclic structure described herein is the total amount of polyamine resins having cyclic structures.

[0054] 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. From the viewpoint of increasing the elastic modulus of the resulting coating film, a curing agent having a rigid structure such as an aromatic ring is more preferable.

[0055] From the viewpoint of increasing the elastic modulus of the coating film, it is also preferable that the polyamine resin having a cyclic structure is 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 derivative is as described above, with cardanol being particularly preferred. Such polyamine resins are sometimes referred to as phenalkamine-based curing agents.

[0056] Polyamine resins having a cyclic structure may have low reactivity with epoxy resins. Therefore, it is preferable that the curing agent that reacts with the epoxy resin contains both a polyamine resin having a cyclic structure and a polyamine resin without a cyclic structure. This ensures the reactivity of the 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 polyetheramines) such as polyoxyethylenediamine and polyoxypropylenediamine can be used.

[0057] When using a polyamine resin having a cyclic structure and a polyamine resin not having a cyclic structure in combination, the amount of the polyamine resin having a cyclic structure is preferably 50 to 99% by mass relative to the total amount of curing agent reacting with the epoxy resin, and the amount of the polyamine resin not having a cyclic structure is preferably 1 to 50% by mass relative to the total amount of curing agent reacting with the epoxy resin.

[0058] The curing agent that reacts with the epoxy resin is preferably formulated in the form of an emulsion, a dispersion, or an aqueous solution.

[0059] The active hydrogen equivalent of the curing agent that reacts with the epoxy resin is preferably 80 to 350 g / eq, and more preferably 100 to 250 g / eq. The active hydrogen equivalent of the curing agent that reacts with the epoxy resin is the number of grams of curing agent containing 1 equivalent of active hydrogen [g / eq], and is the value obtained by dividing the molecular weight of the curing agent that reacts with the epoxy resin by the number of hydrogen atoms in the amino group per molecule. When multiple curing agents that react with the epoxy resin are included, the active hydrogen equivalent described here is the average value of the active hydrogen equivalents of the curing agents that react with the epoxy resin.

[0060] In an aqueous paint composition (P), the amount of curing agent that reacts with the epoxy resin is preferably 5 to 30% by mass relative to the total amount of film-forming components. If the paint composition contains multiple curing agents that react with epoxy resins, the amount of curing agent that reacts with epoxy resins described herein is the total amount of curing agents that react with epoxy resins.

[0061] The water-based paint composition (P) contains one or more pigments selected from extender pigments and coloring pigments.

[0062] Examples of extender pigments include silica, talc, mica, calcium carbonate, and barium sulfate.

[0063] In an aqueous paint composition (P), the amount of extender pigment is, for example, 10 to 50% by mass relative to the total amount of film-forming components. If the paint composition contains multiple extender pigments, the amount of extender pigment described herein refers to the total amount of extender pigments.

[0064] 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.

[0065] In an aqueous paint composition (P), the amount of coloring pigment is, for example, 1 to 20% by mass relative to the total amount of film-forming components. If the paint composition contains multiple coloring pigments, the amount of coloring pigment described herein is the total amount of coloring pigments.

[0066] The water-based paint composition (P) can use pigments commonly used in the paint industry, such as extender pigments, coloring pigments, and rust-preventive pigments.

[0067] 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 phosphate, aluminum phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, magnesium phosphate, and vanadic acid / phosphate mixed pigments. Among these, phosphate-based rust-preventive pigments are preferred from the viewpoint of corrosion resistance. Examples of phosphate-based rust-preventive pigments include salts of phosphate compounds such as phosphoric acid, phosphorous acid, and polyphosphate (magnesium salts, calcium salts, zinc salts, aluminum salts, phosphomolybdate salts, etc.). In this specification, the rust-preventive pigment is sometimes referred to as component (B4) and called (B4) rust-preventive pigment.

[0068] In an aqueous paint composition (P), the amount of rust-preventive pigment is, for example, 1 to 20% by mass relative to the total amount of film-forming components. If the paint composition contains multiple rust-preventive pigments, the amount of rust-preventive pigment described herein is the total amount of rust-preventive pigments.

[0069] Flake-like pigments can be used as pigments, and it is preferable that the aqueous paint composition (P) contains a flake-like pigment as an extender pigment and / or a coloring pigment. Flake-like pigments are pigments that have a thin, flat shape like foil, and 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 mica-like iron oxide. Metal pigments also include alloy pigments such as stainless steel. Furthermore, flake-like 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. Some flake-like pigments are classified as rust-preventive pigments, extender pigments, or coloring pigments as described above.

[0070] Flake-shaped pigments, based on their flake shape, exhibit an effect of inhibiting the penetration of corrosive factors such as water, oxygen, and chlorides, thereby improving the environmental barrier properties of the coating film and contributing to its corrosion resistance. They also exhibit an effect of reducing internal stress in the coating film. By reducing internal stress, the adhesion of the coating film can be further improved, and thicker coating films can be advantageously formed.

[0071] In this specification, a flake pigment has an aspect ratio of 2 or more. In this specification, a flake pigment may be referred to as component (B3) and called (B3) flake pigment.

[0072] In the aqueous coating composition (P), the amount of flake-like pigment is preferably 1.0 to 20.0% by volume relative to the total amount of film-forming components. In other words, the amount of flake-like pigment is preferably 1.0 to 20.0% by volume of the first coating film. While a larger amount of flake-like pigment can improve environmental barrier properties, too much may reduce adhesion to the substrate.

[0073] Furthermore, from the viewpoint of increasing the elastic modulus of the resulting coating film, it is preferable to use a flake-like pigment with an aspect ratio of 2 or more and less than 100. It is even more preferable that the aspect ratio of the flake-like pigment be between 2 and 30.

[0074] 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).

[0075] The flake-like pigment preferably has an average particle size of 1 to 150 μm, and more preferably 3 to 40 μm. While a larger average particle size of the flake-like pigment can improve environmental barrier properties, if it is too large, it can increase the unevenness of the coating film, potentially degrading its appearance.

[0076] In the aqueous paint composition (P), the pigment volume concentration (PVC) is 20-35%, preferably 21-33%, and more preferably 23-32%. From the viewpoint of increasing the elastic modulus of the resulting coating film, a high PVC is preferable. However, if the PVC is too high, the resin component becomes relatively small, and the dispersibility of the pigment tends to decrease, which may lead to a decrease in the storage stability of the paint composition or a decrease in the corrosion resistance of the coating film. Adhesion to the substrate may also decrease.

[0077] The aqueous paint composition (P) may contain, as appropriate for the purpose, other components such as resins not corresponding to component (A1), curing agents not corresponding to component (C1), curing accelerators, film-forming aids, antifreeze agents, surface modifiers (also called wetting agents), dispersants, silane coupling agents, defoaming agents, viscosity modifiers, thickeners, rust inhibitors not corresponding to rust-inhibiting pigments, flash rust inhibitors, settling inhibitors, skinning inhibitors, sagging inhibitors, color separation inhibitors, matting agents, adhesion promoters, leveling agents, drying agents, catalysts, plasticizers, antifungal agents, antibacterial agents, antiviral agents, preservatives, insecticides, antistatic agents, and conductivity promoters.

[0078] The amount of film-forming component contained in the aqueous paint composition (P) is preferably 20 to 80% by mass, and more preferably 30 to 70% by mass.

[0079] The water-based paint composition (P) 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, curing agent, and additives selected as needed during painting. For example, (A1) an agent containing epoxy resin is the main component, and (C1) an agent containing a curing agent that reacts with the epoxy resin is the curing agent. The 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.

[0080] The present invention provides a method for forming a multilayer film, which includes the step of applying an aqueous paint composition (Q) to a first coating film to form a second coating film with a dry film thickness of 10 to 200 μm. In this specification, the step of forming the second coating film may be referred to as step (2). In step (2), it is also possible to apply the aqueous paint composition (Q) multiple times to form multiple second coating films.

[0081] The dry film thickness of the second coating is 10 to 200 μm, and more preferably 20 to 100 μm. When the multilayer film has multiple second coatings, the film thickness of the second coating described here refers to the total film thickness of the second coatings. Dry film thickness is the thickness of the dry coating, and the dry coating is as described above.

[0082] The water-based paint composition (Q) contains an acrylic resin and a coloring pigment.

[0083] The amount of water contained in the aqueous paint composition (Q) is preferably 30 to 90% by mass, and more preferably 40 to 80% by mass.

[0084] Acrylic resins are resins produced by polymerization or copolymerization of acrylic or methacrylic monomers, and optionally with other monomers. Acrylic resins are preferred from the viewpoint of balancing weather resistance, water resistance, adhesion, and price.

[0085] Acrylic or methacrylic monomers are monomers such as acrylic acid, methacrylic acid, and their esters, amides, and nitriles. When preparing acrylic resins, acrylic or methacrylic monomers may be used individually, but it is preferable to use a combination of multiple types.

[0086] Specific examples of acrylic or methacrylic monomers include acrylic acid and methacrylic acid, as well as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, and decyl (meth)acrylate. (meth)acrylate monomers such as dodecyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, etc.; 2-hydroxyethyl (meth)acrylate, 2-hydroxyethyl Functional group-containing monomers such as cypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate, 2-aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, 3-aminopropyl (meth)acrylate, 2-butylaminoethyl (meth)acrylate, glycidyl (meth)acrylate; amide monomers such as acrylamide and methacrylamide; γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, Examples include alkoxysilyl group-containing monomers such as β-(meth)acryloxyethyltrimethoxysilane, β-(meth)acryloxyethyltriethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, γ-(meth)acryloxypropylmethyldiethoxysilane, γ-(meth)acryloxypropylmethyldipropoxysilane, γ-(meth)acryloxybutylphenyldimethoxysilane, γ-(meth)acryloxypropyldimethylmethoxysilane, and γ-(meth)acryloxypropyldiethylmethoxysilane.

[0087] Examples of monomers other than acrylic or methacrylic monomers include aromatic monomers such as styrene, methylstyrene, chlorostyrene, methoxystyrene, vinyltoluene, and vinylpyridine; carboxyl group-containing monomers such as fumaric acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, crotonic acid, and vinyl versatic acid; functional group-containing monomers such as allyl alcohol and allyl glycidyl ether; olefin monomers such as ethylene and propylene; diene monomers such as butadiene and isoprene; vinyl monomers such as vinyl acetate and vinyl chloride; amide monomers such as maleic acid amide; ester monomers such as dialkyl fumarate; and alkoxysilyl group-containing monomers such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane.

[0088] When an acrylic resin is composed of acrylic or methacrylic monomers and other monomers, the proportion of acrylic or methacrylic monomers constituting the acrylic resin is usually greater than 50% by mass.

[0089] The acrylic resin may be modified. Examples of modified acrylic resins include silicone-modified acrylic resin and urethane-modified acrylic resin.

[0090] Silicone-modified acrylic resins can be produced by methods such as using alkoxysilyl group-containing monomers to induce competition between polymerization and siloxane condensation reactions, or by synthesizing a polymer (silicone portion) having siloxane bonds in its main skeleton, and then graft polymerizing the aforementioned acrylic or methacrylic monomers onto the polymer, or by bonding acrylic resin to it. Urethane-modified acrylic resins can also be produced by reacting hydroxyl group-containing acrylic resins with polyols and polyisocyanates. Silicone-modified acrylic resins also include resins referred to as acrylic silicone resins.

[0091] The acrylic resin preferably contains silicon. By using an acrylic resin containing silicon, the stain resistance and weather resistance of the coating film can be improved, and a coating film that is less prone to surface discoloration can be formed. Examples of acrylic resins containing silicon include acrylic resins obtained using alkoxysilyl group-containing monomers in at least a portion of the monomer, and silicone-modified acrylic resins. The proportion of silicon atoms in the acrylic resin is preferably 0.1 to 15% by mass.

[0092] The acrylic resin preferably has a cross-linked structure. The cross-linked structure within the acrylic resin can be formed by the synthesis or modification of the acrylic resin.

[0093] Acrylic resins preferably have a structure derived from cyclic aliphatic monomers. Cyclic aliphatic monomers are monomers having an alicyclic structure (saturated or unsaturated carbon rings that do not have aromaticity, such as cycloalkyl groups). Acrylic resins having a structure derived from cyclic aliphatic monomers can improve the weather resistance of the coating film. Examples of cyclic aliphatic monomers include cycloalkyl (meth)acrylates (e.g., cyclohexyl (meth)acrylate), alkylcycloalkyl (meth)acrylates (e.g., 4-methylcyclohexyl (meth)acrylate), cycloalkylalkyl (meth)acrylates (e.g., cyclohexylmethyl (meth)acrylate, cyclohexylethyl (meth)acrylate, cyclohexylpropyl (meth)acrylate, 4-methylcyclohexylmethyl (meth)acrylate), and crosslinked cyclic (meth)acrylates (e.g., isobornyl (meth)acrylate, adamantyl (meth)acrylate). Among these, cyclohexyl methacrylate (CHMA) is preferred. The proportion of structures derived from cyclic aliphatic monomers is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass, relative to the total amount of acrylic resin.

[0094] The acrylic resin preferably has a structure derived from a polymerizable ultraviolet absorber and / or a polymerizable radical scavenger. Acrylic resins having a structure derived from a polymerizable ultraviolet absorber and / or a polymerizable radical scavenger can improve the weather resistance of the coating film. Examples of polymerizable ultraviolet absorbers include benzotriazole-based ultraviolet absorbing monomers and benzophenone-based ultraviolet absorbing monomers. Radical scavengers can scavenge free radicals and improve photostability. Examples of polymerizable radical scavengers include hindered amine-based polymerizable photostable monomers. The total proportion of structures derived from the polymerizable ultraviolet absorber and polymerizable radical scavenger is preferably 0.2 to 3.0% by mass relative to the total amount of the acrylic resin.

[0095] The acrylic resin is preferably a water-dispersible acrylic resin. A water-dispersible acrylic resin is an acrylic resin that can be distributed in water to form a heterogeneous system (e.g., an emulsion or suspension). The water-dispersible acrylic resin is dispersed in the aqueous paint composition.

[0096] The acrylic resin is preferably in the form of an acrylic resin emulsion or an acrylic resin dispersion. The acrylic resin emulsion can be prepared, for example, by emulsion polymerization in water using water as a medium. More preferably, an acrylic resin emulsion having a uniform structure obtained by emulsion polymerization, or an acrylic resin emulsion having a heterogeneous structure obtained by a multi-step emulsion polymerization method are used, and both of these may be used together. Alternatively, the acrylic resin emulsion can also be prepared as follows: For example, it may be prepared by emulsifying the acrylic resin in water while applying a forced shear force using a high-speed stirrer or the like. An acrylic resin emulsion can be prepared by performing a phase change to water on an acrylic resin polymerized in an organic solvent medium, and if necessary, the organic solvent contained in the acrylic resin emulsion may be removed by distillation or the like.

[0097] In the aqueous paint composition (Q), the amount of acrylic resin is preferably 30 to 70% by mass, and more preferably 40 to 65% by mass, relative to the total amount of film-forming components. If the paint composition contains multiple acrylic resins, the amount of acrylic resin described herein refers to the total amount of acrylic resins.

[0098] The aqueous paint composition (Q) preferably contains a curing agent that reacts with the acrylic resin, more preferably contains at least one curing agent selected from carbodiimide and isocyanate, and even more preferably contains a carbodiimide curing agent. By using these curing agents, the weather resistance of the coating film can be improved. In addition to its high effect in improving weather resistance, the carbodiimide curing agent also has a high effect in increasing the elastic modulus of the coating film. In this specification, the carbodiimide curing agent may be referred to as component (C2) and as "(C2) carbodiimide curing agent". The isocyanate curing agent may be referred to as component (C3) and as "(C3) isocyanate curing agent".

[0099] Examples of carbodiimide curing agents include carbodiimide compounds such as N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimide, N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimidemethiozide, N-tert-butyl-N'-ethylcarbodiimide, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide meso-p-toluenesulfonate, N,N'-di-tert-butylcarbodiimide, and N,N'-di-p-tolylcarbodiimide; carbodiimide compounds obtained by known condensation reactions of polyisocyanates in the presence of a carbodiimide catalyst; and carbodiimide compounds using polyisocyanates and polyalkylene oxides as raw materials.

[0100] Furthermore, carbodiimide group-containing resins are also known as carbodiimide curing agents. Carbodiimide group-containing resins are preferably formulated in the form of a carbodiimide group-containing resin emulsion, a carbodiimide group-containing resin dispersion, or an aqueous solution of a carbodiimide group-containing resin. In this specification, a carbodiimide group-containing resin emulsion means an emulsion obtained by dispersing a carbodiimide group-containing resin in an aqueous medium mainly composed of water, and a carbodiimide group-containing resin dispersion means a dispersion obtained by dispersing a carbodiimide group-containing resin in an aqueous medium mainly composed of water.

[0101] In a water-based paint composition (Q), when a carbodiimide curing agent is used, it is desirable that the acrylic resin has carboxyl groups.

[0102] In the aqueous paint composition (Q), the amount of carbodiimide curing agent is preferably 0.1 to 6.0% by mass relative to the total amount of film-forming components. If the paint composition contains multiple carbodiimide curing agents, the amount of carbodiimide curing agent described herein is the total amount of carbodiimide curing agents.

[0103] Examples of isocyanate curing agents include aliphatic, aromatic, or aromatic aliphatic isocyanate compounds, preferably compounds having two or more isocyanate groups (also called polyisocyanates). Specific examples include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methylcyclohexane diisocyanate, bis(isocyanate-methyl)cyclohexane, isophorone diisocyanate, dimer acid diisocyanate, lysine diisocyanate, and modified forms of these isocyanates. Specific examples of modified forms include biuret modified forms, isocyanurate modified forms, adduct modified forms (e.g., trimethylolpropane adducts), allophanate modified forms, uretdione modified forms, and the like.

[0104] In the aqueous paint composition (Q), when an isocyanate curing agent is used, it is desirable that the acrylic resin has hydroxyl groups and / or amino groups, and it is particularly preferable that it has hydroxyl groups.

[0105] In the aqueous paint composition (Q), the amount of isocyanate curing agent is preferably 0.1 to 6.0% by mass relative to the total amount of film-forming components. If the paint composition contains multiple isocyanate curing agents, the amount of isocyanate curing agent described herein is the total amount of isocyanate curing agents.

[0106] The aqueous paint composition (Q) preferably contains a coloring pigment from the viewpoint of weather resistance. Examples of coloring pigments are those described above. In the aqueous paint composition (Q), the amount of coloring pigment is, for example, 1 to 20% by mass relative to the total amount of film-forming components. If the paint composition contains multiple coloring pigments, the amount of coloring pigment described here is the total amount of coloring pigments.

[0107] The water-based paint composition (Q) may contain pigments commonly used in the paint industry, such as coloring pigments, extender pigments, and rust-preventive pigments. Examples of extender pigments and rust-preventive pigments are those described above. In the water-based paint composition (Q), the amount of extender pigment is, for example, 0 to 20% by mass relative to the total amount of film-forming components. If the paint composition contains multiple extender pigments, the amount of extender pigment described here refers to the total amount of extender pigments.

[0108] In the aqueous paint composition (Q), the pigment volume concentration (PVC) is preferably 10-24%, and more preferably 11-20%. From the viewpoint of increasing the elastic modulus of the resulting coating film, a high PVC is preferable. However, if the PVC is too high, the resin component becomes relatively small, and the dispersibility of the pigment tends to decrease, which may lead to a decrease in the storage stability of the paint composition or a decrease in the corrosion resistance of the coating film. In addition, if the PVC is too high, the weather resistance tends to decrease.

[0109] The water-based paint composition (Q) preferably contains an ultraviolet absorber. The ultraviolet absorber absorbs ultraviolet rays and prevents degradation caused by ultraviolet rays. By using an ultraviolet absorber, the weather resistance of the paint film can be improved.

[0110] Examples of UV absorbers include benzophenone-based UV absorbers, benzoate-based UV absorbers, benzotriazole-based UV absorbers, triazine-based UV absorbers (especially hydroxyphenyltriazine-based UV absorbers), and benzylidene camphor-based UV absorbers. UV absorbers may be used individually or in combination of two or more types, but it is preferable that the UV absorber contains two or more UV absorbers with different absorption peaks. It is preferable that the UV absorber contains a triazine-based UV absorber, and it is particularly preferable that it contains both a triazine-based UV absorber and a benzotriazole-based UV absorber.

[0111] Examples of UV absorbers include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone-2-hydroxy-4-bendyloxybenzophenone, bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4, 4'-Dimethoxybenzophenone, 2,2',4,4'-Tetrahydroxybenzophenone, 2-Hydroxy-4-methoxy-2'-carboxybenzophenone, 2-(2'-Hydroxy-5'-methylphenyl)benzotriazole, 2-[2'-Hydroxy-3',5'-Bis(α,α-(dimethylbenzyl)phenyl]benzotriazole, 2-(2'-Hydroxy-3',5'-Di-t-butylphenyl)benzotriazole, 2-(2'-Hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzo Triazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 2,2'-methylene-bis[4-(1,1,3,3-tetramethylbutyl)-6-(2N-benzotriazole-2-yl)phenol], methyl-3-[3-t-butyl-5-(2H-benzotriazole-2-yl)-4-hydroxyphenol Condensate of [phenyl]propionate and polyethylene glycol, 2-(2-hydroxyphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2,6-di-t-butylphenyl-3',5'-di-t-butyl-4'-hydroxybenzoate, hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate, 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,Examples include 5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-(2'-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2,4-bis(2-hydroxy-4-butyloxyphenyl)-6-(2,4-bis-butyloxyphenyl)-1,3,5-triazine, hydroxyphenyl triazine, 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, and 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine.

[0112] In the aqueous paint composition (Q), the amount of ultraviolet absorber is preferably 0.2 to 3.0% by mass relative to the total amount of film-forming components. If the paint composition contains multiple ultraviolet absorbers, the amount of ultraviolet absorber described herein is the total amount of ultraviolet absorbers.

[0113] The aqueous coating composition (Q) preferably contains a radical scavenger. The radical scavenger can capture free radicals and improve photostability. In this specification, substances that react with free radicals and prevent polymerization reactions (so-called polymerization inhibitors) are also included as radical scavengers. By using a radical scavenger, the weather resistance of the coating film can be improved.

[0114] Examples of radical scavengers include hindered amine compounds, hydroquinone compounds, phenolic compounds, phenothiazine compounds, nitroso compounds, and N-oxyl compounds, with hindered amine light stabilizers (HALS) being particularly preferred.

[0115] Examples of radical scavengers include hindered amine compounds such as bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, 1-{2-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy)ethyl}-2,2,6,6-tetramethylpiperidine, and 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro{4.5}decane-2,4-dione, as well as phenols, o-, m-, or p-cleric compounds. Phenolic compounds such as zole, 2-t-butyl-4-methylphenol, 6-t-butyl-2,4-dimethylphenol, 2,6-di-t-butyl-4-methylphenol, 2-t-butylphenol, 4-t-butylphenol, 2,4-di-t-butylphenol, 2-methyl-4-t-butylphenol, 4-t-butyl-2,6-dimethylphenol, hydroquinone, hydroquinone monomethyl ether, methylhydroquinone, 2,5-di-t-butyl Hydroquinone compounds such as 2-methyl-p-hydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone, 4-methylbenzcatechin, t-butylhydroquinone, 3-methylbenzcatechin, 2-methyl-p-hydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone, t-butylhydroquinone, benzoquinone, t-butyl-p-benzoquinone, 2,5-diphenyl-p-benzoquinone, and phenotia Examples include phenothiazine compounds such as din, nitroso compounds such as N-nitroso-N-phenylhydroxylamine ammonium and N-nitroso-N-phenylhydroxylamine aluminum salt, and N-oxyl compounds such as 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethyl-piperidine-N-oxyl, and 4-methoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl.

[0116] In the aqueous coating composition (Q), the amount of radical scavenger is preferably 0.2 to 3.0% by mass relative to the total amount of film-forming components. If the coating composition contains multiple radical scavengers, the amount of radical scavenger described herein is the total amount of radical scavengers.

[0117] The aqueous paint composition (Q) may contain, as appropriate for the purpose, other components such as resins not corresponding to component (A2), curing agents that react with the resin, curing accelerators, film-forming aids, antifreeze agents, surface modifiers (also called wetting agents), dispersants, silane coupling agents, defoaming agents, viscosity modifiers, thickeners, rust inhibitors not corresponding to rust-inhibiting pigments, flash rust inhibitors, settling inhibitors, anti-skinning agents, anti-sagging agents, color separation inhibitors, matting agents, adhesion promoters, leveling agents, drying agents, catalysts, plasticizers, antifungal agents, antibacterial agents, antiviral agents, preservatives, insecticides, antistatic agents, and conductivity promoters.

[0118] The amount of film-forming components contained in the aqueous paint composition (Q) is preferably 10 to 70% by mass, and more preferably 20 to 60% by mass.

[0119] The water-based paint composition (Q) is preferably a two-component paint composition. For example, (A2) an agent containing an acrylic resin is the main component, and (C2) an agent containing a carbodiimide curing agent, etc., is the curing agent. Pigments, UV absorbers, and radical scavengers may be included in either the main component or the curing agent, but are usually included in the main component. Water is usually included 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.

[0120] Water-based paint composition (P) and water-based paint composition (Q) can each be prepared by mixing various components as appropriate. If the paint composition is a two-component paint composition, the main component and 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 hardener can be prepared by mixing various components as appropriate.

[0121] Preferably, the aqueous paint composition (P) and the aqueous paint composition (Q) have 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).

[0122] In this specification, viscosity is measured using a rheometer (e.g., an Anton Paar MCR302e rheometer) after adjusting the liquid temperature to 23°C.

[0123] The means of applying the water-based paint composition (P) and the water-based paint composition (Q) are not particularly limited, and known application methods such as brush application, roller application, trowel application, spatula application, flow coater application, and spray application (e.g., air spray application, airless spray application) can be used.

[0124] The drying method for the aqueous paint composition (P) and aqueous paint composition (Q) is not particularly limited and may be either natural drying at ambient temperature or forced drying using a drying machine, etc. However, it is preferable that the aqueous paint composition (P) and aqueous paint composition (Q) are paint compositions that are intended to be naturally dried at ambient temperature. An ambient temperature of about 5 to 40°C is assumed.

[0125] In the multilayer film formation method of the present invention, the multilayer film may include a zinc layer as an additional film located closer to the substrate than the first coating film (in other words, between the substrate and the first coating film). In this case, the multilayer film formation method of the present invention is a method of forming a zinc layer, a first coating film, and a second coating film on the substrate in this order. The zinc layer is a layer containing a large amount of zinc powder. The amount of zinc powder contained in the zinc layer is, for example, 30 to 95% by mass. The zinc layer is a film formed by, for example, a zinc-rich primer or a zinc-rich paint.

[0126] In the multilayer film formation method of the present invention, the substrate can be of various shapes, such as two-dimensional substrates such as films, sheets, or plates, or three-dimensional substrates that 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, as well as steel structures such as steel towers, bridges, and plants.

[0127] The substrate may have its surface subjected to pretreatments such as degreasing, chemical conversion treatment, polishing, plating, or metal spraying.

[0128] 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.

[0129] If the substrate has an old paint film on its surface, the substrate surface, including the old paint film, can be coated with the paint composition. If the old paint film is intact, the paint composition can be applied to the old paint film without peeling or removing it from the substrate surface. Since contaminants such as dust and dirt adhere to the old paint film, removing these contaminants can improve the adhesion of the new paint film to the old paint film. 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.

[0130] 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.

[0131] The existing paint film may also contain various additives as other components, such as pigments, dispersants, surface modifiers, antioxidants, plasticizers, rust inhibitors, solvents, antibacterial agents, antiviral agents, viscosity modifiers, fillers, defoamers, charge control agents, stress relievers, penetrants, light guides, brightening agents, magnetic materials, phosphors, ultraviolet absorbers, and radical scavengers.

[0132] In the multilayer film formation method of the present invention, the configuration of the multilayer film may be, for example, a configuration consisting of a first coating film and a second coating film, or a configuration consisting of a zinc layer, a first coating film and a second coating film.

[0133] In the multilayer film formation method of the present invention, the dry film thickness of the multilayer film is preferably 30 to 500 μm, and more preferably 60 to 400 μm. [Examples]

[0134] 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.

[0135] <Examples of paint composition preparation> The main component and hardener were prepared by mixing the raw materials according to the formulations shown in Tables 1-4. The obtained main component and hardener were then mixed with water for dilution as needed, according to the mixing ratios shown in Tables 1-4, to prepare the paint composition. The formulations and mixing ratios shown in Tables 1-4 are based on mass.

[0136] The details of the materials used in the preparation of the primer and intermediate coat paint compositions are shown below. Of the primer and intermediate coat paint compositions, the water-based paint composition (P) contains (A1) epoxy resin, one or more pigments selected from (B1) extender pigments and (B2) coloring pigments, and (C1) a curing agent that reacts with the epoxy resin, with an elastic modulus of 800 to 2500 N / mm². 2 This is a paint composition for forming a coating film. Specifically, paint compositions 1-1 to 1-7 shown in Tables 1 to 2 are aqueous paint compositions (P). (1)(A1) Epoxy resin Epoxy resin 1: ADEKA Resin EM101-50 (ADEKA epoxy resin emulsion: non-volatile content 47% by mass, epoxy equivalent 510 g / eq) Epoxy resin 2: jER W2801 (Mitsubishi Chemical's epoxy resin emulsion: 70% by mass of non-volatile content, epoxy equivalent 190-205 g / eq) Epoxy resin 3: Epulsion EA55 (manufactured by NSC Japan: 55% non-volatile content, epoxy equivalent 495 g / eq) (2)(B1) Extender pigments Extender pigment 1: Calcium carbonate (average particle size 6 μm, specific gravity 2.7, aspect ratio less than 2, non-volatile content 100%) Extender pigment 2: Precipitating barium sulfate (average particle size 3.3 μm, specific gravity 4.5, aspect ratio less than 2, non-volatile content 100%) Extender Pigment 3: Mica A (average particle size 23 μm, aspect ratio 70, non-volatile content 100%, corresponds to (B3) flake pigment) Extender Pigment 4: Mica B (average particle size 15 μm, aspect ratio 70, non-volatile content 100%, corresponds to (B3) flake pigment) Extender Pigment 5: Talc (average particle size 14 μm, aspect ratio less than 2-20, non-volatile content 100%, corresponds to (B3) flake pigment) Extender Pigment 6: Kaolin (average particle size 4 μm, aspect ratio less than 2-20, 100% non-volatile content, corresponds to (B3) flake pigment) (3)(B2) Coloring pigment Coloring pigment 1: Titanium dioxide (white pigment, aspect ratio less than 2, non-volatile content 100%) Coloring Pigment 2: Carbon Black (black pigment, aspect ratio less than 2, non-volatile content 100%) Coloring pigment 3: Iron oxide (oak pigment, aspect ratio less than 2, non-volatile content 100%) Coloring pigment 4: Iron oxide (rust-colored pigment, aspect ratio less than 2, non-volatile content 100%) Coloring pigment 5: Aluminum (average particle size 14 μm, aspect ratio 2-14, non-volatile content 60% by mass, corresponds to (B3) flake pigment) (4)(B4) Rust-preventive pigment Rust-preventive pigment: Aluminum tripolyphosphate K-WHITE#84S (manufactured by Teika Co., Ltd., aspect ratio less than 2, non-volatile content 100% by mass) (5)(C1) Curing agent that reacts with epoxy resin 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 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) Polyamine resin 4: Fujicure FXS-918-FA (T&KTOKA amine resin emulsion; non-volatile content 60% by mass, active hydrogen equivalent 180 g / eq) Polyamine resin 5: Cardolite NX-8101 (Polyamine resin manufactured by Cardolite; non-volatile content 50% by mass, active hydrogen equivalent 135 g / eq) (6) Others Dispersant 1: Floren GW-1640 (manufactured by Kyoeisha Chemical Co., Ltd., non-volatile content 40% by mass) Silane coupling agent: 3-Glycidoxypropyltrimethoxysilane (100% by mass of non-volatile content) Film-forming aid: Dipropylene glycol n-butyl ether Antifreeze: Ethylene glycol (0% by mass of non-volatile content, antifreeze for paints) Viscosity modifier 1: SN Thickener 665T (manufactured by Sunopco, urethane-modified polyether compound, 30% by mass of non-volatile content) Defoaming agent 1: SN Deformer 1312 (manufactured by Sunopco, 50% by mass of non-volatile content) Curing accelerator: Ankamin K-34 (tertiary amine manufactured by EVONIK, 100% by mass of non-volatile content) Rust inhibitor 1: HALOX 650 (manufactured by ICL (benzothiazole-2-ylthio) succinic acid, 100% by mass of non-volatile content) Rust inhibitor 2: Sodium nitrite (100% by mass of non-volatile content)

[0137] The details of the materials used in the preparation of the topcoat paint composition are shown below. Of the topcoat paint compositions, the water-based paint composition (Q) contains (A2) acrylic resin and (B2) coloring pigment, and has an elastic modulus of 80-500 N / mm². 2 This is a paint composition for forming a coating film. Specifically, paint compositions 2-1 to 2-10 shown in Tables 3 to 4 are water-based paint compositions (Q). (1)(A2) Acrylic resin Acrylic resin 1: Acronal 7659 (BASF, acrylic silicone resin emulsion, non-volatile content 50% by mass, acid value / hydroxyl value = 15 / 0) Acrylic resin 2: Homemade resin (acrylic silicone resin emulsion, 45% by mass of non-volatile content, acid value / hydroxyl value = 12.6 / 0, MMA / BA / BMA / CHMA / MAA / LA82 / KBM503 = 20 / 20 / 30 / 3.0 / 1.0 / 1.0) Acrylic resin 3: Acryset EX41 (Nippon Shokubai, acrylic resin emulsion, non-volatile content: 45% by mass, acid value / hydroxyl value = 8 / 13) Acrylic resin 4: Yodzol AD221 (Henkel Japan, acrylic resin emulsion, non-volatile content: 45% by mass, acid value / hydroxyl value = 19.1 / 0) Acrylic resin 5: Barnock WE-301 (manufactured by DIC Corporation, non-volatile content 45% by mass, acid value / hydroxyl value = 0 / 80) (2)(A3) Fluororesin Fluororesin 1: Lumiflon FE4400 (manufactured by AGC Corporation, fluororesin emulsion, non-volatile content 50% by mass, acid value / hydroxyl value = 0 / 24.5) (3)(B1) Extender pigments Extender pigment 2: Precipitating barium sulfate (average particle size 3.3 μm, specific gravity 4.5, aspect ratio less than 2, non-volatile content: 100%) (4)(B2) Coloring pigment Coloring pigment 1: Titanium dioxide (average particle size 0.28 μm, specific gravity 4.0, aspect ratio less than 2, non-volatile content 100%) Coloring Pigment 2: Carbon Black (black pigment, aspect ratio less than 2, non-volatile content 100%) Coloring pigment 3: Iron oxide (oak pigment, aspect ratio less than 2, non-volatile content 100%) (5)(C2) Carbodiimide hardener Carbodiimide compound: Carbodilite E-07S (Carbodiimide resin manufactured by Nisshinbo Chemical Co., Ltd.; Non-volatile content 40% by mass, Carbodiimide equivalent 225-250) (6)(C3) Isocyanate curing agent Isocyanate compound: Barnock DNW-6000 (polyisocyanate compound manufactured by DIC Corporation; non-volatile content 100% by mass, NCO effective content 15.0-16.5% by mass) (7) Others Dispersant 2: DISPERBYK-190 (manufactured by BIC Chemie Japan) Carbodiimide compound: E-07S (manufactured by Nisshinbo Chemical Co., Ltd.) Film-forming aid: Dipropylene glycol n-butyl ether Antifreeze: Ethylene glycol (0% by mass of non-volatile content, antifreeze for paints) UV absorber: EVERSORB 80 (manufactured by Eiko Chemical Co., Ltd., benzotriazole compound, non-volatile content 84%) Viscosity modifier 2: PRIMAL RM-2020NPR (manufactured by Dow Chemical, urethane-associated thickening compound, non-volatile content 20% by mass) Leveling agent: SN Wet 125 (manufactured by Sunopco, silicone-based surfactant, 100% by mass of non-volatile content) Antifoaming agent 2: SN Deformer 1312 (manufactured by Sunopco) Viscosity modifier 3: PRIMAL RM-6000 (manufactured by Dow Chemical Company, urethane-associated thickening compound, non-volatile content 17.5% by mass)

[0138] Evaluation of coating film properties (single-layer film) <Method 1 for preparing the coating film> The paint composition prepared in the above <Example of paint composition preparation> was applied to a polypropylene board using an air spray to a dry film thickness of 20-50 μm, and a test board was prepared by drying it for 7 days in an environment of 23°C and 50% relative humidity.

[0139] <modulus of elasticity> After cutting out a 50mm x 10mm strip of the coating from the test plate prepared using the above <Coating Film Preparation Method 1>, a tensile test was performed on the test piece under the conditions of 23°C and 50% humidity, a speed of 5mm / min, and a grip distance of 30mm. The modulus of elasticity (N / mm²) was calculated from the slope (proportionality constant) within the range where stress and strain are proportional in the stress-strain curve. 2 The following was calculated. The results are shown in Tables 5-9. (Coating film formed from the paint compositions shown in Tables 1-2) ○: 1200 N / mm 2 More than 2100N / mm 2 below △: 800N / mm 2 More than 1200N / mm 2 less than, 2100 N / mm 2 Exceeding 2500 N / mm 2 below ×: 800N / mm 2 Less than 2500 N / mm 2 exceed (Coating film formed from the coating compositions shown in Tables 3-4) ○: 200 N / mm 2 More than 450N / mm 2 below △: 80N / mm 2 More than 200N / mm 2 less than, 450 N / mm 2 Exceeding 500 N / mm 2 below ×: 80N / mm 2 Less than 500 N / mm 2 exceed

[0140] <Water absorption (water absorption amount)> After cutting out a 50mm x 10mm strip of the coating film from the test plate prepared using the above <Coating Film Preparation Method 1>, the weight and film thickness of the coating film were measured. Next, the coating film was immersed in ion-exchanged water at 50°C for 7 days. After that, the coating film was removed from the water, thoroughly wiped, and its weight was measured again. The weight change between before and after immersion was measured to determine the thickness per 1cm². 3 The amount of water absorbed per unit area was calculated. The results are shown in Tables 1-4. (Coating film formed from the paint compositions shown in Tables 1-2) ○: 10g / cm 3 below △: 10g / cm 3 More than 15g / cm 3 less than, ×: 15g / cm 3 That's all. (Coating film formed from the coating compositions shown in Tables 3-4) ○: 29g / cm 3 less than △: 29g / cm 3 More than 33g / cm 3 less than, ×: 33g / cm 3 That's all.

[0141] Evaluation of coating film properties (multilayer films) <Method for preparing the coating film 2> The primer paint composition prepared in the above <Example of paint composition preparation> was applied to a sandblasting plate (70 × 150 × 3.2 mm) using an air spray to a dry film thickness of 55-65 μm, and dried for 7 days at 23°C and 50% relative humidity to produce a primer film. For Examples 1-16 and Comparative Examples 1-5, the topcoat paint composition prepared in <Examples of Paint Composition Preparation> above was applied to the obtained undercoat film using an air spray or applicator to achieve a dry film thickness of 20-60 μm, and the topcoat film was prepared by drying for 7 days in an environment of 23°C and 50°C relative humidity. This resulted in the creation of a test panel with a multilayer film consisting of an undercoat film and a topcoat film. For Examples 17 and 18, the intermediate coating composition prepared in <Example of Preparation of Coating Composition> above was applied to the obtained primer coating film using an air spray to achieve a dry film thickness of 55-65 μm, and the intermediate coating film was prepared by drying for 7 days at 23°C and 50% relative humidity. Next, the topcoat coating composition prepared in <Example of Preparation of Coating Composition> above was applied to the obtained intermediate coating film using an air spray or applicator to achieve a dry film thickness of 20-60 μm, and the topcoat film was prepared by drying for 7 days at 23°C and 50% relative humidity. As a result, a test panel with a multilayer film consisting of a primer coating film, an intermediate coating film, and a topcoat film was prepared. The elastic modulus of the undercoat and intermediate coat films corresponds to the elastic modulus of the single-layer films in Tables 1 and 2, while the elastic modulus of the topcoat film corresponds to the elastic modulus of the single-layer films in Tables 3 and 4. Using primer and intermediate coating compositions corresponding to water-based coating compositions (P), the elastic modulus was obtained from 800 to 2500 N / mm². 2 The undercoat and intermediate coats are considered the first coatings. Specifically, the undercoat coatings in Examples 1-18 and Comparative Examples 3-4, and the intermediate coats in Examples 17 and 18, are considered the first coatings. An elastic modulus of 80-500 N / mm² was obtained using a topcoat paint composition corresponding to the water-based paint composition (Q). 2 The topcoat film in which this is the second coating film corresponds to the second coating film. Specifically, the topcoat films in Examples 1 to 18 and Comparative Examples 1 to 2 and 5 correspond to the second coating film.

[0142] <Adhesion> • Primary adhesion The test plates prepared using the above-described <Coating Film Preparation Method 2> were subjected to adhesion tests according to the adhesion method (pull-off method) described in JIS K 5600-5-7, and the adhesion strength was measured. The fracture state was also confirmed. Adhesion was evaluated according to the following criteria. The results are shown in Tables 5-9. (standard) ○: Adhesion strength of 6 MPa or higher. Cohesive failure within the primer, intermediate coat, or topcoat. △: Adhesion strength of 6 MPa or higher. Interlayer delamination between the primer and the substrate, or between the primer or intermediate coat and the topcoat. Adhesion strength of 4 MPa or more but less than 6 MPa. Cohesive failure within the primer, intermediate coat, or topcoat. ×: Adhesion strength less than 4 MPa. Delamination between the primer and the substrate, or between the primer, intermediate coat, and topcoat. • Secondary adhesion The test plates prepared using the above <Coating Film Preparation Method 2> were immersed in ion-exchanged water at 50°C for 7 days. After that, the coating film was thoroughly wiped off after being removed from the water, and an adhesion test was performed after 1 hour in an environment of 23°C and 50% relative humidity, according to the adhesion test (cross-cut method) described in JIS K 5600-5-6:1999. The results are shown in Tables 5 to 9. (standard) ○: Less than 5% of the coating is peeled off. △: Paint peeling accounts for 5% to less than 15% of the total area. ×: More than 15% of the paint film has peeled off.

[0143] <Long-term corrosion resistance> Tests were conducted on the test panels prepared using the above-described <Coating Film Preparation Method 2> in accordance with JIS K 5600-7-1:1999 "General Test Methods for Paints - Part 7: Long-Term Durability of Coating Films - Section 1: Resistance to Neutral Salt Spray". The test was carried out for 3000 hours, and the degree of rust, blistering, etc., was observed on the test panels after the test, and the long-term corrosion protection was evaluated according to the following criteria. The results are shown in Tables 5 to 9. (standard) ○: No abnormalities △: Only swelling occurs ×: Not only does it swell, but rust also occurs.

[0144] <Weather resistance> For the test boards prepared using the above-mentioned <Coating Film Preparation Method 2>, the appearance of the coating film after 2000 hours from the start of the test was visually observed, referring to JIS K 5600-7-7:2008 "General test methods for paints - Part 7: Long-term durability of coating films - Section 7: Accelerated weathering and accelerated lightfastness (xenon lamp method)". The evaluation was conducted visually under diffused daylight, and rust, blistering, cracking, peeling, loss of gloss, and changes in color were checked. Weather resistance was evaluated according to the following criteria. The results are shown in Tables 5-9. (standard) ○: No abnormalities △: Some abnormalities are visible. ×: Deformed

[0145] <Exterior> The test plates prepared using the above-described <Coating Film Preparation Method 2> were left to stand for 48 hours after painting, referring to "7.8 Appearance of the coating film" in JIS K 5551:2018 "Rust-preventive paint for structures". The appearance of the coating film after 48 hours was observed visually. The evaluation was performed visually under diffused daylight to confirm the absence of irregularities, dents, wrinkles, unevenness, cracks, blisters, holes, and peeling. The appearance was evaluated according to the following criteria. The results are shown in Tables 5-9. (standard) ○: No abnormalities △: Some abnormalities are visible. ×: Deformed

[0146] The results in Tables 5-9 show that the multilayer films produced in Examples 1-18 exhibit excellent adhesion and long-term corrosion protection. Furthermore, these multilayer films also possess excellent weather resistance and appearance. Comparative Examples 1, 2, and 5 had poor adhesion due to the excessively low or high elastic modulus of the undercoat film, and in particular, Comparative Examples 2 and 5 failed to achieve long-term corrosion protection. Comparative Example 3 showed controlled elastic modulus of both the undercoat and topcoat films, resulting in a multilayer film with excellent adhesion and long-term corrosion protection; however, the lack of coloring pigments in the topcoat film resulted in poor weather resistance. Comparative Example 4 had poor adhesion and weather resistance due to the excessively high elastic modulus of the topcoat film.

[0147] Table 1

[0148] Table 2

[0149] Table 3

[0150] Table 4

[0151] Table 5

[0152] Table 6

[0153] Table 7

[0154] Table 8

[0155] Table 9

Claims

1. Step (1) involves applying an aqueous coating composition (P) to a substrate to form a first coating film with a dry film thickness of 20 to 300 μm, Step (2) involves applying an aqueous paint composition (Q) to the first coating to form a second coating with a dry film thickness of 10 to 200 μm. A method for forming a multilayer film, including, The aqueous paint composition (P) comprises (A1) an epoxy resin, (B1) an extender pigment, and (B2) a coloring pigment, and (C1) a curing agent that reacts with the epoxy resin. The aqueous paint composition (Q) comprises (A2) acrylic resin and (B2) coloring pigment, The pigment volume concentration (PVC) of the aqueous paint composition (P) is greater than the pigment volume concentration (PVC) of the aqueous paint composition (Q). The elastic modulus (X) of the first coating film is 800 to 2500 N / mm 2 And, The elastic modulus (Y) of the second coating film is 80 to 500 N / mm 2 And, The present invention relates to a method for forming a multilayer film in which the elastic modulus of the coating film is calculated by performing a tensile test on a strip-shaped test piece measuring 50 mm × 10 mm × 20 to 100 μm under the conditions of 23°C and 50% humidity, at a speed of 5 mm / min, and a grip distance of 30 mm, and then calculating the slope (proportionality constant) within the range in which stress and strain are proportional in the stress-strain curve obtained from the said tensile test.

2. The method for forming a multilayer film according to claim 1, characterized in that the curing agent that reacts with the (C1) epoxy resin includes a polyamine resin having a cyclic structure.

3. The method for forming a multilayer film according to claim 1 or 2, wherein the aqueous paint composition (P) contains (B3) a flake-like pigment as (B1) an extender pigment and / or (B2) a coloring pigment.

4. The method for forming a multilayer film according to claim 1 or 2, characterized in that the second coating film has a crosslinked structure.

5. The method for forming a multilayer film according to claim 1 or 2, characterized in that the aqueous coating composition (Q) contains a (C2) carbodiimide curing agent.

6. The method for forming a multilayer film according to claim 1 or 2, characterized in that the (A2) acrylic resin contains silicon.

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