Aqueous coating composition and method for manufacturing coated article

Abstract

To provide an aqueous coating composition which gives a coating film excellent in water resistance.SOLUTION: The aqueous coating composition contains: a main agent (A) containing a hydroxyl group-containing resin (a1) and an aqueous solvent (a2); and a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group. At least one of the main agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups. The content of the silane coupling agent is, for example, 1 pt.mass or more and 10 pts.mass or less based on 100 pts.mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous coating composition and a method for producing a coated article. [Background technology]

[0002] Conventionally, solvent-based paints have been used for painting automobiles because they tend to improve image clarity and finished appearance. In recent years, environmental concerns have grown, and there has been a growing demand for water-based paints instead of solvent-based paints (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-22948 Summary of the Invention [Problem to be solved by the invention]

[0004] However, coating films formed by water-based paints generally have poor water resistance. An object of the present invention is to provide an aqueous coating composition that can provide a coating film with excellent water resistance. Another object of the present invention is to provide a method for producing a coated article having a coating film formed from the coating composition. [Means for solving the problem]

[0005] The present invention provides the following aspects [1] to [8]. [1] a main component (A) containing a hydroxyl group-containing resin (a1) and an aqueous solvent (a2); a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group, An aqueous coating composition, wherein at least one of the main agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups.

[0006] [2] [1] The aqueous coating composition according to the above [1], wherein the content of the silane coupling agent is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).

[0007] [3] An aqueous coating composition used as a primer surfacer, [1] The aqueous coating composition according to the above [1], wherein the content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).

[0008] [4] An aqueous coating composition for forming a clear coating film, [1] The aqueous coating composition according to the above [1], wherein the content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).

[0009] [5] A step (I) of applying an aqueous primer surfacer (X) to an object to be coated to form a base coating film; Step (II) of applying an aqueous colored base coating composition (Y) onto the base coating film to form a colored base coating film; and a step (III) of applying an aqueous clear coating composition (Z) onto the colored base coating film to form a clear coating film, A method for producing a coated article, wherein at least one of the water-based primer surfacer (X) and the water-based clear coating composition (Z) contains a silane coupling agent having one or more epoxy groups.

[0010] [6] The aqueous primer surfacer (X) comprises a first main component (A1) containing a first hydroxyl group-containing resin (a11) and a first aqueous solvent (a21); a first curing agent (B1) containing a first polyisocyanate compound (b11) and a first organic solvent (b21) having no hydroxyl group, the silane coupling agent is contained in at least one of the first main agent (A1) and the first curing agent (B1), [5] The method for producing a coated article according to the above [5], wherein the content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less per 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11).

[0011] [7] The aqueous clear coating composition (Z) comprises a second main component (A2) containing a second hydroxyl group-containing resin (a12) and a second aqueous solvent (a22); a second curing agent (B2) containing a second polyisocyanate compound (b12) and a second organic solvent (b22) having no hydroxyl group, the silane coupling agent is contained in at least one of the second main agent (A2) and the second curing agent (B2), [5] The method for producing a coated article according to [5] above, wherein the content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12).

[0012] [8] The method for producing a coated article according to any one of the above [5] to [7], wherein both the water-based primer surfacer (X) and the water-based clear coating composition (Z) contain the silane coupling agent. [Effects of the Invention]

[0013] The present invention provides an aqueous coating composition that can provide a coating film with excellent water resistance. The present invention also provides a method for producing a coated article having a coating film formed from the aqueous coating composition. DETAILED DESCRIPTION OF THE INVENTION

[0014] The aqueous coating composition according to this embodiment is a two-component type containing a base agent (A) and a curing agent (B). The base agent (A) contains a hydroxyl-containing resin (a1) and an aqueous solvent (a2). The curing agent (B) contains a polyisocyanate compound (b1) and an organic solvent (b2) that does not contain hydroxyl groups. At least one of the base agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups (hereinafter referred to as an epoxy-group-containing silane coupling agent).

[0015] When the base resin (A) and the curing agent (B) are mixed, the hydroxyl-containing resin (a1) contained in the base resin (A) is crosslinked by the polyisocyanate compound (b1), resulting in a cured coating film. At this time, the epoxy-containing silane coupling agent also reacts with at least one of the hydroxyl-containing resin (a1) and the polyisocyanate compound (b1) to form a crosslinked structure. This increases the crosslink density of the cured coating film, resulting in improved water resistance.

[0016] [Water-based paint composition] The aqueous coating composition according to this embodiment is used, for example, as a coating material for forming a base coating film (so-called aqueous primer surfacer), a coating material for forming a colored base coating film (colored base coating composition), and a coating material for forming a clear coating film (aqueous clear coating composition). When forming a multilayer coating film, the aqueous coating composition according to this embodiment is used as the coating material for forming at least one of the layers, thereby improving the water resistance of the entire multilayer coating film.

[0017] The silane coupling agent also improves adhesion between the cured coating film and the substrate. Therefore, the aqueous coating composition is particularly suitable as an aqueous primer surfacer for automobiles. This is because the primer surfacer is applied directly to the substrate. The aqueous coating composition is also suitable for forming various coating films for repairing automotive paintwork. This is because repair coatings require high adhesion to the existing coating film as well as to the substrate.

[0018] When forming a multi-layer coating film, it is preferable to use a water-based primer surfacer containing an epoxy group-containing silane coupling agent in combination with a water-based clear coating composition containing an epoxy group-containing silane coupling agent, as this will further improve water resistance.

[0019] Hereinafter, the aqueous coating composition for forming a base coating film will be referred to as aqueous primer surfacer (X). The main agent (A) contained in the aqueous primer surfacer (X) will be referred to as the first main agent (A1), and the curing agent (B) will be referred to as the first curing agent (B1). The hydroxyl group-containing resin (a1) contained in the first main agent (A1) will be referred to as the first hydroxyl group-containing resin (a11), and the aqueous solvent (a2) will be referred to as the first aqueous solvent (a21). The polyisocyanate compound (b1) contained in the first curing agent (B1) will be referred to as the first polyisocyanate compound (b11), and the organic solvent (b2) will be referred to as the first organic solvent (b21).

[0020] Hereinafter, the aqueous coating composition for forming a clear coating film will be referred to as the aqueous clear coating composition (Z). The main agent (A) contained in the aqueous clear coating composition (Z) will be referred to as the second main agent (A2), and the curing agent (B) will be referred to as the second curing agent (B2). The hydroxyl group-containing resin (a1) contained in the second main agent (A2) will be referred to as the second hydroxyl group-containing resin (a12), and the aqueous solvent (a2) will be referred to as the second aqueous solvent (a22). The polyisocyanate compound (b1) contained in the second curing agent (B2) will be referred to as the second polyisocyanate compound (b12), and the organic solvent (b2) will be referred to as the second organic solvent (b22).

[0021] Hereinafter, the first main agent (A1) and the second main agent (A2) are collectively referred to as the main agent (A). The first curing agent (B1) and the second curing agent (B2) are collectively referred to as the curing agent (B). The first hydroxyl-containing resin (a11) and the second hydroxyl-containing resin (a12) are collectively referred to as the hydroxyl-containing resin (a1). The first aqueous solvent (a21) and the second aqueous solvent (a22) are collectively referred to as the aqueous solvent (a2). The first polyisocyanate compound (b11) and the second polyisocyanate compound (b12) are collectively referred to as the polyisocyanate compound (b1). The first organic solvent (b21) and the second organic solvent (b22) are collectively referred to as the organic solvent (b2).

[0022] The aqueous coating composition is prepared by a method commonly used by those skilled in the art, for example, by mixing the components by a kneading and mixing method using a kneader or a roll, or a dispersion and mixing method using a sand grind mill or a disperser.

[0023] <Epoxy group-containing silane coupling agent> Silane coupling agents usually have both a reactive silyl group and an organic functional group. Epoxy group-containing silane coupling agents have one or more epoxy groups as organic functional groups. Epoxy group-containing silane coupling agents may have two or more epoxy groups.

[0024] The epoxy group is a three-membered ring (oxirane ring) with an ether bond. The epoxy group is highly reactive and reacts with the hydroxyl group-containing resin (a1) and / or the polyisocyanate compound (b1). This increases the crosslink density of the resulting cured coating film.

[0025] The epoxy group is represented, for example, by the following structural formula (1):

[0026] [ka]

[0027] The epoxy group may be alicyclic. An example of the alicyclic epoxy group is an epoxycyclohexyl group represented by the following structural formula (2).

[0028] [ka]

[0029] The epoxy group-containing silane coupling agent may contain other organic functional groups. However, when the epoxy group-containing silane coupling agent is contained in the main component (A), it is desirable that the organic functional group does not contain an isocyanate group. This is because if the hydroxyl group-containing resin (a1) reacts with the epoxy group-containing silane coupling agent before mixing the main component (A) with the curing agent (B), it is difficult to achieve a high crosslink density in the cured coating film. When the epoxy group-containing silane coupling agent is contained in the curing agent (B), it is desirable that the organic functional group does not contain a hydroxyl group or an amino group (including primary, secondary, and tertiary amino groups, and amino groups bonded to epoxy groups). This is because if the polyisocyanate compound (b1) reacts with the epoxy group-containing silane coupling agent before mixing the main component (A) with the curing agent (B), it is difficult to achieve a high crosslink density in the cured coating film. Other desirable organic functional groups include, for example, an acrylamide group, an acryloyl group, a methacryloyl group, an allyl group, a vinyl group, a styryl group, and a mercapto group.

[0030] The reactive silyl group is not particularly limited as long as it generates a silanol group upon hydrolysis. Examples of reactive silyl groups include trialkoxysilyl groups (the alkoxy group preferably contains 1 to 7 carbon atoms) and dialkoxyalkylsilyl groups (the alkoxy group preferably contains 1 to 7 carbon atoms, and the alkyl group preferably contains 1 to 7 carbon atoms). More specific examples include trimethoxysilyl groups, triethoxysilyl groups, tripropoxysilyl groups, tris(2-methoxyethoxy)silyl groups, dimethoxyalkylsilyl groups, diethoxyalkylsilyl groups, dipropoxyalkylsilyl groups, and bis(2-methoxyethoxy)alkylsilyl groups (the alkyl group may be a linear or branched alkyl group having 1 to 7 carbon atoms). The multiple reactive silyl groups may be the same or different. Among these, trialkoxysilyl groups are preferred because they facilitate improved water resistance. Trialkoxysilyl groups having 1 to 3 carbon atoms are more preferred, and triethoxysilyl groups are particularly preferred.

[0031] The epoxy group-containing silane coupling agent is contained in at least one of the main component (A) and the curing agent (B). In particular, the epoxy group-containing silane coupling agent is preferably contained in the curing agent (B) because of its excellent miscibility with the polyisocyanate compound (b1).

[0032] The content of the epoxy group-containing silane coupling agent is preferably 1 part by mass or more, more preferably 1.1 parts by mass or more, and particularly preferably 1.2 parts by mass or more, per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1). When the content of the epoxy group-containing silane coupling agent is within this range, water resistance is more likely to be improved. When the content of the epoxy group-containing silane coupling agent is within this range, storage stability of the agent containing the epoxy group-containing silane coupling agent is more likely to be improved.

[0033] When the aqueous coating composition is an aqueous primer surfacer (X), the content of the epoxy group-containing silane coupling agent is preferably 1 part by mass or more, more preferably 1.1 parts by mass or more, and particularly preferably 1.2 parts by mass or more, per 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11). The content of the epoxy group-containing silane coupling agent is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11).

[0034] When the aqueous coating composition is an aqueous clear coating composition (Z), the content of the epoxy group-containing silane coupling agent is preferably 1.2 parts by mass or more, more preferably 1.3 parts by mass or more, and particularly preferably 2 parts by mass or more, per 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12). The content of the epoxy group-containing silane coupling agent is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and particularly preferably 6 parts by mass or less, per 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12).

[0035] The aqueous coating composition may contain a silane coupling agent other than the epoxy group-containing silane coupling agent. However, from the viewpoint of water resistance, the proportion of the epoxy group-containing silane coupling agent in all silane coupling agents is preferably 80 mass% or more, and more preferably 90 mass% or more. As mentioned above, it is desirable that the other silane coupling agent contained in the main component (A) does not have an isocyanate group. It is desirable that the other silane coupling agent contained in the curing agent (B) does not have a hydroxyl group or an amino group (including primary, secondary, and tertiary amino groups, and amino groups bonded to epoxy groups).

[0036] <Main ingredient (A)> The main component (A) contains a hydroxyl group-containing resin (a1) and an aqueous solvent (a2). The solid content of the main component (A) is not particularly limited. The solid content concentration of the main component (A) is, for example, 30% by mass or more and 60% by mass or less.

[0037] (Hydroxyl group-containing resin (a1)) The hydroxyl-containing resin (a1) is in the form of an emulsion dispersed in an aqueous solvent (a2). The particle size of the hydroxyl-containing resin (a1) in the main component (A) is not particularly limited. From the viewpoints of ease of viscosity control and the appearance of the resulting coating film, the average particle size of the hydroxyl-containing resin (a1) is preferably 0.01 μm or more and 1.0 μm or less, more preferably 0.05 μm or more and 0.5 μm or less. The average particle size is the 50% diameter (median diameter, D50) in the volume-based particle size distribution measured by dynamic light scattering.

[0038] The solid content concentration of the hydroxyl-containing resin (a1) is, for example, 15% by mass or more and 95% by mass or less of the total solid content contained in the main component (A). When the solid content concentration of the hydroxyl-containing resin (a1) is within the above range, the strength of the resulting coating film is likely to be increased. The solid content concentration of the hydroxyl-containing resin (a1) may be 20% by mass or more, or may be 25% by mass or more, of the total solid content contained in the main component (A). The solid content concentration of the hydroxyl-containing resin (a1) may be 85% by mass or less, or may be 80% by mass or less of the total solid content contained in the main component (A).

[0039] The hydroxyl value of the hydroxyl-containing resin (a1) is preferably from 5 mgKOH / g to 200 mgKOH / g, more preferably from 50 mgKOH / g to 150 mgKOH / g. When the hydroxyl value of the hydroxyl-containing resin (a1) is in the above range, the strength of the resulting coating film is sufficiently high and water resistance is also likely to be improved.

[0040] The acid value of the hydroxyl-containing resin (a1) is not particularly limited and may be, for example, from 5 mgKOH / g to 100 mgKOH / g, or from 10 mgKOH / g to 50 mgKOH / g. When the acid value of the hydroxyl-containing resin (a1) is within the above range, the water dispersibility of the hydroxyl-containing resin (a1) is improved, and the water resistance of the resulting coating film is also likely to be improved.

[0041] The number average molecular weight of the hydroxyl group-containing resin (a1) is not particularly limited and may be, for example, from 1,000 to 100,000, from 2,000 to 50,000, or from 3,000 to 10,000. When the number average molecular weight of the hydroxyl group-containing resin (a1) is within the above range, an excessive increase in viscosity of the aqueous coating composition is suppressed, and the appearance of the resulting coating film is improved, and its strength is also likely to be sufficiently high.

[0042] The hydroxyl value and acid value are both based on the solid content and can be measured in accordance with JIS K 0070. The number average molecular weight is a value calculated as a styrene homopolymer, measured using gel permeation chromatography.

[0043] The hydroxyl group-containing resin (a1) is not particularly limited as long as it has one or more, preferably two or more, hydroxyl groups. Examples of the hydroxyl group-containing resin (a1) include acrylic polyols, polyester polyols, polyether polyols, polyurethane polyols, and polycarbonate polyols. Among these, acrylic polyols are preferred because they tend to improve the physical properties of the resulting coating film, such as appearance, weather resistance, and chemical resistance.

[0044] The hydroxyl group-containing resin (a1) can be obtained, for example, by emulsion polymerization of one or more raw material monomers. The emulsion polymerization is carried out by a method commonly used by those skilled in the art. Specifically, an emulsifier is mixed with an aqueous medium, optionally containing an organic solvent such as alcohol, and the resulting mixture is heated and stirred while the raw material monomers and polymerization initiator are added dropwise. Alternatively, an emulsion mixture in which the raw material monomers, emulsifier, and water are previously emulsified may be added dropwise to the aqueous medium. The aqueous medium may be the same as or different from the aqueous solvent (a2).

[0045] The acrylic polyol emulsion can be obtained, for example, by emulsion polymerization of a raw material monomer mixture containing a (meth)acrylic acid alkyl ester monomer, an acid group-containing ethylenically unsaturated monomer, a hydroxyl group-containing ethylenically unsaturated monomer, and a styrene-based monomer.

[0046] (aqueous solvent (a2)) Examples of aqueous solvents include various types of water such as pure water, ion-exchanged water, tap water, and industrial water. The main component (A) may contain an organic solvent in addition to the aqueous solvent. Examples of organic solvents include diethylene glycol dibutyl ether (dibutyl diglycol), dipropylene glycol dimethyl ether, butyl acetate, ethyl diglycol acetate, propylene glycol methyl ether acetate, n-butyl alcohol, methoxypropanol, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, toluene, xylene, methyl isobutyl ketone, and methyl ethyl ketone.

[0047] (others) The main component (A) may optionally contain a resin that does not contain hydroxyl groups. In addition to the hydroxyl-containing resin (a1) and the aqueous solvent (a2), the main component (A) may optionally contain various additives. Examples of additives include dispersants, antifoaming agents, UV absorbers, hindered amine light stabilizers, antioxidants, viscosity modifiers, surface conditioners, film-forming aids, rust inhibitors, and thickeners. In particular, viscosity modifiers and / or surface conditioners are preferably used, as these further improve the appearance of the resulting coating film.

[0048] Examples of viscosity modifiers include crosslinked resin particles (polymer compounds having a crosslinked structure within the molecule), inorganic viscosity modifiers, cellulose derivatives, and urethane association viscosity modifiers. These may be used alone or in combination of two or more. The amount of viscosity modifier may be, for example, 0.1% by mass or more and 50% by mass or less, or 0.5% by mass or more and 30% by mass or less, of the solid content of the hydroxyl group-containing resin (a1).

[0049] Examples of surface conditioners include silicone-based, acrylic-based, vinyl-based, and fluorine-based surface conditioners. These may be used alone or in combination of two or more. The amount of the surface conditioner may be, for example, 0.1% by mass or more and 10% by mass or less, or 0.2% by mass or more and 8% by mass or less, based on the solid content of the hydroxyl group-containing resin (a1).

[0050] (Method for preparing main agent (A)) The main component (A) can be prepared by mixing the above components by a method known to those skilled in the art, including the same mixing methods as those used to prepare aqueous coating compositions.

[0051] <Curing agent (B)> The curing agent (B) contains a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group. The solid content of the curing agent (B) is not particularly limited. The solid content concentration of the curing agent (B) is, for example, 20% by mass or more and 70% by mass or less.

[0052] (Polyisocyanate compound (b1)) The polyisocyanate compound (b1) is not particularly limited as long as it has an average of two or more isocyanate groups per molecule. Examples of the polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate, pentamethylene diisocyanate, tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate); aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate; and modified products thereof (e.g., urethane compounds, carbodiimides, uretdione, uretonimine, biuret compounds, isocyanurates, etc.).

[0053] The content of the polyisocyanate compound (b1) may be, for example, 20% by mass or more, or 30% by mass or more, of the total solid content of the curing agent (B).

[0054] (organic solvent (b2)) The organic solvent (b2) is not particularly limited as long as it does not have a hydroxyl group. Examples of the organic solvent (b2) include ethylene glycol dimethyl ether (DMM), ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol divinyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol divinyl ether, tetraethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol diisopropyl ether, propylene glycol di-n-butyl ether, propylene glycol diisobutyl ether, propylene glycol diallyl ether, propylene glycol diphenyl ether, dipropylene glycol dimethyl ether (DPDM), dipropylene glycol diethyl ether, and dipropylene glycol di-n-butyl ether. glycol ether-based organic solvents such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ...Examples of suitable organic solvents include ketone-based organic solvents such as acetone, methyl ethyl ketone, methyl amyl ketone, and methyl isobutyl ketone; and ester-based organic solvents such as ethyl acetate, butyl acetate, isobutyl acetate, methyl benzoate, ethyl ethoxypropionate (EEP), ethyl propionate, and methyl propionate. These may be used alone or in combination of two or more.

[0055] (others) The curing agent (B) may contain a curing agent other than the polyisocyanate compound (b1). The content of the other curing agent is, for example, 10 mass % or less of the total solid content of all the curing agents.

[0056] (Method for preparing curing agent (B)) The curing agent (B) can be prepared by mixing the above components by a method known to those skilled in the art, including the same mixing method as that used to prepare the aqueous coating composition.

[0057] <Dilution component (C)> The aqueous coating composition may further contain a diluent component (C). Examples of the diluent component (C) include the same components as the aqueous solvent (a2). The diluent component (C) may be the same as or different from the aqueous solvent (a2).

[0058] The amount of diluent component (C) mixed is appropriately determined taking into consideration the viscosity of the aqueous coating composition, the coating method, etc. The amount of diluent component (C) mixed is, for example, 10 to 70 parts by mass per 100 parts by mass of the solid content of the hydroxyl group-containing resin (a1).

[0059] <Pigment (D)> The aqueous primer surfacer (X) may further contain a pigment (D). The content of the pigment (D) may be, for example, 100 parts by mass or more and 300 parts by mass or less, and 120 parts by mass or more and 200 parts by mass or less, relative to 100 parts by mass of the resin solid content contained in the main agent (A1) of the aqueous primer surfacer (X).

[0060] The pigment (D) is not particularly limited, and examples of the pigment (D) include color pigments such as titanium dioxide, carbon black, iron oxide, and copper phthalocyanine blue; luster pigments such as aluminum flakes and mica flakes; extender pigments such as calcium carbonate, clay, talc, barium oxide, and silica; and rust-preventive pigments such as aluminum tripolyphosphate, aluminum phosphomolybdate, and zinc phosphate.

[0061] In particular, from the viewpoint of the polishability and film-forming properties of the base coating film, it is preferable that at least a body pigment is contained. The proportion of the body pigment may be, for example, 30 to 100 mass % or 40 to 70 mass % relative to 100 mass parts of the total of all pigments.

[0062] [Manufacturing method for coated articles] The coated article is produced by a method comprising the steps of: (I) applying an aqueous primer surfacer (X) to an article to be coated to form a base coating film; (II) applying an aqueous colored base coating composition (Y) on the base coating film to form a colored base coating film; and (III) applying an aqueous clear coating composition (Z) on the colored base coating film to form a clear coating film.

[0063] At least one of the aqueous primer surfacer (X) and the aqueous clear coating composition (Z) contains a silane coupling agent having one or more epoxy groups. This improves the water resistance of the entire multi-layer coating film. In particular, it is preferable that both the aqueous primer surfacer (X) and the aqueous clear coating composition (Z) contain an epoxy group-containing silane coupling agent.

[0064] (I) Process of forming a base coating film In this step, the water-based primer surfacer (X) is applied to the object to be coated to form a base coating film.

[0065] (Method for preparing water-based primer surfacer (X)) A first main component (A1) is prepared by mixing a first hydroxyl-containing resin (a11) and a first aqueous solvent (a21). Separately, a first curing agent (B1) is prepared by mixing a first polyisocyanate compound (b11) and a first organic solvent (b21) that does not have a hydroxyl group.

[0066] The resulting first main component (A1) and first curing agent (B1) are mixed to prepare the aqueous primer surfacer (X). The first main component (A1) and first curing agent (B1) are mixed immediately before coating. After being mixed, the first main component (A1) and first curing agent (B1) may be supplied to a coating device or may be mixed within the coating device. The mixing method is as described above.

[0067] The first main agent (A1) and the first curing agent (B1) are mixed so that the hydroxyl group equivalent of the first hydroxyl group-containing resin (a11) and the isocyanate group equivalent of the first polyisocyanate compound (b11) are in the range of isocyanate group equivalent / hydroxyl group equivalent = 1 / 0.5 to 1 / 2.

[0068] When the aqueous primer surfacer (X) contains an epoxy group-containing silane coupling agent, the epoxy group-containing silane coupling agent is added to at least one of the first main component (A1) and the first curing agent (B1). The silane coupling agent is added in an amount of 1 to 8 parts by mass per 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11).

[0069] (Painting method) The prepared aqueous primer surfacer (X) is applied to the substrate. The amount of the aqueous primer surfacer (X) to be applied is not particularly limited and is appropriately determined depending on the performance required of the coating film. The aqueous primer surfacer (X) is applied, for example, so that the thickness of the base coating film after curing is 20 μm or more and 100 μm or less.

[0070] The method for applying the water-based primer surfacer (X) is not particularly limited. Examples of application methods include air spray application, airless spray application, rotary atomization application, and curtain coating application. These methods may be combined with electrostatic application. In the case of repairs, air spray application is preferred because it is easy to apply localized coating. Application may be performed multiple times.

[0071] After the water-based primer surfacer (X) is applied, it is heated to cure the coating. The curing conditions are appropriately set depending on the amount applied and the composition. Curing is carried out, for example, at a temperature of 40°C or higher and 70°C or lower for about 30 to 60 minutes. After curing, the base coating is usually polished and degreased. Polishing is carried out using sandpaper or the like.

[0072] When repairing, before applying the water-based primer surfacer (X), the target area and its surrounding area are sanded as necessary, and any irregularities are filled in with putty. The area is then sanded again.

[0073] (subject to be coated) The shape of the substrate is not particularly limited. The substrate may be flat or may have a three-dimensional shape. The material of the substrate is also not particularly limited. Examples of the material of the substrate include metal, resin, and glass. Examples of metal include iron, copper, aluminum, tin, zinc, and alloys thereof.

[0074] The metal substrate may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After the surface treatment, the metal substrate may be further coated with an electrodeposition paint. The electrodeposition paint may be either a cationic type or an anionic type.

[0075] Examples of resins include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. It is preferable that a resin substrate be degreased.

[0076] Specific examples of the object to be coated include automobile bodies such as passenger cars, trucks, motorcycles, and buses, or parts thereof.

[0077] (II) Step of forming a colored base coating In this step, the aqueous colored base coating composition (Y) is applied onto the base coating film to form a colored base coating film. The application of the aqueous colored base coating composition (Y) may be carried out multiple times.

[0078] (Method for preparing aqueous colored base coating composition (Y)) The aqueous colored base coating composition (Y) may be a curing type or a lacquer type. The aqueous colored base coating composition (Y) further contains a pigment. Examples of the pigment include the color pigments and / or luster pigments exemplified as pigment (D).

[0079] The curable aqueous colored base coating composition (Y) contains a curable resin (for example, the above-mentioned main component (A)) and a curing agent (for example, the above-mentioned curing agent (B)), and forms a cured coating film by heating. The curable aqueous colored base coating composition (Y) may further contain a silane coupling agent (for example, an epoxy group-containing silane coupling agent).

[0080] The lacquer-type aqueous colored base coating composition (Y) contains water, an organic solvent, and a binder resin dissolved or dispersed therein, and forms a cured coating film by evaporation of the water and the organic solvent. The concentration of the binder resin is not particularly limited and is set appropriately depending on the composition and application.

[0081] The binder resin is not particularly limited. Examples of binder resins include acrylic resins, aminoalkyd resins, alkyd resins, amino resins, isocyanate resins, epoxy resins, vinyl chloride resins, cashew resins, silicone resins, styrene resins, styrenated alkyd resins, cellulose-based resins (e.g., cellulose nitrate), urea resins, vinyl resins, phenolic resins, phthalic acid resins, fluororesins, polyester resins, unsaturated polyester resins, and modified resins thereof (e.g., rosin-modified, phenol-modified, epoxy resin-modified, styrene-modified, acrylic-modified, and urethane-modified). These may be used alone or in combination of two or more. Examples of organic solvents include naphtha, xylene, toluene, and acetone.

[0082] (Painting method) The method for applying the aqueous colored base coating composition (Y) is not particularly limited, and may be the same as that for the aqueous primer surfacer (X). The amount of the aqueous colored base coating composition (Y) to be applied is not particularly limited, and it is applied, for example, so that the thickness of the colored base coating film after curing is 10 μm or more and 100 μm or less. After application, the coating film is cured. The curing conditions are appropriately set depending on the composition of the aqueous colored base coating composition (Y).

[0083] (III) Process for forming a clear coating In this step, the aqueous clear coating composition (Z) is applied onto the colored base coating film to form a clear coating film.

[0084] (Method for preparing water-based clear coating composition (Z)) A second main agent (A2) is prepared by mixing a second hydroxyl-containing resin (a12) and a second aqueous solvent (a22). Separately, a second curing agent (B2) is prepared by mixing a second polyisocyanate compound (b12) and a second organic solvent (b22) that does not have a hydroxyl group.

[0085] The obtained second main agent (A2) and second curing agent (B2) are mixed to prepare an aqueous clear coating composition (Z). The second main agent (A2) and second curing agent (B2) are mixed immediately before coating. After being mixed, the second main agent (A2) and second curing agent (B2) may be supplied to a coating device or may be mixed within the coating device. The mixing method is as described above.

[0086] The second main agent (A2) and the second curing agent (B2) are mixed so that the hydroxyl group equivalent of the second hydroxyl group-containing resin (a12) and the isocyanate group equivalent of the second polyisocyanate compound (b12) are isocyanate group equivalent / hydroxyl group equivalent = 1 / 0.5 to 1 / 1.5.

[0087] When the aqueous clear coating composition (Z) contains an epoxy group-containing silane coupling agent, the epoxy group-containing silane coupling agent is added to at least one of the second main component (A2) and the second curing agent (B2). The silane coupling agent is added in an amount of 1.2 to 10 parts by mass per 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12).

[0088] (Painting method) The prepared aqueous clear coating composition (Z) is applied onto the aqueous colored base coating film. The amount of the aqueous clear coating composition (Z) to be applied is not particularly limited and is appropriately determined depending on the performance required of the coating film. The aqueous clear coating composition (Z) is applied, for example, so that the thickness of the clear coating film after curing is 20 μm or more and 100 μm or less.

[0089] The method for applying the aqueous clear coating composition (Z) is not particularly limited, and examples thereof include the same methods as those for the aqueous primer surfacer (X). Among these, air spray coating is preferred. Coating may be performed multiple times.

[0090] After the aqueous clear coating composition (Z) has been applied, the coating is cured by heating, for example, at a temperature of 40° C. to 100° C. for about 15 to 60 minutes. In this way, a coated article is obtained which comprises the primer coating, the colored base coating, and the clear coating in this order. [Example]

[0091] Hereinafter, the present embodiment will be described in more detail using examples, but the present embodiment is not limited to these examples. In the examples, "parts" and "%" are by mass unless otherwise specified.

[0092] [Preparation example] Based on the formulations shown in Table 1, curing agents HA to HE containing epoxy group (Ep group)-containing silane coupling agents, comparative curing agent Ha containing no epoxy group-containing silane coupling agent, and comparative curing agent Hb containing a silane coupling agent with an amino group instead of an epoxy group were prepared. The storage stability of the obtained curing agents was evaluated by the following method. The evaluation results are shown in Table 1.

[0093] The components shown in Table 1 are as follows: Polyisocyanate compound A: Burnock DNW-5500 (manufactured by DIC Corporation) Polyisocyanate compound B: Bayhydur Ultra 304 (manufactured by Sumika Covestro) Silane coupling agent A: 3-glycidoxypropyltrimethoxysilane Silane coupling agent B: 3-glycidoxypropyltriethoxysilane Silane coupling agent C: N-phenyl-3-aminopropyltrimethoxysilane

[0094] (1) Evaluation of storage stability (1-1) Viscosity The liquid temperature of the sample (curing agent) was adjusted to 23°C. Next, a viscosity cup NK-2 manufactured by Anest Iwata Corporation was immersed in the sample and pulled up. The time from the moment of pulling up until the entire sample was discharged was measured. This was designated as the initial value T0 (seconds).

[0095] Next, the sample was placed in a metal container and sealed. This metal container was stored in a thermostatic chamber at 50°C for 30 days. After that, the metal container was removed from the thermostatic chamber, and the liquid temperature was adjusted to 23°C. Next, the time (T (seconds)) from when the sample was pulled up to when it was discharged was measured in the same manner as above. T-T0 was calculated and evaluated according to the following criteria.

[0096] Best: T-T0 is within 1 second Good: T-T0 is over 1 second and less than 5 seconds Possible: T-T0 is more than 5 seconds and less than 10 seconds Defective: T-T0 longer than 10 seconds

[0097] (1-2) Hue The sample was placed in a metal container and sealed. This metal container was stored in a temperature-controlled room at 50°C for 30 days. After that, the metal container was removed from the temperature-controlled room, and the sample was placed in a test tube, carefully avoiding the introduction of air bubbles, and then sealed. The sample and the Gardner color scale standard solution were placed side by side and observed through the side under diffused daylight for evaluation. If the color of the sample matched, the color score of the Gardner color scale standard solution was recorded. If the color of the sample was between two Gardner color scale standard solutions, the Gardner color score of the solution that was closest to the sample was recorded. The evaluation criteria are as follows:

[0098] Best: 1 Gardner color Acceptable: Gardner color count is 2 to 3 Not allowed: Gardner color count 4 or more

[0099] [Table 1]

[0100] Although curing agents HA to HE contain an epoxy group-containing silane coupling agent, their storage stability is as good as that of curing agent Ha, which does not contain a silane coupling agent. On the other hand, comparative curing agent Hb, which contains a silane coupling agent with an amino group instead of an epoxy group, has poor storage stability.

[0101] In the above preparation examples, various silane coupling agents were added to the curing agent (B) and evaluated, but even when a silane coupling agent is added to the main component (A), it is believed that the effect of the epoxy group-containing silane coupling agent on storage stability is small.

[0102] [Example 1] A water-based primer surfacer (X), a water-based colored base coating composition (Y) and a water-based clear coating composition (Z) were prepared as follows, and coated articles were produced.

[0103] (1) Preparation of water-based primer surfacer (X) Nax E-CUBE WB Plaster Vita Gray (manufactured by Nippon Paint Co., Ltd., solids content approximately 56%) was prepared as the first main agent (A1) containing pigment (D). The first main agent (A1) contained an acrylic polyol in emulsion form as the hydroxyl group-containing resin (a11) and pure water as the aqueous solvent (a21). The solids concentration of the hydroxyl group-containing resin (a11) was 24.4% of the total solids contained in the first main agent (A1). As the first curing agent (B1), the curing agent HA prepared above was prepared. As the diluent component (C), purified water was prepared.

[0104] A primer surfacer was prepared by mixing 100 parts of the first main component (A1), 12.5 parts of the curing agent HA, and an appropriate amount of the diluent (C) using a disper. The content of the silane coupling agent was 1.18 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a11) and the polyisocyanate compound (b11).

[0105] (2) Preparation of aqueous colored base coating composition (Y) A lacquer-type base coat paint was prepared by mixing 100 parts of nax E-CUBE WB412 Silent Black (manufactured by Nippon Paint Co., Ltd., solids content approximately 22%), 50 parts of nax E-CUBE WB 911 S-binder (auxiliary agent, manufactured by Nippon Paint Co., Ltd., solids content approximately 26%), and 45 parts of nax E-CUBE WB R20 standard thinner (diluting component, manufactured by Nippon Paint Co., Ltd.).

[0106] (3) Preparation of Water-Based Clear Coating Composition (Z) A mixture of nax E-CUBE WB (2:1) NN Clear (manufactured by Nippon Paint Co., Ltd., solids concentration approximately 38%) and pure water (aqueous solvent (a22)) was prepared as the second main component (A2). The hydroxyl-containing resin (a12) was present in the mixture in the form of an emulsion. The solids concentration of the hydroxyl-containing resin (a12) was 91.5% of the total solids contained in the second main component (A2).

[0107] As the second curing agent (B2), the curing agent HA prepared above was prepared. As the diluent component (C), purified water was prepared.

[0108] 100 parts of the second main component (A2), 50 parts of the curing agent HA, and an appropriate amount of the dilution component (C) were mixed using a disper to prepare an aqueous clear coating composition (Z). The content of the silane coupling agent was 1.35 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a12) and the polyisocyanate compound (b12).

[0109] (III) Preparation of painted articles (III-1) Formation of the base coating A 60 cm x 40 cm steel plate (substrate) was coated with the water-based primer surfacer (X) using an air spray gun and then air-dried until the paint no longer adhered to the surface when touched with a finger. This coating and drying process was repeated two more times. The steel plate was then heated in an oven set at 60°C for 30 minutes to form a base coating film (cured film thickness: 45 μm). The surface of the resulting coating film was then polished. Finally, the surface of the coating film was degreased.

[0110] (III-2) Formation of water-based base coating The aqueous colored base coating composition (Y) was applied to a substrate having a base coating film using an air spray gun, and air-dried until the paint no longer adhered to the surface when touched with a finger. This application and drying process was repeated two more times to form an aqueous colored base coating film (cured film thickness: 20 μm).

[0111] (III-3) Formation of clear coating film The aqueous clear coating composition (Z) was applied three times using an air spray gun to a substrate having a primer coating and a colored base coating. Each coating was applied with a one-minute interval. The substrate was then left to stand for 15 minutes in an environment with a temperature of 23±2°C and a humidity of 50±2 RH%. The substrate was then heated in an oven set to 70°C for 20 minutes to form a clear coating (cured film thickness: 50 μm).

[0112] [Examples 2 to 8, Comparative Examples 1 and 2] Aqueous primer surfacer (X) and aqueous clear coating composition (Z) were prepared and coated articles were produced in the same manner as in Example 1, except that the types of the first curing agent (B1) and the second curing agent (B2) were changed as shown in Table 2.

[0113] [Evaluation method] The coated articles were evaluated by the following methods. The evaluation results are shown in Table 2. The content of the silane coupling agent in Table 2 is the amount blended per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a11) and the polyisocyanate compound (b11). (2) Coating film performance (2-1) Adhesion The cured clear coating film was cut with an NT cutter (manufactured by NT Corporation) to create 100 grids (11 vertical and 11 horizontal cuts, spaced 2 mm apart) reaching down to the steel plate. Tape (Nichiban Corporation, Cellotape (registered trademark), 24 mm wide) was applied to cover all of the grids and firmly adhered from above with a fingernail or similar. The tape was then peeled off while being pulled so that the angle between the tape and the coating film was approximately 45°. The coating film after tape peeling was evaluated visually. The evaluation criteria are as follows:

[0114] 10 points: Each cut is small and smooth on both sides, and there is no peeling at the intersections of the cuts or within the squares. 8 points: There is slight peeling at the intersections of the cuts, but no peeling is observed within the squares, and the peeling area is less than 5% of the total square area. 6 points: Peeling occurs within the squares and at the intersections of the cuts, and the peeling area is between 5% and 15% of the total square area 4 points: The peeling width within the square is large, and the peeling area is between 15% and 35% of the total square area 2 points: The peeling width within the square is wider, and the peeling area is between 35% and 65% of the total square area 0 points: The peeling area is 65% or more of the total square area

[0115] (2-2) Water resistance 1 (evaluation of adhesion after water immersion test) A thermostatic water bath with a circulating function was set to 40°C and filled with deionized water. The coated article was immersed about 3 / 4 of the way therein. After immersion for 240 hours, the coated article was removed and the water droplets were lightly wiped off. After removal, the coated article was left at room temperature (23°C) for 24 hours and evaluated in the same manner as in the adhesion evaluation (2-1) above.

[0116] (2-3) Water resistance 2 (blister evaluation after water immersion test) A thermostatic water bath with a circulating function was set to 40°C and filled with deionized water. The coated article was immersed about 3 / 4 of the way in this. After immersion for 240 hours, the coated article was removed and the water droplets were lightly wiped off. After removal, the coated article was left at room temperature (23°C) for 1 hour, and the coating film was visually evaluated. The evaluation criteria are as follows: Best: No abnormalities Good: Very small blisters have occurred, but this does not pose a problem for practical use. Acceptable: Blisters of 1mm or more have appeared in some areas Poor: Blisters of 1 mm or more have appeared all over the product

[0117] [Table 2] [Industrial Applicability]

[0118] The present invention provides an aqueous coating composition that can produce a coating film with excellent water resistance. Therefore, the aqueous coating composition is suitable for painting automobiles, particularly for painting automobile repairs.

Claims

1. a main component (A) containing a hydroxyl group-containing resin (a1) and an aqueous solvent (a2); a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group, At least one of the main agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups.

2. 2. The aqueous coating composition according to claim 1, wherein the content of the silane coupling agent is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).

3. An aqueous coating composition used as a primer surfacer, 2. The aqueous coating composition according to claim 1, wherein the content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).

4. An aqueous coating composition for forming a clear coating film, 2. The aqueous coating composition according to claim 1, wherein the content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).

5. A step (I) of applying an aqueous primer surfacer (X) to an object to be coated to form a base coating film; Step (II) of applying an aqueous colored base coating composition (Y) onto the base coating film to form a colored base coating film; and a step (III) of applying an aqueous clear coating composition (Z) onto the colored base coating film to form a clear coating film, A method for producing a coated article, wherein at least one of the water-based primer surfacer (X) and the water-based clear coating composition (Z) contains a silane coupling agent having one or more epoxy groups.

6. The aqueous primer surfacer (X) comprises a first main component (A1) containing a first hydroxyl group-containing resin (a11) and a first aqueous solvent (a21); a first curing agent (B1) containing a first polyisocyanate compound (b11) and a first organic solvent (b21) having no hydroxyl group, the silane coupling agent is contained in at least one of the first main agent (A1) and the first curing agent (B1), 6. The method for producing a coated article according to claim 5, wherein the content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less per 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11).

7. The aqueous clear coating composition (Z) comprises a second main component (A2) containing a second hydroxyl group-containing resin (a12) and a second aqueous solvent (a22); a second curing agent (B2) containing a second polyisocyanate compound (b12) and a second organic solvent (b22) having no hydroxyl group, the silane coupling agent is contained in at least one of the second main agent (A2) and the second curing agent (B2), 6. The method for producing a coated article according to claim 5, wherein the content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12).

8. The method for producing a coated article according to any one of claims 5 to 7, wherein the water-based primer surfacer (X) and the water-based clear coating composition (Z) both contain the silane coupling agent.

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