Method for manufacturing aqueous paint compositions and coated articles

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

[0005]

[0001] The present invention relates to an aqueous paint composition and a method for manufacturing a painted article.

Background Art

[0002] Conventionally, solvent-based paints have been used for automobile painting because they are easy to improve the distinctness of image and finish appearance. In recent years, with the increasing concern for the environment, the demand for aqueous paints has been increasing instead of solvent-based paints. (For example, Patent Document 1)

Prior Art Document

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

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

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

[0009] [5] Step (I) involves applying a water-based primer surfacer (X) to the object to be coated to form a base coating film, Step (II) involves applying a water-based colored base coating composition (Y) onto the aforementioned base coating to form a colored base coating, The process includes (III) applying an aqueous clear coating composition (Z) onto the colored base coating to form a clear coating, A method for producing a painted article, wherein 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.

[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) comprising a first polyisocyanate compound (b11) and a first organic solvent (b21) that does not have a hydroxyl group, The silane coupling agent is contained in at least one of the first main component (A1) and the first curing agent (B1), The method for producing a coated article according to [5] above, wherein the content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less with respect to 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) comprising a second polyisocyanate compound (b12) and a second organic solvent (b22) that does not have a hydroxyl group, The silane coupling agent is contained in at least one of the second main component (A2) and the second curing agent (B2), 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 with respect to 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] A method for manufacturing a painted article according to any one of the above [5] to [7], wherein both the aqueous primer surfacer (X) and the aqueous clear coating composition (Z) contain the silane coupling agent. [Effects of the Invention]

[0013] The present invention provides an aqueous coating composition that yields a coating film with excellent water resistance. The present invention also provides a method for manufacturing a coated article having a coating film formed by the above aqueous coating composition. [Modes for carrying out the invention]

[0014] The aqueous coating composition according to this embodiment is a two-component type containing a main agent (A) and a curing agent (B). The main agent (A) contains a hydroxyl group-containing resin (a1) and an aqueous solvent (a2). The curing agent (B) contains 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 (hereinafter referred to as an epoxy group-containing silane coupling agent).

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

[0016] [Aqueous coating composition] The aqueous coating composition according to this embodiment is used, for example, as a coating for forming an undercoat film (so-called aqueous primer surfacer), a coating for forming a colored base film (colored base coating composition), and a coating for forming a clear film (aqueous clear coating composition). When forming a multilayer coating film, by using the aqueous coating composition according to this embodiment as a coating for forming at least one of the layers, the water resistance of the entire multilayer coating film is improved.

[0017] The silane coupling agent also improves the adhesion between the cured coating film and the object to be coated. Therefore, the aqueous coating composition is particularly suitable as an aqueous primer surfacer for automobiles. This is because the primer surfacer is directly applied to the object to be coated. The aqueous coating composition is also suitable for forming various coating films for repairing automobile coatings. This is because the coating film for repair requires high adhesion to the existing coating film in addition to the object to be coated.

[0018] In order to further improve water resistance, when forming a multi-layer coating, it is preferable to use in combination an aqueous primer surfacer containing an epoxy group-containing silane coupling agent and an aqueous clear coating composition containing an epoxy group-containing silane coupling agent.

[0019] Hereinafter, the aqueous paint composition for forming a base coat film will be referred to as aqueous primer surfacer (X). The main component (A) contained in aqueous primer surfacer (X) will be referred to as the first main component (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 component (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 component (A) contained in the aqueous clear coating composition (Z) will be referred to as the second main component (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 component (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 component (A1) and the second main component (A2) will be collectively referred to as main component (A). The first curing agent (B1) and the second curing agent (B2) will be collectively referred to as curing agent (B). The first hydroxyl group-containing resin (a11) and the second hydroxyl group-containing resin (a12) will be collectively referred to as hydroxyl group-containing resin (a1). The first aqueous solvent (a21) and the second aqueous solvent (a22) will be collectively referred to as aqueous solvent (a2). The first polyisocyanate compound (b11) and the second polyisocyanate compound (b12) will be collectively referred to as polyisocyanate compound (b1). The first organic solvent (b21) and the second organic solvent (b22) will be collectively referred to as organic solvent (b2).

[0022] Water-based paint compositions are prepared using methods commonly used by those skilled in the art. For example, water-based paint compositions are prepared by mixing the components using kneading methods with kneaders or rolls, or by dispersion mixing methods with sand grind mills or dispersers.

[0023] <Epoxy group-containing silane coupling agent> Silane coupling agents typically contain both reactive silyl groups and organic functional groups. Epoxy group-containing silane coupling agents have one or more epoxy groups as organic functional groups. Epoxy group-containing silane coupling agents may also contain 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 hydroxyl group-containing resins (a1) and / or polyisocyanate compounds (b1). As a result, the crosslinking density of the resulting cured coating film increases.

[0025] An epoxy group can be represented, for example, by the following structural formula (1).

[0026] [ka]

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

[0028] [ka]

[0029] The epoxy group-containing silane coupling agent may also contain other organic functional groups. However, if the epoxy group-containing silane coupling agent is included in the main component (A), it is desirable that isocyanate groups are not included as organic functional groups. This is because if the hydroxyl group-containing resin (a1) and the epoxy group-containing silane coupling agent react before the main component (A) and the curing agent (B) are mixed, it will be difficult to achieve a high crosslink density in the cured coating film. If the epoxy group-containing silane coupling agent is included in the curing agent (B), it is desirable that hydroxyl groups and amino groups (including primary, secondary, and tertiary amino groups, and amino groups to which epoxy groups are attached) are not included as organic functional groups. This is because if the polyisocyanate compound (b1) and the epoxy group-containing silane coupling agent react before the main component (A) and the curing agent (B) are mixed, it will be difficult to achieve a high crosslink density in the cured coating film. Other desirable organic functional groups include, for example, acrylamide, acryloyl, methacryloyl, allyl, vinyl, styryl, and mercapto groups.

[0030] The reactive silyl group is not particularly limited as long as it generates a silanol group by hydrolysis. Examples of reactive silyl groups include trialkoxysilyl groups (preferably with 1 to 7 carbon atoms in the alkoxy group) and dialkoxyalkylsilyl groups (preferably with 1 to 7 carbon atoms in the alkoxy group and 1 to 7 carbon atoms in the alkyl group). More specifically, 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 with 1 to 7 carbon atoms). The multiple reactive silyl groups may be of the same type or different types. Among these, trialkoxysilyl groups are preferred because they are more easily found to improve water resistance, trialkoxysilyl groups with 1 to 3 carbon atoms in the alkoxy group are more preferred, and triethoxysilyl groups are particularly preferred.

[0031] The epoxy group-containing silane coupling agent is included 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 included 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, based on 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 tends to improve. Alternatively, 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, based on 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, the storage stability of the agent containing the epoxy group-containing silane coupling agent tends to improve.

[0033] When the aqueous paint 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, based on 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, based on 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, based on 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, based on 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 paint composition may contain silane coupling agents other than epoxy group-containing silane coupling agents. However, from the viewpoint of water resistance, the proportion of epoxy group-containing silane coupling agents to the total silane coupling agents is preferably 80% by mass or more, and preferably 90% by mass or more. As described above, it is desirable that the other silane coupling agents contained in the main component (A) do not have isocyanate groups. It is desirable that the other silane coupling agents contained in the curing agent (B) do not have hydroxyl groups and amino groups (including primary, secondary, and tertiary amino groups, and amino groups to which epoxy groups are bonded).

[0036] <Main ingredient (A)> The main component (A) comprises 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] (Hydroxygroup-containing resin (a1)) The hydroxyl group-containing resin (a1) is in the form of an emulsion dispersed in an aqueous solvent (a2). The particle size of the hydroxyl group-containing resin (a1) in the main component (A) is not particularly limited. In terms of ease of viscosity control and the appearance of the resulting coating film, the average particle size of the hydroxyl group-containing resin (a1) is preferably 0.01 μm or more and 1.0 μm or less, and more preferably 0.05 μm or more and 0.5 μm or less. The average particle size is the 50th percentile diameter (median diameter, D50) in the volume-based particle size distribution measured by dynamic light scattering.

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

[0039] The hydroxyl value of the hydroxyl group-containing resin (a1) is preferably 5 mg KOH / g or more and 200 mg KOH / g or less, and more preferably 50 mg KOH / g or more and 150 mg KOH / g or less. When the hydroxyl value of the hydroxyl group-containing resin (a1) is within the above range, the strength of the resulting coating film is sufficiently high, and the water resistance is also easily improved.

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

[0041] The number-average molecular weight of the hydroxyl group-containing resin (a1) is not particularly limited and may be, for example, 1,000 to 100,000, 2,000 to 50,000, or 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 the viscosity of the aqueous coating composition is suppressed, improving the appearance of the resulting coating film and making it easier to achieve sufficiently high strength.

[0042] Both the hydroxyl value and acid value are based on the solid content and can be measured in accordance with JIS K 0070. The number-average molecular weight is a styrene homopolymer equivalent value 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 hydroxyl group-containing resins (a1) include acrylic polyols, polyester polyols, polyether polyols, polyurethane polyols, and polycarbonate polyols. Among these, acrylic polyols are preferred because they tend to produce good physical properties such as appearance, weather resistance, and chemical resistance of the resulting coating film.

[0044] The hydroxyl group-containing resin (a1) can be obtained, for example, by emulsion polymerization of one or more raw material monomers. Emulsion polymerization is carried out by methods commonly used by those skilled in the art. Specifically, an emulsifier is mixed with an aqueous medium containing an organic solvent such as alcohol as needed, and the raw material monomers and polymerization initiators are added dropwise while the resulting mixture is heated and stirred. Alternatively, an emulsion mixture, in which the raw material monomers, emulsifier, and water have been pre-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] Acrylic polyol emulsions are obtained, for example, by emulsion polymerization of a mixture of raw material monomers including alkyl (meth)acrylate monomers, acid group-containing ethylenically unsaturated monomers, hydroxyl group-containing ethylenically unsaturated monomers, and styrene-based monomers.

[0046] (aqueous solvent (a2)) Examples of aqueous solvents include various types of water such as pure water, deionized water, tap water, and industrial water. The main component (A) may also contain an organic solvent along with 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 group-containing resin (a1) and aqueous solvent (a2), the main component (A) may optionally contain various additives. Examples of additives include dispersants, defoamers, ultraviolet absorbers, hindered amine light stabilizers, antioxidants, viscosity modifiers, surface modifiers, film-forming aids, rust inhibitors, and thickeners. Among these, the inclusion of viscosity modifiers and / or surface modifiers is preferable because it easily improves 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 viscous agents, cellulose derivatives, and urethane-associated viscous agents. These can be used individually or in combination of two or more. The amount of viscosity modifier may be, for example, 0.1% to 50% by mass of the solid content of the hydroxyl group-containing resin (a1), or 0.5% to 30% by mass.

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

[0050] (Method for preparing the main ingredient (A)) The main component (A) can be prepared by mixing the above components by a method known to those skilled in the art. The mixing method is the same as that used for preparing aqueous paint compositions.

[0051] <Hardening agent (B)> The curing agent (B) comprises a polyisocyanate compound (b1) and an organic solvent (b2) that does not have hydroxyl groups. 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 in one molecule. Examples of polyisocyanates 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 versions thereof (e.g., urethanes, carbodiimides, uretdiones, uretonimines, 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 organic solvents (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 ether, dipropylene glycol diisobutyl ether, dipropylene glycol diallyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol diisobutyl ether, tripropylene glycol diallyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether, butylene glycol di-n-butyl ether, 2-butoxyethyl diethoxyethyl ether, 2-butoxyethyl triethoxy ether, 2-butoxyethyl tetraethoxyethyl ether; acetate-based organic solvents such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate;Examples 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 can be used individually or in combination of two or more.

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

[0056] (Method for preparing the hardening agent (B)) The curing agent (B) can be prepared by mixing the above components by a method known to those skilled in the art. The mixing method is the same as that used for preparing aqueous paint compositions.

[0057] <Diluting component (C)> The aqueous paint composition may further contain a diluent (C). The diluent (C) may be the same as the aqueous solvent (a2). The diluent (C) may be the same as the aqueous solvent (a2) or different.

[0058] The amount of diluent (C) to be mixed is set appropriately considering the viscosity of the aqueous paint composition, the painting method, etc. For example, the amount of diluent (C) to be mixed is 10 parts by mass or more and 70 parts by mass or less 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 amount of pigment (D) may be, for example, 100 parts by mass or more and 300 parts by mass or 120 parts by mass or more and 200 parts by mass or less, based on 100 parts by mass of resin solids contained in the main component (A1) of the aqueous primer surfacer (X).

[0060] Pigment (D) is not particularly limited. Examples of pigment (D) include coloring pigments such as titanium dioxide, carbon black, iron oxide, and copper phthalocyanine blue; luminous 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 abrasiveness and film-forming properties of the undercoat, it is preferable that at least an extender pigment is included. The proportion of the extender pigment may be, for example, 30% by mass or more and 100% by mass or less, and 40% by mass or more and 70% by mass or less, based on 100 parts by mass of the total amount of all pigments.

[0062] [Method for manufacturing painted articles] The painted article is manufactured by a method comprising the steps of: (I) applying an aqueous primer surfacer (X) to the object to be painted to form a base coat film; (II) applying an aqueous colored base coating composition (Y) onto the base coat film to form a colored base coating film; and (III) applying an aqueous clear coating composition (Z) onto the colored base coating film to form a clear coating film.

[0063] 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. This improves the water resistance of the entire multi-layer coating film. In particular, it is preferable that both the water-based primer surfacer (X) and the water-based clear coating composition (Z) contain an epoxy group-containing silane coupling agent.

[0064] (I) Process of forming the base coating film In this process, a 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)) The first main component (A1) is prepared by mixing the first hydroxyl group-containing resin (a11) with the first aqueous solvent (a21). Separately, the first curing agent (B1) is prepared by mixing the first polyisocyanate compound (b11) with the first organic solvent (b21) that does not contain hydroxyl groups.

[0066] The obtained first main component (A1) and first hardener (B1) are mixed to prepare a water-based primer surfacer (X). The mixing of the first main component (A1) and first hardener (B1) is performed immediately before painting. The first main component (A1) and first hardener (B1) may be supplied to the painting apparatus after mixing, or they may be mixed within the painting apparatus. The mixing method is as described above.

[0067] The first main component (A1) and the first curing agent (B1) are mixed such 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 equal in the ratio of isocyanate group equivalent to hydroxyl group equivalent = 1 / 0.5 to 1 / 2.

[0068] If 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 water-based primer surfacer (X) is applied to the object to be coated. The amount of water-based primer surfacer (X) to be applied is not particularly limited and is set appropriately according to the performance required of the coating film. For example, the water-based primer surfacer (X) is applied so that the thickness of the base coating film after curing is between 20 μm and 100 μm.

[0070] The method of applying the water-based primer surfacer (X) is not particularly limited. Examples of application methods include air spray painting, airless spray painting, rotary atomization painting, and curtain coat painting. These methods may be combined with electrostatic painting. For repairs, air spray painting is preferred because it allows for easy localized painting. Painting 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 set appropriately depending on the amount applied and the composition. Curing is carried out, for example, at a temperature of 40°C to 70°C for about 30 to 60 minutes. Typically, after curing, the base coating is sanded and degreased. Sanding is carried out using sandpaper or the like.

[0072] When making repairs, before applying the water-based primer surfacer (X), the area to be painted and its surroundings are sanded as needed, and any unevenness is filled with putty. Subsequently, the area is sanded again.

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

[0074] Metallic workpieces may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After surface treatment, metallic workpieces may be further coated with electrodeposition paint. The electrodeposition paint may be cationic or anionic.

[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 the resin-coated object is degreased.

[0076] Examples of objects to be coated include the bodies of automobiles such as passenger cars, trucks, motorcycles, and buses, or parts thereof.

[0077] (II) Process of forming a colored base coating In this process, a water-based colored base coating composition (Y) is applied to the base coating to form a colored base coating. The application of the water-based colored base coating composition (Y) may be performed multiple times.

[0078] (Method for preparing a water-based colored paint composition (Y)) The water-based colored base coating composition (Y) may be of the curing type or the lacquer type. The water-based colored base coating composition (Y) further contains a pigment. Examples of the pigment include the coloring pigments and / or luminous pigments exemplified by pigment (D).

[0079] The curing-type aqueous colored base coating composition (Y) comprises a curable resin (e.g., the main component (A) described above) and a curing agent (e.g., the curing agent (B) described above), and a cured coating film is formed by heating. The curing-type aqueous colored base coating composition (Y) may further contain a silane coupling agent (e.g., an epoxy group-containing silane coupling agent).

[0080] The lacquer-type water-based colored base paint composition (Y) comprises water, an organic solvent, and a binder resin dissolved or dispersed therein. A cured coating film is formed by the evaporation of water and the organic solvent. The concentration of the binder resin is not particularly limited and is set as appropriate depending on the composition and application.

[0081] The binder resin is not particularly limited. Examples of binder resins include acrylic resins, amino alkyd resins, alkyd resins, amino resins, isocyanate resins, epoxy resins, vinyl chloride resins, cashew resins, silicone resins, styrene resins, styrene-modified alkyd resins, cellulosic 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, urethane-modified). These can be used individually or in combination of two or more. Examples of organic solvents include naphtha, xylene, toluene, and acetone.

[0082] (Painting method) The application method for the water-based colored base coating composition (Y) is not particularly limited, and the same method as for the water-based primer surfacer (X) can be used. The amount of water-based colored base coating composition (Y) applied is not particularly limited, and for example, it is applied 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 set as appropriate depending on the composition of the water-based colored base coating composition (Y).

[0083] (III) Process of forming a clear coating In this process, a water-based clear coating composition (Z) is applied to the colored base coating to form a clear coating.

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

[0085] The obtained second main component (A2) and second hardener (B2) are mixed to prepare a water-based clear coating composition (Z). The mixing of the second main component (A2) and second hardener (B2) is performed immediately before painting. The second main component (A2) and second hardener (B2) may be supplied to the painting apparatus after mixing, or they may be mixed within the painting apparatus. The mixing method is as described above.

[0086] The second main component (A2) and the second curing agent (B2) are mixed such 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 in a ratio of 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 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).

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

[0089] The method of applying the water-based clear coating composition (Z) is not particularly limited, and the same method as for the water-based primer surfacer (X) can be used. Among these, air spray painting is preferred. Painting may be performed multiple times.

[0090] After the water-based clear coating composition (Z) is applied, the coating film is cured by heating. Curing is carried out, for example, at a temperature of 40°C to 100°C for about 15 to 60 minutes. In this way, a painted article is obtained that has a primer film, a colored base film, and a clear film in this order. [Examples]

[0091] The embodiment will be described in more detail below using examples, but the embodiment is not limited in any way by these examples. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[0092] [Example of preparation] Based on the formulations shown in Table 1, curing agents HA to HE containing epoxy group (Ep group) silane coupling agents, comparative curing agent Ha without epoxy group silane coupling agents, and comparative curing agent Hb containing a silane coupling agent with amino groups instead of epoxy groups 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: Barnock DNW-5500 (manufactured by DIC Corporation) Polyisocyanate compound B: Bayhydur ultra 304 (manufactured by Sumika Covestro Co., Ltd.) Silane coupling agent A: 3-Glyquidoxypropyltrimethoxysilane Silane coupling agent B: 3-Glyquidoxypropyltriethoxysilane Silane coupling agent C:N-phenyl-3-aminopropyltrimethoxysilane

[0094] (1) Assessment of storage stability (1-1) Thickening properties The liquid temperature of the sample (hardener) was adjusted to 23°C. Next, a viscosity cup NK-2 manufactured by Anest Iwata Corporation was submerged in the sample and then lifted out. The time from the moment of lifting until all of the sample was discharged was measured. This was defined 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 constant temperature room at 50°C for 30 days. After that, the metal container was removed from the constant temperature room and the liquid temperature was adjusted to 23°C. Subsequently, the time (T (seconds)) from the lifting of the sample until 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 within 1 second Good: T-T0 is between 1 and 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 constant temperature room at 50°C for 30 days. After that, the metal container was removed from the constant temperature room, and the sample was carefully placed in a test tube, taking care not to introduce air bubbles, and sealed tightly. The sample and Gardner color number standard solution were placed side by side and observed and evaluated by shining light through from the side under diffuse daylight. If the color of the sample matched, the color number of the Gardner color number standard solution was recorded. If the color of the sample fell between two Gardner color number standard solutions, the Gardner color number of the one closer to the sample was recorded. The criteria for judgment are as follows:

[0098] Best: Gardner, 1 color OK: Gardner color count is 2 or more and 3 or less Not allowed: Gardner color palette of 4 or more

[0099] [Table 1]

[0100] Although curing agents HA through HE contain epoxy group-containing silane coupling agents, their storage stability was 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, had inferior storage stability.

[0101] In the above preparation example, various silane coupling agents were added to the curing agent (B) for evaluation. However, even when the silane coupling agent is added to the main component (A), the effect of epoxy group-containing silane coupling agents on storage stability is considered to be 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 painted articles were manufactured.

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

[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 diluent (C) using a disperser. The silane coupling agent content 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 paint 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., solid content approximately 22%), 50 parts of nax E-CUBE WB 911 S-Binder (auxiliary agent, manufactured by Nippon Paint Co., Ltd., solid content approximately 26%), and 45 parts of nax E-CUBE WB R20 Standard Diluent (diluent component, manufactured by Nippon Paint Co., Ltd.).

[0106] (3) Preparation of the aqueous clear coating composition (Z) As the second main component (A2), a mixture of nax E-CUBE WB (2:1) NN Clear (manufactured by Nippon Paint Co., Ltd., solid content concentration approximately 38%) and pure water (aqueous solvent (a22)) was prepared. The hydroxyl group-containing resin (a12) was present in the mixture in the form of an emulsion. The solid content concentration of the hydroxyl group-containing resin (a12) was 91.5% of the total solid content contained in the second main component (A2).

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

[0108] A aqueous clear coating composition (Z) was prepared by mixing 100 parts of the second main component (A2), 50 parts of the hardener HA, and an appropriate amount of the diluent (C) using a disperser. The silane coupling agent content 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 undercoat A 60cm x 40cm steel plate (the object to be coated) was coated with water-based primer surfacer (X) using an air spray gun, and then air-blown dry until the paint no longer adhered to the touch. This coating and drying process was repeated two more times. Next, the steel plate was heated in an oven set to 60°C for 30 minutes to form a base coating (hardened film thickness 45μm). Then, the surface of the resulting coating was polished. Finally, the surface of the coating was degreased.

[0110] (III-2) Formation of a water-based coating film A water-based colored base coating composition (Y) was applied to an object with a primer coating using an air spray gun, and then air-blown drying was performed until the paint no longer adhered to the touch. This application and drying process was repeated two more times to form a water-based colored base coating (cured film thickness 20 μm).

[0111] (III-3) Formation of clear coating A substrate having a primer film and a colored base film was coated three times with a water-based clear coating composition (Z) using an air spray gun. Each coat was applied with a 1-minute interval between coats. 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±2RH%. Next, the substrate was heated in an oven set to 70°C for 20 minutes to form a clear coating (cured film thickness of 50 μm).

[0112] [Examples 2-5, Reference Examples 1-2 and Comparative Examples 1-2] Except for changing the types of the first curing agent (B1) and the second curing agent (B2) as shown in Table 2, an aqueous primer surfacer (X) and an aqueous clear coating composition (Z) were prepared in the same manner as in Example 1, and a painted article was produced.

[0113] [Evaluation Method] The painted articles were evaluated using the following method. The evaluation results are shown in Table 2. The silane coupling agent content in Table 2 is the amount blended relative to 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 Using an NT Cutter (manufactured by NT Corporation), cuts (11 vertical and 11 horizontal, at 2mm intervals) were made into the hardened clear coating, creating 100 grids. Tape (manufactured by Nichiban Co., Ltd., Cellotape®, 24mm wide) was applied to cover all the grids and firmly pressed down with a fingernail or similar tool. Next, the tape was peeled off while pulling it so that the angle between it and the coating was approximately 45°. The coating after tape removal was evaluated visually. The evaluation criteria are as follows:

[0114] 10 points: Each cut is fine, both sides are smooth, and there is no peeling at the intersections of the cuts or within the grid. 8 points: There is slight peeling at the intersections of the cuts, but no peeling is observed within the grid squares, and the area of ​​peeling is less than 5% of the total grid area. 6 points: There is peeling within the grid and at the intersections of the cuts, and the area of ​​peeling is between 5% and 15% of the total area of ​​the grid. 4 points: The peeling area within each square is wide, and the peeled area is between 15% and 35% of the total area of ​​each square. Points 2: The peeling width within each square is wider, and the peeled area is between 35% and 65% of the total area of ​​each square. 0 points: The area of ​​peeling is 65% or more of the total area of ​​all squares.

[0115] (2-2) Water resistance 1 (Evaluation of adhesion after immersion test) A constant-temperature water bath with a circulation function was set to 40°C and filled with deionized water. Approximately three-quarters of the painted object was immersed in this bath. After immersion for 240 hours, the painted object was removed and the water droplets were lightly wiped off. After removal, the painted object was left at room temperature (23°C) for 24 hours and evaluated in the same manner as the adhesion evaluation (2-1) described above.

[0116] (2-3) Water resistance 2 (Blister evaluation after immersion test) A constant-temperature water bath with a circulation function was set to 40°C and filled with deionized water. The painted items were immersed in this bath to about 3 / 4 of their length. After 240 hours of immersion, the painted items were removed and any water droplets were lightly wiped off. After removal, the painted items were left at room temperature (23°C) for 1 hour, and the coating was visually evaluated. The evaluation criteria were as follows: Best: No abnormalities Good: There are some very small blisters, but it does not affect practical use. Acceptable: Blisters larger than 1mm are present in some areas. Defect: Blisters larger than 1mm are present throughout.

[0117] [Table 2] [Industrial applicability]

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

Claims

1. Step (I) involves applying a water-based primer surfacer (X) to the object to be coated to form a base coating film, Step (II) involves applying a water-based colored base coating composition (Y) onto the aforementioned base coating to form a colored base coating, The process includes a step (III) of applying an aqueous clear coating composition (Z) onto the colored base coating to form a clear coating, The aqueous primer surfacer (X) and the aqueous clear coating composition (Z) both contain a silane coupling agent having one or more epoxy groups. 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) comprising a first polyisocyanate compound (b11) and a first organic solvent (b21) that does not have a hydroxyl group, The first main component (A1) and the first curing agent (B1) are such 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 such that the ratio of isocyanate group equivalent to hydroxyl group equivalent is 1 / 0.5 to 1 / 2. The silane coupling agent is contained in the first curing agent (B1), The content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11). 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), The second curing agent (B2) comprises a second polyisocyanate compound (b12) and a second organic solvent (b22) that does not have a hydroxyl group, The second main component (A2) and the second curing agent (B2) are such 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 such that the isocyanate group equivalent / hydroxyl group equivalent = 1 / 0.5 to 1 / 1.

5. The silane coupling agent is contained in the second curing agent (B2), The content of the silane coupling agent is 1.2% by mass or more and 10% by mass or less, based on 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12). A method for manufacturing painted articles.

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