JP2003053254A - Method for forming multi-layered coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a multi-layered coating film improved in chipping resistance without lowering smoothness, gloss sharpness or the like. SOLUTION: In the method for forming the multi-layered coating film by coating an article to be coated with a hydrophilic organic solvent type base paint (A) and further coating the same with an aqueous color paint (B) and an organic solvent type clear paint (C) in an uncured state and subsequently heating the coated article to cure these coating films at the same time, the hydrophilic organic solvent type base paint (A) comprises a paint containing neutralized matter (a) of an acrylic resin having an acid value of 20-50, a hydroxyl group based on lactone modification and a glass transition temperature of -20-+20 deg.C, a melamine resin (b) having a 1-5C alkoxy group and resin particles (c) as essential components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multi-layer coating film, and its object is to improve chipping resistance and the like without lowering the smoothness and the gloss and image clarity.

[0002]

2. Description of the Related Art The object to be coated has an acid value of 5 to 100.
A hydrophilic organic solvent type base paint containing a neutralized product of a hydroxyl group-containing resin and a melamine resin is applied, and then an aqueous colored paint and a clear paint are applied, followed by heating to simultaneously cure these three-layer coating films. It is already known to form a multilayer coating film by doing so (for example, JP-A-4-25076). This multi-layer coating film has excellent smoothness and gloss and sharpness, and when a metallic coating material is used as the water-based coloring coating material, a metallic coating film having no metallic unevenness and excellent glittering feeling can be formed. However, the above-mentioned multilayer coating film formed as an overcoat coating film on the outer plate portion of an automobile body is likely to be locally peeled off due to collision of pebbles and gravel that are flipped up during traveling (generally, this phenomenon Is called "chipping property"). As a result, the aesthetics of the coated surface deteriorates,
Since the base material to be coated may be exposed and rust may easily occur, it is strongly desired to improve the chipping resistance without deteriorating the smoothness and the gloss sharpness of the multilayer coating film. ing.

[0003]

The object of the present invention is to provide a multi-layer coating film comprising the above-mentioned hydrophilic organic solvent type base coating material, water-based coloring coating material and clear coating material, which have smoothness and gloss. It is to improve chipping resistance without deteriorating sharpness and metallic feeling. As a result of earnest research, as a hydrophilic organic solvent type base paint, the acid value is 20.
50, a neutralized product of an acrylic resin having a hydroxyl group based on lactone modification and having a glass transition temperature of −20 to + 20 ° C., a melamine resin having a carbon number of 1 to 5 alkoxy group, and a coating material containing resin particles. The present invention has been completed by finding that the object can be achieved by using it.

That is, according to the present invention, a hydrophilic organic solvent type base paint (A) is applied to an object to be coated, and in an uncured state, an aqueous colored paint (B) and an organic solvent type clear paint (C). In the method for forming a multilayer coating film in which the coating films are sequentially coated and then these coating films are simultaneously cured by heating, the hydrophilic organic solvent type base coating material (A) has an acid value of 20 to 50 and a hydroxyl group based on lactone modification. With a glass transition temperature of -20
It is characterized in that it is a coating material containing the neutralized product (a) of an acrylic resin having a temperature of up to + 20 ° C, the melamine resin (b) having a carbon number of 1 to 5 alkoxy group, and the resin particles (c) as essential components. A method for forming a multilayer coating film (hereinafter referred to as "the present method") is provided.

The present method will be described in more detail below.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Object to be coated: a substrate on which a multilayer coating film is formed by the present method, and an outer plate portion of an automobile body made of metal or plastic is particularly preferable, but is not limited thereto. There is no such thing. In applying the hydrophilic organic solvent type base coating material (A) to these objects to be coated, a chemical conversion treatment, an undercoat coating with a cationic electrodeposition coating material, an intermediate coating material or the like is appropriately applied in advance, It is preferable to cure the coating film. As the chemical conversion treatment, undercoat paint and intermediate paint, those known per se can be used.

Hydrophilic organic solvent type base coating (A): Neutralized product (a) of acrylic resin having an acid value of 20 to 50, a hydroxyl group based on lactone modification, and a glass transition temperature of -20 to + 20 ° C. Is an organic solvent-based paint containing, as essential components, a melamine resin (b) having an alkoxy group having 1 to 5 carbon atoms and resin particles (c), and a water-based colored paint (B)
Prior to coating, paint on the surface of the object to be coated.

The component (a) has an acid value of 20 to 50, a hydroxyl group based on lactone modification, and a glass transition temperature of -20.
It is a neutralized product of an acrylic resin having a temperature of up to + 20 ° C. This acrylic resin has both a carboxyl group and a hydroxyl group based on lactone modification in the same molecule. Among them, the amount of carboxyl group is 20 to 50 mg KO based on its acid value.
H / g, especially within the range of 30 to 45 mgKOH / g is preferable. When the acid value is less than 20 mgKOH / g, the water-based colored coating material (B) to be subsequently applied is poorly compatible with the coating film, and the ability to absorb water in the coating film of the water-based colored coating material (B) is poor. The coating composition (B) is apt to cause unevenness or sagging, and when the acid value is more than 50 mgKOH / g, the water resistance of the coating composition of the base coating composition (A) itself is deteriorated. . The hydroxyl group based on lactone modification is a crosslinkable functional group with the melamine resin (b), and the content thereof is 40 to 100 based on the hydroxyl value.
mgKOH / g, especially 50 to 80 mgKOH / g is preferred.

The acrylic resin in the component (a) is an unsaturated monomer containing a carboxyl group, an unsaturated monomer containing a hydroxyl group based on lactone modification, acrylic acid or methacrylic acid, and monoalcohols having 1 to 24 carbon atoms. A polymer obtained by copolymerizing monoesters with and as an essential component, and further using other unsaturated monomers as necessary,
The number average molecular weight is preferably in the range of about 20,000 to about 40,000, particularly preferably about 25,000 to about 35,000.

The unsaturated monomer containing a carboxyl group is a compound having at least one polymerizable unsaturated double bond and one carboxyl group in one molecule, and examples thereof include acrylic acid, methacrylic acid, crotonic acid and maleic acid. , Fumaric acid, itaconic acid, and half-monoalkyl (suitably having 1 to 10 carbon atoms) ester compounds of dicarboxylic acids of these, and the like, and one or more of these can be used.

The unsaturated monomer containing a hydroxyl group based on lactone modification is obtained by reacting a lactone with a hydroxyl group-containing compound having at least one polymerizable unsaturated double bond and at least one hydroxyl group in a molecule. Can be obtained. Examples of the hydroxyl group-containing compound include monoester compounds of acrylic acid or methacrylic acid such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate and glycols having 2 to 10 carbon atoms. Lactone is a cyclic compound having an ester group in the ring and has 3 to 7 ring members.
It is preferably in the range of, specifically, α-lactone, β-lactone, γ-lactone, δ-lactone, ε-
Examples include lactones. The esterification reaction of a hydroxyl group-containing compound with a lactone is an esterification reaction of the former hydroxyl group with the carboxyl group generated by the latter ring opening, and the hydroxyl group generated by the ring opening of the lactone ring is bonded to the end of the product. is doing. The ratio of both components in the esterification reaction of the hydroxyl group-containing compound and the lactone is the latter (lactone) per mole of the former (hydroxyl group-containing compound).
Is preferably 1 mol or more, and particularly preferably about 2 to 5 mol.

Acrylic acid or methacrylic acid and 1 to 1 carbon atoms
As the monoesters of 24 monoalcohols, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, pentyl acrylate,
Examples include pentyl methacrylate, hexyl acrylate, hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl acrylate and lauryl methacrylate.

Other unsaturated monomers include the above-mentioned unsaturated monomers containing a carboxyl group, unsaturated monomers containing a hydroxyl group based on lactone modification, acrylic acid or methacrylic acid, and mono-monomers having 1 to 24 carbon atoms. It is a compound having at least one polymerizable unsaturated double bond in one molecule other than monoesters with alcohols. Specifically, glycidyl group-containing unsaturated monomers such as glycidyl acrylate and glycidyl methacrylate; nitrogen-containing unsaturated monomers such as acrylonitrile, acrylamide, N-methylacrylamide, N-methylolacrylamide, N-butoxymethylacrylamide and dimethylaminoethylmethacrylate. Saturated monomers; aromatic ring-containing unsaturated monomers such as styrene, α-methylstyrene and vinyltoluene; vinyl acetate, vinyl chloride and the like.

The ratio of the unsaturated monomer having a carboxyl group and the unsaturated monomer having a hydroxyl group based on the lactone modification is such that the acid value of the acrylic resin as the component (a) is 20.
˜50 mg KOH / g, preferably 30-45 mg KO
The H / g and the hydroxyl value are preferably in the range of 10 to 150 mgKOH / g, particularly preferably 30 to 80 mgKOH / g. Further, the use ratio of monoesters of acrylic acid or methacrylic acid and monoalcohols having 1 to 24 carbon atoms is 20% by weight or more based on the total amount of the monomer components constituting the acrylic resin, and particularly 25 to 80%. A range of weight% is suitable. Similarly, the other unsaturated monomers are suitably in the range of 60% by weight or less, particularly 50% by weight or less. Further, a part of the unsaturated monomer containing a hydroxyl group based on lactone modification is replaced with acrylic acid or methacrylic acid such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate and a glycol having 2 to 10 carbon atoms. It is also possible to substitute monoester ether with other compounds, the ratio of which is 70% of the above hydroxyl value.
It is particularly preferably 50% or less.

Further, it is essential that the acrylic resin in the component (a) has a glass transition temperature (Tg) of -20 to + 20 ° C, preferably -10 to + 10 ° C.
When the Tg is lower than -20 ° C, the viscosity of the applied coating is low, and the coating film of the water-based colored coating (B) applied to the uncured coating surface is likely to be displaced, while when it is higher than + 20 ° C, the base coating is applied. Since the coating film of (A) becomes hard and brittle, and the chipping resistance is lowered, neither is preferable.

Glass transition temperature (Tg) of acrylic resin
Is an equation, 100 / Tg (° K) = W ₁ / T ₁ + W ₂ / T
_It can be determined by applying ₂ + W ₃ / T ₃ ··· to calculate and converting the obtained value (° K) into ° C. In the formula, W ₁ , W ₂ , W ₃ ... Are acrylic resins (a)
% Of monomers used in the preparation of T ₁ , T ₂ , T ₃
.. is the Tg (° K) of the homopolymer of the monomer, Polymer
Hand Book (second edition, J. Brandrup, EH Im
It is a value according to mergut).

The component (a) is obtained by neutralizing the carboxyl group of the above acrylic resin with a basic substance. The neutralization time is preferably before mixing with the melamine resin (b) and the resin particles (c).

The basic substance is preferably water-soluble, for example, ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-
Ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine,
Triethylamine, triisopropylamine, tributylamine, ethylenediamine, morpholine, N-alkylmorpholine, pyridine, monoisopropanolamine, methylethanolamine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine and Examples thereof include triethanolamine, and these may be used alone or in combination of two or more. The amount of these neutralizing agents used is 0.1 to 2.0 equivalents, especially 0.3 to
1.2 equivalents are suitable.

The component (b) is a melamine resin having an alkoxy group having 1 to 5 carbon atoms. Specifically, an imino group obtained by condensation reaction of formaldehyde with some or all of amino groups of melamine may remain, and all or some of the methylol groups of methylolated melamine have 1 to 5 carbon atoms. The melamine resin having an alkoxy group having 1 to 5 carbon atoms in which an imino group, a methylol group or the like formed by etherification with the monoalcohol may remain. The number average molecular weight of this component (b) is 400 to 300.
0 is preferred.

The component (c) is resin particles, and is used for adjusting the fluidity of the hydrophilic organic solvent type base coating material (A) used in the present method and the applied coating film.

By mixing the component (c), it is possible to impart thixotropic properties to the hydrophilic organic solvent type base coating material (A), and thus, when high shear stress is applied during spray coating or the like. Makes it possible to perform spray painting work easily because the viscosity is sufficiently reduced, while on the other hand, when low shear stress is applied after coating on the surface to be coated, the apparent viscosity is It is possible to raise it. As a result, it is possible to prevent the occurrence of coating defects such as sagging and cissing when coating on a vertical surface to be coated or when baking onto that portion after coating, and it is possible to form a coating film with a good finished appearance. The effect is obtained. Examples of such rheology control agents include crosslinked polymer fine particles and polyurea compounds.

The crosslinked polymer fine particles are hardly or not dissolved in the above-mentioned components (a) and (b) and the organic solvent,
Moreover, it is an internally crosslinked particulate polymer that can be stably dispersed.

As a specific example of the crosslinked polymer fine particles, a known intramolecularly crosslinked fine particle polymer obtained by an aqueous emulsion or an aqueous suspension polymerization method or a non-aqueous dispersion polymerization method can be used. Among them, a fine particle polymer having an intramolecular crosslinked structure obtained by an aqueous emulsion or an aqueous suspension polymerization method can be obtained by physical or chemical means such as evaporation or azeotropy of water or precipitation or aggregation of the polymer (particles). , It can be separated in the form of a solid, or when the physical or chemical means is applied, the medium of the target crosslinked polymer particles is directly replaced with water from another resin or an organic solvent. You can also

As the crosslinked polymer fine particles, JP-A-3-66 is used.
No. 770, a polymerizable monomer having at least two radically polymerizable unsaturated groups in the molecule and another radically polymerizable unsaturated monomer containing an allyl group in the molecule. The crosslinked polymer fine particles obtained by emulsion polymerization in the presence of are preferably used. In this case, the polymer fine particles are internally crosslinked by the polymerizable monomer having at least two radically polymerizable unsaturated groups in the molecule.

As crosslinked polymer fine particles, poly (1
2-hydroxystearic acid) and a copolymer of a macromonomer (a) having an average of about 1 or more polymerizable unsaturated double bonds per molecule and an ethylenically unsaturated monomer. So, the solubility parameter (SP value) is 7.
5 to 9.2, and average about 1.0 per molecule.
~ In the presence of a mixture with a macromonomer (b) having about 1.5 polymerizable unsaturated double bonds, each of which has at least two complementary functional groups capable of reacting with each other to bond. At least 0.5 wt% vinyl monomer
In the organic solvent containing the vinyl monomer mixture, the macromonomer (a), the macromonomer (b) and the vinyl monomer are dissolved but the polymer of the vinyl monomer is not substantially dissolved. It is possible to use a dispersion liquid of gel polymer fine particles obtained by copolymerization and cross-linking reaction with. The crosslinked polymer fine particles themselves are known, and are disclosed in Japanese Patent Publication No. 6-7
The details are disclosed in Japanese Patent No. 0110. The macromonomer (a) has a polymerizable unsaturated group-containing reaction product obtained by adding an epoxy group-containing polymerizable unsaturated unsaturated compound to a terminal carboxyl group of poly (12-hydroxystearic acid), and has an epoxy group. A polymerizable unsaturated carboxylic acid is added to a pendant epoxy group-containing copolymer obtained by graft copolymerization or block copolymerization with a polymerizable unsaturated monomer mixture containing a polymerizable monomer. Macromonomers with 1 to about 10 polymerizable unsaturated double bonds are preferred. In particular, macromonomer (a)
Is preferably a macromonomer having one polymerizable unsaturated double bond in one molecule formed by adding an epoxy group-containing polymerizable unsaturated unsaturated compound to the terminal carboxyl group of poly (12-hydroxystearic acid). Is. The macromonomer (b) preferably has a number average molecular weight of 3,000 to 20,000 and a hydroxyl value of 45 to 150. Examples of the combination of complementary functional groups include epoxy group / carboxyl group, alkoxysilyl group / hydroxyl group, epoxy group / phosphoric acid group, isocyanate group / hydroxyl group, and the like.

These crosslinkable polymer fine particles have a high crosslink density and are substantially non-swelling and non-fusing even in an organic solvent having a high polymer dissolving power such as toluene and ethyl acetate. Moreover, when it is added to the hydrophilic organic solvent type base coating material (A) containing an organic solvent, a solution (dispersion liquid) having a high resin content, that is, a high solid content can be obtained with almost no increase in viscosity. Further, the hydrophilic organic solvent type base coating material (A) containing the crosslinked polymer fine particles is
The fine particles also form a cured coating. The average particle diameter of the crosslinked polymer fine particles is about 0.01 to 2 μm, and particularly 0.05 to 0.5.
Is suitable, and when the particle size is within this range, the effect of preventing sagging of the coating film and the finished appearance of the coating film are excellent.

Further, as a resin particle, from a reaction product of an isocyanurate trimer obtained from a diisocyanate compound having 3 to 20 carbon atoms and an amine compound having one or more primary amino groups. The solid particulate polyurea compound can be used as the component (c) (Japanese Patent Publication No. 7-81099). Isocyanurate 3
It is preferred that the monomer is made from a diisocyanate having 3 to 20, preferably 5 to 14, more preferably 8 to 12 carbon atoms, particularly preferably hexamethylene diisocyanate. Examples of suitable diisocyanates include methylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, ω, ω ° dipropyl ether diisocyanate, thiodipropyl diisocyanate, cyclohexyl-1,4-diisocyanate, dicyclohexylmethane-4, 4 ° -diisocyanate,
1,5-dimethyl-2,4-bis (isocyanatomethyl) -benzene, 1,5-dimethyl-2,4-bis (ω
-Isocyanatoethyl) -benzene, 1,3,5-trimethyl-2,4-bis (isocyanatomethyl) benzene, 1,3,5-triethyl-2,4-bis (isocyanatomethyl) benzene, Bayer des Heterocyclic diisocyanates, dicyclohexyldimethylmethane-4,4'-diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate and diphenylmethane-4,4'-diisocyanate sold under the trademark Desmodur TT. Can be given. If desired, heterocyclic trimers of two or three different diisocyanates may be used. It is also possible to use mixtures of the abovementioned heterocyclic triisocyanates.

Second used to make polyurea compounds
Examples of suitable primary amine as a component include benzylamine, ethylamine, n-propylamine, sec-
Propylamine, n-butylamine, sec-butylamine, tert-butylamine, n-pentylamine,
α-methylbutylamine, α-ethylpropylamine,
Examples include β-ethylbutylamine, hexylamine, octylamine, decylamine, stearylamine, cyclohexylamine, aniline and hexamethylenediamine. These primary amines generally contain up to 55 carbon atoms, preferably 1 to 24, more preferably 1 to 12 carbon atoms. Amines with one or more primary amino groups and one or more ether and / or hydroxyl groups can also be used. For example, ethanolamine, 6-aminohexanol, p-methoxybenzylamine, methoxypropylamine, 3,4-
Examples are dimethoxyphenylethylamine, 2,5-dimethoxyaniline, furfurylamine, tetrahydrofurfurylamine, bis (3-aminopropyl) polytetrahydrofuran (having a molecular weight of about 750). Mixtures of the above amines can also be used.

In the reaction of the heterocyclic triisocyanate with the primary amine to make the polyurea compound, it is generally possible to use either the heterocyclic triisocyanate or the primary amine in excess of the stoichiometric amount. For example,
The ratio of the number of amino groups of the primary amine to the number of heterocyclic triisocyanate groups is 0.7 to 1.5, preferably 0.9 to 1.
It can be 1.

The reaction of the heterocyclic triisocyanate with the primary amine can generally be carried out by any selected method by mixing the reaction components and raising the temperature if necessary. This reaction is preferably performed at a temperature of 10 ° C to 150 ° C, more preferably 20 ° C to 80 ° C. Generally, the reaction components can be mixed by any selected method, but it is desirable to add the heterocyclic triisocyanate to the primary amine, and if necessary, it may be divided into several steps. Generally, this reaction is carried out with a solvent such as acetone, methyl isobutyl ketone, 1-methoxy-propanol-2,
It is carried out in the presence of an aliphatic hydrocarbon such as benzene, toluene, xylene, or petroleum ether.

Neutralized product (a) of an acrylic resin having an acid value of 20 to 50, a hydroxyl group based on lactone modification, and a glass transition temperature of -20 to + 20 ° C. in the hydrophilic organic solvent type base coating material (A). The constituent ratios of the melamine resin (b) and the resin particles (c) having an alkoxy group having 1 to 5 carbon atoms can be arbitrarily selected according to the purpose, but on the basis of the total solid content of these three components, (a) The component is 46 to 65% by weight, particularly 50 to 60% by weight, the component (b) is 17 to 53% by weight,
In particular, 27 to 45% by weight, the component (c) is 1 to 18% by weight,
In particular, the range of 5 to 13% by weight is preferable.

The hydrophilic organic solvent type base coating composition (A) contains the above-mentioned components (a), (b) and (c) as essential components, and if necessary, solid color pigments, metallic pigments and light interference. It is also possible to add pigments, extender pigments, ultraviolet absorbers, light stabilizers, anti-settling agents, coating surface adjustment agents, other paint additives, etc., by uniformly mixing these components in an organic solvent. A hydrophilic organic solvent type base coating material (A) is obtained.

Examples of solid color pigments include quinacridone-based organic pigments such as quinacridone red, azo-based pigments such as pigment red, phthalocyanine-based pigments such as phthalocyanine blue, phthalocyanine green, and perylene red, and inorganic pigments such as titanium oxide and carbon black. Examples of the pigment include metallic pigments such as aluminum powder, vapor-deposited aluminum powder, aluminum oxide powder, nickel powder, copper powder, brass powder, and chrome powder.Interference color pigments include pearlescent pearls. Examples thereof include mica powder and pearlescent colored pearl mica powder.

As the organic solvent, those which are generally known for paints can be used, and examples thereof include ester-based, ether-based, alcohol-based, amide-based, ketone-based, aliphatic hydrocarbon-based, alicyclic hydrocarbon-based and aromatic solvents. Examples of the solvent include hydrocarbon solvents, and one or more selected from these solvents can be used.
In particular, among these solvents, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether , Diethylene glycol diethyl ether, diethylene glycol monobutyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, methyl alcohol, ethyl alcohol, allyl alcohol, n-propyl alcohol, isopropyl alcohol, tertiary butyl alcohol, ethylene glycol, 1 2-propylene glycol, 1,3
-Butylene glycol, 2,3-butylene glycol,
It is preferable to use a hydrophilic organic solvent such as hexylene glycol, hexanediol, dipropylene glycol, acetone or diacetone alcohol. These hydrophilic organic solvents are easily dissolved in water, for example, at 20 ° C., 50 parts by weight or more per 100 parts by weight of water dissolve. The ratio of the hydrophilic organic solvent is 2 based on the total weight of the organic solvents contained in the hydrophilic organic solvent type base coating material (A) at the time of coating.
It is suitable to contain 0% by weight or more, especially 40 to 100% by weight.

Further, hydrophilic organic solvent type base paint (A)
In the above, it is possible to replace part of the organic solvent with water such as deionized water to form a mixed system of the organic solvent and water. The content of the organic solvent in the mixed system of the organic solvent and water is preferably 50 to 100% by weight, and the water content is suitably 0 to 50% by weight.

In the present method, the hydrophilic organic solvent type base coating material (A) is applied on the surface of an object to be coated by electrostatic coating, airless spraying, air spraying or the like in a cured coating film of 5 to 25 μm.
It is preferable to apply the coating so that the film thickness is m.

In the method of the present invention, after coating the hydrophilic organic solvent type base coating material (A), the coating film is left at room temperature,
Alternatively, it is dried at a temperature of 100 ° C. or lower for about 1 to 60 minutes to evaporate the water in the coating film, and the uncured coating film surface having a gel fraction of 60% by weight or less, preferably 40% by weight or less, Apply the water-based coloring paint (B).

Regarding the gel fraction of the coating film, the hydrophilic organic solvent type base coating material (A) was applied to the tin plate as a cured coating film so as to have a thickness of 20 μm, and the coating film was dried under predetermined conditions. It was isolated, placed in a mesh net made of stainless steel of 300 mesh, and extracted with a mixed solvent of acetone / methanol = 1/1 (weight ratio) for 6 hours at a reflux temperature. Fraction% = (weight of sample after extraction / weight of sample before extraction) × 100].

The water-based coloring paint (B) is a paint obtained by dispersing a paint resin composition and a coloring pigment in water.

As the paint resin, those known per se which can be dissolved or dispersed in water can be used. Examples thereof include base resins such as acrylic resin, polyester resin and urethane resin, and melamine resin and blocked polyisocyanate compounds. A thermosetting resin composition containing a crosslinking agent is suitable. The ratio of the base resin to the cross-linking agent is 50 to 90% by weight, especially 65 to 90% by weight, based on the total solid content of both components.
80% by weight, the latter 50 to 10% by weight, especially 35 to 20
It is preferably within the range of weight%.

As the color pigment, solid color pigments, metallic pigments, interference color pigments and the like exemplified in the description of the hydrophilic organic solvent type base coating material (A) can be preferably used. Among these, the use of a metallic pigment is more preferable because it is possible to form a metallic coating film having excellent glitter without metallic unevenness.

Of these, non-leafing aluminum flake pigments can be preferably used as the aluminum flakes. For example, metallic aluminum is mechanically pulverized by a stamp mill method, a dry ball mill method, a wet ball mill method or the like. The flakes are made into a flaky form, and a non-leafing type can be obtained by coating a flaking surface with an anti-friction agent such as oleic acid at the time of grinding. In addition, the non-leafing type can be obtained by treating with a metal salt of lead or zinc or a polar solvent. It is suitable that the aluminum flakes have a flaky shape and have a longitudinal dimension of 2 to 50 μm and a thickness of 0.1 to 2 μm.

In order to stably disperse the aluminum flakes in water in the water-based colored coating material (B), it is preferable to further add a passivating agent, a hydrophilic organic solvent and the like, if necessary.

As the passivating agent (passivator), for example, the reaction product described in JP-A-61-47771 can be preferably used. Specifically, a compound (i) containing at least one acidic hydroxyl group bonded to a phosphorus atom and further containing a group (-O-P = O (OH) 2 in the molecule) and at least one epoxide group are included. The reaction product with the compound (ii) contained in the molecule can be used as a passivating agent for aluminum flakes.

The compound (i) is orthophosphoric acid or its monoester, and the esterifying group is alkyl, alkoxyalkyl, aryl, alkyl-substituted aryl, cycloalkyl or heterocyclic group. Specifically, monobutyl phosphate, monoamyl phosphate, monononyl phosphate,
Examples include monocetyl phosphate, monophenyl phosphate and monobenzyl phosphate. Compound (ii) is at least 1
Compounds containing one epoxide group in the molecule, such as phenylglycidyl ether, α-naphthylglycidyl ether, β-naphthylglycidyl ether, and 6 or less carbon atoms on the aromatic ring. Corresponding compounds bearing alkyl substituents, aromatic monoglycidyl ethers such as benzylglycidyl ether; glycidyl benzoate, glycidyl naphthoate and glycidyl esters of substituted benzoic acids, glycidyl esters of naphthoic acid, etc. Glycidyl ester of aromatic monocarboxylic acid,
Cycloaliphatic epoxides such as cyclohexene oxide; polyhydric or hydrogenated glycidyl ethers; glycidyl (meth) acrylate or allyl glycidyl ether-containing monomers and styrene And copolymers with other monomers such as α-methylene and the like.

The ratio of the compound (i) to the compound (ii) is such that, in a system using a compound having one epoxide group as the compound (ii), free P-OH in the product is used.
A range in which at least one group is reserved is preferable. Also,
Even in a system using a compound containing one or more epoxide groups as the compound (ii), free PO in the product is obtained.
A range in which at least one H group is retained is preferable, but gelation may occur during the reaction, and therefore it is preferable to use a compound containing one epoxide group in combination. The reaction of these compounds is preferably carried out at a temperature of about 150 ° C. or lower by mixing and dissolving them in an organic solvent, if necessary. These reaction products contain a free P-OH group and have a positive acid value, and can be used as a passivating agent as they are, but they are neutralized with the above-mentioned amine compound. It is generally used in the form of a salt.

The compounding amount of the passivating agent is such that the aluminum flakes 1
10 parts by weight or less, particularly 0.1 to 3 parts by weight per 0 parts by weight is suitable.

As the hydrophilic organic solvent, those exemplified as the hydrophilic organic solvent described in the hydrophilic organic solvent type base coating material (A) can be preferably used. The content of these hydrophilic organic solvents is 40 parts by weight per 10 parts by weight of aluminum flakes.
It is preferably not more than 5 parts by weight, particularly preferably 5 to 30 parts by weight.

The solid content of the aqueous colored coating composition (B) during coating is preferably 3 to 30% by weight, particularly 5 to 20% by weight.

In this method, the water-based colored coating material (B) is applied to the uncured coating surface without crosslinking and curing the coating film of the hydrophilic organic solvent type base coating material (A). The coating method may be electrostatic coating, airless spraying, air spraying, etc.
m, especially 10 to 20 μm is suitable.

The uncured coating film of the hydrophilic organic solvent type base coating material (A) has an acid value of 20 to 50, has a hydroxyl group based on lactone modification, and has a glass transition temperature of -20 to + 20 ° C.
The neutralized product (a) of the acrylic resin has a strong water absorption property, and when the water-based coloring paint (B) is applied to the uncured coating surface containing such components, the water content in the coating film becomes When the coating film of the hydrophilic organic solvent type base coating material (A) is absorbed, the viscosity of the coating film of the aqueous coloring coating material (B) increases, and when the aluminum pigment contained therein is contained, the aluminum pigment becomes uniform and dense. It was easy to orient in parallel (horizontal), and as a result, it was possible to form a metallic coating film that was white, had a good feeling of glitter, and had a strong flip-flop property. Moreover, it is possible to form a coating film having excellent smoothness without being affected by the surrounding humidity during coating of the water-based colored coating material (B).

In the present invention, after coating the uncured coating surface of the hydrophilic organic solvent type base coating material (A) with the aqueous coloring coating material (B), it is left at room temperature or dried at 80 to 100 ° C. for 5 to 20 minutes. All or most of the water in the coating film (water-based colored paint (B)
It is preferable to apply the clear paint (C) after volatilizing the water content in the coating film of 10% by weight or less).

The clear paint (C) is a water-based coloring paint (B)
It is to be applied to the uncured coating surface of, contains a base resin, a cross-linking agent and an organic solvent, and further contains a solid color pigment, a metallic pigment, an interference pigment, an ultraviolet absorber and the like, if necessary. The thermosetting coating composition has transparency such that the color tone of the water-based colored coating composition (B) can be visually recognized through the clear coating film.

Examples of the base resin which can be used in the clear paint (C) include acrylic resins, polyester resins, alkyd resins and fluororesins containing crosslinkable functional groups such as hydroxyl group, carboxyl group, silanol group and epoxy group. ,
Examples of the resin include urethane resins and silicone-containing resins, and acrylic resin containing a crosslinkable functional group is particularly preferable. As the cross-linking agent, a melamine resin, a urea resin, a (block) polyisocyanate compound, an epoxy compound or a resin, a carboxyl group-containing compound or resin, an acid anhydride, an alkoxysilane group-containing compound or a melamine resin which can react with these functional groups is used. It can be used in combination with a crosslinking agent such as a resin. The melamine resin is a monovalent alcohol having 1 to 8 carbon atoms.
It is preferable to use a melamine resin that is etherified with a melamine or a melamine resin that has 1 to 5 triazine nuclei. An imino group-containing melamine resin can also be used. The ratio of the base resin to the crosslinking agent is 50 to 90% by weight, particularly 65 to 80% by weight, the latter 50 to 10% by weight, and particularly 45 to 20% by weight, based on the total solid content of both components. Are suitable.

The clear coating (C) whose solid content concentration during coating is adjusted to about 30 to about 80% by weight is applied by an electrostatic method or a spray method, and the film thickness of the cured coating film is 5 to 100 μm, preferably After coating the uncured coating surface of the water-based colored coating composition (B) to 20 to 80 μm, 100 to 180 ° C.
The present method is achieved by simultaneously heating the coating films of the hydrophilic organic solvent type base coating material (A), the water-based colored coating material (B) and the clear coating material (C) by heating for 10 to 40 minutes.

[0056]

Effect of the Invention Hydrophilic organic solvent type base paint (A)
Has an acid value of 20 to 50, a hydroxyl group based on lactone modification, and a glass transition temperature of -20 to +
The neutralized product (a) of the acrylic resin having a temperature of 20 ° C. has a strong water absorption property. When the water-based coloring paint (B) is applied to such an uncured coating surface, the water content in the coating film becomes hydrophilic in the lower layer. When it is rapidly absorbed by the uncured coating film of the organic solvent type base coating material (A), the viscosity of the aqueous colored coating material (B) increases, and when the aluminum pigment is contained therein, the aluminum pigment concentration becomes high. And uniformly and densely aligned in parallel (horizontal),
It was possible to form a metallic coating film which was white, had a good brilliance, and had a strong flip-flop property.

2. Since the water-based coloring paint (B) is applied to the uncured coating surface of the hydrophilic organic solvent type base coating material (A), the paint may flow or the surface may be roughened even if the humidity during coating changes. No more need to strictly control the humidity during painting.

3. When the water-based coloring paint (B) is applied to the uncured coating surface of the hydrophilic organic solvent type base paint (A), and the clear paint (C) is applied after preliminary drying, a coating film of the water-based coloring paint (B) is obtained. The clear coating (C) was not mixed with the coating film, and it was possible to prevent the occurrence of armpits and sagging.

4. Since the component (a) contains a hydroxyl group based on lactone modification, viscoelasticity can be imparted to the coating film of the base coating material (A) itself, and chipping resistance can be improved.

5. The glass transition temperature of the component (a) is -20
By adjusting the temperature within the range of to + 20 ° C., the smoothness and chipping resistance of the coating film of the base coating material (A) itself can be improved.

6. By including the resin particles (c) in the base paint (A), the coating film of the water-based colored paint (B) applied to the surface of the uncured coating film does not shift and forms a coating film having excellent smoothness. can do.

[0062]

EXAMPLES Examples and comparative examples relating to the present invention will be described below. All parts and percentages are on a weight basis and coating film thicknesses are for cured coatings.

1. Preparation of sample 1) Hydrophilic organic solvent type base paint (A) (a-1): Neutralized product of acrylic resin (Note 1) 55 parts (solid content), melamine resin (Note 2) 30 parts (solid content) , 10 parts of resin particles (Note 3), 100 parts of titanium dioxide white pigment, and 1 part of carbon black are mixed and dispersed in an equal weight mixed solvent of butyl cellosolve and isopropanol.
Nonvolatile content 45%, viscosity 25 seconds / fod cup # 4/2
0 ° C.

(Note 1) Neutralized product of acrylic resin: acrylic acid 4 parts, "FM-3" (note 4) 12.5 parts, styrene 3
A monomer component consisting of 0 part, 43.5 parts of n-butyl acrylate and 10 parts of 4-hydroxybutyl acrylate (4HBA) was added to butyl cellosolve heated to 120 ° C. over 3 hours to perform copolymerization. Tightly, acid number 31
mgKOH / g, hydroxyl value 55 mgKOH / g (“FM
The hydroxyl value based on -3 "is 23, the hydroxyl value based on 4HBA is 22) Tg is -8 ° C, and the number average molecular weight is about 2800.
An acrylic resin solution having a non-volatile content of 60% was obtained. The carboxyl group was neutralized with methylaminoethanol.

(Note 2) Melamine resin: "Uban 202
0 "(Mitsui Cytec Co., Ltd., trade name, butoxymethyl melamine resin) (Note 3) Resin particles:" Powder 678 "(Kansai Paint Co., Ltd., trade name, styrene / methyl methacrylate /
Fine particles of a copolymer composed of n-butyl acrylate / 1,6 hexanediol diacrylate = 50/20/20/10 (weight ratio), particle diameter 0.01 to 0.1 μm) (Note 4) “FM- 3 ”:“ Daicel Chemical Company, trade name,
4-mol of 4-hydroxybutyl acrylate and lactone 3
It is a reaction product with a mole and has a polymerizable double bond at one end and a hydroxyl group at the other end. "(A-2): 55 parts (solid content) of neutralized product of acrylic resin (Note 5), melamine resin (Note 2) 30 parts (solid content), 10 parts of resin particles (Note 3), 100 parts of titanium dioxide white pigment and 1 part of carbon black are mixed and dispersed in an equal weight mixed solvent of butyl cellosolve and isopropanol. The paint that becomes.
Nonvolatile content 45%, viscosity 25 seconds / fod cup # 4/2
0 ° C.

(Note 5) Neutralized product of acrylic resin: acrylic acid 4 parts, styrene 30 parts, n-butyl acrylate 51
Parts and 4-hydroxybutyl acrylate (4HBA)
A monomer component consisting of 10 parts was added to butyl cellosolve heated to 120 ° C. over 3 hours, and copolymerization was performed to obtain an acid value of 31 mgKOH / g and a hydroxyl value of 55 mgKO.
H / g (hydroxyl value based on 4HBA is 55) Tg is +1
Non-volatile content 60 at 0 ° C, number average molecular weight about 28,000
% Acrylic resin solution was obtained. The carboxyl group was neutralized with methylaminoethanol.

2) Water-based pigmented coating (B) (a): Hydroxyl group-containing acrylic per 10 parts of non-leafing aluminum flakes having a longitudinal dimension of 20 μm and a thickness of 1 μm using oleic acid (anti-friction agent) during grinding. 75 parts of resin emulsion (solid content), "Cymel 325"
(Mitsui Cytec, melamine resin) 25 parts (solid content), ethylene glycol monobutyl ether 10 parts,
A water-based metallic coating composition containing 5 parts of dimethylethanolamine and uniformly dispersed.

3) Clear coating (C) (a): 100 parts of acrylic resin solution (Note 6), Cymel 303 (manufactured by Mitsui Cytec, trade name, melamine resin,
Solid content 88%) 30 parts, 25% dodecylbenzene sulfonic acid solution 4 parts and BYK-300 (manufactured by Big Chemie Japan Co., trade name) 0.5 parts of a mixture was added with Swasol # 1000 to obtain a nonvolatile content 55. %, Viscosity 30 seconds /
A clear paint was obtained by adjusting the temperature to Ford Cup # 4/20 ° C.

(Note 6): 40 parts of Swazol # 1000 (trade name, manufactured by Maruzen Petroleum Co., Ltd.) heated to 120 ° C., 30 parts of styrene, 35 parts of butyl acrylate, 10 parts of 2-ethylhexyl acrylate. A monomer component consisting of 25 parts of 2-hydroxyethyl acrylate and 4 parts of α, α′-azobisisobutyronitrile was added for 3 hours and copolymerized to give a hydroxyl value of 120 and a number average molecular weight of about 6000. An acrylic resin solution having a nonvolatile content of 70% was obtained.

2. Examples and Comparative Examples Degreased and zinc phosphate treated steel sheets (JISG3141,
Cationic electrodeposition paint (“Electron 9400HB”) Kansai Paint Co., Ltd. on a size of 700 × 150 × 0.8 mm
(Manufactured, trade name) was subjected to electrodeposition coating by a conventional method so as to have a film thickness of 20 μm, and heated at 170 ° C. for 20 minutes to be crosslinked and cured.

The coated steel sheet thus obtained was coated with a hydrophilic organic solvent type base coating material (A) (a-1) or (a-2) to a film thickness of 15
It is coated with an air spray so as to be about 20 μm and left at room temperature for 2 minutes (the gel fraction of the coating film of the base coating material (A) is 0%), and then the water-based colored coating material (B) (a). ) Is the film thickness 1
It was coated so as to have a thickness of 0 to 15 μm, and preheated at 80 ° C. for 10 minutes. Then, clear coating (C) is applied to the coated surface.
(A) was coated with an air spray to a film thickness of 35 μm, left at room temperature for 5 minutes, and then heated at 140 ° C. for 30 minutes to cross-link and cure these multilayer coating films.

The performance of the coating film applied in the above steps is shown in Table 1 together with the respective steps.

[0073]

[Table 1]

The test method of the coating film in Table 1 is as follows.

Smoothness: The result of visual observation of the presence or absence of spots, dents, cracks, sagging, etc. on the upper surface of the multilayer coating film. ○ means no or almost no lumps, dents, armpits, sagging, etc., △ means a little lumps, dents, armpits, sagging, etc. × means lumps, dents, armpits, sagging, etc. Significantly recognized.

Vividness: ◯: The fluorescent light in the room reflected on the paint surface is clearly visible, Δ: The fluorescent light in the room reflected on the paint surface is slightly blurred, × is the fluorescent light in the room reflected on the paint surface Indicates that the light appears blurred.

Chipping resistance: At -20 ° C., 50 g of crushed stone No. 7 was applied at a pressure of 4 kg at an angle of 45 ° on the surface of the multilayer coating film.
The results are obtained by visually observing the coated surface after the coating film is impacted by being sprayed at / cm ² . ○ indicates that the peeling of the coating film due to impact stopped at the upper layer portion of the coating film of the base paint (A), the peeling area was small (about 1% or less of the coated surface), and the electrodeposition coated surface was not exposed. , △ shows that most of the base paint (A) coating film peels off (about 30% or more of the coated surface), and there is little exposure of the electrodeposition coated surface. × shows most of the base coating material (A) coating film. Exfoliation, and also the electrodeposition coating film was exfoliated, showing that the steel plate surface of the substrate was exposed.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09D 133/14 C09D 133/14 161/28 161/28 201/00 201/00 (72) Inventor Takashi Noguchi 4-17-1 Higashi-Hachiman, Hiratsuka-shi, Kanagawa F-term in Kansai Paint Co., Ltd. (reference) 4D075 AE08 AE09 CA04 CA38 CA48 CB04 CB13 DA06 DA23 DB01 DB31 DC12 EA06 EA07 EA10 EA19 EB22 EB32 EB35 EB38 EB52 CC53061062 06038 CC061 CD072 CF051 CF052 CG141 CG142 CG171 CG172 CH031 CH032 CH041 CH042 CH171 CH172 CH201 CH202 CP122 DA161 DA162 DB221 DB222 DD001 DD012 DG031 DG062 GA03 GA06 HA066 JB02 KA08 KA20 MA08 MA10 MA12 MA13 MA14 NA01 NA02 PC08 PC08 PC08

Claims (2)

[Claims] 1. A water-based colored coating material (B) in the uncured state, wherein a hydrophilic organic solvent type base coating material (A) is applied to an object to be coated.
And a method for forming a multilayer coating film in which an organic solvent type clear coating material (C) is applied and then these coating films are simultaneously cured by heating, as a hydrophilic organic solvent type base coating material (A),
A neutralized product (a) of an acrylic resin having an acid value of 20 to 50, a hydroxyl group based on lactone modification, and a glass transition temperature of -20 to + 20 ° C, and a melamine resin having a carbon number of 1 to 5 alkoxy group ( A method for forming a multilayer coating film, which is a coating material containing b) and resin particles (c) as essential components. 2. The method for forming a multilayer coating film according to claim 1, wherein the water-based colored coating material (B) is a solid color coating material or a metallic coating material.