JP2003292877A - Aqueous base coating composition and method for forming coating film using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous base coating composition which can suppress mixing or inversion of coating film layers and give a coating film excellent in flip-flop properties in a method for forming a coating film comprising simultaneously hardening a base coating film and a clear coating film on a substance to be coated, and a method for forming the coating film. <P>SOLUTION: The aqueous base coating composition comprises an acrylic emulsion resin obtained by emulsion polymerization of an α,β-ethylenically unsaturated monomer mixture having an acid value of 3-50 and containing at least 65 mass% of a (meth)acrylate bearing a 1-2C ester part, a polyether polyol bearing at least 0.02 primary hydroxy group, in the average, in one molecule and having a number-average molecular weight of 300-3,000 and a water tolerance of at least 2.0, a urethane emulsion resin and a brilliant material. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous base coating composition applied to automobile bodies and the like, a method for forming a coating film using the same, and a coating film obtained by the method.

[0002]

2. Description of the Related Art Generally, a large amount of an organic solvent is volatilized in a coating material for automobiles at the time of coating or baking and curing, and as one of the methods for reducing the processing man-hours, a method of making the coating form aqueous is being studied.

For example, JP-A-7-53913 discloses at least a part of a polymer containing an amide group-containing ethylenically unsaturated monomer, an acidic group-containing ethylenically unsaturated monomer and a hydroxyl group-containing ethylenically unsaturated monomer. Disclosed is an aqueous coating composition containing a resin obtained by neutralization and an aqueous dispersion of carboxyl group-containing acrylic resin particles. However, the present invention is not limited to this, and in general, the conventional aqueous base compositions are often inferior to the solvent-based compositions particularly in the flip-flop property of the metallic coating film.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for forming a coating film, which comprises simultaneously curing a base coating film and a clear coating film on an object to be coated, by controlling the layer mixture and inversion of both coating films, An object of the present invention is to provide an aqueous base coating composition and a coating film forming method capable of obtaining a coating film having a high flip-flop property.

[0005]

According to the present invention, a (meth) acrylic acid ester having an ester portion having 1 or 2 carbon atoms is used.
Acid value 3 to 50 mgKOH / g containing 5% by mass or more
Acrylic emulsion resin obtained by emulsion-polymerizing the α, β-ethylenically unsaturated monomer mixture described in 1. has an average of 0.02 or more primary hydroxyl groups in one molecule and a number average molecular weight of 30.
A water-based coating composition comprising a polyether polyol having a water tolerance of 0 to 3000 and a water tolerance of 2.0 or more, a urethane emulsion resin, and a glittering material, wherein the urethane emulsion resin is a coating resin solid content. It is preferable to contain 3 to 30 parts by mass per 100 parts by mass.

Here, the polyether polyol preferably has at least one primary hydroxyl group in one molecule and has a hydroxyl value of 30 to 700 mgKOH / g, and preferably has two or more hydroxyl groups in one molecule. It is more preferable to have.

Further, it preferably contains a polyester resin or an alkyd resin.

The present invention also includes a step (1) of applying a water-based base paint to an object to be coated to form a base coating film,
A step (2) of forming a clear coating film by applying a clear coating on the base coating film without curing the base coating film;
In the method for forming a coating film, which includes the step (3) of simultaneously heating and curing the base coating film and the clear coating film to form a coating film, the aqueous base coating composition is the aqueous base coating composition. Is a method for forming a coating film.

Further, the present invention is a coating film formed by the above method.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Aqueous Base Coating Composition The aqueous base coating composition of the present invention has an acid value of 3 in which 65% by mass or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion is contained. ~ 50 mg KOH / g α,
Acrylic emulsion resin obtained by emulsion polymerization of β-ethylenically unsaturated monomer mixture, having an average of 0.02 or more primary hydroxyl groups in one molecule, and a number average molecular weight of 300 to 3
000, and contains a polyether polyol having a water tolerance of 2.0 or more, a urethane emulsion resin, and a luster colorant.

The acrylic emulsion resin contained in the aqueous base coating composition of the present invention has an ester part having 1 carbon atom.
Alternatively, the α, β-containing acid value of 3 to 50 mgKOH / g containing 65% by mass or more of the (meth) acrylic acid ester of 2
It is obtained by emulsion polymerization of a mixture of ethylenically unsaturated monomers.

When the amount of the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion contained in the above α, β-ethylenically unsaturated monomer mixture is less than 65% by mass, the coating film obtained is Appearance deteriorates. Examples of the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion include methyl (meth) acrylate and ethyl (meth) acrylate. In the present specification, (meta)
Acrylic acid ester shall mean both acrylic acid ester and methacrylic acid ester.

The acid value of the α, β-ethylenically unsaturated monomer mixture is 3 to 50 mgKOH / g, preferably 7 to 40 mgKOH / g. Acid value is 3mg
If it is less than KOH / g, the workability cannot be improved, and if it exceeds 50 mgKOH / g, the water resistance of the coating film decreases. On the other hand, when the aqueous base coating composition is required to have curability, the α, β-ethylenically unsaturated monomer mixture has a hydroxyl value of 10 to 150 mgKOH.
/ G, preferably 20 to 100 mg KOH / g. If it is less than 10 mgKOH / g, sufficient curability cannot be obtained, and if it exceeds 150 mgKOH / g, the water resistance of the coating film decreases. The glass transition temperature of the emulsion resin obtained by polymerizing the above α, β-ethylenically unsaturated monomer mixture is preferably between −20 ° C. and 80 ° C. from the viewpoint of physical properties of the coating film.

The above α, β-ethylenically unsaturated monomer mixture can have the above acid value and hydroxyl group value by including therein an α, β-ethylenically unsaturated monomer having an acid group or a hydroxyl group. .

Examples of the α, β-ethylenically unsaturated monomer having an acid group include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethyl phthalic acid and 2-acryloyloxyethyl. Succinic acid, 2-acryloyloxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid, ω-carboxy-polycaprolactone mono (meth) acrylate, isocrotonic acid, α-hydro-ω-((1-oxo- 2-propenyl) oxy) poly (oxy (1-oxo-1,6-hexanediyl)),
Maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid and the like can be mentioned. Among these, preferred are acrylic acid, methacrylic acid, and acrylic acid dimer.

On the other hand, as the α, β-ethylenically unsaturated monomer having a hydroxyl group, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate,
Examples thereof include hydroxybutyl (meth) acrylate, allyl alcohol, methacrylic alcohol, and an adduct of hydroxyethyl (meth) acrylate and ε-caprolactone. Preferred among these are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyethyl (meth) acrylate and ε.
An adduct with caprolactone.

Further, the above α, β-ethylenically unsaturated monomer mixture may further contain other α, β-ethylenically unsaturated monomers. Other α and β-
Examples of the ethylenically unsaturated monomer include (meth) acrylic acid esters having 3 or more carbon atoms in the ester portion (for example, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, ( 2-Ethylhexyl (meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, (meth ) Dihydrodicyclopentadienyl acrylate, etc., polymerizable amide compounds (for example, (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl (meth) acrylamide,
N, N-dibutyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide 2,4-dihydroxy-4'-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, etc., polymerizable aromatic compounds (eg, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.) ), Polymerizable nitriles (eg acrylonitrile, methacrylonitrile etc.), α-olefins (eg ethylene, propylene etc.), vinyl esters (eg vinyl acetate, vinyl propionate etc.), dienes (eg butadiene, isoprene etc.) ) Raise this Can. These can be selected depending on the purpose, but (meth) acrylamide is preferably used when hydrophilicity is easily imparted.

The above α, β-other than (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion is used.
The content of the ethylenically unsaturated monomer in the α, β-ethylenically unsaturated monomer mixture must be set to less than 35% by mass.

The emulsion resin (A) contained in the aqueous base coating composition of the present invention is obtained by emulsion polymerization of the above α, β-ethylenically unsaturated monomer mixture. The emulsion polymerization carried out here can be carried out using a generally well-known method. Specifically, the emulsifier is dissolved in water or an aqueous medium containing an organic solvent such as alcohol, if necessary, and the above α,
It can be carried out by dropping the β-ethylenically unsaturated monomer mixture and the polymerization initiator. Similarly, an α, β-ethylenically unsaturated monomer mixture previously emulsified with an emulsifier and water may be added dropwise.

Suitable polymerization initiators include azo oily compounds (for example, azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile)).
And 2,2′-azobis (2,4-dimethylvaleronitrile) and the like, and aqueous compounds (eg, anionic 4,4′-azobis (4-cyanovaleric acid) and cationic 2,2′-). Azobis (2-methylpropionamidine)); and redox oily peroxides (eg, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide and t).
-Butyl perbenzoate) and aqueous peroxides (eg potassium persulfate and ammonium peroxide)
Is mentioned.

As the emulsifier, those usually used by those skilled in the art can be used, but reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.) and Eleminol JS-2 (Sanyo Chemical Co., Ltd.) can be used. Company), ADEKA rear soap NE-20 (manufactured by Asahi Denka Co., Ltd.) and AQUARON HS-
10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and the like are particularly preferable.

Further, in order to control the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used if necessary.

The reaction temperature is determined by the initiator, and for example, it is preferably 60 to 90 ° C. for the azo type initiator and 30 to 70 ° C. for the redox type. In general,
The reaction time is 1 to 8 hours. The amount of the initiator, based on the total amount of the α, β-ethylenically unsaturated monomer mixture, is generally 0.1 to 5% by mass, preferably 0.2 to 2% by mass.
Is.

The emulsion polymerization can be carried out in two steps. That is, first, a part (α, β-ethylenically unsaturated monomer mixture 1) of the above α, β-ethylenically unsaturated monomer mixture is emulsion polymerized, and here, the above α, β-ethylenically unsaturated monomer mixture is obtained. The remainder (α, β-ethylenically unsaturated monomer mixture 2) is further added to carry out emulsion polymerization.

In order to form a coating film having a high appearance, the α, β-ethylenically unsaturated monomer mixture 1 preferably contains an α, β-ethylenically unsaturated monomer having an amide group. Further, at this time, it is more preferable that the α, β-ethylenically unsaturated monomer mixture 2 does not contain an α, β-ethylenically unsaturated monomer having an amide group. Since the mixture of α, β-ethylenically unsaturated monomer mixtures 1 and 2 is the above α, β-ethylenically unsaturated monomer mixture, the above-mentioned α, β-
-The requirement for the ethylenically unsaturated monomer mixture is α, β-
The ethylenically unsaturated monomer mixture 1 and 2 together will fill.

The particle diameter of the acrylic emulsion resin thus obtained is preferably in the range of 0.01 to 1.0 μm. If the particle size is less than 0.01 μm, the effect of improving workability is small, and if it exceeds 1.0 μm, the appearance of the resulting coating film may be deteriorated. The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions.

The above acrylic emulsion resin can be used at pH = 5 to 10 by neutralizing with a base, if necessary. This is because the stability in this pH range is high. This neutralization is preferably carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

The polyether polyol contained in the aqueous base coating composition of the present invention has an average of 0.02 or more primary hydroxyl groups in one molecule and a number average molecular weight of 300 to.
The water tolerance is 3000 and the water tolerance is 2.0 or more. By containing this polyether polyol, the flip-flop property, water resistance, and chipping resistance of the coating film can be improved.

When the average number of primary hydroxyl groups in one molecule of the above polyether polyol is less than 0.02, the water resistance and chipping resistance of the coating film deteriorate. Furthermore, it is preferable to have 0.04 or more primary hydroxyl groups in one molecule, and it is particularly preferable to have one or more primary hydroxyl groups in one molecule. In addition to the primary hydroxyl group, the number of hydroxyl groups including secondary and tertiary hydroxyl groups is preferably 2 or more in one molecule from the viewpoint of water resistance and chipping resistance of the coating film. From the viewpoint of hydroxyl value, the hydroxyl value is 30
It is preferably ˜700 mgKOH / g. When the hydroxyl value is below the lower limit, the curability is lowered and the water resistance and chipping resistance of the coating film are lowered. If the upper limit is exceeded, paint stability,
The water resistance of the coating film decreases. Particularly preferably 50 to 500
It is mgKOH / g.

If the number average molecular weight of the above polyether polyol is less than 300, the water resistance of the coating film decreases, and
If it exceeds 00, the curability and chipping resistance of the coating film deteriorate. It is preferably 400 to 2000. In this specification, the molecular weight is determined by the GPC method using a styrene polymer as a standard.

On the other hand, when the water tolerance of the above polyether polyol is less than 2.0, the water dispersibility is lowered and the appearance of the coating film is deteriorated. In particular, it is preferably 3.0 or more.

The water tolerance used herein is for evaluating the degree of hydrophilicity, and the higher the value, the higher the hydrophilicity. In the present specification, the water tolerance value is measured by mixing 0.5 g of the above polyether polyol with 10 ml of acetone in a 100 ml beaker and dispersing the mixture in a 100 ml beaker, and using a buret for this mixture, deionized water is used. Is gradually added, and the amount of deionized water (ml) required for the mixture to become cloudy is measured. The amount (ml) of this deionized water is taken as the water tolerance value.

In this method, for example, when the polyether polyol is hydrophobic, initially the polyether polyol and acetone were in a good compatible state, but the addition of a small amount of deionized water caused an incompatible state. And white turbidity occurs in the measurement system. On the contrary, when the polyether polyol is hydrophilic, the more hydrophilic the polyether polyol is, the more deionized water is required until cloudiness occurs.
Therefore, the hydrophilic / hydrophobic degree of the polyether polyol can be measured by this method.

The above polyether polyol is preferably contained in the coating resin solid content in an amount of 1 to 40% by mass, more preferably 3 to 30% by mass. If the upper limit is exceeded, the water resistance and chipping resistance of the coating film will decrease, and if the lower limit is exceeded, the appearance of the coating film will deteriorate.

Examples of the above-mentioned polyether polyols include compounds obtained by adding alkylene oxide to active hydrogen-containing compounds such as polyhydric alcohols, polyhydric phenols and polycarboxylic acids. Examples of the active hydrogen atom-containing compound include water, polyhydric alcohols (ethylene glycol, diethylene glycol, trimethylene glycol,
Propylene glycol, 1,4-butanediol, 1,
6-hexanediol, neopentyl glycol, 1,
Dihydric alcohols such as 4-dihydroxymethylcyclohexane and cyclohexylene glycol, glycerin, trioxyisobutane, 1,2,3-butanetriol,
1,2,3-pentanetriol, 2-methyl-1,
2,3-propanetriol, 2-methyl-2,3,4
-Butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,
3,4-hexanetriol, 4-propyl-3,4,
5-heptanetriol, 2,4-dimethyl-2,3
4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,
2,4-pentanetriol, trimethylolethane,
Trihydric alcohols such as trimethylolpropane, pentaerythritol, 1,2,3,4-pentanetetrol,
2,3,4,5-hexanetetrol, 1,2,4,5
-Pentane tetrol, 1,3,4,5-hexane tetrol, tetrahydric alcohol such as diglycerin and sorbitan, pentahydric alcohol such as adonitol, arabitol, xylitol and triglycerin, dipentaerythritol, sorbitol, mannitol and iditol. , Inositol, dulcitol, talose, allose and other hexavalent alcohols, sucrose and other octavalent alcohols, polyglycerin, etc.); polyhydric phenols [polyhydric phenols (pyrogallol, hydroquinone, phloroglucin, etc.), bisphenols (bisphenol A, bisphenol) Sulfone, etc.)]; polycarboxylic acid [aliphatic polycarboxylic acid (succinic acid, adipic acid, etc.), aromatic polycarboxylic acid (phthalic acid, terephthalic acid, trimellitic acid, etc.)]; and two or more of these. blend And the like.

The above polyether polyol is usually prepared by adding an alkylene oxide to the above active hydrogen-containing compound in the presence of an alkali catalyst at 60 to 60 ° C. under normal pressure or pressure.
It is obtained by carrying out an addition reaction at a temperature of 160 ° C.
Examples of the alkylene oxide include alkylene oxides such as ethylene oxide, propylene oxide and butylene oxide, and these may be used alone or in combination.
One or more species can be used in combination. When two or more kinds are used together, the addition format may be either block or random.

As the above polyether polyol, commercially available products can be used, for example, Primepol PX-1000, Sannix SP-750,
PP-400 (both of which are manufactured by Sanyo Chemical Industry Co., Ltd.), PT
MG-650 (manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned.

Furthermore, in order to improve the pigment dispersibility, the above polyether polyol is used in JP-A-59-1382.
As disclosed in Japanese Patent Publication No. 69, an amino resin described later, hydroxyethylethyleneimine (for example, “HEA” of Mutual Pharmaceutical Co., Ltd.), 2-hydroxypropyl-2-aziridinylethylcarboxylate (for example, “HPA of Mutual Pharmaceutical Engineering”).
It can be modified with basic substances such as C ").
The amount of the modifier is 1 to 1 with respect to the above polyether polyol.
0 mass% is preferable. If it is less than 1% by mass, a sufficient modifying effect cannot be obtained, and if it exceeds 10% by mass, the stability of the modified polyether polyol becomes poor.

The urethane emulsion resin contained in the aqueous base coating composition of the present invention is not particularly limited, and examples thereof include diisocyanate and a glycol containing at least two active hydrogens or a glycol having a carboxylic acid group. And the NCO / OH equivalent ratio is 0.5 to
It can be produced by reacting at 2.0 to make a urethane prepolymer, and then neutralizing and chain extending the prepolymer and adding ion-exchanged water.

The diisocyanate used when preparing the urethane prepolymer which is a constituent of the urethane emulsion resin is not particularly limited, but examples thereof include aliphatic, alicyclic, and aromatic diisocyanates. , Specifically, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
4,4'-diphenylmethane diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, metaxylene diisocyanate, lysine diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 3 , 3'-Dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,
Examples thereof include 4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate and their derivatives.

The above-mentioned glycols are not particularly limited, but are those containing at least two active hydrogens, and specifically, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1, 2-propylene glycol, trimethylene glycol, 1,3-butylene glycol, tetramethylene glycol, hexamethylene glycol, hydrogenated bisphenol A, low molecular weight glycol such as ethylene oxide or propylene oxide adduct of bisphenol A, polyoxypropylene glycols Addition product of polyoxypropylene and glycerin, addition product of polyoxypropylene and trimethylolpropane, addition product of polyoxypropylene and 1,2,6-hexanetriol, polyoxypropylene And adducts of pentaerythritol, adduct of polyoxypropylene and sorbitol, methylene - bis - phenyl diisocyanate, polytetramethylene furan polyethers and their derivatives, and the like which is a chain extended with hydrazine.

Further, with adipic acid or phthalic acid,
Ethylene glycol, propylene glycol, 1,3-
Butylene glycol, 1,4-butylene glycol, diethylene glycol, hexanediol, 1,2,6-
Examples thereof include polyesters and polycaprolactone which are condensates of hexanetriol, trimethylolpropane, 1,1,1-trimethylolethane and the like.

The glycol having a carboxylic acid group is not particularly limited, but for example, 2,2
-Dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid and the like can also be used.

The urethane emulsion resin is prepared by using a urethane prepolymer, which is a reaction product of the above-mentioned glycol and an excess of an isocyanate compound, with a cationic, nonionic or anionic surfactant. It can be obtained by subjecting the chain and chain elongation to dispersion by adding ion-exchanged water.

The neutralizing agent used in that case is not particularly limited, but examples thereof include amines such as trimethylamine, triethylamine, tri-n-propylamine, tributylamine, triethanolamine, and hydroxylation. Examples thereof include sodium, potassium hydroxide, and ammonia.

The chain extender is not particularly limited, but examples thereof include polyols such as ethylene glycol and propylene glycol, ethylenediamine,
Propylenediamine, hexamethylenediamine, tolylenediamine, xylylenediamine, diphenyldiamine, diaminodiphenylmethane, diaminocyclohexylmethane, piperazine, 2-methylpiperazine, 1,2
An aliphatic, alicyclic or aromatic diamine such as -bis (2-cyanoethylamino) ethane or isophoronediamine,
And water and the like.

For example, commercial products of the urethane emulsion resin are not particularly limited, but include "Bondick" series, "Hydran" series manufactured by Dainippon Ink, and "Implanyl" series manufactured by Bayer, for example. , Neoletts R-940, R-941, R-
960, R-962, R-966, R-967, R-9
62, R-9603, R-9637, R-9618, R
-9619, XR-9624, etc. made by Avicia "Neolets" series, Sanyo Chemical Co., Ltd. "U-coat",
Examples include "Euplen", "Permarine" series, and "Adekabon Titer" series manufactured by Asahi Denka.

The above urethane emulsion resins may be used alone or in combination of two or more.

The aqueous base coating composition of the present invention is
It is preferable that the urethane emulsion resin is contained in an amount of 3 to 30 parts by mass based on 100 parts by mass of the coating resin solid content. When the content ratio of the urethane emulsion resin is less than 3 parts by mass, the adhesiveness and the like decrease, and when it exceeds 30 parts by mass, the storage stability of the coating composition decreases. It is particularly preferably 10 to 25 parts by mass.

The luster color material contained in the aqueous base coating composition of the present invention is not particularly limited and may be colored, for example, having an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm and a thickness. Is preferably 0.1 to 5 μm.
Further, those having an average particle diameter in the range of 10 to 35 μm are excellent in brilliance and are more preferably used. Specific examples thereof include uncolored or colored metallic glitters such as metals or alloys of aluminum, copper, zinc, iron, nickel, tin, aluminum oxide and the like, and mixtures thereof. In addition, interference mica pigments, white mica pigments, graphite pigments, glass flake pigments and the like can be included.

Generally, the pigment concentration (PWC) of the luster color material is preferably 18.0 mass% or less. If the upper limit is exceeded, the appearance of the coating film will deteriorate. It is more preferably 0.01 to 15.0 mass%, and particularly preferably 0.01 to 13.0 mass%. The pigment concentration of the above-mentioned luster pigment is a calculation formula including other pigments described later,
It is calculated from (total mass of all glitter materials) / (total mass of all glitter materials and other pigments and all resin components) × 100 (%).

The aqueous base coating composition of the present invention may contain a curing agent. As the curing agent, those generally used in paints can be used, and examples of such a curing agent include amino resins and blocked isocyanates. Amino resins and / or blocked isocyanates are generally used from the viewpoint of various properties and cost of the obtained coating film.

The amino resin is not particularly limited, and a water-soluble melamine resin or a water-insoluble melamine resin can be used. Further, among the melamine resins, it is preferable to use one having a water tolerance of 3.0 or more from the viewpoint of the stability of the coating material. The water tolerance can be measured in the same manner as the above polyether polyol.

The above-mentioned blocked isocyanate can be obtained by adding a blocking agent having active hydrogen to polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate and isophorone diisocyanate. Examples thereof include those which dissociate the blocking agent by heating to generate an isocyanate group, which reacts with the functional group in the resin component to cure.

When the above curing agent is contained, its content is preferably 15 to 100 parts by mass, preferably 15 to 100 parts by mass, relative to 100 parts by mass of the resin solid content in the aqueous base coating composition.
More preferably, it is 35 parts by mass. When it is less than 15 parts by mass, curability and the like are deteriorated, and when it is more than 100 parts by mass, adhesion and hot water resistance are deteriorated. Also, at this time,
The aqueous base coating composition of the present invention has a coating resin solid content of 10
The sum of the urethane emulsion resin and the curing agent is preferably 30 to 60 parts by mass per 0 parts by mass.
When the above sum is less than 30 parts by mass, the coating workability is deteriorated, and when it exceeds 60 parts by mass, the storage stability of the paint is deteriorated. It is particularly preferably 35 to 55 parts by mass.

The aqueous base coating composition of the present invention may optionally contain other film forming resin. As such, although not particularly limited, acrylic resin, polyester resin, alkyd resin,
A coating film forming resin such as an epoxy resin can be used.

The above-mentioned other film-forming resins have a number average molecular weight of 3,000 to 50,000, preferably 6,000.
~ 30,000. If it is less than 3000, the coating workability and curability are not sufficient, and if it exceeds 50,000, the non-volatile content at the time of coating becomes too low and the coating workability becomes worse.

The above-mentioned other coating film forming resins are 10 to 10
It is preferable to have an acid value of 0 mgKOH / g, and further 20 to 80 mgKOH / g. If it exceeds the upper limit, the water resistance of the coating film decreases, and if it exceeds the lower limit, the water dispersibility of the resin decreases. Also, 20 to 180 mg KOH / g, and further 30 to
It preferably has a hydroxyl value of 160 mgKOH / g, and when it exceeds the upper limit, the water resistance of the coating film decreases, and when it is less than the lower limit, the curability of the coating film decreases.

The polyester resin is obtained by polycondensing an acid component and an alcohol component. The acid component is not particularly limited, and examples thereof include polyvalent carboxylic acid compounds such as adipic acid, sebacic acid, isophthalic acid, and phthalic anhydride, and anhydrides thereof. Further, as the acid component, a compound having a carboxylic acid group and a hydroxyl group in one molecule such as dimethylolpropionic acid can be used.
The alcohol component is not particularly limited, and examples thereof include polyhydric alcohol compounds such as ethylene glycol, trimethylolpropane and neopentyl glycol.

The alkyd resin is not particularly limited, and can be obtained by polycondensing the acid component, the alcohol component and fats and oils such as coconut oil and linseed oil. Further, the coating film-forming resin may be neutralized with a base such as a tertiary amine such as dimethylethanol or triethylamine, if necessary, and may be dissolved or dispersed in water.

Among the resin components in the water-based coating composition of the present invention, the mixing ratio of the acrylic emulsion resin and the other film-forming resin is based on the total resin solid content of the acrylic emulsion. Resin is 5
To 95% by mass, more preferably 10 to 85% by mass, particularly preferably 20 to 70% by mass, and 95 to 5% by mass of other coating film-forming resin, more preferably 90 to 1% by mass.
5% by mass, particularly preferably 80 to 30% by mass. When the proportion of the acrylic emulsion resin is less than 5% by mass, sagging is suppressed and the coating film appearance is deteriorated, and when it is more than 95% by mass, the coating film appearance may be deteriorated.

The aqueous base coating composition of the present invention also comprises
Other pigments can be included. The above-mentioned other pigments are not particularly limited, and examples thereof include color pigments and extender pigments. Examples of the coloring pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments. Examples thereof include pigments, dioxane-based pigments, quinacridone-based pigments, isoindolinone-based pigments, metal complex pigments, and inorganic-based materials such as yellow lead, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. Examples of the extender pigment include calcium carbonate, barium sulfate, clay, talc and the like.

At this time, the total pigment concentration (PWC) in the aqueous base coating composition is preferably 0.1 to 50%. It is more preferably 0.5 to 40%, and particularly preferably 1.0 to 30%. If the upper limit is exceeded, the appearance of the coating film will deteriorate. The total pigment concentration is (total mass of all other pigments and all luster materials) / (total mass of all luster materials and other pigments, and all resin components) x
It is represented by 100 (%).

When the bright material contained in the aqueous base coating composition of the present invention contains a scaly bright material, it is preferable to further contain a phosphoric acid group-containing acrylic resin. This phosphoric acid group-containing acrylic resin is an acrylic resin obtained by copolymerizing a monomer represented by the following general formula (I) and another ethylenic monomer.

CH ₂ ═CXCO (OY) _n OPO (OH) ₂ (I) (In the formula, X is a hydrogen atom or a methyl group, and Y is a carbon number of 2 to 2.
4 is an alkylene group, and n is an integer of 3 to 30. ) The phosphoric acid group-containing acrylic resin is used to favorably disperse the scaly glitter material. This resin has an acid value of 1
5 to 200 mgKOH / g, the acid value of the phosphate group is 10 to 150 mgKOH / g, and the number average molecular weight is 1
It is preferably 000 to 50,000. Acid value is 15
If it is less than mgKOH / g, it may not be possible to sufficiently disperse the scaly glittering material. The acid value is 200
If it exceeds mgKOH / g, the storage stability of the aqueous base coating composition may be deteriorated. Acid value 15-200mg
Of KOH / g, the acid value due to the phosphate group is 15 to 10
More preferably, it is 0 mgKOH / g.

On the other hand, when the number average molecular weight is less than 1000, the dispersion effect may not be sufficiently obtained,
If the number average molecular weight exceeds 50,000, the appearance of the coating film may deteriorate. The phosphoric acid group-containing acrylic resin may have a hydroxyl value for curing, and the value is preferably 20 to 200 mgKOH / g.

The phosphoric acid group-containing acrylic resin is preferably contained in an amount of 0.01 to 5 parts by mass, more preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the coating resin solid content.
4 parts by mass, particularly preferably 0.2 to 3 parts by mass. If the content of the phosphoric acid group-containing acrylic resin is too small, the water resistance of the coating film may decrease. Further, if the content of the phosphoric acid group-containing acrylic resin is too large, the storage stability of the coating composition deteriorates.

Specific examples of the monomer represented by the above general formula (I) include acid phosphooxyhexaoxypropylene monomethacrylate and acid phosphooxide deca (oxypropylene) monomethacrylate.

The other ethylenic monomer is an ethylenic monomer copolymerizable with the monomer represented by the general formula (I) and may be a mixture of plural kinds of monomers. In addition, the obtained copolymer, that is, the acrylic resin, can be cured by the curing agent. Specific examples thereof include monomers having an acidic group such as a carboxyl group and a sulfonic acid group or a hydroxyl group.

Furthermore, the aqueous base coating composition contains
Other viscosity control agents can be added in order to prevent compatibility with the top coating film and to secure coating workability. As the viscosity control agent, those which generally exhibit thixotropic properties can be used, and examples thereof include crosslinked or non-crosslinked resin particles, swelling dispersions of fatty acid amides, amide fatty acids, and polyamide-based ones such as long-chain polyaminoamide phosphates. ,
Polyethylene type such as colloidal swelling dispersion of oxidized polyethylene, organic acid smectite clay, organic bentonite type such as montmorillonite, aluminum silicate,
Examples of the viscosity control agent include inorganic pigments such as barium sulfate, and flat pigments that exhibit viscosity depending on the shape of the pigment.

Further, the aqueous base coating composition used in the present invention is used as a corrosion inhibitor when a metallic lusterant is used, or to improve the wettability of the luster and improve the physical properties of the coating film. May contain a phosphoric acid ester compound having a long-chain alkyl group having 8 to 18 carbon atoms and having HLB 3 to 12.

The number of carbon atoms in the above alkyl chain is preferably from 8 to 18, and if the number of carbon atoms is less than 8, the wettability is reduced and the adhesion is deteriorated. Further, if the carbon number exceeds 18, crystal of the compound precipitates in the coating material, causing a problem. More preferably, the number of carbon atoms is 10 to 14, the wettability is better, and the adhesion is improved. The HLB of the above compound is 3 to 12, preferably 4 to 8. This value is a Griffin formula based on mass fraction: HLB = 20 × (MH / M) [wherein, MH means the molecular weight of the hydrophilic group part, and M means the molecular weight of the activator].
Required from. The molecular weight of the hydrophilic group portion was the molecular weight of phosphoric acid ester, sulfonic acid, and carboxylic acid. Outside of this range, the wettability decreases, which is not preferable.

Examples of the phosphoric acid ester compound include 2-ethylhexyl acid phosphate and mono-
Or di-diisodecyl acid phosphate, mono-
Alternatively, di-tridecyl acid phosphate, mono- or di-lauryl acid phosphate, mono- or di-nonylphenyl acid phosphate, etc. may be mentioned.

The blending amount of the above components is 0.1 to 5% by mass based on the total amount of resin solids, preferably 0.2.
It is preferably ˜2% by mass. If it is less than the lower limit, the adhesiveness will decrease. On the other hand, if the upper limit is exceeded, the water resistance will decrease.

In the water-based coating composition of the present invention, in addition to the above-mentioned components, additives usually added to the coating, such as a surface conditioner, a thickener, an antioxidant, an anti-UV agent, and an antifoaming agent. Etc. may be blended. The blending amount of these is within the range known to those skilled in the art.

The method for producing the aqueous base coating composition of the present invention is not particularly limited, and any method known to those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll can be used. . Coating Film Forming Method The first step of the coating film forming method of the present invention is a step (1) of forming a base coating film by applying an aqueous base paint to an object to be coated. The article to be coated is not particularly limited,
For example, it can be advantageously used for metals, plastics, foams and the like, especially for metal surfaces and castings, but it can be used particularly preferably for metal products which can be subjected to cationic electrodeposition coating. Examples of the metal products include iron, copper, aluminum, tin, zinc and the like, and alloys containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles and buses. It is particularly preferable that these metals have been previously subjected to chemical conversion treatment with phosphate, chromate, or the like.

An electrodeposition coating film may be formed on the above-mentioned chemical conversion treated steel sheet. As this electrodeposition coating material, a cation type and anion type can be used, but the cation type electrodeposition coating is excellent in corrosion resistance. It is preferable because it gives a coating film.

Examples of the plastic products include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin and the like. Specific examples include automobile parts such as spoilers, bumpers, mirror covers, grilles and door knobs. further,
These plastic products are preferably steam washed with trichloroethane or washed with a neutral detergent. Further, a primer coating may be applied to enable electrostatic coating.

Further, an intermediate coating film may be formed on the electrodeposition coating film or the primer layer. This intermediate coating film is formed by applying an intermediate coating material. The intermediate coating material is not particularly limited, and examples thereof include water-based, solvent-based, and powder-based coatings well known to those skilled in the art.

The method of applying the water-based base paint in the above step (1) is not particularly limited, but when it is applied to an automobile body, in order to enhance the appearance, it is subjected to multi-stage coating by air electrostatic spray coating, preferably two stages. Or by electrostatic spray coating, commonly known as “μμ (micro micro) bell” or “μ (micro)
A method of forming a coating film by a coating method in combination with a rotary atomization type electrostatic coating machine called "bell" or "metabell" can be used. The film thickness of the aqueous base coating film varies depending on the desired application, but is generally 10 to 30 μm as a dry film thickness. If the amount exceeds the upper limit, the sharpness may be deteriorated, or defects such as unevenness or sagging may occur during coating. If the amount is less than the lower limit, the underlying layer may not be concealed and film breakage may occur.

In order to obtain a good finished coating film, the uncured base coating film is heated at 40 to 100 ° C. for 2 to 10 minutes, that is, so-called preheating treatment, before the next step. Is preferred.

The second step in the method for forming a coating film of the present invention is a step (2) of forming a clear coating film by coating a clear coating on the base coating film without curing the base coating film. The clear coating film applied after forming the base coating film is formed to smooth and protect irregularities, flicker and the like caused by the base coating film. Specifically, as the coating method, it is preferable to form the coating film by the rotary atomization type electrostatic coating machine described above. The dry film thickness of the clear coating film is generally preferably about 10 to 80 μm, more preferably about 20 to 60 μm. If it exceeds the upper limit, defects such as cracking or sagging may occur at the time of coating, and if it is less than the lower limit, the irregularities of the base may not be concealed.

The third step in the coating film forming method of the present invention is the step (3) of simultaneously heating and curing the base coating film and the clear coating film to form a coating film.
This is generally called the two-coat one-bake method. The heat curing temperature is not particularly limited, but generally 80 to 1
The temperature is set to 80 ° C, preferably 120 to 160 ° C. If it exceeds the upper limit, the coating film becomes hard and brittle, and if it is less than the lower limit, curing is insufficient. The heat curing time varies depending on the heat curing temperature, but is 10 to 30 minutes at a heat curing temperature of 120 ° C to 160 ° C, for example.

The thickness of the coating film formed by the coating film forming method of the present invention is generally 30 to 300 μm, preferably 50 to 250 μm. If it exceeds the upper limit, the physical properties of the coating film may deteriorate due to internal stress strain, and if it is less than the lower limit, the strength of the coating film itself may decrease.

[0085]

The present invention will be described in detail below with reference to specific examples, but the present invention is not limited to the following examples. In the following, "parts" means "parts by mass".

Production of Acrylic Emulsion Resin A-1 126.5 parts of deionized water was added to a reaction vessel, and the temperature was raised to 80 ° C. with stirring in a nitrogen stream. Then, as the first stage α, β-ethylenically unsaturated monomer mixture, 45.21 parts of methyl acrylate and 27.3 parts of ethyl acrylate were used.
7 parts, 2-hydroxyethyl methacrylate 7.42 parts,
0.5 parts of Aqualon HS-10 (polyoxyethylene alkylpropenyl phenyl ether sulfate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), ADEKA REASOAP NE-20 (α-
Monomer emulsification consisting of 0.5 part of [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxyoxyethylene, 80% aqueous solution manufactured by Asahi Denka Co., Ltd., and 80 parts of deionized water. And an initiator solution consisting of 0.24 parts of ammonium persulfate and 10 parts of deionized water were added dropwise to the reaction vessel in parallel over 2 hours.
After completion of dropping, aging was carried out at the same temperature for 1 hour.

Further, as a second stage α, β-ethylenically unsaturated monomer mixture at 80 ° C., 15.07 parts of ethyl acrylate and 2-hydroxyethyl methacrylate of 1.
86 parts, methacrylic acid 3.07 parts, Aqualon HS-1
0 in 0.2 parts and deionized water in 10 parts monomer emulsion and ammonium persulfate in 0.06 parts and deionized water in initiator solution in parallel for 0.5 hours in a reaction vessel. Was added dropwise. After completion of the dropping, aging was carried out for 2 hours at the same temperature.

Then, after cooling to 40 ° C. and filtering with a 400 mesh filter, 67.1 parts of deionized water and 0.32 part of dimethylaminoethanol were added to pH 6.
5, the average particle size is 150 nm, the nonvolatile content is 20%,
Solid content acid value 20mgKOH / g, hydroxyl value 40mgKO
H / g acrylic emulsion resin A-1 was obtained.

Manufacture of Acrylic Emulsion Resin A-2 The manufacturing method was in accordance with Manufacturing Example 1 and the first stage α, β-ethylenically unsaturated monomer mixture was methyl acrylate 3
Using 3.70 parts, ethyl acrylate 34.88 parts, 2-hydroxyethyl methacrylate 7.42 parts, and acrylamide 4.00 parts, as a second stage α, β-ethylenically unsaturated monomer mixture, Ethyl acrylate 15.8
4 parts, 2-hydroxyethyl methacrylate 1.86 parts,
It was synthesized using 2.30 parts of methacrylic acid. Average particle size 190nm, nonvolatile content 20%, acid value of solid content is 15m
An acrylic emulsion resin A-2 having a gKOH / g and a hydroxyl value of 40 mgKOH / g was obtained.

Production of Acrylic Emulsion Resin A-3 The production method was in accordance with Production Example 1, and methyl acrylate 3 was used as the first stage α, β-ethylenically unsaturated monomer mixture.
0.61 parts, ethyl acrylate 37.97 parts, 2-hydroxyethyl methacrylate 7.42 parts, and acrylamide 4.00 parts were used. Acrylic emulsion resin A-3 having an average particle diameter of 200 nm, a nonvolatile content of 20%, a solid content acid value of 20 mgKOH / g, and a hydroxyl value of 40 mgKOH / g.
Got

Production of Acrylic Resin B Aqueous Solution Dipropylene glycol methyl ether 2 was placed in a reaction vessel.
3.89 parts and 16.11 parts of propylene glycol methyl ether were added, and mixed with stirring in a nitrogen stream to give 1
The temperature was raised to 05 ° C. Then, methyl methacrylate 13.
1 part, ethyl acrylate 68.4 parts, methacrylic acid 2-
An initiator solution consisting of 11.6 parts of hydroxyethyl, 6.9 parts of methacrylic acid, 10.0 parts of dipropylene glycol methyl ether and 1 part of t-butylperoxy 2-ethylhexanoate was added in parallel for 3 hours. And dropped into the reaction vessel. After completion of dropping, aging was carried out at the same temperature for 0.5 hour.

Furthermore, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 part of t-butylperoxy 2-ethylhexanoate was added dropwise to the reaction vessel over 0.5 hour. After completion of the dropping, aging was carried out for 2 hours at the same temperature.

Desolvation equipment was used to reduce the pressure (70 Tor).
r) After distilling off 16.11 parts of the solvent at 110 ° C., 204 parts of deionized water and 7.14 of dimethylaminoethanol.
Parts were added to obtain an acrylic resin B aqueous solution. The resulting acrylic resin B-1 solution has a nonvolatile content of 30.0%, a solid content acid value of 40 mgKOH / g, a hydroxyl value of 50 mgKOH / g,
The viscosity was 140 poise (E type viscometer 1 rpm / 25 ° C.).

Polyether polyol C-1 Prime Pole PX-1000 (bifunctional polyether polyol manufactured by Sanyo Kasei Co., Ltd., number average molecular weight 400, hydroxyl value 278 mgKOH / g, primary / secondary hydroxyl value ratio = 6
3/37, water tolerance infinity) was used.

Polyether polyol C-2 PTMG-650 (bifunctional polyether polyol manufactured by Mitsubishi Chemical Corporation, number average molecular weight 650, hydroxyl value 175 mgK
OH / g, primary / secondary hydroxyl value ratio = 100/0, water tolerance 3.0 ml) was used.

Curing agent Cymel 204 (mixed alkylated melamine resin manufactured by Mitsui Cytec, water tolerance 3.6 ml) was used.

Synthesis of Phosphoric Acid Group-Containing Acrylic Resin 40 parts of ethoxypropanol was charged into a 1-liter reaction vessel equipped with a stirrer, temperature controller, and cooling tube, and 4 parts of styrene and 35.96 parts of n-butyl acrylate were added thereto. 18.45 parts of ethylhexyl methacrylate, 13.92 parts of 2-hydroxyethyl methacrylate, 7.67 parts of methacrylic acid, 20 parts of ethoxypropanol and 20 parts of Phosmer PP (acid phosphooxyhexa (oxypropylene) monomethacrylate manufactured by Unichemical Co., Ltd.) 40 parts of a solution in which 1 part is dissolved and 121.7 parts of a monomer solution consisting of 1.7 parts of azobisisobutyronitrile are heated at 120 ° C
After 3 hours, the mixture was further stirred for 1 hour.

The obtained resin has an acid value of 105 mgKOH /
g, of which acrylic acid varnish having an acid value of 55 mgKOH / g due to a phosphate group, a hydroxyl value of 60 mgKOH / g, and a number average molecular weight of 6000, and having a nonvolatile content of 63%.

Example 1 Emulsion resin A-1 obtained in the above production example was added to 275
Parts, 10 mass% dimethylethanolamine aqueous solution 10
Parts, 33 parts of acrylic resin B-1, 10 parts of polyether polyol C-1, 25 parts of curing agent, Alpaste M
H8801 (Asahi Kasei aluminum pigment) 23.1
Parts, Neoresins Neoletts R-9603 (polycarbonate urethane emulsion resin manufactured by Avicia, non-volatile content 33%) 30 parts, phosphoric acid group-containing acrylic resin 5 parts and lauryl acid phosphate 0.3 parts, and uniformly dispersing. Thus, an aqueous base coating composition was obtained.

Zinc phosphate treated 0.8 mm thick, 3 vertical
Cationic electrodeposition paint "Power Top U-50" (manufactured by Nippon Paint Co., Ltd.) was electro-deposited on a 0 cm wide and 40 cm wide dull steel plate so that the dry film thickness was 20 μm, and heated at 160 ° C. for 30 minutes. In 25 seconds (using a No. 4 Ford cup, measured at 20 ° C.), a pre-diluted gray intermediate coating paint “Olga P-2” (polyester / melamine paint by Nippon Paint Co., Ltd.) was dried. Two stages of coating was performed with air spray so as to have a thickness of 35 μm, and heated at 140 ° C. for 30 minutes.

After cooling, the aqueous base coating composition prepared above was diluted with deionized water for 30 seconds (measured at 20 ° C. using a No. 4 Ford cup). Room temperature 25
"Μμ Bell COPES-IV type" for coating water-based paint so that the dry film thickness will be 20 μm under the conditions of ℃ and 85% humidity
(ABB Industry Co., Ltd.) was applied for two stages.
An interval setting of 1 minute was performed between the two applications. After the second application, the setting was performed with an interval of 5 minutes. After that, preheating was performed at 80 ° C. for 5 minutes.

After preheating, the coated plate was allowed to cool to room temperature and half of the base coating film was masked. Then, "Mcflow O-1800W clear" (acid / epoxy curing clear paint manufactured by Nippon Paint Co., Ltd.) was used as a clear paint. One stage coating was applied so that the dry film thickness was 40 μm, and the coating was set for 7 minutes. Then, the coated plate is dried at 140 ° C for 30 minutes.
After heating for a minute, a coated plate having a coating film composed of a base coating film and a clear coating film, where only the base coating film was cured, was obtained.

Example 2 A coating film was prepared after blending the aqueous base coating composition in the same manner as in Example 1 except that the acrylic emulsion resin A-1 was used in place of the acrylic emulsion resin A-1.

Example 3 Acrylic emulsion resin A-3 was used instead of acrylic emulsion resin A-1, and polyether polyol C-2 was used instead of polyether polyol C-1.
A water-based coating composition was blended in the same manner as in Example 1 except that the above was followed to prepare a coating film.

Example 4 Neoresins A water-based coating composition was blended in the same manner as in Example 1 except that Neoletz R-9603 was used in an amount of 60 parts by mass, and then a coating film was prepared.

Comparative Examples 1 to 3 Neoresins Aqueous base coating compositions were obtained in the same manner as in Examples 1 to 3 except that Neolets R-9603 was not used, and then coated plates were obtained.

Evaluation test The coated boards obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were tested for their flip-flop properties by ALCOPE LM.
Using the R-100 (Kansai Paint Co., Ltd. surface shape measuring device), measure the IV value (a) of the part of the base coating film only and the IV value (b) of the part of the base coating film and the clear coating film. The evaluation was 160 or more, and all were acceptable. Furthermore, the obtained IV values (a) and IV
The value (b) is calculated as ((a)-(b)) / (a) × (100).
Then, the decrease rate was calculated to obtain a pass rate of 10% or less. The evaluation results are shown in Table 1.

[0108]

[Table 1]

As is clear from Table 1, the coating films (Examples 1 to 4) obtained by the 2-coat 1-bake method using the aqueous base coating composition of the present invention are compared with the IV value of the base coating alone. As a result, it was found that the decrease rate of the IV value was small, the influence of the mixed layer of the base coating film and the clear coating film was small, and the coating film obtained by the 2-coat 1-baking method also had a good flip-flop property. However, when an aqueous base coating composition containing no urethane emulsion resin was used (Comparative Examples 1 to 3), the IV value was significantly reduced, and the coating film obtained by the 2-coat 1-baking method had a low flip-flop property. I found out that

[0110]

The aqueous base coating composition of the present invention contains a specific acrylic emulsion resin, polyether polyol, urethane emulsion resin and luster colorant. When formed by the coat 1 bake method, the flip-flop property is good. It is considered that this is because the mixed layer of the base coating film and the clear coating film at the time of forming the clear coating film was suppressed by the urethane emulsion resin present in the base coating film.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09D 5/29 C09D 5/29 167/00 167/00 167/08 167/08 171/08 171/08 175 / 04 175/04 (72) Inventor Akihiro Kanakura 19-17 Ikedanaka-cho, Neyagawa-shi, Osaka F-term in Japan Paint Co., Ltd. (reference) 4D075 AE03 AE09 AE12 BB26Z CB03 CB06 DA06 DA23 DB01 DB02 DB06 DB07 DB31 DB34 DB36 DB38 DB48 DB50 DB53 DC12 DC13 EA06 EA13 EA43 EB22 EB32.

Claims (7)

[Claims] 1. An ester portion containing 65% by mass or more of (meth) acrylic acid ester having 1 or 2 carbon atoms,
Acrylic emulsion resin obtained by emulsion polymerization of an α, β-ethylenically unsaturated monomer mixture having an acid value of 3 to 50 mgKOH / g, having an average of 0.02 or more primary hydroxyl groups in one molecule and a number average molecular weight of 300 to A polyether polyol having a water tolerance of 3000 and a water tolerance of 2.0 or more,
A water-based coating composition comprising a urethane emulsion resin and a glittering material. 2. The aqueous base coating composition according to claim 1, wherein the urethane emulsion resin is contained in an amount of 3 to 30 parts by mass per 100 parts by mass of the coating resin solid content. 3. The polyether polyol has at least one primary hydroxyl group in one molecule and has a hydroxyl value of 30 to 700 mgKOH / g.
The water-based base coating composition according to 1. 4. The polyether polyol has two or more hydroxyl groups in one molecule.
An aqueous base coating composition according to any one of 3 to 3. 5. The aqueous base coating composition according to claim 1, further containing a polyester resin or an alkyd resin. 6. A step (1) of forming a base coating film by applying an aqueous base coating material to an object to be coated, wherein a clear coating material is applied on the base coating film without curing the base coating film. A method for forming a coating film, which comprises the step (2) of forming a film and the step (3) of simultaneously heating and curing the base coating film and the clear coating film to form a coating film, wherein the aqueous base coating composition comprises: Item 6. A method for forming a coating film, which is the water-based coating composition according to any one of items 1 to 5. 7. A coating film formed by the method according to claim 6.