JPWO2006054611A1 - Water-based colored paint, hydrophobic melamine resin aqueous dispersion and method for producing the same, water-based paint composition, and multilayer coating film forming method - Google Patents

Abstract

Manufacturing method of hydrophobic melamine resin aqueous dispersion capable of obtaining a coating film having excellent storage stability and excellent adhesion and surface smoothness, excellent color development, recoat adhesion, and chipping properties The present invention provides a water-based colored paint, a water-based paint composition, and a method for forming a multilayer coating film that can obtain a coating film having water-resistant adhesion. An aqueous colored paint containing a film-forming resin, a curing agent and a pigment, wherein the film-forming resin is an acrylic resin produced by emulsion polymerization having an acid value of 1 to 30 mg KOH / g and a hydroxyl value of 10 to 150 An aqueous colored paint containing an emulsion, wherein the curing agent comprises a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm.

Description

The present invention relates to an aqueous coloring paint, a hydrophobic melamine resin aqueous dispersion and a production method thereof, an aqueous paint composition, and a multilayer coating film forming method.

Resin compositions containing a resin such as an acrylic resin having a functional group such as a carboxyl group and a hydroxyl group and a melamine resin as a crosslinking agent are used in electrodeposition paints, intermediate coatings, top coatings (base coatings and top coatings) in automobile coatings. It is widely used for applications such as water-based paints used for coating). And it has been proposed to use a hydrophobic melamine resin as a crosslinking agent for such water-based paints.

When a hydrophobic melamine resin is used as a crosslinking agent for water-based paints, there is a problem that water dispersibility is poor. As a technique for solving such a problem, a cross-linking agent is used as an aqueous resin dispersion obtained by reacting a hydrophobic melamine resin with an acrylic resin, a polyester resin, an alkyd resin, or the like having a specific acid value, hydroxyl value and molecular weight. However, water dispersibility is not satisfactory (Patent Documents 1 to 4, etc.).

In Patent Document 5, an acrylic resin (A), a hydrophobic melamine resin (B) and a polyester resin (C) having a weight average molecular weight of 5,000 to 100,000, an acid value of 10 to 100 mgKOH / g, and a hydroxyl value of 20 to 200 are heated. An aqueous resin dispersion comprising 20 to 200% thickening ratio before and after the heating treatment is disclosed. This is intended to improve performance such as water dispersibility by modifying a hydrophobic melamine resin using a high acid value acrylic resin or the like.

However, since the aqueous resin dispersion disclosed here is not small in particle size, it is inferior in storage stability, adhesion when applied, and surface smoothness. Further, when this aqueous resin dispersion is used as a crosslinking agent for an aqueous colored paint, the resulting coating film may not have sufficient performance such as color developability, recoat adhesion, chipping property, and water adhesion.

JP 52-107029 A JP 52-103426 A JP-A-53-99232 JP 54-16540 A JP 2002-308993 A

In view of the above situation, the present invention is a method for producing an aqueous dispersion of a hydrophobic melamine resin that has excellent storage stability and can provide a coating film having excellent adhesion and surface smoothness. An object of the present invention is to provide a water-based colored paint, a water-based paint composition, and a method for forming a multi-layer paint film that can obtain a paint film having color developability, recoat adhesion, chipping property, and water adhesion resistance.

The present invention is an aqueous colored paint containing a film-forming resin, a curing agent and a pigment, wherein the film-forming resin is produced by emulsion polymerization having an acid value of 1 to 30 mgKOH / g and a hydroxyl value of 10 to 150. The aqueous curing paint is characterized in that the curing agent contains an aqueous dispersion of a hydrophobic melamine resin having a particle size of 20 to 140 nm.

The hydrophobic melamine resin aqueous dispersion comprises an acrylic resin having an acid value of 105 to 200 mgKOH / g, a hydroxyl value of 100 to 200, and a number average molecular weight of 1000 to 5000, and a hydrophobic melamine resin in a mass of 5/95 to 50/50. It is preferable to be obtained by a production method including a step (1) of mixing and heating at a ratio and a step (2) of dispersing the heated product obtained in the above step (1) with water.

The hydrophobic melamine resin preferably has a solubility parameter (SP) in the range of 9.0 <SP <11.5.
The acrylic resin emulsion preferably has a particle size of 20 to 140 nm.
The acrylic resin emulsion is preferably obtained by two-stage emulsion polymerization.
In the two-stage emulsion polymerization, the acrylic resin emulsion obtained by the second-stage emulsion polymerization preferably has an acid value of 25 to 200 mgKOH / g.

The present invention also includes a step (I) of forming a base coating film by coating a water-based base coating on an object to be coated, and applying a clear coating on the base coating without curing the base coating. A method of forming a multilayer coating film comprising a step (II) of forming and a step (III) of simultaneously heating the base coating film and the clear coating film, wherein the aqueous base coating material is the above-mentioned water-based colored coating material It is also a multilayer coating film formation method characterized by being.
In the multilayer coating film forming method, the object to be coated is preferably subjected to a chemical conversion treatment to form an electrodeposition coating film and an intermediate coating film.
The present invention is also a multilayer coating film formed by the above-described multilayer coating film forming method.

In the present invention, an acrylic resin having an acid value of 105 to 200 mgKOH / g, a hydroxyl value of 100 to 200, and a number average molecular weight of 1000 to 5000 and a hydrophobic melamine resin are mixed and heated in a mass ratio of 5/95 to 50/50. And the step (1) and the step (2) of obtaining a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm by water-dispersing the heating product obtained in the step (1) and the step (1). Is a method for producing a water-based melamine resin dispersion.

In the method for producing the hydrophobic melamine resin aqueous dispersion, the hydrophobic melamine resin preferably has a solubility parameter (SP) in a range of 9.0 <SP <11.5.

The present invention also provides a hydrophobic melamine resin aqueous dispersion obtained by the above-described method for producing a hydrophobic melamine resin aqueous dispersion.
The present invention also provides an aqueous coating composition containing a film-forming resin and a curing agent, wherein the curing agent includes the above-described hydrophobic melamine resin aqueous dispersion. But there is.

In the aqueous coating composition, the coating film-forming resin is an acrylic resin emulsion obtained by emulsion polymerization of a monomer mixture containing 65% by mass or more of a (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion. It is preferable that it contains.
Hereinafter, the present invention will be described in detail.

Water-based colored paint The water-based colored paint of the present invention contains a film-forming resin, a curing agent, and a pigment, and the film-forming resin has an acid value of 1 to 30 mgKOH / g, a hydroxyl value. It contains an acrylic resin emulsion produced by 10-150 emulsion polymerization, and the curing agent contains a hydrophobic melamine resin aqueous dispersion having a particle size of 20-140 nm. In the present invention, it is important to use the hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm together with the acrylic resin emulsion. By using a paint containing these, a coating film having excellent color developability can be obtained. Obtainable. For this reason, the obtained coating film has little blurring feeling. In addition, when the aqueous coloring paint contains, for example, a blue pigment, a coating film having a strong bluish sensation can be obtained, and when it contains a black pigment, a coating film having a jet black feeling can be obtained.

Furthermore, in the formation of a multilayer coating film in automobile coating, when the water-based colored paint is used as a water-based base paint, a paint containing the hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm together with the acrylic resin emulsion. Therefore, a multilayer coating film excellent in recoat adhesion, chipping resistance, and water resistance adhesion can be obtained. Moreover, the coating film excellent in coloring property can also be obtained. For this reason, in the method for forming a multilayer coating film in automobile painting, the water-based colored paint can be suitably used as an aqueous base paint.

Curing agent The curing agent contains an aqueous dispersion of a hydrophobic melamine resin having a particle size of 20 to 140 nm. Since such a hydrophobic melamine resin aqueous dispersion is used, a coating film having excellent color developability can be obtained. In addition, when a hydrophobic melamine resin aqueous dispersion is used as a curing agent in an aqueous base coating material in a multilayer coating film forming method, a multilayer coating film having excellent recoat adhesion, chipping resistance, and water adhesion resistance is obtained. be able to. If it is less than 20 nm, a significant reduction in the solid content of the paint occurs. If it exceeds 140 nm, the water dispersibility is lowered, and the adhesiveness and surface smoothness of the formed coating film may be lowered. It is preferable that it is 30-120 nm, and it is more preferable that it is 50-100 nm. In addition, the particle size of the hydrophobic melamine resin dispersion and acrylic resin emulsion according to the present invention is an average dispersed particle size value measured using ELS-800 (manufactured by Otsuka Electronics Co., Ltd.) under the following conditions.
Sample: Infinite dilution with ion-exchanged water Measurement temperature: 25 ° C

Method for producing hydrophobic melamine resin aqueous dispersion The hydrophobic melamine resin aqueous dispersion comprises an acrylic resin having an acid value of 105 to 200 mg KOH / g, a hydroxyl value of 100 to 200, and a number average molecular weight of 1000 to 5000, and a hydrophobic property. By the manufacturing method including the step (2) of water-dispersing the heated product obtained in the step (1) and the step (1) of mixing and heating the functional melamine resin at a mass ratio of 5/95 to 50/50 It is preferable to be obtained. Thereby, color development property, recoat adhesion, chipping resistance, and water adhesion resistance can be improved. A method for producing such an aqueous dispersion of the hydrophobic melamine resin is also one aspect of the present invention.

Process (1)
In the production method, first, an acrylic resin having an acid value of 105 to 200 mgKOH / g, a hydroxyl value of 100 to 200, and a number average molecular weight of 1000 to 5000 and a hydrophobic melamine resin are mixed in a mass ratio of 5/95 to 50/50. The step of heating is performed [step (1)]. By performing the step (1), a heating product of the acrylic resin and the hydrophobic melamine resin can be obtained.

Acrylic resin The acrylic resin has an acid value of 105 to 200 mgKOH / g. If it is less than 105 mgKOH / g, the particle size may exceed 140 nm. When it exceeds 200 mgKOH / g, there is a possibility of giving a gel during heating. It is preferable that it is 105-180 mgKOH / g.

The acrylic resin has a hydroxyl value of 100 to 200. If it is less than 100, the particle size may exceed 140 nm. If it exceeds 200, reaction control may be extremely difficult. It is preferable that it is 120-180.
In addition, the acid value of the said acrylic resin is a measured value, and a hydroxyl value is a calculated value.

The acrylic resin has a number average molecular weight of 1000 to 5000. If it is less than 1000, the particle size may exceed 140 nm. When it exceeds 5000, there is a possibility of giving a gel during heating. It is preferable that it is 1500-4000.

The number average molecular weight of the acrylic resin is a value measured under the following GPC system measurement conditions.
Equipment: HLC-8220 GPC manufactured by Tosoh Corporation
Column; Shodex KF-606M, KF-603
Flow rate: 0.6 ml / min
Detector; RI, UV254nm
Moving bed; tetrahydrofuran

Standard sample;
TSK STANDARD POLYSTYRENE (manufactured by Tosoh Corporation), A-500, A-2500, F-1, F-4, F-20, F-80, F-700, 1-phenylhexane (manufactured by Aldrich)

The acrylic resin contains, for example, a carboxylic acid group-containing unsaturated monomer, a hydroxyl group-containing unsaturated monomer, and, if necessary, other α, β-ethylenically unsaturated monomer and / or a crosslinkable monomer in a water-soluble organic solvent. The monomer composition can be obtained using a known polymerization method such as solution polymerization.

The carboxylic acid group-containing unsaturated monomer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 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 And poly [oxy (1-oxo-1,6-hexanediyl)], maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid and the like.

Examples of the hydroxyl group-containing unsaturated monomer include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, and ε of hydroxyethyl (meth) acrylate. -Caprolactone adducts can be mentioned. Among these, preferred are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and ε-caprolactone adduct of hydroxyethyl (meth) acrylate.

Examples of the other α, β-ethylenically unsaturated monomers include (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester moiety [methyl (meth) acrylate or ethyl (meth) acrylate]; ester Part of (meth) acrylic acid ester having 3 or more carbon atoms [e.g., 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, dihydrodicyclopentadi (meth) acrylate Anenyl, stearyl methacrylate, etc.]; a polymerizable amide compound [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 compound [for example, styrene , Α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.]; polymerizable nitriles (eg, acrylonitrile, methacrylonitrile, etc.); α-olefins (eg, ethylene, propylene, etc.); vinyl esters [Example If, vinyl acetate, vinyl propionate]; diene [e.g., butadiene, isoprene, etc.] and the like.

The crosslinkable monomer is preferably an unsaturated monomer having two or more unsaturated double bonds. When the unsaturated monomer having two or more unsaturated double bonds is contained, the feeling of separation between the base coating and the clear coating is increased, and the appearance of the coating can be improved.
The unsaturated monomer having two or more unsaturated double bonds is not particularly limited as long as it is a vinyl monomer having two or more unsaturated groups capable of radical polymerization in the molecule. Specifically, for example, vinyl compounds such as divinylbenzene and divinylsulfone; (meth) allyl (meth) acrylate (hereinafter, both allyl and methallyl are expressed as (meth) allyl), diallyl or dimethallyl phthalate, (Meth) allyl compounds such as di (meth) allyl (meth) acrylamide, tri (meth) allyl cyanurate or isocyanurate, tri (meth) allyl trimellitate, bis ((meth) allylnadiimide); mono or polyethylene Mono- or polyoxyalkylene glycol di (meth) acrylate such as glycol di (meth) acrylate, mono- or polypropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythrin Ritorutori (meth) acrylate, glycerol tri (meth) acrylate of (meth) acrylate compounds. In addition, allyloxy polyethylene glycol polypropylene glycol monoacrylate (Blemmer AKEP manufactured by NOF Corporation), dicyclomentenyl acrylate (FANCRYL FA-511A manufactured by Hitachi Chemical Co., Ltd.), dicyclomentenyloxyethyl acrylate (FANCRYL FA- manufactured by Hitachi Chemical Co., Ltd.) 512A), dicyclomentenyloxyethyl methacrylate (manufactured by Hitachi Chemical Co., Ltd. FAKCRYL FA-512M), dihydrodicyclopentadienyl acrylate (commercial product from BASF), 3-cyclohexenylmethyl methacrylate (commercial product from Daicel) ), 3-cyclohexenylmethyl acrylate (commercial product from Daicel), butanediol-1,4-divinyl ether (commercial product from BASF), triallyl isocyanurate (TAIC manufactured by Nippon Kasei Co., Ltd.) Is possible. In the present invention, among these, allyl methacrylate or ethylene glycol di (meth) acrylate is preferable. Particularly preferably, an unsaturated monomer having two or more unsaturated double bonds of 4 atoms or less, preferably 3 atoms or less, when the distance between the unsaturated double bonds is expressed by the number of atoms, Specific examples include allyl methacrylate. In addition, the unsaturated monomer which has two or more unsaturated double bonds can be used individually or in mixture of 2 or more types.

Hydrophobic melamine resin As the hydrophobic melamine resin, conventionally known ones can be used, but the solubility parameter δ (SP) is in the range of 9.0 <SP <11.5. It is preferable. If it is 9.0 or less, the particle size may exceed 140 nm. When it is 11.5 or more, the particle size exceeds 140 nm, and the performance may be deteriorated. More preferably, 9.5 <SP <11.0.

The solubility parameter δ is generally called SP (solubility parameter) among those skilled in the art, and is a scale indicating the degree of hydrophilicity or hydrophobicity of the resin, and the compatibility between the resins. It is also an important measure for judging. The solubility parameter can be numerically quantified based on, for example, a turbidity measurement method (reference document: kW Suh, DH Clarke J. Polymer. Sci., A-1, 5). , 1671 (1967).). The solubility parameter δ in the present specification is a parameter determined by a turbidity measurement method. The solubility parameter according to the turbidity measurement method is, for example, that a resin solid content (predetermined mass) to be measured is dissolved in a certain amount of good solvent (acetone, etc.) and then a poor solvent such as water or hexane is added dropwise. From the respective titration amounts until the resin is insolubilized and turbidity is generated in the solution, it can be determined by a known calculation method described in the above-mentioned reference or the like.

In the step (1), the mixing ratio of the acrylic resin and the hydrophobic melamine resin is preferably 5/95 to 50/50 (mass ratio, acrylic resin / hydrophobic melamine resin). If the blending amount of the acrylic resin is less than 5/95, the particle size may exceed 140 nm. When the blending amount of the acrylic resin is larger than 50/50, there is a possibility that the NV (solid content concentration) of the coating material may be remarkably lowered or reaction control may be extremely difficult. More preferably, it is 10 / 90-40 / 60. In addition, the mixing method of an acrylic resin and hydrophobic melamine resin can be performed by a conventionally well-known method.

In the present invention, in the above step (1), when the blending amount of the acrylic resin with respect to the hydrophobic melamine resin is decreased, the function as the curing agent is lowered when the obtained hydrophobic melamine resin aqueous dispersion is used as the curing agent. There are few things. And although there are few compounding quantities of an acrylic resin, the particle size after water dispersion is 20-140 nm. For this reason, the hydrophobic melamine resin aqueous dispersion obtained by this invention can be used suitably as a hardening | curing agent of an aqueous | water-based coloring paint. In the step (1), in addition to the acrylic resin and the hydrophobic melamine resin, other resins such as a polyester resin may be included within the range not excluding the effect of the present invention.

In the said process (1), it is preferable that the heating temperature is 70-100 degreeC, and, as for the mixing conditions of the said acrylic resin and the said hydrophobic melamine resin, it is more preferable that it is 75-90 degreeC. The heating time is preferably 1 to 10 hours, and more preferably 1 to 5 hours. If it is less than the lower limit, the particle size may exceed 140 nm. Exceeding the upper limit may give a gel.

Step (2)
In the method for producing the hydrophobic melamine resin aqueous dispersion, the heated product obtained by carrying out the step (1) is then dispersed in water to thereby form a hydrophobic melamine resin water having a particle size of 20 to 140 nm. A step of obtaining a dispersion is performed [step (2)]. By performing the step (2), an aqueous dispersion (aqueous dispersion) in which resin particles having a particle diameter of 20 to 140 nm are dispersed in water can be obtained.

In the step (2), the method for water-dispersing the heated product obtained in the step (1) is not particularly limited, and an ordinary resin water-dispersing method can be used. After cooling to a temperature of 50 ° C. or lower, it is preferable to disperse in water by diluting with water. Thereby, a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm can be suitably obtained. If it is not cooled to 50 ° C. or lower, it may not be possible to obtain a particle size of 20 to 140 nm. It is more preferable to disperse in water by cooling to 30 to 40 ° C. and then diluting with water.

In the said process (2), pH can be used at 6.5-10 by neutralizing with a base as needed. This is because the stability in this pH region is high. This neutralization is preferably performed by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after mixing and heating the acrylic resin and the hydrophobic melamine resin. Among them, after mixing and heating the acrylic resin and the hydrophobic melamine resin, a tertiary amine is added, and then the heated product is cooled to a temperature of 50 ° C. or lower and then diluted with water. It is particularly preferable to disperse in water. Thereby, a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm can be suitably obtained.

The aqueous dispersion of hydrophobic melamine resin obtained by the above-described production method is a dispersion of resin particles having a particle diameter of 20 to 140 nm obtained by heating a specific acrylic resin and hydrophobic melamine resin in water. . For this reason, in addition to the water-based colored paint according to the first aspect of the present invention, it can be suitably used as a curing agent for water-based paint compositions used for electrodeposition paints, intermediate paints, top-coat paints, etc., particularly in automobile painting. it can. In addition, since it has a function as a curing agent, it can be used in any application as a curing agent (for example, decorative products, molded products such as machines, electrical parts, fibers, paper processing, adhesives, paints, flame retardants, It can also be applied to plasticizers for concrete. Such an aqueous dispersion of the hydrophobic melamine resin is also one aspect of the present invention. Further, an aqueous coating composition containing the hydrophobic melamine resin aqueous dispersion is also one aspect of the present invention.

Coating film-forming resin The coating film-forming resin contains an acrylic resin emulsion produced by emulsion polymerization having an acid value of 1 to 30 mgKOH / g and a hydroxyl value of 10 to 150.

Acrylic resin emulsion Examples of the acrylic resin emulsion include those obtained by emulsifying the carboxylic acid group-containing unsaturated monomer as a raw material by one-stage or multi-stage emulsion polymerization described later. An acrylic resin emulsion as a film-forming resin in the aqueous colored paint (aqueous base paint) composition of the present invention is a so-called core-shell type acrylic resin emulsion (A) having a core part and a shell part by two-stage emulsion polymerization. ) Is preferable. As the acrylic resin emulsion (A), those having various changes in acid value, hydroxyl group, and Tg can be designed as will be described later, and several types of emulsions having these design values changed can be used in combination. Moreover, the said acrylic resin emulsion (A) can also be used together with the acrylic resin emulsion (B) mentioned later.

When the coating film-forming resin contains a core-shell type acrylic resin emulsion, the core part contains a carboxylic acid group-containing unsaturated monomer having an acid value of 0 to 100 mgKOH / g (a) It is preferable that it is obtained by emulsion polymerization. If it exceeds 100 mgKOH / g, the water resistance of the resulting coating film may be reduced. More preferably, it is 0-50 mgKOH / g.
In addition, the acid value of the said core part is an acid value of the acrylic resin emulsion obtained by emulsion polymerization of the 1st step.

The shell portion is preferably obtained by emulsion polymerization of a monomer mixture (b) containing a carboxylic acid group-containing unsaturated monomer having an acid value of 25 to 200 mgKOH / g. When the acid value is less than 25 mgKOH / g, the stability of the emulsion may be lowered. If it exceeds 200 mgKOH / g, the water resistance of the resulting coating film may be reduced. Preferably it is 30-180 mgKOH / g.

The monomer mixture (a) and / or the monomer mixture (b) can have a hydroxyl group. The hydroxyl value is 10 to 150, preferably 15 to 120. If the hydroxyl value is less than 10, sufficient curability may not be obtained. If it exceeds 150, various performances of the resulting coating film may be deteriorated.

The monomer mixture (a) and / or the monomer mixture (b) may contain a hydroxyl group-containing unsaturated monomer.
As said hydroxyl-containing unsaturated monomer, the hydroxyl-containing unsaturated monomer mentioned above can be mentioned, for example.

Moreover, the said monomer mixture (a) and / or the said monomer mixture (b) may contain a crosslinkable monomer as needed. Examples of the crosslinkable monomer include the crosslinkable monomers described above.
As content of the said crosslinkable monomer, it is preferable that the lower limit is 0.05 mass% and the upper limit is 30.0 mass% in 100 mass% of the said monomer mixture (a) or the said monomer mixture (b). If it is less than 0.05% by mass, the resulting multi-layer coating film has a problem in color development, and the effect of adding these monomers cannot be obtained. If it exceeds 30.0% by mass, it may be difficult to synthesize an acrylic resin emulsion. The content is more preferably a lower limit of 0.5% by mass and an upper limit of 10% by mass.

Furthermore, the monomer mixture (a) and / or the monomer mixture (b) may contain the other α, β-ethylenically unsaturated monomer. Moreover, it is preferable that the glass transition temperature (Tg) of the said core-shell type acrylic resin emulsion is -20-80 degreeC from a viewpoint of the physical property of the coating film obtained.

The monomer mass ratio of the monomer mixture (a) / monomer mixture (b) [core part / shell part] is preferably 50/50 to 98/2, and preferably 70/30 to 95/5. More preferred. When the shell ratio is larger than 50/50, the stability of the emulsion is lowered, and when the shell ratio is smaller than 98/2, the water resistance of the resulting coating film may be lowered.

The acid value and hydroxyl value of the core part obtained by emulsion polymerization of the monomer mixture (a), the acid value and hydroxyl value of the shell part obtained by emulsion polymerization of the monomer mixture (b), the core shell Tg of the type acrylic resin emulsion is a value obtained by calculation from the blending amounts of various unsaturated monomers in the monomer mixture (a) and the monomer mixture (b).

The emulsion polymerization for obtaining the acrylic resin emulsion (A) 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 as necessary, and the monomer mixture (a) or the monomer mixture (b) and a polymerization initiator are heated and stirred. It can be performed by dropping. The monomer mixture (a) or the monomer mixture (b) emulsified in advance using an emulsifier and water may be similarly dropped.

Examples of the polymerization initiator include azo oily compounds (for example, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvalero). Nitrile) etc.) and aqueous compounds (eg anionic 4,4'-azobis (4-cyanovaleric acid), cationic 2,2'-azobis (2-methylpropionamidine)); and redox Oily peroxides (for example, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, etc.) and aqueous peroxides (for example, potassium persulfate, ammonium peroxide, etc.) are preferred.

Examples of the emulsifier include those often used by those skilled in the art. Particularly, reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (Sanyo) Kasei Kogyo Co., Ltd.), Adekaria Soap NE-20 (Asahi Denka Co., Ltd.), Aqualon HS-10 (Daiichi Kogyo Seiyaku Co., Ltd.) and the like are preferable.
In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

The reaction temperature is determined by the polymerization initiator, and for example, it is preferably 60 to 90 ° C. for an azo initiator and 30 to 70 ° C. for a redox system. In general, the reaction time is 1 to 8 hours. The content of the polymerization initiator relative to the total mass of the monomer mixture (a) and the monomer mixture (b) is generally 0.1 to 5% by mass, and preferably 0.2 to 2% by mass.

The particle diameter (A) of the acrylic resin emulsion is preferably in the range of 20 to 140 nm. When the particle diameter is less than 20 nm, there is a risk that the coating solid content (NV) is significantly reduced. When exceeding 140 nm, there exists a possibility that the coloring property of the coating film obtained may fall. The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions. More preferably, it is 30-120 nm, and still more preferably 50-100 nm. In addition, the said particle diameter is the value measured by the method similar to the particle size of the hydrophobic melamine resin aqueous dispersion mentioned above.

The said acrylic resin emulsion (A) can be used by pH = 3-10 by neutralizing with a base as needed. This is because the stability in this pH region is high. This neutralization is preferably performed by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

The acrylic resin emulsion (A) preferably has an acid value of 1 to 30 mgKOH / g. If it is less than 1 mgKOH / g, the stability of the emulsion may be lowered. If it exceeds 30 mgKOH / g, the water resistance of the resulting coating film may be reduced. It is preferable that it is 3-25 mgKOH / g.

The acrylic resin emulsion (A) has a hydroxyl value of 10 to 150. If it is less than 10, the physical properties of the coating film may be lowered. When it exceeds 150, there exists a possibility that the water resistance of the coating film obtained may fall. It is preferable that it is 15-120. In addition, the acid value of the said acrylic resin emulsion is a measured value, and a hydroxyl value is the value calculated | required by calculation from the compounding quantity of the various unsaturated monomers used for the synthesis | combination.

The content of the acrylic resin emulsion (A) in the aqueous colored paint is preferably 5 to 95% by mass, more preferably 10 to 85% by mass, and more preferably 20 to 70% by mass in the solid content of the paint. % Is more preferable. When the said content is outside the said range, there exists a possibility that coating workability | operativity and the external appearance of the coating film obtained may fall.

The film-forming resin is also obtained by emulsion polymerization of an α, β-ethylenically unsaturated monomer mixture containing 65% by mass or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion. The acrylic resin emulsion (B) to be prepared may be included.

There exists a possibility that the external appearance of the coating film obtained as it is less than 65 mass% may fall. Examples of the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester part include methyl (meth) acrylate and ethyl (meth) acrylate. In addition, in this specification, (meth) acrylic acid ester shall mean both acrylic acid ester and methacrylic acid ester.

The α, β-ethylenically unsaturated monomer mixture preferably has an acid value of 1 to 30 mgKOH / g, more preferably 3 to 25 mgKOH / g. When the acid value is less than 1 mgKOH / g, the coating stability is lowered, and when it exceeds 30 mgKOH / g, the water resistance of the coating film may be lowered. On the other hand, when the aqueous coating composition needs to have curability, the α, β-ethylenically unsaturated monomer mixture preferably has a hydroxyl value of 10 to 150, more preferably 20 to 100. It is. If it is less than 10, sufficient curability cannot be obtained, and if it exceeds 150, the water resistance of the coating film may be lowered. In addition, the glass transition temperature of the polymer obtained by copolymerizing the α, β-ethylenically unsaturated monomer mixture is between -20 and 80 ° C. from the viewpoint of the mechanical properties of the resulting coating film. preferable.

The α, β-ethylenically unsaturated monomer mixture can have the acid value and the hydroxyl 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 those similar to the carboxylic acid group-containing unsaturated monomer described above. Among these, acrylic acid, methacrylic acid, and acrylic acid dimer are preferable.

On the other hand, examples of the α, β-ethylenically unsaturated monomer having a hydroxyl group include those similar to the hydroxyl group-containing unsaturated monomer described above. Among these, preferred are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and an adduct of hydroxyethyl (meth) acrylate and ε-caprolactone.

The α, β-ethylenically unsaturated monomer mixture may further contain other α, β-ethylenically unsaturated monomers. Examples of the other α, β-ethylenically unsaturated monomers include (meth) acrylic acid esters having 1 or 2 carbon atoms in the ester portion among the other α, β-ethylenically unsaturated monomers described above. Other than that can be mentioned. These can be selected depending on the purpose, but (meth) acrylamide is preferably used when hydrophilicity is easily imparted.
Furthermore, the α, β-ethylenically unsaturated monomer mixture may contain a crosslinkable monomer. Examples of the crosslinkable monomer include those described above.

In these cases, the α, β-ethylenically unsaturated monomer other than the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion is contained in the α, β-ethylenically unsaturated monomer mixture. Must be set to less than 35% by weight.

The acrylic resin emulsion (B) is obtained by emulsion polymerization of the 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 as necessary, and the α, β-ethylenically unsaturated monomer mixture and the polymerization initiator are heated and stirred. This can be done by dripping. An α, β-ethylenically unsaturated monomer mixture emulsified in advance using an emulsifier and water may be similarly added dropwise.

Examples of the polymerization initiator and the emulsifier include those described above.
In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

The reaction temperature is determined by the initiator, and for example, it is preferably 60 to 90 ° C. for an azo initiator and 30 to 70 ° C. for a redox system. In general, the reaction time is 1 to 8 hours. The amount of the initiator relative to 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.

The emulsion polymerization can be carried out in one stage or in multiple stages, for example, in two stages. That is, first, a part of the α, β-ethylenically unsaturated monomer mixture (α, β-ethylenically unsaturated monomer mixture 1) is emulsion-polymerized, and the α, β-ethylenically unsaturated monomer mixture is added thereto. The remainder (α, β-ethylenically unsaturated monomer mixture 2) is further added to carry out emulsion polymerization. That is, the acrylic resin emulsion (B) may have the structure of the core / shell type emulsion resin.

Here, from the viewpoint of preventing compatibility with the clear coat, 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 α, β-ethylenically unsaturated monomer mixture 1 and 2 together is the α, β-ethylenically unsaturated monomer mixture, the α, β-ethylenically unsaturated compound described above is used. The requirements for the monomer mixture will be met by the combined α, β-ethylenically unsaturated monomer mixture 1 and 2.

The particle diameter of the acrylic resin emulsion (B) thus obtained is preferably in the range of 20 to 500 nm, more preferably in the range of 20 to 140 nm. If the particle diameter is less than 20 nm, the solid content of the coating material is too low and there may be a problem in workability. Moreover, when it exceeds 500 nm, there exists a possibility that the external appearance of the coating film obtained may deteriorate. The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions.

The said acrylic resin emulsion (B) can be used by pH 5-10 by neutralizing with a base as needed. This is because the stability in this pH region is high. This neutralization is preferably performed by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

Pigment Examples of the pigment contained in the aqueous colored paint of the present invention include a luster pigment and a colored pigment. The shape of the glitter pigment is not particularly limited, and may be colored. For example, the pigment having an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm Is preferred. Those having an average particle diameter in the range of 10 to 35 μm are excellent in glitter and are more preferably used. Specific examples include non-colored or colored metallic brighteners such as metals, alloys, and the like such as aluminum, copper, zinc, iron, nickel, tin, and aluminum oxide, and mixtures thereof. When the luster pigment is a flat pigment, those having an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm are preferable. In addition, any of the above luster pigments having an average particle diameter in the range of 10 to 35 μm is excellent in luster and is more preferably used. Other bright pigments include interference mica pigments, white mica pigments, graphite pigments and the like.

On the other hand, examples of the color pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, and isoindo. Examples thereof include linone pigments and metal complex pigments. Examples of inorganic pigments include chrome lead, yellow iron oxide, bengara, carbon black, and titanium dioxide. Moreover, you may contain extender pigments, such as sedimentation barium sulfate, as needed.

The total pigment concentration (PWC) in the water-based colored paint is preferably 0.1 to 50%. More preferably, it is 0.5 to 40%, and particularly preferably 1.0 to 30%. When the upper limit is exceeded, the coating film appearance may be deteriorated. When a bright pigment is included, the pigment concentration (PWC) is generally preferably 18.0% or less. When the upper limit is exceeded, the coating film appearance may be deteriorated. More preferably, it is 0.01 to 15.0%, and particularly preferably 0.01 to 13.0%.

The above-mentioned water-based colored paint can contain other curing agents as long as the curing of the present invention is not inhibited. As said other hardening | curing agent, what is generally used for coating materials other than the hydrophobic melamine resin aqueous dispersion mentioned above can be used together. For example, blocked isocyanate, epoxy compound, aziridine compound, carbodiimide compound, oxazoline compound, metal ion, hydrophilic melamine resin and the like can be mentioned. An amino resin and / or a blocked isocyanate resin are generally used from the viewpoints of various performances and costs of the obtained coating film.

The above-mentioned blocked isocyanate can be obtained by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. Examples include those that dissociate and generate isocyanate groups.

When these hardening | curing agents are contained, it is preferable that the content is 10-100 mass parts with respect to 100 mass parts of resin solid content in an aqueous coloring coating material. Outside the above range, curability may be insufficient.

The water-based colored paint may contain other film-forming resin as necessary. Other film-forming resins are not particularly limited, and film-forming resins such as acrylic resins other than the acrylic resin emulsion, polyester resins, alkyd resins, epoxy resins, and urethane resins can be used.

The other film-forming resin has a number average molecular weight of 3,000 to 50,000, preferably 6,000 to 30,000. When it is less than 3000, workability and curability are not sufficient, and when it exceeds 50000, the non-volatile content at the time of coating becomes too low, and workability may be deteriorated.

The other film-forming resin preferably has an acid value of 10 to 100 mgKOH / g, more preferably 20 to 80 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, Water dispersibility may be reduced. Moreover, it is preferable to have a hydroxyl value of 20 to 180, and further 30 to 160. If the upper limit is exceeded, the water resistance of the coating film is lowered, and if it is less than the lower limit, the curability of the coating film may be lowered.

The blending ratio of the acrylic resin emulsion and the other film-forming resin in the water-based colored paint is 5 to 95% by mass, preferably 10 to 85% by mass, based on the total resin solid content. %, More preferably 20 to 70% by mass, and other film-forming resin is 95 to 5% by mass, preferably 90 to 15% by mass, and more preferably 80 to 30% by mass. When the ratio of the acrylic resin emulsion is less than 5% by mass, the workability is lowered, and when it is more than 95% by mass, the film forming property may be deteriorated.

As said other film-forming resin, it is preferable to use a water-soluble acrylic resin from a compatible point with the said acrylic resin emulsion at the time of baking of a coating film. The water-soluble acrylic resin can be obtained by using the above-mentioned carboxylic acid group-containing unsaturated monomer as an essential component and performing solution polymerization together with other α, β-ethylenically unsaturated monomers. When used as an aqueous coating composition, the component used to obtain the water-soluble acrylic resin may contain 65% by mass or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester moiety. It is preferable from the viewpoint of the appearance of the resulting coating film.

The water-soluble acrylic resin is usually neutralized with a basic compound, for example, an organic amine such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, and dimethylethanolamine, and added to water. Although used by dissolving, this neutralization may be performed on the water-soluble acrylic resin itself or at the time of production of the water-based colored paint.

Moreover, the said water-colored coating material can contain polyether polyol. By including the polyether polyol, the coating film performance can be further improved.
As the polyether polyol, one having at least one primary hydroxyl group in one molecule, a number average molecular weight of 300 to 3000, a hydroxyl value of 30 to 700, and a water tolerance of 2.0 or more is used. It is preferable. If the above conditions are not satisfied, the water resistance may not be lowered or the target appearance may not be improved.

As such a polyether polyol, a compound obtained by adding an alkylene oxide such as ethylene oxide or propylene oxide to an active hydrogen-containing compound such as a polyhydric alcohol, a polyhydric phenol, or a polycarboxylic acid can be used. Specific examples include commercially available products such as Primepole PX-1000, Sanix SP-750 (all of which are manufactured by Sanyo Chemical Industries), and PTMG-650 (manufactured by Mitsubishi Chemical). The polyether polyol is preferably contained in an amount of 1 to 40% by mass, more preferably 3 to 30% by mass in the solid content of the coating resin.

Furthermore, other viscosity control agents can be added to the water-based colored coating material in order to prevent the compatibility with the top coat film and to ensure the coating workability. As the viscosity control agent, those generally showing thixotropy can be used, for example, polyamide-based ones such as crosslinked or non-crosslinked resin particles, swelling dispersions of fatty acid amides, amide fatty acids, and long-chain polyaminoamide phosphates. Viscosity develops depending on the shape of polyethylene, such as colloidal swelling dispersion of polyethylene oxide, organic bentonite such as organic acid smectite clay, montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, etc. A flat pigment etc. can be mentioned.

In addition to the above-mentioned components, additives that are usually added to the paint, for example, surface conditioners, thickeners, antioxidants, ultraviolet inhibitors, antifoaming agents, and the like, may be added to the water-based colored paint. These compounding amounts are within the range known to those skilled in the art.

The method for producing the water-based colored paint is not particularly limited, including those described later, and all methods well known to those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll are used. obtain.

Multi-layer coating film forming method The water-based colored paint can be suitably used as an aqueous base paint for automobiles. For this reason, it can apply to the multilayer coating-film formation method applied to a motor vehicle body, components, etc. As the method for forming a multilayer coating film, for example, the step (I) of forming the base coating film by applying the above-mentioned water-based coloring paint to the object to be coated, without curing the base coating film thereon A method comprising the step (II) of forming a clear coating film by applying a clear coating and the step (III) of simultaneously heating the base coating film and the clear coating film can be mentioned.

The object to be coated used in the method for forming a multilayer coating film can be used for various substrates such as metal molded products, plastic molded products, foams, etc. It is preferable to apply to this.

Examples of the metal molded product include, for example, plates and molded products made of iron, copper, aluminum, tin, zinc, etc. and alloys containing these metals. Specifically, passenger cars, trucks, motorcycles, buses, etc. Car bodies and parts. These metals are preferably subjected to chemical conversion treatment with phosphate, chromate or the like in advance.

An electrodeposition coating film may be formed on the metal molded article subjected to the chemical conversion treatment. As such an electrodeposition paint, a cation type and an anion type can be used, but a cationic electrodeposition paint composition is preferable from the viewpoint of corrosion resistance.

Examples of the plastic molded product include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, and the like, and specifically, spoilers. Automobile parts such as bumpers, mirror covers, grills, door knobs, and the like. Further, these plastic molded products are preferably those washed with steam or neutral detergent with trichloroethane. Furthermore, primer coating for enabling electrostatic coating may be applied.

If necessary, an intermediate coating film may be formed on the object to be coated. An intermediate coating is used to form the intermediate coating film. The intermediate coating contains a film-forming resin, a curing agent, various organic and inorganic coloring components, extender pigments, and the like. The coating film-forming resin and the curing agent are not particularly limited, and specifically, the coating film-forming resin and the curing agent mentioned in the previous water-based colored paint can be used and used in combination. It is what From the viewpoint of various performances and costs of the obtained intermediate coating film, an acrylic resin and / or a polyester resin, an amino resin and / or an isocyanate are used in combination.

Examples of the coloring component contained in the intermediate coating material include those described in the previous aqueous coloring coating material. In general, it is preferable to use a so-called color intermediate coating composition that combines a gray-based intermediate coating composition mainly composed of carbon black and titanium dioxide, a set gray that combines the hues of the top coating, and various coloring components. Further, flat pigments such as aluminum powder and mica powder may be added.
In the intermediate coating material, in addition to the above components, additives usually added to the coating material, for example, a surface conditioner, an antioxidant, an antifoaming agent, and the like may be blended.

As a method of applying the above-mentioned water-based colored paint (water-based base paint) to an object to be coated, from the viewpoint of improving the appearance, multi-stage coating by air electrostatic spray coating, preferably two-stage coating, or The coating method which combined the air electrostatic spray coating and the rotary atomization type electrostatic coating machine called a metallic bell can be mentioned.

Although the film thickness of the coating film at the time of application | coating with the said water-colored coating material (aqueous base coating material) changes with desired uses, it is preferable that it is generally 10-30 micrometers by a dry film thickness. If the dry film thickness is less than 10 μm, the substrate cannot be concealed and the film breaks. If it exceeds 30 μm, the sharpness may be deteriorated, or defects such as unevenness or sagging may occur during coating. is there. In order to obtain a multilayer coating film having a good appearance, it is preferable to heat the obtained base coating film at 40 to 100 ° C. for 2 to 10 minutes before applying the clear paint.

The method for forming a multilayer coating film is to form a clear coating film by coating the clear coating film on the base coating film obtained by applying the water-based colored coating composition (aqueous base coating composition) without heat curing. It is. The clear coating film smoothes and protects unevenness, flickering, and the like caused by the base coating film, and further gives an aesthetic appearance.

The clear paint is not particularly limited, and a clear paint containing a film-forming resin and a curing agent can be used. Furthermore, a coloring component can be contained as long as it does not interfere with the design of the base.
Examples of the form of the clear paint include a solvent type, an aqueous type and a powder type.

Preferred examples of the solvent-type clear paint include a combination of an acrylic resin and / or a polyester resin, an amino resin and / or an isocyanate, or a carboxylic acid / epoxy curing system from the viewpoint of transparency or acid etching resistance. An acrylic resin and / or a polyester resin etc. can be mentioned.

Examples of the water-based clear paint include those containing a resin obtained by neutralizing a film-forming resin contained in the solvent-type clear paint described above as an example with a base with a base. be able to. This neutralization can be carried out by adding tertiary amines such as dimethylethanolamine and triethylamine before or after polymerization.

On the other hand, as the powder type clear paint, a normal powder paint such as a thermoplastic and thermosetting powder paint can be used. A thermosetting powder coating is preferred because a coating film having good physical properties can be obtained. Specific examples of the thermosetting powder coating material include epoxy-based, acrylic-based, and polyester-based powder clear coating materials, and acrylic-based powder clear coating materials having good weather resistance are particularly preferable.

Furthermore, it is preferable that a viscosity control agent is added to the clear paint in order to ensure the coating workability. As the viscosity control agent, those generally showing thixotropy can be used. As such a thing, a conventionally well-known thing can be used, for example. Moreover, a curing catalyst, a surface conditioner, etc. can be included if necessary.

In addition, as a clear paint used in the said multilayer coating-film formation method, from a viewpoint of the influence which it has on the environment by content of an organic solvent, Ford Cup No. 20 in 20 degreeC. 4 is preferably a solvent-type clear paint, a water-based clear paint, or a powder-type clear paint having a clear paint solid content of 50% by mass or more when diluted to a viscosity of 20 to 50 seconds.
Specific examples of the method for applying the above clear paint to the base coating film include a micro-microbell and a coating method using a rotary atomizing electrostatic coater called a microbell.

The dry film thickness of the clear coating film formed by applying the clear paint is generally preferably 10 to 80 μm, and more preferably 20 to 60 μm. When the dry film thickness is less than 10 μm, the unevenness of the foundation cannot be concealed, and when it exceeds 80 μm, there is a possibility that problems such as peeling or sagging may occur during coating.

The clear coating film thus formed forms a cured coating film by being heated simultaneously with the previously formed base coating film. The heat curing temperature is preferably set to 80 to 180 ° C, and more preferably 120 to 160 ° C, from the viewpoints of curability and physical properties of the resulting multilayer coating film. Although the heat curing time can be arbitrarily set according to the above temperature, it is appropriate that the heat curing temperature is 120 ° C. to 160 ° C. and the time is 10 to 30 minutes.

The method for forming a multi-layer coating film also forms the intermediate coating film on the object to be coated to form an intermediate coating film, and without heating and curing the coating, the water-based colored coating (aqueous base coating) is formed thereon. The base coating film can be formed by coating, and then the above-mentioned clear paint can be applied to form a clear coating film, which can be applied by three-coating one-bake in which these are heat-cured. Examples of the various paints used in such a method include the same ones as described above.

The film thickness of the multilayer coating film thus obtained is generally 30 to 300 μm and preferably 50 to 250 μm. When the film thickness is less than 30 μm, the strength of the film itself decreases, and when it exceeds 300 μm, film physical properties such as a cooling / heating cycle may decrease. The multilayer coating film thus obtained is also one aspect of the present invention.
The coated product having a multilayer coating film obtained by the above-mentioned multilayer coating film forming method has a multilayer coating film having extremely high glitter and color development, recoat adhesion, chipping resistance, and water adhesion resistance on the surface thereof. Is.

The aqueous coloring paint of the present invention is a film-forming resin containing a specific acrylic resin emulsion, a specific acrylic resin and a hydrophobic melamine resin are mixed in a specific composition, and the heated product obtained by heating is dispersed in water. Since it contains the hardening | curing agent containing the hydrophobic melamine resin aqueous dispersion with a particle size of 20-140 nm obtained by this, and a pigment, the coating film which has the outstanding coloring property can be obtained.

Moreover, since the said hydrophobic melamine resin aqueous dispersion has the specific particle size obtained by a specific manufacturing method, it has the outstanding storage stability and should be used suitably as arbitrary hardening | curing agents. it can. When an aqueous coloring paint containing the hydrophobic melamine resin aqueous dispersion as a curing agent is used, a coating film having excellent adhesion and surface smoothness can be obtained.

Furthermore, in the method for forming a multilayer coating film in automobile coating, when the water-based colored paint is used as an aqueous base paint, a multilayer coating film having excellent recoat adhesion, chipping property, and water resistance adhesion can be obtained. . Therefore, the water-based colored paint can be suitably used as a water-based base paint.

Since the water-based colored paint of the present invention has the above-described configuration, a coating film having excellent color developability can be obtained. In addition, when used in a method for forming a multilayer coating film, a coating film having excellent recoat adhesion, chipping property, water-resistant adhesion property, and coloring property can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, “parts” and “%” mean “parts by mass” and “% by mass” unless otherwise specified.

Production example 1 Production of acrylic resin emulsion Em-a 226.5 parts of ion-exchanged water was added to a reaction vessel, and the mixture was heated to 80C while being mixed and stirred in a nitrogen stream. Next, 25.21 parts of methyl acrylate, 22.37 parts of ethyl acrylate, 7.42 parts of 2-hydroxyethyl methacrylate, 15 parts of methyl methacrylate, Aqualon HS-10 (polyoxyethylene alkylpropenyl phenyl ether sulfate, Daiichi Kogyo Seiyaku Co., Ltd.) 0.5 parts, Adekari Soap NE-20 (α- [1-[(allyloxy) methyl] -2-nonylphenoxy] ethyl) -ω-hydroxyoxyethylene, manufactured by Asahi Denka Co., Ltd., 1st stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (a)) comprising 0.5 part of 80% aqueous solution) and 80 parts of ion-exchanged water, 0.24 part of ammonium persulfate and ion-exchanged water An initiator solution consisting of 10 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Further, this reaction vessel comprises 23.54 parts of ethyl acrylate, 1.86 parts of 2-hydroxyethyl methacrylate, 4.60 parts of methacrylic acid, 0.2 part of Aqualon HS-10 and 10 parts of ion-exchanged water. A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (b)) and an initiator solution consisting of 0.06 parts ammonium persulfate and 10 parts ion-exchanged water were mixed at 0.5 ° C. at 0.5 ° C. Dripping in parallel over time. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 87.1 parts of ion exchange water and 0.32 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 300 nm, a non-volatile content of 30%, An emulsion resin Em-a having a solid content acid value of 30 mgKOH / g and a hydroxyl value of 40 was obtained.

Production example 2 Production of acrylic resin emulsion Em-b 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to the reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Next, 35.73 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 5.7 parts of 2-hydroxyethyl methacrylate, 20 parts of styrene, 0.5 part of Aqualon HS-10, 0.5 parts of Adekaria soap NE-20 7. first stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (c)) comprising 0.5 part and 49.7 parts ion-exchanged water, 0.21 part ammonium persulfate and ion-exchanged water An initiator solution consisting of 6 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Further, in this reaction vessel, 25.3 parts of butyl methacrylate, 2.4 parts of 2-hydroxyethyl methacrylate, 2.3 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water. A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (d)) and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.4 parts ion-exchanged water, In parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion exchange water and 0.24 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-b having a solid content acid value of 15 mgKOH / g and a hydroxyl value of 35 was obtained.

Production Example 3 Production of acrylic resin emulsion Em-c 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to the reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Next, 35.63 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 5.8 parts of 2-hydroxyethyl acrylate, 20 parts of styrene, 0.5 part of Aqualon HS-10, 0.5 parts of Adekaria soap NE-20 7. First stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (e)) comprising 0.5 part and 49.7 parts ion exchange water, 0.21 part ammonium persulfate and ion exchange water An initiator solution consisting of 6 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Further, in this reaction vessel, 19.85 parts of butyl methacrylate, 2.48 parts of 2-hydroxyethyl acrylate, 7.67 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (f)) and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.4 parts ion-exchanged water, In parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion-exchanged water and 0.4 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-c having a solid content acid value of 50 mgKOH / g and a hydroxyl value of 40 was obtained.

Production example 4 Production of acrylic resin emulsion Em-d 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to the reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Next, 16.78 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 24.65 parts of 2-hydroxyethyl acrylate, 20 parts of styrene, 0.5 part of Aqualon HS-10, 0.5 parts of Adekaria soap NE-20 7. First stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (g)) comprising 0.5 part and 49.7 parts ion-exchanged water, 0.21 part ammonium persulfate and ion-exchanged water An initiator solution consisting of 6 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Furthermore, this reaction vessel was charged with 18.08 parts of butyl methacrylate, 10.54 parts of 2-hydroxyethyl acrylate, 1.38 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water. A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (h)) and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.4 parts ion-exchanged water, at 80 ° C. In parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion exchange water and 0.24 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-d having a solid content acid value of 9 mgKOH / g and a hydroxyl value of 170 was obtained.

Production Example 5 Production of acrylic resin emulsion Em-e 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to a reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Next, 35.63 parts of methyl acrylate, 13.64 parts of butyl methacrylate, 0.73 part of 2-hydroxyethyl acrylate, 20 parts of styrene, 0.5 part of Aqualon HS-10, 0.5 parts of Adekaria soap NE-20 7. First stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (i)) composed of 0.5 part and 49.7 parts ion-exchanged water, 0.21 part ammonium persulfate and ion-exchanged water An initiator solution consisting of 6 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Further, in this reaction vessel, 28.31 parts of butyl methacrylate, 0.31 part of 2-hydroxyethyl acrylate, 1.38 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water. A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (j)) and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.4 parts ion-exchanged water at 80 ° C. In parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion exchange water and 0.24 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-e having a solid content acid value of 9 mgKOH / g and a hydroxyl value of 5 was obtained.

Production example 6 Production of acrylic resin emulsion Em-f 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to the reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Next, 35.65 parts of methyl acrylate, 34.69 parts of butyl methacrylate, 8.28 parts of 2-hydroxyethyl acrylate, 20 parts of styrene, 1.38 parts of methacrylic acid, 0.6 parts of Aqualon HS-10, Α, β-ethylenically unsaturated monomer mixture (monomer mixture (k)) comprising 0.5 part of Adeka Soap NE-20 and 74.4 parts of ion-exchanged water, 0.29 part of ammonium persulfate and ion-exchanged water An initiator solution consisting of 16 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion exchange water and 0.24 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-f having a solid content acid value of 9 mgKOH / g and a hydroxyl value of 40 was obtained.

Production Example 7 Production of acrylic resin emulsion Em-g 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to the reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Subsequently, 43.98 parts of methyl acrylate, 18.57 parts of butyl methacrylate, 7.45 parts of 2-hydroxyethyl acrylate, 20 parts of styrene, 0.5 part of Aqualon HS-10, 0.5 parts of Adekaria soap NE-20 7. First stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (l)) comprising 0.5 part and 49.7 parts ion-exchanged water, 0.21 part ammonium persulfate and ion-exchanged water An initiator solution consisting of 6 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Further, in this reaction vessel, 4.57 parts of butyl methacrylate, 0.83 part of 2-hydroxyethyl acrylate, 4.6 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water. A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (m)) and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.4 parts ion-exchanged water, In parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtering through a 400 mesh filter, 2.14 parts of ion-exchanged water and 0.32 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-g having a solid content acid value of 30 mgKOH / g and a hydroxyl value of 40 was obtained.

Production example 8 Production of acrylic resin emulsion Em-h 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to the reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Next, 34.94 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 5.8 parts of 2-hydroxyethyl acrylate, 20 parts of styrene, 0.69 part of methacrylic acid, 0.5 part of Aqualon HS-10, First stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (n)) comprising 0.5 part of Adeka Soap NE-20 and 49.7 parts of ion-exchanged water, 0.21 ammonium persulfate And an initiator solution consisting of 8.6 parts of ion-exchanged water were dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Furthermore, this reaction vessel was charged with 26.83 parts of butyl methacrylate, 2.48 parts of 2-hydroxyethyl acrylate, 0.69 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water. A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (o)) and an initiator solution consisting of 0.08 part ammonium persulfate and 7.4 parts ion-exchanged water, In parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion exchange water and 0.24 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-h having a solid content acid value of 9 mgKOH / g and a hydroxyl value of 40 was obtained.

Production Example 9 Production of acrylic resin emulsion Em-i 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to a reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. Warm up. Next, 35.73 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 5.70 parts of 2-hydroxyethyl methacrylate, 20.00 parts of styrene, 0.50 part of Aqualon HS-10, Adeka soap soap NE- The first stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (p)) 20 comprising 0.50 part of 20 and 49.70 parts of ion-exchanged water, 0.21 part of ammonium persulfate and ion-exchanged water An initiator solution consisting of 8.60 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Further, in this reaction vessel, 26.05 parts of butyl methacrylate, 2.40 parts of 2-hydroxyethyl methacrylate, 1.55 parts of methacrylic acid, 0.10 parts of Aqualon HS-10 and 24.70 parts of ion-exchanged water. A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (q)) and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.40 parts ion-exchanged water at 80 ° C. In parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion-exchanged water and 0.16 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle size of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-i having a solid content acid value of 10 mgKOH / g and a hydroxyl value of 35 was obtained.

Production Example 10 Production of acrylic resin emulsion Em-j 135.4 parts of ion exchange water and 1.1 parts of Aqualon HS-10 were added to the reaction vessel, and the mixture was heated to 80C while mixing and stirring in a nitrogen stream. Warm up. Next, 35.08 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 0.70 part of allyl methacrylate, 5.70 parts of 2-hydroxyethyl methacrylate, 20.00 parts of styrene, 0.50 of Aqualon HS-10 1st stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (r)) consisting of 0.50 parts of Adekaria soap NE-20 and 49.70 parts of ion-exchanged water, ammonium persulfate 0 An initiator solution consisting of .21 parts and 8.60 parts of ion-exchanged water was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Further, in this reaction vessel, 25.75 parts of butyl methacrylate, 0.30 parts of allyl methacrylate, 2.40 parts of 2-hydroxyethyl methacrylate, 1.55 parts of methacrylic acid, 0.10 parts of Aqualon HS-10 and A second stage α, β-ethylenically unsaturated monomer mixture (monomer mixture (s)) consisting of 24.70 parts ion-exchanged water, and starting with 0.08 parts ammonium persulfate and 7.40 parts ion-exchanged water. The agent solution was added dropwise at 80 ° C. in parallel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion-exchanged water and 0.16 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An emulsion resin Em-j having a solid content acid value of 10 mgKOH / g and a hydroxyl value of 35 was obtained.
Table 1 shows the average particle size, acid value (AV), hydroxyl value (OHV), acid value of the shell part, synthesis method (two-stage emulsification) of the acrylic resin emulsions Em-a to Em-j obtained in the above production examples. Polymerization or one-stage emulsion polymerization) and the amount of shell part (% by mass) in the acrylic resin emulsion are shown together.

Production example 11 Production of acrylic resin Ac-a 50 parts of MFDG (methylpropylene diglycol, manufactured by Nippon Emulsifier Co., Ltd.) was added to the reaction vessel, and the temperature was raised to 130C while stirring in a nitrogen stream. Next, α, β consisting of 14.77 parts of acrylic acid, 32.48 parts of 2-hydroxyethyl methacrylate, 47.75 parts of butyl acrylate, and 5 parts of MSD-100 (α-methylstyrene dimer, Mitsui Chemicals). -An ethylenically unsaturated monomer mixture (monomer mixture (t)) and an initiator solution consisting of 13 parts Kayaester O (tert-butyl peroctanoate, manufactured by Kayaku Akzo) and 10 parts MFDG in parallel over 3 hours And added dropwise to the reaction vessel. After the completion of dropping, an initiator solution consisting of 0.5 parts of Kayaester O and 5 parts of MFDG was further dropped over 0.5 hours. After completion of the dropwise addition, aging was performed at the same temperature for 1 hour.
Next, the mixture was cooled to 50 ° C. to obtain an acrylic resin Ac-a having a nonvolatile content of 60%, a solid content acid value of 110 mgKOH / g, a hydroxyl value of 140, and a molecular weight (Mn) = 3000.

Production example 12 Production of melamine resin aqueous dispersion (MFD-a) 178.5 parts of acrylic resin Ac-a obtained in Production Example 11 and Uban 20SB (fully-butylated melamine resin, manufactured by Nippon Cytec Co., Ltd.) , Non-volatile content 75%) was mixed with 800 parts and stirred at 80 ° C. for 2 hours. Thereafter, 18.3 parts of dimethylaminoethanol was added and uniformly dispersed, cooled to 40 ° C., and then dropped with 1003.2 parts of ion-exchanged water over 1 hour, so that a melamine resin having a nonvolatile content of 35% and a particle size of 120 nm was obtained. An aqueous dispersion (MFD-a) was obtained.

Production Example 13 Production of Melamine Resin Water Dispersion (MFD-b) 178.5 parts of acrylic resin Ac-a obtained in Production Example 11 and 800 parts of Uban 20SB were mixed with each other at 80C for 4 hours. Stir. Thereafter, 18.3 parts of dimethylaminoethanol was added and dispersed uniformly. After cooling to 40 ° C., 1003.2 parts of ion-exchanged water was added dropwise over 1 hour, whereby MFD- having a non-volatile content of 35% and a particle size of 80 nm. b was obtained.

Production Example 14 Production of Melamine Resin Water Dispersion (MFD-c) 357 parts of acrylic resin Ac-a obtained in Production Example 11 and 666 parts of Uban 20SB were mixed and stirred at 80C for 4 hours. . Thereafter, 36.6 parts of dimethylaminoethanol was added and uniformly dispersed, cooled to 40 ° C., and then, 1003.2 parts of ion-exchanged water was added dropwise over 1 hour, whereby MFD- having a non-volatile content of 35% and a particle size of 50 nm. c was obtained.
Table 2 summarizes the particle diameters of the melamine resin aqueous dispersions obtained in the above production examples.

Production Example 15 Production of water-soluble acrylic resin 23.89 parts of dipropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether were added to a reaction vessel, and the temperature was raised to 105C while mixing and stirring in a nitrogen stream. did. Next, 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate, 6.9 parts of methacrylic acid, 10.0 parts of dipropylene glycol methyl ether and t-butyl An initiator solution consisting of 1 part of peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of the dropping, aging was performed at the same temperature for 0.5 hours.
Next, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 part of t-butylperoxy 2-ethylhexanoate was dropped into the reaction vessel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Further, using a solvent removal apparatus, 16.11 parts of the solvent was distilled off at 110 ° C. under reduced pressure (70 torr), and then 6.40 parts of dimethylaminoethanol and then 188.0 parts of ion-exchanged water were added to make the water soluble. An acrylic resin was obtained. The resulting acrylic resin solution had a nonvolatile content of 30.0%, a solid content acid value of 40 mgKOH / g, and a hydroxyl value of 50.

Production example 16 Production of pigment paste mixture A 68.3 g of zircon beads having a diameter of 0.5 mm were added as a dispersion medium to the formulation shown in Table 3 below. This was stirred for 5 hours at 3000 rpm using an SG mill. The zircon beads were separated by filtration to obtain a pigment paste-like mixed liquid A which is a pigment paste of Shanin Blue G314.

Example of paint 1 Production of water-based base paint a 153.3 parts of acrylic resin emulsion Em-b obtained in Production Example 2 and 5 parts of 10% by weight dimethylethanolamine aqueous solution, Prime Pol PX-1000 ( Sanyo Chemical Industries, Ltd., bifunctional polyether polyol, number average molecular weight 1000, hydroxyl value 278, water tolerance infinity) 10 parts, MFD-c obtained in Production Example 14 100 parts, and ethylene glycol monohexyl ether 30 parts and 68.3 parts of the above-mentioned pigment paste mixture A were mixed and stirred, and then 10% aqueous solution of dimethylaminoethanol was added to adjust the pH to 8.5 and dispersed uniformly to obtain an aqueous base paint a. It was.

Examples of paints 2 to 10 Production of water-based base paints b to j The same as in Example 1 of paints except that the types of acrylic resin emulsion and melamine resin water dispersion were changed as shown in Table 4. Aqueous base paints b to j were obtained.

Comparative Example 1 of paint Production of water-based base paint k 153.3 parts of acrylic resin emulsion Em-a obtained in Production Example 1, 5 parts of 10% aqueous solution of dimethylethanolamine, and Primepole PX-1000 10.0 parts, 16.7 parts of the water-soluble acrylic resin of Production Example 15, 40 parts of Euban 20SB, 30 parts of ethylene glycol monohexyl ether, and 68.3 parts of the pigment paste mixture A are mixed. Stir. Further, a 10% aqueous solution of dimethylaminoethanol was added thereto to adjust the pH to 8.5 and uniformly dispersed to obtain an aqueous base paint k.

Comparative Example 2 of paint Production of water-based base paint l Aqueous base as in Comparative Example 1 of paint except that Em-b was used in place of the acrylic resin emulsion Em-a of Comparative Example 1 of paint A paint l was obtained.

Comparative Example 3 of paint Production of water-based base paint m 153.3 parts of acrylic resin emulsion Em-a obtained in Production Example 1 and 5 parts of 10% by weight dimethylethanolamine aqueous solution, Prime Pol PX-1000 ( I) 10 parts, 16.7 parts of a water-soluble acrylic resin obtained by Production Example 15, 37.5 parts of Cymel-327 (hydrophilic methylated melamine, 80% non-volatile content by Nippon Cytec Co., Ltd.), and ethylene After mixing and stirring 30 parts of glycol monohexyl ether and 68.3 parts of the above-mentioned pigment paste mixture A, a 10% aqueous solution of dimethylaminoethanol was added to adjust the pH to 8.5, and the mixture was uniformly dispersed. An aqueous base paint m was obtained.

Paint comparative example 4 Production of water-based base paint n Water base based in the same manner as paint comparative example 3 except that Em-b was used instead of acrylic resin emulsion Em-a in paint comparative example 3 A paint n was obtained.

Comparative examples of paints 5-7 Production of water-based base paints o to q Implementation of paints except that Em-c to Em-e were used in place of acrylic resin emulsion Em-b of paint example 2 In the same manner as in Example 2, aqueous base paints o to q were obtained.

[Evaluation]
The aqueous base paints a to q obtained in Examples and Comparative Examples were each applied to a steel plate with a doctor blade 20 mil and baked at 140 ° C. for 30 minutes to form a coating film. The color developability (white blur feeling, bluish feeling) of the obtained coating film was visually evaluated according to the following criteria. The results are shown in Table 4.

(White blur)
○: No white blur △: Some white blur ×: White blur (bluish)
◎: Strong blueness ○; Slightly blueness △; Slightly blueness ×; Blueness is weak

The stability of the acrylic resin emulsions Em-a to Em-j was evaluated as follows and shown in Table 4.
The change value [change value = (particle size after storage stability−initial particle size) ÷ initial particle size] after storage for 1 month at 40 ° C. is 0: 0 to 50% or less.
Δ: Over 50% and 100% or less.
X: It exceeds 100%. Or sedimentation.

Formation of multi-layer coating film Cathode electrodeposition paint Power Top V-20 manufactured by Nippon Paint Co., Ltd. and polyester-melamine gray intermediate coating paint Organa H-870 (both are trade names) Electrostatic coating machine AutoREA (trade name, manufactured by Lansburg Co., Ltd.) is applied to the above-described aqueous base paints a to q coated on a test plate that has been coated and heat-cured to have a dry film thickness of 25 μm and 40 μm. Apply at an atomization pressure of 5 kg / cm ² , set for about 7 minutes, then apply wet paint on it with a clear paint by spraying, set for about 7 minutes, and then bake and dry at 140 ° C. for 30 minutes. As a coating method, a coating test plate of the first coat of 2 coats and 1 bake (2C1B) was prepared, and left for 30 minutes in a desiccator. In addition, the cured coating film by a base coating material and a clear coating material was applied so that the dry film thickness might be 15 micrometers and 40 micrometers, respectively.

[Evaluation]
About the coating test board obtained by formation of the said multilayer coating film, initial recoat adhesiveness, chipping resistance, and water-resistant adhesion were evaluated by the following methods. The results are shown in Table 4.

(Initial recoat adhesion (NSR property))
1) Apply the same base paint as the first coat on the above-mentioned coating test board, followed by the same clear paint as the first coat, and bake and dry at 140 ° C. for 30 minutes, 2 coats 1 bake (2C1B) Each of the second coating test plates was prepared.
2) The initial recoat adhesion of the obtained multilayer coating film was evaluated by the following evaluation method.
A 2mm bun that reaches the substrate by holding the cutting blade of the cutter (NT cutter (trade name) S type, A type or equivalent) at about 30 degrees with respect to the initial cured coating surface. Eyes were formed, and an adhesive tape (adhesive tape manufactured by Nichiban Co., Ltd.) was evenly crimped with a fingertip so as not to leave bubbles. Immediately after holding one end of the adhesive tape, the adhesive tape was peeled off from the test piece by pulling it perpendicularly to the coated surface. The initial recoat adhesion was evaluated by visually measuring [number of peeled-off meshes] / [number of goose-mesh meshes = 100].

(Chip resistance (CP))
About the coating test board obtained by formation of the said multilayer coating film, evaluation of chipping resistance was performed as follows. Using a gravel tester tester (manufactured by Suga Test Instruments Co., Ltd.), 100 g of No. 7 crushed stone was collided with the coating film at an angle of 30 ° from a distance of 35 cm with an air pressure of 3.0 kgf / cm ² . After washing and drying, a peel test was performed using an industrial gum tape manufactured by Nichiban Co., Ltd., and then the degree of peeling of the coating film was visually observed and evaluated.
Criterion 5: No separation at all 4; Peeling area is small and frequency is low 3; Peeling area is small but frequency is slightly high 2; Peeling area is large but frequency is low 1; Peeling area is large and frequency is high

(Water resistant adhesion)
The coating test plate obtained by forming the multilayer coating film is immersed in warm water at 40 ° C. for 10 days, and after 1 hour of washing, the water resistance of the test plate is evaluated by the initial recoat adhesion (NSR property) evaluation method. The evaluation was performed by the method described in 2).

From Table 4, the water-based base coating material obtained in the Examples was able to obtain a coating film having excellent color developability. In addition, in the formation of a multilayer coating film using the aqueous base paint obtained in the examples, a multilayer coating film excellent in initial recoat adhesion, chipping resistance, and water adhesion resistance could be obtained. On the other hand, the comparative example of the paint did not satisfy all of these.

Production Example 17 Production of Acrylic Resin Ac2 As an α, β-ethylenically unsaturated monomer mixture (monomer mixture (a)), 23.1 parts of acrylic acid, 32.48 parts of 2-hydroxyethyl methacrylate, 39.butyl acrylate. 4 parts, MSD-100 (α-methylstyrene dimer, Mitsui Chemicals) 5 parts were used in the same manner as in Production Example 11 except that the nonvolatile content was 60%, the solid content acid value was 180 mgKOH / g, and the hydroxyl value was 140. An acrylic resin Ac2 having a number average molecular weight (Mn) of 3000 was obtained.

Production Example 18 Production of Acrylic Resin Ac3 As an α, β-ethylenically unsaturated monomer mixture (monomer mixture (a)), 9.4 parts of acrylic acid, 32.48 parts of 2-hydroxyethyl methacrylate, butyl acrylate 53. Except that 12 parts and 5 parts of MSD-100 (α-methylstyrene dimer, manufactured by Mitsui Chemicals) were used, 60% of non-volatile content, solid content acid value 70 mgKOH / g, hydroxyl value 140 in the same manner as in Production Example 11. An acrylic resin Ac3 having a number average molecular weight (Mn) of 3000 was obtained.

Production example 19 Production of acrylic resin Ac4 50 parts of MFDG was added to the reaction vessel, and the temperature was raised to 120C while stirring in a nitrogen stream. Next, an α, β-ethylenically unsaturated monomer mixture (monomer mixture (a)) composed of 14.77 parts of acrylic acid, 32.48 parts of 2-hydroxyethyl methacrylate and 52.75 parts of butyl acrylate, and Kaya ester An initiator solution (b) consisting of 2 parts of O and 10 parts of MFDG was dropped into the reaction vessel in parallel over 3 hours. After the completion of the dropwise addition, an initiator solution (c) consisting of 0.5 part of Kayaester O and 5 parts of MFDG was added dropwise over 0.5 hour. After completion of the dropwise addition, aging was performed at the same temperature for 1 hour.
Next, the mixture was cooled to 50 ° C. to obtain an acrylic resin Ac4 having a nonvolatile content of 60%, a solid content acid value of 110 mgKOH / g, a hydroxyl value of 140, and a number average molecular weight (Mn) = 9000.

Production Example 20 Production of Acrylic Resin Ac5 As an α, β-ethylenically unsaturated monomer mixture (monomer mixture (a)), 14.77 parts of acrylic acid, 16.24 parts of 2-hydroxyethyl methacrylate, 63.butyl acrylate. 99%, MSD-100 (α-methylstyrene dimer, Mitsui Chemicals) 5 parts were used in the same manner as in Production Example 11, except that the nonvolatile content was 60%, the solid content acid value was 110 mgKOH / g, and the hydroxyl value was 70. An acrylic resin Ac5 having a number average molecular weight (Mn) of 3000 was obtained.

Production Example 21 Production of acrylic resin Ac6 A reaction vessel equipped with a stirrer, thermometer, and reflux condenser was charged with 40 parts of ethylene glycol monobutyl ether and 30 parts of isobutyl alcohol, heated and stirred, and reached 100C. 20 parts of styrene, 20 parts of methyl methacrylate, 33 parts of n-butyl acrylate, 20 parts of 2-hydroxyethyl methacrylate, 7 parts of acrylic acid, 1 part of 2,2′-azobisisobutyronitrile, 5 parts of isobutyl alcohol A mixture of monomers consisting of parts was added dropwise over 3 hours. After completion of dropping, the mixture was kept at 100 ° C. for 30 minutes, and then an additional catalyst solution which was a mixture of 0.5 part of 2,2′-azobisisobutyronitrile and 10 parts of ethylene glycol monobutyl ether was required for 1 hour. It was dripped. The mixture was further stirred at 100 ° C. for 1 hour, then cooled, 15 parts of isobutyl alcohol was added, 4 parts of dimethylethanolamine was added at 75 ° C., and the mixture was stirred for 30 minutes to obtain an acrylic resin solution (Ac6). . The obtained resin had a non-volatile content of 50%, an acid value of 54 mg KOH / g, a hydroxyl value of 86, and Mn (number average molecular weight) = 15000.
Table 5 collectively shows the acid value (AV), hydroxyl value (OHV), and number average molecular weight (Mn) of the acrylic resins Ac-a and Ac2 to Ac6 obtained in the above production examples.

Production example 22 Production of acrylic resin emulsion Em-1 135.4 parts of ion-exchanged water and 1.1 parts of Aqualon HS-10 were added to a reaction vessel, and the temperature was raised to 80C while mixing and stirring in a nitrogen stream. did. Next, the first stage α, β-ethylenically unsaturated monomer comprising 25.21 parts of methyl acrylate, 22.37 parts of ethyl acrylate, 7.42 parts of 2-hydroxyethyl methacrylate, and 15 parts of methyl methacrylate. A mixture (monomer mixture (c)) and an initiator solution consisting of 0.21 part of ammonium persulfate and 8.6 parts of ion-exchanged water were dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.
Furthermore, the reaction vessel was charged with a second stage α, β-ethylenically unsaturated monomer mixture consisting of 23.54 parts of ethyl acrylate, 1.86 parts of 2-hydroxyethyl methacrylate and 4.60 parts of methacrylic acid ( A monomer mixture (d)) and an initiator solution consisting of 0.08 part of ammonium persulfate and 7.4 parts of ion-exchanged water were added dropwise in parallel at 80 ° C. over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.
Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 2.14 parts of ion-exchanged water and 0.24 part of dimethylethanolamine were added to adjust the pH to 6.5, an average particle size of 80 nm, and a non-volatile content of 30%. An acrylic resin emulsion Em-1 having a solid content acid value of 30 mgKOH / g and a hydroxyl value of 40 was obtained.

Examples 1-3 Production of hydrophobic melamine resin aqueous dispersions Hydrophobic melamine resin aqueous dispersions MFD-b, MFD-a, MFD-c produced in Production Examples 13, 12, and 14 above were used. Examples 1, 2, and 3 were used respectively.

Comparative Example 1 Production of hydrophobic dispersion of hydrophobic melamine resin 178.5 parts of the acrylic resin Ac-a obtained in Production Example 11 was used as Uban 20SB (fully alkyl melamine resin, manufactured by Nippon Cytec Co., Ltd.). Min. 75%) and mixed with 800 parts. Thereafter, 18.3 parts of dimethylethanolamine was added and dispersed uniformly, and 1003.2 parts of ion-exchanged water was added dropwise over 1 hour to obtain a hydrophobic melamine resin aqueous dispersion. The particle size of the resin particles in this aqueous dispersion was 300 nm.

Examples 4 and 5, Comparative Examples 2-6 Production of Hydrophobic Melamine Resin Water Dispersions (MFD-1-7) According to Table 6, change of species and amount of acrylic resin and melamine resin, reaction temperature and Hydrophobic melamine resin aqueous dispersions (MFD-1 to 7) were obtained in the same manner as in Example 1 except that the reaction time was changed. Table 6 shows the particle size of the resin particles in each aqueous dispersion.

Comparative example 7 Production of hydrophobic melamine resin aqueous dispersion (MFD-8) Acrylic resin solution (Ac6) obtained in Production Example 21 in a reaction vessel equipped with a stirrer, thermometer and reflux condenser. 120 parts, “Uban 28-70W” (trade name, hydrophobic melamine resin, 70% ethylene glycol monobutyl ether solution of butylated melamine, manufactured by Mitsui Chemicals, Inc.) 57.2 parts in this order, and stirred at 70 ° C. for 4 hours. Warming treatment was performed. To 100 parts of the heated product (solid content 56.4%), 4 parts of dimethylaminoethanol was added and dispersed uniformly. After cooling to 40 ° C., 181.7 parts of ion-exchanged water was added to 1 part. MFD-8 was obtained by adding dropwise over time. The particle size of this water-dispersed resin was 180 nm.

Comparative Example 8 Production of hydrophobic melamine resin aqueous dispersion (MFD-9) Acrylic resin solution (Ac6) obtained in Production Example 21 in a reaction vessel equipped with a stirrer, thermometer and reflux condenser. 80 parts and 85.7 parts of “Uban 28-70W” were charged in order and stirred at 70 ° C. for 4 hours for heating treatment. To 100 parts of the heated product (solid content 60.3%), 4 parts of dimethylaminoethanol was added and dispersed uniformly. After cooling to 40 ° C., 181.7 parts of ion-exchanged water was added to 1 part. MFD-9 was obtained by dripping with time. The particle size of this water-dispersed resin was 230 nm.

[Evaluation]
The storage stability, adhesion, and surface smoothness of each hydrophobic melamine resin aqueous dispersion were evaluated by the following methods, and the results are shown in Table 6.
(Storage stability)
Each hydrophobic melamine resin aqueous dispersion was allowed to stand at 40 ° C. for 1 month, and changes in the dispersion were visually evaluated.
○: No change ×: Sedimentation

(Adhesion)
Each hydrophobic melamine resin aqueous dispersion was applied to a steel plate with a doctor blade 20 mil. The adhesion was evaluated by the method shown below after drying at 140 ° C. for 30 minutes.
A 2mm bun that reaches the substrate by holding the cutting blade of the cutter (NT cutter (trade name) S type, A type or equivalent) at about 30 degrees with respect to the initial cured coating surface. Eyes were formed, and an adhesive tape (Cellotape (registered trademark) manufactured by Nichiban Co., Ltd.) was uniformly crimped with a fingertip so as not to leave bubbles. Immediately after holding one end of the adhesive tape, the adhesive tape was peeled off from the test piece by pulling it perpendicularly to the coated surface. At this time, the [number of peeled eyes] / [number of goblet eyes = 100] was visually measured, and the adhesion was evaluated according to the following criteria.
○: 0/100
Δ: 1/100 to 25/100
X: 26/100 to 100/100

(Surface smoothness)
Each hydrophobic melamine resin aqueous dispersion was applied to a glass plate with a doctor blade 20 mil. The surface state after drying at 140 ° C. for 30 minutes was visually evaluated.
○: Smooth △; Slightly round ×;

U20SB; Uban 20SB
U28-70W; Uban 28-70W
C238; Cymel 238 (manufactured by Nippon Cytec Co., Ltd., methyl / isobutylated melamine, nonvolatile content = 100%)
C325; Cymel 325 (Nippon Cytec Co., Ltd., methylated melamine, nonvolatile content = 80%)
Ac / MF ratio; acrylic resin / melamine resin (resin solids mass ratio)

From Table 6, the hydrophobic melamine resin aqueous dispersions obtained in the examples were excellent in storage stability, and the adhesion and surface smoothness of the obtained coating films were also excellent. On the other hand, the thing obtained by the comparative example was not obtained to satisfy all of these.

Example 11 of paint
153.3 parts of the acrylic resin emulsion Em-1 obtained in Production Example 22 and 5 parts of a 10% by mass dimethylethanolamine aqueous solution, 16.7 parts of the water-soluble acrylic resin obtained in Production Example 15, and Primepole PX- 1000 parts (bifunctional polyether polyol manufactured by Sanyo Chemical Industries, number average molecular weight 1000, hydroxyl value 278, water tolerance infinity), 100 parts MFD-1 obtained in Example 1, ethylene glycol monohexyl ether 30 parts and 68.3 parts of the mixture A on the pigment paste of Production Example 16 above were mixed and stirred, adjusted to pH = 8.5 by adding a 10% aqueous solution of dimethylethanolamine, and dispersed uniformly. Paint A was obtained.

Paint Examples 12 and 13 and Comparative Examples 8, 9, and 11
Aqueous base paints B to E and G were obtained in the same manner as in Example 11 except that the types of the acrylic resin emulsion and the melamine resin aqueous dispersion were changed as shown in Table 7.

Paint Comparative Example 10
153.3 parts of the acrylic resin emulsion Em-1 obtained in Production Example 22, 5 parts of a 10% by mass dimethylethanolamine aqueous solution, 33.3 parts of the water-soluble acrylic resin obtained in Production Example 15, and Primepole PX- 1000 parts (bifunctional polyether polyol manufactured by Sanyo Chemical Industries, number average molecular weight 1000, hydroxyl value 278, water tolerance infinity), Cymel 325 (methylated melamine resin, manufactured by Nippon Cytec Co., Ltd., SP = 14.0, 37.5 parts of non-volatile content (80%), 30 parts of ethylene glycol monohexyl ether, and 68.3 parts of mixture A on the pigment paste of Production Example 16 were mixed and stirred, and a 10% aqueous solution of dimethylethanolamine was added. The pH was adjusted to 8.5 and dispersed uniformly to obtain an aqueous base paint F.

[Evaluation]
The aqueous base paints A to G obtained in the paint examples and comparative examples were each applied to a steel plate with a doctor blade 20 mil, and baked at 140 ° C. for 30 minutes to form a coating film. The color developability (white blur feeling, bluish feeling) of the obtained coating film was evaluated by the same method as described above. Further, initial recoat adhesion, chipping resistance, and water adhesion were evaluated by the same methods as described above. The results are shown in Table 7.

From Table 7, the water-based base paints obtained in Examples 11 to 13 of the paints were able to obtain coating films excellent in all of color development, initial recoat adhesion, chipping resistance, and water resistance. On the other hand, none of the paints obtained in Comparative Examples 8 to 11 satisfying all of these conditions was obtained.

The aqueous coloring paint of the present invention can be suitably used as an aqueous base paint in automobile painting.

Claims (14)

An aqueous coloring paint containing a film-forming resin, a curing agent and a pigment,
The coating film-forming resin contains an acrylic resin emulsion produced by emulsion polymerization having an acid value of 1 to 30 mgKOH / g and a hydroxyl value of 10 to 150,
The said hardening | curing agent contains the hydrophobic melamine resin aqueous dispersion with a particle size of 20-140 nm, The water-based coloring coating material characterized by the above-mentioned. Hydrophobic melamine resin aqueous dispersion is an acrylic resin having an acid value of 105 to 200 mgKOH / g, a hydroxyl value of 100 to 200, and a number average molecular weight of 1000 to 5000, and a hydrophobic melamine resin in a mass ratio of 5/95 to 50/50. The aqueous coloring paint according to claim 1, which is obtained by a production method comprising the step (1) of mixing and heating in step (1) and the step (2) of dispersing the heated product obtained in step (1) in water. The water-based coloring paint according to claim 1 or 2, wherein the hydrophobic melamine resin has a solubility parameter (SP) in a range of 9.0 <SP <11.5. The water-based colored paint according to claim 1, 2 or 3, wherein the acrylic resin emulsion has a particle size of 20 to 140 nm. The water-based colored paint according to claim 1, 2, 3, or 4, wherein the acrylic resin emulsion is obtained by two-stage emulsion polymerization. 6. The water-based colored paint according to claim 5, wherein in the two-stage emulsion polymerization, the acrylic resin emulsion obtained by the second-stage emulsion polymerization has an acid value of 25 to 200 mg KOH / g. A step (I) of forming a base coating film by applying a water-based base coating on an object to be coated, and a step of forming a clear coating layer by applying a clear coating thereon without curing the base coating (II) ), And a method for forming a multilayer coating film comprising the step (III) of simultaneously heating the base coating film and the clear coating film,
The method for forming a multilayer coating film according to claim 1, wherein the water-based base paint is the water-colored paint according to claim 1, 2, 3, 4, 5 or 6. The multilayer coating film forming method according to claim 7, wherein the object to be coated is a chemical conversion treatment to form an electrodeposition coating film and an intermediate coating film. A multilayer coating film formed by the multilayer coating film forming method according to claim 7 or 8. A process of mixing and heating an acrylic resin having an acid value of 105 to 200 mgKOH / g, a hydroxyl value of 100 to 200, and a number average molecular weight of 1000 to 5000 and a hydrophobic melamine resin in a mass ratio of 5/95 to 50/50 (1) And the step (2) of dispersing the heated product obtained in the step (1) in water to obtain a hydrophobic melamine resin aqueous dispersion having a particle size of 20 to 140 nm. Body manufacturing method. The method for producing an aqueous dispersion of a hydrophobic melamine resin according to claim 10, wherein the hydrophobic melamine resin has a solubility parameter (SP) in a range of 9.0 <SP <11.5. A hydrophobic melamine resin aqueous dispersion obtained by the method for producing a hydrophobic melamine resin aqueous dispersion according to claim 10 or 11. An aqueous coating composition containing a film-forming resin and a curing agent,
The said hardening | curing agent contains the hydrophobic melamine resin aqueous dispersion of Claim 12, The water-based coating composition characterized by the above-mentioned. The film-forming resin contains an acrylic resin emulsion obtained by emulsion polymerization of a monomer mixture containing 65% by mass or more of a (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion. Water-based paint composition.