JPH05271580A - Aqueous coating composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition, comprising prescribed amounts of an aqueous resin, a curing agent, a metallic pigment and a specific corrosion inhibitor, excellent in corrosion, water and chemical resistances, storage stability and adhesion and useful for automobiles, etc. CONSTITUTION:The objective composition comprises (A) an aqueous resin such as an acrylic resin, (B) a curing agent such as melamine, (C) a metallic pigment such as aluminum and (D) a phosphoric acid ester, composed of a copolymer obtained from (i) an ethylenic monomer containing one or more acidic hydroxyl groups bound to phosphorus atom in the molecule, (ii) an ethylenic monomer containing hydroxyl group and (iii) other ethylenic monomers copolymerizable therewith and having one or more acidic hydroxyl groups bound to the phosphorus atom and/or their salts, 30-150mgKOH/g acid value, 30-150mgKOH/g hydroxyl value and 3000-15000 number-average molecular weight as a corrosion inhibitor for the component (C). The content of the phosphoric acid ester is 0.2-10wt.% expressed in terms of orthophosphoric acid, based on the component (C).

Description

Detailed Description of the Invention

[0001]

The present invention relates to a novel aqueous coating composition,
More specifically, it prevents corrosion of metal pigments, has excellent storage stability and adhesiveness, and has good water resistance and chemical resistance, and is particularly useful as a water-based metallic paint suitable for use in automobiles and the like. Water-based coating composition.

[0002]

2. Description of the Related Art Conventionally, for outer panels of automobiles and the like, metal pigments such as aluminum pigments and
A method of forming a coating film by coating a paint containing mica pigment and a coloring pigment (hereinafter referred to as "base coat") without baking and then coating a transparent paint (hereinafter referred to as "top coat") on the coating to heat-cure, that is, 2 coats 1 On the other hand, a method for forming a baked coating film has been adopted. On the other hand, a low-pollution coating material with a reduced amount of discharged organic solvent has been desired in response to a serious environmental pollution problem these days. Therefore, various methods have been tried in the method of forming a two-coat, one-bake coating film,
Among them, as a powerful method, for example, a method of using a water-based paint for the base coat is known. Various types of water-based paints for use in the base coat have been proposed (JP-A-57-157358 and JP-A-64-157358).
24870), both methods have coating performance equivalent to that of a so-called solvent-type paint containing a large amount of an organic solvent, and are particularly excellent in flip-flop property obtained by a metal pigment such as an aluminum pigment. It has a feature. However, since water is used as a dispersion medium in such an aqueous paint, when a metal pigment is contained, the metal pigment is corroded by water and hydrogen gas is generated, which is not preferable. Conventionally, as a metal pigment used for an aqueous paint, a metal composition in which a saturated or unsaturated fatty acid or a derivative thereof is used as a surface treatment agent and a surfactant is added thereto to impart water dispersibility has been used. However, these water-dispersible metal pigments have poor storage stability in water-based paints, and in particular have a problem that a large amount of hydrogen gas is generated during storage. After that, as a method for improving the storage stability of the metal pigment, many methods using phosphoric acid esters have been proposed. For example, a method using a phosphoric acid ester of caprolactone (JP-A-61-29607).
No. 2), a method using a reaction product of an orthophosphoric acid or a phosphoric acid monoester and an epoxy compound (JP-A-61-61).
-47771) A method using a copolymer of styrene-allyl alcohol and a reaction product of pt-amylphenol and orthophosphoric acid or phosphorus pentoxide (Japanese Patent Publication No.
-46624) and the like are disclosed. However, all of these methods are aimed at suppressing the reaction between the metal and water by the adsorption action on the metal surface by the acidic hydroxyl group bonded to the phosphorus atom, but the effect is insufficient. Or even if the suppression effect is relatively recognized, when using a water-based paint,
There is a problem in the performance of the obtained coating film, such as adhesion, water resistance, chemical resistance, etc., and it cannot always be said to be a practical method. Further, a method has been proposed in which an adsorption layer made of orthophosphoric acid or an organic phosphoric acid compound and a resin coating layer enclosing the adsorption layer are provided on the surface of the metal pigment (Japanese Patent Laid-Open No. 1-129070). However, this method is a method of treating in the manufacturing process of metal pigments, and it is difficult to apply it to commercially available metal pigments and pastes.

[0003]

The present invention overcomes the drawbacks of the prior art, prevents the corrosion of metal pigments, has excellent storage stability and adhesion, and is water and water resistant. The purpose of the present invention is to provide an aqueous coating composition which has good chemical properties and is particularly useful as an aqueous metallic coating suitable for use in automobiles and the like.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to develop an aqueous coating composition having the above-mentioned preferable properties. As a result, an aqueous coating composition comprising an aqueous resin, a curing agent and a metal pigment has been obtained. It was found that the purpose can be achieved by adding a specific phosphoric acid ester compound as a corrosion inhibitor for the metal pigment, and the present invention has been completed based on this finding. That is, the present invention is (a)
Contains an aqueous resin, (b) a curing agent, and (c) a metallic pigment,
And (d) As a corrosion inhibitor for the metal pigment,
(A) an ethylenic monomer containing at least one acidic hydroxyl group bonded to a phosphorus atom in the molecule, (b)
At least one acidic hydroxyl group bonded to a phosphorus atom and / or a salt thereof, which comprises an ethylenic monomer containing a hydroxyl group and (c) a copolymer obtained from these and another ethylenic monomer copolymerizable therewith. Acid value of 30 to 150 mgKOH / g, hydroxyl value of 30 to 15
It contains 0 mg KOH / g and a phosphoric acid ester having a number average molecular weight of 3,000 to 15,000, and the content of the phosphoric acid ester is 0.2 to 10% by weight with respect to the metal pigment in terms of orthophosphoric acid. The present invention provides an aqueous coating composition characterized by the following.

The present invention will be described in detail below. The aqueous coating composition of the present invention contains an aqueous resin, a curing agent, a metal pigment and a corrosion inhibitor for the metal pigment,
As the corrosion inhibitor, one containing an acidic hydroxyl group bonded to a phosphorus atom and / or its salt and a functional hydroxyl group is used. The composition of the present invention containing such a corrosion inhibitor improves not only the effect of preventing corrosion of metal pigments, but also coating properties such as adhesion, water resistance and chemical resistance. In addition, since the corrosion inhibitor can achieve the purpose by being adsorbed on the metal pigment, it does not impair the beauty of the metal pigment.

Examples of the (a) ethylenic monomer containing at least one acidic hydroxyl group bonded to a phosphorus atom used as a raw material in the production of the corrosion inhibitor used in the present invention include (2-acryloyloxyethyl). ) Acid phosphate, (2-methacryloyloxyethyl) acid phosphate, (2-acryloyloxypropyl) acid phosphate, (2-methacryloyloxypropyl) acid phosphate and the like can be mentioned, and these may be used alone or in combination. The above may be used in combination. Of the two acidic hydroxyl groups, one of the acidic hydroxyl groups in these monomers may be an ester type.

Examples of the (b) ethylenic monomer having a hydroxyl group as a raw material include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,
2-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 2-hydroxybutyl methacrylate and the like can be mentioned. These may be used alone or in combination of two or more. further,
(C) Other ethylenic monomers that can be copolymerized with the above-mentioned monomers used as raw materials include, for example, styrene, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2 -Ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, acrylonitrile and the like can be mentioned. These monomers may be used alone or in combination of two or more.

The corrosion inhibitor used in the present invention is produced by copolymerizing the above-mentioned monomers (a), (b) and (c) by a known solution polymerization method in the presence of a usual polymerization initiator. be able to. As the organic solvent used for this polymerization, for example, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate,
Butyl acetate, isobutyl acetate, isopropyl alcohol, n-butanol, isobutanol, butyl cellosolve and the like can be mentioned. Examples of the polymerization initiator include α, α′-azobisisobutyronitrile, α, α′-azobisisovaleronitrile, t-butylperoxybenzoate, di-t-butylperoxide, t-butylperoxy-2. -Ethyl hexanate and the like. When the organic solvent used for producing the polymer is insoluble in water, it is desirable to remove the organic solvent under reduced pressure after producing the polymer and add the water-insoluble organic solvent.

The phosphoric acid ester type corrosion inhibitor comprising the copolymer thus obtained has an acid value of 30 to 150 mg.
KOH / g, hydroxyl value is 30 to 150 mgKOH / g, number average molecular weight is required to be in the range of 3000 to 15000, especially acid value is 50 to 130 mgKOH / g, hydroxyl value is 50 to 100 mgKOH / g, number Average molecular weight 4000-1
Those in the range of 0000 are preferable. The acid value is 3
If it is less than 0 mgKOH / g, the effect of preventing corrosion on the metal pigment is poor, and if it exceeds 150 mgKOH / g, the water resistance of the coating film obtained tends to decrease. Also, the hydroxyl value is 3
If it is less than 0 mgKOH / g, the adhesion and chemical resistance of the coating film obtained will be poor, and if it exceeds 150 mgKOH / g, the water resistance of the coating film obtained will tend to decrease.

On the other hand, if the number average molecular weight is less than 3,000, the water resistance and chemical resistance of the resulting coating film will be poor, resulting in 15,000.
When it exceeds, the solubility in water decreases, and the storage stability of the coating composition becomes poor. The content of the phosphoric acid ester type corrosion inhibitor in the composition of the present invention is 0.2 to the metal pigment in terms of orthophosphoric acid (determined by acid value).
It is chosen to be 10% by weight, preferably 0.5-5% by weight. If the content is less than 0.2% by weight, the adsorption of hydroxyl groups of the phosphoric acid groups on the surface of the metal pigment is not sufficient, resulting in poor corrosion resistance, and if it exceeds 10% by weight, storage stability decreases. The water resistance of the obtained coating film becomes poor.

The corrosion inhibitor has an acidic hydroxyl group (P-OH) immediately after it is obtained by copolymerizing the above-mentioned monomers (a), (b) and (c), and therefore, the present invention When used in the coating composition of, the corrosion inhibitor should be used in the form of its salt, for example, the salt obtained by neutralizing with ammonia, dimethylamine, triethylamine, ethanolamine, dimethylethanolamine, etc. preferable. There is no particular limitation on the water-based resin used as the component (a) in the composition of the present invention, and resins conventionally used in water-based paints such as alkyd resins, polyester resins, acrylic resins, cellulosic resins and polyurethane-based resins can be used. A water-soluble, water-dispersed or emulsified base resin selected from the above is used. As the curing agent of the component (b), for example, a water-soluble or water-dispersible amino resin obtained by condensation or co-condensation of melamine, benzoguanamine, urea or the like with formaldehyde, or a water-dispersible blocked isocyanate resin is used. Be done. As these aqueous resins and curing agents, those already known per se can be used.

The metallic pigment of component (c) used in the present invention is a wide range of conventional pigments, especially aluminum,
Any one can be selected and used from those containing copper, zinc, true chew, nickel, aluminum-copper alloy, aluminum-zinc alloy, aluminum-nickel alloy, aluminum-magnesium alloy and the like. These metal pigments are preferably used in the form of powder or flakes. The composition of the present invention includes other components usually used in the preparation of an aqueous coating composition, such as a coloring pigment,
Extender pigment, water-soluble organic solvent, surface conditioner, thickener,
Deionized water or the like may be contained.

The coating composition of the present invention can be prepared, for example, by mixing various components in desired proportions. If desired, some of the ingredients can be premixed. For example, the metal pigment and the phosphoric acid ester type corrosion inhibitor may be premixed before both of them are incorporated into the coating composition. The water-based coating composition of the present invention is suitably used as a base coat in a two-coat, one-bake coating film forming method that is particularly used in automobiles.

[0014]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The effect of the corrosion inhibitor of the present invention and the coating film performance of the obtained aqueous coating composition were determined as follows.

(1) Corrosion prevention effect of metal pigment (hereinafter referred to as hydrogen gas generation amount) Metal pigment / resin content (water-based resin + curing agent) weight ratio 10/1
A water-based paint of No. 00 was prepared, and the heating residue was adjusted to 18% by weight with deionized water, and the amount of gas generated when stored at 40 ° C. for 30 days was measured and evaluated. ⊚: Gas generation amount of 2 cc per 100 g of water-based coating composition
◯: Gas generation amount is 5 cc or less ×: Gas generation amount exceeds 5 cc (2) Storage stability Metal pigment / resin content (aqueous resin + curing agent) weight ratio 10/1
No. 00 water-based coating composition was prepared and deionized water was used.
The viscosity was adjusted with a Ford cup # 4 so as to be 30 seconds / 20 ° C. After the coating composition was stored at 40 ° C. for 30 days, the viscosity was measured by Ford cup # 4 and evaluated. ⊚: Viscosity change within 2 seconds ◯: Viscosity change within 5 seconds x: Viscosity change over 5 seconds

(3) Adhesion The adhesion was determined according to JIS K-5400 8.5.2 (1990) and the cross-cut tape method. (4) Water resistance The test piece was immersed in warm water at 40 ° C. for 240 hours, and examined for abnormal appearance such as swelling of the coating film and tingling. (5) Chemical resistance The test piece was immersed in a solution having a gasoline / ethanol weight ratio of 90/10 for 3 hours, and the presence or absence of abnormal appearance such as swelling of the coating film and stripes was examined.

In the performance tests of (3), (4) and (5), test pieces were prepared by the following method and evaluated. Steel sheet treated with zinc phosphate, cationic electrodeposition paint [NOF
Co., Ltd., trade name: Aqua # 4200] with a dry film thickness of 20 μm
And then baked at 175 ° C. for 30 minutes, and then coated on the steel plate with an intermediate coating paint [NOF CORPORATION, trade name: High Epico No. 100] so as to have a dry film thickness of 30 μm. The coated plate was prepared by baking at 140 ° C. for 30 minutes. A water-based coating composition was spray-coated on the surface of this coated plate so that the dry film thickness was 15 μm, and dried at 80 ° C. for 3 minutes, and then clear coating [NOF CORPORATION, trade name: Bellcoat No. 6000 clear] to dry film thickness 4
A test piece was prepared by spray coating to a thickness of 0 μm and baking at 140 ° C. for 30 minutes.

Production Example 1 Production of Corrosion Inhibitor P-A In a reaction vessel equipped with a stirrer, a reflux condenser and a thermometer,
Add 500 parts by weight of butyl cellosolve, and add 8 parts under nitrogen atmosphere.
The mixture was heated and stirred at 0 ° C. Then the following monomer mixture was added to 3
It dripped over time. (2-methacryloyloxyethyl) acid phosphate 40 parts by weight 2-hydroxyethyl methacrylate 52.0 parts by weight methyl methacrylate 160 parts by weight butyl acrylate 108 parts by weight 2-ethylhexyl methacrylate 40 parts by weight azobisisobutyronitrile 10 parts by weight butyl cellosolve 80 Parts by weight Then, a mixture of 1 part by weight of t-butylperoxy-2-ethylhexanate and 9 parts by weight of butyl cellosolve was added. The reaction was continued at 80 ° C for 2 hours to give an acid value of 5
0, hydroxyl value 56, number average molecular weight 4500, heating residue 5
A 0% by weight resin solution was obtained. The converted amount of orthophosphoric acid based on the resin solid content was 2.9% by weight.

Production Examples 2 and 3 Production of Corrosion Inhibitors P-B and C Corrosion inhibitors P-B and C were obtained in the same manner as in Production Example 1 with the compositions shown in Table 1. The first is the characteristic value of the obtained corrosion inhibitor.
Shown in the table.

Production Examples 4 to 9 Production of Corrosion Inhibitors P-D to I for Comparison The compositions shown in Table 1 were used to prepare corrosion inhibitors P-D to I for comparison in the same manner as in Production Example 1. Obtained. The characteristic values of these corrosion inhibitors are shown in Table 1.

[0021]

[Table 1]

[0022]

[Table 2] Note 1) Daihachi Chemical Co., Ltd., average molecular weight 196, acid value 550 2) Daihachi Chemical Co., Ltd., average molecular weight 210, acid value 500

Production Example 10 Production of Acrylic Resin Aqueous Dispersion (A-1) for Aqueous Paint In a reaction vessel equipped with a stirrer, a reflux condenser and a thermometer,
Add 113 parts by weight of deionized water, 2 parts by weight of Eleminol ES-12 [trade name, anionic surfactant, Sanyo Kasei Co., Ltd.], 0.25 parts by weight of ammonium persulfate, and add 70 ° C.
It was heated and stirred. Next, the following monomer mixture was added dropwise over 3 hours, after which the reaction was continued at 70 ° C for 2 hours and then neutralized with dimethylethanolamine in an equivalent amount, and the heating residue was 44.5% by weight and the pH was 7.5. A resin dispersion (A-1) was obtained. Methyl methacrylate 40 parts by weight Butyl acrylate 40 parts by weight 2-hydroxyethyl methacrylate 15 parts by weight Methacrylic acid 5 parts by weight

Production Example 11 Production of Acrylic Resin Aqueous Solution for Aqueous Coating (A-2) In a reaction vessel equipped with a stirrer, a reflux condenser and a thermometer,
80 parts by weight of butyl cellosolve was added, and the mixture was heated and stirred at 140 ° C. Next, the following monomer mixture was added dropwise over 3 hours. Methyl methacrylate 45 parts by weight Butyl acrylate 25 parts by weight Styrene 10 parts by weight 2-hydroxyethyl methacrylate 10 parts by weight Acrylic acid 10 parts by weight t-butyl peroxybenzoate 1 part by weight Then, 0.5 parts by weight of t-butyl peroxybenzoate is added. Then, the reaction was continued at 140 ° C for 2 hours, and the heating residue was 55.2% by weight, the acid value was 43, and the number average molecular weight was 460.
A resin solution of 0 was obtained. This product was neutralized with dimethylethanolamine in an equivalent amount, and deionized water was added to the mixture to give an acrylic resin aqueous solution (A-
2) was obtained.

Example 1 Alpaste 1700NL [trade name, aluminum pigment, aluminum pigment content 65% by weight, manufactured by Toyo Aluminum Co., Ltd.] 27.7
Parts by weight, butyl cellosolve 30 parts by weight, Cymel 303
[Product name, melamine-formaldehyde resin, manufactured by Mitsui Cyanamide Co., Ltd.] 35 parts by weight were mixed and stirred until the aluminum pigment was homogeneously dispersed. Next, 31 parts by weight of the corrosion inhibitor P-A obtained in Production Example 1 and 0.5 part by weight of dimethylethanolamine were added to this mixture, and the mixture was stirred for 1 hour. Next, the above mixture was added to 30 parts by weight of the acrylic resin aqueous solution (A-2) obtained in Production Example 11 and stirred for 1 hour. Next, 330 parts by weight of the acrylic resin dispersion (A-1) obtained in Production Example 10, 455.8 parts by weight of deionized water, and 60 parts by weight of butyl cellosolve were added, and the mixture was further stirred for 1 hour. In this way, the weight ratio of metal pigment / resin (water-based resin + hardener) is 1
A water-based coating composition containing 0/100, a heating residue of 21% by weight, and a corrosion inhibitor for an aluminum pigment of 2% by weight in terms of orthophosphoric acid was obtained. The results of performance evaluation are shown in Table 2.

Examples 2 to 10 Aqueous coating compositions having the compositions shown in Table 2 were prepared in the same manner as in Example 1. The performance evaluation results are shown in Table 2.

Examples 11 to 13 Alpaste SAP 110 as an aluminum pigment [trade name, aluminum pigment content 65% by weight, manufactured by Showa Aluminum Co., Ltd.]
A water-based coating composition having the composition shown in Table 2 was prepared in the same manner as in Example 1. The results of performance evaluation are shown in Table 2.

Example 14 (1) Preparation of granular copper powder paste 1 kg of granular copper powder was pulverized in 1.2 liters of mineral spirits in a ball mill for 8 hours to obtain a slurry, which was washed out with mineral spirits. 325
Passed through a mesh screen. Then, it was filtered by a filter press to obtain a granular copper powder paste having a metal content of 80% by weight. (2) Preparation of Aqueous Coating Composition Using the granular copper powder paste obtained in (1), an aqueous coating composition having the composition shown in Table 2 was prepared in the same manner as in Example 1. The results of performance evaluation are shown in Table 2.

Examples 15 and 16 Using the granular copper powder paste used in Example 14 and having the composition shown in Table 2, an aqueous coating composition was prepared in the same manner as in Example 1. The results of performance evaluation are shown in Table 2.

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

[Table 6] Note 1) The value is for orthophosphoric acid equivalent metal pigment 2) ○: No abnormality

Comparative Example 1 27.7 parts by weight of Alpaste 1700NL, 30 parts by weight of butyl cellosolve and 35 parts by weight of Cymel 303 were mixed and stirred until the aluminum pigment was homogeneously dispersed. Next, to this mixture, the corrosion inhibitor P-A 186 obtained in Production Example 1 was added.
Add 3 parts by weight of dimethylethanolamine and 1 part by weight, and
Stir for hours. Next, 30 parts by weight of the aqueous acrylic resin solution for aqueous paint (A-2) obtained in Production Example 11 was added to the above mixture and stirred for 1 hour. Next, 330 parts by weight of the acrylic resin dispersion (A-1) for water-based paint obtained in Production Example 10, 298.3 parts by weight of deionized water, and 60 parts by weight of butyl cellosolve were added, and the mixture was further stirred for 1 hour. Thus, an aqueous coating composition having a metal pigment / resin weight ratio of 10/100 and a heating residue of 27.5% by weight was obtained. Table 3 shows the coating composition, coating characteristics, and performance evaluation results.

Comparative Examples 2 to 8 Aqueous coating compositions having the compositions shown in Table 3 were prepared in the same manner as in Comparative Example 1. The results of performance evaluation are shown in Table 3.

Comparative Example 9 (1) Production of Corrosion Inhibitor P-J A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser and a Dean Stark separator was placed in a reaction vessel equipped with a styrene unit / number of allyl alcohol having a number average molecular weight of 1600. Ratio 2.32 /
1 copolymer 234.7 parts by weight, p-tert-amylphenol 72.2 parts by weight, xylene 350 parts by weight were charged,
The mixture was heated and stirred at 85 to 90 ° C until the solid components were dissolved.
Next, add 43.1 parts by weight of 100% phosphoric acid, and add 140 ° C.
The temperature was raised to. The reaction was carried out at this temperature for 3 hours to obtain a phosphoric acid esterified product having a resin acid value of 100 mgKOH / g. Next, xylene was removed from this reaction product under reduced pressure, then 520 parts by weight of butyl cellosolve was added, and the mixture was stirred until it became homogeneous, then cooled to 70 ° C., and 4 parts by weight of dimethylethanolamine was added. , The reaction was completed.
In this way, the resin acid value is 100 mgKOH / g and the heating residue is 4
0% by weight of corrosion protection PJ was obtained. (2) Preparation of Aqueous Coating Composition A coating composition was prepared in the same manner as in Comparative Example 1 with the formulations shown in Table 3. The results of performance evaluation are shown in Table 3.

Comparative Examples 10 and 11 Using the corrosion inhibitor PJ prepared in Comparative Example 9, a coating composition was prepared in the same manner as in Comparative Example 1 with the composition shown in Table 3.
The results of performance evaluation are shown in Table 3.

[0038]

[Table 7]

[0039]

[Table 8]

[0040]

[Table 9]

[0041]

[Table 10] Note 1) The value is for orthophosphoric acid equivalent metal pigment. 2) Good: Good, bad

In Examples 1 to 16 according to the method of the present invention, the effect of preventing corrosion of metal pigments, the storage stability of the aqueous coating composition, and the adhesion, water resistance and chemical resistance of the obtained coating film are excellent. .. On the other hand, in Comparative Example 1, the amount of the corrosion inhibitor with respect to the metal pigment exceeds 10% by weight, so that the storage stability and the water resistance are inferior, and in Comparative Example 2, the corrosion inhibitor is not blended, so that corrosion Inferior in prevention effect. In addition, Comparative Example 3
Nos. 8 to 8 are inadequate for the purpose of the present invention, because the acid value or hydroxyl value of the corrosion inhibitor and the number average molecular weight are out of the range of the present invention, and the respective performance evaluation results are inferior.
Comparative Examples 9 to 11 are the methods described in Japanese Examined Patent Publication No. 2-46624, but it is difficult to achieve both the corrosion prevention effect and the performance when a coating film is formed.

[0043]

EFFECT OF THE INVENTION The water-based coating composition of the present invention prevents corrosion of metal pigments, has excellent storage stability and adhesiveness, and has good water resistance and chemical resistance. It is preferably used as a base coat in the two-coat, one-bake coating film forming method used in.

Claims (1)

[Claims] (1) A water-based resin, (B) a curing agent, and (C)
(D) an ethylenic monomer containing at least one acidic hydroxyl group bonded to a phosphorus atom in the molecule and (b) a hydroxyl group as a corrosion inhibitor for the metallic pigment. Acid value having at least one acidic hydroxyl group bonded to a phosphorus atom and / or a salt thereof, which comprises a copolymer obtained from the ethylenic monomer (c) and another ethylenic monomer copolymerizable therewith. 30-150 mgKOH / g, hydroxyl value 30-150 mgKOH / g and number average molecular weight 3000-1
Containing 5,000 phosphates,
The content of the phosphoric acid ester is 0.2 to 10% by weight in terms of orthophosphoric acid with respect to the metal pigment, an aqueous coating composition.