JP2811773B2 - Aqueous coating composition and coating method using the same - Google Patents

Description

The present invention relates to a novel and useful aqueous coating composition, and a novel and useful coating method using the aqueous coating composition. More specifically, the present invention provides an aqueous dispersion of a specific copolymer obtained by using a reaction product of a hydroxyl group-containing cellulose derivative and (meth) acrylic acid, and a cross-linking component and a pigment thereof as essential components. Aqueous coating compositions, especially having excellent coating appearance and weather resistance,
The present invention relates to an aqueous coating composition containing a metallic pigment, and a two-coat one-bake coating method using the aqueous coating composition as a composition for a top coat.

[Conventional technology]

A method of improving the fluidity of such a coating composition by blending minute crosslinked polymer resin particles insoluble in a solvent into the coating composition is already well known.

In particular, JP-A-56-157358 discloses a coating having excellent metallic luster by blending specific fine crosslinked polymer resin particles in an aqueous coating and controlling the orientation of a metallic pigment. A method of providing is disclosed.

However, as long as such a method of blending small cross-linkable polymer resin particles insoluble in the solvent is followed, the fusion between the resin particles during the evaporation of the solvent is inevitably reduced. It has been extremely difficult to stably produce a good metallic glossy coating film having such excellent smoothness.

On the other hand, solvent-type metallic paints are also disclosed in
As disclosed in Japanese Patent Publication No. 144374, by blending cellulose acetate butyrate (hereinafter abbreviated as CAB) with a metallic base paint, an excellent metallic coating film having good appearance and performance can be obtained. It is known.

However, hitherto, no effective method for stably converting the polymer containing CAB to aqueous solution has been found.

For example, JP-A-51-28188 discloses a method in which a polymer containing a cellulose derivative of this type is dispersed in water using a large amount of a special emulsifier.

[Problems to be solved by the invention]

However, the aqueous dispersion obtained by such a method has a poor dispersion stabilizer, and is easily aggregated or separated at the time of blending or storage, and a coating film obtained from such an aqueous dispersion is also used. Compared to a coating from a polymer solution containing a solvent-type cellulose derivative, gloss,
There are problems such as remarkably inferior in terms of durability and mechanical strength.

However, the present inventors, in view of the above-described various disadvantages or problems in the prior art, that is, in view of the existence of unsolved problems, in particular, good dispersion stability, and without disturbance of the orientation of the metallic pigment, Accordingly, the present inventors have sought to find an extremely useful aqueous coating composition capable of providing a coating film having excellent metallic luster, and a coating method using the aqueous coating composition, and have enthusiastically started research.

Accordingly, the problem to be solved by the present invention is to provide a new type of water-based paint suitable for use as a base coat composition, which is a metallic base paint. It is also to provide a new metallic coating method used.

[Means for solving the problem]

Accordingly, the present inventors have conducted intensive studies aiming at the problems to be solved as described above, and as a result, obtained by using a reaction product of a hydroxyl group-containing cellulose derivative, particularly, CAB and (meth) acrylic anhydride. The present invention has been completed by finding an aqueous dispersion of a specific copolymer to be obtained and an aqueous coating composition containing a crosslinking component and a pigment thereof as essential components.

That is, the present invention, in part, as an essential component,
Aqueous dispersion of a copolymer of a vinyl group-containing reactant obtained by reacting a hydroxyl group-containing cellulose derivative with (meth) acrylic anhydride and a polymerizable vinyl monomer having a carboxyl group-containing vinyl monomer as an essential component (A ) And a crosslinking component (B) capable of reacting with the copolymer in the aqueous dispersion;
In particular, the present invention aims to provide a very useful aqueous coating composition comprising a pigment (C), which has extremely good dispersion stability and gives a coating film having excellent metallic luster. Finally, the use of such aqueous coating compositions as basecoat compositions, in particular as metallic basecoats, provides new and useful metallic coatings, which can give, inter alia, coatings with excellent metallic luster. It is intended to provide a painting method.

Here, first, the aqueous coating composition used in the method of the present invention can be prepared, for example, by the following method.

That is, 90.00 to 99.95% by weight of a hydroxyl group-containing cellulose derivative and 0.05 to 10.00% by weight of (meth) acrylic anhydride in an inert organic solvent are reacted in an inert organic solvent to obtain 5 to 95% by weight of a vinyl group-containing reactant. Parts and 95 to 5 parts by weight of a polymerizable vinyl monomer containing at least 2% by weight of a carboxyl group-containing vinyl monomer in a copolymerization reaction in the presence of a polymerization initiator to obtain a carboxyl group-containing modified copolymer. A first step of preparing
After neutralizing at least a part of the carboxyl groups present in such a modified copolymer with a basic compound, the neutralized product is dispersed in water. Is set to be 5 or more, and further, with respect to the aqueous dispersion (A) of the carboxyl group-containing modified copolymer thus obtained,
A crosslinking component (B) capable of reacting with the component (A) and a pigment (C)
And an aqueous coating composition of the present invention can be obtained through the third step of mixing the above, but of course, the present invention is not limited thereto.

As the above-mentioned hydroxyl group-containing cellulose derivative, the surface of a coating film formed by coating and drying an aqueous coating resin composition obtained from cellulose as a raw material on a substrate or a substrate does not exhibit tackiness, and It is desirable to use a material capable of giving a coating film having excellent properties and oil resistance.

As typical examples of such hydroxyl group-containing cellulose derivatives, only ester-modified hydroxyl group-containing cellulose derivatives and ether-modified hydroxyl group-containing cellulose derivatives are mentioned.

And specific examples of the ester-modified hydroxyl group-containing cellulose derivative include nitrocellulose, CAB, cellulose acetate propionate, cellulose acetate phthalate, acetyl cellulose, cellulose propionate, cellulose butyrate, cellulose phosphate or cellulose sulfate, and the like. Specific examples of the ether-modified hydroxyl-containing cellulose derivative include methylcellulose, ethylcellulose, butylcellulose, benzylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, oxyethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose.

Among the hydroxyl group-containing cellulose derivatives, it is desirable to use CAB in a form obtained by further subjecting a partially acetylated product of cellulose to butyl esterification, that is, ester modification.

Further, the number average molecular weight of the hydroxyl group-containing cellulose derivative is preferably in the range of 3,000 to 300,000, preferably
A range of 5,000 to 150,000 is appropriate.

Further, the content of hydroxyl groups in the hydroxyl group-containing cellulose derivative is suitably 0.4% by weight or more. When the amount is less than 0.4% by weight, the number of (meth) acryloyl (oxy) groups that can be introduced into the cellulose derivative is reduced, so that the grafting ratio is reduced, and, consequently, the vinyl group-containing modified polymer, which is also called a carboxyl group-containing modified polymer The reaction product (copolymer) itself is not preferable because it tends to be difficult to emulsify.

Only typical representative examples of commercially available hydroxyl group-containing cellulose derivatives include, for example, CAB series, CAP series, and CA series manufactured by Eastman Kodak Company, USA.

The vinyl group-containing reactant as the copolymer is prepared by mixing the hydroxyl group-containing cellulose derivative and (meth) acrylic anhydride in an inert organic solvent at a temperature of 50 to 120 ° C for 10 minutes to 8 minutes. The reaction is carried out by allowing the reaction to take place over a period of time. The reaction proceeds in the absence of a catalyst, but is further promoted by the presence of an esterification catalyst.

As described above, it is difficult to introduce a (meth) acryloyl (oxy) group into a hydroxyl group-containing cellulose derivative in the absence of a catalyst by a normal method, and it is difficult to use a reactive (meth) acrylic acid having good reactivity. This is only possible.

The conversion of the esterification reaction can be measured using an acid value or a Fourier transform infrared spectrophotometer (FT-IR).

Esterification catalysts include amines, alkali metal hydroxides or mineral acids. Preferred half esterification catalysts include trialkylamines such as trimethylamine, triethylamine, and tripropylamine;
Alkyl morpholine; triethylenediamine, N, N'-
Dimethylpiperazine, hexamethylenetetramine, pyridine, pyrazine, quinoline, benzyldimethylamine,
α-methylbenzyldimethylamine, N-alkylimidazoline, triphenylphosphine, tricyclohexylphosphine, and the like.

The use ratio of the hydroxyl group-containing cellulose derivative and acrylic acid anhydride and / or methacrylic anhydride is 90: 1 by weight.
The range of 0 to 99.95: 0.05 is preferable, and the range of 95: 5 to 99.9: 0.1 is particularly preferable. If the use ratio of acrylic acid anhydride and / or methacrylic anhydride is less than 0.05% by weight, the dispersion stability of the carboxyl group-containing modified polymer in the aqueous medium tends to be inferior, which is not preferable. When the use ratio of acrylic acid anhydride or methacrylic anhydride is more than 10% by weight, the carboxyl group-containing modified polymer tends to have a high molecular weight during polymerization, which is not preferable.

Aqueous dispersion (A) of the copolymer used in the present invention
In order to obtain the copolymer in, first, as the inert organic solvent used in preparing the vinyl group-containing reactant, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl propyl ketone or ethyl butyl ketone are used. Solvents are preferred.

The polymerizable vinyl monomer used for the copolymerization reaction with the vinyl group-containing reactant is a polymerizable vinyl monomer containing at least 2% by weight of a carboxyl-containing vinyl monomer. If the amount of the carboxyl group-containing vinyl monomer is less than 2% by weight, the dispersion stability of the resin in the aqueous medium tends to deteriorate, which is not preferable.

As the carboxyl group-containing vinyl monomer, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid and the like are particularly typical.

If only typical polymerizable vinyl monomers other than the carboxyl group-containing vinyl monomer are exemplified, styrene monomers such as styrene, vinyltoluene, 2-methylstyrene, t-butylstyrene or chlorostyrene; acrylic acid Methyl, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, acrylic acid Acrylates such as decyl and dodecyl acrylate; methyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, n-o-methacrylate Methacrylates such as tyl, 2-ethylhexyl methacrylate, decyl methacrylate, dodecyl methacrylate; monomers containing hydroxyl groups such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate; polyethylene glycol Glycidyl group-containing monomers such as glycidyl acrylate and glycidyl methacrylate; (poly) alkylene glycols such as glyceryl acrylate and glycidyl methacrylate;
-N-substituted (meth) acrylic monomers such as methylol (meth) acrylamide and N-butoxymethyl (meth) acrylamide.

It is particularly desirable that the vinyl group-containing reactant is prepared by solution polymerization of the vinyl group-containing reactant and the polymerizable vinyl monomer.

The weight ratio of the vinyl group-containing reactant to the polymerizable vinyl monomer is preferably in the range of 5:95 to 95: 5. When the usage ratio of the vinyl group-containing reactant is less than 5% by weight,
It is not preferable because various properties of the hydroxyl group-containing cellulose derivative may not be utilized. When the usage ratio of the vinyl group-containing reactant is more than 95% by weight, the carboxyl group-containing modified polymer tends to be difficult to self-emulsify, which is not preferable.

Particularly, when the proportion of the polymerizable vinyl monomer used is small, the proportion of the cellulose derivative in the carboxyl group-containing modified polymer is high, so that the cellulose derivative is added to other aqueous acrylic resins, polyester resins, and urethane resins. Features that can be derived. In this case, the method of adding the coating composition of the present invention to the aqueous resin, or at the stage of a carboxyl group-containing modified polymer,
After mixing with the above aqueous resin, a method of dispersing in water can be used.

Examples of the polymerization initiator used in the copolymerization reaction between the vinyl group-containing reactant and the polymerizable vinyl monomer include, for example, azobisisobutyronitrile, benzoyl peroxide and t-butylperoxy-2-ethylhexanate. Radical polymerization initiator.

Examples of the organic solvent used in the copolymerization reaction include alcohols such as methanol, ethanol, propanol and butanol; ether alcohols such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, methyl carbitol and ethyl carbitol; methyl ethyl ketone; Examples thereof include ketones such as diisobutyl ketone and aromatic hydrocarbons such as toluene.

The aqueous coating composition of the present invention is obtained by adding a basic compound in an amount such that the pH of the dispersion becomes 5 or more to the carboxyl group-containing modified copolymer obtained by the polymerization reaction, and converting the modified copolymer into an aqueous medium. Obtained by dispersing in.

The basic compound used here is preferably ammonia or a volatile amine, and the inorganic base is not preferable because it tends to remain in the coating film and deteriorate water resistance.

Examples of the amine include trimethylamine,
Alkylamines such as triethylamine and butylamine; dimethylaminoethanol, diethanolamine,
Alcoholamines such as aminomethylpropanol; or morpholine can be used. Further, polyamines such as ethylenediamine and diethylenetriamine can also be used.

In the present invention, the aqueous medium means water alone or a mixture with a hydrophilic organic solvent in which at least 10% by weight is water. Examples of the hydrophilic organic solvent include alkyl alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol and isobutanol; methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, Glycol ethers such as hexyl cellosolve, methyl carbitol and ethyl carbitol; or glycol ether esters such as methyl cellosolve acetate and ethyl cellosolve acetate, and further, dioxane, dimethylformamide, diacetone alcohol, tetrahydrofuran and the like are used. it can.

The aqueous coating composition used in the present invention has very good dispersion stability, and when it is necessary to further reduce the contained organic solvent, acetone, a solvent having a low boiling point such as methyl ethyl ketone, or butanol or butyl cellosolve. If a solvent that azeotropes with water is used as a reaction solvent or a dispersing agent, after dispersion in an aqueous medium, by distillation at normal pressure or reduced pressure, a stable and easy, low organic solvent Containing coating compositions can be obtained.

In the present invention, examples of the cross-linking component (B) that reacts with the component (A) include a water-soluble or water-dispersible melamine resin. However, among them, only Nicaraq MW-30 (product of Nippon Carbide Industry Co., Ltd.) and "Sumimar M-100" are mentioned.
Hexamethoxymethyl melamine or "Sumimar M-40W" or "Sumimar M-30W" [products of Sumitomo Chemical Co., Ltd.]
And a methoxymethylmelamine resin containing a free methylol group. Further, a hydrophobic melamine resin having a solvent dilution ratio of 20 or less in a water / methanol mixed solvent (weight ratio 35/65) may be used as a water-soluble resin or a melamine resin which is water-dispersed with a dispersant, and is particularly preferable. Is
Hexamethoxymethyl melamine resin.

In the present invention, examples of the pigment (C) include metallic pigments and / or color pigments that are usually used in the field of paints. Among them, if only the typical ones are listed as such metallic pigments,
Examples include aluminum flake and copper bronze flake. On the other hand, only the above-mentioned typical coloring pigments are inorganic pigments such as titanium dioxide, iron oxide, chromium oxide, lead chromate or carbon black; or phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyrimidine. Organic pigments such as yellow, flavanthrone yellow, isoindoline yellow, indanthrone blue or quinacridone violet can be mentioned. In the present invention, at least one of the above-mentioned metallic pigments and coloring pigments is used, but an extender such as talc or kaolin may be used in combination.

Of these various pigments, the coloring pigment or extender is preferably added at the time of blending the crosslinking component (B).
The metallic pigment is preferably added at the time of blending the components (A) and (B).

Next, when the method of the present invention is carried out, the specific mixing ratio of each component in the aqueous coating composition is suitably set as follows. That is, (A)
With respect to 100 parts by weight of the resin solid content of the aqueous dispersion of the copolymer as a component, the solid content of the resin for a crosslinking agent as the component (B) is converted to about 8 to 70 parts by weight, preferably 10 to 60 parts by weight. It is appropriate to mix in a range of about parts by weight. If the amount of the component (B) is less than 8 parts by weight, the curing reaction by heating becomes insufficient, and the moisture resistance and solvent resistance of the coating film tend to decrease. If the amount is more than 70 parts by weight, the chipping resistance and the weather resistance are lowered, and phenomena such as sagging and unevenness occur when the clear topcoat is applied repeatedly, which is not preferable. The pigment as the component (C) may be appropriately added to the composition according to a desired color or the like, and based on 100 parts by weight of the resin solid content of the total of the components (A) and (B). Usually, it is appropriate to mix it in the range of about 1 to 230 parts by weight. The aqueous coating composition of the present invention can be prepared, for example, as follows. That is, the aqueous dispersion of the copolymer prepared as described above and a crosslinking agent, and a metallic pigment when used in metallic coating, according to a conventional method, deionized water, and
If necessary, add additives such as thickeners and defoamers,
Solid content of about 10 to 40% by weight and viscosity of 200 to 5000 cps / 6
It is adjusted to about rpm (B-type viscometer) to obtain an aqueous coating composition as an object of the present invention. The aqueous coating composition obtained in the method of the present invention is extremely suitable as a base coat composition when applied in a two-coat one-bake system. For example, the composition is applied to an object to be coated by spray coating or the like so as to have a dry film thickness of about 10 to 50 μm, and the volatile component becomes about 25% by weight or less by air drying or hot air drying. Then, a clear top coat is applied again by electrostatic spray coating or the like so as to have a dry film thickness of about 15 to 70 μm. Then, after performing normal setting, baking is performed at about 120 to 160 ° C. for about 15 to 30 minutes to obtain a cured coating film. As the clear top coat used here, conventionally known ones can be used. Among them, especially typical ones are aminoalkyd resin, acrylic resin, aminoacrylic resin, amino oil-free aluminum kid resin, silicone polyester resin, fluorine resin or urethane resin type organic solvent dilution type paint. No. As the clear top coat, a high solid type paint that uses a small amount of an organic solvent is desirable from the viewpoint of environmental issues and resource saving, and a powder paint can also be used.

〔The invention's effect〕

The following effects can be obtained by using the aqueous coating composition of the present invention. That is, (1) the aqueous dispersion (A) of the copolymer used in the present invention is obtained by using a cellulose derivative having different compatibility and a carboxyl group-containing vinyl monomer, and these are chemically synthesized. From the place where they are bonded together, they do not cause phase separation, and since they have carboxyl groups, they have self-emulsifying properties in aqueous media and are therefore stable in dispersion. Very good properties.

(2) Since the solvent resistance of the cellulose derivative is good,
When this aqueous coating composition is used as a metallic basecoat composition, it is not baked, and even if a thermosetting resin-based clear topcoat is applied in an uncured state, the metallic pigment contained in the basecoat by the solvent of the topcoat is used. Thus, a coating film having excellent metallic luster can be easily obtained without disturbing the orientation. (3) Since the amount of organic solvent used can be greatly reduced, it is excellent also from the viewpoint of environmental problems and resource saving.

Therefore, the aqueous coating composition of the present invention is extremely suitable as a base coat composition for coating an outer plate such as an automobile, a two-wheeled vehicle, or an electric product, in which aesthetic appearance is important, in a two-coat one-bake method. In particular, decorative paint such as metallic paint is extremely workable, and
Can be done with a satisfactory finish.

〔Example〕

Next, the present invention by reference examples, examples and application examples,
This will be described more specifically. In the following, all parts and percentages are by weight unless otherwise specified.

Reference Example 1 [Preparation Example of Aqueous Dispersion (A) of Copolymer] First, "CA" was placed in a four-necked flask purged with nitrogen gas.
B-553 "(cellulose acetate butyrate manufactured by Eastman Kodak Company, USA; hydroxyl content in one molecule = 4.3%) and 25 parts of methyl ethyl ketone
0 parts and completely dissolved, and further, 0.5 part of methacrylic anhydride was also charged and stirred at 80 ° C.
, And kept at the same temperature for 5 hours to obtain a vinyl group-containing reactant.

Then, the reaction mixture containing the vinyl group-containing reactant is
To 200 parts, 100 parts of methyl ethyl ketone, 100 parts of n-butanol, 10 parts of methacrylic acid, 1 part of methyl methacrylate
60 parts, 70 parts of n-butyl acrylate, and 6 parts of "perbutyl O" (a radical polymerization initiator of tert-butyl peroxy-2-ethylhexanoate manufactured by NOF Corporation) were uniformly mixed. After mixing, 20
0 parts were charged into a four-necked flask purged with nitrogen gas, heated to 80 ° C., and while maintaining the same temperature, the remaining mixture was added dropwise over 4 hours, and further maintained at the same temperature for 4 hours. Meanwhile, the mixture was kept under stirring to obtain a modified copolymer as a carboxyl group-containing modified polymer.

Thereafter, 7 parts of a 28% aqueous ammonia solution and 60 parts of butyl cellosolve were added to the reaction solution containing the modified copolymer obtained in the first step as described above, and the mixture was mixed uniformly. Was dropped over 30 minutes to obtain a milky-white, aqueous dispersion of the target copolymer (A) having a nonvolatile content (NV) of 24.9% and a pH of 7.5.
Hereinafter, this is referred to as aqueous dispersion (A-1).

The viscosity of this product did not change at all even after being left at room temperature for one week.

In addition, the product was subjected to distillation under reduced pressure to remove the organic solvent therefrom to remove methyl ethyl ketone, n-butanol and some butyl cellosolve, whereby a good aqueous dispersion having an NV of 40.1% was obtained.

Reference Example 2 (same as above) For 100 parts of the reaction mixture containing the vinyl group-containing reactant, 150 parts of methyl ethyl ketone and 10 parts of methacrylic acid were used.
Parts, 130 parts of methyl methacrylate, 53 parts of styrene, 150 parts of n-butyl acrylate and "perbutyl O"
The modified carboxyl group-containing copolymer was obtained in the same manner as in Reference Example 1, except that 6 parts were changed so as to be uniformly mixed.

Next, 7 parts of 28% ammonia water was added to the reaction solution containing the modified copolymer, and the mixture was uniformly mixed. Then, 550 parts of ion-exchanged water was dropped over 2 hours, and NV was 31.8%.
In addition, an opalescent aqueous dispersion of the target copolymer having a pH of 7.8 was obtained.

The aqueous dispersion did not show any change after standing at room temperature for one month.

Further, the organic solvent in this aqueous dispersion was distilled off under reduced pressure to remove methyl ethyl ketone. As a result, a good final copolymer aqueous dispersion having an NV of 41.7% was obtained.
Hereinafter, this is referred to as aqueous dispersion (A-2).

Reference Example 3 (same as above) The composition of the substance to be uniformly mixed with the reaction mixture containing the vinyl group-containing reactant was determined by adding 150 parts of methyl ethyl ketone.
Parts, 10 parts of methacrylic acid, 30 parts of methyl methacrylate,
20 parts of n-butyl acrylate and "perbutyl O"
A modified carboxyl group-containing copolymer was obtained in the same manner as in Reference Example 1 except that the amount was changed to 20 parts.

Next, 7 parts of 28% aqueous ammonia was added to the reaction solution containing the modified copolymer and mixed uniformly, and then 550 parts of ion-exchanged water was added dropwise over 2 hours to obtain NV of 31.8%.
And a milky-white aqueous dispersion of the target copolymer having a pH of 7.8 was obtained.

Even after the aqueous dispersion was left at room temperature for one month, no change in viscosity or the like was observed.

Thereafter, when the organic solvent in the aqueous dispersion was distilled off under reduced pressure, methyl ethyl ketone was removed, and NV was reduced to 4%.
1.7% of the desired aqueous dispersion (A) of the target copolymer in the final form was obtained. Hereinafter, the aqueous dispersion (A-
Abbreviated as 3).

Reference Example 4 (Preparation Example of Control Aqueous Copolymer Dispersion) Instead of using a reaction mixture containing a vinyl group-containing reactant, the treatment with methacrylic anhydride was completely absent, that is, "CAB-553" 125 parts of methyl ethyl ketone
To 100 parts of the solution completely dissolved in parts, directly add 150 parts of methyl ethyl ketone, 10 parts of methacrylic acid, 130 parts of methyl methacrylate, 53 parts of styrene, acrylic acid-n
When 150 parts of -butyl and 6 parts of "perbutyl O" were added and the reaction was carried out in the same manner as in Reference Example 2, no aqueous dispersion of the objective copolymer of the present invention was obtained, and the vinyl copolymer was not obtained. It only existed as a mere mixture of the aqueous dispersion of "CAB-553" and this "CAB-553", and did not become aqueous with ion-exchanged water, and separated into two layers.

Reference Example 5 [Preparation Example of Crosslinking Component (B)] In a two-necked flask equipped with a thermometer, a stirrer, a reflux condenser and a produced water separator, 126 parts of melamine, 80 parts
% Paraform, 480 parts of methanol and 57 parts of deionized water.
Reflux dehydration over time.

After the completion of the reaction, methanol, water and formaldehyde were distilled off under reduced pressure until a predetermined non-volatile concentration was reached, followed by cooling to obtain a methoxymethylated melamine resin having an NV of 80.0%. Hereinafter, this is abbreviated as crosslinking agent (B-1).

Reference Example 6 (same as above) In a reaction vessel similar to Reference Example 5, 126 parts of melamine, 80 parts
225 parts of paraformaldehyde and 592 parts of n-butanol were prepared, and pH was adjusted with a 10% aqueous sodium hydroxide solution.
Was adjusted within the range of 9.5 to 10.0, and the reaction was carried out by maintaining the temperature at 80 ° C. for 1 hour.

Then, 888 parts of n-butanol was added thereto, and 5%
Neutralize the pH with a sulfuric acid aqueous solution to 7-75 and at 60-70 ° C, n
-Butanol was concentrated under reduced pressure to give a butoxymethylated melamine resin.

This was a resin solution having an NV of 75% and a dilution ratio of 5 with a mixed solvent of water / methanol = 35/65 (weight ratio).

Then, 10% of this butoxymethylated melamine resin solution
0 parts was transferred to a reaction vessel equipped with a stirrer, and was previously polymerized in butyl cellosolve at 115 ° C., methyl methacrylate / n-butyl acrylate / methacrylic acid = 50/42/8 ( Weight ratio), acid value is 52, 25 ℃
In a solution of an acrylic copolymer resin having a Gardner viscosity of N ₂ and an NV of 40%, an equivalent amount of dimethylaminoethanol was added, and 20 parts of a resin solution prepared by adding an aqueous solution was added.
46 parts of deionized water is gradually added while stirring with a disperser of 000 to 1,500 rpm, and then stirring is continued for another 1 hour to disperse water butoxymethyl with 50% NV. Melamine resin was obtained. Hereinafter, this is abbreviated as a crosslinking agent (B-2).

Reference Example 7 (Preparation Example of Aluminum Pigment Concentrate) In a stirring and mixing vessel, 25 parts of an aluminum paste having a metal content of 60% and 25 parts of butyl cellosolve were mixed, and stirred for 1 hour. To obtain a concentrated aluminum pigment solution. Hereinafter, this is abbreviated as pigment (C-1).

Reference Example 8 (Preparation example of clear topcoat) 250 parts of methyl acrylate, 250 parts of n-butyl methacrylate, 36 parts of n-butyl acrylate, 120 parts of 2-hydroxyethyl acrylate and methacryl Polymerization was performed in xylene using 16 parts of the acid and 15 parts of “perbutyl O” in a conventional manner to obtain an acrylic resin solution having an NV of 55%.

This had a hydroxyl value of 57 and an acid value of 14.

Next, this acrylic resin solution and “Super Beckamine L-127-75B” (melamine resin manufactured by Dainippon Ink and Chemicals, Inc .: NV = 75%) are 75/25 (solid content weight ratio). And then "Swazol # 1500"
[Aromatic hydrocarbon solvent manufactured by Maruzen Oil Co., Ltd.] was used to obtain a target paint having a viscosity of 25 according to Ford Cup No. 4 at 20 ° C. Hereinafter, this is abbreviated as paint (K-1).

Reference Example 9 (same as above) Instead of “Super Beckamine L-127-75B”,
"Barnock DN-950" [Dainippon Ink and Chemicals, Inc.
And trimethylolpropane adduct of hexamethylene diisocyanate), and mixed so that -OH / -NCO = 1/1 (equivalent ratio).
0 "and the viscosity at 20 ° C according to Ford Cup No. 4 is 2
It was adjusted to 5 seconds to obtain the target paint. Hereinafter, this is abbreviated as paint (K-2).

Example 1 A stirring and mixing vessel was charged with 498.7 parts of the aqueous dispersion (A-1).
125.0 parts of the cross-linking agent (B-1), 50.0 parts of the pigment (C-1) and 376.3 parts of deionized water were sequentially added with stirring, and mixed for another hour with stirring.

Next, 3.5 μl of “Acryzol ASE-60” (a thickener manufactured by Rohm and Haas Company, USA) was added to the mixture.
Further, 0.3 part of dimethylaminoethanol was further added to obtain an aqueous coating composition for a metallic base coat having an NV of 30.2% and a Brookfield viscosity (Rotor No. 3, 60 rpm) of 350 cps.

Examples 2 to 6 and Comparative Examples 1 and 2 Various aqueous coating compositions for metallic base coats were obtained in the same manner as in Example 1 except that the composition ratios were changed as shown in Table 1.

The property values for each aqueous coating composition are as shown in the table.

Application Examples 1 to 7 The coating compositions for metallic base coats obtained in Examples 1 to 6 and the clear top coats obtained in Reference Examples 8 and 9 were prepared as shown in Table 2. Coating was performed by a combination of two coats and one bake.

The object to be coated used at this time was subjected to the following pretreatment.

That is, a mild steel sheet treated with "Bonderite # 3030" (a zinc phosphate treating agent manufactured by Nippon Parkerizing Co., Ltd.) is electrodeposited with an epoxy resin-based cationic electrodeposition paint, and then an amino polyester resin A material coated with a system intermediate coating was used as an object to be coated.

First, the coating composition for metallic base coat, 25
° C and in a coating atmosphere where the relative humidity is 60%,
Each of them was spray-painted twice using a spray gun to form a metallic base coating film having a dry film thickness of 30 microns.

A setting for 2 minutes was performed between the two coatings.

At that time, the air pressure of the spray gun was 5 kg / cm ² ,
The flow rate of the paint was 400 ml / min., And the distance between the substrate and the spray gun was 35 cm.

The object to be coated was held such that the application surface on the object to be coated was always vertical.

After the two coatings, the coating was left at room temperature for 3 minutes, then kept at a temperature of 80 ° C. for 10 minutes and air-dried.

Then, after cooling to room temperature, a clear top coat is applied with a spray gun so that the dry film thickness becomes 40 microns, and after setting for 5 minutes, 120 minutes.
Baking was performed at a temperature of about 140 ° C. for 30 minutes.

Various properties were evaluated for each of the thus obtained cured coating films. The results are collectively shown in the same table.

 The capacity of the evaluation judgment is as follows.

Metallic feeling ：: Uniform and uniform, no unevenness, extremely excellent in glittering metallic feeling ：: Excellent △: Slightly poor ×: Poor acid resistance: Spot 5 drops of 10% sulfuric acid aqueous solution on each coated plate, 50 After holding at 90 ° C. for 90 minutes, the coating film was visually evaluated for blistering, discoloration, and the like.

Interlayer adhesion: The coated plate was immersed in warm water of 40 ° C. for 240 hours, pulled up, cut 30 minutes later, and subjected to a peeling test using an adhesive tape.

Moisture resistance test: Each coated plate was placed in a blister box at 50 ° C. and 100% relative humidity for 100 hours, and the presence or absence of blisters was examined.

Storage property of coating composition for metallic base coat: The presence or absence of a change in viscosity when stored at a temperature of 40 for 20 days was examined.

Claims (4)

(57) [Claims] 1. A reaction between a hydroxyl group-containing cellulose derivative and acrylic acid and / or methacrylic anhydride to obtain a vinyl group-containing reactant, and a polymerizable vinyl monomer having a carboxyl group-containing vinyl monomer as an essential component. An aqueous coating composition comprising an aqueous dispersion of a copolymer (A), a crosslinking component (B) that reacts with the copolymer in the aqueous dispersion, and a pigment (C). 2. The method according to claim 2, wherein the hydroxyl-containing cellulose derivative is 0.4%.
The aqueous coating composition according to claim 1, wherein the aqueous coating composition has a number-average molecular weight of 3,000 to 300,000, containing not less than% by weight of hydroxyl groups. 3. A base coat composition comprising a vinyl group-containing reactant obtained by reacting a hydroxyl group-containing cellulose derivative with acrylic acid and / or methacrylic anhydride, and a carboxyl group-containing vinyl monomer as essential components. Aqueous coating composition comprising an aqueous dispersion (A) of a copolymer with a polymerizable vinyl monomer, a crosslinking component (B) that reacts with the copolymer in the aqueous dispersion, and a pigment (C) A method of applying a two-coat, one-bake method, characterized by using an object. 4. The method according to claim 1, wherein the hydroxyl-containing cellulose derivative comprises 0.4
The method for coating according to claim 3, wherein the coating has a number-average molecular weight of 3,000 to 300,000, containing not less than% by weight of hydroxyl groups.