JPS6154827B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a two-coat, one-bake, aqueous coating composition having improved film-forming properties. In recent years, for the purpose of environmental conservation, it has been desired to use water-based paints that use less organic solvents. However, as understood from various patent publications, literature, etc., water-based paints contain water as their main component, so water evaporates slowly during spray coating and flash-off, and coating defects such as sagging and metal unevenness are likely to occur.
In recent years, so-called water-dispersible paints in which resin is dispersed in water have become mainstream as water-based paints that are less likely to cause these coating defects. has become a typical paint for painting the exterior of automobiles. In the case of this type of water-based paint, as is well known, the paint with a lower neutralization rate of the carboxyl groups in the resin by the base has a stronger tendency to disperse, and during spray painting, the viscosity increases with the evaporation of a small amount of water, resulting in sagging and metal unevenness. Hard to occur. On the other hand, water-based paints have less flexibility in solvent composition,
Another problem was that because the surface tension of water is high, wrinkles tend to form during baking and drying. It has long been known that adding a high boiling point organic solvent to the wrinkle defects will make the wrinkles more difficult to deal with. When added to water-based paints whose main component is water-dispersed synthetic polycarboxylic acid resin, these high-boiling point solvents dissolve and swell the dispersed resin, increasing the viscosity and making it viscous enough to spray. In addition to this, a large amount of water had to be added, and this method ultimately had little effect on the armpits. In order to solve these problems, Japanese Patent Application Laid-open No. 52-006739, which the present inventors previously filed, describes adding high-boiling point ethylene glycols to water-dispersed paints with a neutralization rate of 80% or less. This is a characteristic feature. This aqueous coating composition is extremely effective when there are small fluctuations in booth temperature and humidity and other coating conditions such as discharge amount. However, when the present inventors further investigated the coating workability of these water-based paints, they found that the finish quality easily changes due to changes in coating conditions such as booth temperature and humidity, that is, the control range is narrow. It has also been found that there are points that should be improved, such as the fact that it is often difficult to finish uniformly in the case of complex-shaped objects to be coated. In addition, in recent years, the trend in water-based paints is that water-based paints with extremely strong dispersion tendencies, such as water-dispersible paints with low neutralization rates and water-based slurry paints, have become mainstream in order to deal with sagging defects. However, recent research by the present inventors has shown that in the case of large-scale painting, such as automobile exterior painting, where it is difficult to control air conditioning conditions and other painting conditions, it is possible to It has been found that it is almost impossible to use a paint with a strong dispersion tendency, which is susceptible to changes in film quality, alone. Here, the present inventors proposed a two-coat, one-bake coating method, which has been conventionally used to obtain coatings with excellent metallic properties on automobile exterior panels, etc., in which no pigment is added to the metallic base coating. A painting method that finishes by applying a transparent clear paint,
As a result of conducting various researches to take advantage of the advantages of water-dispersed paints and water-soluble paints, we have found that they are resistant to sagging, easy to manage, and can evenly finish even complex-shaped objects, reducing underarm defects. A strong water-based paint composition has been discovered and proposed here. The two-coat, one-bake water-based coating composition of the present invention has as its main component a water-dispersible synthetic polycarboxylic acid resin with a neutralization rate of 80% or less, and metal powder and metal powder in a weight ratio of 3 to 20% based on the resin. The main components are a water-based paint containing methyl alcohol at a ratio of 3 to 30%, and a water-dispersed neutralized water-soluble resin with a neutralization rate of 80% or more of a water-dispersed synthetic polycarboxylic acid resin. It is characterized by comprising a water-based clear paint containing one or two types of ethylene glycols in a ratio of 3 to 30%. In the present invention, the former water-based base paint refers to a water-dispersed synthetic polycarboxylic acid resin with a neutralization rate of 80% or less, a water-based amino resin as a crosslinked resin, and a weight ratio of the water-dispersed synthetic polycarboxylic acid resin to the water-dispersed synthetic polycarboxylic acid resin. So 3
or 20% of metal powder such as aluminum flakes and, if necessary, inorganic or organic pigments, color separation preventive agents, surface conditioners, etc., are added to the water-dispersed synthetic polycarboxylic acid resin at a weight ratio of 3 to 30%. Refers to a water-based paint dispersed and partially dissolved in water containing methyl alcohol and optionally and preferably a water-soluble organic solvent. The latter water-based clear paint is a water-dispersed synthetic polycarboxylic acid resin with a neutralization rate of 80% or more, a water-dispersed neutralized water-soluble resin, a water-based amino resin as a crosslinked resin, and a water-based amino resin as necessary. Additives such as surface conditioners and ultraviolet absorbers, and if necessary, trace amounts of inorganic and organic pigments to the extent that the water-based clear coating film becomes colored and transparent after drying are added to the water-dispersed neutralized resin. , refers to a water-based paint in which 3 to 30% by weight of one or more ethylene glycols is dissolved or partially dispersed in water, preferably containing a water-soluble organic solvent, if necessary. Water-dispersed synthetic polycarboxylic acid resins with a neutralization rate of 80% or less include (a) acrylic acid, methacrylic acid,
Acrylic monomers such as acrylic esters, methacrylic esters, and their derivatives, and vinyl monomers that can be copolymerized with acrylic monomers such as styrene, vinyl acetate, and vinyl toluene (3% or more, preferably 15% or less in the monomer composition) (having a carboxyl group functional monomer) is dispersed in water using an emulsifier or a water-soluble resin as described below, and then subjected to emulsion copolymerization or dispersion copolymerization.
100, a water-dispersed synthetic polycarboxylic acid resin with a number average molecular weight of 3,000 to 30,000 whose carboxyl group has a neutralization equivalent of 80% or less with a base, or (b) a weight ratio to the emulsion copolymer resin or dispersion copolymer resin A water-dispersible synthetic polycarboxylic acid resin obtained by kneading a water-soluble resin described below with a neutralization rate of 50% or less and a neutralization rate of 80% or less. In addition, the water-dispersed neutralized water-soluble resin with a neutralization rate of 80% or more refers to the water-dispersed synthetic polycarboxylic acid resin obtained in (a) and (b) above. The neutralization equivalent of the carboxyl group with a base is
Refers to a resin that has been neutralized to 80% or more, and the neutralization equivalent is set to 80% or more before kneading the crosslinked resin, pigment, etc., during the process of making it into a paint, or after making it into a paint. You may go. In addition, the water-soluble resin refers to the above-mentioned water-dispersed neutralized water-soluble resin or (i) the acrylic monomer listed in (a) above, optionally a vinyl monomer, and preferably a water-soluble organic solvent (n-propyl alcohol, Solution polymerization in alcohols such as isopropyl alcohol, n-butyl alcohol, and isobutyl alcohol, cellosolves such as ethylene glycol monomethyl, monoethyl, and monobutyl ether, and carbitols such as diethylene glycol monomethyl, monoethyl, and monobutyl ether, etc. Obtained acid value 10-100, number average molecular weight 3000-
Water-soluble resin obtained by neutralizing 30,000 resin with base, or (ii) maleic anhydride, phthalic anhydride,
Acid value obtained by condensation synthesis in the water-soluble organic solvent using a polybasic acid such as trimellitic acid, a polyhydric alcohol such as ethylene glycol, propylene glycol, sorbitol, glycerin, and optionally a fatty acid, petroleum resin, or epoxy resin. Ten~
100, a water-soluble resin obtained by neutralizing a resin with a number average molecular weight of 3,000 to 30,000 with a base. Bases that neutralize the carboxyl group include ammonia or organic amines, and suitable organic amines include primary, secondary, and tertiary aliphatic or alicyclic amines, such as isopropylamine and n-butylamine. , n-amylamine, diethylamine, diisopropylamine, n-dibutylamine, diisobutylamine, triethylamine, n-tributylamine, monoethanolamine, ethylmonoethanolamine, diethylethanolamine,
Cyclohexylamine, morpholine, piperidine, etc. are preferable. In addition, as the aqueous amino resin used as the crosslinked resin, melamine, urea, or a condensate of benzoguanamine and formalin, or etherification of these with methyl alcohol, butyl alcohol, etc., as necessary, is used, and the weight ratio to the base resin is Ten~
It is desirable to mix 40%. Next, the methyl alcohol contained in the aqueous base paint of the present invention may be mixed in at any stage from the time of resin polymerization until it becomes viscous for spraying.
Ethylene glycols to be included in the water-based clear paint include ethylene glycol, diethylene glycol, triethylene glycol, glycerin, and the like. These ethylene glycols may also be mixed in at any stage from resin polymerization to viscosity adjustment for spray use. The aqueous base paint containing the water-dispersible synthetic polycarboxylic acid resin obtained by the present invention as a main component has a low neutralization rate of 80% or less, so it rapidly thickens due to the evaporation of a small amount of volatile components in the paint. , it becomes less sticky. Furthermore, since the aqueous base paint of the present invention contains methyl alcohol, it is even more resistant to sagging.
It has been generally known that adding a low boiling point solvent to water-based paints makes them less likely to sag, but this effect cannot be expected in the case of water-based paints. For example, as shown in Reference Example 3 below,
Even if ethyl acetate is used, instead of improving the sagging properties of the paint, it becomes extremely easy to sag. This is because ethyl acetate dissolves the water-dispersed synthetic polycarboxylic acid resin and thickens it, so in addition to ethyl acetate, a large amount of water, which evaporates slowly, must be added in large quantities, which makes it more likely to sag. However, in the present invention, when methyl alcohol is used as a low boiling point solvent, the viscosity of the water-dispersed synthetic polycarboxylic acid resin can be sufficiently lowered.
For example, acetone and ethanol have some effect, but they are not very effective and are not useful. Furthermore, since the coating composition of the present invention has a high neutralization rate of 80% or more in the water-based clear coating applied to the upper layer, it is less susceptible to fluctuations in coating conditions.
In other words, in the case of a water-based paint whose main component is a water-dispersed synthetic polycarboxylic acid resin, the viscosity behavior changes depending on the neutralization rate, and in the case of a water-dispersed neutralized water-soluble resin with a neutralization rate of 80% or more. , has properties similar to so-called water-soluble resins, so the finish variation of the coating film is small due to changes in booth temperature and booth humidity, and it is possible to uniformly coat objects with complex shapes (Japanese Patent Application Laid-Open No. 52-1979) (See No. 8045). Furthermore, the viscosity of the water-based clear paint is significantly reduced by containing ethylene glycols. Water-dispersed neutralized water-soluble resins with a neutralization rate of 80% or more of water-dispersed synthetic polycarboxylic acid resins are different from so-called water-soluble resins obtained by neutralizing solution polymerized resins, and are similar to ethylene glycols. The viscosity decreases significantly with poor solvents.
Therefore, high boiling point solvents such as ethylene glycols have an effect that cannot be obtained with good high boiling point solvents such as butyl carbitol, that is, a strong effect on armpit defects. When painting with these paint compositions, if the water-based clear paint is applied alone, it tends to sag due to the high neutralization rate, but especially if the base paint that is previously applied is a water-dispersible paint and is made of methanol-like paint. Since it contains a solvent that evaporates quickly, the base paint film obtained by applying it in advance has the effect of attracting the clear paint that is applied later, making it difficult to sag (hanging effect). As described above, the coating composition according to the present invention takes advantage of the viscosity behavior of the water-dispersible synthetic polycarboxylic acid resin and the water-dispersible neutralized water-soluble resin derived therefrom. The present invention will be explained in more detail using the following examples and reference examples. Example 1 (1) Preparation of water-based paint <Preparation of paint> A water-dispersible water-based paint was obtained using the following formulation using a conventional paint preparation method. (1) Water-dispersed synthetic polycarboxylic acid resin liquid 80 parts (2) Water-based amino resin (Sumimar manufactured by Sumitomo Chemical Co., Ltd.)
M100; nonvolatile content 97%) 8 parts (3) Aluminum paste (Toyo Aluminum #1109MA) 6 parts (4) Butyl cellosolve 6 parts (5) Carbon black, etc. 100 parts in trace amount Add dimethylethanolamine to this paint to form carboxyl The neutralization equivalent of the base is 60%, and the weight ratio of methyl alcohol to 100% of the non-volatile content of the paint is
Add 10% and further increase the viscosity of the paint with deionized water.
Adjusted to 40 seconds (food cup #4). Water-dispersed synthetic polycarboxylic acid resin liquid (a) Monomer composition Methacrylic acid 7 2-hydroxyethyl methacrylate 5 Styrene 18 Ethyl acrylate 15 (b) Non-volatile content concentration 44% (c) Organic solvent content Isopropyl alcohol in volatile matter 30% (d) Neutralization rate (dimethylethanolamine) 33% (2) Adjustment of water-based clear paint <Adjustment of paint> (1) Water-dispersed synthetic polycarboxylic acid resin liquid (same as for water-based base paints) 70 parts ( 2) Water-soluble resin liquid 20 parts (3) Water-based amino resin (Sumimar manufactured by Sumitomo Chemical)
M100 (non-volatile content 97%) 9 parts (4) Surface conditioner, ultraviolet absorber, etc. 1 part total 100 parts A water-dispersible water-based clear paint was obtained by the usual method using the above formulation. Dimethylethanolamine was added to this paint to make the neutralization equivalent of carboxyl groups 90%, diethylene glycol was added at a weight ratio of 10% based on 100% non-volatile content, and diluted with deionized water for 40 seconds (Food Cup #4). It was adjusted. (3) Spray coating property evaluation The water-based base paint was sprayed using a reciprocating automatic coating machine so that the average film thickness after baking and drying was 15μ, and after 5 minutes of flash-off, the water-based clear paint was applied to the water-based base paint surface. was sprayed so that the average film thickness after baking and drying was 25μ, and then baking at 160°C for 30 minutes to evaluate spray coating properties. Example 2 A two-coat one-bake water-based paint (Base Silver Metallic) containing a water-dispersible synthetic polycarboxylic acid resin manufactured by Nippon Paint was prepared as follows. (1) Water-based paint Add dimethylethanolamine to the above-mentioned water-based paint to make the neutralization rate 65%, add 20 parts of methyl alcohol per 100% non-volatile content, and add deionized water to give a viscosity of 40 seconds (Food cup #4). Adjusted to. (2) Water-based clear paint Add dimethylethanolamine to the water-based base paint to make the neutralization rate 100%, add 10 parts of diethylene glycol per 100% non-volatile content,
Viscosity 40 seconds with deionized water (food cup #4)
The viscosity was adjusted to (3) Evaluation of paintability Spray paintability was evaluated in the same manner as in Example 1 (3). Reference Example 1 In Example 1, the viscosity was adjusted only with deionized water without adding methyl alcohol to the aqueous base paint, and the spray paintability was evaluated in the same manner as in Example 1. Reference Example 2 In Example 1, the viscosity was adjusted only with deionized water without adding diethylene glycol to the water-based clear paint, and the spray coating properties were evaluated in the same manner as in Example 1, except that diethylene glycol was not added to the water-based clear paint. Reference Example 3 Spray paintability was evaluated in the same manner as in Example 1 except that ethyl acetate was added instead of methyl alcohol to the water-based base paint and the viscosity was adjusted with deionized water. Reference Example 4 In Example 1, butyl carbitol was added instead of diethylene glycol to the water-based clear paint, and the viscosity was adjusted with deionized water, but the spray coating property was evaluated in the same manner as in Example 1. Reference Example 5 In Example 1, the neutralization rate of the aqueous base paint was made 100% with dimethylethanolamine, and the spray coating property was evaluated in the same manner as in Example 1 except for the above. Reference Example 6 In Example 1, the neutralization rate of the water-based clear paint was adjusted to 65% with dimethylethanolamine, and the spray coating property was evaluated in the same manner as above. Reference Example 7 In Example 2, the same operations as in Reference Examples 1 to 6 were performed to evaluate spray coating properties (7 ₁ in the table below).
~ ₇₆ ). The results obtained in each of the above Examples and Reference Examples are shown in the table below.

[Table] As is clear from the above table, 2 according to the present invention
Coat 1 bake-type paint compositions are relatively resistant to sagging and can evenly finish complex objects.
It is an extremely valuable and industrially useful paint, as it shows little change in the finish of the paint film due to changes in booth temperature and humidity, and is also effective against underarm defects.

Claims (1)

[Scope of Claims] 1 The main component is a water-dispersed synthetic polycarboxylic acid resin with a neutralization rate of 80% or less, and metal powder in a weight ratio of 3 to 20% and methyl in a weight ratio of 3 to 30% to the resin. Water-based paints containing alcohol and water-dispersed synthetic polycarboxylic acid resins have a neutralization rate of 80
% or more of water-dispersed neutralized water-soluble resin as the main component,
A two-coat one-bake water-based paint composition comprising: a water-based clear paint containing one or more ethylene glycols in a weight ratio of 3 to 30% based on the resin.