JPH0115537B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin composition for paints that has excellent painted surface appearance and is used in applications that require excellent painted surface appearance, such as automobile exterior paints in particular. Paints used outdoors, such as top coat paints for automobiles, have traditionally required long-term weather resistance and excellent painted surface appearance in addition to general performance such as chemical resistance, solvent resistance, and physical performance. Particularly in the case of top coat paints for automobiles, the quality of the appearance of the coated surface has a significant impact on its commercial value, and there is an extremely high demand for improving the appearance. Furthermore, in recent years, due to cost reductions in automobile painting, the film thickness has become thinner and the number of man-hours has also tended to decrease. All of these lead to a decline in the appearance of the painted surface, so the requirements for appearance are as follows:
It's getting even bigger. Various measures have been taken to solve the above deficiencies. For example, increasing the thickness of the paint film is one way to do this, but as mentioned earlier, this leads to increased costs, and depending on the area being painted, it is often impossible to apply a thick film due to sagging, etc. . There are other methods of improvement, such as the use of various conventionally used additives or changes in the composition of thinner, but these are not satisfactory means of improvement and require modification of the coating resin itself. In view of the current situation, the inventors of the present invention have completed the present invention as a result of intensive studies to improve the appearance of painted surfaces. The present invention consists of 20 to 60 parts by weight of styrene, 30 to 80 parts by weight of dialkyl fumarate whose alkyl group has 3 to 12 carbon atoms, and 0 to 50 parts by weight of other copolymerizable monomers, and has a weight average molecular weight of 3000. This is a resin composition for coatings, which has an excellent appearance on the painted surface, and is composed of 0.1 to 40 parts by weight of a copolymer having a molecular weight of ~80,000 and 99.9 to 60 parts by weight of a thermosetting resin. In the present invention, the amount of dialkyl fumarate in the copolymer (A) needs to be 30 to 80 parts by weight based on 100 parts by weight of the copolymer, and if it is less than 30 parts by weight, the appearance of the painted surface cannot be expected to improve. In addition, the amount of styrene needs to be 20 to 60 parts by weight per 100 parts by weight of the copolymer, and if it is less than 20 parts by weight (if the dialkyl fumarate is more than 80 parts by weight), the polymerization rate will decrease. This is not preferable because it may become slow or the degree of polymerization may not increase. Other copolymerizable monomers include 2-ethylhexyl (meth)acrylate, alkyl esters of (meth)acrylate such as lauryl (meth)acrylate, vinyl acetate, dialkyl maleate, dialkyl itaconate, and 2-hydroxyethyl ester. Examples include (meth)acrylate, 2-hydroxypropyl (meth)acrylate, (meth)acrylamide, N-methylol (meth)acrylamide, (meth)acrylonitrile, glycidyl (meth)acrylate, (meth)acrylic acid, itaconic acid, etc. , these can be used alone or in combination as necessary. The weight average molecular weight of the copolymer (A) is preferably in the range of 3,000 to 80,000. 3000
When it is smaller, the chemical resistance and solvent resistance of the resulting coating film decreases, and when it is larger than 80,000, the improvement in the appearance of the coated surface becomes unsatisfactory. The mixing ratio of copolymer (A) and thermosetting resin is
It is 0.1/99.9 to 40/60. If the copolymer (A) content is less than 0.1%, no improvement in the appearance of the painted surface can be expected;
If it exceeds this amount, the chemical resistance and solvent resistance of the resulting coating film will decrease, making it unsatisfactory. Examples of the dialkyl fumarate whose alkyl group has 3 to 12 carbon atoms used in the production of the copolymer (A) include diisopropyl fumarate, dibutyl fumarate, diisobutyl fumarate, di2-ethylhexyl fumarate, dioctyl fumarate, etc. can be mentioned. Copolymer (A) can be, for example, toluene, xylene,
In non-polar solvents such as Solbetsuso #100 or n-
It is obtained by polymerization in a mixed solvent system with a polar solvent such as butanol. As the polymerization initiator, a peroxide such as benzoyl peroxide or cumene hydroperoxide or an azo compound such as azobisisobutyronitrile or azobisvaleronitrile is used. Furthermore, n-dodecyl mercaptan, 2-mercaptoethanol, etc. are used as necessary to adjust the degree of polymerization. Examples of thermosetting resins to be mixed with the copolymer (A) include acrylic resins, alkyd resins, polyester resins, etc. Crosslinking agents that may be added as necessary include amino acids such as melamine and benzoguanamine. Examples include resins, epoxy resins, and isocyanate resins. Among these, it is preferable to use an acrylic resin as the thermosetting resin and a melamine resin as the crosslinking agent especially for automobile top coatings, which is the application in which the present invention can exhibit the most effect. In the following examples, parts represent parts by weight. Examples 1 to 4 and Comparative Examples 1 to 7 A copolymer was prepared from the monomer mixture shown in Table 1 using azobisisobutyronitrile as an initiator in a mixed solvent consisting of 80 parts of Solbetsuso #100 and 20 parts of n-butanol. (A) was obtained, and this copolymer (A), Dianal HR-500 (acrylic thermosetting resin manufactured by Mitsubishi Rayon Co., Ltd., and Yuban 20SE (melamine resin manufactured by Mitsui Toatsu Chemical Co., Ltd.) were expressed. The resulting mixture was diluted with Solbetuso #100 as a thinner and a food cup #4 at 25°C for 25 seconds. A clear paint No. 7 was obtained.Next, the metallic enamel was mixed in the following manner.Dianal HR-560, Yuban 20SE, and Alpaste #1109MA (aluminum paste manufactured by Toyo Aluminum Co., Ltd.) were mixed in a solid content ratio. Blend at 80/20/10, as thinner toluene/n-butyl acetate/butyl cellosolve/Sorbetso #150 = 70/10/10/10
(weight ratio) using food cup #4
The temperature was adjusted to 25℃ for 14 seconds, and a metallic enamel paint was created. After applying the above metallic enamel paint to a dry film thickness of 15μ on a coated plate obtained by applying an automotive electrodeposition primer and an intermediate coat surfacer to a mild steel plate that had been degreased and phosphate chemically treated, 3. The clear paint having the composition shown in Table 1 was applied wet-on-wet to a dry film thickness of 25 to 30μ, left for 10 minutes, and then heated and cured in an electric hot air dryer at 140°C for 30 minutes. . Table 1 shows the evaluation results of the coating film thus obtained.

[Table] From Table 1, the coating film obtained using the composition of the present invention showed excellent performance.

Claims (1)

[Claims] 1 Consisting of 20 to 60 parts by weight of styrene, 30 to 80 parts by weight of dialkyl fumarate whose alkyl group has 3 to 12 carbon atoms, and 0 to 50 parts by weight of other copolymerizable monomers,
Copolymer with weight average molecular weight 3000~80000 0.1~
A resin composition for a paint with excellent appearance on a painted surface, comprising 40 parts by weight of a thermosetting resin and 99.9 to 60 parts by weight of a thermosetting resin.