JPS63171681A - Method for coating automobile body - Google Patents

Abstract

PURPOSE:To eliminate the damage of the overcoat and intermediate coat by chipping and to prevent the generation of orange peel, by coating a specified urethane-based clear paint on the part of the automibile body susceptible to chipping after overcoating. CONSTITUTION:The urethane-based clear paint 10 consisting of 60-70 parts polyester resin, 25-35 parts melamine resin, and 3-15 parts cellulose acetate butylate is coated after overcoating 9 on the part of the automobile body susceptible to stone chipping (e.g., hood top of automobile body and periphery of tyre house). The coat layer 10 of the urethane-based clear paint has practically necessary chipping strength, hence the overcoats 9-7 are protected by the coat layer 10, and the damage of the overcoat and intermediate coat 9 and 8 by chipping is eliminated. Besides, since a stone chipping primer is not applied to the interlayer between the overcoat 9 and the intermediate coat 8, the orange peel due to the primer coat is not caused, and an excellent appearance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coating method for preventing paint films from being damaged (chipping) by pebbles and the like thrown up by wheels while an automobile is running.

(Prior Art) As shown in FIG. 1(A), flying stones 3 caused by tires 2 caused by the running of the vehicle on the outer panel 1 of an automobile directly hit the front part 4 of the rear wheel house and the lower end 5 of the door, causing the outer panel 1 to be damaged. damage the paint film. In order to prevent the paint film from being damaged by stones thrown up by the wheels while driving (i.e. stone pitching), conventional methods have been used to apply a stone chipping primer or rocker panel primer. It was 9. The purpose of these stone chipping primers or rocker panel primers is to prevent scratches from reaching the steel plate base of the vehicle body, thereby preventing the occurrence of rust.

However, there are many cases where pebbles, etc. collide with the paint film at a shallow angle, causing scratches (i.e. bealling) between the intermediate and top coats. Because the colors of the paint film and the top coat are different, the scars are noticeable, making the car body look very unsightly and significantly reducing the product value.

The stone chipping primer or rocker panel primer has been shown to be effective as a measure to prevent the scratches that reach the threaded substrate, but it is not sufficient as a measure to maintain the aesthetic appearance of the car body caused by the bealling phenomenon. I couldn't say that. Therefore, as a coating method that has good peeling resistance and can maintain the aesthetic appearance of the car body even if some peeling occurs, we apply a primer coat, then an intermediate coat, and then a top coat to the car body. In the painting method for automobile bodies, a colored oil-7-real-alkyd resin paint film is formed between the intermediate and top coat layers to simulate the top coat, thereby preventing the top coat from chipping and damage. However, a method has been proposed to make the scar less noticeable due to the pseudo color. (Tokuko Showa 60-
54115) (Problems to be Solved by the Invention) However, since the above technique forms a coating film between the eyebrows of the intermediate coating film and the top coating film, damage to the top coating film cannot be avoided. In addition, if the top coat is damaged, the stone chipping primer between the layers is not the same color or gloss as the top coat, so the damaged area is less noticeable, but the difference in color tone from the surrounding area can be discerned. This results in an unsightly appearance of the car body and a drop in product value.

In addition, due to the stone chipping primer between the intermediate coat and top coat, the painted surface will not be smooth and unevenness will occur.
It has the disadvantage of giving you so-called yuzu skin.

(Means for solving the problem) The present invention applies a specific urethane-based clear paint after baking the top coat to areas that are susceptible to stone chipping, such as the tip of the car body and the area around the tire house. The above-mentioned problems are solved by applying the coating.

In the present invention, as a urethane-based clear paint, a paint having a composition of 60 to 70 parts of polyester resin, 25 to 35 parts of melamine resin, and 3 to 15 parts of cellulose acetate butyrate resin (CAB resin) is used. The urethane-based clear paint with such a composition has a hardness (KHN) of 20 to Table 5 and a breaking elongation of 50 to 15 after baking.
It has a breaking strength of 150 to 300 degrees Celsius, a Tg point (Hybron) of 35 to 50 degrees Celsius, and has excellent chipping resistance. In the present invention, the urethane-based clear paint means a reactive paint that forms urethane bonds at a low temperature of about 120°C.

(Function) The urethane clear paint film applied to the part of the car body that is susceptible to stone chipping has the effect of protecting the paint film of the car from stone chipping.

(Example) Fig. 1 (D) shows a cross section of a part of a ninety-motor vehicle body painted according to the present invention that is easily susceptible to stone tipping, where 6 is a steel plate, 7 is an undercoat layer, and 8 9 is the intermediate coating layer, 9 is the top coating layer, l
O indicates a chipping-resistant coating layer of urethane-based clear paint. The undercoat layer, intermediate coat layer, and top coat layer can be formed by known methods.

As a urethane-based clear paint, polyester resin 80~
40 parts of melamine resin, 20 to 40 parts of melamine resin, and 0 to 20 parts of cellulose acetate butyrate resin,
The paint was applied to the stone depth receiving file, and after drying, the chipping strength, elongation at break, and strength at break of the paint film were measured. The results are shown in Figure 2 (a), (b),
Shown in (c).

In practice, the chipping strength is 3 or more, but from Figure 2 (a), to obtain a chipping strength of 3 or more, the polyester resin should be about 70 to 50 parts, and the melamine resin should be about 20 to 35 parts.
3 to 15 parts, cellulose acetate butyrate resin
It can be seen that it is necessary to use a urethane-based clear paint with a composition within the range of 1. The coating film of the urethane clear paint having a chipping strength of 3 or more has a breaking elongation of 50-151 and a breaking strength of 150-300 of 4/ai.
It can be seen that it has Furthermore, the chipping resistance is improved by setting the Tg point to 35 to 50° C., which is slightly lower than the Tg point of the top coat, depending on the low-temperature characteristics.

(Effects of the Invention) The coating layer of the urethane-based clear paint on the top coat of the part of the automobile body susceptible to stone chipping in the present invention has a chipping strength necessary for practical use. The coating layer below the top coat is protected by the film,
Unlike conventional techniques, the top coat and intermediate coat are not damaged by chipping, and since a stone chipping primer is not applied between the top coat and intermediate coat, the stone chipping may cause peeling. The appearance became better. In addition, from the viewpoint of low-temperature characteristics, the glass transition temperature is slightly lower than that of the top coat paint, to 35 to 50 degrees Celsius, and a mixture of rock salt and gravel is spread on the road surface as an antifreeze measure. It is especially effective on the earth.

Figure 2 (a) shows the relationship between chipping strength and urethane-based clear paint compounding ratio (equal ratio, ←) is the relationship between fracture elongation @) and chipping resistance. (c) represents the relationship between breaking strength (K4/!) and chipping resistance.

In the figure, 1...Jikinko outer plate 2... Tires 3-・・・Stepping stones ４・・・・・・Front part of rear wheel house 5...Lower end of the door 6... Steel plate 7...Undercoat layer 8...Intermediate coating layer 9...Top coating layer 10...Top of body outer plate Patent applicant: Toyota Motor Corporation 1 figure (stomach) 2nd figure (stomach) (0)

Claims (1)

[Claims] In the painting of automobile bodies, after the top coat is applied, polyester resin 60~
A method for painting an automobile body, comprising applying a urethane-based clear paint consisting of 70 parts of melamine resin, 25 to 35 parts of melamine resin, and 3 to 15 parts of cellulose acetate butyrate resin.