JPH08131946A - Painting method for automobile - Google Patents

Abstract

PURPOSE: To reduce cost by lessening the number of processes and to heighten the appearance quality by eliminating the effect of generated dust on an exterior board part in the case where an exclusive interior board color paint is used. CONSTITUTION: After a coating by electrodeposition is formed on a steel sheet, an uppercoating base coating having the same resin composition as that of an uppercoating top coating and prepared to have higher pigment concentratipn than that of the uppercoating top coating is applied to an exterior board part and an interior board plate in common, and the uppercoating top coating is applied further to only the exterior board plate by wet-on-wet coating method and after that the whole body of the resulting steel sheet is baked and dried.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for painting an automobile body, and more particularly to a method for painting a solid paint.

[0002]

2. Description of the Related Art As shown in FIG. 1, when painting an automobile body, different coatings are applied to an outer plate portion 2 and an inner plate portion such as an engine room, a door opening portion and a room. In the inner plate part, the inner plate color using an inexpensive paint is applied wet-on-wet on the intermediate coat film, and also on the outer plate part, the top coat coat is applied on the middle coat coat in order to ensure the concealment of the top coat coat. Has been given.

The process is shown in FIG. After forming an electrodeposition coating film and baking and drying it, apply an intermediate coating to both the outer plate and inner plate, and apply an inexpensive inner plate color to the inner plate wet-on-wet on the intermediate coat. After coating, the car body is put in a furnace to bake and dry the intermediate coating film and the inner plate color coating film. After that, the outer coating is applied with a top coat, and the vehicle body is put in a furnace again to bake and dry the top coat.

A boundary region between the inner plate portion and the outer plate portion is schematically shown in FIG. 3, in which an electrodeposition coating film 8 (generally a dark gray system) is formed on the steel plate 6 and is formed thereon. The intermediate coating film 10 is formed, and the inner coating film 12 is formed on the intermediate coating film 10 in the inner plate portion. On the other hand, in the outer plate portion 2, an overcoat coating film 14 is formed on the intermediate coating film 10.

[0005]

The conventional method of providing the intermediate coating step requires three coating steps and two baking / drying steps after the electrodeposition coating, which requires a large number of steps, and in terms of equipment and man-hours. It is a disadvantage. When the inner coating color is applied on the intermediate coating film 10, dust 12a of the inner coating color may be generated. In the case of a solid type top coat coating, when the coating color is a vivid color with no turbidity and transparency, the hiding property is inferior, so the intermediate coating film 1
When the inner plate color dust 12a is attached to the upper surface of the surface 0, the dust 12a can be seen through the top coating film 14 and the appearance quality is deteriorated.

An object of the present invention is to reduce the number of steps to reduce the cost, and to eliminate the influence of dust in the outer plate portion which occurs when a dedicated inner plate color paint is used, thereby improving the appearance quality. It is a thing.

[0007]

In the present invention, as shown in FIG. 4, after forming an electrodeposition coating film on a steel sheet, it has the same resin composition as that of the top coating film and has the same top coating composition. Topcoat base coating adjusted to a pigment concentration higher than the pigment concentration is applied to both the outer and inner plates, and the topcoat is applied wet-on-wet only to the outer plate. Then, the whole is baked and dried.

The middle coat coating is eliminated, and instead of this, the top coat base coating film is commonly applied to the outer plate portion and the inner plate portion. As a result, the number of coating steps after electrodeposition coating is reduced to two steps, and baking drying is also reduced to one step, thereby reducing the number of steps. Also,
Since the top coat base coat, which is the lower layer of the top coat top coat, is common to the inner plate part and the outer plate part, there is no influence of dust due to the dedicated inner plate color paint as in the conventional case.

The boundary region between the inner plate portion and the outer plate portion is schematically shown in FIG. 5, and the electrodeposition coating film 8 is formed on the inner plate portion 4 and the outer plate portion 2.
An overcoat base coating film 20 is commonly formed on the upper surface, and an overcoat top coating film 22 is further formed on the outer coating portion 2. The inner plate portion 4 is finished with an overcoat base coating film 20. The topcoat base coating film 20 is set to an L value similar to that of the electrodeposition coating film 8. The L value is the L value of the Hunter color difference formulas L, a, and b.

An inexpensive pigment can be used as the base coating material, and the pigment concentration is adjusted to be higher than the pigment concentration of the coating material of the top coating film 22. The tint of the overcoat base coating film 20 is the same as that of the overcoat top coating film 22, or when the combination of the overcoat base coating film 20 and the overcoat top coating film 22 produces a vivid tint, the overcoat base coating film. The tint of 20 may be similar to the tint of the top coating film 22. The topcoat base coating film 20 and the topcoat top coating film 22 have the same resin composition but different solvent settings. In the present invention, it is possible to achieve a vivid color tint at low cost. This is because the inner plate portion 2 may be finished with an inexpensive topcoat base and its concealing property may be secured by a two-layer film with the electrodeposition coating film 8.

[0011]

EXAMPLE One example will be described with reference to FIGS.
The electrodeposition coating film 8 is formed on the steel plate 6 by a usual method. The coating material of the electrodeposition coating film 8 is an epoxy cationic electrodeposition coating material containing titanium oxide, carbon black or the like as a pigment, and the solid content concentration is adjusted to 20% by weight. The paint is applied to a thickness of about 20 μm, and baked and dried at 170 ° C. for 20 minutes to form an electrodeposition coating film 8.

An overcoat base coating film 20 is applied on the inner plate portion 4 and the outer plate portion 2 in common. The top coat base coating film 20 uses an alkyd-melamine resin as a main component resin, and disperses it and a coloring pigment such as red iron oxide or azo red in a dedicated thinner as a solvent to give a solid content concentration of 4
It is a paint adjusted to 7.5% by weight, and the paint is applied by an air spray gun method to a coating thickness of about 15 μm.
To be applied.

On top of the base coating film 20, a wet coating
Topcoat topcoat 22 is applied on-wet. The top coat film 22 of the top coat uses the same alkyd-melamine resin as the resin of the paint of the base coat film 20 of the top coat as a main component resin, and uses it and a coloring pigment such as quinacridone red or ad red as a solvent. It is a paint that is dispersed in a thinner and adjusted so that the solid content concentration is 45.8% by weight. The paint is applied only to the outer plate part 2 by an air spray gun method so that the applied film thickness is about 25 μm. To do.

Thereafter, the topcoat base coating film 20 and the topcoat top coating film 22 are simultaneously baked and dried at 140 ° C. for 20 minutes. The coating composition, coating thickness, coating method, etc. of each coating film are not limited to those shown in the examples. In addition to the air spray method, an airless spray method or an electrostatic coating method may be used as a means for coating the base top coating film and the top coating film.

[0015]

According to the present invention, the intermediate coating is eliminated, and instead the base coating is formed on both the outer plate and the inner plate, so that the coating process after the electrodeposition coating is performed in two steps. It also reduces the number of processes and the number of processes by reducing baking and drying to one process. Also, since the top coat base coat, which is the lower layer of the top coat top coat, is common to the inner and outer plates, there is no dust effect from the dedicated inner plate color paint as in the past, and the appearance of the outer plate is Quality is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an outer plate portion and an inner plate portion for painting an automobile body.

FIG. 2 is a flowchart showing a coating process in a conventional method.

FIG. 3 is a schematic cross-sectional view showing a boundary portion between an outer plate portion and an inner plate portion coated by a conventional method.

FIG. 4 is a flowchart showing a coating method of the present invention.

FIG. 5 is a schematic cross-sectional view showing a boundary region between an outer plate portion and an inner plate portion of a coating film formed according to an example.

[Explanation of symbols]

 2 Outer plate part 4 Inner plate part 6 Steel plate 8 Electrodeposition coating film 20 Topcoat base coating film 22 Topcoat top coating film

Claims (1)

[Claims] 1. An overcoat base coating, which has an electrodeposition coating film formed on a steel plate of an automobile, and has the same resin composition as that of the overcoat top coating film and has a pigment concentration higher than that of the overcoat top coating film. It is characterized in that the film is applied to both the outer plate part and the inner plate part in common, the top coat top coating film is applied wet-on-wet only to the outer plate part, and then the whole is baked and dried. How to paint solid paint for automobiles.