JPS581991B2 - Automotive body painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for topcoating an automobile body mainly using a rotary atomization electrostatic coating method.

Currently, the air atomization method, and in some cases the air atomization electrostatic method, is generally used as the exterior painting method for automobile bodies both domestically and internationally. is low at 40% to 50%.

On the other hand, another coating method, the rotary atomization coating method, is an old technique, but the quality of the finish produced by this coating method is inferior to that by the above-mentioned air atomization method, so it has not been adopted as a top coat.

However, since the paint usage efficiency is high at 70% to 80%, most automobile manufacturers have already adopted it as an intermediate coating.

Recently, from the viewpoint of resource conservation, the use of rotary atomization electrostatic coating method, which has high paint usage efficiency, has been expanded, and one example of this is its adoption in automobile topcoating, and patent applications for this purpose are also being made. Seen a lot.

A characteristic of automotive topcoating is that various paints are applied continuously to a complexly shaped vehicle body, but this poses a problem when painting is mainly performed using a rotary atomization method.

That is, after applying rotary atomization coating to most of the general surface of the exterior panel, it is necessary to apply air atomization coating by hand to areas where it is difficult to form a thick coating film, the periphery of the door, and the inside.

However, in this case, because the degree of atomization of the double-edged type of the rotary atomization method and the air atomization method is different, when the overspray mist of the air atomization coating is deposited on the wet film of the rotary atomization coating, this If the mist does not fully adapt to the wet film and the texture is baked as it is, phenomena such as spots and blisters will occur on the painted surface.

In topcoating, high-grade painted surface quality is required, and the above-mentioned phenomenon becomes a problem as an appearance quality defect.

The present invention has been made to solve this problem, and is an automobile body outer panel painting method in which a rotary atomization electrostatic painting process and an air atomization process are mixed in the same booth.
After rotary atomization electrostatic painting on an automobile body, before the wet film is dry to the touch, the solid content of the wet film applied by the above-mentioned rotary atomization electrostatic painting was immediately after spraying with air atomization alone. This is an automobile body painting method in which air atomization coating conditions are set so that the solid content of the wet film is low, spraying is performed using air atomization, and then simultaneous baking is performed.

Here, "dry to the touch" refers to a state in which the paint does not adhere to the finger even when the finger is lightly pressed against the wet film.

As mentioned above, in the conventional method, most of the required film thickness of the outer panel of an automobile body is painted using rotary atomization electrostatic coating, and then hand-blown air atomization is applied to the areas that are not sufficiently coated. produce defects.

As a result of investigating the cause of this problem, we found that the degree of atomization of the paint differs greatly between rotary atomization painting and air atomization painting, and that the solid content of the wet film formed by rotary atomization painting remains even after flash-off, even after air atomization spraying. It was found that this is due to the fact that the solid content of both solids does not mix smoothly because it is lower than the solid content of the applied paint.

As a countermeasure to this problem, the air atomization coating conditions were adjusted as follows.

In other words, the same paint used for rotary atomization is used and the thinner dilution rate is changed to adjust the sprayed solid content, or the resin or pigment composition used in the rotary atomization paint is not changed, but the solvent composition is changed, or air or air This is a method of changing painting conditions such as air pressure, pattern width, and reciprocating cycle during atomization painting.

The solid content of a wet film formed by rotary atomization coating is higher than that of spray paint even immediately after application due to evaporation of the solvent, and increases with time after application.

When performing air atomization painting by giving a solid content immediately after spraying that is about 10 weight percent lower than the solid content on the wet film surface, both solid content blends well, resulting in the above-mentioned painted surface defects. do not have.

It should be noted that if the difference in solid content exceeds 20% by weight, the poor conformability can be eliminated, but it tends to cause a phenomenon of uneven texture, which is not necessarily preferable.

Note that if air atomization is applied after the wet film formed by rotary atomization is dry to the touch, there is no effect on poor adhesion even if the relationship between the two solid contents is as described above. Needs to be painted.

Example Under the following conditions, rotary atomization coating was performed, and then air atomization coating was applied in the form of a dust so as not to form a continuous film, and baking was performed to evaluate the compatibility of the spray mist.

(1) Rotary atomization coating conditions Painter Minibell G type manufactured by Landsburg, applied voltage -9
0 kV, bell rotation speed 1 2.0 0 O rpm.
Shaving air pressure 4. OK K9/cm2 Pattern width 60cm, Discharge rate 300cc/min (2) Painting booth conditions Temperature and humidity 25℃75%RH. Conveyor speed 3.5m/
0 Painting stage Fixed type 1 stage, Dry film thickness 30μ Object to be coated Door bolts, Spraying distance 25cm (3) Air atomization painting conditions Painting gun Wigoo 70 manufactured by Iwata Painting Machine, Air pressure 5.0K
g/ffl Discharge rate 4 0 0 cc/min Hand-sprayed painting Flat 3 minutes (4) Sprayed paint (solvent-based solid blue paint) (5) Baking 20 minutes at 140°C (6) Painting results

Claims (1)

[Claims] 1. In an automobile body exterior painting method in which a rotary atomization electrostatic coating process and an air atomization process are mixed in the same booth, after the rotary atomization electrostatic coating is applied to an automobile body, before the wet film is dry to the touch. The air atomization coating conditions were set so that the solid content of the wet film immediately after spraying of the air atomization coating alone was lower than the solid content of the wet film applied by the above-mentioned rotary atomization electrostatic coating. An automobile body painting method characterized by spraying with chemical coating and then simultaneous baking.