JPS5951868B2 - Top coating method for automobile bodies - Google Patents

Description

[Detailed description of the invention] The present invention relates to a top coating method for an automobile body.

It is something that Conventionally, air atomization painting or air atomization electrostatic painting has been the mainstream method for top coating automobile bodies.

This air atomization painting or air atomization electrostatic painting makes the paint into fine particles to obtain a uniform coating surface. However, the transfer efficiency is poor, so a large amount of extra paint is required, the amount of paint discharged from the air atomization (electrostatic) paint gun is small, and the amount of organic solvent is high and the solid content is low. Because there are few
When painting a large object such as the outer panel of a car body, this method has the disadvantage that the paint gun must be re-produced many times. For this reason, the rotary atomization electrostatic coating method, which has a large paint output and excellent coating efficiency, has recently attracted attention, and is being put into practical use for the intermediate coating, clear topcoat, and solid topcoat of automobile bodies. .

However, this rotary atomization electrostatic coating method was unsuitable for metallic coating, which is considered to be the most difficult of the automotive top coating methods, due to the following points. . Generally, when applying metallic paint, the color tone of the paint will change depending on the model of the coating machine even if the paint is the same, and the color tone of the paint obtained with rotary atomization electrostatic painting is darker than that of air atomization (electrostatic) painting. It also lacks a metallic feel. This is because the particle size of paint particles sprayed from the spray head of a rotary atomizing electrostatic paint machine is air atomized (electrostatic).
Because they are large compared to the particle size of paint particles from the paint gun,
This seems to be because the aluminum particles in the metallic paint are not finely and uniformly dispersed. For this reason, if a metallic top coat is applied using a rotary atomizing electrostatic atomizer, there is a problem in that the exterior quality of the car body will be impaired, which is not desirable. If corrective painting is performed locally using an air atomization paint machine, color differences will occur in each part of the painted surface for the reasons mentioned above, which will also impair the appearance quality of the car body. I couldn't get it. In order to solve the above-mentioned problems and perform metallic colored coating by the rotary atomization electrostatic coating method, for example, metallic colored coating is performed by using a combination of the rotary atomization electrostatic coating method and the air atomization coating method, and then A method of applying a metallic clear coating using a rotary atomization electrostatic coating method has been implemented. In this method, metallic colored paint is applied to the entire surface of the car body using a rotary atomizing electrostatic coating machine, and then an air atomizing paint gun is applied to the entire painted surface in order to cover up the darkness of the paint color and the loss of metallic feel. It performs an overall mist spray, and can produce a painted surface with little color difference and an excellent metallic feel. However, the above coating method has the disadvantage that it is uneconomical because L-type atomization (electrostatic) coating, which has low coating efficiency, is also used. The method of the present invention significantly increases the rotational speed of the rotary atomizing electrostatic coating machine compared to the conventional rotational speed, thereby improving the metallic coloring that is sprayed from the spray head 1 of the rotary atomizing electrostatic coating machine. The object of the present invention is to provide a coating method that can atomize the paint and thus provide a coated surface with a good metallic feel even when using a rotary atomizing electrostatic coating machine.

The automobile top coating method of the present invention includes a first painting step in which a metallic colored paint is applied using a rotary atomizing electrostatic atomizer, and a metallic paint or solid paint is applied using a rotary atomizing electrostatic atomizer. and a second painting process in which the circumferential speed of the spray head of the rotary atomizing electrostatic atomizer in the first painting process is set to 120 to 300 m/sec, which is faster than in the second painting process. It is characterized by: Hereinafter, the method of the present invention will be explained based on the drawings. The figure is a schematic drawing of a coating process showing an embodiment of the method of the present invention.
In the figure, reference numeral 1 denotes an automobile body (hereinafter referred to as body) which is an object to be coated, and after completion of the intermediate coating, it is transported to the top coating zone A. Top coat painting zone A is body 1
The metallic colored paint coating process (first coating zone) A1 is located in the first half of the conveyance direction of the body 1, and the metallic clear paint coating process (is located in the latter half of the conveyance direction of the body 1).
2nd coating zone) A2. 1st painting zone A1
A pair of side coating machines 11, 11 for coating the vertical surface portion of the body 1, and a top coating machine 21 for coating the horizontal surface portion of the body 1 are disposed.

The side coating machine 11 has rotary atomizing spray heads 11a, ]1b, and 11C at different height positions. Each spray head]
1a, 11b, 11C may be arranged orthogonal to the longitudinal axis of the coating zone A and parallel to each other,
They may be provided in one side coating machine 11 at different height positions. Further, one spray head may be provided so as to be reproducible in the vertical direction. The top coating machine 21 is disposed following the side coating machine 11.

The top coating machine 21 has rotating atomizing spray heads 21a and 21b.
Each of the spray heads 21a, 21b can be reproduced in the horizontal direction and can also be reproduced in the vertical direction. The vertical registration of each spray head 21a, 21b can be performed by raising and lowering the top coating machine 21 itself. In the second coating zone A2, a side coating machine 21 and a top coating machine 22 are disposed, similarly to the first coating zone A1.

The metallic coating of the body 1 in the top coating zone A having the above structure is carried out, for example, as follows.

First, the body 1 is transported to the first coating zone A1, and the vertical surface of the body 1 is electrostatically coated with metallic colored paint that is sprayed by rotation from the side coating machines 11, 11, and then rotary sprayed from the top coating machine 21. The horizontal surface portion of the rib body 1 is electrostatically coated with the metallic colored paint. The body 1 coated with metallic ivy coloring in the first coating zone A1 is then transported to the second coating zone A2, where a metallic clear is wet-on coated and after the second coating process is completed, it is baked and hardened. The peripheral velocity of the spray head of each coating machine in the first coating zone A1 is determined by the degree of atomization of the metallic ivy colored paint to be sprayed.

The finer the paint particles, the more fine and uniform the aluminum particles in the metallic paint will be on the paint surface, resulting in a good paint surface without metal unevenness, but if the paint particles are too fine, the coating efficiency will be poor. I don't like it. In addition, if the paint particles are too small, the paint sprayed from the spray head will be atomized and the solvent will not be lost before reaching the object to be coated, or the solvent will volatilize immediately after the paint particles are applied to the object. This is undesirable because it accelerates the drying of the particles and causes roughness (dusty skin) on the coated skin. The spray head peripheral speed of the coating machine in the first coating zone A1 is 120 to 300 m/sec. This peripheral speed is 80
m/sec diameter spray head with rotational speed of 30,000 to 75,000 r.m.
p. Corresponds to m. If the circumferential speed is less than 120 m/sec, it is not possible to ensure the atomization of the paint particles to the same degree as atomization as described above, which impairs the metallic feel, which is undesirable. Also, if the speed exceeds 300 m/sec, the paint becomes too fine,
This is undesirable because it accelerates the drying of paint particles, resulting in the formation of dusty skin on the painted surface and a decrease in coating efficiency. The metallic colored paint sprayed from the spray head at the above circumferential speed has a paint viscosity of 10~
40 seconds/#4F. Those in the C range are preferred. In particular, metallic colored paints contain a solvent component with a boiling point of 100η or more.
When the content is 0% or more, it is possible to prevent acceleration of drying due to fineness of paint particles. The amount of metallic colored paint discharged from the spray head is 50 to 500 cc/min.More specifically, at a body movement speed of 4 m/min, the amount of metallic colored paint discharged from the side coating machine is 50 to 250 cc/min, and the top coating machine is 50 to 250 cc/min. The discharge rate is 150 to 400 cc/min.

In addition, the coating pattern is 400 to 80% from the viewpoint of coating efficiency.
Adjust the width to 0m/sec. The rotary atomizing electrostatic atomizer used in the first coating zone A should be a non-contact air bearing type rotary atomizing electrostatic atomizer that rotates the spray head at high speed and has no bearing damage and less vibration. preferable. The diameter of the spray head is 70-9
It is 0mm. By using the above non-contact air bearing type coating machine, it is possible to maintain a high circumferential speed and a coating pattern stably for a long period of time. Second painting zone A.

The circumferential speed of the spray head of each sprayer in is set to be slower than the circumferential speed in the first coating zone A. Specifically, the peripheral speed is, for example, 40 to 120 m/sec. Since the paint applied in the second coating zone is a metallic clear paint or solid paint, good coating quality can be ensured even at a peripheral speed that is significantly slower than in the first coating zone A. From the viewpoint of improving the coating efficiency, it is preferable to apply the coating at a spray head peripheral speed as slow as possible as long as the appearance quality of the body is not impaired. Second painting zone A. By rotary atomization electrostatic coating of metallic clear paint or solid paint, it is possible to change the dusty surface of the paint film of body 1, which has passed through the first coating zone A and has been painted with metallic color, to a smooth paint film surface. can. As for the type of paint, physical properties of the paint, painting conditions, etc. used in the second painting step, conventionally known paints and painting conditions can be used. Next, topcoating was carried out by the method of the present invention and the conventional method under the conditions shown in the table below, and the quality of the obtained coated objects was comparatively evaluated.

The results are also shown in the table below. As is clear from the above table, in Example 1 (comparison), the spray head circumferential speed in the first step was as slow as 60 m/sec, so the resulting coating film had poor metal unevenness and a poor metallic feel.
Paint quality deteriorates. In addition, in Example 6 (comparison), the first
This is an example in which an air atomizing electrostatic coating gun was used in the process, and although the quality of the coating film obtained according to this example is good, the coating efficiency is extremely low at 40%. Examples 2-5 (present invention)
In both cases, the metal unevenness and metallic feel of the coating film are good.
Furthermore, it can be seen that the coating efficiency is significantly improved compared to Example 6. As is clear from the above description, in the method of the present invention, the metallic color coating in the first coating process is performed using a rotary atomizing electrostatic coating machine that rotates at high speed. A coating film with a good metallic feel and no metallic unevenness can be obtained.

Therefore, even if correction painting is performed using an air spray gun, no color difference will occur between the correction area and the correction area. In addition, the dust surface of the paint film produced by the rotary atomizing electrostatic coating machine for metallic colored paint is well covered by the rotary atomizing electrostatic coating of the clear paint or solid paint in the second painting process, thus creating a smooth coating. A membrane is obtained. In addition, in the method of the present invention, both the first painting process and the second painting process are performed using a rotary atomizing electrostatic coating machine with excellent coating efficiency. This method has the advantage of providing better coating efficiency than when combined with painting, and is effective in reducing paint costs.

[Brief explanation of the drawing]

The figure is a process diagram showing an example of the coating method of the present invention. In the figure, 1... object to be coated, 11, 12...
Painting machine for side, 21, 22... Painting machine for top.

Claims (1)

[Claims] 1. A first painting process in which metallic colored paint is applied using a rotary atomizing electrostatic coating machine, and a second painting process in which metallic clear paint or solid paint is applied using a rotary atomizing electrostatic coating machine. The circumferential speed of the spray head of the rotary atomizing electrostatic coating machine in the first coating step is 120~
A top coating method for an automobile body, characterized in that the speed is 300 m/sec, which is faster than that in the second coating step.