JP3139356B2 - Electrodeposition method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrodeposition coating method used for undercoating of an automobile body, and more particularly, to a coating which is exposed above an electrodeposition liquid surface when the electrodeposition liquid is coated in a semi-submerged state. The present invention relates to an electrodeposition coating method for preventing uneven drying on the surface.

[0002]

2. Description of the Related Art In a vehicle body, a lower portion of the vehicle body, which is subjected to an impact such as mud or snow that has jumped up during traveling, is required to have a higher rust prevention property than an upper portion of the vehicle body. Further, in order to improve the rust prevention of the automobile body, it is particularly effective to increase the thickness of the electrodeposition coating film. However, it is not preferable from the viewpoint of cost to apply a high film thickness to the upper part of the vehicle body, which does not require such high rust prevention.

Therefore, conventionally, the upper part of the vehicle body has a thin film thickness,
Electrodeposition coating is performed on the lower part of the vehicle body so as to increase the film thickness. As a method of applying the electrodeposition paint in this manner, first, as a first step, the vehicle body is completely immersed in the electrodeposition liquid to perform the entire coating, and then, as a second step, the lower part is painted in a semi-immersed state. Is known (for example, JP-A-60-46397).

[0004]

However, in the above-mentioned coating method, during the second step in which only the lower part is coated in a semi-submerged state, the paint adhering to the upper deposited coating film which is in contact with air is removed. The solvent (mainly water) evaporates and the paint sticks without electrodeposition. Therefore, even after baking and drying of the coating film, the appearance defect is not eliminated, and drying unevenness occurs at the upper portion.

[0005] Such drying unevenness is a coating defect in appearance, and is not realized as a product or requires a sharpening correction of the defective portion. JP-A-60-46398
Japanese Patent Application Laid-Open Publication No. H11-163,086 discloses a method of performing electrodeposition coating while spraying washing water on a draft portion at the time of semi-submerged coating. In this method, the level of the electrodeposition liquid at the draft part has a gentle gradient from the level of the washing water to the level of the electrodeposition liquid at the same time as the liquid level of the electrodeposition liquid is wavy by spraying. It is intended to reduce the step of the coating film generated in the part. Although not described in this publication, spraying washing water onto the surface of the coating film thus exposed can supply insufficient water due to evaporation to the adhered paint or wash away the adhered paint. Is considered to be able to be prevented.

[0006] However, in the method of spraying the washing water onto the draft, there is a problem that the formation of the coating film in the draft portion is hindered by the washing water, and the coating film is easily broken in the draft portion. The present invention has been made in view of such circumstances, and a first step of immersing in an electrodeposition solution to an upper coating position of an object to be coated and performing electrodeposition coating, and thereafter, is located below the upper coating position. In the electrodeposition coating method in which the second step of immersing the electrodeposition liquid in the electrodeposition liquid to the lower coating position and performing the electrodeposition coating continuously, it is possible to effectively remove unevenness of the coating film without problems such as breakage of the coating film at the draft part. The purpose is to prevent it.

[0007]

The feature of the electrodeposition coating method of the present invention that solves the above-mentioned problems is that a first step of immersing the electrodeposition liquid in an electrodeposition liquid up to a coating position above an object to be coated, Thereafter, a second step of immersing the electrodeposition liquid in the electrodeposition liquid to a lower coating position below the upper coating position and performing the electrodeposition coating is performed continuously. This is to carry out the process while bringing the coating surface containing the electrodeposition paint into contact with the coating surface formed in the first step of dispensing.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies on the causes of paint film destruction when spraying washing water, and have found that paint film destruction occurs by the following mechanism. That is, in the washing water, the neutralizing agent (acid) and metal ions in the paint components are more concentrated in the paint, and as a result, water having a higher electrical conductivity than the paint bath is sprayed, and the coating in progress is performed. It was clarified that the film formation was impaired and the coating film was destroyed. And, if a coating liquid containing an electrodeposition paint such as an electrodeposition paint or an electrodeposition paint diluted with deionized water is used, the formation of the coating film in the draft portion proceeds smoothly, and the coating film does not break down, and the drying unevenness also occurs. The present invention has been completed by finding that it can be prevented.

There are no particular restrictions on the type of electrodeposition paint.
It can be applied to both the cation type and the anion type. Examples of the method of bringing the coating liquid containing the electrodeposition paint into contact with the coating surface in the second step include a method of flowing the coating liquid on the coating surface and a method of spraying the coating liquid on the coating surface. Of these, it is preferable to employ a spraying method and spray the draft portion.
In this way, a thin layer of paint also occurs at the upper part of the draft,
In the thin layer, the voltage is applied from the lower part to the upper part, and as a result, the film thickness of the coating film also has a gradient, and foaming is caused by spraying, thereby reducing the amount of steps at the draft part. Can be.

[0010] That is, in the electrodeposition coating method of the present invention, the coating surface exposed during semi-submerged coating can be maintained in a wet state, so that dry unevenness can be reliably prevented.

[0011]

The present invention will be described below in detail with reference to examples and comparative examples. (Embodiment 1) The electrodeposition coating method of this embodiment, which embodies the first aspect of the present invention, was applied to a case where a vehicle body 1 was immersed in an electrodeposition tank 2 for electrodeposition coating as shown in FIG. Electrodeposition tank 2 is deep 2
The vehicle body 1 is electrodeposited while moving from the deep part 20 to the shallow part 21 under the guidance of the hanger rail 10. In the deep part 20, the vehicle body 1 is completely immersed in the electrodeposition liquid 3, and in the shallow part 21, the vehicle body 1 is
It is configured to be in a semi-submerged state.

The shallow part 21 has a spray as shown in FIG.
Device 22 is provided. And the pump 4
The electrodeposition liquid 3 in the bath 2 is supplied to the spray device 22 and
From the playing device 22, a coating liquid composed of the electrodeposition liquid 3 is applied at a pressure of 1
96 KPa (2 kgf / cm ^Two), Discharge rate 20kg / min
So that it is sprayed toward the upper part of the vehicle body 1 and the draft 11
Is configured. The bath temperature of the electrodeposition liquid 3 in the electrodeposition tank 2
And the temperature of the coating solution is 28 ° C.
The coating solids concentration is 20% by weight.

In the present embodiment, the electrodeposition coating was performed as follows using the coating apparatus having the above-described structure. The energization voltage was raised to 200 V at a rate of about 6.7 V / sec for 30 seconds, and then maintained at 200 V for 2 minutes and 30 seconds. The total energization time is 180 seconds. And deep 2
0 for 90 seconds, followed by electrodeposition at the shallow part 21 for 90 seconds, and spraying the coating liquid from the spray device 22 toward the upper part of the vehicle body 1 and the draft part 11 at the shallow part 21 to perform the electrodeposition coating. went. After being sprayed on the upper part of the vehicle body 1, the coating liquid flows downward while wetting the entire coating surface of the upper part of the vehicle body 1, and is collected in the electrodeposition tank 2. In addition, the coating liquid jetted toward the draft portion 11 causes a wavy surface of the electrodeposition liquid 3 in the draft portion 11. Then, after stopping the power supply, the vehicle body 1 was pulled up, washed with water, baked and dried to form an electrodeposition coating film.

The thickness of the formed coating film is 1 at the upper part of the door.
The thickness was 5 μm, and the thickness was 20 μm below the door, and no drying unevenness was observed. The maximum surface roughness of the draft 11 (the maximum value of the difference between peaks and valleys) is 2.96 μm,
The sensory evaluation by visual inspection was at a level of no problem, ie, ○ to-. Further, no abnormalities such as destruction of the coating film were observed in the draft portion 11, and a sound coating film was formed. (Example 2) Electrodeposition coating was carried out in the same manner as in Example 1, except that a coating liquid obtained by diluting the electrodeposition liquid 3 with pure water was used as the coating liquid jetted from the spray device 22. The solid content of the electrodeposition paint in this coating solution was 1% by weight.

The thickness of the formed coating film is 1 at the upper part of the door.
The thickness was 5 μm, and the thickness was 20 μm below the door, and no drying unevenness was observed. The maximum surface roughness of the draft 11 (the maximum value of the difference between peaks and valleys) is 3.32 μm,
In sensory evaluation by visual observation ○ ~ ○ ^- it was no problem with. Further, no abnormalities such as destruction of the coating film were observed in the draft portion 11, and a sound coating film was formed. (Comparative Example 1) Electrodeposition coating was performed in the same manner as in Example 1 except that the spraying of the coating liquid by the spray device 22 was not performed. The thickness of the formed coating film is 15 μm at the top of the door.
The lower part of the door has a thickness of 20 μm, which is the same as that of the first embodiment. However, drying unevenness is seen at the draft part 11, and the maximum surface roughness of the draft part 11 is as large as 5.96 μm. In the evaluation, it was also judged as x. (Comparative Example 2) Electrodeposition was performed in the same manner as in Example 1, except that the washing liquid collected by filtering the electrodeposition liquid 3 with a UF (Ultra Filter) was used as the coating liquid ejected from the spray device 22. Painted. The electrodeposition paint component contained in the washing water is a very small amount of 0.6% by weight in solid content.

The thickness of the formed coating film is 1 at the top of the door.
5 μm and 20 μm below the door.
It was the same as the above, and there was no uneven drying.
In No. 1, since the conductivity increased, current concentration occurred and the coating film was broken, resulting in poor coating. (Evaluation) From the above results, it is apparent that it is essential to use a paint or a paint diluted with pure water (deionized water) as a coating liquid to be sprayed under the conditions of the present example and the comparative example. .

In the above-described embodiment, an electrodeposition tank having two tanks, that is, a deep part and a shallow part, is used, and the case of two-stage coating of full immersion and half immersion is shown. However, the present invention is not limited to this. Of course, the present invention can also be applied to the case of another stage coating as shown in FIG.

[0018]

In other words, according to the electrodeposition coating method of the present invention, it is possible to reliably prevent the occurrence of uneven drying and to prevent the breakage of the coating film at the draft. Further, it is possible to reduce the difference in the coating film thickness in the draft portion.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an electrodeposition coating apparatus used in one embodiment of the present invention.

FIG. 2 is an explanatory view showing a schematic configuration of a main part of an electrodeposition coating apparatus used in one embodiment of the present invention.

FIG. 3 is an explanatory view showing a schematic configuration of a coating apparatus of another embodiment of the electrodeposition coating apparatus used in one embodiment of the present invention.

[Explanation of symbols]

1: body (object to be coated) 2: electrodeposition tank 3: electrodeposition liquid 10: hanger rail 11: draft part 22: spray device

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaaki Tsuchida 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yukihiro Kakemoto 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (58) Field surveyed (Int. Cl. ⁷ , DB name) C25D 13/00

Claims (1)

(57) [Claims] 1. A first step of immersing in an electrodeposition liquid to an upper coating position of an object to be coated and performing electrodeposition coating, and thereafter immersing in an electrodeposition liquid to a lower coating position located below the upper coating position. A second step of continuously performing electrodeposition coating by performing electrodeposition coating, wherein the second step is performed by exposing the coating surface formed in the first step to the coating surface including the electrodeposition coating material by projecting upward from a draft portion. An electrodeposition coating method, wherein the method is performed while contacting a liquid.