JPS63192896A - Method for painting body having narrow gap by electrodeposition - Google Patents

Abstract

PURPOSE:To paint the whole inside of a narrow gap in a body to be painted by electrodeposition by immersing the body in electrodeposition paint to carry out painting by electrodeposition, drying the body and immerising it again in the paint to paint the unpainted part of the inside of the narrow gap. CONSTITUTION:A body to be painted has a narrow gap of <=about 500mum width left between two steel sheets by spacers. The body is immersed in electrodeposition paint to paint the insides of the inlet parts of the gap by electrodeposition. After the body is dried to increase the electric resistance, it is immersed again in the paint to paint the unpainted part of the inside of the gap by electrodeposition. The body is then dried again and a formed paint film is cured. The whole inside of the narrow gap of <=500mum width is surely painted by electrodeposition. It is difficult to paint the whole inside by the conventional technique.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for electrodeposition coating an object having a narrow gap. The coating method of the present invention is useful when electrocoating objects having steel plate joints as narrow gaps, such as automobile rocker panels.

[Prior Art] Automobile body painting requires a high degree of rust prevention and aesthetic appearance, and therefore requires a more complex process than general painting. For example, first a chemical conversion treatment is performed to form a zinc phosphate coating on the body, and then i! Electrodeposition coating is applied, followed by intermediate coating and top coating depending on the purpose.

By the way, in electrodeposition painting, the body is completely immersed in the electrodeposition paint.
This is the process of painting not only the exterior of the body but also every corner of the interior, and is the most important process in terms of rust prevention. Generally, this N coating is carried out by dipping the chemical conversion treated body in a 'R' ¥1 paint tank and applying DC electricity of 200 to 300 V to apply the electric W coating. After that, after cutting off the drippings and washing with water,
This is done by baking and drying at 0°C for about 25 to 30 minutes.

In addition, as a special method, as seen in Japanese Patent Application Laid-Open No. 1710/1983, ';
By forming a ts precipitated insulating layer and hardening it with force, then forming a conductive layer, and forming a new N precipitated insulating layer on the conductive layer by electrophoresis, the electrical insulation potential rs
A method for obtaining thick electrically insulated conductors with uniform thickness is disclosed.

Furthermore, Japanese Patent Laid-Open No. 60-46397 discloses that the entire surface of an automobile body is coated with an electrodeposition coating of the required thickness on the upper part of the body. A method is disclosed for forming a rust-proof 2-electrode 11 coating film that easily prevents the occurrence of steps by applying a coating.

Furthermore, JP-A-61-149497 discloses a wet-on-wet electrodeposition coating of a colored electrodeposition paint and a clear electrodeposition paint made of anionic synthetic resins with different characteristics on an electrically conductive material. A method is disclosed that enables a two-coat electrical sign coating with excellent gloss and weather resistance.

[Problem that the invention seeks to solve]

In electrodeposition coating, the inner surface of a narrow gap of approximately 500 μm or less, such as the steel plate assembly of a rocker panel, is coated only to a small depth, and it is known that INR coating on the inner surface of such a narrow gap is difficult. There is.

Therefore, in order to impart rust prevention to such narrow gaps, methods such as the use of rust-proof steel plates, the application of sealants, and the injection of wax have been employed.

However, with such a method, sufficient rust prevention power cannot be obtained, and an increase in cost due to increased man-hours and material costs cannot be avoided. Furthermore, the above-mentioned publications do not describe coating the inner surface of the narrow gap.

The present invention has been made in view of these problems, and provides an electrodeposition coating method capable of coating the inner surface of a narrow gap to a deep depth.

[Means for solving the problem] The present inventors varied various coating conditions to achieve a width of 200 μm.
We investigated the electrocoatability of the inner surface of the narrow gap. As a result, as shown in FIG. 1, even if the coating voltage was changed, the coating performance on the inner surface of the narrow gap did not improve. Incidentally, when coating the inside of a bag structure with a wide gap, etc., by increasing the coating voltage, the interior can be coated deeper. In comparison, the above results show extremely unique behavior.

Moreover, as shown in FIG. 2, even if the coating time is increased, the heavy loading performance of the inner surface of the narrow gap remains almost constant. Furthermore, the third
As shown in Fig. 4, the coating performance on the inner surface of the narrow gap did not improve even if the temperature and type of paint were changed.

It has also been found that the coating depth in the narrow gap depends only on the thickness of the gap in the narrow gap. This is a unique phenomenon that occurs because the electrical resistance of the electrodeposited film applied to the inner surface of the entrance of the narrow gap does not increase.

As a result of intensive research in view of the above results, the present inventors increased the electrical resistance by once drying the coating film on the inner surface of the entrance of the narrow gap, and further deepened the narrow gap by applying electrodeposition coating. The present invention was completed by discovering that it is possible to perform electrodeposition coating.

That is, the electrodeposition coating method of the object to be coated having a narrow gap of the present invention includes a first coating step in which the object to be coated having a narrow gap is immersed in the electrodeposition paint and the applied '7M. A first step consisting of a first drying step in which the deposited paint is dried and cured to form an electrodeposited coating film, and at least once each, a coating having a 'R electrodeposited coating film whose electrical resistance is increased in the first drying step. A second coating process in which the coating material is electrodeposited and the inner surface of the narrow gap not coated in the first coating process is coated, and a second drying process in which the tV coating film applied in the second coating process is dried and cured. The method is characterized in that the inner surface of the narrow gap, which was not painted in the first step, is painted in the second step.

The N-coated paint used in the present invention may be either an anionic type or a cationic type, but it is preferable to use a cationic type because of its superior antirust performance.

The first painting step and the second painting step can be performed in exactly the same manner as conventional electrodeposition coating, and the first drying step and the second drying step can be performed in the same manner as conventional methods depending on the conditions of the paint used.

Note that the same paint may be used in the first step and the second step, or different paints may be used. The second step can also be carried out by immersing only the narrow gap into the electrodeposited paint layer. If the second step is repeated further, the inner surface of the narrow gap can be further penetrated deeper. It can also be painted.

[Operations and Effects of the Invention] In the electrodeposition coating method of the present invention, a first step consisting of a first painting step and a first drying step is performed on an object having a narrow gap, and then a second painting step and a first drying step are performed on the object to be coated having a narrow gap. The second process consists of two drying steps.
Perform the process. In the first step, an electrodeposited coating film is formed on the inner surface of the narrow gap near the opening. This cured electrodeposited coating has a very high electrical resistance. Therefore, in the second step, the paint releases an electric charge on the inner surface of the deep part of the narrow gap where no electrodeposited film is formed, and that part is coated with N. Therefore, in the second step, the depth at which the coating film is formed on the inner surface of the narrow gap is approximately twice that of the first step.

Therefore, according to the electrodeposition coating method of the present invention, it is possible to perform electrodeposition coating deep into the inner surface of a narrow gap, improving rust prevention performance and eliminating the need to use rust prevention steel plates, sealants, wax, etc. Therefore, it is possible to reduce the cost.

[Example 1 This will be explained in detail below using examples.

(Example) Two cold-rolled steel plates of 70 mm x 150 ms + (thickness Q, 8 nm) were put together with a 200 μm thick spacer in between and held together with clips to prepare the test piece shown in FIG. 5.

First step> This test piece was coated with cationic electrodeposition paint ([PtU-3
0J (manufactured by Nippon Paint Co., Ltd.) and applied a voltage of 220
V, distance between electrodes 1501m, bath temperature 29℃, and energization time 3 minutes? Ifl painting was done. Thereafter, the drippings were removed, the coating was washed with water, and the coating film was dried and cured by baking at 180° C. for 20 minutes.

Second Step> After cooling the test piece to room temperature, electrodeposition coating and baking drying were performed under the same conditions as in the first step. When the obtained test piece was opened and the length of the coating film formed inside from the end face was measured, it was found that the coating film was formed at a length of 3Q+u from both ends.

(Comparative Example 1) A test piece similar to that in the example was prepared, and only the first step was performed to measure the coating depth. The coating film formed on the test piece was formed to a depth of 15u+ from both ends.

(Comparative Example 2) A test piece similar to that in Example 1 was prepared, and only the first step was performed in the same manner except that the current application time was 6 minutes, twice as long as in the Example. When the length of the obtained coating film was examined, it was found that the length was 15 IlltlS from both ends, and the coating properties in the gap were almost the same as in Comparative Example 1.

(Evaluation) It is clear from the comparative example that it is impossible to coat the inner surface of the narrow gap portion deeply even if the energization time for electrodeposition coating is lengthened. -6 According to the N coating method of the present invention, the depth of the coating film that penetrates into the narrow gap is about twice that of the conventional method, and electrodeposition coating can be applied to the deep inner surface of the narrow gap.

[Brief explanation of the drawing]

Figures 1 to 4 are graphs showing conventional electrodeposition coating performance in narrow gaps, Figure 1 is a graph showing the relationship between coating voltage and coating depth, and Figure 2 is a graph showing the relationship between energization time and coating depth. 3 is a graph showing the relationship between bath temperature and coating depth, and FIG. 4 is a graph showing the relationship between paint type and coating depth. FIG. 5 is a perspective view of a test piece used in Examples and Comparative Examples. Patent applicant: Toyota Motor Corporation Agent
Patent attorney Hirotoshi Okawa Patent attorney Akio Maruyama Voltage (V time (minutes) Temperature (°C) Figure 4 Figure 5

Claims (2)

[Claims] (1) A first coating step in which the object to be coated having a narrow gap is immersed in an electrodeposition paint to form an electrodeposition coating, and a first coating step in which the applied electrodeposition paint is dried and cured to form an electrodeposition coating film. a first step consisting of a drying step; and at least once each, the first coating step includes electrodepositing the object having the electrodeposited coating film with increased electrical resistance in the first drying step. a second coating process for coating the inner surface of the narrow gap that was not coated in the second coating process; and a second drying process for drying and curing the electrodeposited coating film applied in the second coating process;
A method for electrodeposition coating an object having a narrow gap, characterized in that the inner surface of the narrow gap, which was not coated in the first step, is coated in the second step. (2) The electrodeposition coating method for an object having a narrow gap according to claim 1, wherein the gap in the narrow gap is 500 μm or less.