JPH03275167A - Electrodeposition coating method - Google Patents

Abstract

PURPOSE:To avoid a coating defect based on the presence of bubbles by repeating introduction and takeout of the material to be coated into/from an electrodeposition coating tank and discontinuously performing electrodeposition coating and conducting electricity while the material to be coated is brought into contact with the electrodeposition coating tank in the interval to takeout of the material from initial introduction thereof. CONSTITUTION:In the case of coating the material 6 to be coated by electrodeposition, electrodeposition coating is discontinuously performed by repeating introduction and takeout of the material 6 to be coated into/from an electrodeposition coating tank 2 at two times at the minimum. However, electricity is conducted at least while the material 6 to be coated is brought into contact with the tank 2 in the interval to final takeout from initial introduction from/ into the tank. As a result, at a time of electrodeposition coating, since not only stagnation of air and bubbles but also fine bubbles are removed from the surface of the material to be coated, a coating defect based on these bubbles is avoided. Therefore, even when the whole coated film is made thin, generation of pinholes is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrodeposition coating method, and more particularly to an electrodeposition coating method that is free from coating defects caused by microbubbles on the surface of an object to be coated. Therefore, the present invention can be widely and advantageously used for electrodeposition coating of various objects to be coated, including automobile bodies and automobile parts.

[Conventional technology]

As is well known, in electrodeposition coating, the object to be coated is immersed in an electrodeposition paint tank, and the paint in the tank is deposited on the surface of the object by electrodeposition. This coating is widely used, for example, to form a base coating film when painting automobile bodies. By the way, when applying this coating to objects with complex shapes, the air may not be sufficiently degassed and air may remain in that area, which cannot be contacted with the electrodeposition liquid and not be coated, or electrodes may occur on the surface of the object. The gas produced by the reaction (mainly due to electrolysis of the solvent) is
This may form gas pockets and disturb electrodeposition, leading to non-uniform coating film thickness, which in turn may cause poor appearance and reduced corrosion resistance of the product. For this reason, conventionally, when storing objects to be coated in a work pallet, it was necessary to adjust the storage direction in consideration of the above points or to create a special jig. In addition, in order to solve these problems that hinder productivity or quality control, Japanese Utility Model Application Publication No. 58-176965 proposes that a work pallet containing objects to be coated be shaken in an electrodeposition paint tank. It has been proposed that the non-uniformity of the electrodeposition coating film can be eliminated by this method. That is, the electrodeposition coating apparatus described in the above publication includes an electrodeposition paint tank, (1) (2) a main body installed on the side of the electrodeposition paint tank, and a frame arranged on the main body so as to be movable up and down. and a hanger held on the frame, a rail is provided at the tip of the frame, and the hanger is configured to be movable and swingable along the rail, and the frame and the hanger are configured to be movable and swingable along the rail. The present invention is characterized in that an actuator is provided between the hangers to swing the hangers.

The principle of bubble removal by the above-mentioned workpiece rocking method is shown in FIG. 4 when it is simply illustrated.

That is, when preparing a workpiece (object to be coated) 6 as shown in FIG. 4(A) and performing electrodeposition coating,
As shown in B), air pocket 10
Air bubbles 11 are often generated. therefore,
Conventionally, as described in the above-mentioned publication, the workpiece 6 is stored on a pallet (not shown) and then rocked as shown in FIG. 4(C). Then, as shown in the figure, the air pockets and bubbles move and separate, and finally, as shown in FIG. 4(D), a bubble-free state is achieved, and good electrodeposition coating can be performed.

In addition, conventional electrodeposition coating using this workpiece rocking method,
If this is illustrated in a Seikl diagram, it is as shown in FIG. 5 at −r. That is, prior to electrodeposition coating, water washing (washing with pure water) is performed in a pure water bath for a predetermined period of time.
After taking out the workpiece from the bath, immerse it in an electrodeposition paint bath.
Electrodeposition coating is performed while electricity is applied. At this time, the workpiece is oscillated for a predetermined period of time. After electrodeposition coating, the workpiece is washed with water again, but this time it is for recovery purposes.

After washing and drying, the workpiece is subjected to the next process, such as intermediate coating.

By the way, when performing electrodeposition coating, in addition to the air bubbles that adhere to the surface of the object to be coated from the beginning as described above, there is also a problem of microbubbles that are generated during the electrodeposition coating process. Such microbubbles cannot be completely removed by simply shaking the object to be coated or simply repeatedly dipping it, and if they remain, it is impossible to avoid the formation of pinhole-like uncoated areas.

These microbubbles are thought to be due to the adsorption of air bubbles when the object to be coated enters the tank (3) (4) and insufficient release of hydrogen gas generated on the surface of the object during electrodeposition coating, and the resulting Preventing contact with objects. In the prior art, these microbubbles are removed by stirring the paint tank, but when the objects to be coated are packaged next to each other, the effect of stirring the paint is extremely small, and other solutions are needed.

[Problem to be solved by the invention]

Therefore, an object of the present invention is to provide an improved electrodeposition coating method that does not cause coating defects caused by microbubbles during electrodeposition coating even if microbubbles are present on the surface of the object to be coated. It is in.

[Means to solve the problem]

According to the present invention, the above-mentioned problem can be solved by intermittent electrodeposition coating by repeating the loading and unloading of the coating object into and out of the electrodeposition paint tank at least twice when applying electrodeposition coating to the coating object. However, the solution is to use an electrodeposition coating method that is characterized by keeping the current flowing at least while the object to be coated is in contact with the electrodeposition paint tank, from the first entry into the tank until the final exit from the tank. can do.

In addition, in the method of the present invention, in order to solve the problem, there is no need to use complicated operations like the conventional workpiece rocking method.

[For production]

When electrodeposition coating is performed as in the present invention, paint flows on the surface of the object to be coated, and furthermore, by exposing the object to the atmosphere, microbubbles adsorbed to the object move and move. It is thought that it can be removed. Therefore, according to the present invention, defects such as pinholes do not occur even if the overall thickness of the electrodeposition coating film becomes thin.

[Example] In carrying out the present invention, electrodeposition coating is carried out as described above: (1) immersing the object to be coated in at least two same-type coating tanks and performing electrodeposition coating each time; and (5) (6) ) ■ It is important that electricity is applied at least while the object to be coated and the electrocoating paint tank are in contact. Here, the electrodeposition coating itself can be performed using, for example, a cationic electrodeposition paint according to a technique commonly used in this technical field. Although the time required for the entire electrodeposition coating, that is, the current application time, may vary depending on the shape and size of the object to be coated and other factors, it is usually about 5 minutes to 20 minutes. The time for each electrodeposition coating is 2 minutes + 2 minutes, 1 minute +
The duration may be equal, such as "1 minute" - 1 minute, or may be varied, such as 5 minutes + 4 minutes + 3 minutes. The time period during which the object to be coated is left out of the tank can also be changed as appropriate.

The electrodeposition coating of the present invention, including pre-treatment and post-treatment, can be performed in the order shown in the block diagram in FIG. 1, for example. The first step is the degreasing process. This process is
For example, place the object to be coated in an alkaline degreasing tank with a bath temperature of 50°C for 4 hours.
This can be done by soaking for minutes. It is common to repeat the 2-minute soak twice. Next, the object to be coated is washed with water. This treatment can be carried out by first immersing the object to be coated in industrial water at a bath room temperature for 4 minutes (2 minutes x 2 steps), and then immersing it in pure water at a bath room temperature for 2 minutes. can. After washing with water, the object to be coated is subjected to chemical conversion treatment. This treatment can be carried out, for example, by immersing the object to be coated in a zinc phosphate bath at a bath temperature of 35° C. for 5 minutes. Subsequently, although not shown in FIG. 1, it is common to add a surface conditioning (tone) treatment between the chemical conversion treatment and the electrodeposition coating. This can be done, for example, by immersing the object to be coated in a bath at bath temperature for 2 minutes. Next, perform electrodeposition coating. Although FIG. 1 shows a combination of first, second, and third electrodeposition coatings, other combinations can of course be used as desired. This coating is carried out using, for example, a cationic electrodeposition paint bath with a bath temperature of 28°C, and a voltage of 300V for the first immersion for 5 minutes and the second immersion for 5 minutes.
This can be done with a second immersion for 4 minutes and a third immersion for 3 minutes.

(7) (8) Next, the object to be coated after electrodeposition coating is washed with pure water.

This water washing is for recovering the object to be coated, and can be performed, for example, in pure water at a bath room temperature for 6 minutes (2 minutes x 3 steps). The final drying process is
For example, this can be done by passing the object to be coated through a drying oven at 200° C. for 50 minutes.

Moreover, the electrodeposition coating of the present invention can be performed using equipment as shown in FIG. The object 6 to be coated after the chemical conversion treatment is immersed in the preparation tank 1 to condition the surface. A drop lifter 4 is used for the loading/unloading tank for the objects 6 to be coated. After the surface preparation is completed, the object to be coated 6 is taken out of the tank by a drop lifter 4 and transferred to an electrodeposition coating process by a pusher 5. In the electrodeposition coating process, the object to be coated 6 is moved using the drop lifter 4 as in the previous process.
is immersed in the electrocoating paint bath 2, and electrocoating is repeated according to a predetermined schedule. After the coating is completed, the object 6 to be coated is immersed in a pure water tank 3 for recovery and washing, and then passed through a drying oven 7 to complete a series of electrodeposition coating steps. Note that, as shown in the figure, continuous electrodeposition coating is possible in the present invention.

Next, the present invention will be explained with reference to Examples and Comparative Examples. The objects to be coated used in this example are shown in Figure 4 (A).
This is a section steel having a shape as shown in FIG. 1, and was subjected to pretreatment of degreasing, water washing, chemical conversion treatment, and surface conditioning under the conditions described above with reference to FIG.

Electrodeposition coating was applied to the object using the cycle shown in FIG. The main coating conditions are shown below: Electrodeposition paint...Cationic electrodeposition paint bath (bath temperature 28°C) Total immersion time of the object to be coated...5 minutes Current application time...5 minutes Applied voltage... 340■ Rocking time: 3 minutes Rocking speed: 10°/10 seconds Number of swings: 2 times on the left, 2 times on the right After completion of painting, under the conditions described above with reference to Figure 1. The object to be coated was collected, washed with water, and dried. When the obtained painted product was evaluated for the occurrence of unpainted dots on each side (Side A, (9), (10), B and C sides shown in Figure 4 (A)), the following results were found: The results shown in Table 1 were obtained.

Electrodeposition coating was performed on the object to be coated according to the cycle shown in Figure 3 (B). The main coating conditions are as follows: Electrodeposition paint...Cationic electrodeposition paint bath (bath temperature 28°C) Total immersion time of coated object...
4 minutes (2 minutes x 2) Current application time: 5 minutes Applied voltage: 340V Oscillation: None After the painting is completed, collect the object to be coated and wash it with water under the conditions described above while referring to Figure 1. and dried. The obtained coated product was evaluated for the occurrence of dotted unpainted areas in the same manner as in Example 1, and the results shown in Table 1 below were obtained.

``Koyu'' - Ichimugi Example 2 8~143~612~18 ... Occurrence location per 100c+fl of painted surface As can be understood from the results in Table 1 above, according to the present invention, the removal of microbubbles can be greatly improved. Therefore, the occurrence of dotted unpainted areas can be significantly reduced. This is because microbubbles have stronger adsorption force than buoyancy.
This can be said to be a very groundbreaking effect.

The procedure described in Example 1 above was repeated until the mosquito spotting was completed. However, in this example, no rocking was performed. By the way, the coating thickness on the outside is 3.
5, that of the inner surface was 25 pWl.

Each side of the obtained coated product (A shown in Figure 4 (A)
When evaluation was made regarding the occurrence of dotted unpainted areas on surfaces (A side, B side, C side, A side, B side, and C side), the results shown in Table 2 below were obtained.

(11) (12) Jun J The procedure described in Example 2 above was repeated one more time.

By the way, the paint film thickness on the outside is 30 marks, and that on the inside is 23.
It was n. The obtained coated product was evaluated for the occurrence of unpainted dots in the same manner as in Example 3, and the results shown in Table 2 below were obtained.

Electrodeposition coating was performed on the object to be coated according to the cycle shown in Figure 3 (A). The main coating conditions are shown below: Electrodeposition paint...Cationic electrodeposition paint bath (bath temperature 28°C) Total immersion time of the object to be coated...
3 minutes (1 minute x 3) Current application time: 5 minutes Applied voltage: 340V Oscillation: None Paint film thickness on outside surface: 24 mark Paint film thickness on inner surface: 18 mark Painting completed Thereafter, the coated object was recovered, washed with water, and dried under the conditions described above with reference to FIG. The obtained coated product was evaluated for the occurrence of dotted unpainted areas in the same manner as in Example 3, and the results shown in Table 2 below were obtained.

Occurrence of dotted unpainted areas on heat surface Example 3 (comparative example) × × △ × 0 Example 4
△ ■ △ ■ ○ Example 5 00000 0... Locations of occurrence per 100c% of painted surface ○... Not occurring, ■... Occurring in 1 to 10 locations Δ... 11...
30 (occurred in tlil places, ×...occurred in 30 or more places) As can be understood from the results in Table 2 above, as in the case of Table 1 above, according to the present invention, microbubbles can be completely removed. Therefore, the occurrence of dotted unpainted areas can be significantly reduced.

〔Effect of the invention〕

According to the present invention, during electrodeposition coating, not only air pockets and bubbles (even microbubbles) are removed from the surface of the object to be coated, so that coating film defects (13) (14) caused by the presence of such bubbles are eliminated. Therefore, pinholes and the like do not occur even if the overall film thickness becomes thinner.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a preferred example of the process for electrodeposition coating according to the present invention, FIG. 2 is a layout diagram showing a preferred example of equipment for electrodeposition coating according to the present invention, and FIG. A cycle diagram showing a preferred cycle example of electrodeposition coating, Figure 4 is a schematic diagram showing the principle of bubble removal using the conventional workpiece rocking method, and Figure 5 is a cycle diagram of a conventional electrodeposition coating. It is a cycle diagram showing an example. In the figure, 1 is a preparation tank, 2 is an electrodeposition paint tank, 3 is a pure water tank,
4 is a drop lifter, 5 is a pusher, and 6 is an object to be coated. (15) Process of electrodeposition coating according to the present invention Figure 1

Claims (1)

[Claims] 1. When electrocoating the object to be coated, the electrodeposition coating is carried out intermittently by repeating the insertion and removal of the object into and out of the electrodeposition paint tank at least twice; An electrodeposition coating method characterized in that electricity is kept on at least while the object to be coated is in contact with the electrodeposition paint tank from the time until the final discharge from the tank.