JP3276022B2 - 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 characterized by an electrodeposition coating process.

[0002]

2. Description of the Related Art Electrodeposition is carried out by immersing an object to be coated in an electrodeposition coating solution made of a water-soluble resin coating and then passing a direct current between the object and the other electrode. The coating is formed by depositing a resin coating on the surface of the object to be coated.

However, when a large voltage is applied to a large object such as an automobile body by applying a required voltage to the object and the tank is immersed in the liquid, a part immersed in the liquid and a part not immersed in the liquid are separated. Non-uniformity of electric resistance occurs during this time, which causes a difference in electrolysis, resin paint unevenly deposits, and washing and baking after electrodeposition coating causes coating defects such as pinholes, When a film such as a pretreatment chemical liquid is formed on the surface of the electrodeposition coating liquid, there is a problem that a pattern of the film is formed on the surface of the object to be coated.

In order to solve such a problem, the method disclosed in Japanese Patent Application Laid-Open No. 61-87898 discloses a method in which a mixture of ultrafiltration liquid and pure water is applied to the surface of an object to be coated immediately before entering the tank. After spraying the aqueous solution, it is made to enter the tank in a non-energized state or a state of applying a low voltage, and then the pressure is increased to a predetermined voltage.In such a method, the electrodeposition liquid in the tank is In addition to being diluted by an aqueous solution or the like, there is a problem that a large amount of cost is required for a control device for multi-stage current supply.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem.
An object of the present invention is to provide a new electrodeposition coating method capable of easily and reliably forming a uniform coating film on the surface of an object to be coated without any adverse effect on the electrodeposition coating liquid itself.

[0006]

That is, the present invention provides an electrodeposition coating method for achieving the above object by applying an electrodeposition coating method to a surface of an object to be coated immediately before entering the electrodeposition coating tank. A step of applying a liquid to impart wettability, and reducing the solid content to about 0.5% on the surface of the object to be coated immediately after being discharged from the tank.
And a spraying step of the suppressed ultrafiltrate .

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The drawings show an example of an apparatus applied to the electrodeposition coating method of the present invention.

In the drawing, an object W to be coated suspended by a hanger 3, that is, an automobile body in this embodiment, is placed in the electrodeposition coating tank denoted by reference numeral 1.
A work transport conveyor 4 for sequentially immersing the workpieces is extended.

At the entrance of the electrodeposition coating tank 1 on the work loading side, showers 7 are provided on both sides of the work transfer conveyor 4 so as to sandwich the work transfer conveyor 4, and these showers 7
One outlet of the pump 6 for circulating the electrodeposition coating liquid and the supply pipe 8
The electrodeposition coating liquid in the tank 1 is sprayed from a small hole provided on the peripheral surface of the shower 7 over the entire surface of the workpiece W which has been conveyed to the position immediately before entering the tank. Prior to being immersed therein, the entire surface of the workpiece W is made wet with the electrodeposition coating liquid.

The electrodeposition coating tank 1 also includes an object W to be coated.
A shower 10 is also provided on the outlet side of the work so as to sandwich the work transport conveyor 4, and an ultrafiltrate from an ultrafilter 12 disposed via a liquid supply pump 11 is supplied to the supply pipe 13. Through the small holes of the shower 10 to discharge 30 to 100 l of the ultrafiltrate per minute to the surface of the object W to be coated, Is removed, and the electrodeposition coating liquid remaining on the surface is wiped off and returned to the tank 1.

On the other hand, one or a plurality of dip rinsing tanks 15 are provided on the lower side of the electrodeposition coating 1, and the workpiece W passing through the electrodeposition coating tank 1 is transferred to the dip water of the dip rinsing tank 15. It is configured to be immersed and washed.

Reference numeral 5 in the drawing denotes an energizing busper disposed along the work transport conveyor 4 to apply a required voltage to the workpiece W.

Next, a description will be given of an electrodeposition coating method performed by using the above-configured apparatus. First, when the workpiece W suspended and supported by the hanger 3 is sent into the electrodeposition coating tank 1 by the work transport conveyor 4, the shower 7 provided at the entrance portion on the loading side is moved to the position immediately before entering the tank. In the above, the electrodeposition coating liquid in the tank 1 is uniformly applied as a mist to the surface of the workpiece W to give wetness.

The amount of the electrodeposition coating liquid to be applied must be such that the surface does not dry even when moisture is evaporated by Joule heat. When a voltage is applied, the electric resistance of the surface is made uniform, the uneven deposition of paint between the immersed portion and the unimmersed portion immediately after entering the tank is suppressed, and regardless of the application of the voltage, In addition, impurities adhering to the surface of the workpiece W are removed, and defects in the electrodeposition coating caused by the impurities are suppressed beforehand. Next, the object to be coated W is immersed in the coating tank 1 for a certain period of time, and when the object W comes out of the tank, the shower 10 arranged on the unloading side causes the surface of the object to be coated W to have a solid content Of ultrafiltration liquid with the concentration reduced to about 0.5% to remove impurities that may cause defects in electrodeposition from the surface of the workpiece W, and at the same time, surplus electrodeposition coating adhered to the surface. The liquid is wiped off and returned to the electrodeposition coating tank 1.

Thereafter, the object to be coated W is immersed in the dip rinsing tank 15 and subjected to a required rinsing treatment in the same manner as in the conventional method.

[0016]

As described above, according to the present invention, since the electrodeposition coating liquid is applied to the surface of the object to be coated immediately before entering the tank to impart wettability thereto, the electric resistance of the surface is improved. To prevent uneven deposition of paint between the immersed part and the unimmersed part that occurs immediately after entering the tank, and also prevent the occurrence of coating defects due to impurities attached to the surface of the workpiece. Can be.

In addition, a solid substance
Foam solid upon ultrafiltrate by blowing, dip rinsing after electrodeposition painting the content was holding about 0.5%
To prevent agglomeration with the object as a nucleus
Eliminates problems such as dot-like unevenness
Enables finishing as a painted surface.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus applied to a method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electro-coating tank 4 Work conveyor 7, 10 Shower 12 Ultrafilter 15 Dip washing tank

Claims (1)

(57) [Claims] 1. A step of applying an electrodeposition coating liquid in the tank to the surface of the object to be coated immediately before entering the electrodeposition coating tank to impart wettability, and the step immediately after leaving the tank from the tank. Solid on the surface of the workpiece
Sprays ultrafiltrate with the content of substances reduced to about 0.5%
That process consists of the electrodeposition coating method.