JPS59193164A - Electrostatic painting device - Google Patents

Abstract

PURPOSE:To enable electrostatic painting of a material to be coated having a high electric resistance value by providing an electrode on the rear of said material and impressing the high voltage of the potential, reverse to the potential of the high voltage to be impressed on a painting machine on said electrode. CONSTITUTION:A corona discharge electrode 11 is provided on a rear 1B side facing a painting machine 4 via a resin plate 1, and the electrode 11 is connected via a high-voltage cable 12 to a high-voltage generator 13 for reverse potential. The generator 13 increases a commercial voltage to the DC high voltage of the potential reverse from the potential of a high-voltage generator 10, impresses the same on each corona pin 11A and forms an ionizing region A of plus ions by discharging corona from the tips of the pins 11A toward the rear 1B of the plate 1. Therefore the electric charge electrified on the front 1A surface of the plate 1 attenuates and the surface potential of the plate 1 is made to roughly the earth potential so that the electrified particles of the sprayed paint stick efficiently on the plate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a .mu. electrostatic coating apparatus which enables good electrostatic coating even on objects having a high electrical resistance value.

In general, electrostatic coating equipment has a minus 30 to 90
By applying a high voltage of about kV and keeping the object to be coated at ground potential, an electrostatic field is formed between the coating machine and the object to be coated, and by supplying paint to the coating machine, The paint is atomized and the atomized paint particles are electrically charged, and the charged paint particles fly along the electrostatic field and are applied to the object to be coated.

By the way, in such an electrostatic coating device, if the object to be coated is a good electrical conductor such as a metal body, the object to be coated is always held at ground potential, so the electrostatic coating is applied over the entire circumference of the object. It is possible to perform coating with sufficiently high effectiveness.

However, the surface of the object to be coated is an electrically poor conductor, that is, materials with high electrical resistance such as various synthetic resins, glass, ceramics, and wood (hereinafter referred to as "synthetic resins").
, or if the surface of the metal plate is treated with these synthetic resins, set the object to be coated at ground potential so that negatively charged paint particles will adhere to it. Therefore, the electric charge given by the paint particles does not escape to the ground, and the surface of the object to be coated becomes saturated with static electricity and becomes negatively charged. This means that no electrostatic effect can be obtained.

That is, the principle of electrostatic painting is that in a state of high electrical potential, there must be a potential difference between the surface of the object to be coated and the paint particles or the tip of the atomizer. The reason why this potential difference is not maintained until the painting is completed is, firstly, because a sufficiently large electrical attraction is exerted between the charged paint particles and the surface of the object to be coated, and secondly, because the charged paint This is to form strong lines of electric force acting on the paint particles in order to transport the particles from the coating machine to the surface of the object to be coated. However, the fact that the electrical resistance of the surface of the object to be coated, such as that of synthetic resin materials, is high means that the above two factors that act on paint particles cannot be obtained sufficiently. This means that the dielectric constant of the object to be coated has a strong influence on the surface condition of the object, which hinders the adhesion of paint particles.

For this reason, in the conventional technology, when applying electrostatic coating to synthetic resin materials, a conductive treatment liquid, which is a type of antistatic agent, is applied in advance to cover the surface of the synthetic resin with a conductive coating film. Then, electrostatic coating was performed by spraying charged paint particles', and the coated object was then placed in a baking oven and baked. Here, as the conductive treatment liquid, for example, a conductive treatment agent consisting of a hydrophilic ionizable organic compound (trade name: "Alkalyt 726J" manufactured by General Mills, USA) whose main component is an aliphatic quaternary ammonium salt is used. A solution diluted with about .5% Inglobilur Q:7 is used, and this conductive treatment liquid is sprayed onto the surface of the synthetic resin using a sprayer; or a conductive film is formed on the surface of the synthetic resin by a depping process. Was.

This conductive film is usually applied to a thickness of about 0.1 Cμm, and absorbs moisture in the air by the action of the hydrophilic ionizable organic compound contained in the conductive treatment liquid, thereby making it easier to absorb moisture. It was designed to maintain the electrical conductivity of the synthetic resin surface.

However, in the conventional technology described above, as described above, moisture in the air is absorbed and thereby the conductivity of the synthetic resin surface is maintained. The humidity inside is generally 20℃ and 40℃.
% or more is required. As a result, the method according to the above-mentioned prior art is subject to restrictions on the humidity of the coating atmosphere, and has the disadvantage that the coating efficiency is inferior to that in the case of coating metal materials even under the same conditions during the extremely dry winter season when humidity is low. On the other hand, if the humidity is too high, a large amount of water will enter between the surface of the object to be coated and the paint film, impairing the adhesion of the paint film.

Particularly in paint booths where temperature and humidity are not controlled, products produced during the rainy season often have the disadvantage of poor adhesion of the paint film. Furthermore, since the conductive treatment liquid uses ionizable organic compounds, spraying it in large quantities can cause pollution, and workers must be careful when handling it. ′ is there. Furthermore, there is a drawback that the application of the conductive treatment liquid tends to cause rust on peripheral equipment. From these points, the coating equipment using the conductive treatment liquid mentioned above requires a dog-like coating booth and an unmanned automatic pre-treatment coating machine in order to be used effectively. There is a problem.

The present invention was developed by focusing on the drawbacks of the electrostatic coating equipment for poor conductors using the conventional conductive treatment liquid described above. In addition, it is possible to maintain a constant potential difference between the surface of the object to be coated and the coating machine side, thereby making it possible to electrostatically coat objects with high electrical resistance. The purpose is to provide coating equipment.

In order to achieve the above-mentioned object, the electrostatic coating device according to the present invention includes a coating machine that sprays a coating material onto the surface of an object to be coated that has a high electrical resistance value, and a high voltage that is at a negative potential for coating. a high voltage generator for applying a high voltage, an electrode disposed on the back side of the object to be coated, and a high voltage generator for a reverse potential that applies a high voltage at a potential opposite to that of the coating machine to the electrode. Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 1 shows a first embodiment of the present invention. In the figure, l is a resin plate (hereinafter referred to as a resin plate) made of a synthetic resin material as an object to be coated, and the resin plate l is The resin plate 1 is suspended from a conveyor 3 which is at ground potential via a hanger 2, and the resin plate 1 is kept at approximately ground potential before the start of coating. Reference numeral 4 denotes a coating machine for electrostatically coating the front surface LA of the resin plate 1, and the coating machine 4 is attached via an insulating arm 5 to a registration locator 6 so as to be movable up and down. Further, the coating machine 4 is connected to a paint pump 8 via a paint hose 7, and is also connected to a high voltage generator IO via a high voltage cable 9. Here, the high voltage generator 101d is configured to step up the commercial voltage to, for example, -90 [kV] DC high voltage and apply it to the coating machine 4.

In addition, a corona discharge electrode is provided on the back side lB facing the coating machine 4 with the resin plate 1 in between.
1A, . . . , each corona bottle IIA has a resin plate l
The rear surface IB is arranged at a predetermined interval in the vertical direction in order to enable corona discharge, and its tip is located at a distance of, for example, about 1 ocrn from the resin plate 1.

The electrode 11 is connected to a high voltage generator 13 for reverse potential via a high voltage cable 12. Then, the high voltage generating device 13 for reverse potential converts the commercial voltage into a double-current high voltage having a potential opposite to that of the high voltage generating device 10, for example, +
The pressure is increased to 30 [kV':l and applied to each corona bottle IIA, so that the voltage of the corona bottle IIA can be increased.

In order to perform coating using the coating apparatus configured as described above, first, -90 [
kV:] is applied to the coating machine 4, and then a predetermined amount of coating material is supplied from the coating f-1 pump 8. As a result, the paint particles electrostatically atomized or air atomized by the atomizer 4 are negatively charged by the high voltage r applied to the atomizer 4,
It flies along the lines of electric force formed between the resin plate l,
Coat the front surface IA of the resin plate 1.

However, due to the negatively charged paint particles, the front IA side of the resin plate 1, which has a large electrical resistance value, becomes electrostatically saturated from the ground potential to a negative value one after another. However, a corona discharge electrode 11 is provided on the back surface IB of the resin plate 1 which faces the coating machine 4 with the resin plate 1 in between, and a high voltage generator 13 for reverse potential is connected to the corona discharge electrode 11. Therefore, corona discharge occurs from the corona bottle IIA to the resin plate l, and the back surface IB of the resin plate l is exposed to the positive ionization zone A.

As a result, the charge on the front IA surface of the resin plate 1 is attenuated, and the surface potential of the resin plate 1 appears to be near earth potential. Therefore, an effective potential difference is maintained between the coating machine 4 and the coating machine 4, and the charged particles of the paint sprayed from the coating machine 4 efficiently adhere to the resin plate 1.

Next, FIG. 2 shows a second embodiment of the present invention, in which the same components as those in FIG. 1 are designated by the same reference numerals and their explanations will be omitted.

However, this embodiment is characterized in that an electric field generating electrode 21 is used in place of the corona discharge electrode 11 used in the above-mentioned embodiment of FFJ 1. That is, the electric field generating electrode 21 is constructed by shielding the entire surface of the electrode pin 21A with a dielectric material 22 such as synthetic resin. With this, when a positive high voltage is applied from the high voltage generator 13 for reverse potential via the high voltage cable 12, corona discharge etc. will not be generated from the electric field generating electrode 21. An electrostatic field E is formed between it and the resin plate 1.

Even with the above-mentioned configuration, the electric charges on the front LA coating surface of the resin plate 1 are attenuated by the action of the electrostatic field E, so that the connection between the front LA coating of the resin plate 1 and the coating machine 4 A predetermined potential difference can be maintained between them, and in this state, electrostatic painting can be efficiently performed by the coating machine 4.In addition, in each of the above-mentioned embodiments, the high voltage generator IO generates a negative high voltage. The explanation has been made assuming that the high voltage generating device 13 for reverse potential is configured to apply a high voltage of 1 to 1 to the coating machine 4 and to the corona discharge electrode 11 or the electric field generating electrode 21. 4 may be made of a glass, and a negative high voltage may be applied to each electrode 11.21. In addition to the above-mentioned coating machine 4, a rotary atomization type or an air atomization type can be used. Furthermore, although the resin plate l is configured to be kept at ground potential before the start of painting, it is possible to apply a reverse potential high voltage to the electrodes at the same time as before the start of painting. There is no need to maintain it at a ground potential. On the other hand, in the first embodiment, a skewer-shaped corona pin IIA is used as the corona discharge electrode 11, but a needle-shaped, net-shaped, etc. can also be used instead.

When a needle-shaped corona pin is used, the electrode thereof may be installed in a registration locator, and the registration locator may be moved up and down together with the coating machine 4. Furthermore, the electric field generating electrode 21 may be of the second type described above.

As explained in detail above, the electrostatic coating device according to the present invention has an electrode provided on the back side of the object to be coated, and applies a high voltage having an opposite potential to the high voltage applied to the coating machine to the electrode. Because of this structure, the charge on the surface of the object to be coated can be attenuated by the action of the ionization sphere generated by the electrode or the electrostatic field formed between it and the object to be coated. A constant potential difference can be maintained between the surface of the object to be coated and the coating machine, and the electrostatic coating by the coating machine can be effectively performed. Therefore, unlike the prior art, there is no need to apply the conductive treatment liquid to the object in advance, and therefore the disadvantages inherent in the prior art do not occur.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an electrostatic coating apparatus according to a first embodiment of the invention, and FIG. 2 is a partial system diagram of an electrostatic coating apparatus according to a second embodiment of the invention. ■...Object to be coated, 4...Painting machine, 8...Paint pump, 10...High voltage generator, 11...Corona discharge electrode, 11A...Corona pin, 13...Reverse Potential high voltage generator, 21... Electric field generating electrode, 21A... Electrode pin, 22... Dielectric, A... Ionization sphere, E.
...Electrostatic field.

Claims (3)

[Claims] (1) A coating machine that sprays paint onto the surface of an object to be coated that has a high electrical resistance value, a high voltage generator that applies a high voltage at a potential of - to the coating machine, and a high voltage generator that applies a high voltage at a potential of - to the coating machine; An electrostatic coating device comprising an electrode disposed on the back side, and a high voltage generator for a reverse potential that applies a high voltage at a potential opposite to that of the coating machine to the electrode. (2) The electrostatic coating apparatus according to claim (1), wherein the electrode is a corona discharge electrode that forms an ionization sphere between the electrode and the object to be coated. (3) Claim (1) wherein the electrode is an electric field generating electrode that forms an electric field between the electrode and the object to be coated.
The electrostatic coating device described in Section 1.