JPS642429B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a planar silent discharge electrode for generating positive and negative ions over one surface, and more specifically, an insulator is provided between a pair of electrodes having different polarities. This invention relates to an intervening planar silent discharge electrode.

An electrostatic powder coating apparatus includes a conventional discharge electrode, for example, a discharge electrode that applies a DC voltage to the tip of an injection gun to generate an ionic current there.

In a conventional electrostatic powder coating apparatus, as shown in FIG. 1, paint powder suspended in the air is discharged from a powder storage tank 192 by compressed air 191 or the like from an injection gun 190 that is placed opposite to and separated from an object 196 to be coated. body 1
94 is ejected from the gun's discharge port 195, and at the same time, a high-voltage DC voltage is applied to the gun's discharge port 195 from the power supply 193 to cause a corona discharge from the gun's tip 195. Powder 194 existing in the painting space using electric lines of force and ion current due to corona discharge.
is charged and the paint powder is transferred to the surface of the object to be coated 196 by Coulomb force due to the electric field existing between the tip 195 of the gun and the object to be coated 196, as shown at 199 in FIG. The usual method is to form a coating powder layer and then bake it by means such as heating to obtain a coating film.

FIG. 2 shows a cross-sectional view taken along plane 198 of the conventional electrostatic powder coating apparatus described in detail with respect to FIG. 1 above. That is, in the conventional electrostatic powder coating method, as shown in the second figure, the gun 195
-1, the current flowing through the gun is concentrated at the front of the gun as shown in the current distribution curve 206, so the coating powder layer 199 becomes thicker at the front of the gun, and as it moves away from the front. It becomes thinner.
Therefore, it is difficult to obtain a uniform coating layer unless the gun is moved. Secondly, as a result of the concentration of current in front of the gun, with the high electrical resistance powder coatings currently in use, the coating layer in the center becomes thicker than the coating thickness can be obtained in the peripheral areas. Since the voltage drop of the ion current exceeds the spark voltage of the powder bed, a reverse ionization phenomenon as shown at 205 occurs in the powder bed, creating small pores in the powder bed, resulting in rough skin and pinholes. For other powder coating methods, this can cause fatal defects.

Because the current and electric field are concentrated in front of the gun, and because corona discharge occurs from the tip of the gun, there is a significant concentration of electric field in this area, and the so-called gradient force causes the powder layer to close to the tip of the gun. It sticks to the legs where the electric field is concentrated, changing the gun's voltage and current characteristics, and it is impossible to stably manage the painting process unless you frequently interrupt the painting process and clean the tip of the gun. Conventional powder coating methods have one major drawback: Furthermore, in conventional powder coating methods, once the physical shape of the gun is determined, the current obtained at that time is always uniquely determined when the voltage to be applied to the gun is determined, and it varies depending on the properties of the powder. It is not possible to select voltage and current independently, which hinders the improvement of coating performance.

The present invention solves all the drawbacks of the electrostatic powder coating method using the conventional powder coating gun described in detail above, and makes it possible to obtain an extremely good coating film without pinholes, rough skin, etc. The present invention provides a planar silent discharge electrode that has good film thickness uniformity and can be used as an innovative electrostatic powder coating device that can be operated continuously for a long period of time.

In the present invention, a plate-shaped electrode is embedded in a plate-shaped insulator, a linear electrode is provided exposed on the surface of the plate-shaped insulator, and a space between the periphery of the linear electrode and the surface of the plate-shaped insulator is provided. This is a planar silent discharge electrode characterized by forming a space for generating silent discharge.

An embodiment of the present invention will be described below with reference to the accompanying drawings. Here, a planar silent discharge electrode of an electric discharge coating apparatus will be explained.

Note that the same drawing symbols have the same names and functions.

A plate-shaped electrode 1 is embedded in a plate-shaped insulator 2, and a linear electrode 3 is exposed and provided on the surface of the plate-shaped insulator 2.

Connecting one end of an AC power source 6 to the linear electrode 3,
The other end is connected to the plate-shaped electrode 1 and grounded via a conductor 8 via a DC power source 7. F is a space for generating a silent discharge between the periphery of the linear electrode 3 and the surface of the plate-shaped insulator 2. In FIG. 4, the planar silent discharge electrodes S are spaced apart from each other in parallel to the object 10 with a space 18 in between.
In this case, the object to be coated 10 is a flat object. now,
The paint powder 11 is fed into a duct 15 little by little by a paint supply device 12, and this duct 15 is connected to a dust collection port 16 and a duct 13 by a fan 17.
The paint is supplied to the coating space 18 in a suspended state in gas by the conveying air flowing through a closed circuit constituted by the duct 14 and the duct 14.

When a high AC voltage is applied between the plate electrode 1 and the linear electrode 3 by the AC power source 6, AC electric lines of force that are convex toward the outside of the planar silent discharge electrode S are created between the plate electrode 1 and the linear electrode 3. A3 occurs, and when the density of the electric lines of force, that is, the electric field strength of this alternating electric field on the surface of the planar silent discharge electrode S, becomes higher than the spark voltage of the gas existing in the vicinity, this planar silent discharge A silent discharge now exists over the entire surface of the electrode S. That is, in this state, positive and negative ions and electrons become plasma and exist all over the surface of the planar silent discharge electrode. Therefore, the conductor 8 is connected by the DC power source 7.
When the potential of the planar silent discharge electrode is kept high through the conductor 9 and the object to be coated is grounded at the same time, the plasma existing on the surface of the planar silent discharge electrode has a specific polarity. Only positive or negative ions are selectively extracted and travel toward the object 10 as shown by arrow 5. In this process, the powder is supplied from the coating powder supply port 15 and sucked onto the surface of the object 10 to form a coating powder layer 19. In this case, painting space 1
Since the lines of electric force existing at 8 are uniform electric fields directed from the planar silent discharge electrode toward the object 10 to be coated,
The coating powder flowing onto the surface of the object 10 and the current density distribution of the current caused by the ion current are extremely uniform, and therefore, an extremely uniform coating layer 19 is formed on the surface of the object 10 in just a few seconds. be done.

The first feature of the powder coating apparatus according to the present invention is that the uniformity of the thickness of the powder coating layer obtained is extremely good, and there are extremely few rough surfaces, pinholes, etc. in the coating film. This is because, as is clear from the explanation regarding FIG. 4, in the powder coating apparatus according to the present invention, the electric field in the coating space 18 is almost a uniform electric field, and the current density of the current flowing into the object to be coated 10 is extremely good. Therefore, unlike the conventional device shown in Fig. 2, there is no occurrence of pinholes or rough skin caused by reverse ionization due to non-uniform current density, and it is possible to obtain a coated powder layer with a uniform thickness. be.
Next, the second feature of the present invention is that the controllability of the resulting coating film thickness is extremely good. That is, in the powder coating apparatus according to the present invention, by adjusting the AC power source 6 and the DC power source 7, the current density flowing through the coating space 18 and the coating space 1 can be adjusted.
Since it becomes possible to independently adjust the electric field strength present at 8, it becomes possible to freely adjust the thickness of the powder coating layer over a very wide range depending on the properties of the powder. For example, for powders with extremely high electrical resistance, it is possible to obtain an extremely thick coating film by keeping the amount of current low and increasing the electric field strength, or it is possible to obtain an extremely thick coating film by keeping the amount of current low and increasing the electric field strength, or by applying a relatively large amount of current and comparing the electric field strength. By lowering the target, it is possible to freely make adjustments such as obtaining a thin coating film.

The third feature of the powder coating apparatus according to the present invention is that continuous automatic operation for an extremely long period of time can be carried out without requiring any maintenance services. This is mainly because the powder does not adhere to the discharge electrode due to the repulsion against the powder that is inherent in the planar silent discharge electrode. That is, as shown in FIG. 4, between adjacent electrodes of the planar silent discharge electrode according to the present invention, alternating electric lines of force A3 convex outward with respect to the surface of the electrodes exist over the entire surface. Therefore, the charged powder particles in this region vibrate alternately on the outwardly curved electric lines of force, and as a result are constantly subjected to a force repelled from the electrode surface by centrifugal force. Therefore, for this reason, powder particles in the coating space never adhere to the surface of the discharge electrode. In addition, in the present invention, since the electric field in the painting space is close to a uniform electric field, there is no concentrated DC electric field at the tip of the gun as seen in conventional equipment, so the gradient force Access of powder to the electrode surface is also completely impossible.

For these two reasons, the discharge electrode of the powder coating device according to the invention will never have paint powder adhering to it and will therefore never be placed at or near the tip of the gun, as in conventional powder coating devices. There is no need to interrupt work or perform maintenance services to remove powder adhesion on the dispersion plate installed. Therefore, it is easy to carry out continuous operation without maintenance for a long period of time.

In these cases, since the conductor is exposed on the surface of the planar silent discharge electrode facing the surface of the object to be coated, lines of electric force can easily pass therethrough, and discharge can be performed at a low voltage.

Further, the problem of residual charge on the surface of the planar silent discharge electrode, which occurs when the electrode is not exposed, does not occur. Therefore, the resistivity value of the insulator or semiconductor used can be selected from a very wide range.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a conventional electrostatic powder coating device, Fig. 2 is a sectional view taken along plane 198 in Fig. 1, and Fig. 3 shows the internal structure of the planar silent discharge electrode of the present invention. FIG. 4 is a longitudinal sectional view showing how the planar silent discharge electrode of the present invention is used, and FIG. 5 is a diagram showing an embodiment of the present invention, which is a schematic diagram of the planar silent discharge electrode. S...Planar silent discharge electrode, 1...Plate electrode, 2
... Plate insulator, 3... Linear electrode.

Claims (1)

[Claims] 1 A plate-shaped electrode is embedded in a plate-shaped insulator, a linear electrode is provided exposed on the surface of the plate-shaped insulator, and a silent discharge is generated between the exposed surface of the linear electrode and the surface of the plate-shaped insulator. A planar silent discharge electrode characterized by having a space formed therein for generating.