JPS6251665B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a unipolar ion generator for charging an object to be charged.

Conventional unipolar ion generators of this type, such as needle electrodes, wire electrodes, and blade-type electrodes to which DC voltage is applied, used in electrostatic powder coating equipment, etc., do not allow air or other gases to be used. The powder thus dispersed and ejected from the paint spout is dispersed by applying a high voltage to needles or blade-shaped electrodes installed near the paint spout, and using the corona discharge generated in these electrodes to disperse the powder. and attracting the charged paint powder to the object to be coated by the action of a high-intensity electric field existing between these electrodes and the object to be coated,
Most of them are based on the basic principle of coating the surface of the object to be coated. However, the conventional unipolar ion generator described above has the following major drawbacks in principle, and as a result, the efficiency of powder application is kept low, and the resulting powder layer is The reality is that it is not possible to obtain a material with sufficiently good properties.

The reason for this is that the values of the voltage applied to the device and the discharge current flowing from the device cannot be independently controlled. That is, if the voltage applied to the device is determined, the value of the current flowing from the unipolar ion generator to the object to be coated is uniquely determined. However, properties such as the electrical resistance value of the powder of the charged object used in powder coating, for example, vary over a significantly wide range. Furthermore, the electrical resistance value of a particular coating powder varies within a significantly large range depending on its storage conditions, the components of the working gas, humidity, and the like. Generally speaking, when it is desired to thickly apply a powder having extremely high electrical resistance, it is required to use as little discharge current as possible and as high an applied voltage as possible. On the other hand, in the case of powder having a low voltage resistance, the properties of the resulting powder layer will be preferable and dense if a large amount of current is passed and the applied voltage is relatively low. However, in the unipolar ion generator of conventional electrostatic powder coating equipment,
If you try to obtain a large current, the applied voltage will inevitably become high, and if you reduce the current, the applied voltage will inevitably become small. It has been practically extremely difficult to effectively apply powder with a relatively low amount of powder. In addition, if the electrical resistance of the powder is extremely high, the voltage drop due to the ion current coming from the unipolar ion generator of the electrostatic powder coating equipment in the powder layer applied to the object to be coated may cause A so-called reverse ionization phenomenon occurs inside the deposited powder layer, which causes pinholes where the powder layer peels off in spots. This phenomenon is more likely to occur as the powder coating layer becomes thicker and as the current density flowing through the powder layer increases. Therefore, when using a coating powder with extremely high electrical resistance, it is necessary to keep the value of the current flowing from the unipolar ion generator to the object to be coated as small as possible. However, as mentioned above, when the current flowing from the unipolar ion generator to the object to be coated is obtained by corona discharge, the inherent property of corona discharge is that if the discharge current is extremely small, that is, corona discharge When the discharge electrode is close to the discharge start voltage, the discharge becomes extremely unstable, and for this reason, in the unipolar ion generator of conventional electrostatic powder coating equipment, if the discharge is to be kept stable, the current will be large. If the discharge current is too high, the powder layer will not adhere well, and conversely, if you try to reduce the discharge current to improve the properties of the powder layer, the voltage will drop and the electric field will become weaker, resulting in poor powder adhesion. As a result, it became difficult to obtain a powder layer thickness, and in addition, the discharge current became extremely unstable, making it extremely difficult to control the coating process.

Furthermore, in order to effectively charge the powder, a discharge electrode with a very sharp shape such as a needle electrode, a linear electrode, or a blade-shaped electrode is used, so if the powder adheres to this part, its discharge characteristics will change. It has changed significantly,
In order to constantly maintain this at an appropriate value, it is required to interrupt the discharge current of the unipolar ion generator of the coating equipment and clean it after every operation.
Further, the adhesion of this powder to the discharge electrode inevitably occurs due to the concentration of the electric field at the discharge electrode, and it is essentially impossible to prevent this in principle.

Therefore, with conventional unipolar ion generators, due to changes in their characteristics, it is necessary to frequently clean the discharge electrode or adjust the voltage to ensure that a coated powder layer of consistent quality is always maintained on the workpiece. It is impossible to get to.

In addition, in the conventional unipolar ion generator,
The powder is not sufficiently charged, which makes it difficult to obtain high coating efficiency. This is because corona discharge is used to charge the powder, so the area where the powder is charged is limited, and the powder is naturally concentrated in this area, so the powder cannot be charged sufficiently. This is because it cannot be charged. If you try to charge the powder in an area where the powder is dispersed, the density of the current flowing from the device to the object will increase,
Especially when the electrical resistance of the powder is high, this can become a major hindrance and inhibit the application of the powder on the object to be coated, and also has the major disadvantage of lowering the charging efficiency of the powder. It is. Furthermore, when applying powder with extremely low resistance, that is,
When applying an electrostatic powder coating containing a large amount of metal powder, sparks may be easily generated from the electrodes of the unipolar ion generator. This is a significant drawback of conventional unipolar ion generators, as it can easily lead to major accidents such as powder explosions.

The present invention solves all the various drawbacks of the unipolar ion generator used in the conventional electrostatic powder coating apparatus and the like for charging objects as described above, and coats a good powder layer. It is possible to apply the powder onto the object to be coated, and it is also possible to form a powder layer with a desired thickness on the object depending on the properties of the powder.
Provides a unipolar ion generator with stable properties of the resulting powder layer, extremely high coating efficiency, and extremely low risk of spark discharge even when coating low-resistance powder. It is something to do.

In the unipolar ion generator for charging an object according to the present invention, a thin linear electrode is exposed on the surface of an insulating layer, and a planar electrode is provided in the insulating layer opposite to the linear electrode. The electrodes are buried and a power source is connected to them to apply alternating voltage.
Furthermore, the present invention is characterized in that a power source is connected to generate a potential difference between the silent discharge electrode pair consisting of the linear electrode and the planar electrode and the object to be coated.

An example of the state of use of the unipolar ion generator of the present invention will be explained with reference to the drawings. In Fig. 3,
The paint powder 19 accumulated in the hopper 20 enters the coating device from the supply device 15, and is suspended in the air flow by the air supplied to the ejector 16 as shown by the arrow 18, and is suspended in the cylindrical insulator. 3, the paint is jetted from the paint spout 0 toward the object 8 to be coated. In this case, near the surface of the insulating layer forming the insulating ring 2 around the coating powder discharge port 0, a linear electrode 1-1 consisting of a thin wire is provided exposed as shown in FIG. A planar electrode 1-2 is buried deeper than the electrode, that is, within the insulating layer. AC voltage is applied from the power source 9 to the linear electrode 1-1 and the planar electrode 1-2, and as a result, as shown in the enlarged detailed view of FIG. 2, the linear electrode 1-1 and the planar electrode 1-2 2, alternating electric lines of force as shown by 1-1.2 are formed. At this time, a protective layer may be provided on the surface of the linear electrode 1-1 so as not to prevent the formation of the electric lines of force. When the number of these alternating electric lines of force, that is, the electric field strength, becomes stronger than the spark voltage of the gas existing on the surface of the insulator ring 2, a silent discharge occurs here, and positive and negative ions come to exist.
Therefore, when a DC electric field is formed, for example, between the object to be coated and these electrodes by the power supply shown at 10 in FIG. Silent discharge region 1-1.
2, unipolar ions with different polarities flow from the front surface of the insulator ring 2 toward the object to be coated 8 as an ion current due to the electric field formed there by the power supply 10. This ionic current is
The powder adheres to the powder floating in the space 21 between the insulator ring 2 and the insulator ring 2 and charges the powder, and as a result, the charged powder is formed between the insulator ring 2 and the object to be coated 8. The powder is attracted to the object 8 to be coated by the action of the electric field, and a coating powder layer is formed thereon. In the unipolar ion generating device having the basic structure as explained above, the ion current flowing from the tip of the device, that is, the insulating ring 2 toward the object 8 to be coated, flows between the insulating ring 2 and the object 8. If the strength of the electric field formed between the It is possible to emphasize the strength of the silent discharge formed in
This makes it possible to adjust the strength of the ionic current over a wide range even if the electric field formed between the insulator ring 2 and the object to be coated 8 is constant. Such a relationship always holds even if the strength of the electric field formed between the insulator ring 2 and the object to be coated 8 by the power supply 10 changes over a fairly wide range, so that the unipolar property according to the present invention In the ion generator, the strength of the current flowing through the coating space 21 can be freely adjusted independently of the electric field strength formed in the coating space 21.

Therefore, in the unipolar ion generator according to the present invention, it is possible to stably supply a current with a low current density even in the extremely strong electric field strength required when applying powder with extremely high resistance. Even in a weak electric field strength, it is possible to flow a large current by increasing the value of the AC voltage applied from the power supply 9, and it meets the current and voltage conditions required for all types of electrostatic powder coating. It becomes possible to fill it freely. This is the first feature of the unipolar ion generator according to the present invention. Next, as is clear from FIG. 2, it is clear that the lines of electric force 1-1.2 formed between the linear electrode and the planar electrode always convex outward. Moreover, these electric lines of force are
The direction is changed every cycle. Therefore, the charged powder present on the front surface of the insulator ring 2 is
Due to the centrifugal force caused by the alternating motion on the lines of electric force, a repulsive force is always applied in the direction away from the insulator ring 2. Therefore, insulator ring 2
On the front side, powder does not adhere to the discharge electrode, and therefore, unlike the electrodes of conventional unipolar ion generators using corona discharge, the voltage-current characteristics of the coating device are affected by the powder adhesion. does not change at all, making it possible to always maintain stable performance. This is the second major feature of the present invention.

As described above, this invention exposes a thin linear electrode on the surface of an insulating layer, and also buries a planar electrode in the insulating layer to generate an ionic current as a silent discharge electrode. It is suitable as a unipolar ion generator for charging an object to be charged, such as a machine drum.

This invention provides a powder-coated unipolar ion generator, in which a linear electrode is exposed near the surface of an insulating layer, and a planar electrode is provided at a deeper position than the linear electrode, facing the linear electrode. By providing electrodes and generating silent discharge, the voltage that exists between the object to be coated and the unipolar ion generator and the discharge current flowing from the unipolar ion generator to the object to be painted can be independently controlled. By adjusting the flow pattern of the ionic current in the coating space according to the properties of the powder and the thickness of the coating film, the efficiency of coating can be significantly increased and the properties of the coating film can be improved. It was also possible to significantly improve the

Further, a linear electrode is provided exposed on the surface of the insulating material layer, and a planar electrode is provided in a position deeper than the linear electrode in the insulating material layer and facing the linear electrode, and between these, Since an AC high-voltage power supply is provided, in the case of an ion generator in which only a plurality of linear electrodes are installed in parallel, it is necessary to precisely equalize the distance between the linear electrodes when installing the AC high-voltage power supply between the linear electrodes. Yes, but
Since the unipolar ion generator of the present invention does not require such a method, it is easy to manufacture. Furthermore, it is easy to make the distance between the linear electrode and the planar electrode facing it uniform, and the generated ionic current is made uniform.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the main parts of the unipolar ion generator of the present invention, FIG. 2 is a diagram showing the formation of an alternating power line in the portion shown in FIG. 1, and FIG. 3 is a longitudinal cross-sectional view showing one state of use of the present invention. It is a front view. 1-1... Linear electrode, 1-2... Planar electrode, 1-
1.2... Alternate power line (silent discharge area), 2... Insulator ring, 8... To be coated, 9... Power source, 10... Power source.

Claims (1)

[Claims] 1 Providing exposed linear electrodes on the surface of the insulator layer,
Further, a planar electrode is buried in the insulating layer to face the linear electrode, and an AC high voltage power source is provided between the linear electrode and the planar electrode, and one end of the DC high voltage power source is connected to both of the electrodes. A unipolar ion generator characterized by being connected to either one of the above.