JPH0884942A - Spray gun for electrostatic painting - Google Patents

Abstract

PURPOSE: To maintain an electrification effect upon paint by an opposed electrode and prevent an article to be painted from becoming contaminated by a back aspiration effect by providing the opposed electrode for promoting the electrification effect and installing the opposed electrode with a resistance element, in an electrostatic spray gun for electrically charging a paint material so that the article is coated electrostatically. CONSTITUTION: If a needle valve 10 is pulled, a voltage is conducted to an electrically charged electrode 4 through an electrode set 3 and consequently, an electric discharge occurs at the tip of the electrode 4. Thus an anionic zone is formed. Besides, a paint is atomized by an air cap 1, and becomes negatively charged when passing through the anionic zone. Then the paint is applied to an article to be painted by a potential gradient and the electric attraction force of a paint. In this case, a discharged electric current runs to the article to be painted side and the opposed electrode 100. However, the anionic zone formed is always stable without being influenced by the humidity of the article because the electric current is controlled by a resistor 101 provided on the opposed electrode 100. Further, the intensity of an electric field is controlled by the presence of the resistor 101, so that a back aspiration phenomenon, is inhibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic coating spray gun for electrostatically coating a coating material such as a coating on an object to be coated.

[0002]

2. Description of the Related Art Generally, an air atomization type electrostatic spray gun has a tip for atomizing paint with compressed air, a hand gun for a grounded handle portion, an auto gun for a grounded mounting portion, the tip portion and a handle. And a barrel formed of resin for insulating the mounting portion or the mounting portion. Then, a charging electrode for charging a voltage of several KV is provided at the tip of the atomized portion so as to project from the paint nozzle, and an ionization zone is created by this charging electrode. By passing the atomized paint through the concentrated ionization zone, while charging the paint, an electric field formed between the charging electrode and the object to be coated,
Conveyance force of atomized air The paint is applied to the object to be coated by the page (2). Here, the effect of charging the paint greatly differs depending on whether the ionization zone formed by the charging electrode is effectively formed. The counter electrode is a known means for effectively forming the ionization zone.

FIG. 1 shows an electrostatic air auto gun as a conventional example. The configuration of the main part will be described with reference to FIG. 1 is an air cap for atomizing the paint to form an elliptical pattern, 2 is a paint nozzle, 3 is an electrode set arranged in the paint passage in the center of the paint nozzle 2 together with the tip of a needle valve for opening and closing the paint,
4 is a needle-shaped charging electrode protruding from the electrode set 3,
The charging electrode 4 extends from the center of the paint nozzle 2 to the vicinity of the intersection of the side air holes 6 of the air cap 1. 7 is a barrel made of resin for insulating the tip part from the mounting part, 8 is several hundreds MΩ
When the object to be coated or a grounding body such as a human approaches, the high resistance of the battery lowers the high voltage of the charging electrode 4 to prevent electric shock or spark to the human. A high voltage cable 13 is supplied with a voltage of several KV from a high voltage generator (not shown). The high voltage cable 13 is electrically connected to the electrode set 3 via the high resistance 8 conduction spring 9. Reference numeral 10 is a needle for opening and closing the paint, and the electrode set 3 having a needle valve at its tip is screwed into the needle. Reference numeral 11 is a needle valve seat nozzle. The needle valve 10 is opened and closed by an air piston set 12 which is operated by air pressure for remote control. 19 is a paint passage, and a flexible paint hose is a barrel 7.
Are connected by a connection joint 20. A counter electrode 15 is connected to the connection joint 18 by a counter electrode guide 16 and a pipe 17, and is screwed into the grounded mounting portion 14. Reference numeral 5 is a stain prevention cover.

In the above, when the needle valve 10 is pulled by the air pressure, the electric circuit from the high voltage cable 13 is turned on almost at the same time, and the voltage sent from the high voltage generator by several KV is transmitted through the electrode set 3. , And is discharged from the tip of the charging electrode 4. This discharge ionizes the air around the tip to form a negative (-) onpage (3) on-sphere. On the other hand, the paint is compressed air,
The paint atomized by the air cap is negatively (-) charged when passing through the ionization zone. The discharge of the charging electrode 4 forms an electric field between the object to be coated and which is positively (+) grounded. The atomized and charged paint particles are carried to the object to be coated or directly to the periphery by the carrying force of atomized air. The paint conveyed to the periphery is applied to the object to be coated by the electric potential gradient of the electric field and the electric attraction of the charged paint. The coating efficiency in electrostatic coating is greatly affected by the degree of charge of the paint when passing through the ionization zone, and the higher the degree of ionization, the higher the charging effect. Counter electrode 1
Reference numeral 5 is a means for increasing the degree of ionization, separately from the electric field between the charging electrode 4 and the object to be coated, and the charging electrode 4 and the counter electrode 15
It is intended to form a stronger ionization zone by creating an electric field between and.

[0005]

In the technique of providing the counter electrode 15 for enhancing the charging effect on the paint and improving the coating efficiency, the counter electrode 15 is separated from the charging electrode 4 by the distance from the object to be coated. In general, the strength of the electric field is set closer to that of the object to be coated. The paint atomized during spraying is transported to the vicinity of the object to be coated by the air stream of atomized air, but the paint particles that did not ride on this air stream partially flow on the electric field on the counter electrode side. The phenomenon in which paint particles flow to the counter electrode 15 and the mounting portion 14 is called blowback. This phenomenon of blowback has a problem of increasing the dirt of the electrostatic spray gun and the dirt of equipment such as a painting robot which is a grounding body.

Further, the distance between the counter electrode and the charging electrode is constant, but the distance between the charging electrode and the object to be coated is not always constant, and the ionization zone and the strength of the electric field change due to changes in the spraying distance. In addition, the discharge current changes depending on the humidity of the coating environment, etc., and stable coating efficiency and throwing power to the back surface of the coated object cannot be obtained. This invention stably maintains an unstable current determined by the charge electrode and the counter electrode load in order to prevent page (4) contamination due to blowback while maintaining the effect of charging the paint by the counter electrode. A device for controlling the limit is provided.

[0007]

[Means for Solving the Problems] A coating material is atomized with compressed air to form a concentrated ionization zone by a charging electrode in the atomization zone to charge the coating material and electrostatically coat an object to be coated. The electrostatic spray gun has a counter electrode for promoting the charging effect, and the counter electrode is grounded with a resistance element.The resistance element is placed as close to the counter electrode as possible. It is characterized in that a resistor is connected.

The electrostatic spray gun is more effective when applied to a remote control type electrostatic air auto spray gun.

[0009]

As described above, the strength of the ionization zone formed by the charging electrode of the air atomization type electrostatic spray gun using the charging electrode depends on the voltage applied to the charging electrode and the current discharged from the charging electrode. The higher the voltage is, the more the predetermined current flows and the more the charging effect on the paint is increased. However, if the current flows too much, the caustic voltage of the charging electrode decreases and the effect disappears. The counter electrode is for passing a predetermined current, but the current is largely influenced by the distance between the charging electrode and the counter electrode and the environment such as humidity. When the distance is short, the charging effect is improved but there is also a lot of blowback. Become. Therefore, in some cases, the distance between the charging electrode and the counter electrode is increased, that is, the length of the barrel 7 is increased, and the charging effect is increased by increasing the charging voltage. As shown in FIG. 3, the current to the counter electrode abruptly causes an ionization action at a limit distance from the charging electrode to facilitate the flow. Therefore, in the past, it was not possible to get closer than a certain limit distance.

Page (5) The present invention provides an ionization zone formed in a charging electrode by stably controlling a current flowing from the charging electrode to the counter electrode by adding a predetermined resistance element to the counter electrode. Can be stabilized at the maximum value, and the coating efficiency can be stably ensured. At the same time, the strength of the electric field formed between the charging electrode and the counter electrode can be controlled and weakened, and blowback can be suppressed to a minimum. Also,
By adding a resistance element to the counter electrode, the distance between the charging electrode and the counter electrode can be shortened, so that the barrel length can be shortened and the electrostatic spray gun as a whole can be miniaturized.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. As an embodiment of the present invention, FIG. 2 shows a sectional view in which a resistance element is added to a counter electrode of an electrostatic air auto gun. Conventional example For the same components as those shown in FIG. 1, corresponding parts are designated by the same reference numerals, and the description thereof is omitted in principle. Figure 4,
FIG. 5 shows an experimental result comparing the effects of the conventional example and the present invention.

In FIG. 2, the air cap 1, the paint nozzle 2, the tip including the electrode set 3 and the charging electrode 4, the insulating portion of the barrel 7, and the mounting portion 14 including the air piston 12 have the same mechanism as in the conventional example of FIG. It consists of 100 is a counter electrode, 101 is a resistor provided as a resistance element, 10
2 is an insulating guide made of an insulating resin, 103 is a resistor, and is screwed into a grounded connection joint 18 with an insulating pipe extending the counter electrode. The counter electrode 100 is arranged closer to the charging electrode 4 than the counter electrode 15 in FIG. Then, the resistor is attached to a position as close as possible to the tip of the counter electrode 100. The reason why the resistor is attached in the vicinity is to ensure the safety by reducing the electric capacity accumulated in the tip part as much as possible. The discharge current of the charging electrode 4 concentrates on the tip of the counter electrode 100, but the page (6) current flowing by the electric resistance of the resistor 101 is controlled to several μA. Although the resistor 101 differs depending on the charging voltage applied to the charging electrode, a resistor of several thousand MΩ is connected in this embodiment. In this embodiment, a single resistor is connected, but the entire rod-shaped counter electrode 100 is in the range of several thousand MΩ.
Of course, the same effect can be obtained even if it is made of one having a resistance element.

In the above structure, the charge electrode 4 is charged and an ionization zone is formed. The discharge current flows through both the object side and the counter electrode 100, but the distance on the object side is long, and the spray distance thereof constantly changes, so that the discharge current tends to flow more toward the counter electrode 100 side which is closer. . Also,
If the environmental humidity is high, the flow becomes easier. However, since the current is controlled by the resistor 101 of the counter electrode 100, a stable ionization zone is always formed without being influenced by the condition and humidity of the object to be coated. Further, since the discharge current is controlled to the necessary minimum by the resistor 101, the electric field strength is also controlled, so that the blowback phenomenon is reduced. Moreover, since the counter electrode 100 is close to the charging electrode 4,
The electric field formed between the mounting portion 14 and the mounting portion 14 also weakens and the mounting portion 1
This also results in a reduction of paint stains on the No. 4 paint.

Next, the experimental results comparing the present invention with the conventional example will be described. FIG. 4 is an experimental result of measuring the blowback amount under each experimental condition. The blowback amount was measured by measuring the amount of paint mist adhering to the cover attached to the attachment portion 14 side and setting the experiment condition A to 1
It is a value expressed as a ratio as 00. FIG. 5 shows the measured throwing power values under the same conditions as above. The throwing power values are obtained by suspending a pipe having a diameter of 60 mm on an object to be coated, spray coating at a predetermined spraying distance, and coating on the back surface of the pipe. It is a value comparing the degree with the comparative limit sample. In the limit sample, one that is not coated on the back surface at all is 0, and one that is coated on the back surface with the same thickness as the front surface is 10, and the numbers are evenly distributed between them.

FIG. 6 shows the experimental conditions for the experimentally symmetrical products A to D. Page (7) A is a conventional example In Fig. 1, when the distance between the charging electrode and the counter electrode is changed, B is when the counter electrode is removed, and C is when the charging voltage is increased by another model with a long insulating resin barrel. , D show the experimental results when the resistor 101 of the present invention is connected. From this result, the blowback value is C with a long barrel and a high charging voltage.
It has been confirmed that the values are almost the same as, and the throwing powers are almost the same as A, B, and so on.

[0016]

As described above, a resistance element is added to the counter electrode and the unstable current flowing to the counter electrode is stably controlled to a necessary minimum, whereby coating conditions such as spray distance and humidity can be controlled. It is possible to obtain stable throwing power and coating efficiency that are not largely affected by the coating environment conditions, and it is possible to minimize the blowback phenomenon of the paint mist. Further, since the charging electrode and the counter electrode can be brought close to each other, the electrostatic spray gun can be downsized and the electrostatic effect can be obtained at a relatively low voltage.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a conventional electrostatic air auto gun.

FIG. 2 is a sectional view of an essential part in which a resistor is added to a counter electrode of an electrostatic air auto gun as an embodiment of the present invention.

FIG. 3 is a characteristic diagram of a current flowing through a counter electrode.

FIG. 4 is a bar graph showing the experimental results showing the experimental conditions and the blowback amount.

FIG. 5 is a bar graph showing experimental results showing experimental conditions and throwing powers.

FIG. 6 shows experimental conditions of Page (8) experimentally symmetrical products A to D.

[Explanation of symbols]

 3 Electrode Set 4 Charging Electrode 100 Counter Electrode 101 Resistor 102 Insulated Electrode Guide 103 Insulated Pipe

Claims (3)

[Claims] 1. An electrostatic spray for atomizing a coating material with compressed air to form an ionization zone concentrated by a charging electrode in the atomization zone to charge the coating material and electrostatically coat an object to be coated. A spray gun for electrostatic coating, characterized in that the gun has a counter electrode for promoting a charging effect, and the counter electrode is grounded with a resistance element. 2. The electrostatic coating spray gun according to claim 1, wherein the counter electrode has a resistance element, wherein the resistance element has a resistor connected to the counter electrode as close to the counter electrode as possible. Spray gun. 3. The electrostatic spray gun is a remote control type electrostatic air auto spray gun.
Spray gun for electrostatic coating described