JPH08108106A - Method for electrostatic coating and electrostatic coating machine - Google Patents

Abstract

PURPOSE: To provide a method for electrostatic coating and an electrostatic coating machine for performing electrostatic coating of a llq. coating, especially a metallic color coating beautifully and with high coating efficiency. CONSTITUTION: At least one auxiliary electrode 4 is arranged on the outside of a main electrode 2 rotating at an ultrahigh speed and a DC high electric voltage with the same polarity as that of the main electrode 2 is applied thereon to generate at least two stage corona electric discharge and to improve thereby electric charging rate of an atomized coating and to improve the coating efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic coating method and an electrostatic coating machine using a liquid coating material, particularly a metallic coating material.

[0002]

[Problems and problems of the prior art] For coating metal products,
The air spray coating method that sprays the paint atomized by compressed air onto the object to be coated and the electrostatic coating method that uses electrostatic force are widely used, but the electrostatic coating method has high coating efficiency. Therefore, expansion of the range of use is required.

The principle of the electrostatic coating method is to apply a high DC voltage to the discharge electrode provided in the electrostatic coating machine as a counter electrode to charge the atomized coating material. It is applied to an object to be coated by electrostatic force. Although there are a rotating cup type, a corona pin, and the like as an electrode shape for charging the paint, a rotating cup type discharge electrode having high coating efficiency is often used. When a cup-shaped electrode is used, the atomized paint is affected by the air flow in the coating chamber and the centrifugal force generated by the rotating cup, but since compressed air is not used for atomization, the discharge electrode is generally formed. Fly on electric lines of force. Therefore, the coating efficiency is higher than that of the air spray coating, as well as that of the electrostatic coating using a discharge electrode having another shape.

By the way, when a metallic paint is electrostatically applied as a paint, particularly when electrostatically applied by a rotating cup type electrode, a high voltage is applied to the main discharge electrode so that the aluminum foil piece contained in the atomized paint is applied. As a result, electrostatic induction occurs, and the flat plate portion of the aluminum foil piece flies in a posture along the lines of electric force and is applied in a state of being vertically aligned with respect to the surface of the object to be coated. In this case, it is difficult to obtain a metallic color. On the other hand, in the case of air spray painting, the orientation of the aluminum foil pieces is not constant, and the flat plate portions that are parallel to the surface of the object to be coated are mixed together, so that a metallic color appears. Therefore, electrostatic coating could not be used when applying a metallic color.

In order to solve this problem, Japanese Patent Publication Nos. 62-24139 and 62-24140 disclose a device for increasing the atomization degree by extremely increasing the rotation speed of the cup-shaped electrode. In this case, as shown in FIG.
The atomized paint 101 that has separated from the electrode 2 by means of the corona discharge 1
It contacts with 19 and adsorbs the negative ions 114, and is negatively charged as a whole. Electrostatically atomized paint particles 101
Rides on the lines of electric force 110 toward the object 121 to be coated by a strong Coulomb force. The atomized paint 101 flying toward the object 121 is strongly affected by the air flow in the vicinity of the object 121 as compared with the fine particles formed by a normal cup electrode, and the flight speed is significantly reduced, resulting in atomization. The attitude of the paint particles, and hence the attitude of the aluminum foil piece 104, is also disturbed. Therefore, a metallic color similar to that of air spray appears on the surface of the object to be coated.

However, in the case of this apparatus, since the rotational speed of the electrode 2 is extremely high and a strong centrifugal force acts on the paint, the initial velocity of the atomized paint particles 101 becomes extremely high. Therefore, the time for passing through the corona discharge zone 119 becomes extremely short. Therefore, the atomized paint 101 is scattered without being sufficiently charged. Some of the paint particles that have not been charged move toward the article 121 due to the ionic wind generated from the electrode 2, but most of them do not adhere to the article 121 due to the air flow (not shown) in the coating chamber. It is discharged to the outside of the room or falls on other objects to be coated as dust, causing defective painting. Therefore, as the number of revolutions was increased and the degree of atomization was increased, the metallic color was obtained, but the coating efficiency was decreased. If the applied voltage is increased or the corona discharge current is increased in order to solve this, the risk of developing spark discharge increases, and thus the charging rate cannot be improved.

Therefore, in the case of applying a metallic color, after the electrostatic coating, the coating efficiency is sacrificed, and the correction coating by air spray is performed to obtain the metallic color.

Therefore, an object of the present invention is to provide an electrostatic coating method and an electrostatic coating machine which do not require correction coating by air spray even if a metallic coating is used. The technical problem for this is to increase the contact time between the corona discharge and the paint and improve the charging rate by using a high-speed rotary coating machine.

[0009]

Means for Solving the Problems The means provided by the present invention is to atomize a coating material which has been atomized by an ultra-high-speed rotating electrode by electrostatically coating the material by atomizing two or more stages of corona discharge toward an object. It is characterized in that the paint is charged. Further, the electrostatic coating machine comprises a main electrode to which ultra high speed rotation is applied and a high DC voltage is applied, and at least one auxiliary electrode which is arranged coaxially with the main electrode and to which a high DC voltage of the same polarity is applied. That is, the auxiliary electrode is an electrode integrated with the main electrode, and the auxiliary electrode is a position adjusting electrode.

[0010]

The operation of the present invention will be described with reference to examples.

[0011]

[Embodiment 1] FIG. 1 shows a super-high-speed rotation type main electrode 2 and auxiliary electrode 4.
Is an example of being integrally formed. Reference numeral 96 is a rotary shaft for rotating the electrode driven by an air motor (not shown). Reference numeral 94 is a pore that guides the paint to the main electrode 2, and is connected to a paint supply source (not shown) through the paint supply connector 93. For the method of driving these ultra-high speed rotating electrodes and the method of supplying paint, see Japanese Patent Publication No. 62-24.
139, Japanese Patent Publication No. 62-24140 and the like are used.

In FIG. 1, 2 is a cup-shaped main electrode having a diameter of 65 mm, and 4 is an auxiliary electrode 4 having a diameter of 100 mm, which is integrally formed by machining aluminum.
The tips of the main electrode 2 and the auxiliary electrode 4 have a sharp ring shape, and the tips are formed so as to be located substantially on the same plane.

In this embodiment, as shown in FIG. 1, lines of electric force 110 are formed from the main electrode 2 toward the article 121 to be coated, and corona discharge 119A is generated. Electric lines of force 111 are formed from the auxiliary electrode 4 toward the article 121 to be coated, and corona discharge 119B is generated. Among the atomized paints that have left the main electrode 2 due to the centrifugal force due to the ultra-high speed rotation, the paint particles that have adsorbed the negative ions 114 by the corona discharge 119A and have been charged are subjected to a strong Coulomb force in the direction of the object to be coated 121, and thus become electrically Take the force line 110 and start flying. Further, the atomized paint that has not been charged by the corona discharge 119A scatters in the direction of centrifugal force, is charged by the corona discharge 119B generated from the auxiliary electrode 4, and rides on the electric force line 111 by the strong Coulomb force to the coated object 121. Go to On the other hand, the object to be coated 12
The atomized paint 101 heading to 1 drastically reduces the flight speed due to air resistance during flight and changes direction due to the air flow in the coating chamber, disturbing the orientation of the paint particles, and hence the aluminum foil pieces, and thus causing a metallic color. Will be obtained. Therefore, electrostatic coating with high coating efficiency and metallic color is possible.

In the case of this embodiment, the electrode structure is simple and maintenance is easy. Further, even if the particles scatter from the main electrode 2 and adhere to the auxiliary electrode 4, they are atomized and charged by centrifugal force, so that maintenance is easy.

[0015]

[Embodiment 2] FIG. 2 is a view showing an embodiment of the present invention including a position adjustment type auxiliary electrode 4.

In FIG. 2, 2 is an aluminum ultra-high speed rotating cup type main electrode, and 4 is a ring type auxiliary electrode. The auxiliary electrode 4 is a ring-shaped electrode made of stainless steel having a diameter of 125 mm, and is supported and arranged by the position adjusting means 72. A paint connector 93 is supplied to the main electrode 2 by a paint supply device (not shown). Further, 96 is an air motor for ultra-high speed rotation, and compressed air is generated by the connector 95.
Supplied through. Reference numeral 73 is a column of the electrostatic coating machine 61.

A DC power source 4 is used for the main electrode 2 and the auxiliary electrode 4.
1 to protection resistor 14, cable 81, and current limiting resistor 1
A high voltage having a negative voltage of 70 kv is applied according to a conventional method through 5 and 20. The current limiting resistors 15 and 20 may normally have the same size.

A DC voltage having the same polarity as that of the main electrode may be applied to the auxiliary electrode 4 in a pulse form. In that case, a DC voltage that is almost equal to the voltage applied to the main electrode 2 is used as the basic voltage, and 1
A pulse voltage higher by 0 to 15% may be superimposed. The metallic color can be adjusted as compared with the case of simply applying a direct current.

In the case of this embodiment, since the position of the auxiliary electrode 4 can be adjusted, the direction of the lines of electric force can be adjusted. Further, if two or more auxiliary electrodes are provided, the spray pattern can be adjusted according to the size of the article 121 to be coated, so that the paint can be prevented from spreading excessively.

The above embodiment is applied to a paint having a high electric insulation property such as a petroleum solvent-based paint. However, if an intermediate tank for electric insulation is provided in the paint feeding route, it is similarly applied to a water-based paint. be able to.

The present invention has an effect of being applied to metallic paints by means of an ultra-high-speed rotating type discharge electrode, but is not limited to metallic color paints, and can be applied to general paints and electrostatic coating of liquid products. It does not prevent its use.

When the present invention is used under a vacuum condition, the voltage of the main discharge electrode can be lowered, so that the voltage applied to the main electrode and the auxiliary electrode may be correspondingly lowered.

[0023]

EFFECTS OF THE INVENTION According to the present invention, when a metallic color paint containing aluminum foil pieces is rotated at an extremely high speed and subjected to centrifugal force to be extremely atomized and electrostatically coated, the atomized paint has two or more stages of corona discharge. As a result, the electrostatic charge is generated, which makes it possible to achieve a beautiful metallic color coating as well as electrostatic coating with high coating efficiency.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, which is equipped with an integral auxiliary electrode of Example 1;

FIG. 2 is a diagram showing a second embodiment including a position adjustment type auxiliary electrode.

FIG. 3 is a diagram illustrating a conventional method.

[Explanation of symbols]

 2, main electrode 4, auxiliary electrode 61, electrostatic coating machine

Claims (4)

[Claims] 1. In electrostatic coating performed by charging a paint atomized by an ultra-high speed rotating electrode, the atomized paint is charged by corona discharge of two or more stages toward an object to be coated. Electrostatic coating method 2. A main electrode which is rotated at a very high speed and to which a high DC voltage is applied, and at least one auxiliary electrode which is arranged coaxially with the main electrode and to which a high DC voltage of the same polarity is applied. Electrostatic coating machine 3. The electrostatic coating machine according to claim 2, wherein the auxiliary electrode is an electrode integrated with the main electrode. 4. The electrostatic coating machine according to claim 2, wherein the auxiliary electrode is a position adjustment type electrode.