JP4026111B2 - Electrostatic powder coating method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrostatic powder coating method, and more particularly to a method of electrostatically applying a charged powder coating to an object having a recess.
[0002]
[Prior art]
Today, as environmental protection progresses, electrostatic powder coating is attracting attention as a pollution-free coating method that replaces solvent coating. It is used not only for home appliances and automotive parts, but also in various other fields. . Electrostatic powder coating is a method in which a powder coating material conveyed by air is sprayed from a gun toward a grounded object to be coated, and is applied onto the object to be coated using static electricity. The powder coating is applied to the surface of the object to be coated in a charged state. After being sprayed from the electrostatic gun, an external charging system that gives the powder a charge outside the electrostatic gun and the electrostatic gun It is broadly divided into an internal charging system that gives electric charge to the powder inside the electrostatic gun before being sprayed.
[0003]
The former corona discharge gun known as an externally charged electrostatic gun utilizes corona discharge generated from a pin-type electrode at the tip of the gun to which a high voltage is applied to a workpiece to be grounded. Powder particles are charged when ions generated by corona discharge adhere to the powder sprayed from the tip of the gun, and the powder particles follow the air flow from the gun and the lines of electric force from the gun to the object to be coated. It is applied to the surface of the object to be painted under the influence of electrical force.
On the other hand, the friction charging gun known as the latter internal charging type electrostatic gun, the powder particles are charged by friction between the friction charging portion inside the gun and the powder, and when it is ejected from the gun, it rides on the air flow. Move and apply to the surface of the object.
[0004]
The former corona discharge gun has almost no effect on the coating performance depending on the type of paint and the usage atmosphere, and the coating efficiency on a wide flat surface is high, but the Faraday gauge is caused by the generation of an electric field between the gun and the object to be coated. The effect of entering the recess is not so good due to the effect. On the other hand, the latter frictional charging gun does not have an external electric field like the corona discharge gun, so it has good penetration performance into the recess, but it has a lower coating efficiency on the flat surface than the corona discharge gun, and is recovered and reused. Since the charging characteristics of the powder coating material deteriorates, it may be difficult to use from the viewpoint of production management. Therefore, for an object to be coated having both a flat part and a concave part, the concave part is coated with a frictional charging gun, and a corona discharge gun that charges the powder paint to the same polarity as the frictional charging gun is used for a wide flat part. And painting is done.
[0005]
[Problems to be solved by the invention]
However, when a triboelectric charging gun and a corona discharge gun that charge the powder coating to the same polarity are used in combination, the coating efficiency of the coating onto the object to be coated is low, and the finished appearance of the coating film is also deteriorated due to electrostatic roughening.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrostatic powder coating method capable of efficiently coating the entire surface over not only the flat portion but also the concave portion of the object to be coated.
[0006]
[Means for Solving the Problems]
Electrostatic powder coating method according to the present invention is a electrically grounded electrostatic powder coating method for electrostatically coating wears charged powder coating on the surface of the object to be coated, friction powder coating The first application to the object to be coated is electrostatically charged to the positive polarity by the charging gun , and the charged polarity of the charged powder coating applied to the object by the first application is replaced with the negative polarity. The powder coating is electrostatically charged to a negative polarity by a corona discharge gun , and the second application to the object to be coated is performed.
The charge polarity can be replaced by spraying negative ions on the object to be coated.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
With reference to FIGS. 1-3, the electrostatic powder coating method which concerns on embodiment of this invention is demonstrated. As shown in FIG. 1, the object to be coated 1 includes a concave portion 2 and a flat portion 3 and is electrically grounded. A friction charging gun 4 is disposed in front of the article 1 to spray the powder coating by friction charging. Powder particles 5 charged to positive polarity by friction between a friction charging portion (not shown) and a powder coating in the friction charging gun 4 are jetted from the friction charging gun 4 to the object to be coated 1 together with the conveying air. Since an electric field is not formed between the object to be coated 1 and the frictional charging gun 4 as in the case of a corona discharge gun described later, the charged powder particles 5 are not affected by the Faraday gauge effect. It is applied electrostatically on the surface of the object 1, particularly also in the recess 2. In this way, the first application is performed.
[0008]
Next, as shown in FIG. 2, an ion shower nozzle 6 is disposed in front of the article 1 and a DC power source 7 is connected to the ion shower nozzle 6. Negative ions 8 are emitted from the ion shower nozzle 6 toward the object 1 to be coated. In response to the electric force generated by the electric field formed between the object 1 to be electrically grounded and the ion shower nozzle 6, the negative ions 8 move toward the object 1 to be coated 1 It adheres to the positive polarity powder particles 5 coated on the surface of the powder, and the charging polarity of the powder particles 5 is changed from positive polarity to negative polarity. In addition, since such replacement of the charging polarity is performed in an extremely short time, the positive polarity ions adhering to the powder particles 5 and the negative polarity from the ion shower nozzle 6 during the replacement from the positive polarity to the negative polarity. The ions 8 are neutralized with each other, the electrostatic adhesion force of the powder particles 5 to the object 1 to be coated is reduced, and the powder particles 5 are not dropped from the surface of the object 1 to be coated.
[0009]
Next, as shown in FIG. 3, a corona discharge gun 9 is disposed in front of the article 1 to be charged and ejected by charging the powder paint by corona discharge. A pin-type electrode 10 for generating corona discharge is provided at the tip of the corona discharge gun 9, and a DC power source 11 is connected to the pin-type electrode 10. By applying a high voltage from the DC power source 11 to the pin-type electrode 10, corona discharge is generated from the pin-type electrode 10 to the workpiece 1 that is electrically grounded. Negative ions generated by the corona discharge adhere to the powder particles 12 ejected from the tip of the corona discharge gun 9 together with the carrier air, and as a result, the powder particles 12 are negatively charged. The negative powder particles 12 are produced from the electric force generated by the electric field and the gun 9 formed between the pin-type electrode 10 to which a high voltage is applied and the workpiece 1 that is electrically grounded. It moves toward the object to be coated 1 under the influence of the air flow and electrostatically overlaps the gaps of the powder particles 5 already coated on the surface of the object 1 and the powder particles 5. Apply to. In this way, the second application is performed.
[0010]
As described above, the concave portion 2 and the flat portion 3 are uniformly coated on the surface of the article 1 to be coated. Therefore, taking advantage of the characteristics that the frictional charging gun has good penetration performance into the recesses and the ability to efficiently coat the flat part of the corona discharge gun, not only the flat part of the object to be coated but also the recesses. The entire surface can be efficiently painted.
[0011]
As described in this embodiment, the triboelectric gun used in the first application generally has a powder paint charged to a positive polarity due to the material such as resin used as the triboelectric charging unit. Is. The corona discharge gun used in the second application is more stable in corona discharge than the negatively charged powder coating is positively charged, and the coating efficiency and finished appearance are better. For this reason, a corona discharge gun for charging the powder coating material to a negative polarity is generally used.
In this embodiment, the first application using the frictional charging gun can be performed by a corona discharge gun, while the second application using the corona discharge gun can be performed by a frictional charging gun.
[0012]
【The invention's effect】
As described above, according to the electrostatic powder coating method of the present invention, the powder coating is electrostatically charged to the positive polarity by the frictional charging gun , and the first application is performed on the object to be coated. The charged polarity of the charged powder coating applied to the object to be coated is applied to the negative polarity, and the powder coating is electrostatically charged to the negative polarity with a corona discharge gun to apply the second coating to the object to be coated. Therefore, taking advantage of the property that the frictional charging gun has good penetration performance into the recess and the ability to efficiently coat the flat part of the corona discharge gun, not only the flat part of the object to be coated The coating thickness of the entire surface can be made uniform over the recess, and the coating can be performed efficiently. As a result, the total amount of paint discharged from the paint gun could be reduced, and the amount of recycled paint could be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a state of first application in an electrostatic powder coating method according to an embodiment of the present invention.
FIG. 2 is a diagram showing a state of replacement of charging polarity of powder particles in the embodiment.
FIG. 3 is a diagram showing a state of second application in the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 To-be-coated object, 2 recessed part, 3 plane part, 4 frictional charging gun, 5,12 powder particle, 6 ion shower nozzle, 7,11 DC power supply, 8 negative polarity ion, 9 corona discharge gun, 10 pin type electrode.

Claims (2)

An electrostatic powder coating method in which a charged powder coating is electrostatically applied on the surface of an object that is electrically grounded,
The powder coating is electrostatically charged to the positive polarity with a frictional charging gun , and the first application to the object is performed.
The charged polarity of the charged powder coating applied to the object to be coated by the first application is replaced with negative polarity,
An electrostatic powder coating method characterized in that a powder coating is electrostatically charged to a negative polarity by a corona discharge gun and second coating is performed on an object to be coated. The electrostatic powder coating method according to claim 1, wherein the charging polarity is replaced by spraying negative ions on an object to be coated.

Images