JPH11179247A - Electrostatic powder coating method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic powder coating method to adhere acryl type powder paint on the surface of an aluminum wheel efficiently and uniformly. SOLUTION: An aluminum alloy-made road wheel 2 is set on a specified position and a spray gun 11 charging the powder paint by the friction 22 is arranged in the circumference of the load wheel 2, and the acryl type powder paint 3 housed in a feed container 31 is forcibly fed into the spray gun 11, and the powder paint 3 is ejected from the spray gun 11 toward the load wheel 2 to be stuck on the surface of the load wheel 2, and an oversprayed paint 3a is recovered, then is returned into the feed container 31. Also the oversprayed paint 3a is removed electrostaticity it is recovered and returned to the feed container 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrostatic powder coating method for electrostatically applying an acrylic powder coating to the surface of an aluminum alloy road wheel, and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, steel road wheels have been used. However, in recent years, aluminum alloy road wheels (hereinafter simply referred to as “aluminum”) have been used for the purpose of reducing the weight and improving the appearance and design of automobiles. Wheels)). The aluminum wheel is produced by melting, casting (for example, low pressure casting) or forging and then machining the Al-Si-Mg-based alloy and applying a coating to the surface of a material obtained. The coating of aluminum wheels has been performed by a so-called solvent-type paint using an organic solvent in order to improve the design and impart corrosion resistance. However, in order to prevent environmental pollution, emission regulations for organic solvents are becoming stricter, and aluminum wheels are often coated using powder paint.

[0003] As a paint used for powder coating of aluminum wheels, polyester resin powder and epoxy resin are generally used. However, since aluminum wheels are used outdoors, the requirements for weather resistance are severe, and these powders are used. If the paint is used in a clear paint, the requirements cannot be met. Therefore, acrylic powder coatings are being used from the viewpoint of corrosion resistance and weather resistance.

[0004] In powder coating, a powder coating is generally electrostatically adhered to the surface of an object to be coated. For example, a corona pin (electrode) is provided at the tip of a spray gun for ejecting the powder coating. A corona charging method in which a high voltage is applied to the corona pin to attach the powder coating charged by corona ions to the object to be coated, or the powder coating charged by friction with the inner wall of the spray gun is caused to fly only by an air flow to be coated. There is a triboelectric charging method for attaching to a coating. In the corona charging method among these methods, the electric field is formed concentrated on the edge portion of the object to be coated and not formed in the concave portion due to the Faraday gauge effect. Therefore, a large amount of the powder coating adheres to the edge portion. In addition, due to the reverse ionization phenomenon, the accumulated charge of the powder coating material and the free corona ions attached to the object to be coated becomes too large, causing a spark discharge to cause a crater-like defect on the coated surface. On the other hand, according to the triboelectric charging method, an electric field is not formed around the object to be coated and the reverse ionization phenomenon does not occur. The powder coating layer can be efficiently attached. That is, the design property and corrosion resistance of the aluminum wheel can be expected to be improved by the friction gun type spray gun.

[0005]

According to the friction charging method, however, the powder paint obtains electric charge only by friction charging with the spray gun, so that the value of the charge amount is lower than that of the corona charging method. In particular, acrylic powder coatings have not been used in tribocharging type powder coating, because they are less likely to triboelectrically charge than polyester or epoxy resin particles from the viewpoint of triboelectric charging.

Accordingly, an object of the present invention is to provide an electrostatic powder coating method capable of efficiently and uniformly applying an acrylic powder coating to the surface of an aluminum wheel. Another object of the present invention is to provide an electrostatic powder coating apparatus that can efficiently and uniformly apply an acrylic powder coating to the surface of an aluminum wheel.

[0007]

According to a first aspect of the present invention, a road wheel made of an aluminum alloy is set at a predetermined position, and a powder paint is frictionally charged around the road wheel. A spray gun is arranged, the acrylic powder paint contained in the supply container is pumped to the spray gun, and the frictionally charged acrylic powder paint is ejected from the spray gun toward the load wheel to load the road wheel. The overspray paint that has not adhered to the surface of the road wheel and that has not adhered to the road wheel is collected in the collection container and returned to the supply container, and between the time when the overspray paint is collected and returned to the supply container. The technical means of eliminating electricity was adopted.

In the first invention, the collected free-charged paint can be agitated in the collection container, and this operation makes it possible to remove the charge from the paint.

In order to achieve the above object, according to a second aspect of the present invention, a holding means for holding an aluminum alloy road wheel at a predetermined position and an acrylic powder paint disposed around the road wheel by friction. A spray gun charged and ejected to the road wheel, a supply container containing the acrylic powder paint, and a pressurizing means for pressure-feeding the acrylic powder paint contained in the supply container to a spray gun, A technology comprising: a conductive collection container that stores overspray paint; a return unit that returns the paint in the collection container to the supply container; and a charge removal unit that is provided in the collection container and removes the paint. Tactics were adopted. In the second invention, the static elimination means may include a first static elimination means which is pressurized air for bubbling the paint in the collection container. In the second invention, the static eliminator may include a second static eliminator for neutralizing the pressurized air. In the second invention,
The static elimination means may include means for mechanically stirring the paint in the collection container.

According to a third aspect of the present invention, there is provided a spray booth including a holding means for holding an aluminum alloy road wheel and a triboelectric spray gun disposed around the holding means, and an acrylic powder. A supply unit including a supply container that supplies paint to the spray gun, a collection container that collects overspray paint that has not adhered to the load wheel, and a collection unit that includes a return unit that returns the paint to the supply container; And a static eliminator for ionizing the air flowing into the spray booth.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of an electrostatic powder coating apparatus according to one embodiment of the present invention, FIG. 2 is a schematic view of the spray gun of FIG. 1, and FIG. 3 is a sectional view of an aluminum wheel. The electrostatic powder coating apparatus 1 of the present invention includes a spray booth 10 for spraying an acrylic powder coating (hereinafter also referred to as a powder coating) 3 on the surface of an aluminum wheel 2, and an overspray coating 3.
and a spray booth 10 for collecting the
A supply unit 30 for supplying the powder paint 3 to the supply unit 30 and a supply unit 40 for replenishing the supply unit 30 with the new powder paint 3b.

The spray booth 10 is provided with an intake port 15 for taking in circulating air, and a spray gun 11 for spraying the charged powder coating material 3 toward the aluminum wheel 2 supported therein. Is the inlet 15
It is installed in. 1 indicates the flow of circulating air. As shown in FIG. 2, the spray gun 11 has an air passage 111 connected to the high-pressure unit 13 in FIG.
Connector 11 having powder passage 112 connected to 4
0 and the gun body 11 with the charging tube 113 inside
4 and a nozzle 116 having a deflector 115. The charging tube 113 is formed of a fluororesin such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene-perfluoroalkylvinylether (PFA) to charge the powder coating to a predetermined polarity (for example, positive). In addition, a conductive layer (not shown) (for example, an aluminum alloy) is formed on the inner peripheral surface or the outer peripheral surface to continuously charge the powder coating, and the conductive layer is grounded, so that the powder coating is accumulated in the charging tube 113. It is configured to remove charge. Reference numeral 117 denotes a meter for measuring the charge value of the powder coating.

Next, the collecting section 20 has a collecting container 22 for collecting the overspray paint 3a sprayed from the spray gun 11 and not adhered to the aluminum wheel 2, and a cartridge collector 23 installed on the upper part thereof. . The collection container 22 is formed of a conductor such as a metal. The collection container 22 has an air diffuser 24 for stirring the paint collected therein, a filter 26 for preventing the collected paint from flowing into the cartridge collector 23, and a supply unit via the collection pipe 25. 30. A fan 27 for discharging the circulating air is provided inside the cartridge collector 23, and a filter 28 for purifying the circulating air is provided at the outlet thereof.

The supply unit 30 has a supply container 31 communicating with the collection container 22. The supply container 31 is
5 and a rotary sheave 36 connected to the collection pipe 25. A supply pump 53 and a supply container 53 containing the new powder paint 3b are connected to the cyclone 35 via a supply pipe 51.

The aluminum wheel 2 shown in FIG. 3 has a disk portion 2c having a hub portion 2a on which an axle is mounted, a design portion 2b provided around the hub portion 2a, and a rim portion 2d integrally formed on the outer periphery thereof. Having. The aluminum wheel is produced by, for example, melting an aluminum alloy ingot (AC4CH material or the like), and then casting (low-pressure casting, gravity casting, high-pressure casting or the like), heat treatment, processing, or the like. Instead of casting, a forging or melt forging technique can be used.

According to the apparatus shown in FIG. 1, an acrylic powder coating can be applied to the surface of an aluminum wheel as follows. First, the aluminum wheel 2 on which the base treatment has been performed is set at a predetermined position of the spray booth 10, and then the spray gun 11 is arranged around the aluminum wheel 2. By operating the powder supply pump 52, the powder paint 3b in the supply container 53 is removed.
Cyclone 35, rotary sheave 36 with pressurized air
Into the supply container 31 via the
To the spray gun 11. Spray gun 1
The powder coating material 3 supplied to 1 is joined with the pressurized air introduced from the high-pressure unit 13, is pressure-fed into the charging tube 113, and is triboelectrically charged by contact with the inner peripheral surface thereof. It is jetted from the tip and becomes mist by the action of the deflector 115 and is applied to the surface of the aluminum wheel 2.

A portion of the paint sprayed from the spray gun 11 does not adhere to the surface of the aluminum wheel 2 but remains in the spray booth 10 as overspray paint 3a. The overspray paint 3a is fed into the collection container 22 by the circulating air flowing from the intake port 15,
Deposits on its bottom. This overspray paint 3a
Is supplied from the bottom of the collection container 22 through the collection pipe 25 and the cyclone 35 and the rotary sheave 36 to the supply container 3.
Returned within 1.

Here, in the present invention, the collection container 2
An air diffuser 24 is arranged in the inside 2, and is configured to blow compressed air from the air diffuser 24. According to this configuration,
Since the paint deposited in the collection container 22 is bubbled, the overspray paint is discharged by contact with the conductor (collection container). As a result, even when the aluminum wheel is continuously coated, the charge value of the powder coating ejected from the spray gun is recovered, and an aluminum wheel having a predetermined film thickness can be obtained. In this case, by using the air ionized by the static eliminator as the pressurized air, static elimination can be performed more effectively. Instead of the above-described static elimination means (bubbling the paint with pressurized air), a mechanical stirring means (an impeller or a stirring rod) is provided in the collection container 22, and this is rotated to stir the paint. Also, the overspray paint can be neutralized.

In the present invention, a static eliminator 4 (or 4 ') which will be described later is provided near the intake port 15 as shown in FIG. The ionized air may be mixed with the air, and the collected powder may be neutralized while the overspray paint is being collected in the collection container 22. Furthermore, in the present invention, the above-described static elimination effect can be further enhanced by keeping the spray gun 11 clean and reducing the amount of overspray paint stored in the collection container 22.

In the present invention, any of a voltage application type static eliminator and a self-discharge type static eliminator can be used as a neutralizer for ionizing air. As shown in FIG. 4, the voltage application type static eliminator 4 includes a high-voltage power supply unit 41 that outputs a voltage of 5 to 9 KV when a commercial AC voltage is input, and a static elimination electrode 42 to which a high voltage is applied. Corona discharge is performed between the ion generating electrode (43) and the ground electrode 44 to ionize air near the electrodes to generate ions of almost the same polarity. In the self-discharge type static eliminator 4 ', a neutralizing electrode 42' is formed by a grounded electrode support 45 and a conductive brush (ion generating electrode) 46 as shown in FIG. To generate amphoteric ions and perform neutralization and neutralization.

In the present invention, before the surface of the aluminum wheel is subjected to the electrostatic powder coating, the surface of the aluminum wheel is subjected to a base treatment such as alkali degreasing, chemical conversion and water washing. As the chemical conversion treatment, the aluminum wheel is immersed in an aqueous solution containing chromic acid, sulfuric acid, nitric acid, hydrofluoric acid, an inorganic acid such as phosphoric acid, and a suitable additive, or the aqueous solution is applied to the surface of the aluminum wheel. It is preferable to perform a chromate treatment for spraying. For example, an acrylic powder coating is applied on the surface of the base-treated aluminum wheel by the method of the present invention and baked at 150 to 200 ° C. for 10 to 40 minutes to form a primer layer having a thickness of about 30 to 60 μm. . Next, on the primer layer, for example, an acrylic metallic paint (Nippon Paint Co., Ltd., Super Rack) is applied and baked at 120 to 140 ° C. for 10 to 40 minutes to form a base coat layer having a thickness of 10 to 30 μm. Further, an acrylic powder clear paint is applied on the base coat layer and baked at 150 to 200 ° C. for 10 to 40 minutes to form a top coat layer having a thickness of 30 to 60 μm. The thickness of the entire coating film obtained as described above is preferably from 70 to 150 μm. When the thickness of the coating film is less than 70 μm, a coating film having a uniform thickness cannot be obtained and the corrosion resistance is insufficient.
If it exceeds, the adhesiveness is reduced. The present invention can be applied not only to the above-described metallic coating but also to a clear coating and the like.

[0022]

[Example] 24 aluminum wheels made of AC4CH material
0 pieces were prepared, all were alkali-degreased, washed with water, subjected to chromium chromate treatment (5 to 20 mg / m ² ), washed with water and dried. Acrylic powder paint (Acrylic powder paint, A50, manufactured by Nippon Paint Co., Ltd.) was applied to the surfaces of these aluminum wheels by the apparatus shown in FIG. Here, the inside of the collection container 22 was constantly blown with air, and the collected overspray paint was bubbled to remove electricity, and then returned to the supply container 31. Charge value of powder paint sprayed on each aluminum wheel (spray gun meter 1
17 is indicated by curve A in FIG. For comparison, a powder coating was applied to the surface of the aluminum wheel under the same conditions as above except that air was not blown into the collection container 22. The charge value of the powder paint sprayed on each aluminum wheel is shown by curve B in FIG.

FIG. 6 shows that when air is blown into the collection container 22, the charge value of the powder coating material is 2 μA or more. As a result of baking the powder coating by heating each aluminum wheel, it was confirmed that all aluminum wheels had a uniform film thickness. On the other hand, when air is not blown into the collection container 22, the charge value of the powder paint becomes 2 μA or more at the initial stage of coating, but thereafter, the charge value decreases,
Although the charge value of the powder paint slightly recovers immediately after the cleaning of the spray gun, the charge value of the powder paint is about 1 to 1.5 μA. In most of the aluminum wheels having the charging value shown by the curve B in FIG. 6, the base of the aluminum alloy was exposed at the deep portion of the air hole on the design surface.

In the above experiment, the surface potential around the spray gun and inside the collection container was measured. As a result, when air was not blown into the collection container, the surface potential was 5 to 10 KV around the spray gun and 2 to 5 KV in the collection container, whereas the air potential in the collection container was When blowing, the surface potential around the spray gun is 0 to 1K
V, the surface potential in the collection container was 1-2 KV. That is, it was confirmed that the overspray paint was neutralized by blowing air into the collection container.

[0025]

As described above, according to the present invention, the acrylic powder in the supply container is adhered to the surface of the aluminum wheel by the triboelectric spray gun, and the overspray paint is recovered and supplied. Since the charge is removed before being returned to the container, the charge value of the powder coating can be maintained at a constant level, and a powder coating layer having a uniform film thickness can be efficiently formed. As a result, it is possible to achieve a reduction in coating cost and an improvement in the design and corrosion resistance of the aluminum wheel.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an electrostatic powder coating apparatus according to one embodiment of the present invention.

FIG. 2 is a sectional view of the spray gun of FIG. 1;

FIG. 3 is a cross-sectional view of an aluminum alloy road wheel.

FIG. 4 is a schematic sectional view showing an example of a static eliminator used in the present invention.

FIG. 5 is a schematic sectional view showing another example of the static eliminator used in the present invention.

FIG. 6 is a diagram showing a charge value of an acrylic powder paint.

[Explanation of symbols]

1 electrostatic powder coating equipment, 2 aluminum wheels, 3 acrylic powder paint, 3a overspray paint, 10
Spray booth, 11 spray guns, 20 collection unit,
22 collection container, 30 supply unit, 31 supply container

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masashi Hirata 5200 Mikajiri, Kumagaya City, Saitama Prefecture Inside the Kumagaya Plant, Hitachi Metals Co., Ltd. 72) Inventor Tadayuki Shirase 5200 Mikajiri, Kumagaya City, Saitama Prefecture Inside the Kumagaya Plant of Hitachi Metals Co., Ltd. Nippon Paint Plant Engineering Co., Ltd., 5-5-1 Nishinakajima, Yodogawa-ku, Osaka-shi, Osaka

Claims (7)

[Claims] 1. An aluminum alloy road wheel is set at a predetermined position, a spray gun for frictionally charging the powder coating is arranged around the road wheel, and an acrylic powder coating housed in a supply container is supplied. The powder paint is sent to the spray gun, the powder paint is ejected from the spray gun toward the load wheel and adheres to the surface of the load wheel, and the overspray paint is collected in a collection container, and then the supply paint is collected in the supply container. And discharging the overspray paint from before collecting the overspray paint to returning it to the supply container. 2. The electrostatic powder coating method according to claim 1, wherein the collected overspray paint is stirred in a collection container. 3. A holding means for holding an aluminum alloy road wheel at a predetermined position, a spray gun disposed around the road wheel and frictionally charging an acrylic powder paint and ejecting the acrylic powder coating to the road wheel; A supply container for storing the acrylic powder coating material, a pumping means for pressure-feeding the powder coating material stored in the supply container to the spray gun, a conductive recovery container for storing overspray paint, An electrostatic powder coating apparatus, comprising: a return unit for returning paint in a container to the supply container; and at least one charge removing unit provided in the collection container for discharging the paint. 4. The electrostatic powder coating apparatus according to claim 3, wherein the static elimination means includes a first static elimination means that is pressurized air for bubbling the paint in the collection container. 5. The electrostatic powder coating apparatus according to claim 4, wherein the static elimination means includes a second static elimination means for eliminating static electricity from the pressurized air. 6. The electrostatic powder coating apparatus according to claim 3, wherein the static elimination means includes a stirring means for mechanically stirring the paint in the collection container. 7. A spray booth including a holding means for holding an aluminum alloy road wheel and a triboelectric spray gun disposed therearound, and a supply including a supply container for supplying an acrylic powder paint to the spray gun. Unit, a collection container including a collection container for collecting the overspray paint that has not adhered to the road wheel, and a collection unit including a return unit for returning the paint to the supply container; and a static elimination unit for ionizing air flowing into the spray booth. An electrostatic powder coating device comprising: