JP5602002B2 - Powder coating equipment - Google Patents

Description

  The present invention relates to an apparatus for performing powder coating by mounting a powder coating nozzle for controlling a discharge pattern of a powder coating on a gun tip of an electrostatic powder coating gun.

  Powder coating, which does not contain organic solvents and can collect and reuse overspray powder that has not adhered to the object to be coated, has been adopted in many products in recent years as an environmentally friendly coating.

  It started with road materials such as guardrails and fences, and is widely used in products used at home such as refrigerators and air conditioner outdoor units. Recently, it is also widely used for automobile body painting.

  In powder coating, metallic colors among paint colors were difficult to achieve high brightness like solvent coating, but recently, it is possible to paint with high brightness and high smoothness similar to solvent coating. Thus, the metallic color is often applied by powder coating.

  Metallic powder coating is performed by mixing a powder paint with an aluminum pigment coated with silica, acrylic resin, or both.

  The mixing method of the aluminum pigment and the powder coating is roughly divided into the following two methods.

  One of them is a dry blend method in which an aluminum pigment is mixed with a powder paint and then painted.

  The other is, for example, mixing aluminum pigment with powder paint while heating at around 50 ° C., fixing the aluminum pigment to powder paint by heat, or dispersing aqueous or solvent emulsion in powder paint. However, this is a bonding method in which the aluminum pigment is fixed (attached) to the powder coating.

  In the case of painting with a small lot, a dry blend method that is easy to manufacture is often adopted. However, in the dry blend method, since the powder paint and the aluminum pigment are separated, the ratio of the aluminum pigment in the recovered powder is easily changed, and when the recovered powder is reused, the design properties may be different. Therefore, there are many disposable coatings.

  In the case of mass production coating, a bonding method that allows reuse of recovered powder is often adopted. In the bonding method, since the powder paint and the aluminum pigment are integrated, the design is difficult to change. However, not all aluminum pigments adhere to the powder coating even in the bonding powder coating. Generally, about 3 to 5% of the aluminum pigment is present in the powder paint as in the case of the dry blend, although it varies depending on the production method and the aluminum pigment ratio.

  For example, general solid powder paints that are not metallic colors are manufactured in consideration of a peak in the particle size distribution around 30 to 35 μm. Generally, a powder coating contains 5% or more of fine powder of 5 μm or less. This fine powder has a coating efficiency lower than that of powder coating particles having a charging efficiency of around 30 μm. For this reason, the amount of fine powder added to the recovered powder increases, and in the case of painting only the recovered powder, the coating efficiency is lower than that of the new powder.

  By the way, the corona gun creates an electric field between the corona electrode at the tip of the gun and the object to be coated, and the corona discharge causes the powder paint discharged from the gun to adhere to the workpiece. When metallic coating is performed, aluminum pigment tends to adhere to the corona electrode at the tip of the gun, regardless of bonding and dry blending of the metallic powder coating.

  And when an aluminum pigment adheres to a corona electrode, the corona discharge from a corona electrode leaks and the surroundings of the powder coating material discharged from the corona gun falls remarkably. Sometimes, the leak becomes large, and the paint stops due to voltage (current) abnormality.

  Moreover, the aluminum pigment adhering to the corona electrode peels off and adheres to the coating film as spits. Even in a general solid powder coating, fine powder adheres to the corona electrode, and the attached fine powder peels off and adheres as a spit to the coating film, causing a coating film defect.

  For this reason, conventionally, rinse air is applied to the corona electrode to the powder coating nozzle that is attached to the gun tip of the corona gun to control the discharge pattern of the powder paint so that aluminum pigment and fine powder do not adhere to the corona electrode. There is one provided with an air outlet for jetting (Patent Document 1).

Japanese Patent Laid-Open No. 11-19538

  However, when rinsing air is flowed from the powder coating nozzle attached to the tip of the corona gun toward the corona electrode, the rinsing air flows into and mixes in the discharge pattern of the powder coating formed by the powder coating nozzle. As a result, the discharge pattern of the powder coating is disturbed, making uniform coating difficult and causing a problem of non-uniform film thickness.

  In addition, the corona gun charges the powder coating particles with the ion wind of corona discharge from the corona electrode. However, the supply of the rinse air reduces the charging effect on the powder coating particles, and the coating to the object to be coated. The amount of powder paint attached decreases.

  Actually, using a flat nozzle having slit-shaped discharge ports to form a discharge pattern of powder paint spreading flatly in a fan shape, conveyor speed: 1.0 m / min, hanger pitch: 1200 mm, voltage of corona gun: 100 kV, discharge amount: 100 g / min, conveying air: 78 l / min, reciprocating speed: 28 m / min, reciprocating vertical movement amount: 800 mm, distance between flat nozzle, tip and object to be coated: 150 mm When a metal plate having a width of 800 mm and a height of 600 mm was subjected to a coating experiment, as shown in Table 1, five types of powder paints (paint A: metallic / dry blend, paint B: metallic bonding, paint C: polyester) System white, paint D: epoxy black, paint E: polyester hammer tone). Who in passing the rinsing air 175MPa is than without flow rinsing air had less adhesion amount per one object to be coated.

  As described above, even if the amount of powder coating adhered to the object to be coated decreases, if rinse air is not flowed, as shown in Table 2, the powder coating particles pass over the corona discharge electrode pins as time passes. As the amount of powder coating particles adhering and adhering to the surface increased, the particles peeled off and spits repeatedly occurred on the painted surface.

  Table 2 shows the state of adhesion of the powder coating to the corona electrode when a coating experiment was performed under the same conditions as in Table 1. ◎: No adhesion, ○: Adhesion started, Δ: Adhesion, ×: Adhered powder It was evaluated that peeling (spit) occurred.

  Next, when there are places where it is difficult to paint with an automatic coating machine, such as the inside corners of switchboards and the inside surfaces of range hoods that use many uneven members such as C-shaped channels for installing ventilation fans. Requires the use of a hand-held corona gun or a free-arm painting robot, with the nozzle at the tip of the corona gun close to 30-50 mm where painting is difficult.

  In such a case, if rinse air is emitted from the tip of the nozzle, the powder paint on the coated surface that adheres to the object to be coated may be blown off by the rinse air. In addition, since the distance between the object to be coated and the nozzle at the tip of the corona gun is close, there is a problem that the adhesion of the powder coating to the corona electrode is remarkably accelerated due to the rebound of the discharged powder coating.

  In view of this, the present invention prevents the powder paint from adhering to the object to be coated by rinsing air while preventing the powder paint from adhering to the corona electrode. Even if the distance from the nozzle is reduced, the powder coating material adhered to the object to be coated is not blown off by the rinsing air.

In order to solve the above-mentioned problems, the present invention is equipped with a powder coating nozzle equipped with a discharge port for controlling a discharge pattern of a powder coating material at the tip of a corona gun, and the discharge port is provided with a corona electrode. In the powder coating equipment provided with the air outlet for ejecting the rinsing air toward the outlet, when the distance between the object to be coated and the outlet becomes closer, the ejection of the rinse air from the air outlet is stopped or weakened. This is done intermittently.

  Since the current value of the corona gun increases as the distance between the object to be coated and the discharge port approaches, the distance between the object to be coated and the discharge port can be adjusted by adjusting the amount of rinse air jetted by fluctuations in the current value of the corona gun. When the air pressure approaches, it becomes possible to control to stop or weaken the ejection of rinse air from the air outlet.

  When the discharge of the powder coating material to the object to be coated is stopped, the rinsing air is ejected from the air outlet, whereby the corona electrode can be cleaned when the coating is stopped.

  As the powder coating nozzle of the present invention, a nozzle having a slit-shaped discharge port that forms a discharge pattern of a powder coating that spreads flatly in a fan shape can be used.

  The powder coating apparatus according to the present invention intermittently ejects rinse air for cleaning the corona electrode, specifically, when the distance between the object to be coated and the discharge port approaches, the rinse from the air outlet port. By controlling the spraying of rinse air that cleans the corona electrode only when coating is stopped, the spraying of air is stopped or weakened, while preventing the powder paint from adhering to the corona electrode. Prevents a decrease in the amount of powder paint adhering to the object to be painted, and even if the distance between the object to be coated and the nozzle at the tip of the corona gun approaches, the powder paint adhering to the object to be painted is blown away with rinse air. Can be prevented.

It is a perspective view which shows the example of the nozzle used for the powder coating apparatus which concerns on this invention. It is a front view of the nozzle of FIG. It is a side view of the nozzle of FIG. It is a vertical side view of the nozzle of FIG. It is a graph which shows the relationship between the gun distance of a corona gun, and an electric current value.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
In the powder coating apparatus according to the present invention, a powder coating nozzle 1 that forms a discharge pattern A of a powder coating is mounted on the tip of a corona gun.

  As the powder coating nozzle 1, for example, a so-called flat nozzle having a slit-shaped discharge port 2 that forms a discharge pattern A of a powder coating that spreads flatly in a fan shape is used.

  The slit-shaped discharge port 2 is formed in a mountain-shaped portion at the tip of the nozzle cylindrical portion.

  The powder coating nozzle 1 is made of a fluorine resin.

  In the powder coating nozzle 1, the electrode wire 3 is inserted from the rear end of the nozzle cylindrical portion toward the front chevron, and the corona electrode 4 formed at the tip of the electrode wire 3 is connected to the slit-shaped discharge port 2. By projecting to the center of the tip and applying a DC high voltage to the corona electrode 4 through the electrode wire 3, ions are generated by corona discharge in the vicinity of the corona electrode 4, and the powder paint discharged from the discharge port 2 is charged. Is granted.

  The electrode wire 3 is inserted into an air passage 5 formed from the rear end of the nozzle cylindrical portion of the powder coating nozzle 1 toward the front end of the chevron, and corona from the air outlet 6 at the front end of the air passage 5. Rinse air is jetted toward the electrode 4 so that the powder coating material does not adhere to the corona electrode 4.

  In the powder coating apparatus according to the present invention, rinse air is intermittently ejected from the air outlet 6 as follows.

  For example, it is possible to prevent the powder paint from adhering to the corona electrode 4 by performing an intermittent operation in which rinse air is jetted for 3 seconds during coating and then stopped for a certain period of time.

  The stopping time varies depending on the type of powder paint. The following five kinds of powder paint (paint A: metallic dry blend, paint B: metallic bonding, paint C: polyester white, paint D: epoxy black, In the case of paint E: polyester hammer tone), the stop time during which the powder paint did not adhere to the corona electrode 4 was as shown in Table 3.

  Next, for example, when coating the inner surface of the switchboard or the inner surface of the range hood, it is necessary to bring the powder coating nozzle 1 close to 30 to 50 mm, and the powder coating nozzle 1 is close to the object to be coated. If a large amount of rinse air is ejected from the air outlet 6, not only the pattern is disturbed by the rinse air, but also the powder paint adhered by the rinse air may be blown off. The powder on the corona electrode 4 can be reduced by increasing the amount of rinse air when painting away from the object to be painted or when painting is stopped. The paint is prevented from adhering.

  When the rinse air has an ejection amount of 0.015 MPa or less, it is possible to paint without blowing off the powder paint adhering to the painted surface, but the powder paint adheres to the corona electrode 4 as time passes. .

  For this reason, the amount of rinse air ejected is 0.1 MPa when painting away from the object to be painted or when painting is stopped. In order to remove the powder paint adhering to the corona electrode 4, it may be 0.05 MPa or more.

  As shown in the graph of FIG. 5, the current value of the corona gun increases when the gun tip approaches the object to be coated.

  For this reason, the rinse air can be adjusted by the fluctuation of the current value of the corona gun.

  For example, as shown in the graph of FIG. 5, when the gun distance to the object to be coated is 50 mm or less, the constant current control is 80 μA, so the rinse air is stopped when the current value reaches the maximum (80 μA). The air pressure (amount) can be controlled to gradually increase according to the current value.

  When the object to be coated is, for example, a range hood, when the current value is minimum (40 μA), the distance between the object to be coated and the gun tip is greatly separated, so that the rinse air at that time is 0.05 MPa. Even if it was set strongly, no blow-off by rinsing air was observed, and no powder paint adhered to the corona electrode 4 and the cleaning was good. Further, when the current value is zero, that is, when the discharge of the powder coating material is turned off, the corona electrode 4 can be completely cleaned by flowing the rinse air ejection amount at a maximum of 0.1 MPa for 3 seconds. it can.

  Further, when the corona gun approaches the object to be coated, the current value increases. For example, if the distance between the object to be coated and the corona gun becomes 150 mm, the current value becomes 53 μA. Therefore, using the electropneumatic proportional valve, the rinse air is set to 0.03 MPa, When the distance is reduced to 230 mm and the current value is reduced to 42 μA, there is no object to be coated in front of the corona gun. Therefore, by setting the rinse air to 0.05 MPa in advance by the electropneumatic proportional valve, the corona electrode Complete cleaning can be performed.

  Thus, by rinsing the rinse air intermittently, a stable charge can be given to the powder paint while preventing or removing the powder paint from adhering to the corona electrode 4 and stable coating can be performed.

1 Powder coating nozzle 2 Discharge port 3 Electrode wire 4 Pin type discharge electrode 5 Air passage 6 Air outlet

Claims (4)

At the tip of the corona gun, a powder coating nozzle equipped with a discharge port for controlling the discharge pattern of the powder coating is mounted, and an air outlet port for blowing rinse air toward the corona electrode is provided at the discharge port. In a powder coating apparatus, when the distance between the object to be coated and the discharge port approaches , the powder is characterized in that it is intermittently performed so as to stop or weaken the ejection of rinse air from the air outlet port. Body painting equipment. The ejection amount of the rinsing air, powder coating apparatus according to claim 1, characterized in that the adjustment in accordance with the variation of the current value of the corona gun.   2. The powder coating apparatus according to claim 1, wherein the rinsing air is ejected from the air outlet when the discharge of the powder coating material to the object to be coated is stopped. The powder coating apparatus according to any one of claims 1 to 3 , wherein the powder coating nozzle has a slit-shaped discharge port for forming a discharge pattern of a powder coating spread in a fan shape. .

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