JP5574697B2 - Electrostatic coating gun and electrostatic coating method - Google Patents

Description

  The present invention relates to an electrostatic coating gun and an electrostatic coating method for applying a charged paint to an object to be coated by electrostatic force.

  Many products such as automobile bodies and peripheral parts such as wipers, aluminum wheels and bumpers are painted. Painting is indispensable for LCD TV frames and mobile phones that have grown rapidly in recent years.

  In general, there are two types of paint guns: spray guns that spray solvent and electrostatic paint guns that use static electricity to reduce overspray powder as much as possible. A paint gun is used.

  Generally, electrostatic coating guns include a corona discharge electrostatic coating gun that charges a paint by corona discharge, and a friction charging electrostatic coating gun that charges a paint by frictional charging.

  A corona discharge electrostatic coating gun has a corona electrode installed at the tip that ejects paint to the object to be coated, forms an ionization region with the object to be coated by corona discharge, and charges the paint particles. It is.

  Corona discharge electrostatic coating guns include a gun that sprays liquid paints such as solvent paints and water-based paints, and a gun that sprays powder paints obtained by grinding paint resin into powder. For example, the body of an automobile is often used with an electrostatic coating gun using a solvent or a water-based paint in recent years, and the electrostatic coating gun using a powder paint is used for a wiper or an oil filter.

  Also, in recent years, from the viewpoint of quality improvement and smoothness, electrodeposition coating is applied to the undercoat, and then overcoating is applied by electrostatic coating, electrostatic coating on galvanizing, resin There are also many cases where electrostatic coating is applied to the skin.

JP-A-2005-349306

  By the way, the corona discharge electrostatic coating gun has a built-in high voltage generating device having a high voltage generating circuit, and a high voltage is supplied to the corona electrode.

  Therefore, in order to increase the charging efficiency of the paint particles and improve the application efficiency to the object to be coated, it is sufficient to incorporate a large high voltage generator, but this causes the problem that the gun itself becomes large and heavy. Occurs.

  For this reason, it is desired to improve the coating efficiency without increasing the size of the high voltage generator.

  Improvement of the coating efficiency is also desired in the triboelectric electrostatic gun.

  In addition, when a high voltage is applied to the corona electrode at the tip of the paint injection port, most of the ions discharged from the corona electrode reach the object to be coated as free ions, and the free ions cause electrostatic repulsion. As a result, there is a problem that so-called scaling occurs on the object to be coated.

  In addition, the lines of electric force generated by the corona discharge electrostatic coating gun tend to concentrate on the convex portion of the object to be coated, and do not easily reach the concave portion.

  Therefore, there is a problem that the paint collects on the convex part of the object to be coated, and the film pressure of the convex part becomes thick, so that coating with a uniform film thickness cannot be performed. There was also a problem that was sacrificed.

  Further, when undercoating or recoating is performed, there is a problem that resistance is generated between the object to be coated and the grounding wire, and electrostatic repulsion or scaling occurs.

  On the other hand, in the case of the friction charging electrostatic coating gun, the charging of the paint is much larger than the charging by the corona discharge electrostatic coating gun, and the paint can reach into the recess. When doing so, there was a problem that the paint also came to the operator's hand side and soiled the operator's hand.

  Therefore, the present invention reduces the concentration of the paint on the convex part by controlling the amount of charge on the paint in the corona discharge electrostatic paint gun and the frictional electrostatic paint gun, and into the concave part. It is intended to solve the problem of getting the operator around and making the operator's hand dirty.

  It is another object of the present invention to provide a method capable of satisfactorily applying an electrostatic force to an object to which a charged paint is difficult to adhere.

The present invention employs the following means in order to solve the above problems.
First, a corona discharge is connected to a high voltage generator and charged by an electric field generated by a corona electrode installed at the spray port of the paint, and the charged paint is sprayed onto the object to be coated by electrostatic force. An electrostatic coating gun is characterized in that an electrode connected to a DC power source is provided in the vicinity of the corona electrode.

  The paint used may be either a solvent or water-soluble solution paint or a powder paint.

  In addition, a friction charging electrostatic coating gun having a friction charging tube, friction charging the powder coating in the friction charging tube, spraying the charged powder coating onto the object to be coated and applying electrostatic force, An electrode connected to a DC power supply is provided in the vicinity of the injection port.

  In the case of the above-mentioned corona discharge electrostatic coating gun, the flow of free ions can be adjusted by adjusting the polarity applied to the electrode connected to the DC power source to the opposite polarity or the same polarity as that of the corona electrode. It is possible to activate the ion wind and to reduce the amount of free ions that cause electrostatic repulsion. As a result, the coating efficiency can be improved, the coating around the recesses can be improved, and the occurrence of scaling can be prevented.

  Also, in the case of a frictional charging electrostatic coating gun, the polarity applied to the electrode connected to the DC power supply can be made opposite to the polarity of the frictionally charged powder paint, or conversely, It is possible to stabilize the charge amount of the powder paint, reduce the backflow of the charged powder paint to the operator's hand, and prevent the operator's hand from being soiled.

  It is desirable to install a plurality of electrodes connected to the DC power source in a ring shape around the spray nozzle for both a corona discharge electrostatic coating gun and a frictional charging electrostatic coating gun.

  Moreover, the polarity given to the electrode of the DC power source can be switched to positive or negative or grounded according to the painting situation.

When the charged paint is difficult to apply due to electrostatic force, electrostatic coating can be performed by applying a DC voltage having a polarity opposite to the polarity of the charged paint to the object to be coated.
The DC voltage applied to the object to be coated may be a low voltage.

  As described above, according to the present invention, by installing an electrode connected to a DC power supply in the vicinity of the paint injection port, the charge amount to the paint can be controlled and the coating efficiency can be improved. In addition, the concentration of the paint on the convex portion can be reduced, and the contact with the concave portion can be improved.

  In addition, in the case of the friction charging type electrostatic coating gun, the charge amount can be stabilized and the backflow of the paint to the operator's hand side can be reduced.

  Further, by applying a DC voltage having a polarity opposite to the polarity of the charged paint to an object to which the charged paint is difficult to adhere, it can be applied by electrostatic force.

It is a schematic side view which shows an example of the corona discharge type electrostatic painting gun concerning this invention. It is a circuit diagram which shows an example of the DC power supply used in this invention. It is a schematic side view which shows the other example of the corona discharge type electrostatic coating gun which concerns on this invention. (A) is a schematic front view of the corona discharge electrostatic coating gun of FIG. 3 as viewed from the front side of the electrode connected to the DC power source, and (b) is another example of the electrode connected to the DC power source from the front side. FIG. It is a schematic side view which shows the other example of the corona discharge type electrostatic coating gun which concerns on this invention. It is a schematic side view which shows the other example of the corona discharge type electrostatic coating gun which concerns on this invention. It is a schematic side view which shows an example of the friction charging type electrostatic coating gun which concerns on this invention. It is a schematic side view which shows the other example of the friction charging type electrostatic coating gun which concerns on this invention. FIG. 9 is a graph comparing the friction current values of the friction charging electrostatic coating gun of FIG. 7 and the friction charging electrostatic coating gun of FIG. 8. (A) is the schematic of the coating surface of a coating experiment, (b) is the schematic which shows the mode of the coating experiment of the corona type electrostatic coating gun using a powder coating material. It is a perspective view of a brake pad. It is a schematic side view which shows an example of the electrostatic coating method of a brake pad. It is a schematic side view which shows the other example of the electrostatic coating method of a brake pad. It is a schematic plan view which shows the other example of the electrostatic coating method of a brake pad. It is a schematic perspective view which shows an example of the electrostatic coating method of a pole transformer.

Embodiments of the present invention will be described below.
FIG. 1 shows a schematic diagram of a corona discharge electrostatic coating gun 1 using a powder coating 4.

  The corona discharge electrostatic coating gun 1 has a high voltage generator 2 built in the gun. When the trigger 3 is pulled, the powder coating 4 and the compressed air 5 are supplied to the gun tip, and the gun tip spray port The powder coating 4 is sprayed from. Further, by pulling the trigger 3, a high frequency voltage is supplied to the high voltage generation circuit of the high voltage generator 2, and a DC high voltage of tens of thousands of volts generated by the high voltage rectification circuit is applied to the corona electrode 6 at the tip of the gun tip. And an electric field is generated between the object to be coated A and a corona discharge field is formed, and an electric charge is induced in the powder coating 4 injected from the gun tip injection port. When the charged powder coating 4 approaches the object A to be coated by the jet air, electricity having a polarity opposite to the electric charge of the powder coating 4 is induced on the surface of the object A to be grounded. An electrostatic force acts between the surface of the object to be coated A and the powder paint 4 is applied to the surface of the object to be coated A by both the suction force due to the static electricity and the blowing force of the jet air.

  In the corona discharge electrostatic coating gun 1 of FIG. 1, an electrode 8 connected to a DC power source 7 is provided in the vicinity of the corona electrode 6 connected to the high voltage generator 2.

As shown in FIG. 2, the DC power source 7 outputs, for example, direct current of a predetermined voltage to the changeover switch 11 from the output power from the battery 27 of 24 V by the regulator 10. The change-over switch 11 applies a positive voltage or a negative voltage to the electrode 8 based on the control signal. The negative voltage here means a voltage of 0 volts or less. Further, the electrode 8 can be grounded by the changeover switch 11.
When a DC voltage having the same polarity as that of the corona electrode 6 connected to the high voltage generator 2 is applied to the electrode 8, the ion wind from the corona electrode 6 is activated and the charging efficiency of the powder coating material 4 is improved.

  On the contrary, by applying a DC voltage having the opposite polarity to the corona electrode 6 connected to the high voltage generator 2 to the electrode 8, the ion wind from the corona electrode 6 is weakened. Can be weakened. Further, even in the article A to be coated having corner portions, it is possible to prevent electric lines of force from concentrating on the corner portions, so that it is possible to coat the concave portions.

  If the distance between the corona electrode 6 and the electrode 8 is too close, as the coating time elapses, the paint adheres to the electrode 8, the tip of the electrode 8 is insulated, and the effect of installing the electrode 8 is lost. An appropriate distance is selected in consideration of the wearing efficiency and dirt on the tip of the electrode 8. For this reason, it is desirable that the electrode 8 be movable back and forth with respect to the corona electrode 6.

  Further, the electrode 8 may be a single needle-like electrode as shown in FIG. 1, but the needle-like electrode may be provided in a ring shape like the corona discharge electrostatic coating gun 1 shown in FIG. Instead of a needle-like electrode, a ring-shaped one may be used.

  When the electrodes 8 are provided in a ring shape, a plurality of electrodes 8 may be directed toward the object A to be coated as shown in FIG. 4A, or as shown in FIG. You may make it face in the direction.

  Next, FIG. 5 shows a schematic view of a corona discharge electrostatic coating gun 1 using a solvent or water-soluble liquid paint 9.

  The corona discharge electrostatic coating gun 1 shown in FIG. 5 has a high voltage generator 2 built in the gun, and when the trigger 3 is pulled, the liquid paint 9 and the compressed air 5 are supplied to the tip of the gun. 9 is sprayed. Further, by pulling the trigger 3, a high frequency voltage is supplied to the high voltage generation circuit of the high voltage generator 2, and a DC high voltage of tens of thousands of volts generated by the high voltage rectification circuit is applied to the corona electrode 6 at the tip of the gun tip. And an electric field is generated between the object to be coated A and a corona discharge field is formed, and charges are induced in the particles of the liquid paint 9 sprayed from the spray port of the gun tip. When the charged particles of the liquid paint 9 approach the object A to be coated by the jet air, electricity having a polarity opposite to the charge of the particles of the liquid paint 9 is induced on the surface of the object A to be grounded. The electrostatic force acts between the particles 9 and the object A to be coated, and the particles of the liquid paint 9 are applied to the surface of the object A by both the suction force by the static electricity and the spraying force of the jet air. The

The corona discharge electrostatic coating gun 1 shown in FIG. 5 is also connected to a DC power source 7 in the vicinity of the corona electrode 6 connected to the high voltage generator 2, as in the corona discharge electrostatic coating gun 1 shown in FIG. The electrode 8 connected to is provided.
The configuration of the DC power source 7 is the same as that shown in FIG.

  When a DC voltage having the same polarity as that of the corona electrode 6 connected to the high voltage generator 2 is applied to the electrode 8, the ion wind of the corona electrode 6 is activated, and the charging efficiency is improved.

  On the contrary, by applying a DC voltage having the opposite polarity to the corona electrode 6 connected to the high voltage generator 2 to the electrode 8, the ion wind of the corona electrode 6 is weakened. Can be weakened. Further, even in the article A to be coated having corner portions, it is possible to prevent electric lines of force from concentrating on the corner portions, so that it is possible to coat the concave portions.

  If the distance between the corona electrode 6 and the electrode 8 is too close, as the coating time elapses, the paint adheres to the electrode 8, the tip of the electrode 8 is insulated, and the effect of installing the electrode 8 is lost. An appropriate distance is selected in consideration of the wearing efficiency and dirt on the tip of the electrode 8. For this reason, it is desirable that the electrode 8 be movable back and forth with respect to the corona electrode 6.

  Further, the electrode 8 may be a single needle electrode as shown in FIG. 5, but may be provided in an annular shape as shown in FIG. May be used.

Next, FIG. 7 shows a schematic view of the frictional charging type electrostatic coating gun 12 according to the present invention.
The friction charging electrostatic coating gun 12 is provided with a friction tube 13 made of a non-conductive resin. When the trigger 3 is pulled, the powder coating 4 and the compressed air 5 are supplied into the friction tube 13. Friction occurs with the body paint 4, and the powder paint 4 is charged by this friction, and the charged powder paint 4 is sprayed toward the object A. When the charged powder coating 4 approaches the object A to be coated by the jet air, electricity having a polarity opposite to the electric charge of the powder coating 4 is induced on the surface of the object A to be grounded. An electrostatic force acts between the surface of the object to be coated A and the powder paint 4 is applied to the surface of the object to be coated A by both the suction force due to the static electricity and the blowing force of the jet air.

  The powder coating 4 is charged by contact (friction) with the friction tube 13. When the powder coating material 4 is charged (for example, plus (+)), the friction tube 13 is charged with minus (−). Therefore, unless the negative (−) charge of the friction tube 13 is quickly released, the powder coating 4 conveyed one after another is not charged. For this reason, as shown in FIG. 7, the frictional charging type electrostatic coating gun 12 generally grounds (grounds) the friction tube 13 so as to release the electric charge.

  In the triboelectric electrostatic gun 12, the contact method (friction) between the friction tube 13 and the powder coating 4 and the contact speed are naturally important. However, it is also important how quickly the charge (charge opposite to the powder coating particles) charged in the friction tube 13 is released. Generally, tetrafluoroethylene (polytetrafluoroethylene) is used for the friction tube 13. The reason is that when tetrafluoroethylene rubs against a general resin, it immediately shows minus (−) and charges the resin to (+). In addition, since the sliding property is good, the powder coating 4 is difficult to stick.

  In order to quickly release the charged electric charge of the friction tube 13, in the electrostatic charging type electrostatic coating gun 12 shown in FIG. 8, instead of grounding (grounding) the friction tube 13, a DC voltage of plus 12 V is applied from the DC power source 7. ing.

  The friction current values of the friction charging electrostatic coating gun 12 shown in FIG. 7 with the friction tube 13 grounded and the friction charging electrostatic coating gun 12 shown in FIG. As a result of measurement, as shown in the graph of FIG. 9, the friction charging electrostatic coating gun 12 shown in FIG. 8 in which a positive 12 V DC voltage is applied to the friction tube 13 is shown in FIG. It was confirmed that the current value was more stable and the amount of charge of the powder coating material 4 was almost constant as compared with the friction charging electrostatic coating gun 12 shown.

  By the way, the frictional charging type electrostatic coating gun 12 does not have the corona electrode 6 like the corona discharge type electrostatic coating gun 1, and therefore no electric field is formed with the object A to be coated. That is, the coating is performed only by frictional charging of the powder coating material 4. In general, in the corona discharge electrostatic coating gun 1, several percent of the electric field generated from the corona electrode 6 contributes to the charging of the powder coating 4, but most (nearly 99%) is free ions, The electric field is formed on A. Free ions tend to concentrate on the convex part of the article A to be coated, but on the other hand, it is difficult to reach the concave part. For this reason, in the case of the corona discharge electrostatic coating gun 1, the discharged powder coating 4 gathers a lot at the convex part, becomes a thick film, and sacrifices around the concave part, for example, the gap.

  On the other hand, in the case of the friction charging type electrostatic coating gun 12, since there is no corona electrode 6, the charged powder coating 4 easily enters the recess. Further, since the charging to the powder coating 4 is very large as compared with the corona, for example, in the case of manual blowing, the powder coating 4 is likely to adhere to the operator.

  In order to prevent back flow to the operator's hand side, the triboelectric electrostatic coating gun 12 of FIGS. 7 and 8 has at least one electrode at the rear of the powder coating 4 near the injection port. 8 is applied, and a positive (+) DC voltage, which is the same as the polarity of the frictionally charged powder coating material A, is applied to the electrode 8. Since the powder coating A is charged with minus (−) due to frictional charging, for example, when a DC voltage is applied to the electrode 8 from a plus (+) 12 V battery, the powder to the rear of the gun The spraying back of the paint A is reduced, and the dirt on the operator's hand in continuous coating is reduced.

Next, the result of the coating experiment of the corona discharge electrostatic coating gun 1 using the powder coating 4 will be shown.
In the coating experiment, as shown in FIG. 10, a corona discharge electrostatic coating gun 1 provided with a ring-shaped electrode 8 as shown in FIG. 4B is installed in a reciprocator 14 as shown in FIG. went.

The ring-shaped electrode 8 is installed at the tip of the gun so as to be movable back and forth, so that the distance from the corona electrode 6 to the electrode 8 can be changed.
The electrode 8 is connected to the DC power supply via a changeover switch, and a positive voltage or a negative voltage can be given by the changeover switch. In the coating experiment, 0 V was applied to the needle-like electrode 8. Check the change in the coating amount for the case (same as the case where the needle-shaped electrode 8 is not installed), the case where the needle-shaped electrode 8 is grounded, and the case where a plus 24 volts is applied to the needle-shaped electrode 8 did.

In the coating experiment, a receiving plate 16 having a width of 800 mm and a height of 600 mm is hung on the conveyor 15, and a coating amount measuring plate 17 having a height of 300 mm, a width of 450 mm, and a thickness of 0.8 mm is placed on the front surface of the receiving plate 16. The powder coating 4 was sprayed from the -80 kV corona electrostatic gun 1 toward the coating amount measuring plate 17.
Other coating conditions are as follows.

Conveyor speed: 1.0 m / min
Distance between gun tip and backing plate 16: 200 mm
Reciprocator 14 speed: 20 m / min
Reciprocator 14 stroke: 600 mm
Discharge rate: 50 g / min

  The electrode 8 was moved back and forth so that the amount of application was maximized. When the electrode 8 is grounded, the position where the coating amount is maximized is 80 mm at the horizontal distance from the corona electrode 6, and when the electrode 8 is given plus 24 volts, the horizontal distance from the corona electrode 6 is 120 mm. there were.

The coating experiment was performed 10 times each, and the average was defined as the coating amount. The coating efficiency was expressed in% by dividing the weight of the powder coating 4 applied to the coating amount measuring plate 17 by the discharge amount (g) of the actual coating time.
The results of the coating experiment are summarized in Table 1.

  As described above, when the electrode 8 is grounded, the horizontal distance from the corona electrode 6 to the electrode 8 at which the maximum coating amount is obtained is 80 mm, but when a positive voltage of 24 volts is applied to the electrode 8 The maximum coating amount was obtained at a position where the horizontal distance from the corona electrode 6 to the electrode 8 was 120 mm. This is presumably because the ions discharged from the gun tip were activated by the plus (+) ion wind from the electrode 8 even when the horizontal distance from the corona electrode 6 to the electrode 8 was increased.

  Further, in the mass production line, the electrode 8 is easily soiled when continuous coating is performed. In particular, as the distance from the corona electrode 6 is shorter, the paint adheres to the electrode 8 and when the insulating state is approached, the activation of the corona electrode 6 is reduced, and the coating efficiency is lowered.

  As a result of the above coating experiment, when the electrode 8 was grounded, the coating efficiency decreased after 8 hours as in the case where the electrode 8 was not present, that is, when 0 V was applied to the electrode 8. When a DC voltage of +24 V was applied to 8, the coating efficiency after 8 hours was almost the same as the initial efficiency.

  In the above-described coating experiment, a positive (+) DC voltage was applied to the electrode 8. For example, by applying a negative (-) DC voltage and adjusting the voltage and current, the coating film A was coated. It can be adjusted according to the location. Also, the electrode 8 can be grounded (grounded), plus (+) minus (-) DC voltage, current, and ground can be switched with a changeover switch, depending on the shape of the object A to be painted or coated The film thickness can be controlled according to the location of the object A.

  Next, Table 2 shows the results of a coating experiment using the corona discharge electrostatic coating gun 1 using the liquid paint 9 having the form shown in FIG. In Table 2, the distance from the electrode is the horizontal distance from the corona electrode 6 to the surface including the tip of the annular electrode 8.

  In Table 2, the initial is at the start of painting, and after 8 hours is after 8 hours of continuous painting, including a one-hour stop in the middle, and each value indicates the coating efficiency (%). .

  The corona discharge electrostatic coating gun 1 includes a high pressure generator 2. The voltage of the conventional corona discharge electrostatic coating gun 1 is 60 KV. In the coating experiment shown in Table 2, a gun with a voltage of 30 KV was used.

  A coating experiment using the conventional 60 KV corona discharge electrostatic coating gun 1 was performed in the same manner, but the initial coating efficiency was 37% and the coating efficiency after 8 hours of continuous coating was 36%.

  As a result of the coating experiment, when the electrode 8 of the corona discharge electrostatic coating gun 1 is grounded (grounded), the corona electrode 6 is activated by the grounded ring-shaped electrode 8 to generate a 30 KV high-voltage generator. The corona discharge electrostatic coating gun 1 using 2 showed the same coating efficiency as the corona discharge electrostatic coating gun 1 using the 60 KV high pressure generator 2. However, in the vicinity of 10 to 20 mm from the electrode, the efficiency is greatest, but since the distance from the electrode is short, the paint adheres to the grounded electrode 8 in a short period of time, and the effect is drastically reduced.

  Further, when a positive (+) 12 V DC voltage is applied to the electrode 8, the coating efficiency at the position near 70 mm from the corona electrode 6 as shown in Table 2 is the maximum value equivalent to that when the electrode 8 is grounded. Indicated. Since the distance from the corona electrode 6 is increased, the electrode 8 is not easily soiled, and stable coating can be performed even for long-time coating.

  In the coating experiment of Table 2, plus (+) 12 V was used, but the numerical value of the DC voltage applied to the electrode 8 may be changed depending on the voltage and shape of the high voltage generator 2. Also, the electrode 8 can be grounded (grounded), plus (+) minus (-) DC voltage, current, and ground can be switched with a changeover switch, depending on the shape of the object A to be painted or coated The film thickness can be controlled according to the location of the object A.

  Next, when it is difficult to apply the charged paint to the object A to be coated with electrostatic force, the electrostatic charge is applied to the object A by applying a DC voltage having a polarity opposite to the polarity of the charged paint. Painting becomes possible.

  For example, a brake pad is one of automotive parts that have recently increased in electrostatic powder coating. Since the use of aluminum wheels has increased and the outer surface of the brake pads can be seen well from the space of the wheels, the brake pads are also painted in the same color according to the color tone of the car body to improve the appearance. It has become.

  By the way, the brake pad 18 includes a metal base plate 19 and a pad portion 20 as shown in FIG.

  Pad part 20 is made of skeletal material (asbestos, barium sulfate, metal fiber), lubricant (coke, graphite, metal sulfide), abrasive (metal oxide, mineral, metal), damping material (rubber system), pH adjustment However, in recent years, the amount of iron powder in the pad portion 20 has decreased, and the conductivity of the pad portion 20 has been lost.

  For this reason, when the brake pad 18 is electrostatically coated, the side surface portion of the non-conductive pad portion 20 has a problem that the coating of the paint is poor and the side surface portion of the pad portion 20 cannot be satisfactorily coated. .

  In order to improve the coating of the side surface portion of the pad portion 20, conventionally, it has been necessary to perform so-called pre-heating coating, in which the brake pad 18 is preheated or heat is applied during molding. It was.

  In the present invention, without applying this pre-heating coating, a DC voltage having a polarity opposite to the polarity of the charged paint is applied to the brake pad 18 during electrostatic coating, so that the pad portion 20 having no electrical conductivity can be obtained. The charged paint was made to adhere well to the side surface.

  As a method of performing electrostatic coating while applying a DC voltage having a polarity opposite to the polarity of the charged paint to the brake pad 18, the following method can be employed.

  For example, as shown in FIG. 12, two corona discharge electrostatic coating guns 1 that discharge a negative (−) charged powder coating are installed above the coating booth 21, and on the insulating belt 22 of the coating booth 21. Coating is performed by spraying a negative (−) charged powder coating toward the brake pad 18 that moves on the pad. The brake pad 18 moves on the insulating belt 22 with the pad portion 20 facing downward, and the conductive wire 23 connected to the DC power source contacts the pad portion 20 during the movement, and the plus portion of the conductive wire 23 increases. (+) 24V is applied.

  As a method for energizing the brake pad 18, as shown in FIG. 13, the energization line 23 may be brought into contact with the metal base plate 19 and the pad portion 20 may be energized via the base plate 19.

  Further, as shown in FIG. 14, the energization line 23 may be energized in the center of the insulating belt 22 on which the brake pad 18 is placed.

  The DC voltage supplied to the energization line 23 should be a low voltage in consideration of safety.

  Next, for example, the pole transformer 24 is provided with a large number of fins 25 on its outer surface as shown in FIG. 15 and requires heavy corrosion protection, and it is necessary to apply a powder coating of 100 μm or more on the surface of galvanization. There is.

  However, since the interval between the fins 25 is narrow and the depth of the fins 25 is wide, when coating is performed using a corona discharge electrostatic coating gun, charged powder is placed in the gaps between the fins 25 and 25. The body paint is difficult to enter, and can only be applied to a film thickness of about 50 μm. In addition, the back of the fin 25 and the inner surface of the fin 25 may be struck.

  In order to solve such a problem, according to the present invention, when coating is performed using a corona discharge electrostatic coating gun, the pole transformer 24, which is the object to be coated, is placed on the insulating base 26, and the pole When the outer surface of the transformer 24 was connected to a DC power source and a positive (+) 24 V was applied, a negative (-) charged powder coating was sprayed from a corona discharge electrostatic coating gun, and coating was performed. While making a sound, the powder paint entered the depths of the fins 25, and the powder paint could be uniformly attached to the whole with a film thickness of 100 to 150 μm.

  As described above, when electrostatic coating is performed while applying a DC voltage to the object A, it is possible to safely perform thick coating even on resin parts such as bumpers of automobiles.

  Since resin parts have insulating properties, when electrostatic coating is performed, a conductive agent solution is first applied, and then electrostatic coating is performed by a corona discharge electrostatic coating gun using a solution paint. As the coating film is formed, static electricity tends to accumulate on the surface, and small sparks such as sparks are generated on the painted surface.

However, if electrostatic coating is applied to the hanger of the object to be coated while applying a positive (+) 24V DC voltage only in the painting booth, small sparks such as sparks are almost eliminated, and the conductive agent coating film is applied. It was also possible to improve the poor coating of the parts with few.
Except for the painting booth, the hangers are grounded (grounded) for safety.

DESCRIPTION OF SYMBOLS 1 Corona discharge type electrostatic painting gun 2 High voltage generator 3 Trigger 4 Powder paint 5 Compressed air 6 Corona electrode 7 DC power supply 8 Electrode 9 Liquid paint 10 Regulator 11 Changeover switch 12 Friction charging electrostatic painting gun 13 Friction tube 14 Reciprocator 15 Conveyor 16 Receiving plate 17 Coating amount measuring plate 18 Brake pad 19 Base plate 20 Pad part 21 Coating booth 22 Insulating belt 23 Conductor 24 Pole transformer 25 Fin 26 Insulating base 27 Battery A

Claims (11)

  A corona discharge type static electricity generator that is connected to a high-voltage generator, charges the paint by an electric field generated by a corona electrode installed at the paint injection port, and sprays the charged paint onto the object to be coated by electrostatic force. A corona discharge electrostatic coating gun characterized in that an electrode connected to a low voltage DC power source is provided in the vicinity of an electrode connected to the high voltage generator.   The corona discharge electrostatic coating gun according to claim 1, wherein the paint is a solvent or a water-soluble solution paint.   The corona discharge electrostatic coating gun according to claim 1, wherein the paint is a powder paint.   In the triboelectric charging gun, the triboelectric charging gun is equipped with a triboelectric charging tube, triboelectrically charges the powder coating in the triboelectric charging tube, and sprays the charged powder coating onto the object to be coated by electrostatic force. A friction charging electrostatic coating gun characterized in that an electrode connected to a low-voltage DC power source is provided in the vicinity of.   2. The corona discharge electrostatic coating gun according to claim 1, wherein the polarity applied to the electrode connected to the DC power supply is opposite to the polarity of the electrode connected to the high voltage generator.   2. The corona discharge electrostatic coating gun according to claim 1, wherein the polarity applied to the electrode connected to the DC power supply is the same as the polarity of the electrode connected to the high voltage generator.   5. The triboelectric charging gun according to claim 4, wherein the polarity applied to the electrode connected to the DC power supply is opposite to that of the frictionally charged powder coating material.   5. The triboelectric charging gun according to claim 4, wherein the polarity of the electrode connected to the DC power source is the same as that of the frictionally charged powder coating material.   The electrostatic coating gun according to any one of claims 1 to 8, wherein the electrode connected to the direct current power source is provided in a ring shape around a paint injection port.   5. The electrostatic coating gun according to claim 1, wherein the polarity applied to the electrode of the DC power source is switched between positive and negative. In the electrostatic coating method in which the paint is charged and sprayed on the object to be coated, or the object to be coated is immersed in the fluidized tank of the charged paint, a low-voltage DC power supply is connected to the object to be coated, An electrostatic coating method characterized in that a polarity opposite to that of the charged paint is applied to the surface.