JPS6057905B2 - Electrostatic coating method and device - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electrostatic coating method and apparatus.

More specifically, the present invention applies a metallic coating of a liquid type paint having a low electrical resistance (usually 10"Ω or less) or two coats of a metallic base to a metallic object having an insulating baked coating film on top. This invention relates to an improved electrostatic coating method and device that can further improve the quality of the painted surface by preventing the occurrence of crater-like paint surface defects that occur when clear painting is performed.For painting automobile bodies, etc. It is a well-known fact that electrostatic coating methods are widely adopted and used.

There are various types of electrostatic coating methods, and each method has been confirmed to have significant effects, such as saving paint and labor costs, and improving and uniformizing product quality. Such electrostatic coating generally involves forming an insulating baked coating film over a metal object by electrodeposition or spray painting, and
Furthermore, an intermediate coating film and a top coating film are formed above the coating film by electrostatic coating.
However, when electrostatic painting is carried out according to such a method, in other words, a commonly used high voltage, usually 90 to 120 KV1, is applied to the formed insulator baked coating film, and the coating is repeated according to the electrostatic painting method. When coating is carried out, crater-like coating defects often occur in the resulting wet coating film. This is because when a high voltage is applied as described above, a large amount of charge is accumulated in the electrostatic wet paint film, causing reverse ionization, and dielectric breakdown occurs in the underlying insulator baked paint film due to reverse ionization. However, electric charge is locally released from the upper electrostatic wet coating film toward the metal object, and the surface tension becomes higher in that area than in the outer periphery. It is of course undesirable to sell articles with crater-like coating defects on the market as products. When electrostatically painting a metal insulator that does not have an insulator baking coating film, even if the applied voltage is as high as 90 to 120 KV, and even as high as 100 to 300 pA. Even when current flows between the electrostatic coating device and the object to be coated, no crater-like coating defects occur, and not only can the coating be performed normally, but the coating efficiency is also high. The purpose of the present invention is to
To eliminate the above-mentioned drawbacks, that is, to have an insulating baked paint film on a metal workpiece, or a wet paint film such as a metallic paint film on the insulator baked paint film. When applying electrostatic coating to the object to be coated, the odor obtained from the electrostatic coating wet painted surface 3
An object of the present invention is to provide a method and an apparatus that enable better electrostatic coating by preventing the occurrence of crater-like coating surface defects.

According to the present invention, the purpose of this is to maintain the current flowing between the electrostatic coating device and the object to be coated to a small value below a set value when a high voltage is applied to the wet electrostatically coated surface of the object to be coated. This can be achieved by preventing back ionization from occurring. The present invention is a method for applying electrostatic coating of metallic coating or two coats of metallic base and clear coating to a metal object having an insulator baked coating film on the upper side, and in which an electrostatic coating device and an electrostatic coating are applied when a high voltage is applied. In order to continuously maintain the current flowing between the object and the object at a set value of 100 pA or less, the applied voltage must be changed immediately after reading the current value, or the coating equipment must be adjusted according to the reading value. This electrostatic painting method is characterized by moving back and forth. Furthermore, the present invention provides an apparatus for electrostatically applying metallic coating or two coats of metallic base and clear coating to a metal object having an insulating baked coating film on the upper side. In order to continuously maintain the current flowing between the device and the object to be coated at a set value of 100 pA or less, the following means are used: (1) A device for measuring the current value and connected to the rear of the electrostatic coating device. (2) a high voltage application control system for varying the applied voltage according to the measured current value.

Furthermore, the present invention provides an apparatus for applying electrostatic coating of metallic coating or two coats of metallic base and clear coating to a metal object having an insulator baking coating film on the upper side, and the electrostatic coating apparatus when applying high voltage. In order to continuously maintain the current flowing between the device and the object to be coated at a set value of 100 μA or less, the following means are used: (1) A device for measuring the current value, which is located behind the electrostatic coating device. (2) a cylinder means drive system for driving the reciprocating cylinder means in response to the measured current value; and (3) a cylinder means drive system for moving the coating device back and forth. An electrostatic coating apparatus is characterized in that it includes a combination of reciprocating cylinder means coupled thereto via an insulator.

In order to completely prevent the occurrence of crater-like coating surface defects, it is advantageous to keep the current flowing between the electrostatic coating device and the object to be coated as constant as possible at a small value of 100 μA or less when high voltage is applied. .

In particular, it is desirable to keep this current constant at a small value of 20 μA or less. Note that this current value does not depend on whether the electrostatic coating device used is a fixed type or a mobile type. According to the present invention, this is unavoidable when further electrostatic coating is performed on a metal article (object to be coated) which has an insulating baked coating film formed by electrocoating or spray coating. It is possible to prevent the occurrence of crater-like paint surface defects.

This new discovery is particularly good news for the automobile manufacturing industry, which is typified by electrostatic painting of automobile bodies, and will greatly contribute to improving product value. Of course, it is needless to mention here that the present invention can be applied to other related fields. Furthermore, based on research conducted by the present inventors, crater-like paint surface defects are likely to occur when applying metallic paint or 2-coat metallic base or clear paint on an insulator baked paint film, so this book is particularly suitable for such cases. It has been found that the effects obtained by applying the invention are very large. Further, according to the present invention,
The current value is limitedly controlled to 100 pA or less by employing a general feedback circuit, and there is no need to keep the current value strictly constant. The invention will now be described in more detail with reference to the accompanying drawings.

In the drawings, FIG. 1 is a schematic diagram of an electrostatic coating device according to one preferred embodiment of the present invention and a time chart showing its behavior mode, and FIG. 2 is a time chart according to another preferred embodiment of the present invention. 1 is a schematic diagram of an electrostatic coating device.

In FIG. 1, 1 represents a fixed electrostatic coating device.

Here, the object to be painted is indicated by 2, and above it,
An insulator baking coating film 3 and a wet electrostatic coating film 4 are sequentially formed. The object 2 to be coated is suspended by a hanger 8 and conveyed by a conveyor 9. The moving direction of the object 2 to be painted, that is, the painting direction, is indicated by an arrow X. Normally, when the distance (gun distance) between the electrostatic coating device 1 and the object to be coated 2 changes, the amount of current flowing therebetween also changes according to the distance change.

For example, as the distance between the two becomes shorter, the amount of current flowing between them increases, and therefore the amount of charge remaining on the wet electrostatic coating film 4 increases, resulting in a crater-like shape due to reverse ionization. Paint surface defects are caused. The illustrated device is
In order to achieve this, it is possible to prevent crater-like coating defects from occurring due to an increase in the flowing current.
A configuration is adopted in which the value of the flowing current is held substantially constant below a set value (100 pA or less, preferably 20 μA or less). As shown in the figure, a high voltage generator 19 is connected to the electrostatic coating device 1, and an ammeter 10 is further arranged behind the device 19.

The ammeter 10 continuously measures the value of the current flowing between the electrostatic coating device 1 and the object to be coated 2, and transmits the information to the high voltage application control system 21. The control system 21 immediately processes the sent information and sends a necessary signal to the high voltage generator 19 so that the applied high voltage is reduced to a low voltage if, for example, the current is flowing too much. The time chart in FIG. 1 clearly shows this type of behavior. In the figure, 5 is a time chart of applied high voltage, 6 is that of high voltage current, and 7 is that of paint discharge. As the paint starts to be discharged and electrostatic coating is performed, the gun distance becomes shorter, so the value of the current flowing between the electrostatic coating device 1 and the object to be coated 2 increases. The ammeter 10 detects this current change and notifies the high voltage application control system 21 of it. Subsequently, by the action of this control system 21, the applied high voltage 5 is changed from a high voltage to a low voltage as shown in the time chart. In this way, the value of the current flowing between 1 and 2 can be kept almost constant at a small value below the set value. When one cycle of coating is completed, the applied high voltage, current and paint discharge are each returned to zero, and when the object 2 to be coated is conveyed again, the previous process is repeated once again. Figure 2 shows
This shows an alternative method to that shown in FIG. 1, and the electrostatic coating device used here is not a fixed type but a mobile type.

The illustrated electrostatic coating device is represented by a rotary cup 12 and a drive motor 13 for the cup for the sake of simplicity. It is a cup type electrostatic coating machine. A reciprocating cylinder means is coupled to this device via an insulated support rod 14 for moving it back and forth depending on the measured current value. The moving direction of the coating device is indicated by arrow Y in the figure.
It is shown. Here, the reciprocating cylinder means is coupled to the cylinder 11 and a piston (not shown) in the cylinder 11, as shown, and moves the guide bar 15 as the piston moves, thus moving the coating device back and forth. It is composed of a connecting rod 18 for moving to. The guide bar 15 is supported by a support 17 via a bearing 16. In FIG. 2, an object 2 to be painted has an insulator baking coating film 3 already formed thereon, and is transported to a painting position while being suspended from a hanger 8.

A conveyor 9 is used for conveyance here, and the conveyance direction is as follows.
In the figure, it is indicated by an arrow x. When the gun distance changes after electrostatic coating starts, the current flowing between the rotary cup 12 and the object 2 to be coated also changes in accordance with the change. Subsequently, the ammeter 10 that has detected the change in current notifies the cylinder means drive system 22 of the extent of the change, and the drive system 22 that has received this information moves the rotary cup 12 forward or backward via the cylinder means. move it. -The locus drawn by the tip of the cup 12 is indicated by a chain line T.
(The sprayer only moves back and forth, not sideways, so the cup 12'' is only shown for convenience in its temporal positional relationship.) In this way, by keeping the gun distance constant, , 12, and 2 can be kept almost constant at a small value below the set value.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electrostatic coating device according to one preferred embodiment of the present invention and a time drawing showing its behavior, and FIG. It is a schematic diagram of an electric coating device. In the figure, 1 is an electrostatic coating device, 2 is an object to be coated, 3 is an insulator baking coating film, 4 is a wet electrostatic coating film, 8 is a hanger for an object to be coated, 9 is a conveyor, 10 is an ammeter, 11 is a cylinder, 12 is a rotating cup, 13 is a drive motor for the cup, 14 is an insulated support rod, 15 is a guide bar, 16 is a bearing, 17 is a support body, 18 is a connecting rod, 19 is a high voltage generator, 20 is a high voltage cable , 21 is a high voltage application control system, and 22 is a cylinder means drive system.

Claims (1)

[Scope of Claims] 1. In a method of applying electrostatic coating of metallic coating or two coats of metallic base and clear coating to a metal object having an insulating baked coating film above, the electrostatic coating device and The current flowing between the object and the object to be painted is 1
Immediately after reading the current value in order to continuously maintain the set value at 00 μA or less, the applied voltage is varied in accordance with the read value, or the coating device is moved back and forth in accordance with the read value. Electrostatic painting method. 2. In equipment that performs electrostatic painting of metallic paint or two coats of metallic base and clear paint on a metal workpiece that has an insulator baking paint film above, when high voltage is applied between the electrostatic painting equipment and the workpiece. The current flowing in 1
In order to continuously maintain the set value below 00 μA, the following means are used: (1) an ammeter connected to the rear of the electrostatic coating device for measuring the current value; and (2)
An electrostatic coating device characterized by comprising a high voltage application control system for varying an applied voltage according to a measured current value. 3. In equipment that applies electrostatic coating of metallic paint or 2-coat metallic base and clear paint to a metal workpiece that has an insulator baking paint film on the upper side, when a high voltage is applied, between the electrostatic painting equipment and the workpiece. The current flowing in 1
In order to continuously maintain the set value below 00 μA, the following means are used: (1) an ammeter connected to the rear of the electrostatic coating device for measuring the current value; (2) an ammeter for measuring the current value; (3) a cylinder means drive system for driving the cylinder means for reciprocating motion in accordance with the electric current value; and (3) a reciprocating motion for moving the coating device back and forth and coupled thereto via an insulator. An electrostatic coating device characterized in that it comprises a cylinder means for use in combination.