JPH08173858A - Electrostatic coating method of powder coating material and booth therefor - Google Patents

Abstract

PURPOSE: To provide an electrostatic coating method and a booth therefor in which a powder coating material of less atmospheric pollution is adopted to obtain a stable and smooth coating film without a reverse ionization phenomenon and adhesiveness in painting is increased to lower costs. CONSTITUTION: An electrostatic coating booth 3 whose ceiling part 4 and wall surfaces 65 are formed of a dielectric such as reinforced concrete is evacuated to low vacuum of 50-250Torr according to the particle size distribution. Voltage applied to an electrostatic coating apparatus 103 is lowered almost in proportion to the vacuum of the coating booth 3 to perform electrostatic coating, thereby reverse ionization is prevented and Faraday cage effect is relaxed and also adhesiveness in painting is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic coating method and an electrostatic coating chamber using a powder coating, and more particularly to a top coating for automobiles and the like.

[0002]

2. Description of the Related Art Since powder coatings do not contain petroleum-based solvents that pollute the atmosphere, their widespread use is expected in top coatings for automobiles and the like that use large amounts of coatings. However, powder coating has low spreading efficiency despite being electrostatically coated, and its cost is significantly higher than that of liquid coating, so that it has not spread. The coating efficiency is not limited to powder coating, but unnecessary electric lines of force in the electrostatic coating chamber and air flow in irregular directions significantly reduced the coating efficiency. The other major factors related to the coating efficiency are the charge ratio and the electric field strength of the powder coating, but the degree of influence changes depending on the particle size distribution of the coating. That is, the smaller the particle size, the higher the charging rate. On the other hand, the particle size distribution affects the smoothness of the coating film and the film thickness in addition to the charging rate. The smaller the particle size, the better the smoothness. However, when powder coating is applied, problems such as reverse ionization, which is a problem peculiar to electrostatic coating of powder coating, and the Faraday cage effect occur, which greatly affects the film thickness and the smoothness of the coating film. However, it was not possible to freely select the optimum voltage and the optimum particle size distribution for obtaining a high coating efficiency and a smooth coating film.

To explain the above problems in more detail,
Since the coating room for electrostatic coating is usually formed of a conductor such as a steel plate, the electric force has spread not only to the object to be coated but also to the ceiling and side walls of the coating room. These unnecessary lines of electric force not only reduce the coating efficiency because the charged powder paint is attracted by the Coulomb force, but also delay the discharge of the charged powder paint to the outside of the coating room. I needed attention. When this air supply collides with the object to be coated, an irregular air flow is formed in the coating chamber, further decreasing the coating efficiency.

The quality of the charging rate is greatly influenced by the electrode structure of the electrostatic coating machine, but is further influenced by the voltage applied to the electrodes. That is, when the applied voltage is increased, the discharge current is increased, the charge ratio of the paint is increased, and therefore the coating efficiency is increased. Further, the higher the voltage, the greater the electric field strength between the discharge electrode and the counter electrode, and the stronger the attraction to the object to be coated, which is the counter electrode, and the higher the coating efficiency. That is, increasing the voltage doubles the contribution to the improvement of the coating efficiency. Therefore, it is preferable to apply as high a voltage as possible for electrostatic coating,
When the electric field strength exceeds 6 kv / cm, sparks are generated and it becomes a dangerous state. On the contrary, when the electric field strength is 2 kv / cm or less, the coating efficiency is remarkably reduced. Therefore, in the case of liquid paint, it is slightly lower than the spark voltage, but 3.0-4.5 kv /
Electrostatically coated with a relatively strong electric field strength of cm. For example, when the distance between the electrodes is 20 to 30 cm, a high voltage of at least 60 kv is applied, and electrostatic coating is usually performed at a high voltage of 90 to 125 kv. However, in the case of the powder coating, the voltage cannot be increased because the reverse ionization phenomenon occurs. For example, at a distance between the electrodes of 20 to 30 cm, 75 k
It was difficult to set v or more.

The reverse ionization phenomenon in powder coating occurs as follows. When DC high voltage is applied to the discharge electrode of the electrostatic coating machine to generate corona discharge, air ions having the same polarity as the discharge electrode are generated. The powder coating particles adsorb the generated air ions and become charged. The charged powder coating material flies on the line of electric force formed between the discharge electrode and the grounded object forming the counter electrode, and flies to the object to be coated. At that time, the air ions adsorbed on the powder coating applied are discharged toward the counter electrode to lose the electric charge, return to the air and are released into the air. The release of air ions allows the newly charged powder coating particles to be further applied to increase the film thickness. However, as the coating progresses, the insulating property of the surface of the object to be coated increases and the discharge from air ions is hindered, so the electric charge of the same polarity as that of the discharge electrode gradually accumulates in the coating film, and the charged new paint particles It will hinder the adhesion. At this time, if the particle size of the paint particles is small, the required film thickness cannot be obtained. Therefore, if the coating voltage is increased in order to obtain the required film thickness, the amount of accumulated charge in the coating composition further increases and eventually exceeds the dielectric breakdown voltage of the coating composition, causing a so-called reverse ionization phenomenon. This phenomenon causes a small spark discharge on the surface of the coating film, destroys the coating film, and causes cissing or dent phenomenon on the surface of the coating film. Therefore, in the case of electrostatically coating the powder coating, it was unavoidable to reduce the electric field strength by sacrificing the coating efficiency and to set the electric field strength to 2.5 kv / cm or less. That is, the distance between the electrodes was 20 to 30 cm, and the coating voltage had to be 75 kv or less, which was considerably lower than the spark voltage.

On the other hand, even if the coating voltage is set to 75 kV or less, if the article to be coated is a box-shaped product, the electric flux line density to the inner corners is low, so that charged paint particles cannot reach.
There was a problem that the so-called Faraday cage effect occurred and the inner corners could not be painted. That is, the Faraday cage effect can be alleviated by reducing the electric field strength, and hence the applied voltage. However, the voltage is lowered, for example, the voltage is set to 40 kv or less, and the electric field strength is 2.0 k.
When it was reduced to v / cm or less, the coating efficiency was remarkably lowered as described above, so that the voltage could not be lowered sufficiently. Therefore, in electrostatic coating of powder coating, the electric field strength was set to 2.0 to 2.5 kv / cm. Therefore, as compared with electrostatic coating of liquid coating, the coating efficiency is poor, the Faraday cage effect is not sufficiently eliminated, and the film thickness at the corners of the box-shaped product becomes insufficient. Therefore, in order to secure the film thickness at the inner corners of the box-shaped product, the particle size has to be large, for example, 80 to 150 μm. However, if the particle size is increased, the film thickness becomes larger than necessary in the portions other than the corners, which not only increases the coating cost but also makes it difficult to be smoothed by heating and melting, resulting in poor appearance. Therefore, it was unavoidable to mix powder coating having a small particle size, for example, 10 to 30 μm. Therefore, the particle size distribution of the powder coating material has a wide particle size distribution of, for example, 10 to 150 μm including a coating material having a large particle diameter and a coating material having a small particle diameter. However, since the powder coating having a small particle diameter has a slow falling speed and a high charging rate, it is attracted to the ceiling of a coating chamber formed of a conductor and stays in the air for a long time. In this case, if the velocity of the air flow in the coating chamber, that is, the wind velocity, is low, the powder concentration in the air increases and the risk of dust explosion increases. Inevitably, the wind velocity was 0.5 m / sec. However, increasing the speed of the air flow not only discharges the surplus powder coating that floats in the air, but also hinders the coating of the charged powder coating toward the coating object. This resulted in a significant decrease in efficiency.

Therefore, in order to reduce the coating cost, a method of collecting and reusing the surplus powder coating which has not been applied has been taken. According to this method, the paint that has not been applied is collected, so it is thought that the paint cost will decrease, but the quality of the reused paint is unavoidably deteriorated, and the paint failure increases, which is not necessarily a cost reduction. There wasn't.

To solve this problem, Japanese Patent Publication No. 50-31
At 182, an apparatus for electrostatically coating powder coating in a vacuum coating chamber and vacuum drying is disclosed. According to this apparatus, since electrostatic coating is performed under vacuum, the powder coating used does not oxidize, so that there is an effect that the quality does not easily deteriorate. However, since the vacuum coating chamber is not formed of a dielectric material, the electrostatic effect extends not only to the object to be coated, but also to the inner walls and ceiling of the device, other transport hangers, chains and rails, static electricity addition devices, etc. Therefore, the charged powder coating material is fully retained in the coating chamber, and the coating material adheres to those electric conductor devices, resulting in extremely poor coating efficiency.

In view of the problems of the prior art, the present invention provides a coating room environment with the optimum conditions for electrostatic coating of powder coatings without the risk of fire or explosion, and at the same time, improves the coating efficiency. A method and apparatus for maximizing is provided.

[0010]

Therefore, the means provided by the present invention is to reduce the pressure in an electrostatic coating chamber formed of a dielectric material to a low degree of vacuum, and to use a powder coating in the coating chamber for static electricity. It is characterized by electrocoating, the low vacuum degree is determined by the particle size of the powder coating, and the low vacuum degree is 50t.
It is characterized in that it is not less than orrr and not more than 250 torr. Further, it is characterized in that the voltage for electrostatic coating is lowered substantially in proportion to the degree of vacuum. Further, the electrostatic coating chamber is made of a dielectric material and has a means for forming and maintaining a low degree of vacuum, and includes that the dielectric material is reinforced concrete.

[0011]

According to the means of the present invention, since the electrostatic coating chamber maintained at a low degree of vacuum is made of a dielectric material, an electric force in a direction other than the object to be coated, such as the ceiling or the wall of the electrostatic coating chamber, is applied. The line is erased. Therefore, the coating efficiency is improved and the uncoated electrostatic coating does not stay in the air for a long time. Therefore, even if there is no air flow in the coating chamber, the excess powder coating material can be discharged, and stable coating work can be continued. Further, since there is no air flow, the powder coating which has been electrified and rides on the lines of electric force and which is directed to the object to be coated almost adheres to the object to be coated, so that the coating efficiency is remarkably improved. Furthermore, since the vacuum degree in the electrostatic coating chamber is a low vacuum degree of 50 torr or more, and reinforced concrete can be used as a dielectric, even if a large-sized coating chamber is formed, the vacuum degree can be maintained easily and stable electrostatic coating work can be performed. it can. Furthermore, since the coating voltage is lowered according to the degree of vacuum, the reverse ionization and Faraday cage effects do not appear, and the inside of the box-shaped product can be coated uniformly.

More specifically, according to the means of the present invention, the particle size distribution determines 50 to 250 torr.
Discharge is performed in a coating chamber that is depressurized to a low vacuum degree of r. Generally, a discharge under a low degree of vacuum of 10 torr or more follows Paschen's law as shown in the textbook of discharge engineering.
That is, under a low vacuum, the discharge voltage decreases in proportion to the degree of vacuum, and discharge occurs at a voltage lower than the voltage under normal pressure. Therefore, even if the voltage is lowered and electrostatic coating is performed, the charging rate that is the same as under normal pressure can be obtained. On the other hand, the discharge resistance from the air ions adsorbed by the powder coating that has been adsorbed also decreases almost in proportion to the degree of vacuum, and therefore discharge is performed smoothly, so that reverse ionization does not occur and the particle size is extremely small. The required film thickness can be obtained without using a large powder coating, for example, even if a powder coating having a particle size of 60 μm or less is used. Also, since the voltage is reduced almost in proportion to the degree of vacuum and electrostatic coating is performed,
The electric field is relaxed and the influence of the unevenness of the object to be coated is small, so that the required film thickness can be obtained without using a powder coating having a particularly large particle size. On the other hand, even if the electric field strength is reduced, the discharge electricity amount does not change, so the charge ratio of the powder coating does not change,
Rather, it is not necessary to use a powder coating having a particularly large particle size, so that the charging rate is improved and the coating efficiency is improved. Furthermore, since a paint having a particularly large particle size is not used, a smooth coating film can be obtained without including a powder paint having a particularly small particle size. It does not contain powder paint with a particularly small particle size, and under vacuum, the falling velocity of fine particles follows Stokes' law or Allen's law,
Since the falling speed increases according to the degree of vacuum, the excess paint can be easily discharged, and the atmosphere in the coating chamber can be kept clean without exhausting or supplying air.

That is, as shown in the textbook of chemical engineering, the falling velocity of fine particles is inversely proportional to the square of the particle diameter under normal pressure according to Stokes' law. For example, the specific gravity is 1.2
When the particle diameter of the powder coating material of 1.6 is 60 μm or more, the falling speed under normal pressure is 15 cm / sec or more, which is a sufficient falling speed even without air flow. However, the particle size is 3
In the case of 0 μ, it decreases to 4.5 to 6.0 cm / sec under normal pressure, and in the case of 20 μ, it decreases to 2 cm / sec or less,
Almost no natural fall and fills the painting room. However, if the coating chamber is depressurized to 250 torr or less, the powder coating of 20μ follows the Allen's law and the falling speed is 15 to 20 cm /
sec is obtained, and the fall velocity is sufficient. Also, the particle size is 1
In the case of 0 μ, 15 to 20 cm / sec can be obtained at 50 torr. Therefore, the degree of vacuum in the coating chamber may be determined according to the particle size. In practice, the particle size distribution is 6 to ensure smoothness.
It is preferably 0 μm or less, and therefore, it is preferably 250 torr or less in order to secure a sufficient falling speed. Further, in the present invention, since reverse ionization does not occur, a paint having a small particle size can be used, but even if the particle size is 10 μm or less, there is no great difference in the smoothness of the obtained coating film, so there is no need to set it to 50 torr or less, On the other hand, the cost required for maintaining the vacuum condition increases significantly. Therefore, the degree of vacuum in the coating room is 50t.
It is preferable that it is not less than orrr and not more than 250 torr.

Further, according to the present invention, since reinforced concrete can be used substantially as a dielectric material, it is possible to form a large electrostatic coating chamber. Since a large electrostatic coating room can be formed, the lines of electric force do not reach the conductive equipment such as lighting fixtures installed on the ceiling or the upper part of the wall of the coating room. In addition, the columns of the electrostatic coating machine placed in the coating room and the protective electrodes that limit the lines of electric force to the conductive equipment such as the reciprocator are installed, and a high DC voltage of the same polarity as the voltage applied to the electrostatic coating machine is applied. Can be applied. Regarding these protective electrodes and electrostatic coating machines, Japanese Patent Application Nos. 6-281101 and 6-281104
Can be used. Therefore, unnecessary lines of electric force are not generated from the electrostatic coating machine. Further, even if an overhead traveling type conveyor is used as the transfer device, the length such as a hanger can be set with a margin, so that a protective electrode for limiting the direction of the lines of electric force can be provided. Therefore, unnecessary electric lines of force are not generated. Therefore, the coating efficiency is improved and the electrified paint does not stay in the air for a long time. Therefore, it is easy to discharge the excess paint. That is, since no electric line of force is formed from the discharge electrode of the electrostatic coating machine to the upper part of the object to be coated, such as the ceiling of the electrostatic coating chamber, and since the pressure is reduced to a vacuum of 250 torr or less, the downward direction of the coating chamber is reduced. Even if there is no air flow, and even if the particle size is 60 μm or less, the degree of vacuum is lowered according to the particle size, so that a sufficient falling speed can be obtained and the excess powder paint does not fill the coating chamber.

[0015]

[Embodiment] Next, based on an embodiment in which an electrostatic coating of an automobile is performed using a powder coating having a particle size distribution of 30 to 60 [mu], the mode and operation of the present invention will be described in detail. The electrostatic coating chamber 3 according to the invention is usually maintained while maintaining a vacuum degree of 200 torr. In order to maintain the environment of the electrostatic coating chamber 3, a powder dropping speed of 15 cm / sec is required.
ec is sufficient for the normal injection amount. Particle size distribution is 3
The falling speed of the powder coating material of 0 to 60 μ is 1.2 to 1.
6, in the case of particle size 30μ, under normal pressure 3.5-4.5c
Although it is m / cec, at 200 torr, since it follows Allen's law, a fall velocity of 25 to 35 cm / sec is obtained, which is a fall velocity sufficient to maintain the environment of a clean coating room.

FIG. 1 is a vertical sectional view of a continuous electrostatic coating apparatus showing the present embodiment, and is a layout diagram thereof. Further, FIG. 3 is a diagram showing an air supply system of the pressure adjusting chamber. In FIG. 2, the article-to-be-coated 74 and the carriage first enter the inlet-side pressure adjustment chamber 2. The pressure adjustment chamber 2 on the inlet side has an atmospheric pressure of 760
From torr to the operating condition of the electrostatic coating chamber 3, that is, 200
The atmospheric pressure can be adjusted periodically up to torr. When an object to be coated enters the inlet side pressure adjusting chamber 2 in the atmospheric pressure state, the first sealing door 5 is closed and the exhaust system 10 is activated to reduce the pressure within a predetermined time. Entrance side pressure adjustment chamber 2
When the atmospheric pressure of is equal to the atmospheric pressure of the electrostatic coating chamber 3, that is, 200 torr in this case, the second airtight door 6 attached to the partition walls of the inlet side pressure adjusting chamber 2 and the electrostatic coating chamber 3 opens. The article to be coated is sent to the electrostatic coating chamber 3. When the object to be coated has finished entering the electrostatic coating chamber 3, the second sealing door 6 is sealed, and the air supply systems 11 and 12 of the inlet side pressure adjusting chamber 2 are activated to return to atmospheric pressure. Then, the 1st sealing door 5 opens and the next to-be-coated article is contained. The above operation is repeated in the pressure adjusting chamber 2. The movement of the coated object during this period is intermittent,
By combining stop and fast-forward, continuous movement, that is, continuous production, becomes possible as the whole flow. The object to be coated that has entered the electrostatic coating chamber 3 is electrostatically coated while being stopped or continuously moving. When the coated object reaches the outlet side fixed position of the electrostatic coating chamber 3, the outlet side pressure adjusting chamber 4
The third closed door 7 provided on the partition wall of
It moves to the outlet side pressure adjustment chamber 4 adjusted to 0 torr. After entering, the third airtight door 7 is closed, the air supply systems 13 and 14 are operated, and the pressure is atmospheric pressure or 760 torr.
Back up. Subsequently, the fourth closed door 8 on the outlet side is opened, and the article to be coated moves to the drying step. The next step after electrostatic coating is a baking and drying step, but an apparatus under normal atmospheric pressure can be used.

Next, the structure, operation and action of each chamber will be described in detail.

The inlet side pressure adjusting chamber 2 has a closed pressure-resistant structure using reinforced concrete, and as shown in FIG. 2, has two fresh air supply systems, a natural air supply system 11 and a forced air supply system 12. Has been done. As shown in FIG. 3, in the natural air supply system 11, the distributor 30 is attached to the upper part of the pressure adjusting chamber 2 at an appropriate pitch, and the pressure adjusting valve 21, the first orifice 22,
Header 23, heater 29, second orifice 24, stop valve 25, filter 26, eliminator 27,
It communicates with the outside via a cyclone scrubber 28.
The pressure adjusting valve 21 is adapted to be opened by a signal separately given when returning from a vacuum state to atmospheric pressure, and is automatically closed when the pressure adjusting chamber 2 becomes atmospheric pressure. The heater 29 is capable of heating to 15 ° C. in winter. The orifices 22 and 24 limit the amount of supply air, and are installed by measuring the supply speed and determining the diameter. When the pressure in the pressure adjusting chamber 2 becomes 730 torr due to natural air supply, the forced air supply system 11
Operates, the stop valve 33 opens first, and then 750t
When it becomes orrr, the stop valve 36 opens, and the blower 37 further operates, and stops when the atmospheric pressure is reached. As shown in FIG. 3, the forced air supply system 12 includes a pressure regulating valve 34, a header 35, a stop valve 36, a blower 37, a filter 38, an eliminator 39, and a shower scrubber 4.
0, heater 41.

As shown in FIG. 2, a suction nozzle 50 is attached to the wall surface near the lowermost portion of the inlet side pressure adjusting chamber 2 and is connected to the exhaust system 10. The exhaust system 10 is composed of a vacuum pump and an electric valve, the capacity of which is determined by the production volume. Car production is 1 in 2 minutes
Air supply and exhaust of the inlet side pressure adjustment chamber 2 and opening / closing operation of the door for a stand

[Table 1] Shown in In this case, six vacuum pumps having an ultimate vacuum of 50 torr and an exhaust capacity of 20 m ³ / min are required. In addition, in the pressure adjusting chamber 2, as other auxiliary equipment, on the floor part,
It is equipped with a carrier such as a trolley, and is provided with a passage and lighting when an operator enters.

The ceiling portion 64 and the wall surface 65 of the electrostatic coating chamber 3 are
As shown in FIG. 1, it is made of reinforced concrete.
When the article to be coated is a small product, a resin product such as FRP can be used as the wall material, but it is preferable to use reinforced concrete because it has high pressure resistance. The size of the electrostatic coating chamber 3 may be set to a size large enough to accommodate an automatic coating machine such as the electrostatic coating machine 103 or a robot. Electrostatic coating room 3
A lighting fixture 71 is appropriately attached to the wall surface of the. Further, a window 70 for monitoring is installed appropriately. Further, a door 9 having a pressure resistance that allows an operator to enter and exit from the outside is provided as appropriate. On the floor surface of the electrostatic coating room 30, a steel grating 72 is laid. A conveyor 73 that conveys the article to be coated can pass through the center of the floor surface.
The article to be coated 74 is placed on a dolly, but all the conductors including the article to be coated are grounded. The lower zone of the electrostatic coating chamber 3 is a dust collection chamber 63. The excess atomized paint that has not been applied to the object to be coated 74 falls and is collected by the collecting water 76 stored at the bottom of the dust collecting chamber 63 due to gravity and downward electrostatic force. As a means for maintaining the vacuum state of the electrostatic coating chamber 3, the dust collection chamber 6
Nozzles 78 are attached to the wall surface near the lowermost end of 3 at an appropriate pitch, and are connected to an exhaust system 68 arranged outside the coating chamber. The exhaust capacity of the exhaust system 68 may be determined according to the size of the coating chamber. Further, 66 is an air supply valve for emergencies, which is normally closed.

The electrostatic coating machine 103 is not limited to this, but it is preferable to use an electrostatic coating machine with a shaping electrode for limiting the direction of the lines of electric force from the electrodes. Since the voltage applied to the electrostatic coating machine 103 is maintained at 200 torr, the distance between the electrodes is 20 to 30 cm, and 25 to 30 kv, which is slightly lower than the spark voltage, is used. Sparks tend to occur when the electric field strength exceeds 6 kv / cm under normal pressure. Under a low vacuum of 200 torr, it is approximately proportional to the degree of vacuum at 1.6 kv / cm.
Sparks are easily generated due to the electric field strength. therefore.
A practical electric field strength is 9 to 1.2 kv / cm. Therefore, when the distance between the electrodes is 20 to 30 cm, a practical voltage is 25 to 32 kv. In this case 95-125 under normal pressure
It is possible to obtain a discharge current almost equal to that when a high voltage of kv is applied. Therefore, as compared with the case of applying 40 to 75 kv under normal pressure, the charging rate is improved and the coating efficiency is improved. On the other hand, with respect to the unevenness of the article to be coated and the Faraday cage effect, the voltage is lowered, so that the electric field is relaxed and a more uniform coating film can be obtained. In order to change the film thickness and smoothness of the coating film, when changing the particle size distribution, the vacuum degree is proportionally changed with the above case of 200 torr as the standard, and the voltage to the electrostatic coating machine is changed to the vacuum degree. It may be changed in proportion.

The high-voltage generator 100 and the paint supply device 102 of the electrostatic coating machine 103 are installed outside the electrostatic coating chamber 3, and the electrostatic coating gun and electrodes in the electrostatic coating chamber 3 are connected to the X-ray cable 104. And paint hose 105. A protective electrode 107 formed of a thin metal wire is arranged on the lighting fixture 71 and the reciprocator 108 that reciprocates the electrostatic coating machine 103 so that the lines of electric force do not reach and the polarity is different from that of the electrostatic coating machine 103. Is applied and a DC high voltage having almost the same voltage is applied. Further, when an overhead traveling type conveyor is used as the transfer device, it is preferable to dispose the protective electrode so that the lines of electric force of the electrostatic coating machine do not go above the article to be coated.

The outlet side pressure adjusting chamber 4 is installed to return the pressure of the electrocoating chamber 3 to the atmospheric pressure, and may have substantially the same structure and material as the inlet side pressure adjusting chamber 2. The operation table of the door of the outlet side pressure adjusting chamber and the object to be coated, and the required vacuum pump capacity are the same as those of the inlet side pressure adjusting chamber shown in Table 1.

[0024]

According to the present invention, since the electrostatic coating chamber is made of a dielectric material, the direction of the lines of electric force from the electrostatic coating machine can be limited, and there is no air flow in the coating chamber. Therefore, the coating efficiency is increased. Further, since the interior of the coating chamber is electrostatically coated at a low degree of vacuum, back ionization does not occur, and electrostatic coating can be performed at a low voltage almost proportional to the degree of vacuum, so that the Faraday cage effect is mitigated. Therefore, the particle size distribution of the powder coating material can be freely selected according to the required film thickness or smoothness. Therefore, it is not necessary to include the powder coating material having an extremely large particle size, so that a smooth coating film can be obtained, and the charging rate is improved, and the coating efficiency is improved. Moreover, since it is not necessary to include paint with an extremely small particle size, it is possible to easily discharge the extra power paint even at a low vacuum degree. Therefore, stable coating can be continued. Furthermore, since the coating room is vacuum, a safe coating environment can be obtained without the risk of fire or explosion.

The electrostatic coating chamber of the present invention exerts its effect by using a powder coating, but it does not prevent the use of an aqueous coating or a high boiling point petroleum solvent coating. In this case, fresh air may be supplied according to the amount of paint used.

[Brief description of drawings]

[Figure 1] Sectional view of the electrostatic coating room

[Fig. 2] Layout plan of electrostatic coating chamber and pressure adjustment chamber

FIG. 3 is a diagram showing an air supply system of a pressure adjusting chamber.

[Explanation of symbols]

 3, electrostatic coating room 64, electrostatic coating room ceiling 65, electrostatic coating room wall surface 74, article 103, electrostatic coating machine

Claims (6)

[Claims] 1. A powder coating material characterized in that an electrostatic coating chamber formed of a dielectric material is decompressed to an atmospheric pressure of a low vacuum degree, and electrostatic coating is performed using the powder coating material in the coating chamber. Electrostatic coating method 2. The electrostatic coating method for powder coating according to claim 1, wherein the atmospheric pressure is determined by the particle diameter of the powder coating. 3. The electrostatic coating method for powder coating according to claim 1, wherein the atmospheric pressure is 50 torr or more and 250 torr or less. 4. The electrostatic coating method for powder coating according to claim 1, wherein the voltage for electrostatic coating is reduced substantially in proportion to the degree of pressure reduction. 5. An electrostatic coating chamber for powder coating formed of a dielectric material, which has means for forming and maintaining a low degree of vacuum. 6. The electrostatic coating chamber for powder coating according to claim 5, wherein the dielectric material is reinforced concrete.