JPS598182B2 - Layered charging type powder coating equipment - Google Patents

Description

[Detailed Description of the Invention] This invention involves passing powder paint, which is dispersed and suspended in a gas to form a layer, through a space sandwiched between a pair of planar silent discharge electrodes facing each other, and from these electrodes. The paint powder is sufficiently charged by unipolar ion showers that alternately pass in opposite directions across the layer of suspended paint powder, thereby obtaining extremely high coating efficiency. The present invention relates to a new electrostatic powder coating device.

The electrostatic powder coating method has many advantages such as non-pollution, excellent coating film, simplified process, and resource saving, so its scope of application is gradually expanding as a new coating method. Even today, this method still has major drawbacks compared to the liquid paint method that uses thinner and the like, which has been widely used in the past.

It has relatively low transfer efficiency. This drawback is usually about 30 to 60%, and becomes serious especially when a large capacity coating machine is used. In other words, in the electrostatic powder coating process, if the overspray paint is not collected, the economic efficiency of the painting process will be significantly reduced.However, if the coating efficiency is low, the collected paint will be mixed with some dust. For example, since changes in properties such as particle size distribution cannot be avoided, reused paints have a serious drawback in that the performance of the paint film inevitably deteriorates. The coating efficiency of electrostatic powder coating method is relatively low;
In particular, when a large amount of powder is injected from one gun, the performance decreases significantly, and most of the paint powders used are powders with extremely high electrical resistance that are difficult to charge. However, no reliable method has been developed to apply this like a liquid paint in the form of a thin film to the periphery of a rotating cup, for example, to form evenly distributed droplets and at the same time to charge the droplets. There is a big reason. In the case of liquid-based electrostatic coating, the droplets ejected from the gun are usually already charged by the time they leave the gun, whereas in the conventional electrostatic powder coating method, When injected from the tip of the gun, most of the powder is usually uncharged or charged with variable polarity due to contact charging, and this powder flies from the gun to the object to be coated. ≦ due to the ionic current flowing from the tip of the gun to the workpiece on the way
Usually, it is partially charged. However, in this case, it is difficult to reliably disperse the paint powder in the current region of the ionic current flowing from the tip of the gun toward the object to be coated. This current flowing from the gun toward the workpiece is less likely to occur because the charge of most of the particles between it and the workpiece is masked by the already charged particles that stay nearby. Especially when the airflow in the booth is perpendicular to the lines of electric force from the gun to the workpiece, the uncharged particles ride the airflow and immediately become ionized by the ionic current. It is essentially difficult to increase the coating efficiency because it is carried away outside the area where it exists. At the same time, with conventional guns, in order to sufficiently charge the particles flying from the tip of the gun toward the workpiece, a large amount of current is passed from the gun toward the workpiece. A large amount of current must be passed through the powder layer deposited on the surface of the powder layer, and the current flowing through the powder layer causes a significantly large voltage drop within the powder layer. In extreme cases, reverse ionization occurs and the smoothness of the coating film is lost.In extreme cases, it can cause the occurrence of yuzu skin, clay stains, etc. A major drawback of the electrostatic powder coating method was that it was not possible with the painting method. In order to improve the drawbacks of the electrostatic powder coating method, which mainly involves passing a current from the tip of the gun toward the object to be coated, a corona discharge electrode or the like is installed inside the gun. An internal charging type electrostatic powder coating device was devised in which the powder is charged inside the gun by generating a corona discharge, and the current flowing from the tip of the gun to the object to be coated is not used to charge the particles. has already been put into practical use.

However, with these internally charged electrostatic powder coating devices, the tip of the corona discharge electrode gradually wears out due to discharge, or the tip of the corona discharge electrode is coated with highly insulating paint powder. In some cases, the gun has a very serious defect in that it is difficult to stably maintain a sufficient discharge over a long period of time due to causes such as corrosion, and at the same time, the processing capacity of the gun contact is low. In some cases, even if the performance of the gun is obtained, it has a serious drawback that a single gun cannot have a large processing capacity. As described in detail above, this invention addresses the low coating efficiency of external loading type electrostatic powder coating equipment and the long-term charging capacity of internal charging type electrostatic powder coating equipment. It is possible to solve the drawbacks such as lack of stability and low processing capacity, and to obtain a coating film with high coating efficiency and good smoothness over a range of processing capacity from small to extremely large. At the same time, the present invention provides a new electrostatic powder coating device whose performance is extremely stable over a long period of time.

In the electrostatic powder coating apparatus according to the present invention, after the powder coating is made into a state in which particles are dispersed and suspended in a gas by either an electric method or an electrodynamic method that does not use air, The paint powder is dispersed and ejected from a slit-shaped paint spout, and the paint powder ejected from this is dispersed and suspended in a layered state in the gas with each particle well separated. These planar silent discharge electrodes are arranged so as to sandwich the paint particles from both sides, and these planar silent discharge electrodes are operated one by one alternately so that plasma exists on the surface, and at the same time By applying a voltage between the silent discharge electrode in operation and the silent discharge electrode in such a manner that a relative potential with a constant direction always exists between the two electrodes, the layered structure described above can be achieved. The particles are reliably charged by sufficiently charging the suspended particle powder layer traveling in the space surrounded by the silent discharge electrode from both sides alternately with a monoptic ion shower, and then facing each other. Mechanical arrangement such that the powder coating that has escaped the space sandwiched between the planar silent discharge electrodes advances toward the object to be coated, and a voltage applied between both silent discharge electrodes and the object to be coated. By doing so, the particles can be charged extremely reliably, thereby achieving extremely high coating efficiency.

Furthermore, according to this method, the charge density of the charged powder passing between the layered planar silent discharge electrodes can be reliably spread over a wide range by the electric field strength applied between the silent discharge electrodes. Since it is possible to control the charge density of particles, it is possible to reliably control the charge density of particles, and by adjusting this voltage appropriately, it is possible to control even particles that are easily charged or particles that are difficult to charge. This makes it possible to charge to a desired charge density, thereby making it possible to obtain a high coating efficiency and a smooth coating film. In the electrostatic powder coating apparatus according to the present invention, when the powder coating particles are charged, the particles are separated in the gas and suspended relatively sparsely, and are not repelled from the essential VC electrode surface. Its greatest feature is that even if a large amount of particles are supplied, they can be charged reliably and at a desired charge density because they are supplied in a layered manner while being subjected to a similar action. The particle charging device of the electrostatic powder coating device according to the present invention described in detail above can be easily realized by the charged particle generator proposed by the inventor in Japanese Patent Application No. 1978-78222. The particle charging mechanism by this method is the same as that which the inventors have already solved in their earlier application. Next, embodiments of the present invention will be described in detail using the drawings.

FIG. 1-1 shows a longitudinal sectional view of an electrostatic powder coating apparatus according to the present invention. Figure 1-2 is A and A in Figure 1-1.
2 shows a horizontal cross-sectional view indicated by . As shown in Figures 1-1 and 1-2, the powder paint 7 stored in the hopper is transferred into the Ejiekshio-25 by the high pressure air for dispersion indicated by the powder supply device 8. Then, it passes through the transition section 10 and reaches the slit 11, where it becomes a layered powder particle that is sufficiently dispersed and suspended, and the planar silent discharge electrodes 5 are spaced apart from each other. , 6 through the space 12 between them. In the shallow parts of the inner surfaces of the planar silent discharge electrodes 5 and 6, there are two groups of silent discharge electrodes 1-1 and 1-, respectively, in the insulating layer.
2,..., 2-12-2,... and 3-1, 3-2
, , 4-1, 4-2, . The electrode 6 is connected to an AC power source 14. Power supplies 3 and 14 are typically 10 to 2, depending on a control device not shown in the diagram.
The AC voltages in the range of 00 Hz are applied between adjacent silent discharge electrodes with the phase shifted by 1/4 of one cycle. For this reason, the silent discharge electrodes 5 and 6 fall near the inner surface of one of the silent discharge electrodes to generate a silent discharge, and when a silent discharge is generated on one side, no silent discharge is generated on the other side.

At this time, a voltage is applied between the silent discharge electrodes 5 and 6 by the power supply 15 so that the polarity is always the same from the side where silent discharge occurs to the electrode where no silent discharge occurs. Therefore, for example, single polar ions, either positive or negative, are always blown out from the slit 11 from the electrode where a silent discharge is occurring to the electrode where a silent discharge is not occurring. The ion showers exist in the sandwiched space and pass through the powder layer heading toward the object 17 to be coated, and the ion showers alternately cross at right angles and pass through the powder layer in which thin particles are suspended. .

In this way, the thin powder particle layer ejected from the slit 11 by the ion shower flowing perpendicularly to the thin powder particles is reliably charged, and the charge density is lower than that of the electrode 5.
6, it is possible to reliably control the electric field strength existing between the two electrodes, so that it is possible to reliably charge the paint powder to a desired charge density with a desired electrode.
The power source 16 is a high voltage device that applies a common voltage U to the planar silent discharge electrodes 5 and 6 via the power source 15. It is possible to form an electric field between the silent discharge electrodes 5 and 6 that drives the monopolar paint powder, which is reliably charged as described above, from the coating device to the object to be coated. . However, this power source does not necessarily need to be incorporated into the coating apparatus, and may be connected to the object to be coated. As explained in detail above, in the electrostatic powder coating apparatus according to the present invention, the powder particles are suspended in gas inside the coating apparatus and form a thin layer, and the progress of this powder particle layer is Since the particles are charged by the ion shower in the direction perpendicular to the direction, the particles are charged in an extremely ideal state, and therefore a very high coating efficiency can be obtained.

In this method, the silent discharge generated on the surface of the silent discharge electrodes essentially has the ability to block the flying powder particles due to the particle repulsion force that each electrode has. This feature has already been explained in detail by the inventor in connection with the charged particle generator (Japanese Patent Application No. 78222/1989), and for example, the performance of this charged particle generator is limited over a very long period of time. It does not require any maintenance in order to be maintained stably, and like the tip of other internally charged electrostatic powder coating equipment discharge meters, the discharge characteristics are similar to those of the fused electrostatic powder coating. The stability of driving will not be impaired due to an accident where the vehicle is damaged. In the electrostatic powder coating apparatus according to the present invention, there are planar silent discharge electrodes spaced apart from each other in order to charge particles inside the apparatus, as shown in Fig. 1-1 and Fig. 1-2. As shown in FIG. 2, electrode groups 1-1, 2-1, 1-2, 2 disposed inside the hollow conical surface 5 are not limited to the flat plate-like ones. -2, . . . and electrode groups 3-1, 4-1, 3-2, 4-2, . It is possible to form coaxial conical electrodes such as planar silent discharge electrodes which are spaced apart from each other.Other numbers in FIG. 2 refer to FIGS. Since all devices having the same shaft paths as shown in the figures are designated by the same numbers, other detailed explanations will be omitted in FIG.

FIG. 3 shows an electrostatic powder coating apparatus according to the present invention for large-capacity processing, which is particularly suitable for application to an Ω-type conveyor. The electrostatic powder paint, indicated by arrow 7' in FIG. After that, the particles pass through the pipe 22 connected to the pipe 22 and pass through the slit 11 opened toward the side surface at the tip of the pipe 22 to form a thin layer of dispersed suspended particles covering the entire horizontal radial circumference. It is made to be. In this case, in order to uniformly maintain a sufficient suspended state of particles, the hollow cylinder 22 is held by a bearing 22 by a driving pulley, a belt 24, etc., and is given rotational motion. is often preferable. The planar silent discharge electrodes are 5 and 6 in Figure 3.
As is clear from the cross-sectional view shown by, concentric silent discharge electrodes 1-1, 2-1, 1-2, 2-2, . ..., 3-1, 4-1, 3-2, 4-2, ..., etc. are buried. The connection status of the electrode to the power source is shown in Figure 1-1.
As is clear from the same numbers as in FIG. 2, the voltage application situation is the same as in FIGS. 1-1 and 2. The figures 14-1 and 14-2 correspond to the power supply 14 in Figures 1-1 and 2, and the figures 15-1 and 15-2 in Figure 3 correspond to the power supply 14 in Figures 1-1 and 2. This corresponds to the power supply 15 in Figure 2.

The objects to be coated are shown in the figures 17-1 and 17-2, which are conveyed on the omega-shaped conveyor 21. By using the electrostatic powder coating apparatus according to the present invention shown in FIG. 3, it is possible to form a radial layer of suspended powder over the entire circumference, which is particularly required for Ω-type conveyors. This fully satisfies the requirement for extremely large amounts of powder coating capability, and enables extremely high efficiency. In addition, in Fig. 3, 5' and 65 are guard rings of the opposing planar silent discharge electrodes, and the power supply 16V is applied to the planar silent discharge electrodes to connect them to the objects to be coated 17-1 and 17-2. A voltage is applied between them. na trigram, 5' and 6
Although not shown in the figure, this is constructed of an insulating material with appropriate electrical resistance, and a planar silent discharge electrode is appropriately embedded in the surface facing the object to be coated, so that it is formed on the object to be coated. Efficiency may sometimes be further increased by passing a small amount of current through the guard ring towards the object to be coated to further ensure the degree of adhesion of the powder. This is the first
The same applies to the electrostatic powder coating apparatus according to this method shown in FIGS. 1 and 2. The slit used in the electrostatic powder coating apparatus according to the present invention described in detail above does not necessarily have to be a slit in the sense of the word, and powder particles suspended in gas are dispersed and emitted in a suitable layered manner. In order to form a uniform suspended layer of particles in the space VC between the silent discharge electrodes, a large number of holes, etc. in close succession are required for this purpose. Any of these can be used.

In Figure 3, the linear silent discharge electrodes 5, 6 and their guard rings 55, 6' are shown so as to separate the powder from the paint powder supply pipe 2 so that they do not rotate. Of course, this may also be mechanically coupled to 22 and rotated. In this case, it becomes possible to ensure even higher uniformity of radiation of the powder layer over the entire circumference. Regarding the electrostatic powder coating apparatus according to the present invention, the electrodes in FIG. 3 do not necessarily need to be arranged concentrically, but may be arranged radially, or at a certain angle with the radiation. may be set.

Next, embodiments of the present invention will be described in detail.

In the electrostatic powder coating apparatus according to the present invention shown in FIG. 3, the insulators of the planar silent discharge electrodes 5 and 6 are made of glass with relatively low electrical resistance, and the insulators are formed at a depth of 0.3 Tm from the surface. Conductive electrodes are buried on concentric circles with a thickness of 0.3 m and 1 nm with a pitch of 3 m, and these are connected in the same phase in a circle, and a 6000 V AC sine wave AC voltage is applied to this at a frequency of 50.
Hz is applied through electric wires 13 and 14, and the interval between 5 and 6 is maintained at 5 (7n). To this, an AC rectangular wave voltage of 1 voltage with a peak value of 12000 V at 100 Hz is applied by power supplies 15-1 and 15-2. The voltage is applied between the planar silent discharge electrodes 5 and 6, and the inner diameter of the donut-shaped planar silent discharge electrode is 10cri!
The outer diameter is 30 cm, the DC voltage applied by the power source 16 is 100 K, the distance between the object to be coated and the outer periphery of the planar silent discharge electrode is maintained at 30 cr, and a powder layer is placed in the middle of the space 12. If the position of the slit is selected so that a This is a significantly higher transfer efficiency compared to conventional equipment.

[Brief explanation of drawings]

Fig. 1-1 is a longitudinal cross-sectional view of one embodiment of the present invention, Fig. 1-2 is a cross-sectional view taken along the line A-A, Fig. 2 is a longitudinal cross-sectional view of another embodiment, and Fig. 3 is a longitudinal cross-sectional view of another embodiment. FIG. 7 is a vertical cross-sectional view of another embodiment. 5 and 6... Planar silent discharge poles, 12... Space, 11
. . . Paint spout, 13 and 14 . . . Power source for applying silent discharge excitation AC voltage, 15 .

Claims (1)

[Scope of Claims] 1. A pair of planar silent discharge electrodes spaced apart from each other in parallel to each other, a slit-shaped paint spout opening toward the space sandwiched between these silent discharge electrodes, and these silent discharge electrodes. A power source for applying silent discharge excitation AC voltage so that the discharge electrodes operate alternately one at a time, and a relative potential so that one electrode always has the same polarity with respect to the other electrode during silent discharge generation. An electrostatic powder coating apparatus, characterized in that it has a power source and is configured to generate a potential difference between an object to be coated and the pair of silent discharge electrodes. 2. According to claim 1, the silent discharge electrodes are donut-shaped electrodes that are spaced apart from each other on the same axis,
An electrostatic powder coating device characterized in that a slit-shaped paint spout is opened on the side surface of one end of a hollow cylinder having the same axis as the above-mentioned hollow cylinder, facing toward a space sandwiched between donut-shaped silent discharge electrodes.