JPS6211631B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic coating method using a paint that is easily dried and solidified, such as a water-based paint or a quick-drying paint.

Conventionally, a thin film of paint is formed on the inner peripheral surface of a rotating cup that is rotated at high speed, and the paint is electrostatically atomized using a high voltage applied between the knife edge at the tip of the rotating cup and the object to be painted. Electrostatic coating methods in which paint is scattered onto the surface of the object to be painted are widely used. However, in such electrostatic coating methods using rotating cups, it is extremely rare to use paints that dry and harden easily, such as water-based paints or quick-drying paints. This is because the paint supplied into the rotating cup spreads in a thin film on the inner circumferential surface of the rotating cup due to the centrifugal force caused by high-speed rotation, so it dries easily. This is because it has the disadvantage that it accumulates on the knife edges and disturbs the coating pattern. Therefore, when performing electrostatic painting using water-based paint, for example, continuous operation is not possible, and it is necessary to interrupt the painting operation every 30 to 40 minutes to clean the rotating cup. There was a problem that the work performance deteriorated significantly.

The present invention was made in order to solve these problems of the conventional examples, and its purpose is to use paints that dry and harden easily, such as water-based paints and quick-drying paints, for long periods of time. To provide an electrostatic coating method that enables continuous coating.

FIG. 1 shows the overall structure of an electrostatic coating apparatus using an electrostatic coating method according to an embodiment of the present invention, and FIG. 2 is a longitudinal cross-sectional view of the main parts of the same. In each of the above figures, 1 is a rotary cup, and an inner cylinder 2 and an outer cylinder 3 made of a metal material such as aluminum.
It atomizes paint using static electricity and jetted air. A cylindrical shaft 4 integrally protruding from the center of the rear part of the inner cylindrical body 2 is screwed onto the tip of a rotary shaft 5. The inner cylindrical body 2 has an inner peripheral surface whose diameter gradually increases in a tapered shape toward the front from the center of the inner cylindrical body 2, and an opening 6 is bored at the center of the inner cylindrical body 2. This opening 6 communicates with a paint supply passage 7 which is bored through the axial center of the rotary shaft 5 in the axial direction through the through hole of the cylindrical shaft 4 . Furthermore, a knife edge portion 8 is provided at the tip of the inner cylindrical body 2 by making the tapered slope even steeper. On the other hand, an annular hollow chamber 9 is provided between the rear bottom of the outer cylinder 3 and the rear bottom of the inner cylinder 2.
is formed, and this annular hollow chamber 9 is connected to the inner cylindrical body 2.
It communicates with a plurality of communication passages 11 formed at equal intervals in a collar body 10 provided around the outer periphery of the tip of a rotary shaft 5 to which the rear part of the cylindrical shaft 4 is screwed. The rotating shaft 5 is the main body 12
It is rotatably mounted within the shaft by a bearing 13, and is driven to rotate at high speed by a drive shaft 14 via a pulley 15 and a transmission belt 16. An air reservoir 17 is formed in the main body 12 and communicates with the communication passage 11 . Air is supplied to this air reservoir 17 from the outside through a compressed air supply pipe 18 , and the communication passage 11 of the collar body 10 is supplied with air from the outside through a compressed air supply pipe 18 . Air can be introduced into the annular hollow space 9 of the rotary cup 1 via the rotary cup 1. A paint distribution pipe 19 is provided in the paint supply path 7 of the rotating shaft 5, and the tip 19a of the paint distribution pipe 19 opens slightly inward from the knife edge portion 8 of the inner cylinder 2. . A paint supply pipe 20 is connected to the base end of the paint distribution pipe 19, and paint is supplied from a paint tank 21 through this paint supply pipe 20. Further, compressed air is supplied to the compressed air supply pipe 18 from an air compressor 22. Furthermore, a high voltage E is applied between the rotating cup 1 and the object 23 to be coated.

The knife edge portion 8 of the inner cylinder 2 protrudes slightly forward than the opening edge of the outer cylinder 3, and there is a small gap between the outer peripheral surface of the inner cylinder 2 and the inner peripheral surface of the outer cylinder 3. A gap 24 is formed. Air compressor 2
When compressed air is supplied from 2, a high-velocity compressed air stream is ejected from the gap 24 toward the object 23 to be coated. Tight rotating cup 1
The inside of the paint pipe 19 has a negative pressure with respect to the atmospheric pressure, and the paint discharged from the tip 19a of the paint distribution pipe 19 is attracted by the flow of compressed air and is atomized and diffused in all directions. At this time, most of the paint scatters in front of the rotary cup 1 and adheres to the surface of the object 23 due to electrostatic force, but a portion of the paint adheres to the inner peripheral surface of the inner cylindrical body 2 of the rotary cup 1. It is diffused into a thin film by centrifugal force, and is electrostatically atomized and scattered from the knife edge portion 8. Therefore, in the present invention, the atomization effect by static electricity is incidental, and the atomization effect by air is the main one. The atomized paint is scattered and applied onto the surface of the object 22 by compressed air flow and electrostatic force.
At this time, even if the surface of the object to be coated 23 has considerable irregularities, the uneven coating is eliminated by the flow of compressed air.

According to the inventors' experiments, the diameter is 35 mm and the depth is
Using a 30 mm inner cylinder 2, a round coating pattern with a diameter of about 20 to 25 cm was obtained when the tip of the rotary cup 1 and the object 23 to be coated were separated by 30 cm. The pressure of compressed air at this time is approximately 2.5Kg/cm ²
The rotation speed of rotating cup 1 was 3000 rpm.
As the paint, a water-based paint that is particularly easy to dry and solidify was used, and almost no disturbance in the paint pattern was observed even after 4 hours of continuous operation. The tip 19a of the paint distribution pipe 19 that discharges the paint has an inner diameter of about 2.5 mm. When conducting the experiment, a synthetic resin pipe was added to the tip of the aluminum pipe to connect the tip 1 of the paint distribution pipe 19.
Adjustment was made so that 9a was about 5 mm inward from knife edge portion 8. 3 and 4 show other embodiments. In the embodiment in FIG. 3, the tip 19a of the paint distribution pipe 19 is substantially flush with the knife edge portion 8, and in the embodiment in FIG. The tip 19a of the paint distribution pipe 19 was adjusted to be about 5 mm outward from the knife edge 8. Good coating patterns were obtained in both the embodiments shown in FIGS. 3 and 4, but when the tip 19a of the paint distribution pipe 19 was made to protrude further outward, the paint was atomized. Efficiency decreased and paint particles became coarser, resulting in uneven coating.
On the other hand, if the tip 19a of the paint distribution pipe 19 is pushed deeply into the rotary cup 1, the atomization effect due to air will be reduced and the atomization effect due to static electricity will become the main one. When the paint dries and sticks to the inner peripheral surface of the body 2 and the knife edge part 8,
The atomization efficiency decreased and the coating pattern became disordered. Therefore, for the inner cylinder body 2 with a diameter of about 35 mm,
If the tip 19a of the paint distribution pipe 19 is adjusted within the range from 5 mm inside the knife edge 8 to 5 mm outside, a generally good coating pattern can be obtained for a long time. be. Further, the pressure of the compressed air can be in the range of 1.5 to 4 kg/cm ² and the rotation speed of the rotary cup 1 can be in the range of 1,500 to 20,000 rpm. Regarding the diameter of the rotary cup 1, a relatively large diameter of 65 mm or more is not preferable because the atomizing effect of the air will be weakened, and it is appropriate to use a relatively small diameter of about 20 to 40 mm. Furthermore, although the distance between the knife edge portion 8 of the inner cylinder body 2 and the opening edge of the outer cylinder body 3 was approximately 3 mm in experiments conducted by the present inventors, we believe that a distance of approximately 2 to 6 mm may be usable. It can be done. Also, according to experiments, the rotary cup 1 could be used either downward or sideways; however, when used sideways, the tip 19a of the paint distribution pipe 19 should be slightly inward from the knife edge 8 as shown in the embodiment in FIG. It is advisable to adjust it. As described above, the present inventors added a synthetic resin pipe to the tip of the aluminum pipe to create the tip 19 of the paint distribution pipe 19.
Although the position of a is adjusted, it is advantageous if the entire paint distribution pipe 19 is made of a metal pipe because electrostatic atomization is promoted by corona discharge at the tip 19a.

The present invention is constructed as described above, and the paint is discharged from the tip of the paint distribution pipe disposed near the center point of the opening edge of the rotary cup toward the object to be coated, and the paint is discharged from the tip of the paint distribution pipe disposed near the center point of the opening edge of the rotary cup. Since compressed air is injected from the rear all the way around the knife edge in the direction of the object being painted, the pressure inside the rotating cup is negative compared to the atmospheric pressure, and the air is discharged from the tip of the paint distribution pipe. Paint is attracted to the flow of compressed air and is atomized and dispersed, and because the atomization effect of the compressed air flow is greater than the electrostatic atomization effect, it does not dry and solidify. Even if easily deposited paint adheres to the knife edge, there is little disturbance in the paint pattern, and since the paint is discharged from near the center of the opening edge of the rotary cup, the paint does not reach the inner circumferential surface of the rotary cup. It has the advantage that there is less adhesion and buildup, and therefore the paint pattern is less likely to be disturbed even when painting is done continuously over a long period of time, especially when using water-based paints or quick-drying paints. It's convenient. Furthermore, because of the adhesion effect of the paint due to static electricity, the painting efficiency is higher than that of painting with a spray gun.When the same amount of paint was used to paint tiles, approximately 800 tiles could be painted with the spray gun, whereas the method of the present invention The data shows that approximately 1,200 sheets can be coated, and the coating efficiency is improved by about 1.5 times.

[Brief explanation of the drawing]

FIG. 1 is a front view of one embodiment of the present invention, FIG. 2 is a longitudinal cross-sectional view of the same essential parts, and FIGS. 3 and 4 are longitudinal cross-sectional views of main parts of different embodiments of the present invention. . 1 is a rotating cup, 5 is a rotating shaft, 8 is a knife edge portion, 18 is a compressed air supply pipe, 19 is a paint distribution pipe, 19a is a tip, 20 is a paint supply pipe, and 24 is a gap.

Claims (1)

[Claims] 1. A metal rotary cup whose inner peripheral surface gradually expands in diameter toward the front and whose opening edge is formed into a knife-edge shape is driven to rotate at high speed, The paint is discharged from the tip of the paint distribution pipe to be placed in the direction of the object to be painted, and from the rear of the knife edge of the rotating cup,
A stream of compressed air is injected along the entire circumference of the knife edge in the direction of the object to be painted, and the paint is applied to the surface of the object by the high voltage applied between the rotary cup and the object and the compressed air flow. An electrostatic painting method that is characterized by making it fly.