JPH0114822B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to an electrostatic coating method. For example, when manufacturing a polytetrafluoroethylene roller by applying polytetrafluoroethylene powder to an aluminum roller base, the polytetrafluoroethylene powder is charged to a predetermined polarity while an electric field is applied around the roller base. Generally, an electrostatic coating method is employed in which charged polytetrafluoroethylene powder is applied to the electric field and adsorbed onto the surface of the roller base. Prior Art As a conventional example of this type of electrostatic coating method, the configuration shown in FIGS. 1 and 2 is known. In the method shown in FIG. 1, polytetrafluoroethylene powder introduced from a hopper 1 is ejected by compressed air supplied from a compressor 2 toward a roller base 4 via a charger 3 installation part, while a bias A high voltage is applied between the injection nozzle 6 and the roller base 4 using the power source 5 to create an electric field around the roller base 4, and the polytetrafluoroethylene powder charged by the charger 3 is placed on this electric field and rotated. It is designed to electrostatically adhere to the surface of the roller base 4. However, in the case of such a spray method, in order to improve the dispersion of polytetrafluoroethylene powder and ensure uniform application, it is necessary to provide a sufficient distance between the spray nozzle 6 and the roller base 4. Therefore, the dispersion space becomes wider and the amount of polytetrafluoroethylene powder dissipated increases accordingly, resulting in more waste. Further, since the distance between the injection nozzle 6 and the roller base 4 is large, a fairly high voltage (60 KV or more) bias power source 5 is required to obtain a predetermined electric field strength. In order to suppress the dissipation of polytetrafluoroethylene powder, it is possible to increase the electric field strength, but this not only requires a higher voltage bias power supply 5, but also increases the ion current density in the dispersion space and reduces the electric field potential. This causes the inconvenience of increasing uneven coating. On the other hand, the method shown in FIG.
A bias power source 5 is used to apply a bias between the roller base 4 immersed in the dispersion liquid 8 and the tank 7, and the polytetrafluoroethylene powder in the dispersion liquid 8 is dispersed. Orethylene powder is electrodeposited on the surface of the roller base 4. In this method, in order to make the coating film thickness of polytetrafluoroethylene uniform, it is necessary to slowly rotate the roller base 4 and gradually lift it out of the dispersion liquid 8, which not only takes a lot of manufacturing time but also , under the influence of gravity during lifting,
There is a difference in the thickness of the coating film between one end and the other end of the roller base 4, which has the disadvantage that it is not possible to apply the film to a uniform thickness. Purpose This invention solves the above-mentioned drawbacks of the conventional method, eliminates the needless waste of coating powder, allows coating to be uniform and controlled to a desired thickness, and increases processing speed and processing speed. It is an object of the present invention to provide an electrostatic coating method that can reduce the desired space for coating. Summary of the Invention By the action of a phase electric field curtain formed to surround a bias-applied coating roller, charged powder is circulated around the coating roller and is uniformly adhered to the coating roller. Embodiment A first embodiment of the present invention is shown in FIGS. 3 to 5.
Explaining based on the figure, the electrostatic coating method of this embodiment uses an aluminum roller base 11 as the object to be coated, coats polytetrafluoroethylene powder 1 thereon, and then forms a polytetrafluoroethylene roller. This is applied to manufacturing, and the roller base 11 is arranged horizontally. The roller base 11 is surrounded by a phase electric field curtain 13, and positively charged polytetrafluoroethylene powder 12 is introduced through an introduction path 14 formed upward by opening one end of the space enclosed by the curtain 13. Injected. The phase electric field curtain 13 belongs to a type of unequal alternating electric field, and uses a multiphase AC power source to move charged particles in a phase advancing direction along the curtain surface in a non-contact manner. Here, an example is shown in which a three-phase power supply 15 is used as a multiphase AC power supply, and the sheets of the phase electric field curtain 13 correspond to the respective phases u, v, and w of the three-phase power supply 15, as shown in FIG. The electrodes 16... are arranged in parallel in accordance with the order of phase progression, and these electrodes 16... are covered with an insulating sheet 17, and each output terminal of the three-phase power supply 15 is connected to the corresponding electrode 16.
...is connected to... On the other hand, the phase electric field curtain 13 and the roller base 11
A high voltage is applied between them by a bias power supply 18, thereby creating an electric field in the space surrounding the roller base 11 in which lines of electric force extend toward the roller base 11. The voltage of the bias power supply 18 and the voltage of the three-phase power supply 15 are applied to the phase electric field curtain 13 in a superimposed manner. The electrical charge of the polytetrafluoroethylene powder 12 is
This is carried out by a predetermined charging means (such as a corona discharge tube) 19 arranged near the entrance of the introduction path 14. The polytetrafluoroethylene powder 12 (positive polarity) dropped through the introduction path 14 into the open end of the space enclosed by the phase electric field curtain 13 moves in the direction of movement as the phase of the three-phase power supply 15 advances. At the same time, a part of the polytetrafluoroethylene powder 13 is transferred to the roller base 11 by the action of the electric field created between the phase electric field curtain 13 and the roller base 11. It is attracted to the surface and adheres electrostatically. The phase electric field curtain 13 has a substantially horizontal lower surface area, a semicircular upper surface area surrounding the roller base 11, and is composed of polytetrafluoroethylene powder that moves as the phase of the three-phase power source 15 changes. 12 goes around the roller base 11 along the curtain surface, and when it reaches above the introduction end, it falls back to the original introduction end due to its own weight, so that it constantly circulates around the roller base 11. Therefore, the polytetrafluoroethylene powder 12 does not dissipate from the air space surrounded by the phase electric field curtain 13. While repeating such circulation movement, the polytetrafluoroethylene powder 12 gradually adheres to the surface of the roller base 11, and the polytetrafluoroethylene coating is uniformly applied. If the operation in which the polytetrafluoroethylene powder 12 is conveyed while being released from the surface of the phase electric field curtain 13 is established based on FIG. Line-charged polytetrafluoroethylene powder 1
2 (positive polarity), the electric force tries to move away from the curtain surface as a vector sum of the gradient force E acting in the tangential direction of the electric force line, the centrifugal force F' generated by the curvature of the electric force line A, etc. Force F acts. Since the direction of this force F is biased toward the phase advancing direction, as a result, the polytetrafluoroethylene powder 12 is transported in the phase advancing direction while floating. In the case of this electrostatic coating method, the polytetrafluoroethylene powder 12 circulates around the roller base 11 in a large amount without being dissipated due to the action of the phase electric field curtain 13 as described above, so the bias power supply The electric field obtained by 18 is also strong enough to impart directionality to the roller base 11 to the polytetrafluoroethylene powder 12, so that the ionic current density around the roller base 11 is also small, and the ion current density around the roller base 11 is small. The electric field blocking potential brought about by the electrical charge of the polytetrafluoroethylene powder 12 attached to the substrate 11 becomes relatively strong,
The coating thickness becomes more uniform, and the film thickness can be easily controlled by adjusting the bias. Introduction path 1 for polytetrafluoroethylene powder 12
For example, as shown in FIG. 3, the polytetrafluoroethylene powder 12 is poured into the phase electric field curtain 13 in a sufficiently dispersed state by passing it through a sieve 20 and letting it fall under its own weight as much as possible.
It is preferable that it be fed into the installation section. The polytetrafluoroethylene powder 12 is applied while rotating the roller base 11, thereby further improving the effect of uniform application.
Since the polytetrafluoroethylene powder 12 circulates around the roller base 11, it is not necessarily necessary to rotate it as described above. The outer surface of the phase electric field curtain 13 to which a high voltage is applied and the introduction path 14 continuous thereto are grounded to prevent electric shock from occurring even if a hand or the like touches these parts. In this example, good results were obtained by setting the phase electric field curtain 13 and other conditions as shown in Table 1, but these values will of course vary depending on the application conditions.

[Table] When the roller diameter r is within a range of about 10 cm≦r≦50 cm, it is preferable that the inner diameter R of the circular portion of the device is set so that R>3r. As is clear from the above results, in the case of this electrostatic coating method, the bias power supply 18 only needs to have a voltage of 3 to 6 KV, which is much lower than the conventional case, which requires 60 KV or more. can do. In the sheet structure of the phase electric field curtain 13,
In addition, as shown in FIG. 5, some of the electrodes 16 are exposed on the surface side of the insulating sheet 17 where the polytetrafluoroethylene powder 12 moves, and the creeping discharge of the exposed electrodes 16 causes the polytetrafluoroethylene powder to The charging means 19 provided separately for charging the powder 12 may be omitted, or the charging process may be supplemented by this part. In addition, polytetrafluoroethylene powder 1
The second charging process may be performed by natural charging due to friction. A second embodiment of the invention is shown in FIG. In this embodiment, the roller base 11 is opposite to the first embodiment.
A bias is applied from the side to the phase electric field curtain 13 side. Therefore, in this case, the polytetrafluoroethylene powder 12 needs to be negatively charged so that it is attracted by the electric field and electrodeposited on the roller base 11. Here, high voltage is not applied to the phase electric field curtain 13 side, but high voltage is applied to the roller base 11 and its supporting parts, so shield these parts to prevent electric shock when installing or removing the roller base 11. It is necessary to give sufficient consideration to the The other configurations are the same as those of the first embodiment. A third embodiment of the invention is shown in FIG. In this embodiment, the phase electric field curtain 13 has an L-shaped cross section, charged polytetrafluoroethylene powder 12 is introduced from the introduction path 14 on the opposite side of the vertical surface 13a of the curtain 13, and the curtain 13 is transported. Due to the action, the horizontal surface portion 13b to the vertical surface portion 13
The polytetrafluoroethylene powder 12 is circulated in the vicinity of the vertical surface portion 13a of the curtain 13 by the repeated action of upward movement of the polytetrafluoroethylene powder 12 along the direction a and natural fall due to its own weight. The roller base 11 is disposed laterally near a vertical surface portion 13a where the polytetrafluoroethylene powder 12 circulates up and down, and is rotated. A part of the phase electric field curtain 13 is connected to the introduction path 1
The polytetrafluoroethylene powder 12 introduced into the introduction path 14 is smoothly introduced into the horizontal surface area 13b of the curtain 13. A bias power source 18 is connected to the roller base 11 side. 15 is a three-phase power source that drives the phase electric field curtain 13. In the case of this embodiment, since the upper part of the apparatus is open, the structure is simple, and the roller base 11 can be easily attached and detached, which greatly improves work efficiency. Furthermore, since the polytetrafluoroethylene powder 12 circulates up and down, it will not be dissipated and will not be wasted even if the top is open. Note that since the polytetrafluoroethylene powder 12 is circulated toward the vertical surface portion 13a of the phase electric field curtain 13, rotation of the roller base 11 is essential for uniform application. A fourth embodiment of the invention is shown in FIGS. 8 and 9. In this embodiment, two phase electric field curtains 13, 13 are arranged so that the cross section is U-shaped, and the charged polyurethane is introduced from an introduction path 14 provided near the upper end of one vertical surface portion 13a. Tetrafluoroethylene powder 12 (positive polarity) is introduced, and this polytetrafluoroethylene powder 12 is circulated in the vertical direction along two opposing vertical surface portions 13a, 13a. The roller base 11 is vertically disposed at an intermediate portion between two vertical surfaces 13a, 13a, and rotated so that the polytetrafluoroethylene powder 12 is uniformly applied to its entire circumferential surface. As in the case of the first embodiment, the bias power supply 18 is applied to the phase electric field curtain 13 side in a superimposed manner with the three-phase power supply 15. Charged polytetrafluoroethylene powder 12
The injection is carried out from above one vertical surface part 13a, but as shown by the imaginary line in FIG. You may also do so. It goes without saying that the direction of application of the bias power source 18 is not limited to this example, and can be arbitrarily set depending on the charging polarity of the polytetrafluoroethylene powder 12. In this embodiment, two of the phase electric field curtains 13
If the roller base 11 is sequentially rotated and conveyed between the vertical surfaces 13a, 13a parallel to the vertical surfaces 13a as shown in FIG. 9, the coating process can be performed continuously. This can significantly improve work efficiency. Although the conveyance means and rotation means in this case are not shown,
As for its configuration, various known structures can be used. In the configuration shown in FIG. 8, if the roller base is cylindrically surrounded by a polyhedral phase electric field curtain having such a cross-sectional shape and a polyphase AC power source is connected to each curtain surface, the area around the roller base can be Since the polytetrafluoroethylene powder is circulated up and down over the entire circumference of the roller, rotation of the roller base is not necessarily necessary for uniform application. A fifth embodiment of the invention is shown in FIG. In this embodiment, the configuration of the phase electric field curtain 13 is as follows:
In addition to the configuration of the first embodiment, an auxiliary curtain section 13' facing the rising surface section 13c of the upper half of the curtain section is separately arranged in parallel, and the polygons in the road area where the two curtains face each other are improved. The effect of upward movement of the tetrafluoroethylene powder 12 is greatly improved. In the figure, reference numeral 21 denotes a power supply unit for superimposing voltages of a three-phase power supply for driving the curtain and a bias power supply and applying the superimposed voltages to the curtain side. Here, the polytetrafluoroethylene powder 12 first descends after reaching the position directly above the roller base 11 via the ascending transfer path section sandwiched between two curtain surfaces, and is thereby caused by its falling and the suction effect by the electric field. , the effect of electrodeposition of the polytetrafluoroethylene powder 12 on the roller base 11 is improved. Since the adsorption of the polytetrafluoroethylene powder 12 is biased toward the upper circumferential region of the roller base 11, in this case, the adsorption of the polytetrafluoroethylene powder 12
Rotating is an essential requirement for uniform application. In each of the above embodiments, the case where polytetrafluoroethylene powder is applied has been described, but the electrostatic coating method of the present invention can be similarly applied to powders such as acrylic powder and PVC powder. Of course. Effects According to the present invention, the charged powder can be effectively electrodeposited onto the coating roller body without requiring a very high bias, and the ionic current density around the coating roller body is also small, so that the powder is once applied to the coating roller body. The electric field blocking potential due to the charged powder adhering to the body becomes relatively strong, allowing uniform coating, and the coating film thickness can be easily controlled by adjusting the bias. Furthermore, not only is the powder not scattered and wasted, but the processing speed is also increased, improving work efficiency. Moreover, since the coating process does not occupy much space, the apparatus for applying this method can also be configured compactly.

[Brief explanation of drawings]

1 and 2 are schematic views showing a conventional example, FIG. 3 is a schematic sectional view showing a first embodiment of the present invention, FIG. 4 is an explanatory view showing the structure of the phase electric field curtain, and FIG. FIG. 5 is a sectional view showing another sheet structure example of the phase electric field curtain, FIG. 6 is a schematic sectional view showing the second embodiment, FIG. 7 is a schematic sectional view showing the third embodiment, and FIG. and FIG. 9 are a schematic sectional view and a schematic slope view showing the fourth embodiment, respectively,
FIG. 10 is a schematic sectional view showing the fifth embodiment. 11...Roller base (coating object), 12...Polytetrafluoroethylene powder (charged powder), 13
... Phase electric field curtain (phase electric field), 13'... Auxiliary curtain part (phase electric field), 15 ... Three-phase power supply (phase electric field), 14 ... Introducing path, 18 ... Bias power supply, 19 ... Charging means , 21...Power supply section.

Claims (1)

[Claims] 1. A bias is applied to the roller body to which the coating material is to be applied, and a phase electric field curtain using a multiphase AC power source is formed to surround the roller body, and the charged coating material is applied. An electrostatic coating method characterized in that the coating material is fed between a roller body and a phase electric field curtain, and the coating material is circulated and conveyed in a floating state around the roller body by the action of the phase electric field curtain, so that it is uniformly adhered to the roller body. 2. The electrostatic coating method according to claim 1, wherein the coating roller body is rotated.