JPH043422B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a plasma processing method. More specifically, the present invention relates to a method of subjecting the surface of a product (object to be treated) made of a synthetic resin material such as polypropylene or polyethylene to a low-temperature plasma treatment with oxygen plasma in order to modify its surface.

BACKGROUND OF THE INVENTION It is well known that in recent years, materials for automobile parts have been shifting to synthetic resin materials that are lightweight and have excellent design. However, when synthetic resin materials such as polypropylene and polyethylene, which are relatively inexpensive and easily available, are used for example on vehicle exterior panels, the adhesion between the surface of the material and the coating applied thereon is poor. , which often causes undesirable delamination. One way to solve this problem is to improve the adhesion of the coating film by modifying the surface of the resin material prior to painting. For example, the surface of the resin material may be treated with glow discharge, corona discharge,
There are known techniques for oxidizing (introducing polar groups) or etching (improving the so-called anchor effect) the surface of the material by exposing it to radio wave discharge, microwave discharge, etc. Such technology is called plasma processing technology.

By the way, when plasma-treating resin parts, taking into account the heat resistance of the parts, the main method is to create a vacuum inside the processing container and turn the processing gas into plasma, the so-called low-temperature plasma (or low-pressure plasma) processing method. It is used. Here, in order to reduce the pressure inside the processing container and maintain the vacuum during processing, we first perform rough evacuation using an oil rotary pump, then evacuate using a mechanical booster pump, and then maintain the vacuum pressure. is commonly used.

The above-mentioned oil rotary pump is a type that repeatedly suctions, compresses, and exhausts air by rotating its eccentric rotor, so it generates high heat while the rotor rotates, and therefore keeps the oil temperature below about 80℃. Equipped with air or water cooling means to control However, even if the compression part of this oil rotary pump has the above-mentioned cooling means, cooling is limited to only a very small part.
High temperatures of approximately 200-300°C are common. If oxygen gas, which is a plasma processing gas, were to flow into the pump while the compression part of the pump was in such a high temperature state, an explosion would naturally occur in the rotor compression part, causing the side wall of the casing to separate from the main body, and the pump to be damaged. itself is damaged. In order to avoid this problem, a method of rough evacuation using a water ring pump and then evacuation using a mechanical booster pump can be considered. However, when this method is used, water ring pumps require more power and have lower exhaust capacity than oil rotary pumps (in other words, the ultimate vacuum pressure is higher), so the exhaust time naturally becomes longer, especially for automobile parts. A new problem arises in that mass production lines such as these cannot respond to production strategies.

OBJECT OF THE INVENTION The object of the present invention is to provide a low-temperature plasma processing method using oxygen gas or a mixed gas containing oxygen gas as a plasma processing gas, which eliminates the risk of gas explosion during the exhaust treatment of such gas. Another object of the present invention is to provide an improved plasma processing method that allows rapid evacuation.

Composition of the Invention According to the present invention, in a method of evacuating the inside of a processing container containing an object to be processed and subjecting the object to low-temperature plasma treatment using oxygen gas or a mixed gas containing oxygen gas, This can be achieved by performing vacuum evacuation processing using a combination of a sealed pump, an oil rotary pump, and a mechanical booster pump.

In carrying out the present invention, rough evacuation is performed from atmospheric pressure using a water ring pump and an oil rotary pump, then evacuation is performed from a vacuum pressure below the maximum suction pressure to 0.01 to 1 Torr using a mechanical booster pump, and then oxygen gas or oxygen It is preferable to stop the oil rotary pump at the same time as supplying the mixed gas containing gas, and to perform exhaust treatment using a water ring pump and a mechanical booster pump.

Further, a processing container, a mechanical booster pump, and a water ring pump are arranged in series, and the water ring pump is connected to the discharge port side of the mechanical booster pump at the last stage, and an oil rotary pump and the mechanical booster pump are arranged in parallel. It is preferable to carry out exhaust treatment.

In addition, it is preferable to arrange the processing container and the mechanical booster pump in series, and to perform the exhaust treatment by disposing a water ring pump and an oil rotary pump in parallel on the discharge port side of the mechanical booster pump at the last stage.

EXAMPLES The implementation of the present invention will now be described with reference to the accompanying drawings.

First, for comparison, a conventional plasma processing method will be explained with reference to FIG. 1 in the figure is a cylindrical processing container, made of stainless steel (SUS304), and has an internal volume of 5 m ³ . The object to be treated (not shown) is accommodated in this container 1 via suitable hanger means.
The processing container 1 includes a vacuum leak valve 6 for returning the inside of the container to atmospheric pressure, and a two-point Pirani vacuum gauge 14 for displaying the vacuum pressure and outputting a relay signal.
is installed.

To introduce plasma into the processing container 1, first, a 2450 MHz microwave is generated by the microwave oscillator 15, passed through an isolator, a power monitor detection section, and a three-stub tuner (none of which are shown), and then passed through a waveguide. Plasma generation furnace 1 by 16
7. On the other hand, a gas cylinder 19 compressed and sealed with a plasma processing gas (oxygen gas here) is prepared, and by opening and closing a valve 20 of the gas cylinder 19, a flow meter is set.
21, an appropriate amount of oxygen gas is passed through the nylon gas tube 22 to the plasma generating tube 1.
Supply to 8. Plasma is generated in this plasma generation tube 18 that is perpendicular to the plasma generation furnace 17, and the plasma is transferred to the processing vessel 1 through a fluoro connector and a flange (both not shown), which are connectors made of Teflon (a registered trademark of fluorocarbon resin). The liquid is sent to the shower pipe 35 inside, from which it is sprayed onto the object to be treated.

The pump configuration for evacuation of the inside of the processing container 1 is as follows: An exhaust duct 2 is attached to the bottom of the processing container 1 to connect it to each vacuum pump. The vacuum pump used here is ^{a mechanical} booster pump (required power
7.5kW) 3, and a mechanical booster pump capable of pumping speed ^600m3 /hr, maximum suction pressure 100Torr and ultimate pressure 2Torr (power
3.7kW) 4. On the way to these vacuum pumps, a main control valve 7, a pressure control valve 8 for setting the vacuum pressure, and an operation valve 9 for setting the vacuum pressure that can be manually operated are installed. 10, 11 and 12 in the figure are vacuum valves for adjusting the bypass circuit, respectively. 13 is a vacuum switch that outputs a signal by detecting pressure, and 14 is a two-point Pirani vacuum gauge that displays the vacuum pressure and outputs a relay signal. This conventional pump configuration has oil mist traps 24 and 31, respectively.
Oil rotary pumps 23 and 30 equipped with
400 m ³ /hr and ultimate pressure of 5 × 10 ^-3 Torr), the rotor compression part of these pumps is designed to perform rough evacuation in the container due to the inflow of oxygen gas. An explosion occurs.

Next, the plasma processing method of the present invention will be explained with reference to FIG. The plasma processing apparatus shown in FIG.
Unlike the plasma processing apparatus shown in FIG ^. The oil mist trap 26 is connected to the exhaust system.
The pump configuration includes an oil rotary pump 25 (having a capacity of pumping speed of 400 m ³ /hr and ultimate pressure of 5 × 10 ^-3 Torr) (required power of 11 kW). In the plasma processing apparatuses shown in FIGS. 1 and 2, the same reference numerals are given to the same means for easy understanding.

Since the introduction of plasma into the processing container 1 is as previously explained in FIG. 1, the explanation will be omitted here to avoid duplication. The vacuum evacuation process according to the present invention will be explained with reference to the time chart shown in FIG. Close it and then start evacuation. The main control valve 7 and the control valve 8 open, and at the same time, the water seal pump 5 and the oil rotary pump 25 operate. After a predetermined period of time has elapsed, the vacuum valve 12 closes and the pressure inside the processing container 1 begins to be reduced. Vacuum switch 13 detects the preset pressure of 100 Torr (first pressure detection)
After that, the mechanical booster pump 4 starts operating according to the signal it emits. Then 2
After the point type Pirani vacuum gauge 14 detects a pressure of 100 Torr (second pressure detection)
Pressures are set at 100 Torr and 0.01 Torr), and the mechanical booster pump 3 starts operating according to the relay signal issued by it, and the vacuum valve 11 is closed. Furthermore, the Pirani vacuum gauge 14 described above
When 0.01 Torr is detected (third pressure detection), the vacuum valve 10 and the main control valve 7 are closed, and at the same time, the control valve 29 is closed and the oil rotary pump 25 is stopped. As a result, an exhaust flow is formed only on the piping side of the control valve 8. This exhaust flow also flows through vacuum valves 10 and 1
1 and the control valve 29 are closed, the flow does not flow to the oil rotary pump side and the bypass side, and a series of flows passing through the pumps 3, 4, and 5 are thus formed. Furthermore, when the Pirani vacuum gauge 14 detects a pressure of 0.01 Torr, the vacuum valve 20 is opened by the pressure signal generated by the Pirani vacuum gauge 14, and the oxygen gas in the cylinder 19 is quantified by the flow meter 21. It is sent into the processing container 1 through 18. The oxygen gas that has flowed into the container passes through the pumps 3 and 4 along with the previous series of exhaust flows, flows in the water ring pump 5 while contacting water, and is finally released into the atmosphere. By adjusting the opening degree of the operation valve 9 in advance, it is possible to set the plasma processing vacuum pressure to a predetermined plasma processing vacuum pressure under a predetermined gas supply amount.

After supplying oxygen gas and setting a predetermined vacuum pressure, microwaves are oscillated to turn the oxygen gas into plasma, thereby surface-treating the object to be processed in the processing container. After the plasma treatment is completed, the pressure control valve 8 is first closed while maintaining the inside of the pump in a vacuum state (first stop), and after a predetermined time, the entire vacuum pump is stopped (second stop).
After the pump is stopped, the vacuum leak valve 6 is opened and the inside of the processing container 1 is returned to atmospheric pressure to complete a series of plasma processing.

Effects of the Invention According to the present invention, the water flowing inside the water ring pump is
Because it is constantly cooled to maintain exhaust capacity,
There is no need to worry about high temperatures caused by the rotation of the rotor.
Therefore, the risk of explosion when exhausting oxygen gas can be eliminated. Furthermore, according to the present invention, exhaust treatment can be completed in a much shorter time than with conventional methods.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a plasma processing apparatus for carrying out the conventional method, FIG. 2 is a schematic diagram showing a preferred example of a plasma processing apparatus for carrying out the method of the present invention, and FIG. 2 is a time chart of evacuation processing when carrying out the method of the present invention using the apparatus shown in FIG. In the figure, 1 is a processing container, 2 is an exhaust duct, 3 and 4 are mechanical booster pumps, 5 is a water ring pump, and 25 is an oil rotary pump.

Claims (1)

[Claims] 1. Vacuuming the inside of the processing container containing the object to be processed,
A method of subjecting a workpiece to low-temperature plasma treatment using oxygen gas or a mixed gas containing oxygen gas, the method comprising:
A plasma processing method characterized by performing vacuum evacuation processing using a combination of a water ring pump, an oil rotary pump, and a mechanical booster pump. 2. Roughly pump from atmospheric pressure using a water ring pump and an oil rotary pump, and then from a vacuum pressure of 0.01 to less than the maximum suction pressure using a mechanical booster pump.
Claim 1, in which the vacuum is evacuated to 1 Torr, and then oxygen gas or a mixed gas containing oxygen gas is supplied, at the same time the oil rotary pump is stopped, and the evacuation process is performed using a water ring pump and a mechanical booster pump. plasma treatment method. 3. A processing container, a mechanical booster pump, and a water ring pump are arranged in series, and the water ring pump is connected to the discharge port side of the last mechanical booster pump, and the oil rotary pump and the mechanical booster pump are arranged in parallel. 2. The plasma processing method according to claim 1, wherein the plasma processing method is performed by performing exhaust processing. 4. The exhaust treatment is performed by arranging a processing container and a mechanical booster pump in series, and arranging a water ring pump and an oil rotary pump in parallel on the discharge port side of the mechanical booster pump at the last stage. The plasma treatment method described in .