JPH0129142B2 - - 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. By the way, when synthetic resin materials such as polypropylene and polyethylene, which are relatively cheap and easily available, are used for the outer panels of vehicles, for example, the adhesion between the material surface 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 paint film by modifying the surface of the resin material prior to painting, such as glow discharge or corona discharge on the surface of the resin material before painting. ,
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 create a vacuum inside the processing container and maintain the vacuum during processing, a common method is to first perform rough evacuation with an oil rotary pump, then evacuate with a mechanical booster pump, and then maintain the vacuum pressure. It is used in many ways.

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 is provided with the above-mentioned cooling means, cooling is limited to only a small part.
High temperatures of approximately 200 to 300 degrees Celsius are often encountered. 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. Pump damage is not only dangerous for workers;
This means a long period of work stoppage and an increase in repair costs.

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 exhaust processing of such gas. An object of the present invention is to provide an improved plasma processing method.

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 and a mechanical booster pump.

In carrying out the present invention, rough evacuation is performed from atmospheric pressure using a water ring pump, and then 0.01
It is preferable to perform plasma treatment by evacuation to ~1 Torr and then supplying oxygen gas or a mixed gas containing oxygen gas.

Additionally, it is preferable to arrange the processing container, the mechanical booster pump, and the water ring pump in series, and to connect the water ring pump to 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 objects to be treated (not shown) are accommodated in this container 1 via suitable hanger means. The storage container 1 is equipped with 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.

In order to introduce plasma into the processing container 1, first, a 2450MHz microwave is generated by the microwave oscillator 15, and an isolator, a power monitor detection unit, and a three-stub tuner (all not shown) are used.
After passing through the plasma, it is transmitted to the plasma generation furnace 17 via the waveguide 16. On the other hand, a gas cylinder 19 compressed and sealed with plasma processing gas (oxygen gas here)
By opening and closing the valve 20, an appropriate amount of oxygen gas based on the instructions from the flow meter 21 is supplied to the plasma generation tube 18 through the nylon gas tube 22. 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 30 inside, and is sprayed onto the object to be treated from there.

The pump configuration for evacuation processing 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 pumps used here are a mechanical booster pump 3 with an exhaust speed of 2000 m ³ /hr, a maximum suction pressure of 10 ^Torr , and an ultimate pressure of 5 × 10 ^-4 Torr; This is a mechanical booster pump 4 having an ultimate pressure of 2 Torr. On the way to these vacuum pumps, there are a main control valve 7, a control valve 8 for setting vacuum pressure,
A manually operable operation valve 9 is attached for setting the vacuum pressure. 1 in the diagram
0, 11 and 12 are vacuum valves for bypass circuit adjustment, 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. In this conventional pump configuration, an oil rotary pump 2 equipped with an oil mist trap 24
3 (pumping speed ^400-600m3 /hr, ultimate pressure 5x
10 ^-3 Torr), an explosion occurs in the rotor compression section of this pump due to the inflow of oxygen gas.

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 equipment shown in Figure 1, its pump configuration has a pumping speed of 600 m ³ /hr and an ultimate pressure.
A water ring pump 5 with a capacity of 17 Torr (at a water temperature of 15°C) is used. 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 operates. After the specified time has passed,
The vacuum valve 12 closes and the pressure inside the processing container 1 begins to be reduced. Pressure preset by vacuum switch 13
After detecting 100 Torr (first pressure detection), the mechanical booster pump 4 starts operating in response to the signal it generates. Next, after the two-point Pirani vacuum gauge 14 detects a pressure of 100 Torr (second pressure detection) (this vacuum gauge has previously detected 100 Torr and 0.01 Torr).
The mechanical booster pump 3 starts operating according to the relay signal issued by the booster pump 3, and the vacuum valve 11 closes. Further, when the Pirani vacuum gauge 14 detects a pressure of 0.01 Torr (third pressure detection), the vacuum valve 10 and the main control valve 7 are simultaneously closed, and an exhaust flow is formed only on the piping side of the control valve 8. This exhaust flow also does not flow to the bypass side due to the closure of vacuum valves 10 and 11, thus creating a flow chain through pumps 3, 4 and 5. Further, when the Pirani vacuum gauge 14 detects a pressure of 0.01 Torr, the vacuum valve 20 is opened by the relay signal issued by the Pirani vacuum gauge 14.
Oxygen gas in the cylinder 19 is quantified by a flow meter 21 and sent into the processing container 1 via a gas tube 22 and a plasma generation tube 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 coming into contact with water, and is finally released into the atmosphere. Here, by adjusting the opening degree of the operation valve 9 in advance, it is possible to set in advance 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 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 rotor rotation.
Therefore, the danger of explosion when exhausting oxygen gas can be eliminated. According to the present invention, this can be achieved without complicating the configuration of the device.

[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, and 5 is a water ring 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 and a mechanical booster pump. 2 Roughly pump from atmospheric pressure using a water ring pump, then evacuate from a vacuum pressure below the maximum suction pressure to 0.01 to 1 Torr using a mechanical booster pump, and then supply oxygen gas or a mixed gas containing oxygen gas. The plasma processing method according to claim 1, which performs plasma processing. 3. The plasma processing method according to claim 1, wherein 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. .