JPH0129141B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to plasma treatment technology, and more specifically, in order to modify the surface of a product made of a synthetic resin material such as polypropylene or polyethylene, the surface of the product is treated with microwave discharge plasma. Concerning the method of plasma treatment.

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. However, undesirable delamination often occurs in this technical field. One way to solve this problem is to improve the adhesion of the paint film by modifying the surface of the resin material. For example, the surface of the resin material can be treated with glow discharge, corona discharge, radio wave discharge, micro Techniques are known in which the surface of the material is exposed to wave discharge or the like to oxidize (introduce polar groups) or etch (improve the so-called anchor effect). Such technology is called plasma processing technology.

By the way, when performing plasma processing as described above, it is necessary to reduce the pressure in the reaction chamber to create a vacuum state in order to improve the processing effect, and in order to maintain this state, batch processing is currently mainstream. It's summery. On the other hand, when this processing technology is introduced into a mass production process such as the manufacture of automobile parts, where many large and complex-shaped resin material parts must be surface treated at the same time, it is necessary to create a vacuum state in a short time and process them in one go. Therefore, it is necessary to plasma-process a larger number of objects. In view of this need, recently, plasma processing using microwave discharge in which the plasma generation portion and the reaction chamber (ie, processing container) are separated has been widely used. In plasma processing using such a microwave discharge method, plasma is generated in a plasma generation part outside the processing container (a combination of a plasma generation furnace and a plasma generation tube perpendicular to it), and this plasma is transported into the processing container. The plasma is then irradiated and diffused using a shower tube installed inside the container.

Although plasma generation in a vacuum occurs in an avalanche manner (because the electrons with the lowest mass are accelerated in the strong electric field of the microwave), floating electrons are not as abundant in a vacuum as they are in the atmosphere. As a result, a stable discharge cannot be obtained, that is, a phenomenon occurs in which the processing gas supplied to the plasma generation furnace through the plasma generation tube is not turned into plasma. For this reason, in microwave discharge, the processing gas is generally heated several hundred times before being supplied to the plasma generation reactor using a Tesler coil or the like.
The process gas is ionized by KV discharge in the atmosphere, and this ionized and electron-generated processing gas is used as a trigger to be supplied into the plasma generation reactor to facilitate microwave discharge. However, the pre-ionization of the processing gas by the Tesler coil discharge, which is currently commonly used, is carried out on a processing gas tube (usually a nylon tube) that is far away from the generating furnace, for example, about 1 to 5 m. Because it is ionized,
Since the excited processing gas is deactivated and its effectiveness is reduced, discharge failures, that is, non-generation of plasma, frequently occur in the generating furnace. Furthermore, the nylon processing gas tube is melted by the discharge energy of the ionized and excited processing gas, creating a hole in it, and the air enters through the hole, making it impossible to obtain the desired vacuum pressure. , the processing effect is significantly reduced due to the inflow of impure gases other than the processing gas.

Purpose of the Invention An object of the present invention is to provide a technique that enables stable microwave discharge without damaging the processing gas introduction system when implementing a plasma processing method using microwave discharge plasma. .

According to the present invention, the above-mentioned object is to generate a plasma such as oxygen in the orthogonal part between the plasma generation furnace and the plasma generation tube (hereinafter referred to as strong electric field region) where a strong electric field is formed by microwaves. This can be achieved by preliminarily exciting the processing gas immediately before supplying it.

Pre-excitation of the process gas can advantageously be carried out according to the invention by means of a high-voltage discharge on the plasma generating tube. That is, an auxiliary discharge of about 200 to 800 KV, preferably about 400 to 500 KV, using a Tesler coil, etc., on the generator tube located upstream of the processing gas on the center axis of the generator tube, where the microwave and plasma generator tube are perpendicular to each other. The processing gas can be pre-ionized and excited by a voltage discharge. When high-voltage discharge is performed using a Tesler coil or the like, it is advantageous to perform it on the generating tube located about 260 to 400 mm upstream of the processing gas from the orthogonal center of the microwave and plasma generating tube. The discharge by a Tesler coil or the like on the generator tube may be synchronized with the microwave oscillation, or may be performed after the microwave oscillation. In any case, it is advantageous to limit the duration of this discharge to about 3 seconds or less.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the invention will now be described with reference to the accompanying drawings.

A preferred example of an apparatus for carrying out the method of the invention is shown in FIG. Cylindrical processing container 1
is made of stainless steel (SUS304),
The opening and closing parts are vacuum sealed. The means 16 inside the processing container 1 is a shower tube, and plasma is injected from this tube onto the object to be processed placed inside the container, that is, inside the processing chamber. The processing chamber is continuously evacuated in the direction of the arrow from an exhaust port 17 connected to a vacuum pump (not shown) for evacuating the processing chamber in order to maintain a vacuum state even during plasma processing.

As shown in the diagram, plasma is introduced into the processing container 1 as follows: First, a microwave oscillator 2 generates a 2450MHz microwave, and the reflected microwave is emitted outside the system. Microwaves are sent to an isolator 3 for separation, and then passed through a power monitor detection section 4 for measuring input reflected power, a three-stub tuner 5 for minimizing reflected power, and then generated by a waveguide 6. It is transmitted to the furnace 7. Inside the plasma generation furnace 7,
By adjusting the position of the plunger 23 in advance, the electric field strength of the microwave can be controlled to be the strongest.

On the other hand, a gas cylinder 9 in which plasma processing gas (oxygen gas in this case) is compressed and sealed is prepared, and by opening and closing the valve 10, an appropriate amount of oxygen gas is supplied through the nylon gas tube 12 based on the instructions from the flow meter 11. It is supplied to the microwave generator tube 8.
As shown in the figure, the microwave generating tube 8 is perpendicular to the generating furnace 7, and has a portion (outside diameter 30 mm) penetrating the inside of the generating furnace and a portion exposed outside the generating furnace (connected to the gas tube 12 on the upstream side of the processing gas). The part to be attached has an outer diameter of 10
mm, and the downstream part where the processing gas is turned into plasma has an outer diameter of 60 mm). This generator tube through which the process gas passes is a quartz tube. Here, in order to connect the gas tube 12 and the plasma generation tube 8, Teflon (trade name of fluorocarbon resin) is used.
I used Fluoro Connector 13, a connector manufactured by

Plasma is generated in the plasma generation tube 8, and this plasma is transferred to the fluoro connector 14 and the flange 15.
The liquid is sent to the shower pipe 16 through which it is sprayed onto the object to be treated (not shown).

In this example, the Tesler coil 18 is placed on the plasma generating tube 8 and the processing gas is pre-excited by its high voltage discharge. Tesla coil 18 is several hundred
It is possible to generate KV high voltage, and its control mechanism is built into a separate control panel (not shown).

The arrangement of the Tesler coil 18 will be explained with reference to FIG. As shown in the figure, a high voltage cable 19 for discharging the tip of the coil 18 is connected to a Teflon tube 2.
0, the processing gas upstream part of the generation tube 8, that is, the part exposed from the generation furnace 7 (approximately 260 to 400 mm from the center position where the microwave and the generation tube intersect at right angles and plasma is generated, preferably approximately 260mm position)
Attach to the fixing band 21. Further, the main body of the Tesler coil 18 is attached to the generating furnace using a fixing band 22. For reference, the arrangement of the Tesler coil 18 according to the conventional method is shown in FIG. 3 (the reference numbers are the same as in FIG. 2). In the conventional method,
The high voltage cable 19 of the Tesler coil 18 is attached to the gas tube 12 approximately 1 to 5 meters away from the plasma generation center position.

Next, a preferred implementation of the method of the present invention using the apparatus shown in FIG. (not shown) to create a vacuum of approximately 0.01 to 0.05 Torr. After reaching the above degree of vacuum, the gas valve 10 is opened and the oxygen gas in the cylinder 9 is introduced into the container 1. When introducing this oxygen gas, the flow meter 1
1 controls the outflow of oxygen gas to a predetermined flow rate, and the controlled gas is flowed into the container 1 via the gas tube 12 and the generation tube 8. After setting the system to a predetermined plasma processing pressure, the microwave oscillator 2 oscillates microwaves,
This microwave is transmitted into the generating furnace 7 via the isolator 3, the power monitor detection section 4, the three-stub tuner 5, and the waveguide 6. In addition, the electric field strength of the microwave is adjusted in advance by adjusting the position of the plunger 23 in the generation furnace 7 so that it becomes the strongest. At the same time as the microwave oscillation, the Tesler coil 18 is also operated for about 1 second under timer control, and the
Discharge with high voltage of 400-500KV. Due to this discharge, the oxygen gas flowing inside the plasma generating tube 8,
Although the degree of ionization is much lower than that caused by microwave discharge (plasma state), it is ionized and generates electrons. Because this ionized oxygen gas has a short transport distance, it is supplied to the strong electric field region of the microwave without deactivating its ionized state, and the generated electrons act as a trigger and instantly become high. It becomes a plasma state with energy. In other words, the ionized oxygen gas is in a microwave discharge state, and the microwave reflected power is minimized. The plasma-formed oxygen gas is then sent to the shower tube 16 in the processing container 1 via the fluorocarbon connector 14, and is shower-diffused from there to the object to be processed.

When the above process was carried out by varying the microwave output and the amount of oxygen supplied in the range of 400 to 1200 W and 1 to 7 minutes, it was confirmed that the microwave discharge probability was constant at 100% in both cases. Ta.
This means that the method of the present invention can achieve 100% discharge under any conditions and stably supply plasma-forming gas.

For comparison, the experiment was repeated following the same procedure as described above except using the apparatus shown in FIG. In this case, a microwave discharge probability of only 50 to 80% was obtained at most, and this also varied as the microwave output and oxygen content changed.

The results obtained are shown in FIGS. 4 and 5. In the figure, data at indicates the method of the present invention, and data at indicates the conventional method. The main processing conditions applied in the above experiment are as follows: Microwave output vs. discharge probability (Figure 4) Vacuum pressure = 0.5 Torr Oxygen amount = 4/min Number of measurements = 40 times (measurement interval 20 minute) Oxygen amount vs. discharge probability (Figure 5) Vacuum pressure = 0.5 Torr Microwave output = 800W Number of measurements = 40 times (measurement interval 20 minutes) When the method of the present invention is implemented, the discharge by the Tesler coil is Since the plasma generating tube was manufactured using a synthetic resin, there was no damage to the tube due to discharge heat, and there were no problems such as air leakage or deterioration of treatment effectiveness due to holes.

Effects of the Invention According to the present invention, plasma-forming gas can be stably introduced into the processing container without damaging the processing gas introduction system. In fact, according to the present invention, no discharge failure occurs in the plasma generating furnace.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a preferred example of an apparatus for carrying out the method of the present invention, FIG. 2 is an explanatory diagram showing details of the apparatus shown in FIG. Fig. 3 is a schematic diagram showing an example of an apparatus for carrying out the conventional method, Fig. 4 is a graph showing the relationship between microwave output and microwave discharge probability, and Fig. 5 is a graph showing the relationship between the amount of oxygen and the microwave discharge probability. It is a graph showing the relationship with microwave discharge probability. In the figure, 1 is a processing container, 2 is a microwave oscillator,
7 is a microwave generator, 8 is a microwave generator tube,
9 is a processing gas cylinder, and 18 is a Tesler coil.

Claims (1)

[Scope of Claims] 1. A plasma processing method using microwave discharge plasma, which includes a step of preliminarily exciting a processing gas for plasma immediately before supplying the processing gas to a strong electric field region caused by microwaves. Processing method. 2. The plasma processing method according to claim 1, wherein the preliminary excitation of the processing gas is carried out by high voltage discharge on a plasma generating tube. 3. The plasma processing method according to claim 2, wherein the high voltage discharge is performed in synchronization with microwave oscillation or after microwave oscillation, and the discharge time is within 3 seconds.