JPS6048338A - Method of treating with plasma - Google Patents

Abstract

PURPOSE:To treat quite uniformly and simultaneously a plurality of complicated and large articles such as automotive parts or the like, by causing high frequency discharge between a plurality of discharge electrodes arranged in electrically parallel in a treating container and opposite electrodes. CONSTITUTION:A plurality of discharge electrodes (preferably planar in shape) 8a-8d are arranged in electrically parallel in a treating container (preferably of stainless steel or the like) at a distance of within 80cm from an object 2 to be treated and preferably along the shape of the object. High frequency discharge is generated between the discharge electrodes 8a-8d and opposite electrodes to generate a plasma. The plasma is generated, for example, in such a manner that after the air in the container 1 is exhausted via an exhaust port 3, and a plasma treating gas (e.g. O2, or the like) is fed from a cylinder 5, high frequency waves are generated by a high frequency generator 7 to cause discharge to generate a plasma. The opposite electrodes are placed on the inner wall of the treating container or other positions.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to plasma processing technology. More specifically, the present invention relates to products made of polyolefin plastic materials such as polyethylene and polypropylene.
The present invention relates to a method of treating the surface of a workpiece with high-frequency discharge plasma in order to modify the surface of the workpiece.

BACKGROUND OF THE INVENTION In recent years, plastic products, particularly products made of polyolefin plastic materials such as those mentioned above, have been widely coated. By the way, if such a product is coated with a paint that is normally used for painting steel plates, etc., the adhesion between the product surface and the coating film applied thereon is extremely poor, resulting in defects. Desired delamination occurred from time to time. In addition, in order to solve this problem, it has been essential to pre-treat the surface of the product before painting with a special paint containing chlorinated resin or the like.

The above-mentioned surface treatment is very complicated and requires a large amount of expense. Recently, so-called "plasma treatment technology" has been used as an alternative to base treatment. Plasma treatment technology modifies the surface condition by irradiating the surface of plastic products with plasma of an excited processing gas such as oxygen or nitrogen, thereby improving the adhesion of commonly used paints without special surface treatment. It aims to improve sexuality. Commonly used plasma processing techniques include glow discharge, corona discharge,
There are various methods such as high frequency discharge and microwave discharge. Above all, the high frequency discharge method is most suitable for painting large products such as automobile parts on an industrial scale.

However, when performing plasma processing using high-frequency discharge, if the most common high frequency of about 13.56 MHz is applied and it is carried out in a processing apparatus with electrodes provided on the entire inner wall of the processing container, the object to be processed will be damaged. cannot be processed satisfactorily. In fact, the shape of the object to be processed is complex,
When trying to treat multiple objects at the same time, the degree of treatment (processability) of the recessed parts of the objects and the surfaces to be processed located far from the short poles may be poor, resulting in unsatisfactory adhesion with the paint film. The current situation is that it is not possible to obtain sex.

OBJECT OF THE INVENTION The purpose of the present invention is to eliminate the non-uniformity of processing that has been a problem with conventional plasma processing technology, that is, to eliminate areas that are difficult to process and to achieve extremely high performance even when processing complex and large products. The object of the present invention is to provide a plasma processing method that can perform uniform processing.

According to the present invention, when performing plasma processing using high-frequency discharge, high-frequency electric current is generated between a plurality of discharge electrodes and a counter electrode that are electrically connected in parallel and arranged in a processing container. This can be achieved by generating high-frequency plasma by causing a discharge.

Although the discharge electrode can take any shape,
Advantageously, it is plate-shaped. Furthermore, the discharge electrode is
It is advantageous to arrange it along the shape of the object to be treated.

The counter electrode may be disposed within the inner wall of the processing vessel, as is commonly practiced in this technical field, or may be independently disposed at a suitable location other than the inner wall of the processing vessel. .

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

First, for comparison, the conventional high-frequency processing technique is explained with reference to FIGS. A processing object (here, a U-shaped processing object) 2 is accommodated. The air in the processing container 1 is exhausted from the exhaust port 3 by an oil rotary pump 4 to reduce the pressure. Next, oxygen gas is sent from an oxygen gas cylinder 5 into which a plasma processing gas (oxygen gas in this case) is compressed, and introduced into the processing container 1 through a gas inlet 6 provided in the processing container 1. . Next, a predetermined high frequency is oscillated by the high frequency oscillator 7, and the inner wall of the processing container 1 and the cylindrical electrode 8 provided along it are
A discharge is caused between the two and a high frequency plasma is generated. This plasma is injected onto the object to be processed.

FIG. 3 shows a modification of the plasma processing apparatus shown in FIGS. 1 and 2. In FIG. In this device, the cylindrical electrode 8 is abolished, and instead, a plurality of (four in this case) electrodes are used.
The discharge electrodes 8a, 8b, 8c, and 8d are electrically connected in series and arranged.

The discharge electrodes are arranged along the U-shaped object 2 to be treated. Here, too, the object to be processed 2 is housed in the processing container 1, and the air in the container 1 is exhausted from the exhaust port 3 by the oil rotary pump 4 to create a reduced pressure state. Next, oxygen gas is sent from the oxygen gas cylinder 5 and introduced from the gas inlet 6 provided in the container 1. Next, the high frequency oscillator 7 is caused to oscillate to cause discharge between the electrodes 8a to 8d and the inner wall of the container 1, thereby generating plasma. This plasma is injected onto the object to be processed.

Next, the high frequency plasma technology according to the present invention will be explained with reference to FIG. Although the illustrated plasma processing apparatus is similar to that shown in FIG. 3, the arrangement of the discharge electrodes is different. That is, while the discharge electrodes in FIG. 3 are provided in electrical series, the discharge electrodes in FIG. 4 are connected to the waveguide cable branch 9.
are electrically connected in parallel. In addition, when carrying out the present invention, it is advantageous for the discharge electrode to be provided at a distance of 80 cm or less from the object to be processed, along the shape of the object to be processed.

A workpiece (here, a U-shaped workpiece) 2 is housed in a processing container 1 made of stainless steel via a suitable hanger means (not shown). The air in the processing container 1 is exhausted from the exhaust port 3 using the oil rotary pump 4 to reduce the pressure. Then,
Oxygen gas is sent from an oxygen gas cylinder 5 in which plasma processing gas (oxygen gas in this case) is compressed and sealed, and introduced into the processing container 1 through a gas inlet 6 provided in the processing container 1 . At the same time, the high-frequency oscillator 7 causes electric discharge between the inner wall of the processing container 1 and four electrodes 8a to 8d electrically connected in parallel by the waveguide cable branch 9 in the processing container 1. to be generated. This plasma is injected onto the object to be processed.

Next, the improvement in plasma processability that can be achieved by the present invention will be described with reference to examples.

Example 1 (Conventional example): A U-shaped polypropylene product (object to be treated) was plasma-treated using the conventional high-frequency plasma processing apparatus shown in FIGS. 1 and 2. Details of the processing equipment and processing conditions used here are listed below: Dimensions of processing container: Diameter 1000 mm x Length 2000 mm Material of processing container: Stainless steel (SUS304) Microwave frequency: 2450 MHz Microwave oscillation output: 500 W High frequency Frequency: 13.56MHz High frequency oscillator output: 500W Pressure inside the processing container in reduced pressure state: 0.5 Torr Processing gas (amount introduced): O2 (1000ml/min) Processing time:
Dimensions of object to be processed for 30 seconds: 100mm x 400mm x 200mm
(U-shaped product) Material of the object to be treated: Polypropylene Electrode: Diameter 1400mm x Length 1700mm x Thickness 3m
After processing the cylindrical punched metal made of aluminum, the degree of processability achieved was evaluated in terms of contact angle (water wettability) and adhesion at various locations on the surface of the workpiece. FIG. 5 shows the evaluation parts of the object to be treated. In other words, 11 points A, B, C, D on the surface of the object to be processed,
E, F, G, H, I, J and K are the evaluation sites. The obtained evaluation results are shown in Table 1.

Example 2 (Conventional example): Using the conventional high frequency plasma processing apparatus shown in FIG. 3, the same workpiece as in Example 1 was plasma treated. The plasma processing apparatus and processing conditions used in this example were basically the same as those in Example 1 above, except for the difference in the shape of the electrodes as shown in the drawings and described below.

Electrodes: 200 mm x 200 mm x 3 mm aluminum plate-shaped punched metal electrodes Number of electrodes: 4 (8a, 8b, 8c and 8d) After the treatment, the degree of processability achieved was measured in the same way as in Example 1 above. Contact angle (water wettability) and adhesion were evaluated at 11 evaluation sites on the surface. The obtained evaluation results are shown in Table 1 below.

Example 3 (Example of the Invention): The plasma treatment described in Example 2 above was repeated using the plasma treatment apparatus according to the invention illustrated in FIG. That is, in this example, the electrodes 8a to 8d are not electrically connected in series, but are electrically connected in parallel using the waveguide cable branch 9. The details of the processing apparatus and processing conditions except for the shape of the electrodes are basically the same as those of Example 2 above.

After the treatment, the achieved degree of treatability was evaluated in the same manner as in Example 1, and the evaluation results shown in Table 1 below were obtained.

In Table 1 above, "contact angle" refers to the angle of the water droplet on the surface of the workpiece when 5 μl of deionized water (pure water) is dropped onto the surface of the workpiece after plasma treatment. It was measured using a contact angle measuring device at 20° C. and 50 to 60% RH (relative humidity).

The contact angle means that the smaller the angle, the greater the hydrophilicity and therefore the greater the plasma treatment effect. Furthermore, "adhesion" refers to applying a urethane-modified polyester paint to a predetermined film thickness on the object to be treated after plasma treatment, baking it at 100°C for 30 minutes, and then peeling off the diagonal tape after leaving it for 24 hours. This was measured in a test. In other words, "adhesion" means carving 100 goblets on the paint film, applying tape, then peeling off the tape, and measuring the number of goblets that remain attached to the tape (number of peelings). This is what I did. Of course, the closer the adhesion is to O/100, the better.

As can be understood from the evaluation results listed in Table 1 above, in the case of Example 1, it was possible to treat the entire object to be treated fairly uniformly, but the overall treatment level was low and it was not suitable for use. There wasn't. In the case of Example 2, since the electrodes are arranged in series, the processing performance is excellent on the bottom and left side of the workpiece near the high-frequency oscillator, whereas the top and right side of the workpiece far from the oscillator have excellent processing performance. On the other hand, the processability decreased significantly. The inventors of the present invention attempted to increase the output and extend the processing time as a countermeasure to this problem, but the former required a significant increase in equipment investment, and the latter was undesirable because it resulted in a decrease in productivity.

On the other hand, in Example 3 (an example of the present invention), extremely excellent processability could be obtained by electrically connecting a plurality of discharge electrodes in parallel. This is thought to be due to the fact that despite the low output of the high frequency, excellent processability was achieved by arranging the small electrodes electrically and in a uniform and efficient manner.

Effects of the Invention According to the present invention, as is clear from the above description, since a plurality of discharge electrodes are electrically connected and arranged in parallel along the shape of the object to be treated, it is possible to eliminate areas with poor processability. Even complex and large products can be plasma-treated extremely uniformly.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a conventional plasma processing apparatus, FIG. 2 is a vertical sectional view of the apparatus shown in FIG. 1, and FIG.
FIG. 4 is a schematic diagram showing a preferred example of the plasma processing apparatus according to the present invention, and FIG. FIG. In the figure, 1 is a processing container, 2 is an object to be processed, 3 is an exhaust port, 4 is an oil rotary pump, 5 is an oxygen gas cylinder, 6 is a gas inlet port,
7 is a high frequency oscillator, 8a to 8d are discharge electrodes, and 9 is a waveguide cable branch. 8 (21 Figure 4 4) l2 Figure 41

Claims (1)

[Claims] 1. A plasma processing method using high-frequency discharge, which generates high-frequency discharge between a plurality of discharge electrodes and a counter electrode arranged electrically connected in parallel in a processing container. A plasma processing method characterized by generating plasma. 2. The plasma processing method according to claim 1, wherein the discharge electrode has a plate shape. 3. arranging the discharge electrode along the shape of the object to be treated;
A plasma processing method according to claim 1 or 2.