JPS5971336A - Surface treatment of formed rubber material - Google Patents

Abstract

PURPOSE:To impart excellent non-tackiness to a vulcanized formed rubber material, to effect the treatment of only the desired surface of the material effectively and safely even if the material has complicate shape, and to improve the appearance and the sealing property of the rubber material, by treating the surface of a formed rubber material with nitrogen gas plasma. CONSTITUTION:A formed rubber material 2 is set in e.g. a reactor 1 made of Pyrex glass. An oil rotary pump 5 is operated, the valve 7 is closed, the oil rotary pump 5<1> and the oil diffusion pump 15 are operated, and the valve 18 is opened to evacuate the reactor to high vacuum. Nitrogen gas is introduced from the nitrogen bomb 9 through the valves 10, 11 into the reactor 1 at a pressure of about 0.01-0.1Torr, and excited by the high-frequency discharge system composed of a high-frequency source 12, a matching transformer 13 and a copper coil 14 at a discharge electric power of preferably 10-30W to generate nitrogen plasma. After the low-temperature plasma treatment for >=15min, the leak valve 8 is opened to obtain the treated product.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of molded rubber materials. More specifically, the present invention relates to a surface treatment method for the purpose of making a vulcanized molded rubber material non-adhesive.

Conventionally, various methods have been proposed for the purpose of making rubber non-adhesive, and they can be roughly classified as follows.

(a) Improvement of rubber materials: As a compound of rubber materials, materials that are effective in making them non-adhesive,
For example, add talc, celite, graphite, etc.

Although this achieves a certain degree of tack reduction, it is not possible to completely eliminate tackiness due to the inherent properties of rubber as an organic substance.

(b) Chemical treatment: The surface of the molded rubber material is modified by chemical treatment such as sulfuric acid treatment and halogen treatment. This method has its own processing problems in terms of safety and hygiene, pollution, etc., and also has the disadvantage that the rubber itself tends to deteriorate.

(o) Physical processing: The surface of the rubber material is coated with another material.

This method has problems with the adhesion and strength of the coating film and the rubber layer, and also has the disadvantage that it is difficult to apply it to objects with complex shapes. Furthermore, there are problems with the coating method itself, such as the coating not being uniform, and the coated material often flying off or being washed away.

Another physical treatment method that has recently become popular is to sputter-etch the surface of the rubber material to reduce the contact area and further crosslink the surface layer to prevent adhesion. .

However, this method has the disadvantage that the rubber surface becomes rough and loses its glossy surface, and that the sealing performance is poor if the pressing pressure is low.

The present invention differs from methods having such drawbacks by treating the surface of the molded rubber material with nitrogen plasma.
Achieves non-stick properties that are superior in terms of operation and effectiveness.

The drawings are schematic diagrams of an apparatus and method to which the present invention is applied, and specifically, the processing of molded rubber material is carried out as follows.

(1) Setting the molded rubber material 2 in the Pyrex reactor 1. At this time, the surfaces that are not in contact with the plasma will not be processed, so be careful how you support them. In addition, the code|symbol 3 is an O-ring, and 4 is a Pirani vacuum gauge.

(2) First, operate the oil rotary pump 5 to pump the inside of the reactor.
Non-exhaust to the order of O-3 Torr. At this time, if moisture or dirt adheres to the inner wall of the reactor, it will take time to reach this degree of vacuum, so it is more efficient to thoroughly wash and dry the reactor in advance. In addition, all the codes|symbols 6-8 are valves.

Next, close the valve 7, operate the oil rotary pump 5' and the oil diffusion pump 15, and slowly open the valve 18 so that the inside of the baffle 17 connected to the ionization vacuum gauge 16 does not exceed 10''-' Torr. , evacuate the inside of the reactor to high vacuum. At this time, to avoid the influence of oxygen, 1O
It is desirable to exhaust to the order of -5 Torr.

(3) From the nitrogen gas introduction system consisting of the nitrogen gas cylinder 9 and valves 10 to 11, about 0.001 to 0.5
Torr, preferably about 0.01-0. I Torr
into the reactor until the pressure reaches . If the nitrogen gas pressure is lower than this, the discharge will not continue, and if the nitrogen gas pressure is increased more than this, the discharge will become unstable and a homogeneous treated surface will not be obtained.

The nitrogen gas used must be of high purity; if it contains oxygen or moisture, the anti-stick effect may not be obtained, or even if it is obtained, the effect will be reduced. Because it does.

(4) High frequency source (frequency 13.56 MHz)
12, a high frequency discharge system consisting of a matching box 13 and a copper coil 14 is used to excite nitrogen to generate nitrogen plasma.

At this time, a matching box is used to adjust the difference between the incident wave power and the reflected wave power (effective discharge power) to be maximized to suppress loss as much as possible.

The effective discharge power is desirably about 10 to 30 W, because if it is less than this, the efficiency is poor, and if it is more than this, the treated surface may become rough.

(5) After performing low-temperature plasma treatment for a certain period of time, generally 15 minutes or more in order to obtain a certain anti-adhesive effect, the discharge, introduction of nitrogen gas, and operation of the oil rotary pump are sequentially stopped, and the leak valve (8) is opened. Air is introduced into the reactor and the treated material is taken out.

The surface treatment of molded rubber materials carried out in this way can be applied to natural rubber and synthetic rubber, such as styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber,
It is widely applied to various rubber materials vulcanized from acrylic rubber, chloroprene rubber, hydrin rubber, ethylene-propylene (-diene) copolymer rubber, silicone rubber, fluororubber, isoprene rubber, butadiene rubber, butyl rubber, etc. It has the following characteristics.

(1) Since only the surface portion in contact with the plasma is treated at a relatively low temperature, the properties of the molded rubber material itself to be treated are not impaired.

(2) By masking unnecessary parts of the molded rubber material, only the desired surface can be treated.

(3) Even if the shape of the molded rubber material is complex, such as various valves, it can be effectively treated because it is a gas phase reaction.

(4) Unlike conventional chemical treatments, it is safe because no dangerous chemicals are used.

(5) Since the exhaust gas is nitrogen gas after plasma treatment, it is safe for public guests.

(6) Since the anti-adhesion effect is achieved without roughening the surface of the molded rubber material, there are no problems in terms of appearance and sealing performance.

Note that the present inventor has previously proposed a method of making a molded rubber material non-adhesive by treating the surface of the molded rubber material with oxygen plasma and ashing it (Japanese Patent Application No. 1987-1).
(Refer to No. 2291), this oxygen plasma treatment method burns the surface of the molded rubber material at low temperature to change only the surface layer into an inorganic layer without affecting the inside of the material, thereby making it non-adhesive. In contrast, in the method of the present invention, the surface layer of the molded rubber material is brought into contact with nitrogen plasma, and at this time, the processing conditions such as gas pressure and effective discharge power are completely changed, and high-purity nitrogen gas that does not contain oxygen is used. By using it, the degree of crosslinking of the surface layer is increased, and non-adhesiveness is achieved with a surface condition that is completely the same as that of an untreated surface.

Molded rubber materials surface-treated by the method of the present invention have shown effective prevention effects against adhesion, including adhesion to metal materials and resin materials.

Next, the present invention will be described in detail with reference to examples.

Example 1 Various rubber sheets having a thickness of 21 μm were subjected to nitrogen plasma treatment according to the illustrated apparatus and method.

The processing conditions are as follows.

Nitrogen gas pressure Q, Q5 Torr effective discharge power
20 W Treatment time: 30 minutes The various rubber sheets treated in this way were evaluated for non-adhesion as follows.

0) Place a metal (s) on the rubber sheet placed on the hot plate.
25a) Place a cylindrical container upside down, apply a constant pressure load (1~) to the bottom of the container with its upper edge in contact with the sheet, and leave at 120°C for 16 hours and then at room temperature for 2 hours. This causes adhesion between the metal upper end surface and the rubber surface.

(2) Next, the load is removed, and pressurized air is sent in from a pressure nozzle installed at the bottom of the container to float the container so that only the weight of the sheet acts on the adhesive surface.

(3) Air is pumped into the container from the bottom of the container at a constant rate to increase the internal pressure.

(4) When the pressure rises to a certain level, air begins to leak from the adhesive surface, so the maximum pressure at this time is measured by a pressure sensor attached to the pressure nozzle, and this value is used as a parameter corresponding to the adhesive force.

For comparison, an untreated sheet was also evaluated for tackiness. The results obtained are summarized in the following table for adhesive strength (
(converted to peeling force per unit area),
All values are average values for 6 samples.

Table 1 Fluororubber 1.20 ~ Non-adhesive Note 2) Nitrile rubber 0.67 phydrin rubber -0
,98 Silicone rubber 0.75 ttNote 1)
The treated surface has no roughness and has the same gloss as the untreated surface 2) Equivalent to 3/d from the weight of the rubber Example 2 A fluororubber valve seat used in a reed valve for secondary air supply of an engine is installed. The same nitrogen plasma treatment as in Example 1 was performed on the valve seat.

A reed valve was fixed to the valve seat treated in this way, a weight with a constant load was placed on it via a bottom plate, and a surface pressure of 1.7~ was applied to the tip of the reed.
C. for 20 hours, and then cooled under no load. A water column manometer (mH20) in which a closed air chamber is provided on the valve seat side opposite to the reed valve mounting surface, air with gradually increased pressure is fed into it, and the air pressure at the time when the reed valve is fully opened is connected to the closed air chamber. The non-adhesiveness between the valve seat and reed valve was evaluated.

The results obtained (average values for 6 samples) are shown in Table 2 below.
is shown as the value of valve opening pressure.

Table 2 Yes 1.3XiO2 No 2.5X10s As described above, the material treated with nitrogen plasma by the method of the present invention not only has excellent non-adhesive properties, but also has no roughness on the surface, so it has a good appearance. Also, there are no problems with the sealing performance against liquids and gases when the pressure is low.

[Brief explanation of drawings]

The drawings are schematic illustrations of an apparatus and method applying the invention. In this drawing, reference numeral 1 indicates a reactor, 2 indicates a molded rubber material, 5 indicates an oil rotary pump, 9 indicates an oxygen gas cylinder, 12 indicates a high frequency generator, 13 indicates a matching device, and 14 indicates a copper coil. Representative Patent Attorney Yoshi 1) Toshio

Claims (1)

[Claims] 1. A method for surface treatment of a molded rubber material, which comprises treating the surface of the molded rubber material with nitrogen plasma.