JPS5819464B2 - Surface treatment method for molded rubber materials - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for surface treatment of molded rubber materials.

More particularly, it relates to a method for surface treatment of molded rubber materials with improved surface properties.

Various proposals have been made to improve the surface properties of molded rubber materials, such as reducing surface friction resistance, imparting solvent resistance, water repellency or ozone resistance, and removing tackiness. For the purpose of
6-134, 35-4608), peracetic acid solution (36-190), chlorine gas, bromine gas, sodium sulfonate solution (37-3807)
, alkaline aqueous solution (Publication No. 45-34706), alkyl hypohaland (Publication No. 50-27503), bromine, iodine and berooxonisulfuric acid (Publication No. 53-2775)
No. 1), antimony pentafufluoride (Japanese Patent Application Laid-open No. 50-234
No. 83), polyamine (No. 51-55379), polyorganosiloxane (No. 54-90375), or graphite (No. 54-22482)
Methods of treatment with various chemicals such as heat (No. 51-30883) and ultraviolet light (No. 54-57576) have been proposed.

However, in many of these methods, the rubber surface becomes hard when treated with various chemicals, and when used for sliding parts, fine cracks and racks occur on the surface, and in the worst case, the rubber surface becomes hard. There are various drawbacks such as the surface not losing its rubber elasticity and the molding material forming large cracks.

Graphite treatment and ultraviolet treatment also have the disadvantage that they cannot withstand long-term use because the treatment depth is shallow.

The antimony pentafluoride treatment method uses antimony pentafluoride as a mixed stream with an inert carrier gas.
After treatment, a method of sequentially washing with an aqueous alkali metal carbonate solution and water is used, and the surface condition of the rubber material treated in this way is improved, but a compound of antimono, which is a toxic element, is used. This raises undesirable issues such as the problem of improving the working environment and wastewater treatment.

When using molded rubber materials as sliding materials such as oil sheets and O-rings, they must maintain good rubber elasticity, have low surface friction resistance, and have excellent chemical and oil resistance. is required.

Furthermore, it is also necessary that it does not cause problems such as environmental destruction.

As a result of various studies on surface treatment methods for molded rubber materials that meet all of these requirements, the inventors of the present invention discovered that, in the method using antimony pentafluoride, a more reactive fluorine gas was used instead of antimony pentafluoride. It has been found that these problems can be solved by using this method (see Japanese Patent Application No. 55-133542).

By the way, when a molded rubber material is used as a sliding material, the sliding material used has a large amount of wear due to contact with metal, so even if the molded rubber material is fluorinated, the surface treatment layer must be sufficiently thick. It is desired that it be large.

In order to increase this thickness, it is possible to increase the fluorination treatment temperature, lengthen the fluorination treatment time, or increase the fluorine gas concentration, but under these conditions, the fluorination treatment is sufficient. As a result, the surface hardening occurs due to side reactions such as cross-linking reactions accompanying the fluorination reaction, and phenomena such as cracks occurring during deformation impair the rubber-like behavior. It cannot be said that it is necessarily sufficient to be used as a.

The following two points are presumed to be the causes of the curing reaction accompanying such fluorination.

(1) Since the radicals generated by the addition of fluorine are stable, the crosslinking reaction subsequently proceeds.

(2) Since the rate of diffusion of fluorine into the rubber to be treated is slow compared to the reaction rate between fluorine and the surface of the rubber to be treated, if the treatment time is increased to increase the thickness of the fluorine treated layer, etc. The fluorination near the surface of the rubber to be treated progresses to the level of polytetrafluoroethylene, and the surface portion changes to the point where it is no longer rubbery but plastic-like.

Based on this estimation, the molded rubber material was swollen with a solvent and then subjected to fluorination treatment in order to suppress the crosslinking reaction on the surface of the rubber to be treated and to help the diffusion of fluorine gas into the rubber to be treated. In addition, it is possible to obtain a surface treated layer with a low coefficient of friction and a sufficient thickness while maintaining sufficient rubber elasticity on the surface of the molded rubber material.

Therefore, the present invention relates to a method for surface treatment of molded rubber materials,
This surface treatment is carried out by swelling the molded rubber material with a solvent and then holding it in a fluorine gas atmosphere, preferably in a fluorine gas atmosphere diluted with an inert gas.

The molded rubber material to be surface treated is natural rubber, conjugated diene rubber such as acrylonitrile-butadiene copolymer rubber, styrene-butadiene copolymer rubber, chloroprene rubber, isoprene rubber, acrylic rubber, ethylene-
In addition to various synthetic rubbers such as propylene (-diene) copolymer rubber, butyl rubber, epichlorohydrin rubber, chlorosulfonated polyethylene (Hypalon), fluororubber, and silicone rubber, vulcanizing agents and other compounding agents, such as fillers and reinforcing agents, It is a vulcanized product of a rubber compound containing softeners, plasticizers, anti-aging agents, processing aids, etc. as necessary.

Swelling with a solvent performed prior to the fluorination treatment of these molded rubber materials can be carried out by, for example, a method of immersing the molded rubber material in a solvent at a temperature of about 0 to 100°C, preferably about 10 to 50°C. This is done by methods such as spraying.

A wide range of solvents can be used for this, and generally ketones, esters, ethers, alcohols, amides, halogenated hydrocarbons, freons, aromatic compounds, etc. Specific examples include acetone, methyl ethyl ketone, butyl acetate, tetrahydrofuran, methanol, isopropanol, dimethylformamide, trichlorethylene, methylene chloride, trifluorotrichloroethylene, benzene, and toluene.

The molded rubber material thus subjected to the swelling treatment with the solvent is subjected to a fluorination treatment.

Fluorine gas as a fluorination treatment agent can be used alone or as a mixed gas diluted to about 100 times with an inert carrier gas such as helium, argon, nitrogen, carbon tetrafluoride, or sulfur hexafluoride. Normal pressure to pressurized (~
about 10 to 150°C, preferably about 20 to 150°C, under pressure conditions of
Under temperature conditions of 100° C., preferably a recycled air stream is used.

The molded rubber material treated in a fluorine gas atmosphere, preferably in a mixed gas atmosphere with an inert carrier gas, is immediately placed in an aqueous alkali metal carbonate solution to remove the fluorine gas adhering to its surface. Soaked and cleaned.

As the alkali metal carbonate, sodium carbonate, potassium carbonate, hydrogen carbonate, potassium hydrogen carbonate, etc. are used in the form of an aqueous solution with a concentration of about 5 to 30 minutes.

The immersion treatment is carried out at a temperature of about 10 to 100°C for about 5 to 30 minutes, preferably about 10 to 15 minutes, and the soaking process is carried out for about 10 to 15 minutes.
Wash for 0 to 15 minutes and dry under warm air.

Next, the present invention will be explained with reference to examples.

Example 1 Outer diameter 14mm, thickness in the radial direction of the ring part 1.91My+
Fifty neorene type O-rings were immersed in trichlene for one hour at room temperature, then taken out, and excess solvent adhering to the surface was wiped off.

This swollen 0-'J ring has an inner diameter of 80rrtjn and a length of 3
After degassing the inside of the reactor, it was filled with fluorine gas diluted to 1/3 concentration with nitrogen gas to 1 atm, and then the diluted fluorine gas was introduced at a flow rate of about 120772 A/min. flowed.

After continuing this state at 40℃ for 4 hours, the internal 0-1,
One ring was taken out, washed with 10% carbonic acid solution and running water for 10 minutes each, and dried at 80°C for 15 hours.

The O-ring has been surface-treated to be uniform in appearance, and no cracks are observed during deformation.

The thickness of the surface treatment layer was measured by EPMA (electron beam microanalysis) to be approximately 40μ, and the thickness of the layer was 1.41A-
The static friction force under f load was 0.40 kl/.

Examples 2 to 5 In Example 1, various solvents were used instead of trichlene as the swelling solvent.

All O-IJ rings that have been treated with fluorine gas have a uniform surface treatment, and no cracks are observed during deformation.

The measured thickness of the surface treatment layer and the static friction force of that layer are shown in the following table.

Comparative example 1 In Example 1, no solvent immersion was performed.

The O-ring that has been treated with fluorine gas has a uniform surface treatment and shows no cracks when deformed.

However, the measured thickness of the surface treatment layer is approximately 5μ,
The static friction force of that layer was 0.68 to 9.

Comparative Example 2 In Comparative Example 1, the fluorination treatment temperature was changed from 40°C to 80°C.
'CK raised.

Although the fluorine gas-treated 〇-ring has a uniform surface treatment in appearance, cracks are observed during deformation.

The measured thickness of the surface treatment layer was approximately 30μ, and the static friction force of that layer was 0.59A-9.

From the comparison between each of the above examples and each comparative example, it can be seen that those which were swollen with a solvent and then treated with fluorine gas are superior in all respects such as static friction force and appearance.

When treated with fluorine gas without solvent swelling, the thickness of the fluorinated layer is smaller than that with solvent swelling, and the static friction force is also larger.

Therefore, when the processing temperature is increased, the thickness of the processing layer becomes thicker.
Static frictional force is also reduced, but cracks cannot be avoided on the surface during deformation.

Claims (1)

[Claims] 1. A method for surface treatment of a molded rubber material, which comprises swelling the molded rubber material with a solvent and then holding the material in a fluorine gas atmosphere. 2. The surface treatment method for a molded rubber material according to claim 1, wherein the molded rubber material is maintained in a fluorine gas atmosphere diluted with an inert gas. 3. A method for surface treatment of a molded rubber material according to claim 1 or claim 2, wherein the material is maintained in a circulating fluorine gas stream.