Method of preparing a molded sealing composition for sealing against permeation of carbon dioxide gas

Abstract

An object of the present invention is to provide a molding composition having an excellent properties to seal carbon dioxide. The composition is made of fluoro thermoplastic elastomer having a reinforcing filler such as carbon black or white carbon having a particle diameter of not more than 100 nm. The composition can be used as a sealing materials such as O-ring, oil seal, gasket, hose, tube or diaphragm for sealing carbon dioxide.

Description

1. 1. Field of the Invention2. The present invention relates to a molding composition for sealing carbon dioxide, and a molded composition having an excellent sealing property to be able to be used for sealing carbon dioxide. Also, the present invention relates to a sealing device to provide a seal between relatively movable portions on one of which a portion of the sealing device is held, sealingly contacting with another movable portion at a seal lip of the sealing device.3. 2. Related Art4. Conventionally, Freon gas has been used in almost all automobile air-conditioners, refrigerators or the like as a coolant. But from the point of view of environment disruption (the depletion of the ozone layer, global warming or the like), new coolants other than Freon gas have been recently extensively studied. Carbon dioxide is considered to be one of a most hopeful next generation of coolants. In the case of conventional Freon gas, sealing materials such as hydrogenated NBR, EPDM (Ethylene-...

AI Technical Summary

Benefits of technology

41. The molding composition of the present invention shows excellent properties in anti-permeability to carbon dioxide gas and in resistance of swelling and blistering when contacting carbon dioxide. Therefore, the molding composition can be effectively used for molding sealing articles (lip seal, packing, gasket, O-ring, or the like) , hoses, tubes, diaphragms, or the like which contact with carbon dioxide.42. According to the present invention, fluoro rubber and fluoro thermoplastic elastomer which preferably contain at least one common copolymer component in both rubber and thermoplastic elastomer are combined to form a sliding sealing portion of a sealing device for sealing carbon dioxide so that excellent bonding strength can be obtained between the interface of both rubber and thermoplastic elastomer without using any adhesives. There is no need to use adhesives between an interface of both rubber and thermoplastic elastomer. And as a result not only the cost of the adhesion process can be eliminated but also high durability in sliding sealing portion can be attained.43. On the other hand, by using fluoro thermoplastic elastomer in the sliding sealing portion, rubbery elasticity that has not been attained when fluoro resin has been used can be secured. And an excellent property in decreasing permeation of carbon dioxide gas across the sealing device is also attained and also an excellent property in responding to the portion to be sealed is attained.44. Moreover, by varying volume ratio of fluoro rubber to fluoro thermoplastic elastomer, a sealing device having a desired carbon dioxide permeability can be obtained.45. The invention is shown in more detail in the following examples and these embodiments should not be interpreted as limiting the scope of the present invention.

Problems solved by technology

In the case of conventional Freon gas, sealing materials such as hydrogenated NBR, EPDM (Ethylene-Propylene-Diene terpolymer) or the like have been used as sealing materials, but these materials have some defects such as swelling and blistering which occurs in the sealing materials when contacting carbon dioxide.

These undesirable phenomena tend to cause the sealing device to be unusable.

Particularly, the addition of a non-reinforcing filler with a large particle size such as mica or graphite for aiming to decrease in gas permeability of these rubber materials makes blisters occur easily, resulting in an unusable condition as a molded composition for sealing carbon dioxide.

But these materials have a defect in processability or flexibility which rubber materials usually have.

When these resin like materials are used as sealing materials--especially such a sealing means as a rotating shaft seal, a reciprocating shaft seal or the like, response to an axis to be sealed is slow when the axis is biased.

This phenomena causes a microscopical gap between the seal lip and the axis and then to cause leakage of a sealing medium.

In addition, when the sealing material made of vinylidene fluoride resin is assembled with an axis having splines (grooves made in the direction of the axis), a scratch is easy to occur by the splines and the scratch may not allow to keep optimum sealing performance.

This type of fluoro rubber has excellent flexibility but the anti-permeability to carbon dioxide is not good.

8. When fluoro thermoplastic elastomer containing MT carbon black is used for sealing devices for sealing carbon dioxide, both permeability of and swelling due to exposure to carbon dioxide is large, and a blister phenomena can be seen so that these compositions cannot be safely used in the seal for sealing carbon dioxide.

When using reinforcing filler having a particle diameter of larger than 100 nm, the reinforcing effect of the particle is insufficient to cause blisters in molded articles.

When the amount of fillers is used in an amount of more than the above mentioned phr range, there arises a difficulty in blending elastomer with the filler.

On the other hand, when the amount of fillers is less than the above mentioned phr range, there arise blisters in cured articles.

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