Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1999-07-23
2000-09-19
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524449, 428447, 428493, 428495, 428517, C08K 300
Patent
active
061213608
DESCRIPTION:
BRIEF SUMMARY
The invention is concerned with gaskets (including spirally wound gaskets), in particular with gaskets having a sealing-enhancing layer which is based on exfoliated vermiculite.
Exfoliated vermiculite is a known heat-resistant resilient material. Exfoliated vermiculite is conventionally formed by expanding mineral vermiculite using gas, this material being referred to herein as "gas-exfoliated vermiculite". The gas may be thermally generated, in which case the product is called "thermally-exfoliated vermiculite" (TEV). TEV may be made by flash-heating mineral vermiculite to 750-1000.degree. C., at which temperature the water (free and combined) in the ore vaporises rapidly and the steam generated forces apart the silicate sheets which form the raw material, so bringing about an expansion of 10-20 times perpendicular to the plane of the sheets. The granules formed have a chemical composition which (apart from the loss of water) is virtually identical to that of the raw material. Gas-exfoliated vermiculite may also be made by treating raw vermiculite with a liquid chemical, eg hydrogen peroxide, that penetrates between the silicate sheets and subsequently evolves a gas, eg oxygen, to bring about exfoliation. A different form of exfoliated vermiculite is known as "chemically-exfoliated vermiculite" (CEV) and is formed by treating the ore and swelling it in water. In one possible preparation method, the ore is treated with saturated sodium chloride solution to exchange magnesium ions for sodium ions, and then with n-butyl ammonium chloride to replace sodium ions with n--C.sub.4 --H.sub.9 NH.sub.3 ions. On washing with water swelling takes place. The swollen material is then subjected to high shear to produce an aqueous suspension of very fine (diameter below 50 microns) vermiculite particles.
It is known to utilise exfoliated vermiculite as a layer of a sheet gasket, eg an automotive head gasket, and for other purposes. For example, GB 2 193 953 B discloses forming sheet-like gaskets formed from particles of gas-exfoliated vermiculite. Because such particles do not cohere well, they are bound together by fine particles of CEV. The use of CEV as a binder retains heat resistance and resilience, whereas the use of other binders could result in an incompressible structure. However, although exfoliated vermiculite has excellent heat resistance and a high degree of resilience, it has poor water resistance.
GB 2 123 034 B describes making a flexible sheet material, eg for a gasket, by subjecting an aqueous suspension to electrophoresis. The suspension contains an expanded layer silicate, eg CEV with a particle size below 50 microns, and a dispersed organic polymeric material, eg acrylic polymer, acrylonitrile-butadiene copolymer, epoxy resin, or natural rubber.
A sealing element for a gasket for the exhaust system of an internal combustion engine is disclosed in GB 2 217 742 A. This sealing element comprises relatively coarse particles of TEV (passing a 2 mm sieve) bonded together by fine CEV particles (about 100 microns in size). This element is stated to disintegrate quickly if exposed to water as the fine CEV particles are readily dispersed in water. In order to improve water-resistance, GB 2 217 742 A proposes bringing the element into contact with a solution of an aluminate or a zirconyl salt. Further improvement is achieved by treatment with a solution of a silicone elastomer. An example is given of impregnation of a sheet (which had already been treated with sodium aluminate) by a 15% solution of silicone elastomer in toluene, the solids uptake being 3% by weight.
It is an object of the present invention to provide a gasket comprising a layer of sealing enhancing material which is based on exfoliated vermiculite, the layer having improved water resistance.
The invention provides a gasket comprising a sealing layer formed from a resilient material which comprises particles of chemically-exfoliated vermiculite bonded together, wherein the layer also comprises a hydrolysis-resistant polymer coupled to the vermicu
REFERENCES:
patent: 4271228 (1981-06-01), Foster
patent: 4477094 (1984-10-01), Yamamoto
patent: 4629199 (1986-12-01), Yamamoto
Atkinson Alan W.
Bond Stephen P.
Hoyes John R.
West Adam M.
Cain Edward J.
Flexitallic Investments, Inc.
Mason Dwayne J.
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