Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-08-02
2004-05-11
Tucker, Philip (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S341000, C428S521000, C427S535000, C427S393500, C427S421100, C427S429000, C427S430100
Reexamination Certificate
active
06733893
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a coated silicone rubber article and more particularly to a coated silicone rubber article comprising a silicone rubber substrate having a cured polyisobutylene coating on a surface thereof. The present invention also relates to a method of preparing the article.
BACKGROUND OF THE INVENTION
Silicone rubber is useful in a variety of applications by virtue of its unique combination of properties, including high thermal stability, good water resistance, excellent flexibility, high durability, and good adhesion to various substrates. For example, silicone rubber is widely used in the automotive, electronic, construction, appliance, and aerospace industries. However, silicone rubber also exhibits high permeability to gases, water vapor, and hydrocarbons compared to organic rubber, e.g., butyl rubber. Although this property can be beneficial in certain applications, such as gas-separation membranes, high permeability is undesirable in applications where gas and/or liquid retention is important. Organic solvents can diffuse into silicone rubber causing swelling, significantly decreasing the physical properties of the material.
One approach to reducing the permeability of silicone rubber features coating the surface of the rubber with a less permeable material. Coated silicone rubber articles and methods for their preparation are well known in the art. For example, U.S. Pat. No. 4,395,462 to Polmanteer discloses an article of manufacture comprising a silicone rubber substrate having a cured coating on at least one surface thereof, said coating being cohesively bonded to the substrate and comprising in the uncured state (a) a peroxide-curable fluoroelastomer gum wherein the repeating units are derived from the polymerization of at least one fluorine-containing ethylenically unsaturated organic compound, (b) an amount of an organic peroxide sufficient to achieve curing of said fluoroelastomer gum and (c) an amount of an epoxide compound sufficient to react with the acidic by-products evolved during curing of said gum.
U.S. Pat. No. 6,074,703 to Eckberg et al. discloses a method for reducing oil permeability, comprising the steps of (a) applying a curable fluorosilicone coating to a substrate; and (b) curing the fluorosilicone coating on the substrate, wherein the fluorosilicone coating comprises a vinyl containing fluorosilicone, hydrogen-containing siloxane, and a catalytic amount of a platinum group hydrosilylation catalyst.
U.S. Pat. No. 5,024,863 to Gibbon discloses a method for manufacturing an engine gasket for a vehicle engine having reduced oil permeability, the method comprising the steps of first, forming the engine gasket in the desired shape from a silicone rubber compound, the engine gasket having an inner surface exposed to hot engine oil and an outer surface; and next, applying a silicone varnish coating to at least the inner surface of the engine gasket after the gasket is formed, whereby the inner surface is substantially coated by the silicone varnish coating.
European Patent Application No. EP 0 764 681 B1 to Walker et al. discloses an engine gasket having reduced oil permeability and resistance to bleed, comprising a heat cured silicone rubber compound having a coating of a material selected from the group consisting of parylene N, parylene C, parylene D and mixtures thereof.
European Patent Application No. EP 0624 464 B1 to Lee et al. discloses a multi-layer composite film comprising a core layer of very low gas transmission material, two intermediate layers sandwiching the core layer and two outer layers sandwiching the two intermediate layers. The core layer contains an O
2
of CO
2
barrier material such as polyvinyl alcohol. The intermediate layers are a protective plastic material such as a polyolefin. The outer layers are a silicone resin derived from a silane solution.
U.S. Pat. No. 5,962,127 to Maxson discloses a silicone gel product comprising (A) a silicone gel selected from the group consisting of organosilicone and halogenated organosilicone gels, wherein the gel has tacky surface and (B) a fluorocarbon elastomer film adhering to the surface of the silicone gel.
Japanese Patent Application No. JP 2001026748 A discloses a silicone rubber member comprising a surface protective layer consisting of overcoat material comprising a urethane resin, formed on the silicone rubber base material.
Although the aforementioned references disclose coated silicone rubber articles having a range of permeabilities, there remains a need for a coated silicone rubber article having superior resistance to gases and liquids.
SUMMARY OF THE INVENTION
The present invention is directed to a coated silicone rubber article comprising a silicone rubber substrate having a cured polyisobutylene coating on a surface thereof.
The present invention is also directed to a method of preparing a coated silicone rubber article, comprising the steps of:
(a) applying a curable polyisobutylene composition to a surface of a silicone rubber substrate; and
(b) curing the polyisobutylene composition.
The coated silicone rubber article of the present invention exhibits reduced permeability to liquids and gases compared with the same article absent the cured polyisobutylene coating. For example, the cumulative permeation for 2-propanol through the coated article is typically not more than 10% of the cumulative permeation through the uncoated silicone rubber substrate. Moreover, the desirable physical properties of the silicone rubber, such as thermal stability, flexibility, and durability, are maintained in the coated article.
The method of the present invention employs conventional coating techniques and equipment. Furthermore, the method uses readily available silicone and polyisobutylene compositions. Also, the polyisobutylene composition effectively wets the surface of the silicone rubber substrate, thus facilitating the coating process.
The coated silicone rubber article of the present invention has numerous uses, including gaskets, o-rings, adhesives, insulators, encapsulants, and containers.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
A coated silicone rubber article according to the present invention comprises a silicone rubber substrate having a cured polyisobutylene coating on a surface thereof. The silicone rubber substrate can comprise any silicone rubber, filled or unfilled, known in the art. Moreover, the silicone rubber substrate can have any desired shape. As used herein, the term “silicone rubber” refers to a product prepared by curing (vulcanizing or cross-linking) an organopolysiloxane polymer. The mechanical and chemical properties of the silicone rubber substrate depend on the type of polymer, nature and amount of other components in the formulation, processing technique, and method of cure. For example, the silicone rubber substrate can have a hardness of from 5 to 90 Shore A and a consistency ranging from a soft gel to a tough elastomer.
The silicone rubber substrate can be prepared by converting a curable silicone composition into a desired shape by conventional methods, such as compression molding, injection molding, extrusion, and calendaring; and then curing the composition. As used herein, the term “curing” means the conversion of a liquid or semisolid composition to a cross-linked product. Examples of curable silicone compositions include, but are not limited to, hydrosilylation-curable silicone compositions, peroxide curable silicone compositions, condensation-curable silicone compositions, epoxy-curable silicone compositions; ultraviolet radiation-curable silicone compositions, and high-energy radiation-curable silicone compositions.
Curable silicone compositions and methods for their preparation are well known in the art. For example, a suitable hydrosilylation-curable silicone composition typically comprises (i) an organopolysiloxane containing an avera
Suzuki Toshio
Toth Simon
DeCesare Jim L.
Dow Corning Corporation
Feely Michael
Milen Larry A.
Tucker Philip
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