Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1996-05-31
2001-10-02
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S393500
Reexamination Certificate
active
06296907
ABSTRACT:
FIELD OF INVENTION
The invention relates to a curable silicone composition, which when applied to a gasket and cured, reduces the coefficient of friction of the gasket.
BACKGROUND OF INVENTION
Gaskets are used to provide a seal between two engaging surfaces. For example gaskets are used in window assemblies to provide a seal against external air infiltration and water leakage. In a typical window assembly, in order to provide a tight seal, the gasket material must be somewhat resilient and able to conform to any irregularities between the mating surfaces of the window glass and a structural component such as a window frame. In applications where an engaging surface such as the glass slides across a face of a gasket generating lateral forces, the gasket must also provide resistance to tearing. Examples of applications where the gasket must resist tearing due to sliding or lateral movement of an engaging surface include sliding glass doors and automotive sunroofs. Typically, gaskets are prepared from elastomeric materials including natural or organic and synthetic rubbers, such as EPDM, SBR, butyl, nitrile and neoprene, chlorosulfonated polyethylene, fluorocarbon containing compounds, urethanes and silicones. Silicone rubbers have excellent molding and extrusion properties and are used to form gaskets with good temperature resistance, resistance to compression set and tensile strength. In stationary sealing applications, silicone rubber gaskets perform well. However, silicone rubber inherently possesses a high coefficient of friction and thus in applications where one or both mating surfaces in contact with the gasket may move lateral to the surface of the gasket there is a tendency to tear. Silicone rubber formulations having good resistance to tear generally are not pliant enough to provide an effective seal in relatively low pressure applications such as automotive sunroofs. Therefore, in applications where lateral forces are generated on the gasket, silicones have not been the material of choice.
U.S. Pat. No. 4,223,897 discloses an anti-stick, non-liquid absorbing laminated gasket The laminated gasket comprises a metallic core and a bonded fibrous layer. The fibrous layer contains a liquid impermeable, resinous impregnate. An anti-stick coat lies along an outer face of the fibrous layer. The anti-stick coat is selected from a group consisting of polytetrafluoroethylene, silicones, polysiloxanes talc, and bentonite. The gaskets are used to seal stationary mating surfaces against fluid leaks in conduits for steam or air, and automotive parts such as carburetors, manifolds and cylinder heads.
U.S. Pat. No. 5,368,315 discloses a non-stick automotive gasket which comprises a resilient material having a polymeric fluorocarbon coating obtained by impregnating the resilient material with a saturant having dispersed therein polymeric fluorocarbon particles. The non-stick gaskets of the patent are used to seal stationary mating surfaces.
U.S. Pat. No. 5,468,815 discloses a curable silicone release formulation for preparing a laminate of a substrate and adhesive. In this application the user typically applies one face of the adhesive to a surface with a release liner in place on the second exposed adhesive surface. The applicator then applies pressure to the release liner to secure the adhesive to the surface. In applying pressure to the release liner, a user often encounters resistance due to friction. The cured coating of the patent is said to reduce the coefficient of friction in this instance.
U.S. Pat. No. 5,080,973 discloses a low friction, high adhesion release coating for disposable diaper tape based on at least 15% by weight of a reactive polydialkylsiloxane, preferably a reactive dimethylsiloxane, at least 40% by weight of a reactive silicone high adhesion agent and crosslinking agent. The composition contains a suitable noble metal catalyst and is heat cured.
None of the above patents disclose a method of lowering the coefficient of friction of a gasket by coating the gasket with a composition containing a curable silicone resin and a lubricating filler which is not soluble in the coating properties.
SUMMARY OF THE INVENTION
In the present invention, the coefficient of friction is lowered by applying a coating containing a curable silicone resin mixed with at least one lubricating filler which is not soluble in the coating to the gasket and curing the resin on the surface of the gasket. Gaskets treated in this manner, exhibit a marked reduction in surface coefficient of friction. The lubricating filler is maintained in place on the surface of the gasket by the resin thus prolonging the friction reducing effects. Because of the reduced coefficient of friction silicone rubber gaskets exhibit improved resistance to tear.
DESCRIPTION OF THE INVENTION
The present invention relates to gaskets coated with a curable silicone resin mixed with at least one lubricating filler. Gaskets treated in this manner exhibit reduced coefficient of friction and are less susceptible to tearing due to lateral or sliding motion of a mating surface against the surface of the gasket.
According to the present invention, the curable silicone coating composition comprises:
A. a curable silicone resin
B. a catalyst
C. at least one lubricating filler not soluble in the coating composition and
D. optionally a solvent.
The components may be combined in any manner with mixing which assures that the lubricating filler will be distributed uniformly throughout the coating composition. In a preferred embodiment the silicone resin and catalyst, and lubricating filler and solvent are mixed separately then combined with constant stirring. The composition is then applied to a gasket in any known manner such as dipping, rolling, brushing, spraying, etc. and cured at elevated temperatures.
The gaskets which are coated according to the present invention may be composed of any elastomeric resilient materials which are known to those skilled in the art. These materials include for example, natural or organic and synthetic rubbers such as EDPM, SBR, butyl, nitrile and neoprene, chlorosulfonated polyethylene, fluorocarbon containing compounds, urethanes and silicones. Silicone rubbers are preferred, particularly the so-called heat curable rubbers, because of their high mechanical strength, low compression set and resistance to temperature and weathering. In general heat curable silicone rubber formulations consist of polydimethylsiloxanes with reactive vinyl groups, surface modified finely dispersed silica, a suitable crosslinker and a catalyst. Additional components may include added fillers, hot air stabilizers, flame retardant materials or pigments. As a rule these rubbers are vulcanized with the aid of various peroxides. The gaskets are formed by known methods such as compression molding or extrusion.
The curable silicone resin of the present invention are those resins known in the art. Silicone resins are highly cross-linked high molecular weight siloxane systems and are thus available as powders or flakes or as solutions in organic solvents. In general curable silicone resins employed in the present invention are represented by the formula
R
a
SiO
4−a/2
(I)
where the substituent R represents an organic substituent, hydrogen or hydroxyl group, the organic constituent itself may be functional. Examples of an organofunctional would be an alkoxy group, alkenyl group or alkynyl group. The variable “a” is not greater than three.
Examples of R in the above formula as an organic constituent are optionally substituted monovalent hydrocarbon radicals having from 1 to 18 carbon atoms. Examples of monovalent hydrocarbon radicals represents by R are alkyl radicals, such as the methyl, ethyl, n-propyl, isopropyl, 1-n-butyl, 2-n-butyl, isobutyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl and tert-pentyl radicals; hexyl radicals such as the n-hexyl radicals; heptyl radicals, such as the n-heptyl radical; octyl radicals, such as the n-octyl radical and iso-octyl radicals, such as the 2,2,4-trimethylpentyl radical
Brooks & Kushman P.C.
Cameron Erma
Wacker Silicones Corporation
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