Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-02-17
2002-07-02
Dawson, Robert (Department: 1712)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C525S479000, C525S477000, C528S017000, C528S039000, C528S901000, C556S482000, C524S588000, C524S127000, C524S123000, C524S323000, C524S366000, C524S493000, C524S497000, C524S448000, C427S387000, C277S591000
Reexamination Certificate
active
06413354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to oil resistant silicone compositions. More particularly, the present invention relates to oil resistant condensation curing silicone compositions which are suitable for sealing and gasketing applications. Methods of making and using such condensation curing silicone compositions are also provided.
2. Brief Description of Related Technology
Conventional room temperature vulcanizable (“RTV”) silicone compositions have excellent sealing and adhesive properties. Such compositions can be formed into gaskets which are used extensively in the automotive industry. For example, several patents assigned to Loctite Corporation and set forth in more detail below, disclose various oil resistant silicone sealant compositions.
In particular, U.S. Pat. No. 4,514,529 (Beers) generally discloses a low modulus, high elongation RTV silicone composition having oil resistance. This composition may include a devolatilized silanol-terminated diorganosiloxane of 2,000 to 250,000 Cst, a devolatilized diorganosiloxane fluid plasticizer terminated with triorganosiloxy groups, a cross-linking agent, a catalyst and a filler. Articles formed from such a composition can be used as, e.g., gasket sealants, as well as formed-in-place gaskets for use on internal combustion engines.
U.S. Pat. No. 4,673,750 (Beers), U.S. Pat. No. 4,735,979 (Beers) and U.S. Pat. No. 4,847,396 (Beers) generally disclose adhesion promoter compositions for use in auto-adhering, one-component RTV silicone sealant systems having oil resistance. The adhesion promoters set forth in these patents include glycidoxyalkyl substituted mixed alkoxy-oxime silanes and di-substituted mixed oxime-alkoxysilylalkyl ureas, respectively. The RTV silicone compositions which contain these oxime adhesion promoters generally include polydimethylsiloxanes, trimethylsilyl terminated polydimethylsiloxanes and various other fillers, additives and catalysts. Such compositions may be used to, e.g., make formed-in-place gasket materials.
International PCT Publication No. WO 93/19130 discloses a one-part RTV silicone rubber composition as a formed-in-place gasket having oil resistant properties. Such a composition includes a diorganopolysiloxane, a M-stopped plasticizer, such as for example, R
3
—Si—(OSiR
2
)
x
—OSi—R
3
, gamma-aminopropyltriethoxysilane, a catalyst, a crosslinker and various fillers. M-stopped silicone plasticizers are generally trimethyl terminated non-reactive silicone compositions. The compositions disclosed by this International patent publication are reported to have oil resistance and good adhesive properties and are especially adapted for use in the automobile industry.
As might be expected for gasketing articles and adhesives used in the automobile industry, such as engine seals and gaskets, retention of adhesion and maximization of joint movement after oil immersion at elevated temperatures is highly desirable. Silicone plasticizers are conventionally used to modify silicone gasketing compounds, such as for example, to lower the modulus of the composition and improve joint movement and the extrudability of the finished product. All of the RTV silicone adhesive compositions set forth above contain M-stopped silicone plasticizers for accomplishing such goals.
It would be desirable to provide such silicone adhesive compositions without using M-stopped plasticizers
SUMMARY OF THE INVENTION
The present invention provides a silicone composition, which includes a silanol terminated silicone fluid, an organic plasticizer, a filler and a crosslinker. The reaction product of this composition forms an oil resistant adhesive silicone composition.
The invention also provides a method of applying a silicone composition to a surface exposed to oil during its intended use. This method includes applying to the exposed surface a composition that includes a condensation curing silanol terminated silicone polymer, an organic plasticizer, a filler and a crosslinker. The method further includes forming the composition into an appropriate sealing configuration and allowing the composition to cure at room temperature into an oil resistant silicone adhesive.
Also, the invention provides a method of using an oil resistant mechanical seal, which remains adhesive after exposure to oil. This method includes applying a seal forming amount of a composition on a surface of a mechanical part. The composition is formed from a condensation curing silanol terminated silicone polymer, an organic plasticizer, a filler and a crosslinker. The method further includes forming a seal between at least two mechanical surfaces by room temperature vulcanization, wherein the seal remains competent when exposed to oil.
Still further, the invention provides a method of using an oil resistant sealing member that remains adhesive after immersion in oil. This method includes forming a seal between two or more surfaces by applying therebetween the oil resistant sealing member formed from a composition that includes a condensation curing silanol terminated silicone polymer, an organic plasticizer, a filler and a catalyst.
It has been found surprisingly that by substituting such M-stopped silicone plasticizers with organic plasticizers in these RTV silicone systems that compositions are formed with significantly improved adhesive properties and resistance to oil.
The present invention will be more fully understood by a reading of the section entitled “Detailed Description of the Invention”.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to condensation curing silicones having improved adhesive properties when exposed to oil. Conventional RTV silicones having M-stopped silicone plasticizers, however, are less desirable for adhesives and articles that are exposed to high temperature oils, such as for example, engine O-rings and gaskets typically used in the automotive industry. Surprisingly, as noted above, it has been found that by substituting an organic plasticizer for the M-stopped silicone plasticizer in such RTV silicone compositions that improved adhesive and oil resistance is obtained.
The present invention provides a silicone composition that includes a silanol-terminated silicone fluid, an organic plasticizer for maintaining adhesion of the composition after exposure and/or immersion in oil, a filler and a crosslinker. The reaction product of this composition is an oil resistant adhesive.
As used herein, “silanol terminated silicone fluid” includes room temperature condensation curing silicone polymers. Such polymers are conventional silicone polymers that are able to cure/vulcanize using moisture from the air at ambient temperature (approximately 25° C.). Higher curing temperatures, however, can also be used, such as for example 50° C., so long as the oil resistant and adhesive properties of the cured elastomers are not compromised.
The silicone polymers of the present invention typically contain functional groups capable of reacting with moisture to substantially cure the composition. Typically, such condensation curing silicone polymers include, for example, polydiorganosiloxanes having terminal hydroxyl groups that are curable to an elastomer upon cross linking. Other silicone compositions, however, can be used in the present invention so long as they are capable of condensation curing to form the oil resistant silicone compositions as described in more detail below.
In the present invention, these silicone polymers can have viscosities that range from about 2,000 Cst to about 200,000 Cst. Desirably, these polymers can range in viscosity from about 4,000 Cst to about 50,000 Cst. Viscosity ranges for these polymers of from about 6,000 Cst to about 20,000 Cst can also be used in the present invention.
The adhesive silicone compositions of the present invention also include one or more organic plasticizers. As used herein, “organic plasticizer” refers to carbon atom-containing plasticizers that do not contain silicone atoms. Any conventional organic plasticizer ab
Haas Hans E.
Kovacs Frank L.
Bauman Steven C.
Dawson Robert
Loctite Corporation
Peng Kuo-Liang
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