Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-11-29
2003-09-02
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S273000, C525S281000, C525S342000
Reexamination Certificate
active
06613846
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The present invention relates to peroxide curable fluoroelastomer compositions. In particular the present invention relates to such compositions that include a siloxane or silazane that contains one or more SiH functionalities. The invention further relates to a method of curing such compositions and to shaped articles obtained from curing such compositions.
2. Background of the Invention.
Fluoroelastomers (elastomeric perfluoropolymers) and in particular perfluoroelastomers are polymeric materials which exhibit outstanding high temperature tolerance and chemical resistance. Consequently, such compositions are particularly adapted for use as seals and gaskets in systems in which elevated temperatures and/or corrosive chemicals are encountered. They are useful in industries such as, chemical processing, semiconductor, aerospace, petroleum, automotive etc.
The outstanding properties of fluoropolymers are largely attributable to the stability and inertness of the copolymerized fluorinated monomer units which make up the major portion of the polymer backbone, e.g., tetrafluoroethylene (TFE), vinylidene fluoride (VDF), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE) and perfluoro(alkyl vinyl) ethers (PAVE). In order to completely develop elastomeric properties, fluoropolymers are typically crosslinked, i.e. vulcanized. The fluoroelastomers can be ionically cured by addition of suitable curing agents (for instance polyhydroxylic compounds, such as Bisphenol AF or Bisphenol A), and accelerators (for instance ammonium, phosphonium, or aminophosphonium salts), and in the presence of bivalent metals oxides and/or hydroxides (for instance MgO, Ca(OH)
2
). Peroxide-curable fluoroelastomers have also been developed, which contain iodine and/or bromine atoms along the polymeric chain and/or in terminal position. Such iodine and/or bromine atoms can be introduced by suitable iodinated and/or brominated comonomers, or by using iodinated and/or brominated chain transfer agents during the polymer preparation (see for instance U.S. Pat. Nos. 4,243,770, 4,501,869 and 4,745,165). Curing such polymers in the presence of free radicals, coming for instance from a peroxide, the iodine and/or bromine atoms act as cure-sites owing to the homolytic scission of the carbon-halogen bonds.
Although cured fluoroelastomers with good physical properties can be obtained from these so-called peroxide curable fluoroelastomers, there is a desire to further improve these compositions. U.S. Pat. No. 5,656,697 discloses peroxide curable fluoroelastomer compositions that show improved cure speed and good cross-link density. This is accomplished by adding to the composition certain metal-organic hydrides including for example silylhydride compounds.
U.S. Pat. No. 5,902,857 teaches to add a bisolefin compound to the compositions of U.S. Pat. No. 5,656,697 to improve certain mechanical properties of cured fluoroelastomers obtainable from such compositions. The bisolefin compound is taught to act as a coagent in the curing reaction.
Despite the many different peroxide-curable fluoroelastomer compositions known in the art, it would be desirable to find further compositions having beneficial properties. In particular, it would be desirable to find compositions that allow for easy, cost-effective processing such as, for example, good mold release and reduced mold fouling, as well as compositions that have good curing properties such as speed of cure and cross-link density. Furthermore, the cured elastomers obtainable from such compositions desirably have excellent physical and mechanical properties including high tensile strength, high elongation at break, and low compression set.
SUMMARY OF THE INVENTION
The present invention provides a curable fluoroelastomer composition comprising:
(a) a fluoroelastomer comprising a cure site component having a halogen capable of participation in a peroxide cure reaction;
(b) an organic peroxide; and
(c) a siloxane or silazane comprising one or more SiH groups.
In a specific embodiment of the invention, the siloxane or silazane comprises one or more —QSiH groups wherein Q is oxygen (O) or nitrogen (N).
It has been found in connection with the invention that such curable composition can be readily cured at high speed and to a good cross-link density. Moreover, cured fluoroelastomers can be obtained that have good physical and mechanical properties. Further, the compositions generally have improved processing properties, in particular better mold release, less mold fouling, improved skin-cure properties and better flow characteristics.
The invention also provides a method of making shaped articles by curing the curable fluoroelastomer composition and to the shaped fluoroelastomeric articles obtainable from such method.
DETAILED DESCRIPTION OF THE INVENTION
The siloxanes for use in the curable fluoroelastomer composition are compounds that include one or more Si—O bond and at least one SiH group, preferably an —O—SiH group. The siloxanes for use in this invention include low molecular weight compounds as well as polysiloxanes which comprise repeating siloxy groups. The polysiloxanes can be linear, branched or cyclic. Examples of low molecular weight siloxanes include for example alkoxy silanes corresponding to the formula:
(R
a
)
s
(R
b
O)
t
SiH
w
wherein each R
a
independently represents an alkyl group such as for example methyl or ethyl or another lower alkyl (C
1
-C
7
alkyl group) or an alkyl group substituted with a substituent such as for example an aryl group, an ester, an alkoxy etc., or aryl group optionally substituted such as for example with an alkyl group, an ester, an alkoxy etc., each R
b
independently represents an alkyl group, preferably a lower alkyl group and which may optionally be substituted, t and w represent an integer of at least 1 and the sum of s+t+w being 4. Examples of siloxanes according to the above formula include HSi(OCH
2
CH
3
)
3
and (CH
3
)
2
(CH
3
CH
2
O)SiH.
In accordance with another embodiment in connection with the present invention, the siloxane is a polysiloxane (oligomer or polymer), comprising a polysiloxy backbone. Such polymer or oligomer may be terminated by an SiH group and/or may contain SiH groups distributed along the backbone. The SiH groups may form part of the backbone or they can be present in a side group attached to the backbone.
For example, polysiloxanes for use in the curable fluoroelastomer compositions of the invention include those that correspond to the formula:
wherein R
1
, R
2
, R
3
, R
6
, R
7
, R
8
and R
9
each independently represents hydrogen, an alkoxy group, an alkyl optionally substituted such as for example with an aryl group, an ester, an alkoxy etc., or aryl group optionally substituted such as for example with an alkyl group, an ester, an alkoxy etc., R
4
and R
5
each independently represents an alkoxy group, an alkyl or aryl group each of which may optionally be substituted, x represents a value of 0 to 150, y represents a value of 0 to 150 and with the proviso that when x=0, at least one of R
1
, R
2
, R
6
, R
7
, R
8
and R
9
represents a hydrogen atom.
Specific examples of siloxanes for use in the curable fluoroelastomer composition include 1,1,3,3 tetraisopropyl disiloxane, diphenyl-1,1,3,3-tetrakis(dimethylsiloxy)disiloxane available from United Chem, silylhydride terminated poly(dimethylsiloxane), poly(methyl hydro siloxane) and copolymers of dimethylsiloxane and methylhydrosiloxane.
Further siloxanes for use in this invention may be cyclic such as those corresponding to the formula:
wherein R
c
represents hydrogen, an alkyl group or an aryl group, R
d
and R
e
each independently represents an alkyl or aryl group, i is at least 1 and the sum of i+j is at least 3. Specific examples of cyclic siloxanes according to the above formula are 1,3,5-trimethyl cyclosiloxane and 1-phenyl-3,3,5,5-tetramethyl cyclosiloxane.
Polysiloxanes and siloxanes having OSiH groups are known in the art and can be produced according to well-known proce
Coggio William D.
Hare Erik D.
Hintzer Klaus
Kolb Robert E.
Scott Peter J.
3M Innovative Properties Company
Lilly James V.
Szymanski Brian E.
Wilson D. R.
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