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
2000-06-20
2003-09-23
Mulcahy, Peter D. (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...
C524S544000, C524S545000
Reexamination Certificate
active
06624251
ABSTRACT:
FIELD OF INVENTION
The present invention relates to fluorine containing thermoplastic vulcanizate (“TPV”) compositions comprising a continuous thermoplastic fluorocarbon resin phase and a dispersed amorphous vulcanized fluorine containing elastomer phase, which is useful as a melt formable material having rubber elasticity. Further it relates to a process for producing a fluorine containing thermoplastic vulcanizate composition, which comprises melt blending the above mentioned thermoplastic fluorocarbon resin and the non-vulcanized amorphous fluorine containing elastomer, followed by dynamically vulcanizing this blend to form chemically cross-linked elastomer particles dispersed in the thermoplastic fluorocarbon resin.
The compositions of this invention have the highly desirable property of low compression set, that is when articles made of the composition are compressed for long periods of time, even at high temperatures, they have a strong tendency to return to their original size and shape. Another advantage is that articles made from the composition of this invention are highly fluid resistant, even to fluids containing chemically basic components, such as large or small molecules containing primary, secondary or tertiary amines. Articles molded from the composition of the present invention can find use as seals and gaskets in applications where high temperatures and harsh chemical environments are common, for example in certain types of automotive or aerospace applications.
BACKGROUND OF THE INVENTION
A two phase composition comprising a continuous phase thermoplastic material and a disperse phase elastomer, produced by dynamically vulcanizing the elastomer while the discrete phase elastomer is dispersed in the continuous phase thermoplastic material, is known, for example, in Coran et al. U.S. Pat. Nos. 4,348,502, 4,130,535, 4,173,556, 4,207,404 and 4,409,365.
Fluorocarbon resins and fluorine containing elastomers are excellent in heat resistance, and a two phase blend obtainable by a combination of these materials, is considered to be excellent in heat resistance as well. Such a fluorine containing two phase blend is discussed by Pazos and Rees in EP patent 168020. The elastomer used is substantially a vinylidene fluoride/hexafluoropropylene elastomer, and as its vulcanization method, polyol vulcanization by a combination of bisphenol AF, an acid receiving agent and an onium salt, or peroxide vulcanization by a combination of an organic peroxide and a polyfunctional unsaturated compound, is employed.
The compounds disclosed in EP 168020 require oven vulcanization (post cure) following dynamic vulcanization. By only dynamically vulcanizing the materials the mechanical properties tend to be inadequate, particularly the permanent strain. In addition, following dynamic vulcanization, the compositions also tend to powder, rendering them extremely difficult to subsequently melt process in standard thermoplastic processing equipment. Finally, the compounds of EP 168020A are inherently susceptible to chemical attack and degradation by chemically basic moieties.
To address some of these problems, Kamiya and Saito in U.S. Pat. No. 5,354,811 describe alternate two phase dynamically vulcanized compounds based on fluorocarbon resin continuous phase and a dispersed fluorocarbon elastomer dispersed phase. The fluorine containing elastomers of U.S. Pat. No. 5,354,811 have vulcanizable sites selected from the group consisting of epoxy groups, carboxylic acid groups, carboxylic acid derivative groups, sulfonic acid groups and sulfonic acid derivative groups. These chemically functional cure sites allow vulcanization to proceed quickly and fully in a short period of time. Such materials were shown to have adequate properties without the need of a post cure.
SUMMARY OF THE INVENTION
A major advantage of the present invention is that it operates to compose and produce fluorocarbon based TPV's which solve problems such as TPV powdering upon synthesis, poor melt processing, and poor physical and mechanical properties, without subjection to a post cure processing cycle. Furthermore, it is the intent of the present invention to overcome these problems without resorting to chemically modifying standard commercial fluoroelastomers, or producing fluoroelastomers from their monomer constituents, with special cure site monomers. This invention provides a two phase composition comprised of fluorinated polymers, that is useful as a thermoplastic vulcanizate which is excellent in mechanical properties, excellent in heat resistance, excellent in fluids resistance, including fluids containing basic moieties, and easily melt processible. In addition, a process for its production is disclosed.
It has been found that the desired two phase composition can be obtained by using as the fluoroelastomer component a blend of two or more fluoroelastomers with at least one of the fluoroelastomers being a terpolymer of vinylidene fluoride/tetrafluoroethylene/propylene. The present invention has been accomplished on the basis of this discovery.
DETAILED DESCRIPTION OF INVENTION AND BEST MODE OF THE INVENTION
The present invention provides a fluorine containing thermoplastic vulcanizate composition comprising a continuous phase of at least one melt formable thermoplastic fluorocarbon resin and a dispersed vulcanized elastomer phase containing a blend of two or more fluoroelastomers with at least one of the fluoroelastomers being a terpolymer of vinylidene fluoride/tetrafluoroethylene/propylene. The vinylidene fluoride/tetrafluoroethylene/propylene fluoroelastomer comprises between 5 and 95 weight percent of the total dispersed elastomer phase, while the total dispersed elastomer phase comprises from between 40 and 90 weight percent based on the total amount of the continuous phase and the disperse phase combined.
Further, the present invention provides a process for producing a fluorine containing thermoplastic vulcanizate composition, which comprises a step of melt blending at least one melt formable thermoplastic fluorocarbon resin and at least one fluorine containing elastomer with at least one of the fluoroelastomers being a terpolymer of vinylidene fluoride/tetrafluoroethylene/propylene while exerting a mixing shear force at a temperature higher than the melting point of the thermoplastic fluorocarbon resins.
The present invention is now further described in detail with reference to the preferred embodiments and the best mode.
The thermoplastic fluorocarbon resin useful for the present invention is required to have thermoplasticity, i.e., it is required to be melt formable. Namely, it must be a resin whereby the melt flow or the volume flow rate described in ASTM D-1238, or ASTM D-2116, can be measured at a temperature higher than the melting point. It is preferably a thermoplastic fluorocarbon resin which can be melt formed at a temperature at which there is no problem of deterioration of the fluorine containing elastomer. Among thermoplastic fluorocarbon resins, all fluorocarbon resins except for polytetrafluoroethylene resins which cannot be melt formed, may be employed.
The thermoplastic fluorocarbon resin useful for the present invention is a thermoplastic fluorocarbon resin having a fluorine content of at least 35% by weight, which can be obtained by polymerizing an ethylenically unsaturated compound containing a completely or partially fluorinated fluoroolefin, preferably at least one fluoroolefin selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, vinylidene fluoride, vinyl fluoride, trifluoroethylene chloride and a perfluoroalkylvinyl ether (wherein the alkyl group has from 1 to 8 carbon atoms).
The ethylenically unsaturated compound may, for example, be a non-fluorinated olefin such as ethylene or propylene, an alkylvinyl ether, or a perfluoroalkyl ethylene, in addition to the above olefins.
Preferred among such polymers is a tetrafluoroethylene/hexafluoropropylene/vinylidene fluoride terpolymer, a tetrafluoroethylene/ethylene copolymer, a tetrafluoro
Freudenberg-NOK General Partnership
Mulcahy Peter D.
Wangerow Ronald W.
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