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
2000-06-27
2001-10-30
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S200000
Reexamination Certificate
active
06310141
ABSTRACT:
BACKGROUND
This invention relates to preparing compositions that include a fluoroelastomer and a fluoroplastic.
Fluoroelastomers are elastomers prepared by curing an uncured fluoroelastomer precursor (“gum”) made from monomers containing one or more atoms of fluorine, or copolymers of such monomers with other monomers, the fluoromonomer(s) being present in the greatest amount by mass. Fluoroelastomers have been used successfully in a number of applications due to their ability to withstand high temperatures and aggressive chemicals, as well as the ability of the fluoroelastomer gum to be processed using standard elastomer processing equipment. In addition, fluoroelastomers have been used in fuel management systems such as automotive fuel hoses, filler neck hoses, injector o-rings, and the like. Fuel management applications require low fuel vapor permeation in combination with good low temperature properties, sealability, and flexural properties.
Fluoroelastomers with high fluorine content show good fuel permeation resistance. However, high-fluorine content fluoroelastomers such as high-fluorine content terpolymers based on tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene have some limitations. For example, when the tetrafluoroethylene content (and thus the fluorine content) is high, flexibility and processability tend to be compromised. With respect to processability, the high fluorine content may render a fluoroelastomer too stiff for curative incorporation on standard processing equipment such as roll mills or Banbury mixers, which requires a material with a melting point less than about 100° C. On the other hand, when the hexafluoropropylene content, at the expense of vinylidene fluoride, is too high, both the polymerization rate and the cure rate may become unacceptably slow for commercial production.
Fluoroplastics are uncured plastics based on polymers made with monomers containing one or more atoms of fluorine, or copolymers of such monomers with other monomers, the fluoromonomer(s) being present in the greatest amount by mass. Examples include melt-processable co- and terpolymers based upon tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. Such fluoroplastics have melting points greater than 100° C. and exhibit good resistance to fuel vapor permeation, as well as good low temperature properties, but compromise the flexural properties needed for flexible fuel management applications. For example, in fuel hoses the stiffness of these materials can lead to disadvantages such as wrinkling when the hoses are loaded onto forming mandrels, increased push-on force during hose installation, and sealing concerns at connection points.
SUMMARY
The invention provides compositions that combine the flexibility, low temperature properties, and processability of fluoroelastomers with the low vapor permeation associated with higher melting fluoroplastics. In one aspect, these advantages are achieved by providing a cured, latex-blended composition that includes: (a) a fluoroelastomer that is the reaction product of a plurality of monomers, at least two of which are selected from the group consisting of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, and perfluorovinyl ethers; and (b) a fluoroplastic having a melting point of at least 100° C. (preferably between 110 and 320° C.), in which the fluoroplastic is the reaction product of a plurality of monomers, at least two of which are selected from the group consisting of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, ethylene, and perfluorovinyl ethers. The fluoroelastomer forms a continuous phase. Preferably, the composition includes at least 50% by weight of the fluoroelastomer precursor and no greater than 50% by weight of the fluoroplastic.
In one embodiment, the fluoroelastomer includes the reaction product of 20-60 wt. % tetrafluoroethylene, 10-40 wt. % vinylidene fluoride, and 30-50 wt. % hexafluoropropylene. In another embodiment, the fluoroelastomer includes the reaction product of 0.1-10 wt. % of a perfluorovinyl ether in addition to these three monomers. A useful perfluorovinyl ether has the formula CF
2
═CF(OCF
2
CF(CF
3
))
m
O(CF
2
)
n
CF
3
where m=0-2 and n=0-6. Specific examples include PMVE (m=0, n=0), PPVE (m=0, n=2), PPVE-2 (m=1, n=2), and combinations thereof.
The fluoroelastomer may optionally include the reaction product of a cure-site monomer with the aforesaid monomers. Cure-site monomers facilitate subsequent curing by peroxide technology of the composition. Examples of suitable cure-site monomers include halogenated monomers, e.g., brominated monomers such as of bromotrifluoroethylene, 3,3,4,4-tetrafluoro-4-bromo-1-butene, bromo-substituted perfluorovinyl ethers, and combinations thereof The amount of cure-site monomer preferably ranges from 0.05 to 5 wt. %. Other cure-site monomers may also be employed.
Examples of suitable fluoroplastics include tetrafluoroethylene-hexafluoropropylenevinylidene fluoride terpolymers having a melting temperature ranging from 100 to 260° C., hexafluoropropylene-tetrafluoroethylene-ethylene terpolymers, ethylene-tetrafluoroethylene copolymers, hexafluoropropylene-tetrafluoroethylene copolymers, and tetrafluoroethyleneperfluoro(alkoxy alkane) copolymers.
The cured composition may be provided in the form of a shaped article or as a coating on a substrate. The properties of the cured composition make it particularly useful in articles for fuel management applications such as fuel hoses, seals, gaskets, o-rings, filler neck hoses, liners, and the like. The cured composition is also useful in chemical processing applications such as hoses, gaskets, seals, o-rings, liners, containers and the like.
The invention further features a method of preparing the above-described composition by providing a fluoroelastomer precursor and fluoroplastic in the form of separate latices; combining the two latices to form a blend, which optionally is coagulated and dried; and curing the blend. Coagulation may be accomplished using a high pressure homogenizer. Alternatively, the blend may be coagulated under high shear in the presence of dissolved gases. These methods are preferable to methods such as melt blending or dry blending because it enables the preparation of compositions that are substantially homogeneous. This feature, in turn, yields compositions with improved physical properties.
The fluoroelastomer precursor itself is too sticky to be coagulated using a high pressure homogenizer. However, the inclusion of the fluoroplastic makes it possible to process fluoroelastomer precursor-containing compositions using this method. Accordingly, it is possible to prepare a fluoroelastomer composition using coagulation methods normally associated with fluoroplastics.
In another aspect, the invention features a cured blend that includes: (a) a fluoroelastomer that is the reaction product of a plurality of monomers, at least two of which are selected from the group consisting of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, and perfluorovinyl ethers; and (b) a fluoroplastic having a melting point of at least 100° C. (preferably between 110 and 320° C.), in which the fluoroplastic is the reaction product of a plurality of monomers, at least two of which are selected from the group consisting of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, ethylene, and perfluorovinyl ethers, the composition being further characterized in that a least one of the monomers reacted to form the fluoroelastomer precursor, fluoroplastic, or both, is a perfluorovinyl ether in an amount ranging between 0.1 and 10% by weight. The fluoroelastomer forms a continuous phase. Preferably, the composition includes at least 50% by weight of the fluoroelastomer precursor and no greater than 50% by weight of the fluoroplastic.
In yet another aspect, the invention features a core-shell polymer that includes: (a) a fluoroelastomer precursor shell having a melting point less than 100° C. (pr
Chen Lisa P.
Hintzer Klaus
Kaspar Harald
Killich Albert
Kolb Robert E.
Dyneon LLC
Harts Dean M.
Lilly James V.
Michl Paul R.
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