Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1998-09-11
2000-10-03
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C08L 2712
Patent
active
061274860
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention concerns an article comprising a blend of a fluoropolymer and a thermoplastic polymer
BACKGROUND OF THE INVENTION
PTFE (polytetrafluoroethylene) is an advantageous material for a variety of purposes. The material is used in a wide variety of areas especially in its microporous form, for example, as expanded PTFE (ePTFE), e.g., in clothing articles, packings, filter membranes, medical implants, etc.
It is known that PTFE can be provided with fillers to obtain specific properties of this material. Fillers include particles of carbon, metal, metal oxides, glass or plastics. In this case the particle fillers are added to the PTFE starting material in the form of powder.
EP- B1-0 184 392 discloses structures and membranes, in which the pores of the finished structures are filled with solutions of polymers or monomers, that are then polymerized. However, these variants are confined to certain membranes or films, since a solvent that must fully wet the membranes must be used and the concentration of dissolved polymer or monomer must be kept very low. At high concentration of fillers the pores are clogged and the porosity is limited. In addition, these methods are limited to very open-pore membranes, since small-pore systems exhibit extremely reduced material transport after this treatment.
Filter membranes are a special example of application of ePTFE. The membranes used for industrial filters are typically cleaned at specific intervals. Scraping contamination from the surface of a filter membrane is included in this cleaning. In this example it is obvious that the membrane must be as abrasion-resistant as possible so that it withstands repeated mechanical cleaning.
Another example of a desired property of ePTFE is stability relative to energy rich radiation, e.g. gamma or beta radiation. Since ePTFE becomes brittle when exposed to energy rich radiation one can consider stabilizing the overall structure of filled ePTFE relative to the effect of energy rich radiation by selecting an appropriate filler in an appropriate amount.
The filler in ePTFE is generally found in the intermediate spaces of the porous ePTFE formed by the nodes and fibrils. For example, when filter membranes made of filled ePTFE are subject to mechanical stress, for example, by scraping off filter residues, part of the filler is released from the ePTFE structure on each exposure of the surface to mechanical stress, which ultimately adversely affects the properties of the material.
SUMMARY OF THE INVENTION
In the present invention an article of a fluoropolymer, especially ePTFE is combined with a thermoplastic in order to impart properties of the thermoplastic to the ePTFE. This allows the ePTFE to be used in different applications as a result of properties imparted to the ePTFE, for example, improved abrasion resistance, as well as stability relative to the effect of energy rich radiation.
The term "article" shall refer to sheet-like or film-like material, films, membranes, tubes, fibers, hollow fibers, gaskets, etc. The thickness of film of the invention is typically between about 20 .mu.m and a few hundred .mu.m.
The following description of the invention refers especially to expanded polytetrafluoroethylene (ePTFE), although the invention embraces fluoropolymers in general as starting material for a fluoropolymer-thermoplastic mixture (blend).
The blend of ePTFE and a thermoplastic has a co-continuous intertwined structure. Each polymer is in the form of a continuous structure, wherein the structures of each polymer are intertwined with one another to form a co-continuous macrostructure. Each structure remains independent of the other even though intertwined.
The term "co-continuous" means that both the ePTFE component and the thermoplastic component each separately has a continuous phase structure so that the two components jointly form an intertwined macrostructure. For example, if one were to remove the ePTFE structure from the co-continuous structure the continuous thermoplastic phase would still e
REFERENCES:
patent: 3941860 (1976-03-01), Couchoud et al.
patent: 4749752 (1988-06-01), Youlu et al.
Morphology and Mechanical Properties of Ultr-High Molecular Weight Polyethylene-Poly(tetrafluoroethylene) Blend Films.
"Technische Kunstsoffe auf Basis sich durchdringender Netzwerke (IPN) aus Polyamid und Silikon" . By R. Keuerleber; (1983).
Burger Wolfgang
Gleinser Winfried
Witzko Richard
Cain Edward J.
W. L. Gore & Associates GmbH
Wheatcraft Allan M.
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