Method for physically converting PTFE particles to fibers

Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – By calendering

Reexamination Certificate

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Details

C264S041000

Reexamination Certificate

active

06187238

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a fiber material comprised of PTFE, suitable for use in a wide range of applications due to its new structure. For example, it may be used to produce diaphragms for the electrolysis of alkali chlorides and filter layers used for various engineering purposes. Moreover, the invention relates to a method for the production of this new fiber material. PTFE fibers are generally known as monofilament fibers, suitable for the production of staple fibers of different length and diameter, yarns and woven fabrics. The disadvantage of these prior art PTFE fibers is that filter layers or diaphragms cannot be produced solely from such fibers obtained by aspiration from a suitable dispersion. These fibers are generally too rigid and have too high a resilience.
According to a known method, PTFE, fiber is produced by milling PTFE sodium chloride and inorganic additives, such as ZrO
2
and TiO
2
, at elevated temperatures in a ball mill (GDR patent 244 365). The PTFE fibers, produced according to this very cumbersome and expensive method, are suitable in principle for use in fabricating filter layers and diaphragms. It must, however, be noted that the diaphragms produced solely from these fibers are inferior in performance to asbestos-containing diaphragms, especially when used in the electrolysis of alkali chlorides. This is apparently due to the structure of these PTFE fibers, which is monofilamentous in contrast to that of asbestos fibers.
OBJECTS AND SUMMARY OF INVENTION
An object of the invention is therefore to provide a fiber material of PTFE, which has a wide range of applications and that can be produced economically.
Briefly stated, the invention provides a new structure of PTFE fibers suitable for the production of diaphragms for alkali chloride electrolysis or filter layers. Such material consists of fiber bundles, each comprised in turn of individual microfibrils, and including structure presenting irregularly shaped interstices between the microfibrils. This new type of fibrous PTFE, with which hydrophilizing additives can optionally be admixed, can be economically manufactured.


REFERENCES:
patent: 4853189 (1989-08-01), Holland
patent: 5009971 (1991-04-01), Johnson et al.
patent: 5188712 (1993-02-01), Dilmore et al.
patent: 5266276 (1993-11-01), Chinh et al.
patent: 5365006 (1994-11-01), Serrand

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