Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,...
Patent
1995-06-02
1997-12-23
Edwards, Newton
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
428364, 204252, 204296, D02G 300, C25B 900, C25B 1300
Patent
active
057005729
DESCRIPTION:
BRIEF SUMMARY
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.sub.2 and TiO.sub.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 THE 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 fiberous PTFE, with which hydrophilizing additives can optionally be admixed, can be economically manufactured.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a fluid bed apparatus for use in producing the PTFE fiber according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Pursuant to the invention, a PTFE dispersion, consisting of a salt solution with PTFE particles and optionally hydrophilizing additives, is treated in a hot gas/vapor stream at temperatures between 140.degree. C. and 210.degree. C. in a fluidized bed apparatus of charged with inert solids of the type depicted in FIG. 1. The PTFE dispersion contains a salt solution, which consists preferably of NaCl and the concentration of which advantageously lies between 100 g/L and the saturation limit. The ratio of PTFE to sodium chloride can lie between 1:1 and 1:10, based upon the dry weight of each. Unlike other PTFE fibers, the fiber material according to the invention demonstrates a certain hydrophilicity even without the addition of special hydrophilizing agents.
For certain applications, however, it may be advisable to hydrophilize the fiber material further by means of suitable additives. These additives may include, for example, compounds from the group long known for providing these benefits, such group including zirconium dioxide, titanium dioxide, silicon dioxide, kaolin, aluminum oxide, magnesium oxide, magnesium hydroxide calcium carbonate, etc. In these cases, the mixing ratio of PTFE to the additive should lie between 20:1 and 1:5, based upon the dry weight of each.
Alternatively, the principle of polymer-identical modification may be used to modify the hydrophilic properties of the fiber material according to the invention. For this modification, a quantity of a PTFE powder, which has been highly functionalized by irradiation in an electron beam accelerator or in a gamma radiation source with an output of 2,000 to 10,000 kGy, optionally in the presence of ammonium or alkali
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Backhauss Lothar
Berndt Karlheinz
Horx Manfred
Klatt Bruno
Koelling Hartmut
Edwards Newton
Heraeus Elektrochemie GmbH
Magdeburger Energie - und Umwelttechnik GmbH
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