Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Patent
1994-09-29
1997-12-16
Yamnitzky, Marie
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
428373, 428374, 428422, 428370, 264113, 264127, 264147, 264291, 156229, 156296, B32B 0702, D01F 0804, D01D 0542
Patent
active
056983000
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a moulded article made of polytetrafluoroethylene (PTFE) which is shaped as a film, tape or fibre, and a process for the production thereof.
Because of its thermal stability and its chemical inertness, PTFE is a valued material. AT-B 370,674 discloses monoaxially stretched films made of sintered PTFE which in the stretch direction have values for strength of between 50 N/mm.sup.2 and 140 N/mm.sup.2. These films are produced by first pressing PTFE powder to form a cylindrical moulded article. Subsequently the moulded article is sintered, whereupon films are peeled off, heated to temperatures of at least 327.degree. C. and stretched.
GB-A-2 025 835 describes the production of porous PTFE moulded articles by the paste-extrusion process, a pasty composition, containing essentially PTFE powder and a lubricant, being forced through dies, whereupon the lubricant is removed by drying. Then the moulded article is heated to above the crystallite melting point of the PTFE (327.degree. C.) and stretched during heating.
AT-B 391,473 discloses the production of a monoaxially stretched moulded article made of PTFE, a pasty PTFE powder-containing composition being continually processed to form a moulding which is led over a plurality of rollers or rolls and is heated and stretched, the moulding, before application of the stretching, being heated to a temperature between 327.degree. and 450.degree. C., preferably between 350.degree. and 390.degree. C., sintered during this and then stretched. This process permits the production of a monoaxially stretched moulded article from PTFE with strength values in the stretching direction of at least 500 N/mm.sup.2 and a density of between 1.80 and 2.30 g/cm.sup.3.
In order to increase the range of application of PTFE, it would be desirable for crimped fibres made of PTFE to be available. The invention therefore has the object of making available PTFE fibres having a stable and permanent crimp.
This aim is achieved according to the invention by means of a bicomponent moulded article of polytetrafluoroethylene (PTFE) which is composed, in the manner of the side-by-side type, of two PTFE components which shrink under the effect of heat and differ in their hot-air shrinkage by at least 1%. If, for example, a fibre of this kind is heated to temperatures above 200.degree. C., it crimps insofar as it can shrink freely during the heat treatment.
It is known from the Ullmann "Encyklopadie der technischen Chemie", 4th edition, volume 11, pages 283-284, Verlag Chemie that nylon fibres can be provided with a crimp by bicomponent spinning. According to this process, two polymer melts with different properties are spun from a die hole to form a filament. In this there are in principle two possibilities for arranging the two polymers in the fibre: a core-sheath arrangement and a side-by-side arrangement. In the first arrangement, one polymer surrounds the other in the manner of a sheath and in the latter the fibres consist of two imaginary half-cylinders which are joined to one another via their planes of section. However, it is not possible to produce PTFE fibres having a stable crimp using this process.
The invention is based on the recognition that a bicomponent film consisting of two or more PTFE layers which differ in their shrink properties can be processed in a simple manner to form a crude bicomponent fibre, which can be provided with a stable crimp by heating to a temperature above 200.degree. C.
A preferred embodiment of the bicomponent moulded article according to the invention is therefore designed as a film, tape or fibre. The fibre is expediently fibrillated.
The invention relates to a moulded article made of PTFE which is obtained by heat treatment of the aforementioned bicomponent moulded article.
A preferred embodiment of the moulded article is characterized in that it is in the form of a crimped fibre. This fibre can be processed in a conventional manner to form a needled felt consisting exclusively of PTFE. The crimped PTFE fibre has strength values of a
REFERENCES:
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patent: 5064593 (1991-11-01), Tamaru et al.
patent: 5225131 (1993-07-01), Tamaru et al.
patent: 5246772 (1993-09-01), Manning
patent: 5320888 (1994-06-01), Stevens
patent: 5399307 (1995-03-01), Dalton et al.
patent: 5418045 (1995-05-01), Pike et al.
Ullmanns "Encyklopadie der technischen Chemis", 4th Edition, vol. 11, pp. 283-284, Verlag Chemie, date not given.
Bachmaier Josef
Wimmer Adalbert
Lenzing Aktiengesellschaft
Yamnitzky Marie
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