Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Patent
1991-02-26
1993-09-21
Ryan, Patrick J.
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
428371, 428373, 428359, 264184, D02G 300
Patent
active
052467767
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to so-called "aramid" fibers, that is to say fibers of linear macromolecules made from aromatic groups which are joined to each other by amide linkages at least 85% of which are directly joined to two aromatic rings, and, more precisely, aramid fibers produced from optically anisotropic spinning compositions.
It is known to produce such aramid fibers in the form of multifilaments, each of the unit filaments having a linear density of about 1.8 dtex, namely a diameter of about 13 .mu.m. Such fibers are described, for instance, in the following patents or patent applications: EP-A-21 484, EP-A-51 265, EP-A-118,088, EP-A-138,011, Ep-A-168,879, EP-A-218,269, EP-A-247,889, EP-A-248,458, Ep-A-315,253, Ep-A-331,156, EP-A-3,671,542, U.S. Pat. No. 3,767,756, U.S. Pat. No. 3,869,429, U.S. Pat. No. 3,869,430, U.S. Pat. No. 4,340,559, U.S. Pat. No. 4,374,977, U.S. Pat. No. 4,374,978, U.S. Pat. No. 4,419,317, U.S. Pat. No. 4,466,935, U.S. Pat. No. 4,560,743, US. Pat. No. 4,622,265, U.S. Pat. No. 4,698,414, U.S. Pat. No. 4,702,876, U.S. Pat. No. 4,721,755, U.S. Pat. No. 4,726,922, U.S. Pat. No. 4,783,367, U.S. Pat. No. 4,835,223, U.S. Pat. No. 4,869,860.
The methods described in these documents consist essentially in dissolving in a suitable solvent, generally concentrated sulfuric acid, an aromatic polyamide (polymer, copolymer or mixture of polymers) of a molecular structure compatible with the obtaining of a liquid-crystal solution at the spinning temperature of a concentration of generally between 12 and 20% by weight polyamide, extruding the solution through a spinneret, drawing the liquid veins emerging from said spinneret through a layer of air and coagulating them in optimal manner, generally in an aqueous solution of sulfuric acid, in order to assure the high mechanical properties known for these aramid fibers.
The difficulties in effecting such a coagulation increase very rapidly when the diameter of the elementary liquid filament penetrating into the coagulation bath increases.
Thus in U.S. Pat. No. 4,698,414, the maximum filament linear density claimed is about 6.7 dtex, which corresponds to a maximum filament diameter of about 24 .mu.m. It is furthermore stated that the operations of spinning elementary filaments of a diameter of between about 17 and 24 .mu.m are already disturbed by difficulties in coagulation.
This maximum limit of 17 .mu.m, or about 2.7 dtex in terms of linear density, is also claimed or indicated as preferred value in numerous patents or patent applications, such as, for example EP-A-51,265, Ep-A-118,088, Ep-A-138,011, US-A-4,340,559, U.S. Pat. No. 4,374,977, U.S. Pat. No. 4,374,978, U.S. Pat. No. 4,419,317, U.S. Pat. No. 4,560,743.
Furthermore, even before the Coagulation operation, the difficulties in sufficiently orienting molecules of polymers in liquid veins of a high diameter have up to now been considered difficultly compatible with the obtaining of elementary filaments having both a high diameter and high mechanical properties (see, for instance, EP-A-138,011, US-A-374,978, U.S. Pat. No. 4,419,317, U.S. Pat. No. 4,560,743).
The Japanese patent application ("Kokai") published under No. 61-55,210 very briefly describes the production of a monofilament from paraphenylene diamine, terephthaloyl chloride and 4,4'-diaminodiphenylether. This monofilament has a linear density a 100 denier and a tenacity of 16.8 g/denier, no indication being given as to the initial modulus of this monofilament. The properties indicated are obtained only after a hot super-drawing step (draw ratio of 1.8), both the prior spinning operation and the above drawing operation being carried out, in particular, at very low speed. This monofilament is, in fact, obtained from a semi-rigid aromatic copolyamide, the spinning solutions used for the production of this type of fiber being known furthermore to be of low polymer concentration and optically isotropic in the molten state amd at rest. Such aromatic polyamides contain a large fraction of bonds which are responsible for a weak mol
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Meraldi Jean-Paul
Ribiere Joel
Edwards N. O.
Michelin Recherche et Technique
Ryan Patrick J.
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