Process for producing filament and filament assembly composed of

Details Process for producing filament and filament assembly composed of Process for producing filament and filament assembly composed of

1995-05-03

2000-04-18

Dixon, Merrick

Plastic and nonmetallic article shaping or treating: processes

Forming continuous or indefinite length work

Shaping by extrusion

264175, 264205, 26421112, 524420, D01D 512

Patent

active

060511753

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to processes for producing a heat-resistant filament and filament assembly of high strength and high elastic modulus each composed of a thermotropic liquid crystal polymer. Further, the invention relates to processes for producing a filament and a filament assembly in which a thermotropic liquid crystal polymer is mixed with another extrudable polymer and to the above filament assembly.


BACKGROUND OF THE PRIOR ART

Since the emergence of a thermotropic liquid crystal polymer, the heat resistance thereof and the attainability of high strength and high elastic modulus thereby have been noted and thus some prior arts have been developed with respect to the process for producing the fiber (see, for example, U.S. Pat. Nos. 3,975,487, 4,468,364 and 4,161,470 and Japanese Patent Laid-Open Gazette No. 196716/1988).
It is known that the thermotropic liquid crystal polymer can have high strength and high elastic modulus only by spinning if it is performed under appropriate conditions. Further, it is known that the heat treatment and redrawing can improve the strength and elastic modulus thereof. In particular, it is reported that some types exhibit a strength improvement to 5 to 6 times the original.
In the spinning of the above conventional thermotropic liquid crystal polymer filament, it has been necessary to conduct the spinning with the use of a nozzle having a very minute aperture for obtaining a fine denier filament because it is difficult to increase the draft ratio thereof. Further, extrusion abnormalities such as melt fracture are likely to occur. Thus, the extrusion rate cannot be made high resulting in extremely poor productivity.
Therefore, with respect to the properties of the obtained filament, no processes have been established for stably producing a filament with the ultimately high strength and elastic modulus at high productivity except on a laboratory scale.
The inventors have conducted extensive investigations into the causes of the low productivity of the prior art, the difficulty in stably producing a product with high strength and high elastic modulus and the poor spinning operation efficiency (end breakage, denier nonuniformity and product quality dispersion, etc.) in connection with the melt spinning of the thermotropic liquid crystal polymer filament. As a result, the following has been found.
(1) The thermotropic liquid crystal polymer as a starting material is not always uniform.
A first reason for this cause is an inevitable consequence of the technology of polymerizing the thermotropic liquid crystal polymer. Other reasons are that the cause relates to the heat history difference and heat deterioration after polymerization and the increase of polymerization degree by heat treatment. With respect to these, a rapid product quality improvement has been attained in recent years by virtue of, for example, polymerization and subsequent treatment technologies and post-polymerization filter technologies. However, the improvement is still not satisfactory.
(2) The melting point of the thermotropic liquid crystal polymer is so high that, after leaving the spinning nozzle, the surface of the filament is cooled by the temperature of the atmosphere with the result that the draft ratio cannot be made high.
Thus, a skin layer is formed at the surface of the filament, thereby creating a structural difference between the inner part and the surface part. This is an obstacle to the high quality (for example, high strength, elastic modulus and elongation). In the spinning of the customary thermoplastic polymers, the draft ratio can be increased in the form of a melt having left the nozzle to thereby orient the molecules. However, with respect to the thermotropic liquid crystal polymer, greater belief is in that the orientation is completed in the nozzle, and the thought has not arrived at a concept of stably increasing the draft ratio upon leaving the nozzle.
(3) The nozzle diameter is reduced for increasing the orientation in the nozzle. Further, the

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patent: 5019309 (1991-05-01), Brunnhofer
patent: 5296185 (1994-03-01), Chau et al.
patent: 5321069 (1994-06-01), Owens

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