US 4,734,240 AGranted

Melt-extrusion of polymer which is capable of forming an anisotropic melt phase to form large shaped articles exhibiting improved polymeric orientation

AssigneeHoechst Celanese Corporation

InventorsTai-Shung Chung, Sunil K. Garg, Daniel Palangio

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Abstract

An improved technique is provided to melt-extrude a liquid crystalline polymer to form large elongated solid shaped articles which exhibit significantly improved polymeric orientation. The molten polymer which is capable of forming an anisotropic melt phase is extruded through a converging die that is provided with at least one enclosed cooling zone at an interior location within the flowing molten polymer wherein a cooling fluid is circulated. This cools the molten polymer adjacent the cooling zone with the concomitant increase in its melt viscosity. Such increased melt viscosity at the interior of the stream of the molten polymer contributes to the uniformity of the polymeric orientation imparted within the converging die as well as during subsequent drawdown outside the extrusion orifice. Such improved polymeric orientation leads to the formation of an improved product (e.g., a three-dimensional rod) which exhibits an unusually high tensile modulus in the direction of its length. The present invention accordingly overcomes difficulties encountered in the prior art wherein melt-extruded shaped articles significantly larger than fibers heretofore often have exhibited substantial internal heterogeneity and a highly oriented skin and a core of a substantially lesser polymeric orientation.

Claims16

Dependent claims

A process of melt-extrusion for the formation of a solid elongated shaped article having a cross-sectional area of at least 7.times.10.sup.-4 square inch, a minimum thickness of at least 30 mils, and a polymeric orientation substantially in the direction of its length which exhibits improved polymeric orientation uniformity throughout the interior thereof comprising:

(a) providing in a laterally confined zone a moving stream of molten polymer which exhibits an anisotropic melt phase,
(b) passing said stream of molten polymer which exhibits an anisotropic melt phase through a converging die to produce an elongated extrudate while providing at the interior of said stream of molten polymer while present in said converging die at least one enclosed cooling zone wherein a cooling fluid is circulated whereby the portion of the molten polymer adjacent to said cooling zone is cooled and the melt viscosity thereof is increased while maintaining said polymer in the molten state, and
(c) subjecting the resulting elongated extrudate outside the extrusion die to the cooling of its exterior and to a drawdown of approximately 1.5:1 to 10:1 while forming said solid elongated shaped article,
whereby the increased melt viscosity at the interior of said stream of molten polymer created in step (b) contributes to the uniformity of the polymeric orientation which is imparted in steps (b) and (c).

1 more element

Dependencies are inferred from the claim text.