MELT-SPINNING FINE POLYESTER FILAMENTS WITH HIGH WITHDRAWAL SPEEDS
Poly(ethylene terephthalate) filaments of enhanced dyeability, low boil-off shrinkage (even in as-spun condition), good thermal stability over a large temperature range, and useful as texturing feed yarns and/or as hard yarns requiring no further drawing are prepared by spinning at a withdrawal speed (V in yards/minute) of at least about 5500 yards/minute and with a polymer temperature (Tp) measured (in .degree.C) in the filter pack at a point 50-100 mils above the center of the spinneret plate of wherein (L) and (D) are the length and diameter (in mils) of the spinneret capillary and (w) is the throughput (in pounds/ hour) per capillary. The filaments are characterized by a long period spacing above 300 .ANG. in their as-spun condition, and, whether in as-spun condition or after heat-treatment, by a low skin-core value as measured by a differential birefringence in relation to their stress measured at 20% extension which correlates approximately with the spinning speed), a large crystal size, and low amorphous orientation. The continuous filament yarns may be draw-textured to provide textured yarns which also show enhanced dyeability. The staple fiber yarns also have very useful properties as compared with conventional staple yarns. A preferred process of spinning at these extremely high speeds is characterized by the use of a spinneret with capillary-dimensions that produce high shear as the polyester is extruded and is applicable also to copolyesters, whose filaments show a similar low skin-core in relation to their stress at 20% extension, the precise values for copolymers being different from the relationship for poly(ethylene terephthalate).