Process for preparing poly(tetramethylene terephthalate) yarn

Claim 1

A process for preparing yarn comprised of a polymer of at least 85 percent (by weight) of poly (tetramethylene) terephthalate with a spun denier per filament of from about 0.6 to about 50, comprising the steps of sequentially: a. preparing a polymer comprised of at least 85 percent (by weight) of poly (tetramethylene) terephthalate wherein said polymer has a relative viscosity of from about 10 to about 50; b. extruding the filaments of said polymer through a spinnerette, wherein: 1. the spinning temperature is from about 240 to about 280° centigrade, and 2. the extruded filaments are taken up at a windup speed of from about 1000 to about 10,000 feet per minute; and c. thereafter drawing said filaments to a draw ratio of from about 1.0 to about 5.0, said filaments being passed over a heated object comprising a pin or plate at a temperature of from about 60 to about 180 ° centigrade during said drawing step; provided that, during said extrusion step, the spinning threadline tension per extruded filament (as measured about 70 inches from the face of the spinnerette) is at least 0.09 grams per filament, and the total spinning threadline tension (i.e., the tension on the yarn bundle) is at least - 0.4 + 0.00174 (total spun denier of yarn) + 0.052 (relative viscosity of polymer) - 0.0366 (spinning temperature, in degrees centigrade) + 0.1414 (number of filaments extruded) + 0.00381 (windup speed in feet per minute) - 0.000000332 (windup speed in feet per minute) 2 .