Stretching and heat crystallization of poly(meta-phenylene isophthalamide) fibers

Claim 1

IN THE PRODUCTION OF A STRAND OF FIBERS SPUN FROM POLY(META-PHENYLENE ISOPHTHALAMIDE) HAVING AN INHERENT VISCOSITY OF AT LEAST 0.6 IN CONCENTRATED SULFURIC ACID AT 30*C. AT A CONCENTRATION OF 0.5% BY WEIGHT, WHICH POLYAMIDE STRAND IS AMOIRPHOUS IN THE AS-SPUN CONDITION, THE IMPROVEMENT FOR FORMING AN ORIENTED CRYSTALLINE STRAND WHICH COMPRISES DRAWING THE AMORPHOUS STRAND AT TEMPERATURES BELOW 220*C. TO 3-6 TIMES THE ORIGINAL LENGTH INTO A UNIFORMLY ORIENTED AMORPHOUS STRAND AND THEN HEATING THE STRAND AT TEMPERATURES BETWEEN 300* AND 350*C. FOR AT LEAST 0.2 SECOND WITH THE STRAND UNDER TENSION UNTIL CRYSTALLIZED IN THE ORIENTED CONDITION, THE TENSION BEING SUFFICIENT TO PREVENT RETRACCTION BY MORE THAN 10% OF THE ORIGINAL LENGTH AND INSUFFICIENT TO DRAW THE STRAND.