Method of treating filamentary tows

Claim 1

A PROCESS FOR THE PRODUCTION OF FILAMENTARY TOWS OF SYNTHETIC LINEAR POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYESTERS BASED ON TEREPHTHALIC ACID AND STEREOREGULAR POLYPROPYLENE, WHICH HAVE VARIABLE SHRINKAGE CHARACTERISTICS ALONG THEIR LENGTH AND WHICH ARE SUITABLE FOR CONVERSION INTO STAPLES FIBERS AND SPUN YARNS, COMPRISING SUBJECTING A SUBSTANTIALLY UNIFORM TOW OF UNDRAWN FILAMENTS WITH A BIREFRINGENCE OF 0-12X10-3, TO MOLECULAR ORIENTATION IN A DRAWING PROCESS USING DRAWING CONDITIONS ONE PARAMETER OF WHICH SELECTED FROM DRAW RATIO AND TEMPERATURE, IS CONTINUOUSLY VARIED BETWEEN DEFINED LIMITS AT SUBSTANTIALLY UNIFORM TIME INTERVALS, SO THAT AT A GIVEN TWO SPEED THE ATTAINED OPTICAL BIREFRINGENCE OF THE FILAMENTS BECOMES 15-200X10-3 AND THEIR SHRINKAGE IN BOILING WATER FOR 10 MINUTES 10%60%, THE INTERVALS CORRESPONDING TO A TOW LENGTH WHICH IS GREATER THAN FIVE TIMES THE SHORTEST FIBRE LENGTH INTO WHICH THE TOW IS TO BE CONVERTED BUT LESS THAN 100 M., USING DRAW RATIOS BETWEEN 2:1 AND 5:1, IN A LIQUID MEDIUM MAINTAINED AT A TEMPERATURE OF 10* C. -100* C., FOLLOWED BY CONVERTING THE TOW INTO STAPLE FIBRES, TOPS AND YARNS, CARE BEING TAKEN THAT THE TEMPERATURE OF THE FILAMENTS, FIBRES, TOPS AND YARNS IS NOT ALLOWED TO RISE ABOVE 50* C. IN ORDER NOT TO EFFECT THE SHRINKAGE PROPERTIES OF THE FILAMENTS AND FIBRES BEYOND THE SPECIFIED LIMITS OF SHRINKAGE CHARACTERISTICS, BEFORE A SUBSEQUENT HEAT SHRINKING OPERATION.