Patent ID: 7585445

Claim:
A method for producing high-tenacity polypropylene fibers with an individual denier of less than 2 dtex having a tenacity above 6 cN/dtex and an elongation below 40%, comprising the steps of: melt spinning a plurality of fiber strands comprising about 60,000 to 120,000 filaments from a polypropylene melt with a melting point≦250° C.; withdrawing the fiber strands at a withdrawal speed<100 m/min., while simultaneously cooling the fiber strands with a gaseous cooling medium; combining all fiber strands to a tow; drawing the withdrawn fiber strands in at least three draw zones, with a partial drawing of the fiber strands occurring in each of the draw zones to achieve a total draw ratio greater than about 4:1, and with the fiber strands undergoing in the first draw zone a partial drawing of at least 70% of the total draw; and cutting the drawn fiber strands to produce polypropylene fibers of a predetermined fiber length.