Method of producing a polyester filament yarn having a high level of twist

Abstract

The present invention relates to a method of producing a twisted polyester filament yarn having a high level of twist used for a woven or knitted crepe fabric. A method of this invention comprises imparting a high level of twist to a polyester filament yarn which has particular properties, and heat setting said twisted polyester filament yarn. The first of these properties which the polyester filament yarn has is that a boil-off shrinkage in boiling water is in the range of 0% to 5%. The second is that a thermal shrinkage stress at 140.degree. C. in hot air is more than 0.03 g/de. The third is that a ratio of a thermal shrinkage stress at 180.degree. C. in hot air to a thermal shrinkage stress at 140.degree. C. is more than 1.0. The polyester filament yarn which has above mentioned properties can be obtained by repeating heat treatment several times at a temperature from 160.degree. C. to 220.degree. C. in hot air, stretching the polyester filament yarn in a range of 2% to 10% and successively shrinking it in the same range, or by being subjected to heat treatment at a temperature from 160.degree. C. to 220.degree. C. in hot air, shrinking restrictively the polyester filament yarn in a range of 0% to 10% under the relaxed state.

Dependencies are inferred from the claim text.