Abstract: There are described polyester fibers and filaments which, following reaction with carbodiimides, have capped carboxyl end groups, the carboxyl end groups being predominantly capped by reaction with mono- and/or biscarbodiimides which are present in the fibers and filaments in an amount of from 30 to 200 ppm, based on the weight of the polyester, the free carboxyl end group content being less than 3 meq/kg of polyester, and the fibers and filaments additionally containing at least 0.02 percent by weight of at least one free polycarbodiimide or of a reaction product containing still reactive carbodiimide groups, and also a process for the preparation thereof.The filaments described are suitable in particular for producing papermaker's machine wire-cloths.

Abstract: In core yarns, a) the polyester material of the core filaments has an average molecular weight corresponding to a relative solution viscosity of at least 1.9, and b) the core has a specific strength of at least 60 cN/tex, the core yarns producing a seam length to rupture of more than 800 cm in a sewing test under aggravated conditions.The core yarns are obtainable by a process comprising the measures of: i) producing multifilament yarns based on polyesters having an average molecular weight corresponding to a relative solution viscosity of at least 1.9 by melt spinning polyester with a takeoff speed of at least 1500 m/min.

Abstract: Polyester fibers and filaments which contain carboxyl end groups closed off by reaction with carbodiimides, whereinthe closing off of the carboxyl end groups has predominantly been carried out by reaction with mono- and/or biscarbodiimides which the fibers and filaments still contain in the free form, however in as little an amount as less than 30 ppm (by weight) of the polyester,the content of free carboxyl end groups is less than 3 meq/kg of polyester andthe fibers and filaments still contain at least 0.05% by weight of at least one free polycarbodiimide or a reaction product which still contains reactive carbodiimide groups, and a process for their preparation are described.The filaments described are particularly suitable for the production of paper making machinery screens.