High-strength polyester threads and method for producing the same

High strength polyester filaments having a tear strength of >70 cN/tex consisting of

• α) a polyester comprising at least 85 mol % of poly(C2-4-alkylene) terephthalate.
• β) from 0.1 to 2.0% by weight of an incompatible, thermoplastic, amorphous, polymeric additive having a glass transition temperature in the range from 90 to 170° C., and
• γ) from 0 to 5.0% by weight of further additives,
• where the sum of α), β) and γ) is equal to 100%, the ratio of the melt viscosity of the polymeric additive β) to the melt viscosity of the polyester component α) is from 1:1 to 7:1, and the polymeric additive β) is present in the yarn in the form of fibrils having a mean diameter of ≦80 nm which are distributed in the polyester component α).