Process for the production of high strength yarns by spin-stretching and yarns produced by the process, especially from polyamide-6 and polyester filaments

An improved process for the production of high-tenacity technical-grade yarns of polyamide and polyester, having a low reference elongation, by spin-drawing in which filaments extruded from a spinneret are cooled in a cooling zone by being exposed to a stream of air, said filaments being passed over a preparation device and then passed directly over a plurality of sets of rolls, said plurality of sets of rolls forming roll systems, said filaments being drawn between at least two sets of rolls in at least one draw field, said filaments being subjected to a temperature of greater than or equal to 160.degree. C. on at least one set of rolls and subsequently being passed over a set of let-down rolls, constituting a let-down roll system, immediately prior to being wound up at a windup speed of greater than or equal to 2,200 m/min., the improvement comprising:

• (a) heating a set of rolls, said set of rolls being positioned in advance of a minimum of one draw zone, said set of rolls being heated to a constant temperature, said temperature being in a range of (T.sub.G -20.degree. C.) to (T.sub.G +65.degree. C.), wherein T.sub.G is the temperature of the glass transition point, said filaments being drawn over said set of rolls without the use of additional stationary draw means;
• (b) maintaining a set of rolls at a temperature in excess of 110.degree. C., said set of rolls being positioned following a minimum of one draw zone, said yarn having a tension of not less than 0.2 g/dtex upon leaving said roll system;
• (c) permitting said yarn to remain in said let-down roll system for a residence time, said residence time being selected to be at least 0.2 sec.;
• (d) maintaining said windup speed of said yarn at a speed not less than 2.5% less than the peripheral speed of said let-down roll system;
• and,
• (e) adjusting the temperature of said let-down roll system to a temperature of less than or equal to 60.degree. C.