Method of producing polypropylene yarns

A method of producing polypropylene yarns composed of a plurality of continuous and substantially oriented individual filaments by melt spinning and stretching them in an integral process, comprising the steps of:

• (a) simultaneously extruding a sufficient number of said individual filaments for forming at least 8 continuous filament yarns, each consisting of at least 10 filaments, at an extrusion speed of at least 400 meters per minute into an essentially vertical air quenching zone for solidification of said filaments;
• (b) arranging said filaments to form a substantiallly planar array of parallel and mutually distance yarn strands in a number corresponding to step (a);
• (c) together stretching said filaments to achieve said substantial orientation by passing said yarn strands, while maintaining them in said array, over peripheral surface portions of a sequence of rotating cylinders each having a diameter greater than about 300 mm and all having parallel axes of rotation, each strand passing over said surface portions along a discrete path which is substantially defined by a plane intersecting perpendicularly with the rotation axis of any cylinder;
• each strand being in frictional contact with said peripheral surface portions for a contact path length of from 1.0 to 6.5 meters;
• at least 50 percent of said path length of frictional contact being provided on a total number of from 2 to 6 cylinders;
• and
• (d) finally winding said yarn strands obtained as product yarns at a speed of at least 1000 meters per minute.