Patent ID: 8052905

Claim:
A process for the preparation of polymer yarns from ultra high molecular weight homopolymers or copolymers, wherein the process comprises the following steps: (a) preparing a suspension of a homopolymer or copolymer and a spinning or gelling solvent of a non polar nature and having a long carbon atoms chain, in the a vessel, followed by its transfer to a mixer, under continuous stirring and room temperature to form a homogenized mixture, under inert conditions created by a constant flow of N 2 , and at a weight of homopolymer or copolymer to solvent ratio from 2/98 to 30/70, wherein said ultra high molecular weight homopolymer or copolymer is reactor bimodal or multimodal; (b) feeding said homopolymer or copolymer suspension, under inert conditions, to the extruder; (c) extruding said suspension under gel forming conditions, at a temperature in excess of 150° C., and under inert conditions; (d) spinning the gel obtained from the extrusion in a spin block with a multi holed spinneret, so as to obtain non-stretched filaments with diameters of at least 1 mm, at a temperature in excess of 150° C., maintaining the inert conditions; (e) cooling the non-stretched filament bundles, coming from the spin block, by immersion in a tank with a circulation system, wherein the renovation of cold water enters said tank at a temperature which does not exceed 5° C. and at a spot directly opposite and aligned with the center of the filament bundle, defining an immersed spray cooling system, guaranteeing a perfect homogeneity of the cooling system; (f) treating said non stretched yarn with a second extraction solvent for the removal of the first spinning solvent, and later recovering these solvents in a solvent separation process; (g) drying said non stretched yarn for the removal of the second solvent; and (h) stretching said dry yarn by means of a stretching system, in a continuous manner, comprising at least one stretching step.