Process for producing stretched filaments of ultrahigh-molecular-weight polyethylene

Claim 1

A process for producing a stretched article of ultrahigh-molecular-weight polyethylene, which comprises (1) melt-kneading a mixture composed of (A) 15 to 80 parts by weight, per 100 parts by weight of the components (A) and (B) combined, of ultrahigh-molecularweight polyethylene having an inherent viscosity [η], determined at 135°C in decalin, of at least 5 dl/g and (B) 85 to 20 parts by weight, per 100 parts by weight of the components (A) and (B) combined, of a paraffinic wax having a melting point, determined by the DSC method, of 40 to 120°C and a weight average molecular weight (Mw), determined by the GPC method, of at least 230 but less than 2,000 in a screw extruder while maintaining the temperature of the mixture at 180 to 280°C, (2) melt-extruding the molten mixture through a die kept at a temperature of 180 to 300°C, (3) cooling the resulting unstretched extrudate to solidify it, and (4) subjecting the unstretched solidified extrudate to a stretching treatment at a temperature of 60 to 140° C at a stretch ratio of at least about 3:1 when step (2) is carried out while a draft is applied to the unstretched extrudate or at a stretch ratio of at least about 10:1 when step (2) is carried out in the absence of a draft.