Process for producing stretched article of ultrahigh-molecular weight polyethylene

Claim 1

A process for producing a stretched filament of ultrahigh-molecular-weight polyethylene, which comprises (1) melt-kneading a mixture composed of (A) 15 to 50 parts by weight, per 100 parts by weight of components (A) and (B) combined, of ultrahigh-molecular-weight polyethylene having an inherent viscosity (72 ), determined at 135° C. in decalin, of at least 5 dl/g, and (B) 85 to 50 parts by weight, per 100 parts, by weight of components (A) and (B) combined, of a mixture of 95 to 20% by weight, per 100 parts by weight of components (b 1 ) and (b 2 ) combined, of a fatty acid (b 1 ) selected from the group consisting of capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid, and from 5 to 80% by weight, per 100 parts by weight of the fatty acid(b 1 ) and component (b 2 ) combined, of a low softening point hydrocarbon polymer (b 2 ) having a softening point, determined by the method of JIS K-2531, of from 50° to 130° C. and a weight average molecular weight (Mw), determined by the GPC method, of from 50 to 2,000, and selected from the group consisting of aliphatic hydrocarbon resins produced from, as main raw materials, a C 4 fraction, a C 5 fraction or a mixture of these fractions obtained by cracking of petroleum or naphtha, and aromatic hydrocarbon resins produced from, as main raw materials, a C 9 fraction or a mixture of these fractions obtained by cracking of petroleum or naphtha, in a screw extruder while maintaining the mixture at a temperature ranging from the melting point, determined by the DSC method, of the mixture to 300° C., (2) melt-extruding the molten mixture through a die kept at a temperature ranging from the melting point, determined by the DSC method, of the mixture 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 ranging from the melting point, determined by the DSC method, of component (B) to a point 20° C. above the melting point of the mixture at a stretch ratio of either at least about 3:1 when step (2) is carried out while a draft is applied to the unstretched extrudate or at least about 10:1 when step (2) is carried out in the absence of a draft, and dissolving the component (B) with a solvent to remove the component (B) before, during or after the stretching treatment, whereby the amount of the component (B) remaining in the stretched filament is not more than about 10% by weight.