PROCESS FOR PRODUCING STRETCHED ARTICLE OF ULTRAHIGH-MOLECULAR WEIGHT POLYETHYLENE

摘要

A stretched article of ultrahigh-molecular-weight polyethylene is produced by (1) melt-kneading a mixture composed of (A) 15 to 80 parts by weight, per 100 parts by weight of components (A) and (B), of ultrahigh-molecular-weight polyethylene having an inherent viscosity [ eta ], determined at 135 DEG C in decalin, of at least 5 dl/g, and (B) 85 to 20 parts by weight, per 100 parts by weight of components (A) and (B), of an aliphatic compound (b1) of at least 8 carbon atoms having a melting point, determined by the DSC method, of at least 10 DEG C and a boiling point of at least 130 DEG C and selected from aliphatic carboxylic acids, aliphatic alcohols, aliphatic acid amides, aliphatic carboxylic acid esters, aliphatic mercaptans, aliphatic aldehydes and aliphatic ketones, optionally up to 80% by weight of the aliphatic compound (b1) being replaced by a hydrocarbon polymer (b2) having a softening point, determined by the method of JIS K-2531,of not more than 130 DEG C and a weight average molecular weight (Mw), determined by the GPC method, of not more than 2,000, in a screw extruder while maintaining the mixture at a temperature from the melting point, determined by the DSC method, of the mixture to 300 DEG C, (2) melt-extruding the molten mixture through a die kept at a temperature from the melting point, determined by the DSC method, of the mixture to 300 DEG C, (3) cooling the resulting unstretched extrudate to solidify it, and (4) subjecting the unstretched solidified extrudate to a stretching treatment at a temperature from the melting point, determined by the DSC method, of component (B) to a point 20 DEG C above the melting point of the mixture at a stretch ratio of either at least 3:1 when step (2) is carried out while a draft is applied to the unstretched extrudate or at least 10:1 when step (2) is carried out in the absence of a draft.