Process for producing modified ultrahigh-molecular-weight polyolefins

Claim 1

A process for producing a stretched molded article of a graft-modified ultrahigh-molecular-weight polyolefin composition, which comprises mixing 5 to 80% by weight of a powder having a particle diameter of 1 to 500 μm of an ultrahigh-molecular-weight polyolefin having an intrinsic viscosity [η] of 5 to 30 dl/g, 20 to 95% by weight of a normally solid flowability improver (B) having a melting point 20°-70° C. lower than the melting point of the ultrahigh-molecular-weight polyolefin (A), 0.1 to 20 parts by weight, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), of a monomer (C) selected from the group consisting of ethylenically unsaturated carboxylic acids, derivatives of the carboxylic acids, ethylenically unsaturated epoxy monomers and ethylenically unsaturated silane monomer, and 0.01 to 5 parts by weight, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), of a radical initiator (D) at the melting point of the flowability improver (B) or a higher temperature but below the melting point of the ultrahigh-molecular-weight polyolefin (A) to form a dispersion in which the flowability improver (B) forms the dispersion medium and the ultrahigh-molecular-weight polyolefin (A) forms the disperse phase, the monomer (C) and the radical initiator (D) exist dissolved or uniformly dispersed in the dispersion medium, and the ultrahigh-molecular-weight polyolefin (A) exists swollen with the flowability improver (B); melt-kneading the dispersion at the melting point of the ultrahigh-molecular-weight polyolefin (A) or a higher temperature; extruding the melt-kneaded mixture through a die to form an extruded article; stretching the extruded article; and removing the flowability improver (B) from the molded article before, during or after the stretching.