Process for injection compression molding

Abstract

A process for injection compression molding ultra high molecular weight polyethylene having an intrinsic viscosity of 3 dl/g or higher measured at 135.degree. C. in decalin and a melt index of 0.01 g/10 min or less comprises, (a) heating the ultra high molecular weight polyethylene to 170.degree.-240.degree. C., (b) adjusting the volume of the mold cavity V.sub.1 equal to the volume of the molded article V.sub.0, (c) injecting ultra high molecular weight polyethylene having a volume V.sub.0 into the mold cavity through a runner portion at a shear rate of at least 20,000 sec.sup.-1, (d) instantaneously expanding the mold cavity to adjust its volume V.sub.1 to satisfy the relation: 1.2 V.sub.0 .ltoreq.V.sub.1 at a time from T.sub.1 (immediately before completion of injection) and a time T.sub.2 (after completion of injection while there is a pressure difference between the cavity and the runner portion, and the ultra high molecular weight polyethylene in the runner portion being solidified), and (e) compressing the volume of the mold cavity V.sub.1 to satisfy the relation: V.sub.1 =V.sub.0 while the ultra high molecular weight polyethylene in the mold cavity is still in a molten state.

Dependencies are inferred from the claim text.