Continuous process for manufacture of crosslinked, oriented polyethylene extrudates

Claim 1

A multi-stage process for producing high strength, highly oriented, crosslinked polyethylene products of low creep and improved thermal resistance, which comprises: forming a mixture of uncrosslinked polyethylene of at least 200,000 weight average molecular weight, and UV sensitizer compound capable of generating free radicals upon UV irradiation; extruding said molten polyethylene mixture to form an extrudate thereof, and subjecting the extrudate to a first stage of elongating draw at an elongational strain rate of from about 0.03 to 0.1 S -1 and at a draw ratio of from about 5 to 8; subjecting the extrudate to a subsequent stage of elongating draw, at an elongational strain rate of from about 0-001 to about 0.01 S -1 and at a draw ratio of from about 1.1 to 2.5; and cooling the extrudate to solidify it; wherein the extrudate, during the subsequent stage of drawing elongation is subjected to UV irradiation appropriate for the UV sensitizer to cause crosslinking of the polyethylene as the extrudate thereof undergoes said subsequent stage of drawing elongation.