Process for extruding a modified high molecular weight poly(ethylene terephthalate) resin

Claim 1

A process for extruding a bubble-free article from a polymeric composition selected from the class consisting of: (a) poly(ethylene terephthalate) resin; (b) a uniform blend of poly(ethylene terephthalate) resin with a compatible polymer, the amount of the compatible polymer being at most about 10 weight percent of the blend; and (c) a uniform blend of a poly(ethylene terephthalate) resin with an incompatible polymer and a compatibilizing agent, the total amount of the incompatible polymer and compatibilizing agent being at most about 20 weight percent of the blend; said process comprising: (1) premixing an organic diisocyanate with said polymeric composition or individual components of said composition, in any order, the amount of said diisocyanate being sufficient to increase the melt viscosity of said polymeric composition to the desired level without causing excessive crosslinking; (2) introducing the premix of step (1) into the feed section of a twin-screw extruder having a cold feed section, a hot plastication zone, a kneading zone maintained at an average temperature of about 280° to 320° C., a venting zone maintained at an average temperature of about 280° to 320° C. and at a pressure of less than about 1.33 kPa, a metering zone maintained at an average temperature of about 260° to 280° C., and an extrusion due maintained at an average temperature of about 255° to 265° C., all the temperatures being wall temperatures; and (3) operating the extruder at about 30-120 rpm and at a pressure of about 350 kPa or less to recover the extruded article from the die.