Patent ID: 6328919
Filing Date: 2001-12-11
Classification: B29C,B29K

Abstract:
A method of plasticating and extruding a thermoplastic material comprising a polycarbonate having a bulk density in the range of about 0.15 g/cm.sup.3 to about 0.4 g/cm.sup.3 into a sheet, profile, or film comprising the steps of:(a) introducing the thermoplastic material into a single screw extruder comprising a conventional frame means, a hopper, vented barrel with a feed throat opening, a two stage extruder screw contained therein and optionally a melt pump; wherein the two stage screw extruder comprises,(i) a feed section having a screw lead to diameter ratio greater than about 1 and a constant channel depth of at least about 12 percent of the screw diameter,(ii) a transition section having a compression ratio of at least 3:1 and a length of at least 5 turns,(iii) a first metering section which is at least about 3 turns long,(iv) optionally, a mixing section,(v) a venting section,(vi) a second transition section, and(vii) a second metering section(b) extruding a plasticated thermoplastic material through a sheet die, profile die, or film die, and(c) recovering a thermoplastic sheet, profile, or film.