Process of producing thermplastic resin sheet and the like and molding screw therefor

Claim 1

A process for the production of a thermoplastic resin sheet comprising the steps of introducing a thermoplastic resin into a resin extruder, said resin extruder comprising a housing and a screw contained therein, said screw having a first extruding stage comprisisng a feeding section, a compressing section and a metering section provided successively from where said thermoplastic resin is introduced into said screw, said screw also having a mixing section in which at least one spur gear is provided, said spur gear having a clearance between a crest of said gear and said housing of from 0.1--3 mm and a thickness of from 0.1-1 times the diameter D of said screw, said screw additionally having a first pressure releasing section, a shearing section and a stress relaxing section provided successively after said first extruding stage, said stress relaxing section having a second pressure releasing section provided adjacent said shearing section; extruding a molten thermoplastic film from said resin extruder; introducing said thermoplastic film into a slit in a cooling device, said slit having cooling water flowing therethrough in a co-current direction with said thermoplastic film; and recovering a thermoplastic resin sheet.