Heating system for extrusion of thermoplastics

Claim 1

Apparatus for making a film of thermoplastic polymeric material having improved properties including supply means for continuously delivering molten thermoplastic polymeric material under pressure, conduit means connected at one end to said supply means for receiving molten thermoplastic polymeric material therefrom, a die connected to the opposite end of said conduit means, said die having blades which together define an elongated orifice from which the molten thermoplastic polymeric material is extruded as a flat, thin, continuous film, a continuous heat shield formed of thermal insulating material connected at one end to said supply means and at its opposite end in snug contact with said die at a location adjacent to its extrusion orifice, said heat shield surrounding and being spaced from the remainder of said die and said conduit means to provide a passage therebetween, and means for continuously circulating a heated gas through said passage, said circulating means including openings in said heat shield at locations adjacent to said supply means and along opposite sides of said die, a blower, a heater, and ducts extending between said blower, heater, and heat shield openings to provide, with said heat shield, a generally closed system for the heated gas.