Apparatus for producing flat film from thermoplastic material

Claim 1

APPARATUS FOR PRODUCING FLAT FILM FROM THERMOPLASTIC MATERIAL, COMPRISING AN EXTRUDER HAVING A DIE THROUGH WHICH A TUBE OF SAID MATERIAL CAN BE CONTINUOUSLY EXTRUDED, A COOLING DEVICE LOCATED IN THE PATH OF THE EXTRUDED TUBE TO EFFECT COOLING AND SETTING OF THE TUBE, A HEATER DEVICE OPERABLE TO HEAT THE COOLED AND SET TUBE TO A SOFTENING TEMPERATURE WHICH WILL PERMIT ORIENTATION OF THE MOLECULES OF THE THERMOPLASTIC MATERIAL, TUBE ENGAGING MEANS OPERABLE TO ENGAGE THE PERIPHERY OF THE TUBE BETWEEN THE COOLING AND HEATER DEVICES AND TO MOVE IT TOWARDS THE HEATER DEVICE, A SEALING MEMBER ENGAGEABLE WITH THE INTERIOR SIDES OF THE TUBE AT A POSITION BETWEEN THE COOLING AND HEATER DEVICES TO FORM WITHT EH TUBE A SEAL PREVENTING THE ENTRY INTO THE TUBE PORTION BETWEEN THE SEALING MEMBER AND THE COOLING DEVICE OF GAS CONTAINED IN THE TUBE PORTION BETWEEN THE SEALING MEMBER AND THE HEATER DEVICE, MEANS OPERABLE TO INTRODUCE GAS AT SUPERATMOSPHERIC PRESSURE THROUGH SAID SEALING MEMBER INTO THE INTERIOR OF THE PORTION OF THE TUBE SOFTENED BY SAID HEATER DEVICE, AND NIP ROLLERS OPERABLE TO FLATTEN THE HEAT-SOFTENED TUBE, TO ENTRAP THEREIN GAS INTRODUCED BY SAID LAST-NAMED MEANS, AND ALSO TO MOVE THE TUBE AWAY FROM THE HEATER DEVICE AT A LINEAR SPEED GREATER THAN THAT AT WHICH THE TUBE IS MOVED BY SAID TUBE ENGAGING MEANS THEREBY TO EFFECT SIMULTANEOUS LATERAL AND LENGTHWISE STRETCHING OF THE HEAT-SOFTENED PORTION OF THE TUBE.