Polyester film extrusion with edge bead control

Claim 1

A process for forming a film of a thermoplastic film-forming, polyester comprising the steps of: (a) heating and plasticizing the polyester; (b) feeding the heated and plasticized polyester to a die having an elongated die opening and a deckled area therein, thereby producing a flowing stream of the polyester; (c) heating and plasticizing a second organic polymer; (d) feeding the heated and plasticized second organic polymer into the die and directing it into the flowing stream of the polyester adjacent to but spaced inwardly of the steam's outer edges and sufficiently upstream of the elongated die opening to eliminate the existence of any dead spaces adjacent said deckled area where said polyester or second polymer could accumulate and to permit overlapping of the polyester and the second polymer in the areas near both opposite edges of the elongated die, thereby forming a composite stream of the polyester and second polymer; (e) extruding the composite stream from the elongated die opening to form a film comprising a central portion of the polyester and two edge portions of the polyester and the second polymer, the central portion of the polyester covering at least a major part of the width of the film; and (f) drawing the film from the die opening at a rate greater than the rate of extrusion to thereby reduce the thickness of the film.