Method and apparatus for stretching beaded-edge films

Claim 1

APPARATUS FOR BIAXIALLY ORIENTING A THERMOPLASTIC POLYMERIC FILM HAVING A WEB AND BEADED LONGITUDINAL EDGES INCLUDING A PAIR OF LATERALLY SPACED TRACKS DISPOSED IN SUBSTANTIALLY PARALLEL RELATIONSHIP AND ADAPTED TO SLIDABLY ENGAGE WITH THE BEADED EDGES OF THE FILM, MEANS OFR DELIVERING THE FILM IN-BETWEEN SAID TRACKS, AN ELONGATED DUCT CONNECTED TO EACH OF SAID TRACKS IN HEAT-CONDUCTING RELATIONSHIP AND EXTENDING SUBSTANTIALLY COEXTENSIVELY THEREWITH, MEANS FOR CIRCULATING A HEATED FLUID THROUGH SAID DUCTS FOR HEATING THE BEADED EDGES OF THE FILM, RADIANT HEAT PANELS POSITIONED BETWEEN SAID TRACKS AND ADJACENT TO THE PATH OF THE FILM FOR HEATING THE FILM WEB, MEANS FOR INSULATING THE BEADED EDGES OF THE FILM FROM THE HEAT SUPPLIED BY SAID RADIANT PANELS, MEANS POSITIONED TO ENGAGE WITH AND GUIDE THE FILM BEADED EDGES AS THE FILM LEAVES SAID TRACKS, MEANS OPERATIVE AT A SPEED GREATER THAN SAID FILM DELIVERY MEANS FOR ADVANCING THE FILM ALONG SAID GUIDE MEANS AND LONGITUDINALLY STRETCHING THE SAME, SAID GUIDE MEANS BEING DISPOSED ALONG DIVERGENT PATHS TO INDUCE TRANSVERSE STRETCHING OF THE FILM WEB CONCOMITANTLY WITH THE LONGITUDINAL STRETCHING THEREOF, AND MEANS FOR REGULATING THE TEMPERATURE OF THE FILM WEB AND BEADED EDGES DURING THE STRETCHING THEREOF TO MAINTAIN A UNIFORM TEMPERATURE DIFFERENTIAL THEREBETWEEN.