Process for biaxially elongating thermoplastic polymeric films

Claim 1

A PROCESS FOR BIAXIALLY ELONGATING POLYMERIC FILM WHICH COMPRISES THE STEPS, IN SEQUENCE, OF ELONGATING A SUBSTANTIALLY AMORPHOUS, CRYSTALLIZABLE, POLYMERIC FILM SELECTED FROM THE GROUP CONSISTING OF FILMS OF POLYETHYLENE TEREPHTHALATE, POLYHEXAMETHYLENE, ADIPAMIDE, POLYCAPROLACTAM, POLYHEXAMETHYLENE SEBACAMIDE POLYETHYLENE-2,6NAPHTHALATE, POLYETHYLENE-1,5-NAPHTHALATE, POLYTETRAMETHYLENE-1,2-DIOXYBENZONATE AND COPOLYMERS OF ETHYLENE TEREPHTHALATE AND ETHYLENE ISOPHTHALATE, SAID COPOLYMERS CONTAINING AT LEAST 70* ETHYLENE TERPHTHALATE, IN ONE DIRECTION AT A TEMPERATURE T1 BETWEEN THE SECOND ORDER TRANSITION TEMPERATURE OF THE FILM AND ABOUT 35* C. ABOVE SAID TRANSITION TEMPERATURE, THEREAFTER, SUBJECTING THE FILM TO A TEMPERATURE WITHIN A RANGE OF ABOUT 25*C. ABOVE T1 TO JUST BELOW THE CRYSTALLINE MELTING TEMPERATURE RANGE OF THE FILM WHILE RESTRICTING DIMENSIONAL CHANGE OF THE FILM,AND THEREAFTER, ELONGATING THE FILM IN A DIRECTION AT RIGHT ANGLES TO THE DIRECTION OF PREVIOUS ELONGATION AT A TEMPERATURE WITHIN A RANGE OF ABOUT 130*C. BELOW TO ABOUT 30*C. BELOW THE CRYSTALLINE MELTING TEMPERATURE RANGE OF THE FILM.