Polytetrafluoroethylene films and method for making same

Claim 1

AS A NEW ARTICLE OF MANUFACTURE: A THIN, UNFUSED, UNSINTERED, FLEXIBLE, DENSE FILM OF COHERING PARTICLES OF POLYTETRAFLUOROETHYLENE HAVING A TENSILE STRENGTH OF AT LEAST 3,500 P.S.I. IN AT LEAST ONE DIRECTION AND A TENSILE STRENGTH OF BETWEEN 650 AND 1,000 P.S.I. IN A DIRECTION TRANSVERSE TO SAID ONE DIRECTION, SAID FILM BEING FORMED BY PASSING FIBRILLOUS PARTICLES OF TETRAFLUOROETHYLENE OF A SIZE BELOW 24 MICRONS, AS DETERMINED BY SEDIMENTATION TEST MEASUREMENT, IN A SUBSTANTIALLY UNIFORMLY THICK LAYER BETWEEN CALENDER ROLLS AT A RAISED NON-SINTERING TEMPERATURE BELOW 400* F. WHILE MAINTAINING ONE CALENDER ROLL IN CONTACT WITH ONE SURFACE OF SAID LAYER AT A TEMPERATURE AT LEAST ABOUT 100* F. ABOVE THE TEMPERATURE OF ANOTHER CALENDER ROLL IN CONTACT WITH THE OPPOSITE SURFACE OF SAID LAYER.

Claim 2

A METHOD OF MAKING A TOUGH, CALENDERED, UNFUSED FILM CONSISTING ESSENTIALLY OF POLYTETRAFLUORETHYLENE, COMPRISING FEEDING FIBRILLOUS PARTICLES OF POLYTETRAFLUOROETHYLENE AS A FLUFFY LOOSE SUBSTANTIALLY UNIFORMLY THICK LAYER TO THE NIP OF CALENDER ROLLS, SAID PARTICLES BEING OF A SIZE NOT GREATER THAN ABOUT 24 MICRONS, AS DETERMINED BY SEDIMENTATION MEASUREMENT, AND CALENDERING SAID PARTICLES AT A RAISED NON-SINTERING TEMPERATURE BELOW 400* F. INTO A COMPACT DENSE UNSINTERED FILM BY PASSING SAID LAYER OF PARTICLES BETWEEN CALENDER ROLLS OPERATING AT THE SAME SURFACE SPEED WHILE MAINTAINING ONE CALENDER ROLL IN CONTACT WITH ONE SURFACE OF SAID FILM AT A TEMPERATURE AT LEAST ABOUT 100* F. ABOVE THE TEMPERATURE OF ANOTHER CALENDER ROLL IN CONTACT WITH THE OPPOSITE SURFACE OF SAID FILM.