Polytetrafluoroethylene granular powders

Claim 1

POLYTETRAFLUOROETHYLENE GRANULAR POWDER SUITABLE FOR FARBICATION BY LEAVING COMPRESSING AND SINTERING INTO NONPOROUS POLYTETRAFLUOROETHYLENE SHEETING LESS THAN 0.5 INCH THICK, SAID POWDER BEING ONE CONTAINING A SUBSTANTIAL PROPORTION OF FIBROUS POLYTETRAFLUOROETHYLENE PARTICLES AND HAVING AN AIR-PERMEABILITY SUB-SIEVE SIZE OF LESS THAN 5 MICRONS, A WET-SIEVE SIZE OF LESS THAN 50 MICRONS WITH LESS THAN 6 WEIGHT PERCENT RETENTION ON A STANDARD 230 MESH SIEVE, A RATIO OF WET-SIEVE SIZE TO AIR-PERMEABILITY SUB-SIEVE SIZE IN THE RANGE OF 5 TO 12, AND EXHIBITING ANISOTROPIC EXPANSION, UPON BEING VERTICALLY COMPRESSED INTO A 1/2 INCH CUBE AND SINTERED, SUCH THAT AS BETWEEN DIMENSIONS OF SAID CUBE 30 MINUTES AFTER COMPRESSING UNDER 2000 P.S.I. AND DIMENSIONS OF SAID CUBE AFTER THEREAFTER SINTERING AT 380*C. FOR 30 MINUTES AND COOLING TO ROOM TEMPERATURE, THE PROPORTIONAL INCREASE IN VERTICAL AXIAL DIMENSION IS 1.16 TO 1.28 TIMES THE PROPORTIONAL INCREASE IN THE SUM OF THE HORIZONTAL AXIAL DIMENSIONS.