Patent ID: 9549829
Date: 2017-01-24
CPC Classifications: A61F,A61L,B29C,B29K,Y10T

Claim:
1. A method of processing PTFE, comprising: extruding a compounded PTFE resin with a lubricating agent through an extruder in a machine direction to form a PTFE ribbon extrudate, wherein the compounded PTFE resin comprises polytetrafluoroethylene or comprises polytetrafluoroethylene and a copolymer of polytetrafluoroethylene; calendering the PTFE ribbon extrudate in the machine direction to form a planar layer of PTFE having an upper surface and a longitudinal length in a machine direction of an extruder used to produce the layer of PTFE and having a width in a cross machine or transverse direction; selectively applying a stretching agent to the layer of PTFE in a predetermined pattern comprising a plurality of first lateral zones within the layer of PTFE being substantially saturated with the applied stretching agent and a plurality of second lateral zones within the layer of PTFE lacking a saturated level of the applied stretching agent; providing a tentering machine; stretching the layer of PTFE in the tentering machine in the transverse direction to the machine direction while the plurality of the first lateral zones of the layer of PTFE are fully saturated with the stretching agent throughout their thicknesses during stretching; and sintering the layer of PTFE; wherein the plurality of the first lateral zones have a shape selected from the group consisting of squares, rectangles, circles, ellipses and combinations thereof; and wherein, after stretching and sintering, the plurality of the first lateral zones of the PTFE layer have a Gurley Number of greater than about 1,500 seconds for 100 cc of air at a pressure of 12.4 cm of water, and the plurality of the second lateral zones of the PTFE layer a Gurley Number of less than about 15 seconds for 100 cc of air at a pressure of 12.4 cm of water.