US 5,321,109 AGranted

Uniformly expanded PTFE film

AssigneeImpra, Inc.

InventorsCharles F. Bosse, Rajagopal R. Kowligi

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Abstract

A uniformly expanded PTFE film is provided by extruding a PTFE film and gripping the unexpanded film about its periphery with a number of symmetrically disposed gripping members each equidistant from the center of the film. The extruded PTFE film is heated to a temperature in the range of 200-300 degrees Centigrade before expanding the extruded PTFE film. The gripping members are simultaneously rotated through an arc away from the center of the film, as by pivotally securing each gripping member to the end of an associated expansion arm and rotating the end of each expansion arm away from the center of the film while maintaining the gripping members equidistant from the center of the film. The expansion arms are uniformly rotated by a geared shaft powered by a drive mechanism that extends through the wall of an oven for coupling to an external motor.

Claims1

Dependent claims

A PTFE film uniformly expanded in multiple directions, the PTFE film having a center, the PTFE film being produced by the process comprising in combination the steps of:

a. extruding a film of PTFE:
b. securing the periphery of the extruded PTFE film to a plurality of symmetrically-disposed film gripping members, each of said film gripping members being equidistant from the center of the PTFE film, the plurality of film gripping members exceeding four in number;
c. heating the extrude PTFE film to a temperature in the range of 200-300 degrees Centigrade before expanding the extruded PTFE film;
d. simultaneously rotating each of the plurality of film gripping members through an arc away from the center of the PTFE film to stretch and expand the film while maintaining the plurality of film gripping members equidistant from the center of the PTFE film;
and
e. maintaining the pulling force exerted by each film gripping member radial relative to the center of the PTFE film.

3 more elements

Dependencies are inferred from the claim text.