Apparatus for stretching polymer films

摘要

An apparatus for expanding polymer films such as PTFE films includes gripping the unexpanded film about its periphery with a number of symmetrically disposed gripping members each equidistant from the center of the 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. Also disclosed is an expanded PTFE film made in accordance with such process.