E.i. Dupont De Nemours and Company

Charles Nelson Jolliffe

Albert W Forrest, Jr

David E Heyer

An improved process for simultaneous biaxial stretching of a thermoplastic polymer film having beaded edges in a tenter frame consisting of gripping the beaded edges of the film with tenter clips and increasing the temperature of the beaded edges to within the film orientation temperature range prior to or during simultaneous stretching, and in subsequent stretching or heat-setting steps, by focusing heat on the beaded edges of the film. Thermoplastic films, such as polyethylene terephthalate and polyethylene naphthalate, having a final thickness of from 0.2 to 350 microns after simultaneous stretching can be prepared.

Film bead heating for simultaneous stretching

A method is provided for the production of ultrathin films having a thickness of 2.5 microns or less, including film having a thickness as low as about 0.2 microns. Film of thermoplastic polymer, preferably polyester film, less than 25 microns in thickness and in thermal equilibrium with the surrounding air is simultaneously stretched at least twice and up to about five times its original dimensions in the machine and cross-machine directions under conditions such that thicker regions are maintained at an elevated temperature by radiant heating and at least a 0.1.degree. C. temperature differential is established between the thicker (hotter) regions and the thinner (cooler) regions of the film prior to stretching the film beyond its elastic limit. The ultrathin films produced according to this invention have acceptable uniform thickness necessary for commercial applications thus providing consistent electrical performance when used as the dielectric medium in miniature capacitors and uniform heat transfer characteristics suited for high resolution thermal transfer media or digital stencils.

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Circleville, OH, United States of America

Charles Nelson Jolliffe