Production of iodine stainable polyester polarizer film

A process for preparing an iodine stainable polyester film which consists of:

• (a) extruding a moving molten web of polyester film;
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• (b) quenching said moving beg to solidify it in a substantially amorphous form;
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• (c) applying an anchor coating to at least a portion of the surface of said film wherein said anchor coating promotes adhesion of polyvinyl alcohol to polyester film;
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• (d) applying a coating of a dispersed aqueous composition of polyvinyl alcohol to at least a portion of the surface of said film;
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• (e) stretching the moving web in a direction transverse to the direction of motion while heating said web at a temperature of from about its glass transition temperature to about 160.degree. C.;
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• (f) crystallizing said moving web by heating it to a temperature in the range of 130.degree. C. to 240.degree. C. without stretching said web;
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• (g) cooling said web to substantially ambient atmospheric room temperature
• (h) subsequently passing said web through a staining bath containing iodine and one or more iodine salts;
• (i) subsequently passing said web through an aqueous stabilizing bath containing boric acid and borax, with the proviso that said polyvinyl alcohol be from 95 to 99 percent hydrolyzed and that the dry coating weight of said polyvinyl alcohol be from 1.0 to about 2.1 pound of coating per thousand square feet of film prior to stretching.