Cellulose ester compositions having low birefringence and films made therefrom comprising a plasticizer

Abstract

The present inventions relate to cellulose esters having low hydroxyl content for use in optical applications, such as liquid crystal display (LCD) films. Films with low hydroxyl levels and a given ratio of non-acetyl ester to hydroxyl level have low intrinsic birefringence. These films can be cast, molded, or otherwise oriented without an appreciable birefringence or optical distortion (i.e. retardation). These films are useful in polarizer, protective, and compensator films and in molded optical parts, such as lenses. The resins of the present inventions can also be made to have '+C plate' behavior either by melt or solvent based processing, which is uncharacteristic of cellulose esters. Such +C behavior allows films having unique compensatory behavior. Other embodiments of the invention relate to methods of melt casting films while minimizing birefringence. Another embodiment of the invention is directed to films made from the cellulose esters described herein further comprising a plasticizer.