Method of producing thermoplastic polycarbonate films having...

Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Light polarizing article or holographic article

Reexamination Certificate

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C264S040100, C264S210200, C264S211120

Reexamination Certificate

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06913714

ABSTRACT:
A method of preparing a thermoplastic polycarbonate film having an optical retardation value of less than or equal to 20 nm, is described. The method includes: (a) forming a molten extrudate (20) of a thermoplastic polycarbonate polymer in an extruder (11) having a terminal die (17) through which the molten extrudate is passed, the molten extrudate having a temperature of 150° C. to 400° C. upon emerging from terminal die (17); and (b) passing molten extrudate (20), from die (17), between two counter-rotating rolls (23and26) each having an elastomeric polymer surface (35and38), the counter-rotating rolls having a roll speed ratio and a nip (41), the distance between the terminal die (17) and the nip (41) being a die-nip distance (47). The extrudate temperature, the roll speed ratio and the die-nip distance (47) are each selected such that a thermoplastic polycarbonate film (32) having an optical retardation value of less than or equal to 20 nm is formed.

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