| 摘要 |
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 DEG C to 400 DEG C upon emerging from terminal die (17); and (b) passing molten extrudate (20), from die (17), between two counter-rotating rolls (23 and 26) each having an elastomeric polymer surface (35 and 38), 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. <IMAGE> |
