Method for producing low birefringence plastic film

1 . An extrusion process, comprising:

feeding a thermoplastic polycarbonate resin to an extruder;

heating the resin in the extruder to a melt temperature that is above a glass transition temperature of the resin, thereby producing a melt of the thermoplastic polycarbonate resin;

extruding the melted resin downwardly through an extrusion nozzle orifice having a slot configuration;

passing the melted resin downwardly into a gap between two calendering rolls at least one of which has a highly polished surface, and wherein the calendering rolls are maintained at a roll temperature of less than the glass transition temperature; and

cooling the thermoplastic polycarbonate resin film to below its glass transition temperature as the thermoplastic polycarbonate resin film advances through the gap.

2 . An extrusion process, comprising:

extruding melted thermoplastic polycarbonate resin downwardly through an extrusion nozzle orifice, wherein the melted thermoplastic polycarbonate resin has a viscosity of less than or equal to 600 Pa.s;

passing the melted thermoplastic polycarbonate resin through a gap between two calendering rolls, wherein at least one of the calendering rolls has a polished surface, wherein the calendering rolls have a roll temperature of less than or equal to about 140° C.; and

cooling the melted thermoplastic polycarbonate resin to below its glass transition temperature to form a polycarbonate film;

wherein the polycarbonate film has a retardation of less than or equal to about 35 nm.

3 . The process of claim 2 , wherein the melt viscosity is about 100 Pa.s to about 275 Pa.s.

4 . An extrusion process, comprising:

feeding a thermoplastic polycarbonate resin to an extruder;

heating the resin to a temperature sufficient to attain a melt viscosity of less than or equal to about 300 Pa.s;

extruding the heated resin; and

passing the extruded resin through a gap between two solid metal calendering rolls to produce a film;

wherein the film has a birefringence of less than or equal to about 50 nm.

5 . The process of claim 4 , wherein the calendering rolls are maintained at a roll temperature of less than the glass transition temperature.

6 . The process of claim 5 , wherein the roll temperature is less than or equal to about 140° C.

7 . The process of claim 4 , wherein the viscosity is about 100 Pa.s to about 275 Pa.s.

8 . The process of claim 4 , wherein the resin is extruded at a melt temperature of about 275° C. to about 360° C.

9 . The process of claim 8 , further comprising extruding the resin at a rate of about 10 to about 100 feet per minute.

10 . The process of claim 4 , wherein the resin has a weight average molecular weight of less than or equal to about 30,000.

11 . The process of claim 4 , wherein the film has a thickness of about 100 μm to about 600 μm.