| 摘要 |
Extruded, smooth finished solid sheet or film, which may have a thickness < 1 mm, comprised of a thermoplastic plastic (such as polycarbonate) with a glass transition temperature > 50.degree.C, which under conditions of orientation displays optical birefringence, may be manufactured into a flat strip with smooth finished surfaces, to yield a strip which has characteristics as follows: -- optical birefringence path difference less than or equal to 54 nm (single pass); -- low surface roughness; -- low variation in thickness; by extrusion of the plastic in a thermoplastic state, through a slot nozzle; wherein during or after the smoothing of the two surfaces one of the surfaces of the strip is cooled to below the glass transition temperature, while the other surface and the predominant part of the interior region of the strip remain in the thermoplastic state and the strip is cooled to below the glass transition temperature, under conditions which minimize the deforming forces on the surfaces of the extruded strip. |
