PURPOSE: To obtain a film with a stable stretchability and a high Young's modulus by re-stretching a biaxially oriented film of a specific polyether-ester with a specific range of refractive index and density.
CONSTITUTION: A polyether-ester is needed to contain more than 80mol% of a formula structural unit. An unstretched film is made by sufficiently drying pellets of polyether-ester under reduced pressure and then by supplying it into a well-known melt-extruder. This unstretched film is biaxially stretched and heat-treated. This biaxially stretched and heat-treated film needs to have the values of birefringence and refractive index of thickness direction in the range of 0.02W0.05 and 1.53W1.56 respectively at the center of the film. Moreover, it needs to have the values of refractive index of longer direction and density in the range of 1.70W1.76 and 1.44W1.47g/cm3 at the edge of the film respectively.
ABE KOICHI
YOSHII TOSHIYA
