PREPARING HIGH-STRENGTH POLYETHER-ESTER FILM

摘要

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 0.02-0.05 and 1.53-1.56 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 1.70-1.76 and 1.44-1.47g/cm<3> at the edge of the film respectively.