BIAXIALLY DRAWN POLYHEXAMETHYLENE ADIPAMIDE FILM AND PROCESS FOR PRODUCING SAME

摘要

Provided is a biaxially drawn film composed substantially of polyhexamethylene adipamide, which has a refractive index of at least 1.560 in both the longitudinal direction and the transverse direction and an ultraviolet absorbance E268 of not more than 0.4, as measured at a wavelength of 268 m.mu. on a film solution in formic acid. The film preferably exhibits a shrinkage factor of not more than 5% in both the longitudinal direction and the transverse direction, as measured after dipping in hot water at 135.degree.C for 10 minutes. The film is prepared by heat-treating a biaxially drawn polyhexamethylene adipamide film in an inert gas atmosphere at a temperature higher than the drawing temperature employed but lower than the melting point of the film.