The generation of biaxial optical anisotropies in polyimide films by an uniaxial stretch method

Abstract

A new biaxial-retardation film prepared from the uniaxial-stretched polyimide (PI) film was developed for compensating the viewing angle of liquid-crystal displays. A new aliphatic PI showing high transparence and low glass-transition temperature was firstly prepared for the biaxial-retardation film purpose. Both retardations in x-y and x-z planes of PI films were highly increased after stretching them uniaxially at 260 degrees C. Good uniformity of birefringence in well-stretched PI films was observed visually with two crossed polarizers. The birefringence variations of nx-ny (difference of refractive indexes between x- and y-axes) and nx-nZ during the stretching process were highly affected by PI structure.