Copolycarbonate optical films developed using birefringence dispersion control

A retardation film is a type of optical film that is widely used as a polarization transformation material to improve the image quality of flat panel displays (FPDs). One of the issues associated with retardation films has been the wide-banding of birefringence dispersion. A conventional optical design method that uses double-layered retardation films has been adopted to achieve wide-band properties. However, this conventional method has problems that have led to the demand for a single retardation film with wide-band birefringence properties. This situation motivated us to develop birefringence dispersion control (BDC) and to develop new polymers based on our novel molecular design. Wide-band characteristics are obtained using copolymers or miscible blends of polymers comprised of positive and negative anisotropic monomer units at specific volume fractions. The wide-band properties appear in a narrow range near the birefringence zero point, which is determined by the monomer volume fractions. The relationship between the orientation functions and birefringence dispersion is also clarified using theoretical studies, polarized IR and birefringence measurements. We have successfully industrialized a wide-band retardation film consisting of a newly developed copolycarbonate (co-PC) with a fluorene ring using the novel BDC theory. This film exhibits superior optical properties in FPDs. A retardation film consists of optical polymer to control polarized light by the oriented birefringence. One of the issues of the films is wide-banding of birefringence. We have researched a novel molecular design to control dispersion, and found that the wide-band properties appear in a narrow range near the birefringence zero point, which is determined by the volume fractions of the positive monomer units to the negative units. The wide-band retardation film has been industrialized using a novel co-PC with a fluorene ring based on the molecular design.