Birefringence Analysis of Injection-Molded Polycarbonate (Pc) Substrates

Abstract

To obtain a polycarbonate (PC) substrate with low optical anisotropy, birefringence and refractive index ellipsoids are analyzed for injection-molded PC substrates annealed under various conditions. The relationship between azimuth and incident angles and retardation shows that, for oblique rays from the fast axis direction, retardation increases directly with incident angle. However, for oblique rays from the slow axis direction, retardation decreases with increasing incident angle up to 15°and then increases. Photo-elastic experiments with PC films show that the fast axis direction has a low refractive index. These results indicate that the PC refractive index ellipsoid is pie-shaped. Optical anisotropy parallel to the disk surface associated with the annealing temperature (Ta) shows two different temperature dependences. In one case, retardation increases with Ta up to 100°C, and then decreases. In the other case, the opposite occurs. In both cases, if changes in the fast axis direction are considered, the results indicate that annealing causes relaxation of the compressive stress produced thermally below the Tg in the radial direction.