| 摘要 |
PURPOSE:To obtain a base plate of optical disk having a high CN ratio, by molding a resin by means of injection molding while an ultrasonic wave is being applied to the resin in a molding cavity. CONSTITUTION:An ultrasonic wave oscillator 2 is operated just after a resin is injected in a molding cavity 13 and is stopped when the resin substantially solidifies. As the resin, all the resins showing refractive index anisotropy can be used, but polycarbonate resin is effective because of the balance of its other characteristics. In general, an ultrasonic wave vibration is applied to a polymeric substance in its molten state, i.e. above its glass transition temp., sliding diffusion and segmental movement of the molecular chains and dispersion of the side chains are induced. By giving activation energies to be necessary for these molecular relaxations by means of the ultrasonic wave vibration and by relaxing the molecular orientation which has occurred when the resin is poured at an ultrahigh speed into a flat cavity by means of injection, the double refraction can be reduced and the CN ratio can be improved. |
