| 摘要 |
PURPOSE:To obtain an optical disc substrate with properties such that the change of a birefringence caused by the heat given during drying or metal thin film adhering in following process may never happen and the birefringence at the time when it is finished is small, furthermore, the distribution in its radial direction is uniform, by anealing the substrate having a distribution of the birefringence of specified pattern in its radial direction. CONSTITUTION:A substrate having latently a circumferential tensile stress which becomes strong as it goes to the inner peripheral surface of the substrate is formed through a formation of a substrate having a distribution of birefringence in specified pattern in its radial direction in order that the birefringence is largest in the inner peripheral portion of the substrate and it becomes small an it goes to the outer peripheral portion. Following this, the substrate is given with as anealing and it is changed in its shape through the heating contraction in the radial direction. The circumferential tensile stress moving towards to the inner peripheral portion of the substrate is offset with the circumferentially directional compression stress produced by the heating contraction moving towards the inner peripheral portion of the substrate. As a result, any stress resides no longer in the region of the inner peripheral portion and the birefringence in the vicinity of the inner peripheral portion becomes considerably small, so that the birefringence is very small ranging over the whole inner surface of the substrate surface and the distribution in the radial direction becomes uniform. |
