| 摘要 |
PURPOSE:To obtain an optical disc base, very small in birefringence and provided with no aging, by a method wherein the base is molded under specified injection molding conditions and, thereafter, heat treatment is applied under specified conditions upon manufacturing the optical disc base made of polycarbonate. CONSTITUTION:In a first process, polycarbonate resin is molded by injection under the resin temperature of 300-400 deg.C and the mold temperature of 50-150 deg.C. In case the resin temperature is too high, the transparency of the resin is inferior, however, in case the resin temperature is too low, a molded form, whose optical strain is small, can not be obtained. In case the mold temperature is too high, deformation upon releasing from a mold is increased, however, when the same is too low, the molded form, whose optical strain is small, can not be obtained. Heat treatment is effected in a second process as described below. In this case, the heat treatment temperature is within the range of (T-90) deg.C and (T-5) deg.C and preferably it is within the range of (T-85) deg.C and (T-15) deg.C when the glass transition temperature of the resin, measured by a differential scanning calorimeter, is shown by T deg.C. In case the heat treatment temperature is too low, the aging of refringence can not be resolved. In case the same is too high, the configuration of a group or a pit is changed. |
