A method for manufacturing a substrate for optical disks, wherein a carrier with a distribution gradient of the double refraction is annealed.

摘要

PURPOSE:To impart long term stability and heat resistance by making birefringence after annealing about zero, by a method wherein a molding of a base is performed so as to form a birefringence distribution at a gredient whose birefriengence in the vicinity of an outer and inner circumferential parts of a doughnutlike recording part is specified by making use of polycarbonate as the quality of the material of the base. CONSTITUTION:Injection molding of a plastic base is performed so that a recording part possesses a birefringence distribution, In this instance, polycarbonate is used as the material of the plastic base. Then molding of the plastic base is performed so that the birefringence distribution provided with an ingredient is formed on a doughnutlike recording part in a manner that a value of the birefringenece is -10--30nm in the vicinity of an outer circumferential part and +10-+30nm in the vicinity of an inner circumferential part. Annealing is performed in succession. It is preferable that a heating temperature of the annealing is lower by 10-60 deg.C than the glass transition temperature of the plastic base and that the time is 1-6 hours. With this construction, the value of the birefringence is controlled to + or -10nm or lower after heat treatment, and the value does not vary for a long period of time.