POLYCARBONATE FORMING MATERIAL FOR OPTICAL DISK SUBSTRATE

摘要

PROBLEM TO BE SOLVED: To decrease bubble defects produced in a transparent substrate by using a molding material consisting of polycarbonate pellets having a specified range of viscosity average mol.wt. and controlling the content of pellets of a size which pass through a sieve of a specified mesh size and which does not pass through a sieve of another specified mesh size to a specified value or smaller in the total weight of pellets. SOLUTION: Since little optical distortion is required for a polycarbonate molding material for an optical disk substrate, the viscosity average mol.wt. of the polycarbonate is required to the range from 10,000 to 20,000. The content of pellets having 0.86 to 1.68 mm size (which passes through a sieve of 1.68 mm mesh size and does not pass through a sieve of 0.86 mm mesh size) is preferably <=20 ppm of the total weight of pellets. The polycarbonate produced from 2,2-bis(4-hydroxyphenyl)propane(bisphenol A) or the like is used.