| 摘要 |
PROBLEM TO BE SOLVED: To obtain a polycarbonate copolymer substrate having excellent thermal stability and low double refraction by using two kinds of bivalent phenols in a specified proportion and incorporating a specified amt. of a phosphorus compd. SOLUTION: In this polycarbonate copolymer, at least 80 mol.% of the whole aromatic dihydroxy component consists of (a) 1,1-bis(4hydroxyphenyl)-3,3,5- trimethylcyclohexane and (b) 4,4'-(mphenylenediisopropylidene)diphenyl and/or 2,2-bis(3-methyl-4-hydroxyphenyl)propane, and the components (a) and (b) are included by 99:1 to 20:80 molar ratio. The optical disk substrate is produced by forming the copolymer and the disk substrate contains a phosphorus compd. by 1×10<-5> to 9×10<-5> pt.wt. calculated as phosphorus atoms to 100 pts.wt. of the substrate. The proportion of the component (a) to the component (b) is further preferably controlled to 80:20 to 30:70. |
