| 摘要 |
PROBLEM TO BE SOLVED: To provide a substrate for optical discs which enables an increase of the numerical aperture and a shortening of wavelengths in optical heads. SOLUTION: The substrate comprises a hydrogenated styrene copolymer having a weight average molecular weight of >=60,000 g/mol which contains from 85 to 95 wt.% hydrogenated styrene polymer unit. The retardation (absolute value) at an incidence angle of 0 or 30 deg. from the normal direction of the substrate surface at a wavelength of 633 nm is <=10 nm in a single pass, and the thickness of the substrate is <=0.7 mm. |
