Optical recording medium and substrate for use therein

摘要

An optical recording medium for recording and reproducing information by making use of a change in the physical properties of a recording layer caused by exposure to light. A substrate for the optical recording medium is made from a hydrogenated styrene polymer having a nuclear hydrogenated styrene polymer unit content of 80 wt% or more and has a glass transition temperature of 110 DEG C or more, a light transmission at 400 nm of 88 % or more, and a retardation absolute value at 0 DEG and 30 DEG from a direction normal to the substrate plane of 30 nm or less. This optical recording medium is suitable for high-density optical recording which makes it possible to increase the numerical aperture and reduce the wavelength of an optical head.