| 摘要 |
PROBLEM TO BE SOLVED: To provide a substrate for an optical recording medium having simple constitution, wherein the change of the warpage of the substrate by the change of environment is suppressed. SOLUTION: The optical recording medium provided with a substrate consisting of thermoplastic resin, provided with embossed pits or guide grooves and having 0.3-1.2 mm thickness, a reflection layer provided thereon and a transparent protective layer provided thereon and having 3-200 μm thickness and reproducing recorded information based on the change of the light intensity of the reflected light of the irradiation light beam from the transparent protective layer side, is characterized in that the resin used for the substrate has 15×10<-6> (1/hr) water absorption velocity defined by formula (1). water absorption velocity (1/hr) = saturated water absorption (wt.%)/[time until saturation (hr)×100]...(1). |
