| 摘要 |
PROBLEM TO BE SOLVED: To perform recording and reproduction in the disk proximity type head of a floating head or the like satisfactorily by allowing an optical disk substrate for performing recording and reproduction, by specifying the distance between a recording surface and a recording and reproducing head to be constituted of a material, having the loss tangent of not smaller than a specific value for reducing the vibration of the substrate. SOLUTION: In order to make smaller the amplitude of vibration to be generated when the force of the vibration from the outside or the like is applied to an optical disk, a material which easily absorbs energy of distortion to be applied to the substrate by the vibration of the substrate is used. Then, a loss tangent tan δ at 25 deg.C at a frequency 100 Hz is preferably 0.02 or larger and more preferably 0.05 or larger. When this value is 0.02 or larger, the energy of the vibration can be sufficiently absorbed to make the vibrating amplitude of the substrate smaller. Here, the upper limit of the tan δ is preferably 1.5 or smaller and more preferably 0.8 or smaller. |
