| 摘要 |
PURPOSE:To prevent a substrate from being broken or peeled off under an environmental condition by constituting a titled medium so that an adhesive agent for sticking two pieces of disk-shaped substrates satisfies a specified expression. CONSTITUTION:Under coat layers 22a, 22b and recording layers 23a, 23b are provided on two pieces of disk-shaped substrates 21a, 21b, respectively, ring- shaped inside and outside spacers 25, 27 are placed between through adhesive agent layers 24a, 24b, 26a and 26b, and they are joined by placing the recording layers to the inside. A thickness (d) of the adhesive agent layer and a modulus of rigidity G are made to satisfy the expression. In this way, the larger the ratio d/G is, the smaller the shearing stress and the peeling stress applied to the adhesive agent become, and if it exceeds a range of this expression, a surface deflection is generated when a disk is rotated. Accordingly, when preserving and carrying the disk, the substrate is prevented from being broken or peeled off, a difference of a thermal expansion of the time when a temperature has changed, and a damage by an external impact can be prevented. |
