Glass material for a substrate, glass substrate, and information recording medium employing the same

摘要

A glass material for a substrate, or a glass substrate, consists essentially of the following glass ingredients: from 45 to 70 wt % of SiO₂, from 1 to 10 wt % of Al₂O₃, from 0.5 to 8 wt % of B₂O₃, from 7 to 20 wt % of Li₂O+Na₂O+K₂O, from 0.1 to 10 wt % of MgO, from 0.1 to 10 wt % of CaO, from 1 to 15 wt % of MgO+CaO, from 0.5 to 10 wt % of TiO₂, from 0.5 to 10 wt % of ZrO₂, from 0 to 5 wt % of ZnO, and from 0 to 8 wt % of La₂O₃. The glass material, or the glass substrate, has uniform composition between at the surface and in the interior and has an amorphous structure. With this design, it is possible to obtain high mechanical strength without strengthening treatment, a linear thermal expansion coefficient close to motor components, and excellent chemical durability.