GLASS COMPOSITION, ITS PRODUCTION, SUBSTRATE FOR INFORMATION RECORDING MEDIUM USING THE SAME, INFORMATION RECORDING MEDIUM AND INFORMATION RECORDING APPARATUS

摘要

PROBLEM TO BE SOLVED: To obtain a glass composition mass-producible by a continuous production method, readily providing high surface smoothness, having a high Young's modulus and low density and to further provide a substrate having a small flexure and resonance even in high-speed rotation, a recording medium capable of reducing a flying height and an information recording apparatus having an increased recording capacity and a shortened access time by using the glass composition. SOLUTION: This glass composition comprises 40-55 mol% silicon dioxide (SiO2), 0.5-6 mol% aluminum oxide (Al2O3), 2-20 mol% lithium oxide (Li2O), 0-10 mol% sodium monoxide (Na2O), 2-30 mol% R2O (R2O=Li2O+Na2O), 5-25 mol% magnesium oxide (MgO), 0-25 mol% calcium oxide (CaO), 0-10 mol% strontium oxide (SrO), 10-40 mol% RO (RO=MgO+CaO+SrO), 0-10 mol% titanium dioxide (TiO2) and 0-5 mol% zirconium oxide (ZrO2).