| 摘要 |
PROBLEM TO BE SOLVED: To obtain a glass substrate high in cleanness and smoothness and suitable for high density recording by specifying the acid resistance of the glass substrate and the average surface roughness of the recording surface of the glass substrate. SOLUTION: At least one of the surfaces of the glass substrate is used as the recording surface, and the glass substrate has the acid resistance such that the etching rate is not more than 45 nm/min when it is brought into contact with 0.1 wt.% hydrofluoric acid at 50 deg.C and the average surface roughness Ra of the recording surface is less than 0.3 nm. The glass composition satisfying an etching rate condition in the case of 0.1 wt.% hydrofluoric acid is preferably comprised of, by molar percentage, 63 to 70% SiO2, 4 to 11% Al2O3, 5 to 11% Li2O, 6 to 14% Na2O, 0 to 2% K2O, 0 to 6% MgO, 1 to 9% CaO, 0 to 3% SrO, 0 to 2% BaO, 0 to 5% TiO2, and 0 to 2.5% ZrO, with the proviso that the difference of the amounts of SiO2 and Al2O3 (SiO2-Al2O3) is not less than 56.5% and the amount of RO (RO=MgO+CaO+SrO+BaO) is 2 to 15%. |
