| 摘要 |
PURPOSE:To obtain a glass composition having excellent chemical durability, providing lens of refractive index distribution type with a large angle of aper ture, comprising Li2O, Na2O, K2O, Al2O3, B2O3, TiO2, SiO2, ZrO2, GeO2, MgO, SnO2 and PbO having given mol%, respectively. CONSTITUTION:The glass composition has the following composition of 3-22mol% Li2O, 0-20mol% Na2O, 0-20mol% K2O, 3-20mol% Na2O+K2O, 0-20mol% Al2O3, 0-25mol% B2O3, 2-25mol% TiO2, 40-62mol%SiO2, 3-10mol% ZrO2, 0-20mol% GeO2, 0-20mol% MgO, 0-10mol% SnO2 and 0-15mol% PbO. The main characteristics of this inventions are that the glass composition contains 2-35mol% TiO2 as a component for raising refractive index of prepared glass and contains 3-10mol% ZrO3. Consequently, the composi tion has improved chemical durability and its refractive index distribution close to an ideal refractive index distribution near to the circumferential part.
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