| 摘要 |
This invention is related to glasses particularly useful in the fabrication of multifocal lenses for ophthalmic applications. The inventive glasses exhibit a refractive index between 1.599-1.602, an Abbe number between 40.5-41.5, a density between 2.64-2.66 g/cm3, a transmission of visible radiation at 400 nm through a thickness of 10 mm greater than 83%, a softening point between 670.degree.-680.degree.C, a birefringence upon sealing, measured as described, between -150 and +150 nm/cm, and consist essentially, expressed in terms of weight percent on the oxide basis, of: SiO2 52-57 K2O 11.0-16.0 B2O3 2.5-7.0 CaO 2-3.5 Al2O3 0-1 ZrO2 1-1.5 Li2O 0.3-0.8 TiO2 15.0-16.2 Na2O 5.4-8.2 AS2O3 0.1-0.4 with the condition that M=69-72 where M=? ¢ 760x%Li2O+270x%Na2O+170x%K2O+185x%CaO+130x%TiO2!. |
