| 摘要 |
PCT No. PCT/US97/04984 Sec. 371 Date Sep. 22, 1998 Sec. 102(e) Date Sep. 22, 1998 PCT Filed Mar. 25, 1997 PCT Pub. No. WO97/36834 PCT Pub. Date Oct. 9, 1997The invention concerns glasses characterized by the fact that they have a refractive index higher than 1.740; a dilatation coefficient alpha , between 25 and 300 DEG C., between 65 and 70x10-7/ DEG C.; and a Littleton point not exceeding 635 DEG C. but higher than 600 DEG C.; they have the following composition, expressed in weight percent of oxides: - SiO2 23-32.0 - Al2O3 1.5-5.0 - B2O3 5-9.0 - PbO 43-54.0 - Li2O 0-0.5 - Na2O 0-1.0 - K2O 0-1.0 - with Li2O + Na2O + K2O <1.0 - BaO + SrO 4-9.0 - TiO2 0-4.0 - ZrO2 0-2.0 - La2O3 0-3.0 - Nb2O5 0-3.0 - As2O3 0-0.3 - Sb2O3 0-0.4 - with ZrO2 + La2O3 + Nb2O5 1.5-4.0 - Use for the production of segments to be used in the manufacture of multifocal lenses, particularly photochromic.
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