Glass compsns. for joining to photochromic glass - for use in mfr. of ophthalmic lenses

摘要

Glass compsns. as described in the parent patent, are for segments or buttons to be joined to photochromic or phototropic glasses for producing multifocal ophthalmic lenses, the glass compsns. having a refractive index of 1.58-1.71, a softening temp. of 630-675 degrees C a steam point of 450-500 degrees C and a thermal expansion coefft. of 45-60 x 10-7/degrees C. These compsns. comprises o-8% Al2O3, 3-7% B2O3, 30-60% PbO and 30-55% SiO2. The refractive index of the new compsns. can be up to 1.75 while the softening temp. remains below 660 degrees C. The compsns. claimed comprise 28-50% SiO2, 1-10% B2O3, 2-9% Al2O3, 0-5% TiO2, 0-6% ZrO2 and 0-2% total of one or more of Ta2O5, Nb2O5, Gd2O3, Y2O3, WO3 and Bi2O3. Compsns. can be modified by addn. of 0-6% La2O3, 0-10% BaO, 0-3% Li2O and/or Na2O, 0-3% TiO2, the sum of which is not >10%. Good fusion is obtd. with a borosilicate photochromic glass.