Deutsche Spezialglas Ag

Schott Glass Technologies, Inc.

Reinhard Kassner

Werner Behr

Karl-Heinz Mader

Lee M Cook

The invention relates to a glass of high refractive index suitable for the close-vision part of multifocal, in particular phototropic multifocal, spectacle lenses. The glass has a composition (in % by weight, based on oxide) of: SiO.sub.2 28-40; B.sub.2 O.sub.3 0-8.5; Li.sub.2 O 0-1; Na.sub.2 O 0-2.5; K.sub.2 O 0-5; CaO 0-6; SrO 0-6; BaO 6-12; ZnO 9-16; PbO 32-40; TiO.sub.2 0.3-7; ZrO.sub.2 0.4-5; .SIGMA. Li.sub.2 O+Na.sub.2 O+K.sub.2 O 0-5, and a refractive index n.sub.e of 1.66-1.81, an expansion coefficient .alpha..sub.20-300 of 5.7-6.8.times.10.sup.-6 K.sup.-1, a softening point of 650.degree.-700.degree. C. and a glass transition temperature Tg of 520.degree.-560.degree. C.

Ophthalmic glass of high refractive index

The invention relates to a glass of high refractive index suitable for the close-vision part of multifocal, in particular phototropic multifocal, spectacle lenses. The glass has a composition (in % by weight, based on oxide) of:

A high-refractive index phototropic glass having a refractive index of 1.69 to more than 1.7, an Abbe coefficient of at least 35 and a density of at most 3.5 g/cm.sup.3, has a composition (in % by weight based on oxide) of: SiO.sub.2 15-33; B.sub.2 O.sub.3 12-22; .SIGMA. SiO.sub.2 +B.sub.2 O.sub.3 30-50; Li.sub.2 O 0.5-5.0; Na.sub.2 O 0-3; K.sub.2 O 0-11; .SIGMA. alkali oxides 4-12; BaO 0-23; SrO 0-23; .SIGMA. SrO+BaO 0-23; ZrO.sub.2 5-14; Nb.sub.2 O.sub.5 15-24; Ta.sub.2 O.sub.5 2-11. As the carrier of the phototropism, the glass also has 0.10 to 0.35 of Ag.sub.2 O; 0.15-0.65 of Cl; 0.15-0.45 of Br and 0.005-0.030 of CuO. The glass can also be doped with 1-3 ppm of gold or one or more platinum metals, especially palladium.

High-refractive index phototropic glass

A highly refractive, low-density phototropic glass in which the carriers of phototropy are precipitates containing silver, halogens and copper oxide, and which has a density equal to or less than 3.0 g/cm.sup.3, a refractive index equal to or greater than 1.60 and an Abbe number equal to or greater than 40, consisting essentially of, in % by weight on an oxide basis:

Highly refractive, low-density, phototropic glass

An ophthalmic glass particularly useful as a segment glass consists essentially of, in weight percent:

Highly prefractive, low dispersion optical glass suitable for multifocal

An optical quality glass suitable for use in ophthalmic lenses having a refractive index of at least 1.59, an Abbe number of at least 40.5, a density of no greater than 2.67 g/cm.sup.-3, and a coefficient of thermal expansion .alpha. of less than 90.times.10.sup.-7 per .degree.C. contains at least 90 mole % of SiO.sub.2, Li.sub.2 O, Na.sub.2 O, K.sub.2 O, CaO, and TiO.sub.2, and essentially does not contain Al.sub.2 O.sub.3, B.sub.2 O.sub.3, or oxides of elements having atomic weights above 90, such as Nb.sub.2 O.sub.5, La.sub.2 O.sub.3, or ZrO.sub.2.

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Alfeld, Germany

Reinhard Kassner