Ophthalmic glass of high refractive index
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United States of America Patent
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Aug 20, 1996
Grant Date -
N/A
app pub date -
Oct 21, 1994
filing date -
Oct 22, 1993
priority date (Note) -
Expired
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Abstract
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 0.3-5; .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.
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