Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1999-07-09
2000-09-19
Group, Karl
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 79, 501 90, 351159, C03C 3068, C03C 3066
Patent
active
061211761
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
The present invention relates to glasses having a refractive index of more than 1.880, an Abbe number of more than or equal to 30.4, and a density of less than 4.1.
Such glasses are of great interest for ophthalmic applications, particularly in the case of large corrective-vision levels: the high refractive index allows limiting the thickness of the glasses. The moderate density and the relatively high Abbe number also contribute to the comfort of the wearer.
Moreover, it is advantageous to have glasses that are easy to manufacture and that have a low manufacturing cost. For that purpose, a low cost of raw materials and a low tendency toward devitrification are desired elements.
PRIOR ART
Glasses presenting optical properties and a similar density to those described above are already known, but they are not satisfactory insofar as the cost of manufacture and the resistance to devitrification is concerned.
Thus, European Patent No. B-570,687 describes glasses having the following composition, expressed in wt % based on the oxides:
______________________________________ SiO.sub.2 5-8
B.sub.2 O.sub.3 15-21
ZrO.sub.2 3-10
TiO.sub.2 7-17
Nb.sub.2 O.sub.5 20.5-26
with ZrO.sub.2 + Nb.sub.2 O.sub.5 29-45
La.sub.2 O.sub.3 19-32
Y.sub.2 O.sub.3 0-9
CaO 8-16
SrO 0-5
BaO 0-5
MgO 0-5
with CaO + SrO + BaO + MgO 8-16
ZnO 0-5
Li.sub.2 O 0-2
K.sub.2 O 0-2
with Li.sub.2 O + Na.sub.2 O + K.sub.2 O 0-2
______________________________________
These glasses have a refractive index of more than 1.88, an Abbe number of more than 29, a density of less than 4.1, and an integrated transmission from 380 to 800 nm of more than 79% (under a thickness of 10 mm).
However, they present two disadvantages: liquidus viscosity. The liquidus temperature is on the order of 1150.degree. C.; at this temperature, the viscosity is only a few poise. raw materials very high.
Other glasses whose composition presents a certain analogy with that of the glasses of the invention are known.
Thus Japanese Patent No. A-3-5340 (1991) describes glasses having a refractive index of 1.83-1.88, whose proportion is, in wt %:
______________________________________ SiO.sub.2 2-14
B.sub.2 O.sub.3 8-25
with SiO.sub.2 + B.sub.2 O.sub.3 22-29
CaO 13-25
MgO 0-10
with CaO + MgO 13-25
La.sub.2 O.sub.3 15-28
BaO + SrO + ZnO 0-12
with La.sub.2 O.sub.3 + BaO + SrO + ZnO 15-28
ZrO.sub.2 1-9
TiO.sub.2 6-15
Nb.sub.2 O.sub.5 6-20
with ZrO.sub.2 + TiO.sub.2 + Nb.sub.2 O.sub.5 24-38
K.sub.2 O + Na.sub.2 O + Li.sub.2 O 0-3
______________________________________
Although this document mentions glasses that can have a refractive index of at most 1.88, the highest refractive index of the glasses described in the example reaches only 1.8725, with most of the glasses specifically described having much lower indices. Moreover, the CaO content of these prior glasses is much higher than that of the glasses of the invention.
German Patent No. C-4,242,859 claims glasses with a high refractive index whose composition, defined very broadly, is close to the composition of the glasses of the invention, from which it differs notably by a lower ZrO.sub.2 (<8%) content and by the obligatory presence of fluorine. The five specific examples described differ from the glasses of the invention in other compositional differences affecting one or more constituents.
SUMMARY OF THE INVENTION
The invention concerns glasses having a refractive index of more than 1.880, an Abbe number of more than or equal to 30.4 and a density of less than 4.1, having the following chemical composition expressed in wt % based on the oxides:
______________________________________ SiO.sub.2 6-9
B.sub.2 O.sub.3 15-19
with SiO.sub.2 + B.sub.2 O.sub.3 <26
Nb.sub.2 O.sub.5 12 to <20.5
ZrO.sub.2 8-10
TiO.sub.2 7-11
La.sub.2 O.sub.3 23-32
with ZrO.sub.2 + TiO.sub.2 + La.sub.2 O.sub.3 .gtoreq.44
Y.sub.2 O.sub.3 0-5
WO.sub.3 0-5
CaO 8-&
REFERENCES:
patent: 4612295 (1986-09-01), Sagara
patent: 4732876 (1988-03-01), Nagamine et al.
patent: 5288669 (1994-02-01), Grateau et al.
Corning S.A.
Group Karl
Peterson Milton M.
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