Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1998-02-02
1999-08-03
Group, Karl
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 56, 501 58, 501 59, 501 65, 501 67, 501 78, 501903, 501905, C03C 3068, C03C 3095, C03C 408
Patent
active
059325011
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to ophthalmic glasses with a refractive index of at least 1.58 which, in addition to having high transmittance in the visible range and a low intrinsic coloration, possess a strong, and even complete absorption in the ultraviolet spectrum, while being nonphotochromic.
For some years, great attention has been paid to the harmful effects of ultraviolet radiation (UV) on humans. Among the parts of the body that require an effective protection against the biological damages caused by solar radiation or UV radiation in general, the eye is often cited because of its relative fragility. This fragility is at the origin of the development of numerous colored glasses intended to filter solar radiation.
Moreover, it is well known that the effects of UV radiation are not limited to interaction with living matter, but can also result in the degradation of organic materials (paints, plastics, etc.) Similarly, the sun is not the only source capable of emitting UV radiation that can be at the origin of this degradation. There are several types of artificial sources, such as halogen or xenon lamps, which can emit a non-negligible amount of ultraviolet radiation.
Thus, it would be of certain interest to be able to have available a glass that is transparent in the visible range but offers good protection against ultraviolet radiation. Such glasses are of particular interest for lighting, bottling, protection against radiation, ophthalmic lens design, and other similar applications.
For ophthalmic applications, it is known that the photochromic glasses which include halide crystals, are activated by the absorption of UV radiation. This absorption clearly is reflected in a variation of the transmission of the visible spectrum by the glass, and a certain protection of the eyes offered because such glasses strongly absorb radiations with wavelengths of less than 320 nm and, less so, radiation between 320 and 400 nm. Although this radiation spectrum is less dangerous than that of the shorter wavelengths, it must be eliminated in some cases.
However, for other applications, no change in transmission must occur at the time of exposure to UV radiation or to the sun. Therefore, it is essential to be able to obtain a clear cutoff of UV radiation without the development of photochromism.
Moreover, the trend observed in the market of eyewear is the use of high-index materials. Indeed, surface-coated lenses with strong negative powers have thick edges if a conventional glass with an index of 1.523 is used. In comparison to the lenses elaborated in such glasses, the use of high-index glasses allows, for the same correction, an increase in the radius of curvature of the lens and consequently a reduction in the thickness.
Until now, glasses that combined the benefits of a high refractive index and a clear cutoff between ultraviolet radiation and the visible spectrum while remaining nonphotochromic and colorless were not known.
The object of the present invention is to provide essentially transparent nonphotochromic glasses, with a refractive index of at least 1.58, presenting an abrupt cutoff at approximately 400 nm with respect to ultraviolet radiation, characterized by the following composition, expressed in weight percentages based on oxides:
______________________________________ SiO.sub.2
30-52 ZnO 0-8
B.sub.2 O.sub.3
12-22 PbO 0-2
ZrO.sub.2
5-14 Y.sub.2 O.sub.3
0-15
Al.sub.2 O.sub.3
0-12 La.sub.2 O.sub.3
5-25
Li.sub.2 O
1.5-3.5 TiO.sub.2
0-2
Na.sub.2 O
0-6 HfO.sub.2
0-2
K.sub.2 O
2-9 Nb.sub.2 O.sub.5
0-2
MgO 0-5 Ta.sub.2 O.sub.5
0-2
CaO 0-5 MoO.sub.3
0-2
SrO 0-9 WO.sub.3
0-2
BaO 0-14 SnO 0-4
Sb.sub.2 O.sub.3
0-4 SnO.sub.2
0-4
As.sub.2 O.sub.3
0-4 CdO 0-1
CuO 0.15-1 F 0-2
Cl 0-3 Br 0-3
I 0-2
______________________________________
______________________________________ Li.sub.2 O + Na.sub.2 O + K.sub.2 O (X.sub.2 O)
7-14
MgO + CaO + SrO + BaO (XO)
12-20
ZrO.sub.2 + Al.sub.2 O.sub.3
<15
F + Cl + Br + I 0.2-4.0
TiO.sub.2 + PbO + Nb.sub.2 O.sub.5
.ltoreq.2
___
REFERENCES:
patent: 4438211 (1984-03-01), Mennemann et al.
patent: 4642297 (1987-02-01), Mennemann et al.
patent: 4839314 (1989-06-01), Boudot et al.
patent: 5023210 (1991-06-01), Krumwiede et al.
patent: 5145805 (1992-09-01), Tarumi et al.
patent: 5281562 (1994-01-01), Araujo et al.
Corning Incorporated
Group Karl
Nwaneri Angela N.
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