DE4025261C1 - Highly refractive optical glass for spectacle lens - contains oxide(s) of silicon, boron, aluminium, lithium, sodium, potassium, calcium, barium, lead, zirconium and rare earth metals - Google Patents

Abstract

Highly refractive, low dispersive optical glass has a refractive index ne of at least 1.79, an Abbe number Ve of at least 35, a density d of at most 4.5g. cm-3, a linear thermal coefft. of expansion alpha 20-300 of 7.7.10 power (-6) k-1, to 8.7.10 power (-6). K-1 and a compsn. in wt. % based on oxide, of 4-13.9 Si02; 7.26 B203; 0-4 Al203; 0-2 Li20; 0-2 Na20; 0-4 K20; 0.1-4 sigma R20; 1-12 CaO; 0-9 BaO; 5-15 PbO; 2-10 Zr02; 15-40 La203; 0-3 Bi203; 0.1-3 Y203; 3-7.9 Nb205; 0-15 Ta205; and 0-0.5 sigma As203+Sb203. USE - Glass is useful as spectacle glass for unifocal- and polyfocal-correction spectacles.

Description

The invention relates to a high refractive low dispersive optical Glass.

High refractive low dispersive optical glasses are used in particular for Correction of refractive errors used as a spectacle lens. For strong Apertures occur, however, still relatively large center thicknesses (for plus glasses) or edge thicknesses (for minus glasses). One is therefore anxious to reach as high refractive indices, but at the same time the highest possible score is sought. Especially bad sighted need glasses with high Abbezahl, as the disturbing color fringes with higher diopters. These color fringes can only by higher Abbezahlen be mitigated.

Such a glass is z. B. from DE-PS 32 01 344 known. This glass in the system

SiO₂-B₂O₃-alkali-alkaline earth-La₂O₃-ZrO₂-TiO₂-Nb₂O₅

has refractive powers of 1.79-1.82 and Abbe 32 and is suitable for both spectacles and remote parts.

The object of the invention is a high-refractive low to find dispersive optical glass, which continues from its Abbe number forth is improved and that is different from his melting behavior and his coefficient of thermal expansion forth not only as a unifocal - but in particular can also be used as Mehrfokalkorrekturglas.

This object is achieved by the glass described in claim 1 solved.  

The glass has a refractive index n _e of at least 1.79, an Abbe number ν _e of at least 35, a density of at most 4.5 g · cm ^-3 and a linear thermal expansion coefficient in the temperature range of 20-300 ° C (α _{20 -300} ) of 7.7 × 10 ^-6 × K ^-1 to 8.7 × 10 ^-6 × K ^-1 and has an oxide-based composition by weight

SiO₂ 4 to 13.9 B₂O₃ 7-26 Al₂O₃ 0-4 Li₂O 0-2 Na₂O 0-2 K₂O 0-4 ΣR₂O 0.1-4 CaO 1-12 BaO 0-9 PbO 5-15 ZrO₂ 2-10 La₂O₃ 15-40 Bi₂O₃ 0-3 Y₂O₃ 0.1-3 Nb₂O₅ 3 to 7.9 Ta₂O₅ 0-15 As₂O₃ + Sb₂O₃ 0-0.5

A glass with the further improved Abbe number ν _e of at least 38 and a linear thermal expansion coefficient α in the range of 20-300 ° C (α _20-300 ) of 8.0 · 10 ^-6 · K ^-1 to 8.4 · 10 ^-6 · K ^-1 has a composition in wt .-% based on oxide of SiO₂ 9-12; B₂O₃ 14-18; Na₂O 0.1-2; CaO 8-12; PbO 7-12; ZrO 4-7; La₂O₃ 30-35; Y₂O₃ 0.1-3; Nb₂O₅ 4-7.9; Ta₂O₅ 1-10.

A glass with this composition and this coefficient of expansion is especially suitable for use as Nahteil a a Mehrfokalkor rekturglas.

SiO, B₂O₃ and Al₂O₃ serve as glass formers. In this case, SiO₂ comes in quantities from 4 to 13.9 wt .-%, preferably in amounts of 9-12 wt .-% for use. B₂O₃ contains the glass in proportions of 7-26 wt .-%, with proportions of 14-18 wt .-% to be favoured. The glass may further up to 4 wt .-% Al₂O₃ ent  hold. Preferably, however, a Al₂O₃-free glass is used, since Al₂O₃ under very unfavorable conditions when merging with another Glass can promote devitrification tendencies. A small proportion of 0.1-4 wt .-% of alkali oxides (R₂O) promotes the easy melting of the Mince. On the addition of lithium oxide, however, in the preferred dispensed with, since lithium oxide can promote devitrification. In a preferred embodiment comes as the only alkali oxide Na₂O in quantities between 0.1 and 2 wt .-% for use.

In amounts of 1-12 wt .-% calcium oxide raises the refractive index and provides for a low density. Preference is given to a CaO content of 8-12% by weight. barium oxide can be present in amounts of up to 9 wt .-%, but is in the Generally, the acid resistance of the glass decreases and therefore becomes preferably omitted. The proportion of at least 5 wt .-% of lead oxide in The glass ensures a high refractive index, improves the hydrolytic Resistance of the glass and has a significant influence on the Viskosi ty. However, a proportion of 15 wt .-%, in particular of 12 wt .-% should not be exceeded. Zirconium dioxide in proportions of 2-10% by weight, preferably 4-7 wt .-%, the refractive index increases with little influence on the Dispersion and promotes chemical resistance. The relative high proportion of 15-40 wt .-%, preferably from 30-35 wt .-% of La₂O₃ required to achieve the desired high refractive index. Niobium oxide is in an amount of 3-7.9% by weight, preferably 4-7.9% by weight in the glass, Tantalum oxide in an amount of 0-15 wt .-%, in particular 1-10 wt .-% and yttria in an amount of 0.1-3 wt%. These oxides increase the Refractive index and contribute significantly to the reduction of possibly before present devitrification tendency, where tantalum and yttrium oxide the Dispersion of the glass affect only relatively small.

The glasses according to the invention are very particularly suitable for the production of eyeglass lenses because of their high refractive indexes and Its low dispersion gives a light, cosmetically pleasing correction glasses, which are also largely free of color in larger formats seams are. Especially suitable are the glasses as melted  Near parts in multi-focus spectacle lenses, because of their low dispersion also have only a corresponding small chromatic aberration.

Examples

The glasses exemplified in the table were melted from conventional batch components at 1250 ° C in platinum crucible, two hours at 1400 ° C purified to a casting temperature of about 1200 ° C cooled with stirring and poured into preheated molds at this temperature. The castings were in a chamber furnace at a rate of 40 ° C / hr. cooled and then the physical data such as refractive indes (n _e ), Abbezahl (ν _e ), density (d) (g · cm ^-3 ), the thermal expansion coefficient α in the range of 20-300 ° C, and the transformation temperature Tg T in ° C determined.

Table 1

Claims (4)

1. High-refractive, low dispersive optical glass characterized by
a refractive index n _e of at least 1.79
an Abbe number ν _e of at least 35
a density d of at most 4.5 g · cm ^-3
a linear thermal expansion coefficient α _20-300 of 7.7 × 10 ^-6 × K ^-1 to 8.7 × 10 ^-6 × K ^-1
and an oxide-based weight percent composition of SiO₂ 4 to 13.9 B₂O₃ 7-26 Al₂O₃ 0-4 Li₂O 0-2 Na₂O 0-2 K₂O 0-4 ΣR₂O 0.1-4 CaO 1-12 BaO 0-9 PbO 5-15 ZrO₂ 2-10 La₂O₃ 15-40 Bi₂O₃ 0-3 Y₂O₃ 0.1-3 Nb₂O₅ 3 to 7.9 Ta₂O₅ 0-15 ΣAs₂O₃ + Sb₂O₃ 0-0.5 2. Gas according to claim 1, characterized by
a refractive index n _e of at least 1.79
an Abbe number ν _e of at least 38
a density d of at most 4.5 g · cm ^-3
a linear thermal expansion coefficient α _20-300 of 8.0 × 10 ^-6 × K ^-1 -8.4 × 10 ^-6 × K ^-1
and an oxide-based weight percent composition of SiO₂ 9-12; B₂O₃ 14-18; Na₂O 0.1-2; CaO 8-12; PbO 7-12; ZrO₂ 4-7; La₂O₃ 30-35; Y2O₃ 0.1-3; Nb₂O₅ 4-7.9; Ta₂O₅ 1-10. 3. Glass according to claim 1 or 2, characterized by
a content of Ta₂O₅ of 5-10 wt .-%. 4. Use of a glass according to at least one of claims 1 to 3 as spectacle lens for unifocal and multi-focal correction spectacles.