DE19828992C1 - Lead-free optical glass of barium light flint glass, barium crown glass, crown glass, crown flint glass or boron crown glass type - Google Patents

Abstract

A lead-free optical glass having specified contents of silicon, boron, barium, alkali metal and other oxides is new. A lead-free optical glass having a refractive index (nd) of 1.50-1.56 and an Abbe number (vd) of 50-64 has the composition (by wt.) 62-75% SiO2, 5-9.5% B2O3, 4.5-21% BaO, 0 to less than 14% ZnO, 0-0.5% CaO, 1-7% TiO2, 2-10% Na2O, 4.5-8% K2O, 0-1% ZrO2, 0-1% Nb2O5, 0-1% Ta2O5, 0-0.5% F<-> and usual amounts of refiners. The sum of ZnO + CaO is \-0.05% and the sum of BaO + ZnO + CaO is <= 25%.

Description

The invention relates to lead-free optical glasses which have refractive indices n _d between 1.50 and 1.56 and removal numbers ν _d between 50 and 64. These glasses belong to the optical glass types: Barium flint glasses (BaLF), Barium crown glasses (BaK), Crown glasses (K), Crown flint glasses (KF), Boron crown glasses (BK).

Since the glass components PbO and As ₂ O _{3 have been} discussed in public as environmentally harmful in recent years, there is also a need for PbO-free and preferably As ₂ O ₃ -free glasses among manufacturers of optical devices with the respective optical properties.

Also for the production of light glass parts, i.e. glasses with a low density, it is desirable to do without PbO.

By simply replacing the lead oxide with one or more stocks Parts succeed in reproducing the desired and influenced by PbO optical and glass properties usually not. Instead are new developments or far-reaching changes in the glass together setting necessary.

The patent literature already contains some documents in which lead free glasses with optical values from the range mentioned become. However, these glasses have various disadvantages.

German patent DE 973 350 describes glasses with a refractive index that varies within a wide range and a relatively high dispersion in relation to the refractive index. These glasses contain only up to 5% by weight of alkaline earth oxides, furthermore SiO ₂ and / or B ₂ O ₃ and F up to 30% alkali oxides and at least one component from the group Al ₂ O ₃ , TiO ₂ , Sb ₂ O ₃ , As ₂ O ₃ , PbO, the sum of these five oxides and the alkali metal oxides being between 35 and 69.85% by weight. A disadvantage of these glasses, in addition to the possible presence of PbO and As ₂ O ₃ in amounts of up to 55 or up to 5% by weight, is that the high refractive index is achieved by using expensive components or components which lead to a yellow tinge. Another disadvantage is the sometimes very high content of alkali oxides, which leads to poor chemical resistance of the glasses.

From DE 26 21 741 glasses from the SiO ₂ -R ₂ O-ZnO-TiO ₂ system are known, which due to their content of color components can be used as glasses for partial absorption edge filters.

From JP 60-54249 B2 optical glasses are known, the 10-20 wt .-% CaO and contain no BaO. CaO is required here in order to achieve high payoffs pass. However, CaO has the disadvantage, especially compared to BaO, that it does not raise the refractive index so much.

GBO-free optical glasses are also known from GB 804,451 and GB 812,576. Their refractive indices n _d of at least 1.56 or 1.54 can only be achieved by using relatively expensive, high-melting or yellow-tinged components. The glasses of the first-mentioned document contain up to 20% by weight of TiO ₂ . The relatively low-SiO ₂ glasses of the last-mentioned document contain up to 20% by weight of ZrO ₂ and up to 9% by weight of TiO ₂ , the sum of TiO ₂ and ZrO _{2 being} up to 20% by weight.

On the other hand, JP 8-34633 A discloses SnO ₂ -containing glasses which contain only small amounts of TiO ₂ . TiO ₂ serves as protection against solarization and has no significant influence on the non-optical properties. These glasses will not have good chemical resistance.

DE 196 50 692 A1 describes lead-free crown glasses which contain both TiO ₂ and BaO only as optional components with a maximum of <1% by weight or a maximum of 3% by weight.

DE 196 09 735 A1 describes lead-free crown flint glasses in which ZnO, CaO and BaO are only optional components. B ₂ O ₃ is also not mandatory and must remain limited to less than 5% by weight.

The glasses of JP 52-45616 A also contain high proportions of the relatively expensive and high-melting component ZrO ₂ (2-20% by weight), as a result of which the crystallization stability of these glasses is reduced. The same applies to the glasses of US 2,523,265 containing 2-15% by weight of ZrO ₂ ; you need this component to improve the chemical resistance since they contain only 33 to 55% by weight of SiO ₂ .

Accordingly, the chemical resistance of the glasses from US 5,523,265 (45-60% by weight SiO ₂ ) and from JP 62-13293 B2 (23-61% by weight) will not be high.

Lead-free optical barium crown glasses and light barium flint glasses and also barium flint glasses with at most 60% by weight SiO _{2 are also} described in older, not previously published German applications by the applicant.

DE 198 27 568.4 names glasses with 45-60% by weight SiO ₂ . Their good chemical resistance is guaranteed by the presence of ZrO ₂ and TiO ₂ .

DE 197 38 428 C1 presents glasses with 40-60% by weight SiO ₂ and 0.5-3.5% by weight Al ₂ O ₃ . The latter component serves to improve acid resistance.

It is an object of the invention to provide lead-free optical glasses with a refractive index n _d between 1.50 and 1.56 and an Abbe number ν _d between 50 and 64, which have good melting and processing properties and good chemical resistance and good crystallization stability exhibit.

This object is achieved by glasses described in claim 1.

The glasses contain 62 to 75% by weight of SiO ₂ . With higher proportions the meltability would deteriorate, with lower proportions the acid resistance would be reduced. In addition, a high SiO ₂ content enables a low refractive index. An SiO ₂ content of more than 63% by weight is preferred.

To improve not only the acid resistance, but overall the chemical resistance, the glasses contain 1 to 7% by weight of TiO ₂ , preferably at least 4% by weight. TiO ₂ increases the refractive index and reduces the Abbe number.

To further improve the chemical resistance and to vary the refractive index and Abbe number, the glasses can each contain up to 1% by weight of ZrO ₂ , Nb ₂ O ₅ and Ta ₂ O ₅ . However, since Nb ₂ O ₅ and Ta ₂ O ₅ are relatively expensive components, these two components are preferably dispensed with.

The glasses contain 2 to 10% by weight of Na ₂ O (preferably 3.5 to 9% by weight) and 4.5 to 8% by weight of K ₂ O. Na ₂ O and K ₂ O serve to improve the Meltability. At higher contents, the thermal expansion coefficient, the transformation temperature and the acid resistance are adversely affected. At lower contents, economical production is difficult due to high melting temperatures.

The glasses also contain B ₂ O ₃ , between 5 and 9.5% by weight. With this component, the meltability is improved without there being any negative effects on the expansion coefficient, that is to say its increase. However, if the proportions of B ₂ O _{3 are} too large, the chemical resistance, in particular the alkali resistance, will deteriorate. In a preferred embodiment, the B ₂ O ₃ content is at least 8% by weight.

The glasses contain 4.5 to 21% by weight of BaO, around the specified range of paying off. With a higher salary, the Devitrification tendency increase. Especially for glasses with low Abbe paying or for low density glasses can also limit the BaO content may be preferred to at most 7% by weight.

To stabilize against crystallization, the glasses contain at least 0.05 % By weight of ZnO and / or CaO. The CaO content is between 0 and 0.5% by weight, while the ZnO content is between 0 and less than 14 % By weight; especially if a low density is desired it is a maximum of 2% by weight. In these quantities, ZnO enables Increase the crushing value and stay in the middle of paying off.

The sum of BaO, ZnO and CaO is at most 25% by weight, otherwise Refractive index and Abbe number would be too high. In addition, the chemical Resistance deteriorate. The sum mentioned is preferably me at most 23.5% by weight.  

The glasses can contain up to 0.5% by weight of F ^- . This is particularly preferred for achieving special refractive indices in the field of crown glasses and boron crown glasses. F ^- is added for example as KF or KHF ₂ . As is generally known, due to the high evaporation tendency of F-containing compounds, a certain excess of F ^- , based on the desired content, must usually be added.

To improve the glass quality, the batch can be used to refine the Glases one or more refining agents known per se in the usual menus gene can be added. So the glass has a particularly good inner glass quality with regard to freedom from bubbles and streaks.

Is not As ₂ O ₃ as refining agent, but instead z. B. Sb ₂ O ₃ , preferably up to 0.5 wt .-%, which is possible without losses in terms of glass quality, the lead-free glasses according to the invention are additionally arsenic-free.

In a preferred embodiment, the sum of Sb ₂ O ₃ and F ^- , which also has a refining function, is between 0.05 and 0.8% by weight. In this way an excellent inner glass quality is achieved.

Within the composition range according to the invention, there is a particularly preferred composition range of glasses with refractive indices n _d between 1.53 and 1.56 and payoff numbers ν _d between 50 and 55. It is (in% by weight on an oxide basis): SiO ₂ 62- 65; B ₂ O ₃ 8-9.5; BaO 4.5-7; ZnO 0-2; CaO 0-0.5 with ZnO + CaO ≧ 0.05; TiO ₂ 4-7; Na ₂ O 6.5-9.5; K ₂ O 6-8; ZrO ₂ 0-1; F ^- 0-0.5.

Even in the manufacture of glasses in this preferred range, if desired, customary refining agents in usual amounts or the above ge named preferred variants can be used.

The glasses according to the invention have a negative anomalous partial dispersion on in the blue region of the spectrum.  

In order to explain:

The partial dispersibility, the so-called relative partial dispersion, in the blue part of the spectrum is shown by the expression

reproduced.

The "normal line" by definition obeys in the blue area of the spectrum of the equation

P _{g, F} = 0.6438 - 0.001682. ν _d .

Glasses whose partial dispersion lies on this straight line are called "Normal glasses" called.

In the case of glasses which have a behavior of the dispersion which deviates from the "normal glasses", the ordinal difference Δ P _{g, F} by which the relevant P _{g, F} - ν _d point is shifted from the "normal line" is given:

A rough classification of these glasses with anomalous partial dispersion into two groups is common, depending on whether P _{g, F} "above" (positive partial dispersion: Δ P _{g, F} = pos.) Or "below" (negative partial dispersion: Δ P _{g, F} = neg.) of the "normal straight line".

Glasses with abnormal partial dispersions are important for the correction of Residual color defects, the so-called secondary spectrum.

Examples:

There were five examples of glasses according to the invention made from conventional raw materials melted.

Table 2 shows the respective composition (in% by weight on an oxide basis), the refractive index n _d , the Abbe number ν _d , the partial dispersion in the blue region of the spectrum P _{g, F} and the anomaly of this partial dispersion Δ P _{g, F} , the Density ρ [g / cm ³ ], the thermal expansion coefficient α _20/300 [10 ^-6 / K] and the _{transformation temperature} T _g [° C] of the glasses are listed.

The glasses according to the invention were produced as follows: the raw substances for the oxides, preferably carbonates and nitrates, were weighed out. The refining agent (s) was added and then it was good mixed. The glass batch was continuously at approx. 1380-1400 ° C Melted animal melting unit, then refined and good homo embarrassed. The casting temperature was 1270-1290 ° C.

Table 1 shows a melting example.

Table 1

Melting example for 100 kg calculated glass

The properties of the glass thus obtained are shown in Table 2, Example 1 given.  

Table 2

Glass compositions (in% by weight on an oxide basis) and essential properties:

Further properties were determined for glass No. 5: its acid resistance according to ISO 8424 (SR) is 1.0; its alkali resistance according to ISO draft 10629 (AR) is 2.0, and its spectral degree of transmission at wavelength λ = 400 nm and a sample thickness d = 25 mm τ _{i 400 nm / 25 mm} is 0.955.

The glass composition area according to the invention offers a further group of optical glasses of the glass types BaLF, BaK, KF, K and BK with the optical data mentioned, which are lead-free and, in a preferred embodiment, also As ₂ O ₃ -free. The lead-free nature of the glasses is not only advantageous due to the environmental protection concept mentioned, but also has a positive effect on their density and their transformation temperature.

The glasses have the following advantages: They have a high chemical resistance, especially an acid resistance of SR = 2.3 or better and an alkali resistance of AR = 3.3 or better. The high chemical resistance of the glasses is essential for further processing such as grinding and polishing. The glasses have high crystallization stability. As a result, the manufacture of glasses in larger melting units, eg. B. in an opti's tub. A measure of a crystallization stability that is sufficient for such a production is the viscosity at the upper devitrification limit: it should be ≧ 1000 dPas for continuous production. This is achieved with the glasses according to the invention. The glasses are easy to melt and easy to process. With at least 550 ° C, they have relatively high transformation temperatures Tg. Their density ρ is very low at a maximum of 2.9 g / cm ³ . The transmission of the glasses in the visible range of the spectrum is high. The glasses show a negative partial dispersion in the blue region of the spectrum.

Claims (7)

1. Lead-free optical glasses with a refractive index n _d between 1.50 and 1.56 and an Abbe number ν _d between 50 and 64, characterized by the following composition (in% by weight on an oxide basis)
SiO ₂ 62-75 B ₂ O ₃ 5-9.5 BaO 4.5-21 ZnO 0 - <14 CaO 0-0.5 with ZnO + CaO ≧ 0.05 with BaO + ZnO + CaO ≦ 25 TiO ₂ 1-7 Na ₂ O 2-10 K ₂ O 4.5-8 ZrO ₂ 0-1 Nb ₂ O ₅ 0-1 Ta ₂ O ₅ 0-1 F ^- 0-0.5 and, if necessary, refining agents in the usual amounts. 2. Lead-free optical glasses according to claim 1, characterized by the following composition (in wt .-% on oxide basis)
SiO ₂ 62-75 B ₂ O ₃ 5-9.5 BaO 4.5-21 ZnO 0-2 CaO 0-0.5 with ZnO + CaO ≧ 0.05 TiO ₂ 1-7 Na ₂ O 3.5-9.5 K ₂ O 4.5-8 ZrO ₂ 0-1 F ^- 0-0.5 and, if necessary, refining agents in the usual amounts. 3. Lead-free optical glasses according to claim 1 or 2, characterized by the following composition (in wt .-% on an oxide basis) with a refractive index n _d between 1.53 and 1.56 and an Abbe number ν _d between 50 and 55
SiO ₂ 62-65 B ₂ O ₃ 8-9.5 BaO 4.5-7 ZnO 0-2 CaO 0-0.5 with ZnO + CaO ≧ 0.05 TiO ₂ 4-7 Na ₂ O 6.5-9.5 K ₂ O 6-8 ZrO ₂ 0-1 F ^- 0-0.5 and, if necessary, refining agents in the usual amounts. 4. Lead-free optical glasses according to at least one of claims 1 to 3, characterized in that the glasses contain 0-0.5 wt .-% Sb ₂ O ₃ . 5. Lead-free optical glasses according to at least one of claims 1 to 4, characterized in that the sum of F ^- and Sb ₂ O _{3 is} 0.05-0.8 wt .-%. 6. Lead-free optical glasses according to at least one of claims 1 to 5, characterized, that the glasses are free of Ar except for inevitable impurities senoxide. 7. Lead-free optical glasses according to at least one of claims 1 to 6 with a density ρ of at most 2.9 g / cm ³ , an acid resistance SR of 2.3 or better, an alkali resistance AR of 3.3 or better and a transformation temperature Tg of at least 550 ° C.