DE19827568C1 - Lead-free optical barium flint glasses, light flint glasses and crown glasses - Google Patents

Abstract

Lead-free optical barium flint glasses, light flint glasses and crown glasses have specified barium, zinc, titanium and zirconium oxide contents. Lead-free optical barium flint glasses, light flint glasses and crown glasses have the composition (by wt., on oxide basis) 45-60% SiO2, 4.5-9% B2O3, 5-21% BaO, 2.1-16% ZnO, 0.5-4.9% TiO2, 2-6% Na2O, 4.5-8% K2O, <= 11% Na2O + K2O, 0.01-1% ZrO2 and optionally usual amounts of refiners. Preferred Features: The glasses are free from arsenic oxide.

Description

The invention relates to lead-free optical barium flint glasses (BaF), barium light flint glasses (BaLF) and barium crown glasses (BaK), which have refractive indices n _d between 1.54 and 1.62 and numbers ν _d between 46 and 57.

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.

Various documents can already be found in the patent literature, in de lead-free glasses with optical values from the range mentioned be written. However, these glasses show the most diverse night egg le.

The glasses of US 2,523,265 contain high proportions of the expensive and high-melting component ZrO ₂ (2-15% by weight), as a result of which the crystallization stability of these glasses is reduced. The same also applies to the glasses of JP 52-45616 A containing 2-20% by weight of ZrO _{2. In} addition, they also contain high proportions of TiO ₂ , as a result of which the Abbe number takes on low values and the glasses receive a yellow color cast.

On the other hand, JP 8-34633 A discloses ZrO ₂ -free, SnO ₂ -containing glasses which contain only small amounts of TiO ₂ . TiO ₂ serves as solarization protection and practically not as a glass component with a significant influence on the non-optical properties. These relatively low refractive index glasses will not have good chemical resistance.

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

The glasses of US 5,523,265 require a high alkali oxide content. They will also have poor chemical resistance. The same applies to the glasses from JP 62-13293 B2 with Na ₂ O contents of 7-22% by weight.

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.

From US 5,300,467 optical glasses with refractive index values between 1.57 and 1.75 and payoffs between 30 and 55 are known to be high Total content of alkaline earth oxides MgO + CaO + SrO + BaO from 25-53% by weight %, with mandatory BaO of 15-45 wt .-% and SrO with 0.5-20 % By weight and optionally MgO with 0-4% by weight and CaO with 0-15% by weight available. The high total content of alkali oxides as well as SrO here required to the desired optical properties, the crystallization stability and chemical resistance of the glasses.

From GB 804,451 and GB 812,576 BaO-free optical glasses are known. Their refractive indices n _d of at least 1.56 or 1.54 can only be achieved through the use of expensive, high-melting or yellow-tinged components. The glasses of the first-mentioned document contain 5-20% by weight of TiO ₂ . The glasses of the latter document contain 5-20% by weight of TiO ₂ + ZrO ₂ with up to 20% by weight of ZrO ₂ and up to 9% by weight of TiO ₂ .

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.

It is an object of the invention to find lead-free optical barium flint, barium light flint and barium crown glasses with a refractive index n _d between 1.54 and 1.62 and an Abbe number ν _d between 46 and 57, which have good melting and processing properties and have good chemical resistance and good crystallization stability.

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

The glasses contain 45-60% by weight SiO ₂ . At lower levels, acid resistance and crystallization stability would be reduced, at higher levels, meltability would deteriorate. An increase in the SiO ₂ content to improve the acid resistance is no longer expedient in particular if larger amounts of alkali oxides are required to ensure good meltability.

To improve not only the acid resistance, but overall the chemical resistance, the glass contains 0.5% by weight (preferably <0.5% by weight) to 4.9% by weight of TiO ₂ . In addition, TiO _{2 is used} to achieve high refractive indices and to achieve low payoffs, especially with high refractive indices. The glasses preferably contain at least 1% by weight of TiO ₂ . The PbO freedom of the glasses also has a positive effect on the acid resistance.

The glasses contain 2-6% by weight Na ₂ O and 4.5-8% by weight K ₂ O, the sum of which should not exceed 11% by weight. Na ₂ O and K ₂ O serve to improve the meltability. At lower than the specified levels, economical production is difficult due to high melting temperatures. At higher contents, the coefficient of thermal expansion, the transformation temperature and the acid resistance are negatively influenced. It is preferred to limit the K ₂ O content to at most 7% by weight; and, in particular in order to achieve a high acid resistance, the maximum content of Na ₂ O with its smaller and therefore more easily diffusing cations from the glass is preferably 5.1% by weight, particularly preferably 4.5% by weight. limited. In a preferred embodiment, the sum of the alkali oxides is limited to a maximum of 9.5% by weight.

The glasses also contain B ₂ O ₃ , between 4.5 and 9% 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. It is therefore preferred to limit the maximum content of B ₂ O ₃ to 6.5% by weight. However, B ₂ O ₃ contents between 6 and 9% by weight can also be preferred, in particular at high SiO ₂ contents.

The glasses contain 5 to 21 wt .-% BaO to pay off the types of glass To reach BaF, BaLF and BaK. A content of at least 7 is preferred % By weight. Above the maximum salary, the Ent increase in glazing tendency.

To stabilize against crystallization, the glasses contain at least 2.1 % By weight ZnO. ZnO fractions of up to 16% by weight serve to increase the refractive index increase and remain in the range of medium payoffs. Would that If the desired high refractive indices were achieved by BaO alone, the glasses would lie due to their payoffs in the area of heavy crown glasses (SK).

The sum of BaO and ZnO is preferably at least 13% by weight particularly preferably at least 13.5% by weight, so that the glasses are relatively high Have refractive indices in combination with high numbers. In particular for glasses in the lower area of the BaLF type of glass, it can also make sense to limit this sum to a maximum of 18% by weight.

A balanced ratio between BaO and ZnO on the one hand and TiO ₂ on the other hand is essential for achieving the mentioned range of refractive index and Abbe number with good chemical resistance and crystallization resistance. Therefore, in preferred embodiments of the invention in which the glasses have relatively high refractive indices, the weight ratio (BaO + ZnO) / TiO _{2 is} limited to at least 5 and at most 30. For glasses with low refractive indices and a comparatively high TiO ₂ content (≧ 4% by weight), a ratio (BaO + ZnO) / TiO ₂ of at most 4.5 can also be useful.

The glasses can also contain up to a total of 1% by weight of CaO and / or SrO. These components are used to fine-tune n _d and ν _d and to suppress crystallization, but they make the batch more expensive as additional components.

If CaO and / or SrO are present, the sum of CaO, SrO and BaO be at most 21% by weight. When adding one or both of these compos nenten to a preferred embodiment of the invention, in which the BaO Content in the glass is only a maximum of 15% by weight, the sum should also consist of CaO, SrO and BaO amount to a maximum of 15% by weight.

An essential component of the glasses according to the invention is ZrO ₂ , which is present with at least 0.01% by weight, preferably with at least 0.1% by weight and particularly preferably with at least 0.3% by weight. This component serves to improve the chemical resistance and to fine-tune the refractive index and Abbe number. Their share is limited to a maximum of 1% by weight, otherwise the batch will become unreasonably more expensive.

DE 197 38 428 C1 describes lead-free optical barium flint glasses which, in terms of their refractive indices and numbers (n _d between 1.55 and 1.66 and ν _d between 39 and 52), partially correspond to the glasses described in the present application, which, however, are realized through a different area of composition. Compared to those glasses, Al ₂ O ₃ can be dispensed with in the glasses described here with a high ZnO content and the TiO ₂ content can be kept low. Compared to those glasses, the glasses described here have high transmissions at 400 nm and have a negative anomalous partial dispersion 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 ser ".

In the case of glasses which have a behavior of the dispersion which differs from the "normal glasses", the ordinal difference ΔP _{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: ΔP _{g, F} = pos.) Or "below" (negative partial dispersion: ΔP _{g, F} = neg .) the "Normalge straight" lies.

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

The glasses can contain up to 0.5% by weight of F. This is particularly useful for achieving extreme refractive indices in the BaK area. A content of up to 0.2% by weight of F. is preferred. 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 0.6% by weight. In this way an excellent inner glass quality is achieved.

Within the composition range for glasses with the above-mentioned refractive indices and payoffs, there are various preferred composition ranges of glasses whose optical data n _d , ν _d vary within a narrower range.

These are (with details of the composition ranges in% by weight on an oxide basis):

• - SiO ₂ 45-60; B ₂ O ₃ 4.5-9; BaO 7-21; ZnO 2.1-16; with BaO + ZnO ≧ 13.5; TiO ₂ 1-4.9; Na ₂ O 2.4-5.1; K ₂ O 4.5-7; with Na ₂ O + K ₂ O 7-11; ZrO ₂ 0.3-1; F 0-0.2.

These glasses of the optical glass types BaF, BaLF and BaK have refractive indices n _d between 1.55 and 1.61 and payoff numbers ν _d between 47 and 56.

• - SiO ₂ 45-50; B ₂ O ₃ 4.5-9; BaO 18-21; ZnO 2.1-16; TiO ₂ 3.5-4.9; with (BaO + ZnO) / TiO ₂ 5-10; Na ₂ O 2-6; K ₂ O 4.5-8; with Na ₂ O + K ₂ O ≦ 11; ZrO ₂ 0.1-1; F 0-0.2.

These glasses with high BaO and TiO ₂ fractions and comparatively low SiO ₂ fractions belong to the optical glass types BaF and BaLF and have refractive indices n _d between 1.58 and 1.62 and numbers ν _d between 46 and 51.

• SiO ₂ 48-55 (preferably 48-53); B ₂ O ₃ 4.5-6.5; BaO 14-21; ZnO 9-16; with BaO + ZnO 30-37; TiO ₂ 1-2; with (BaO + ZnO) / TiO ₂ 15-30; Na ₂ O 2-4.5; K ₂ O 4.5-6; with Na ₂ O + K ₂ O 7-9.5 (preferably 7-9); ZrO ₂ 0.3-1; F 0-0.2.

These low-TiO ₂ glasses have refractive indices n _d between 1.56 and 1.59 and payoff numbers ν _d between 53 and 57 and thus belong to the optical glass types BaLF and BaK.

• - SiO ₂ 55-60; B ₂ O ₃ 6-9; BaO 5-15; ZnO 2.1-10; with BaO + ZnO 13-18; TiO ₂ 4-4.9; Na ₂ O 3.5-6; K ₂ O 5-7.5; with Na ₂ O + K ₂ O ≦ 11; ZrO ₂ 0.3-1; F 0-0.2.

These glasses with TiO ₂ contents in the upper range within the interval of the main claim are light-weight flint glasses. They have refractive indices n _d between 1.54 and 1.56 and numbers ν _d between 50 and 53.

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

Examples

There were six examples of glasses according to the invention made from conventional raw materials fen 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 ΔP _{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.

For examples 4 and 5, further glass properties were determined, which are described in Table 3 are listed and u. a. the good chemical resistance ment: These glasses belong to the acid resistance class 1 and the alkali -Resistance class 1.

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 wt .-% on an oxide basis) and essential egg properties of the glasses

Table 3

Other properties of glasses No. 4 and 5

Here mean:
SR: Acid resistance according to ISO 8424
AR: Alkali resistance according to ISO draft 10629
τ _{i400 nm / 25 mm:} spectral _{pure transmittance} at the wavelength λ = 400 nm and a sample thickness d = 25 mm.

An upper devitrification limit (OEG), i.e. H. the liquidus temperature of the am highest meltable phase was not at all determinable, since the two Glä water (measured from 800 to 1040 ° C (Ex. 4) or 750 to 1050 ° C (Ex. 5) with a tempering time of 60 min.) show no measurable devitrification.

The glass composition area according to the invention offers a further group of optical glasses of the glass types BaF, BaLF and BaK with the aforementioned optical data, which are lead-free and, in a preferred embodiment, also As ₂ O ₃ -free.

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 = 2.3 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. They show temperatures of 700 to 1100 ° C, holding times of 60 min. and an associated viscosity interval of 8. 10 ² to 2. 10 ⁸ dPas no measurable or very little devitrification. The glasses are easy to melt and easy to process. With at least 550 ° C they have relatively high transformation temperatures T _g . Their density ρ is comparatively low at a maximum of 3.3 g / cm ³ . The transmission of the glasses in the visible range of the spectrum is very high. This is documented by specifying the transmission at λ = 400 nm (τ _{i400 nm / 25 mm} ). The glasses show a negative partial dispersion in the blue region of the spectrum.

Claims (12)

1. Lead-free optical barium flint glasses, barium light flint glasses and barium crown glasses with a refractive index n _d between 1.54 and 1.62 and an Abbe number ν _d between 46 and 57, characterized by the following composition (in% by weight based on oxide)
SiO ₂ 45-60 B ₂ O ₃ 4.5-9 BaO 5-21 ZnO 2.1-16 TiO ₂ 0.5-4.9 Na ₂ O 2-6 K ₂ O 4.5-8 with Na ₂ O + K ₂ O ≦ 11 ZrO ₂ 0.01-1 F 0-0.5 and, if necessary, refining agents in the usual amounts. 2. barium flint, barium light flint and barium crown glasses according to claim 1, characterized, that the sum of BaO and ZnO is at least 13.0% by weight. 3. Barium flint, barium light flint and. Barium crown glasses according to claim 2 with a refractive index n _d between 1.55 and 1.61 and an Abbe number ν _d between 47 and 56, characterized by the following composition (in% by weight based on oxide)
SiO ₂ 45-60 B ₂ O ₃ 4.5-9 BaO 7-21 ZnO 2.1-16 with BaO + ZnO ≧ 13.5 TiO ₂ 1-4.9 Na ₂ O 2.4-5.1 K ₂ O 4.5-7 with Na ₂ O + K ₂ O 7-11 ZrO ₂ 0.03-1 F 0-0.2 and, if necessary, refining agents in the usual amounts. 4. Barium flint and barium light flint glasses according to claim 2 with a refractive index n _d between 1.58 and 1.62 and an Abbe number ν _d between 46 and 51 characterized by the following composition (in wt .-% on an oxide basis)
SiO ₂ 45-50 B ₂ O ₃ 4.5-9 BaO 18-21 ZnO 2.1-16 TiO ₂ 3.5-4.9 Na ₂ O 2-6 K ₂ O 4.5-8 with Na ₂ O + K ₂ O ≦ 11 ZrO ₂ 0.1-1 F 0-0.2 and a weight ratio (BaO + ZnO) / TiO ₂ of 5-10 and if necessary refining agents in the usual amounts. 5. Barium light flint and barium crown glasses according to claim 1 or 2 with a refractive index n _d between 1.56 and 1.59 and an Abbe number ν _d between 53 and 57 characterized by the following composition (in% by weight on an oxide basis)
SiO ₂ 48-55 B ₂ O ₃ 4.5-6.5 BaO 14-21 ZnO 9-16 with BaO + ZnO 30-37 TiO ₂ 1-2 with (BaO + ZnO) / TiO ₂ 15-30 Na ₂ O 2-4.5 K ₂ O 4.5-6 with Na ₂ O + K ₂ O 7-9.5 ZrO ₂ 0.3-1 F 0-0.2 and a weight ratio (BaO + ZnO) / TiO ₂ of 15-30 and possibly refining agents in the usual amounts. 6. Barium light flint glasses according to claim 2 with a refractive index n _d between 1.54 and 1.56 and an Abbe number ν _d between 50 and 53, characterized by the following composition (in wt .-% on oxide basis)
SiO ₂ 55-60 B ₂ O ₃ 6-9 BaO 5-15 ZnO 2, 1-10 with BaO + ZnO 13-18 TiO ₂ 4-4.9 Na ₂ O 3.5-6 K ₂ O 5-7.5 with Na ₂ O + K ₂ O ≦ 11 ZrO ₂ 0.3-1 F 0-0.2 and, if necessary, refining agents in the usual amounts. 7. Barium flint, barium light flint and barium crown glasses after at least one of claims 1 to 5, characterized, that the glasses contain up to a total of 1% by weight of CaO and / or SrO and the sum of CaO + SrO + BaO is up to 21% by weight. 8. barium flint, barium light flint and barium crown glasses according to claim 6, characterized, that the glasses contain up to a total of 1% by weight of CaO and / or SrO and the sum of CaO + SrO + BaO is up to 15% by weight.   9. Barium flint, barium light flint and barium crown glasses according to at least one of Claims 1 to 8, characterized in that they contain 0-0.5% by weight of Sb ₂ O ₃ . 10. barium flint, barium light flint and barium crown glasses according to at least one of claims 1 to 9, characterized in that the sum of F and Sb ₂ O _{3 is} 0.05-0.6% by weight. 11. Barium flint, barium light flint and barium crown glasses after at least one of claims 1 to 10, characterized, that they are free of arsenic oxide except for inevitable impurities. 12. Barium flint, barium light flint and barium crown glasses according to at least one of claims 1 to 11 with a density ρ of at most 3.3 g / cm ³ , an acid resistance SR of 2.3 or better, an alkali resistance AR of 2.3 or better and a transformation temperature T. _g of at least 550 ° C.