KR20140025481A - High-refractive-index optical glass - Google Patents

Abstract

FIELD OF THE INVENTION The present invention relates to high refractive index optical bismuth oxide glasses and also to the manufacture and use of such glasses.
High-permeability optical glass comprising the following composition is described.
-Bi ₂ O ₃ 40 or more
Σ SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ 20-59
-R ₂ O 0-10
-RO 0-30
-Other Ingredients 0.01-20
The glass has a refractive index n _d of at least 1.9 and less than 2.2 and / or an Abbe number ν _d of at least 10 and less than 21 and / or a glass transition temperature T _g of less than 420 ° C.

Description

High refractive index optical glass {HIGH-REFRACTIVE-INDEX OPTICAL GLASS}

The present invention relates to the preparation and use of high refractive index optical bismuth oxide glass and such glass.

In recent years, the trend of miniaturization in the market of optical and optoelectronic technologies (in the fields of imaging, projection, telecommunications, optical information technology, mobile drive and laser technology) is increasing. This can be seen from the smaller size of the final product than ever, which naturally requires further miniaturization of the individual parts and parts of such an end product. As far as manufacturers of optical glass are concerned, this development involves a significant reduction in the volume requirements of the raw glass, even with an increase in the number of end products. At the same time there is a significant amount of scrap in the manufacture of such miniaturized parts from block and / or ingot glass, depending on the proportion of the product, and the work of such very small parts is more expensive than larger parts. There is pressure on glass makers to increase prices from additional processes because of the need. Apart from the process of performing conventional cutting of glass parts, for example for hot rolling and for making optical parts from block or ingot glass, near-net-shape or nearly such as gobs or spheres The manufacturing process carried out in the final shape can be obtained immediately following the melting of the glass. Execution of the nearly final shape is suitable for repressing.

Such an implementation can be converted to an optical component such as a lens, an aspherical component by precise compression or accurate molding. This process allows a smaller amount of glass melt (distributed over a larger number of smaller parts of the material) to flexibly contact for a short equipping time. However, due to the relatively small run size and generally small geometry, the added value produced by the process cannot be derived from the value of the material alone. The product must be pressed without complex redressing, cooling and / or post-cooling work. Since high geometrical accuracy is required, accurate devices using high quality and therefore expensive mold materials must be used in such compaction processes. The operating life of such a mold thus greatly affects the profitability of the product and / or the material produced. A very important factor for the long operating life of the mold is a very low operating temperature, but this temperature can only be reduced to the extent that the viscosity of the material to be compacted is sufficient for the compacting process. Thus the process temperature and thus the transformation temperature T _{g of the} glass to be treated And there is a direct causal relationship between the profitability of such a pressing process; The lower the deformation temperature of the glass, the longer the operating life of the mold and the greater the profit. This relationship leads to the need for low T _g glass, ie glass having a low melting point and strain point, ie glass having a viscosity suitable for processing at very low temperatures.

An additional request from the point of view of the melt treatment is the recent increase in "short" glass, i.e. glass which exhibits very small changes within a certain viscosity range, with a relatively small change in temperature with respect to temperature. Is a demand. This behavior has the advantage that the hot forming time, ie the mold closing time, can be shortened in the melting process. This first reduces throughput, i.e. cycle time. Next, since this is advantageous for the mold material, it has a positive effect on the overall manufacturing cost as well as described above. Such "single" glass also has the advantage of being able to cool faster than the corresponding "longer" glass to allow the processing of relatively large crystallized glass to be processed. It is thus possible to avoid prenucleation, i.e. the formation of crystal nuclei which may be problematic in subsequent secondary hot forming steps. This opens the possibility that such glass can form fibers.

In addition, the glass has chemically sufficient resistance, and it is desirable to have a very small coefficient of expansion.

Although glasses with the same optical properties and / or similar chemical compositions are described in the prior art, these glasses have significant drawbacks.

DE 11 2006 001070 describes bismuth oxide glass. Absorbance curves are only described for the two examples with relatively low Bi ₂ O ₃ content (30 and 35 mol%). This document does not address the problem that there may be a deterioration in transmission for glass with a high bismuth oxide content.

The prior art (eg DE 10 2007 050 172) states that Cr may be present as a common impurity in the glass.

It is an object of the present invention to provide an optical glass that can be made by combining a low strain temperature and an excellent pure transmission with excellent pure desirable optical properties (n _d / υ _d ). The glass must have an absorbance edge λ ₅ (ie, wavelength at 5% pure transmission) measured for glass samples having an excellent absorption edge or UV edge position or 10 mm thickness of less than 440 nm. It must be able to be processed by precise compression and suitable for use in imaging, projection, telecommunications, optical information technology, mobile drive and laser technology. They must also melt easily and have satisfactory crystal stability that allows for easy processing and production in continuous devices. Preference is given to “sweet” glasses having a viscosity in the range of 10 ^7.6 to 10 ¹³ dPas.

The above object is achieved by the embodiments of the invention described in the claims.

In particular, a high refractive index optical glass is provided comprising the following composition (mol% relative to oxide).

-Bi ₂ O ₃ 40 or more

Σ SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ 20-59

-R ₂ O 0-10

-RO 0-30

-Other Ingredients 0.01-20

In particular, the glasses of the invention have a refractive index n _d of at least 1.9, preferably at least 2.0, most preferably at least 2.08 and / or preferably less than 2.2, more preferably less than 2.15. The glass has an Abbe number of 10 ≦ υ _d ≦ 21, preferably 15 or more and / or 18 or less.

1 shows the intra transmisiion curve of the glass according to Example 1, where the solid line represents the internal transmission of the modified glass with a Cr content of 6 ppm (German "Reintransmission") and the dotted line is less than 2 ppm. Internal transmission of the strained glass with Cr content is shown.
2 shows the viscosity curve of the glass according to the invention according to the illustrated glass 2. In FIG. 1, the vertical line represents the temperature interval ΔT, where the viscosity of the glass drops from 10 ^7.6 dPas to 10 ¹³ dPas. In this case, ΔT has a value of 440 to 386 ° C, that is, 54K.

In an embodiment of the invention, the glasses of the invention have a strain temperature T _g ≤ 480 ° C, preferably T _g ≤ 450 ° C, more preferably T _g ≤ 420 ° C, and most preferably T _g ≤ 400 ° C. Have According to the invention, "low T _g glass" is a glass having a low strain temperature T _g , ie preferably T _g not exceeding 480 ° C.

A "sweet" glass is a glass that generally has a sharp viscosity curve in the 10 ² to 10 ¹³ dPas viscosity range, that is, its viscosity varies significantly in this viscosity range even when the change in temperature is relatively small. In the context of the glass of the present invention, the term "sweet" preferably applies to a viscosity range in the range of 10 ^7.6 to 10 ¹³ dPas. The temperature range ΔT in which the viscosity of this glass falls from 10 ^{7. 6} to 10 ¹³ dPas is preferably not more than 80K, preferably not more than 70K, particularly preferably not more than 60K.

For the purposes of the present invention, the "internal quality" of glass means that the glass contains a very small proportion of bubbles and / or streaks (ie, striae) and / or identical scratches. Or preferably glass that does not contain these. In one embodiment, the glass of the present invention has no streaks that can be captured by the shadow method in at least one direction, preferably in two orthogonal directions. In the shadow method, the glass sample is held between the light source and the observer's eye, and the shadow-casting streak is measured by moving and tilting the glass sample (MIL-G-174A and similar criteria) or Light is shined through the glass sample and streaks present in the glass sample are projected as shadows on the projection screen (ISO 10110-4). In addition, the glass preferably has a bubble class B1, more preferably B0 according to ISO 101100-3.

In the following, unless otherwise indicated, the expression "without X" or "without component X" means that the glass is substantially free of this component X, i.e., only as impurities, even if such components are present in the glass as much as possible. Present, but not added to the glass composition as individual components. X can be any component, for example F or Li ₂ O.

In the following, all proportions of the glass component are mole% relative to the oxide, unless otherwise indicated.

The basic glass system of the glass of the present invention is glass having a high bismuth oxide content.

The glass of the present invention has a Bi ₂ O ₃ ratio of at least 40 mol%, preferably at least 45 mol%, particularly preferably at least 48 mol%. The Bi ₂ O ₃ ratio is preferably no more than 70 mol%, more preferably no more than 60 mol%, particularly preferably no more than 55 mol%. Bi ₂ O ₃ contributes to the desired viscosity temperature behavior (“sweet” glass) at a viscosity in the range of 10 ^7.6 to 10 ¹³ dPas. It also reduces T _g and increases the density of the glass. The latter guarantees a high refractive index. However, because the intrinsic color of Bi ₂ O ₃ adversely affects the transmission of glass and the UV edge λ ₅ shifts excessively in the long wavelength range, i.e., larger than 400 nm, it should not exceed the maximum ratio of 70 mol%. Likewise, the ratio should not be below the minimum of 40 mol% in order to reliably obtain the combination of high refractive index and low T _g of glass.

Apart from Bi ₂ O ₃ , the glass of the present invention is a further glass former containing SiO ₂ , B ₂ O ₃ and / or Al ₂ O ₃ in a total amount of 20 to 59 mol%, preferably 55 mol No more than%, and most preferably no more than 50 mole%.

The glass of the invention preferably contains at least 8 mol%, more preferably at least 10 mol% and / or up to 25 mol%, more preferably up to 20 mol% SiO ₂ . Since SiO ₂ increases the glass transition temperature and the viscosity of the glass and also decreases the refractive index, the maximum ratio of SiO ₂ should not exceed 25 mol%.

The glass of the invention is also preferably at least 18 mol%, more preferably at least 19 mol% and / or preferably at most 34 mol%, more preferably at most 30 mol%, most preferably at most 25 mol% It contains B ₂ O ₃ in an amount of. The strongly networked properties of B ₂ O ₃ increase the stability of the glass, increasing crystallinity and chemical resistance.

The total content of oxides B ₂ O ₃ and SiO ₂ (B ₂ O ₃ + SiO ₂ ) is preferably at least 20 mol%, particularly preferably at least 25 mol%, more preferably at least 30 mol%, even more Preferably it is 35 mol% or more. The addition of these components is preferred because it inhibits the demixing of the glass. In addition, the total content of oxides B ₂ O ₃ and SiO ₂ is preferably not more than 60 mol%, more preferably 55 mol%, even more preferably 50 mol%, most preferably 45 mol%. When the total amount exceeds 60 mol%, the desired high refractive index is no longer obtained.

The ratio of the content of B ₂ O ₃ to the sum of the contents of B ₂ O ₃ and SiO ₂ (B ₂ O ₃₎ in order to obtain the optimum conductivity of the glass during melting the glass by high frequency heating as described below. / B ₂ O ₃ + SiO ₂ ) is preferably at least 0.5.

In addition, the glass of the invention is preferably at least 1 mol%, more preferably at least 3 mol%, even more preferably at least 4 mol% and / or preferably 11 mol%, more preferably 10 mol%, most preferably 9 Al ₂ O ₃ is preferably contained in an amount of no greater than mol%.

The content ratio of SiO _{2 to} the content of Al ₂ O ₃ is preferably 1.5 or more, preferably 2.0 or more and / or preferably less than 6.0, more preferably less than 3.5.

The ratio of the content of SiO ₂ to the total content of B ₂ O ₃ and Al ₂ O ₃ (SiO ₂ / Al ₂ O ₃ + B ₂ O ₃ ) is preferably less than 2.0, more preferably less than 1.5.

In an embodiment of the invention, the glass contains all three components SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ . When all three of these components are present, in particular when present in the above-mentioned ratios, the glass has a particularly high degree of crosslinking, and therefore has a particularly high stability against devitrification, especially upon reheating. The addition of these three components is advantageous because they crosslink differently in the glass and thus in particular give high stability against devitrification.

In the glass of the present invention, the sum of alkali metal oxides R ₂ O selected from the group consisting of Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O and / or Cs ₂ O is from 0 to 10 mol%. Preferred is not more than 5 mol%, more preferably not more than 3 mol%, more preferably not more than 2 mol%, particularly preferably not more than 1 mol%. The value not exceeding 5 mol% should not exceed this value because devitrification may occur during reheating. Nevertheless, addition of at least one alkali metal oxide, in particular Na ₂ O, in an amount of at least 0.1 mol% is preferred because the alkali metal optimizes the melting behavior, ie acts as a flux. They can also be used to lower the deformation temperature T _g and to finely adjust Abbe's number.

In an embodiment of the invention, the glass does not have Li ₂ O and / or Cs ₂ O. Surprisingly, Cs ₂ O can cause devitrification in the glass system of the present invention. Li ₂ O reduces the refractive index and is therefore undesirable as a component of the glass. The glass of the present invention preferably does not contain Li ₂ O.

In order to control the viscosity-temperature behavior in a fluid manner, the glasses of the present invention may optionally contain one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO and / or BaO. The proportion of each component should not exceed 10 mol%, preferably 7 mol%, particularly preferably 6 mol%. The glass of the present invention may contain MgO, CaO, SrO or BaO in an amount of 0.5 mol% or more, preferably 1 mol% or more. Alkaline earth metal oxides contribute to a sharp viscosity curve. Higher proportions in the glass lead to devitrification, especially on reheating, so the maximum proportion should not exceed 10 mol%.

The glass of the present invention may have Zn0 in a proportion of less than 10 mol%, preferably less than 7 mol%, particularly preferably less than 5 mol%. ZnO contributes to the desired viscosity-temperature behavior (“short” glass) in the viscosity range of 10 ^7.6 to 10 ¹³ dPas.

However, in a variant of the invention, the glass has less than 5 mole percent divalent oxide RO (which encompasses alkaline earth metal oxides and ZnO) or no RO. The addition of the RO component surprisingly leads to a decrease in the refractive index of the glass of the present invention and is therefore undesirable.

In an embodiment of the invention, the total content of R ₂ O + RO is less than 5 mol%, preferably not more than 4 mol%.

The glass has at least 0.01 to 20 mol%, preferably at least 0.03 mol%, more preferably at least 0.01 mol%, most preferably at least 0.3 mol% and / or preferably less than 10 mol%, more than one additional component. Preferably less than 7 mol%, even more preferably less than 8 mol%, most preferably less than 4 mol%. Such additional components contribute to stabilizing the glass against devitrification, ie crystallization or separation, especially upon reheating. In addition, fine adjustment of the optical position can be affected by such components. The additional components are preferably La ₂ O ₃ , Nb ₂ O ₅ , Gd ₂ O ₃ , Ga ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , TiO ₂ , ZrO ₂ , HfO ₂ , GeO ₂ , TeO ₂ , SeO ₂ , CeO ₂ , WO ₃ , As ₂ O ₃ and / or Ta ₂ O ₅ . Each of these components may be present in an individual proportion of at least 0.01 mol%, preferably at least 0.05 mol%, unless otherwise indicated below. The glass of the present invention may preferably contain three or more, four or more of the aforementioned additional components.

The glass of the present invention has a La ₂ O ₃ content of at least 0.01 and / or less than 6 mol%, more preferably less than 5 mol%. WO ₃ and / or Nb ₂ O ₅ are present in the glass in an amount of at least 0.01 mol% in each case and / or in each case less than 6 mol%, preferably less than 5 mol%, particularly preferably less than 4 mol%. Can be. The optical position can be adjusted by these components. However, at larger ratios they result in a higher viscosity of the glass.

The glass may contain TiO ₂ . It may be present at least 0.01 mol%, preferably at least 0.2 mol%, more preferably at least 0.5 mol% and / or less than 6 mol%, preferably less than 3 mol%, particularly preferably less than 2 mol%. . The addition of TiO ₂ has a positive effect on the high refractive index and increases the stability of the glass upon reheating. However, this component results in increased T _g and viscosity. It can also lead to an increase in the dispersion of the glass and adversely affect the transmission of the glass due to absorption in the UV range. Therefore, a content of more than 6 mol% is undesirable.

ZrO ₂ is preferably in small amounts in the glasses of the invention, such as at least 0.01 mol%, more preferably at least 0.04 mol% and / or preferably less than 2 mol%, more preferably less than 1 mol%, most preferred. Preferably less than 0.05 mol%. When the glass component is melted in the ZAC tank, ZrO ₂ from the tank material can be introduced in the glass melt. In certain embodiments, the glass does not contain ZrO ₂ .

In a variant of the glass the glass contains at least one component of TiO ₂ or ZrO ₂ , preferably both components. The total content of TiO ₂ + ZrO ₂ is preferably at least 0.04 mol%, more preferably at least 0.1 mol%, particularly preferably at least 0.2 mol% and / or less than 5 mol%, more preferably less than 3 mol% Most preferably less than 2 mole%. These components can act as nucleating agents, and therefore they can lead to devitrification of the glass when present in increased amounts, so that contents above those indicated are undesirable. However, when they are present in small amounts in the glass, crystallization occurs only under certain conditions and can be used in a targeted manner in the melting process, for example to make glass crust during melting with a cooled melt tank or HF, and thus the tank or Contamination of the glass by the crucible material can be prevented.

The glass may additionally contain GeO ₂ in an amount of preferably at least 0.01 mol%, more preferably in an amount of at least 0.5 mol% and / or less than 5 mol%. Germanium oxide has a favorable effect on the stability of the glass upon reheating. However, the addition of large amounts of germanium oxide is undesirable because this compound is very expensive. In one embodiment the glass does not contain GeO ₂ .

Ta ₂ O ₅ Again at a rate of at least 0.01 mol%, preferably at least 0.05 mol%, most preferably at least 0.1 mol%, and / or less than 3 mol%, preferably less than 2 mol%, most preferably less than 1 mol%. May be present in the glass. The glass preferably does not contain Ta ₂ O ₅ .

Gd ₂ O ₃ may be present in the glass in a proportion of at least 0.04 mol%, preferably at least 0.05 mol% and / or less than 2 mol%, preferably less than 1 mol%. This component has a small absorption band in the visible region, so the glass preferably does not contain Gd ₂ O ₃ .

The glass also contains Ga ₂ O ₃ in an amount of preferably at least 0.01 mol% and / or in an amount of less than 5 mol%. In particular, the total content of Al ₂ O ₃ + Ga ₂ O ₃ is preferably less than 11 mol%, more preferably less than 10 mol%.

HfO ₂ is at least 0.01 mol%, preferably at least 0.03 mol%, particularly preferably at least 0.04 mol%, and / or less than 1 mol%, preferably less than 0.5 mol%, particularly preferably 0.25 mol% in the glass. May be present below. This component can be added to adjust the refractive index and Abbe's number and, along with the other additional components, stabilize the glass so that the glass does not separate during the reheating process, such as recompression.

In addition, the glass preferably contains at least 0.5 mol%, more preferably at least 1 mol%, even more preferably at least 2 mol% and / or preferably less than 10 mol%, more preferably 6 mol% of TeO ₂ . It may contain at a ratio of less than%.

Cerium oxide may be present in the glass to adjust the oxidation state. CeO ₂ may be present in a proportion of preferably less than 1 mol%, more preferably less than 0.5 mol%, even more preferably less than 0.25 mol%. However, the glass preferably does not contain CeO ₂ because this component causes some discoloration (yellowish color) of the glass.

In one embodiment, the glass contains As ₂ O ₃ in an amount of preferably less than 0.2 mol%, more preferably in an amount less than 0.1 mol% and / or preferably at least 0.05 mol%, more preferably 0.02 It may be contained in an amount of at least mol%, even more preferably at least 0.01 mol%. This component acts alone or together with other refining agents mentioned below, but also serves to correct the redox state of Bi ₂ O ₃ .

The glass of the present invention may contain a small amount of a conventional refining agent. The sum of the refining agents added is preferably not more than 1.0 mol%, more preferably less than 0.5 mol%. As a refining agent, at least one of the following components may be present in the glass of the present invention (mol%).

Sb ₂ O ₃ 0-1 and / or

SO ₄ ^{2 -} 0-1, and / or

F ^- 0-1 and / or

Inorganic Peroxide 0-1

As the inorganic peroxide, for example, zinc peroxide zinc, lithium peroxide and / or alkaline earth metal peroxide can be used.

In one embodiment, the glass contains Bi ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ and R ₂ O, in particular Na ₂ O, up to 91 mol%, preferably 95 mol%.

In another embodiment of the present invention, the glass of the present invention preferably has a Bi ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , La to a degree of at least 95 mol%, more preferably at least 98 mol%. ₂ O ₃ , Ta ₂ O ₅ , TiO ₂ , ZrO ₂ , HfO ₂ , GeO ₂ and R ₂ O, in particular Na ₂ O.

In one embodiment of the present invention, the glass of the present invention preferably contains the aforementioned components up to a degree of at least 90 mol%, more preferably at least 95 mol%, most preferably at least 99 mol%.

In one embodiment of the present invention, the glass of the present invention also preferably contains no other ingredients not mentioned in the claims. That is, in such embodiments, the glass consists essentially of only the components mentioned herein. The expression “consist essentially of” means that the other components are present only as impurities at best and are not intentionally added as individual components to the glass composition.

The glass preferably contains no components not mentioned above.

The glass of the present invention is an optical glass, preferably color imparting components such as V, Cr, Mn, Fe, Co, Ni and / or Cu, and / or optionally active such as laser active components such as Pr, Nd , Sm, Eu, Tb, Dy, Ho, Er and / or Tm. In addition, the glass preferably contains no unhealthy components such as oxides of Pb, Cd, Tl and Se.

The invention also relates in particular to high refractive glass with improved internal transmission τ _i in the range λ (τ _ip ) to λ (τ _ip +400 nm), and / or especially after reheating. τ _ip is the internal transmission in the pass range or the degree of reinstransmission in the pass range, and λ (τ _ip ) is a wavelength greater than the beginning of the passage or transmission range of the glass, i.e. the internal transmittance is less than τ _ip The range does not go down. The change in the internal transmission (τ _i ) of the glass in the wavelength range λ (τ _ip ) to l (τ _ip +400 nm) is preferably at most 2%, preferably at most 1%, more preferably at most 0.9% to be.

The glass of the present invention preferably has an internal transmittance (τ _ip ) at 600 nm and / or 700 nm of at least 95%, more preferably at least 98%.

The inventors have found that when the glass has a high Bi ₂ O ₃ content, i.e., 40 mol% or more, the transmission of the glass is slightly worsened in the range of λ (τ _ip ) to λ (τ _ip +400 nm), ie internal transmission. (τ _ip) has been found that the extent that the wavelength λ (τ _ip) after the internal transmission is reached in the long wavelength direction again slightly reduced to λ (τ _ip +400 nm). The "sag" in this internal transmission curve increases after reheating the glass above the strain temperature. Deterioration in internal transmission is undesirable and should be avoided for the use of glass, even if very small, especially less than 3%.

In the case of optical glass, Cr as a color imparting material is not added as a component to the glass unless the glass is a colored glass. However, Cr is present in some glass stocks. The prior art states that Cr as a usual amount of impurities does not cause problems in bismuth oxide glass. However, the inventors have surprisingly found that conventional Cr contamination on glass affects internal permeation, and that the degradation of permeation can be avoided if the glass has a low Cr content.

Although Cr has a reabsorption band in the region mentioned, this band does not account for the extent of "stretching" over a large wavelength range or degradation of transmission after reheating. Without being bound by theory, it is believed that the interaction between multivalent Cr and Bi of glass occurs and Cr is involved in the redox mechanism of Bi, resulting in additional degradation of permeation. This effect appears to occur especially in glass with a high bismuth oxide content.

The glass of the invention therefore preferably has a Cr content of less than 4 ppm, preferably less than 3 ppm, more preferably less than 2 ppm.

1 shows a glass according to the invention according to example 1 in a conventional material having a chromium content of 6 ppm and a strain having a chromium content of 6 ppm (solid line) and a variant having a chromium content of less than 2 ppm (dashed line) Shows the internal transmission curve of.

In addition, the glass of the present invention preferably contains less than 3 ppm platinum component, more preferably less than 2 ppm platinum component, most preferably less than 1 ppm platinum component. In order to achieve this preferred value of the platinum component, the glass of the invention is preferably melted in a melting apparatus which does not contain platinum, for example a fused silica tank or a ZAC tank. The preferred low content of platinum component makes it possible to achieve UV edge positions of (τ _c ) 440 nm or less, which is not very common for glass with the described high refractive index.

Fluorine and fluorine-containing compounds also tend to evaporate during melting or melting, thus making it difficult to accurately set the glass composition. The glass of the present invention therefore preferably does not contain fluorine.

The invention also provides a glass having an absorption edge τ ₅ at up to 440 nm, preferably 430 nm, more preferably 425 nm.

The glass of the present invention has excellent chemical resistance. In particular, it enables acid resistance (AR) below 52.3 according to ISO 8424 and / or alkali resistance below 4.3 according to ISO 10629.

The glass of the present invention has an unusual relative partial dispersion ΔP _{g , F} of 0 to 60 × 10 ⁻⁴ , measured on a sample cooled at a cooling rate of about 20 K / h.

The glass of the present invention has a coefficient of thermal expansion α _20-300 of less than 11 × 10 ⁻⁶ / K, more preferably less than 10 × 10 ⁻⁶ / K.

In addition, the combination of crystal stability and viscosity-temperature profile of the glass of the present invention enables substantially trouble-free (re) treatment (pressing or re-pressing and hot rolling) of the glass.

In particular, these glasses are suitable for near-net-shape processing, such as the production of accurate gobs, and also for the precise compression for the production of optical components having the correct final form. In this context, the viscosity-temperature profile and processing temperature of the glass of the present invention is preferably fixed such that such near-final-geometry or quasi-normal heat formation can be performed using sensitive accuracy machines. do.

The invention also provides the use of the glass of the invention in the fields of imaging, projection, telecommunications, optical communications, mobile drives and laser technology.

The present invention also provides an optical component obtained by compressing the above-described glass, in particular an optical component produced by precision compression, and also provides a method of manufacturing the optical component by precision compression of the above-mentioned glass.

The invention also provides an optical component comprising the glass of the invention. The optical component here may in particular be a lens, an aspherical component, a prism and a compact component. The term "optical component" according to the present invention also includes preforms of such optical components, such as spheres, gobs, precision gobs and the like.

The present invention also provides a method for providing the glass of the present invention, which comprises a direct induction heating step of mixing the use of an alternating electromagnetic field and / or oxidative melting of the glass.

For the purposes of the present invention, the combination of melting and stirring magnetic fields, in particular high frequency magnetic fields, means that the energy administered to the melt by inductive coupling is greater than the energy released from the melt by the removal of heat. Only in this way is it possible to heat or maintain the melt by high frequency (HF) heating.

The molar ratio of B ₂ O ₃ to the sum of SiO ₂ and B ₂ O ₃ is preferably at least 0.5. This ratio is necessary, in particular for low alkali or alkali free glass, in order to reliably enable bonding to high frequencies. In addition, the low viscosity of the glass with high acid bismuth content is advantageous for melting with HF heating.

The process preferably further comprises introducing a fragment or mixture of the above-mentioned composition into a skull crucible.

The crucible is preferably made of aluminum. Skull crucibles allow melting in the same material so that particularly pure glass can be obtained. The mixture can be melted batchwise or in a device continuously.

The process preferably further comprises the following steps:

Liquefying a portion or glass piece of the mixture by a burner or Kanthal heater,

Coupling a high frequency magnetic field to the molten material so that the remaining mixture or fragment is melted by heat input.

After this, further processing of the glass is followed either continuously or batchwise.

Further treatment is carried out in a conventional method (in platinum) or in a second plant using HF heating, which is available for refining, especially in the case of aggressive glasses.

Processes which can preferably be used are described in DE # 10257049-A.

The invention will be illustrated by a series of examples below. However, the present invention is not limited to these examples.

Example

The following examples are intended to illustrate preferred glass according to the present invention and are not intended to limit the protection scope of the present invention by these glasses.

The raw material for the oxide is weighed, one or more refining agents such as Sb ₂ O ₃ are added and the components are continuously mixed well. The glass mixture is melted at about 900 ° C. in a continuous melting apparatus, which causes the oxygen to fill up. That is, oxygen is introduced into the melt and the melt is refined (920 ° C.) and homogenized again. At a casting temperature of about 890 ° C., the glass is cast and processed to the desired shape. In large quantities, for continuous devices, the temperature is experienced to be replaced by at least about 100 K, and the material can be processed by a semi-final geometric compression process.

The properties of the glass obtained by this method are shown in Table 2 after Example 1.

In Tables 2 to 4, all contents given for glass are mole% relative to oxide.

All glasses according to the invention have a Cr content of less than 2 ppm, a glass transition temperature T _g of 420 ° C. or less, a refractive index n _{d of} 2.05 or more, Abbe's number υ _{d in} a range of 10 or more and 21 or less, an absorption edge λ of less than 430 nm. ₅ , it can be easily processed, can be reheated to a temperature higher than T _g , and has a very high resistance to acids and alkalis. In addition, the glass according to the present invention exhibits no transmission deterioration of 0.9% or more of the glass at wavelengths ranging from λ (τ _ip ) to λ (τ _ip +400 nm) and has an internal transmission of 95% or more.

All transmissions were measured for 10 mm thick glass samples.

In the table, RHT (T ₁ ) refers to a test in which the glass is reheated to a temperature at which the glass has a viscosity of 10 ⁹ dPas for at least 20 minutes, preferably at least 2 hours, and RHT (T ₂ ) indicates that the glass is 10 ⁵ dPas. Refers to a test that is reheated to a temperature having a viscosity. The abbreviation "p" means that the test passed, that is, the glass did not show devitrification or blur after the test. The abbreviation “np” indicates that this test did not pass, ie, the glass became devitrified or blurred upon reheating after the test. The reheat test was performed under normal atmosphere (air) but not under non-oxidizing conditions.

Claims (10)

Optical glass containing the following composition (mol% relative to oxide):
-Bi ₂ O ₃ 40 or more
Σ SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ 20-59
-R ₂ O 0-10
-RO 0-30
-Other Ingredients 0.01-20 The glass of claim 1, wherein the glass has a Cr content of less than 4 ppm, preferably less than 3 ppm, more preferably less than 2 ppm. The glass according to claim 1, wherein 8 to 25 mol% SiO ₂ , 18 to 34 mol% B ₂ O ₃ and / or 1 to 11 mol% Al ₂ O ₃ are present in the glass. . The glass of claim 1, wherein the glass comprises La ₂ O ₃ , Nb ₂ O ₅ , Gd ₂ O ₃ , Ga ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , TiO ₂ , ZrO ₂ , Preferably at least 0.03 to 10 mol%, more preferably at least one component selected from the group consisting of HfO ₂ , GeO ₂ , TeO ₂ , SeO ₂ , CeO ₂ , WO ₃ , As ₂ O ₃ and / or Ta ₂ O ₅ . Glass containing 0.1 to 7 mol%. Glass according to one or more of the preceding claims, containing 0.01 to 0.20 mol% As ₂ O ₃ and / or 0.02 to 0.50 mol% Sb ₂ O ₃ . Glass according to one or more of the preceding claims, having an absorption edge τ ₅ (wavelength with 5% (pure) transmission) of less than 440 nm, preferably less than 430 nm, more preferably less than 425 nm. . The reduction of the internal transmission of the glass at wavelengths in the range λ (τ _ip ) to λ (τ _ip +400 nm) is less than 2%, preferably less than 1%, more preferably Glass less than 0.9%. The glass of claim 1, wherein the glass has a refractive index n _d of at least 1.9 and less than 2.2 and / or an Abbe number υ _d of at least 10 and less than 21 and / or a glass transition temperature T _g of less than 420 ° C. . Use of the glass according to one or more of claims 1 to 8 for the fields of imaging, projection, telecommunications, optical communications, mobile drives and / or laser technologies and / or optical components. As a manufacturing method of the optical glass in any one of Claims 1-8,
A direct induction heating step of the mixture by stirring magnetic field and / or oxidative melting of the glass.

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