TWI598312B - Highly refractive optical glass - Google Patents

Description

High refractive index optical glass

The present invention relates to a high refractive index yttria optical glass, and to the manufacture and use of the glass.

In recent years, the market trends in optical and optoelectronic technologies (applied in imaging, projection, communication, optical information technology, mobile hard disk and laser technology) have gradually moved toward miniaturization. This can be seen by smaller and smaller end products, and the gradual miniaturization of individual components of such end products is naturally required. In the case of manufacturers of optical glass, this development has been accompanied by a significant reduction in the volume requirement of the raw glass, although the number of end products has increased. At the same time, there is a significant amount of waste in a significant amount of product due to the manufacture of such smaller components from block and/or strip glass, and the processing of such very small parts requires greater in the case of larger components. The cost, and thus the price pressure imposed by other processors on the glass manufacturer, has increased.

In addition to separating the glass for the optical component by, for example, hot-rolling the preform and the conventional self-blocking or strip-shaped glass, it is possible to directly obtain the ideal near-net shape or near the final geometric shape of the preform, such as melting, after the glass is melted. The process of a ball or ball (sphere). Prefabricated parts close to the final geometry are suitable for re-pressing.

Such preforms may also advantageously be converted to optical components such as lenses, aspherical components, etc. by precision profiling or precision molding. This process allows a smaller glass melt volume (distributed over a large number of smaller pieces of material) to be flexibly countered by short equipment time. However, due to the relatively small operating dimensions and generally small geometries, the added value generated by this process cannot be derived solely from the value of the material. The product needs to leave the press in a state that does not require complicated reconditioning, cooling, and/or cold processing. Due to the high geometric accuracy required, precision instruments using high quality and therefore expensive mold materials are required for this profiling process. Therefore, the operational life of such molds has a significant impact on the profitability of the product and/or the resulting material. A very important factor in the high operating life of the mold is the extremely low operating temperature, but it can only be reduced to the extent that the viscosity of the material to be pressed is still sufficient for the pressurization process. Therefore, there is a direct causal relationship between the processing temperature (and thus the transition temperature T _{g of the} glass to be processed) and the profitability of this molding process: the lower the transition temperature of the glass, the longer the operating life of the mold The bigger the profit. This relationship has led to the need for "low Tg glass", a glass with a low melting point and a transition point, in other words a glass suitable for viscosity at very low temperatures.

Another desire from the viewpoint of processing melts has recently been the increasing demand for "short" glass, that is, glass whose viscosity exhibits a large change in a specific viscosity range by a relatively small change in temperature. This behavior has the advantage of reducing the hot forming time (i.e., mold closing time) during the melting process. This first increases the output, which is to reduce the cycle time. Secondly, it is mild to the mold material, which, as mentioned above, also has a positive effect on the total manufacturing cost. These "short" glasses have a faster cooling than the corresponding "longer" glass. Further advantages of glass having a relatively high tendency to crystallize can also be processed. Thereby pre-nucleation is avoided, that is, a crystal nucleus which may become a problem in the subsequent secondary thermoforming step is formed. This opening can also pull the glass to create the possibility of fibers.

Furthermore, it is also desirable for the glass to have sufficient chemical resistance and to have a very small expansion coefficient.

While glass having similar optical positions and/or comparable chemical compositions has been described in the prior art, such glasses have significant drawbacks.

DE 11 2006 001070 describes yttria glass. It only reveals absorption curves for two examples with relatively low Bi ₂ O ₃ content (30 and 35 mol %). The disclosure does not describe the possible transmission degradation problems in the case of glass with a high cerium oxide content.

In the prior art (see, for example, DE 10 2007 050 172) it is stated that Cr can be present as a common impurity in glass.

It is an object of the present invention to provide an optical glass that achieves a desired optical position (n _d / v _d ) in combination with a low transition temperature and excellent pure transmission. The glass shall also have an absorption edge or UV edge position or absorption edge τ _{5 of} less than or equal to 440 nm on a glass sample having a thickness of 10 mm (ie a wavelength of 5% pure transmission) and shall also It can be processed by precision molding and is suitable for applications in imaging, projection, communication, optical information technology, mobile hard disk and laser technology. It should also be easily melted and easy to process, and has satisfactory crystal stability, making it Manufactured in a continuous apparatus. Extremely "short" glass in the viscosity range of 10 ^7.6 to 10 ¹³ dPas is required.

The above object is achieved by the specific example of the invention described in the scope of the patent application.

In particular, a high refractive index optical glass comprising the following composition (based on moles in moles) is provided:

In particular, the glass of the present invention has 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 10 v _d The Abbe number of 21 is preferably at least 15 and/or not more than 18.

In one embodiment of the invention, the glass of the invention has a transition temperature _Tg 480 ° C, preferably T _g 450 ° C, better T _g 420 ° C and the best T _g 400 ° C. According to the present invention, "low Tg glass" system having a low glass transition temperature T _g that is preferably not more than 480 deg.] C of the T _g.

"Short" glass is generally a glass having a very steep viscosity curve in the viscosity range of 10 ² to 10 ¹³ dPas, that is, its viscosity greatly varies within this viscosity range even for relatively small temperature changes. In the case of the glass of the present invention, the term "shortness" applies to a viscosity range preferably from 10 ^7.6 to 10 ¹³ dPas. This glass viscosity of from 10 down to 10 ¹³ dPas ^7.6 The preferred temperature range △ T is not more than 80K, preferably not more than 70K, particularly preferably not more than 60K.

For the purposes of the present invention, "internal quality" of glass means that the glass contains a very small proportion of bubbles and/or streaks and/or the like, or preferably does not. In one embodiment, the glass of the present invention does not have stripes that can be identified in at least one direction, preferably in two orthogonal directions, by a shading method. In the shadow method, a glass sample is held between the light source and the observer's eye, and the stray of the projected shadow is measured by moving and tilting the glass sample (MIL-G-174A and the like), or the light is irradiated through the glass sample. The streaks present in the glass sample are projected onto the projection screen as shadows (ISO 10110-4). Further, according to ISO 10110-3, the glass preferably has a bubble level B1, more preferably B0.

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, ie, at most this component is present as an impurity in the glass, and It is not added to the glass composition as an individual component. X is any component such as F or Li ₂ O.

In the following, unless otherwise indicated, the proportions of all glass components are in mole percent and are based on oxides.

The base glass system of the glass of the present invention is a glass having a high cerium oxide content.

The glass of the invention has a Bi ₂ O ₃ ratio of at least 40 mol%, preferably at least 45 mol%, particularly preferably more than 48 mol%. The Bi ₂ O ₃ ratio does not exceed 70 mol%, preferably does not exceed 60 mol%, and particularly preferably does not exceed 55 mol%. Bi ₂ O ₃ contributes to the desired viscosity temperature behavior ("short" glass) in the viscosity range from 10 ^7.6 to 10 ¹³ dPas. Furthermore, it makes T _g and decrease the density of the glass increases. The latter ensures a high refractive index. The maximum ratio of 70 mol% should not be exceeded, as the inherent color of Bi ₂ O ₃ will adversely affect the emission of the glass, and the UV edge ₅ will move too much into the longer wavelength range, ie greater than 440 nm. This ratio should also be no less than a minimum of 40 mol% to ensure a high refractive index of the low _Tg bonded glass.

In addition to Bi ₂ O ₃ , the glass of the present invention comprises SiO ₂ , B ₂ O ₃ and/or Al ₂ O ₃ as an additional glass forming agent in a total amount of from 20 to 59 mol%, preferably not more than 55 mol. The ear % and the best do not exceed 50% by mole.

The glass of the present invention preferably comprises at least 8 mole%, more preferably at least 10 mole%, and / or no more than 25 mole%, more preferably not more than 20 mole% of SiO _2. The maximum proportion of SiO ₂ should not exceed 25 mol%, since SiO ₂ leads to increased glass transition temperature and glass viscosity and also causes a decrease in refractive index.

Furthermore, the glass of the present invention preferably comprises at least 18 mol%, more preferably at least 19 mol%, and/or preferably no more than 34 mol%, more preferably no more than 30 mol%, and most preferably no more than 25 moles of B ₂ O ₃ . The strong network formation properties of B ₂ O ₃ improve the stability of the glass to crystallization and chemical resistance.

The total content of the oxides B ₂ O ₃ and SiO ₂ (B ₂ O ₃ + SiO ₂ ) is preferably 20 moles, especially good 25 mol%, better 30% or even better 35 moles %. It is preferred to add two components so that demixing of the glass does not occur. Further, the total content of the oxides B ₂ O ₃ and SiO ₂ is preferably not more than 60 mol%, more preferably not more than 55 mol%, still more preferably not more than 50 mol%, and most preferably not more than 45 mol%. . If the total content exceeds 60 mol%, the desired high refractive index is no longer achievable.

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

Furthermore, the glass of the present invention preferably further comprises at least 1 mol%, more preferably at least 3 mol%, still more preferably 4 mol%, and/or preferably no more than 11 mol%, more preferably no more than 10 mol%, preferably no more than 9 mol% of Al ₂ O ₃ .

The content of SiO _{2 to} the content of Al ₂ O ₃ is preferably at least 1.5, preferably at least 2.0, and/or preferably not more than 6.0, more preferably not more than 3.5.

The ratio of the content of SiO _{2 to the} sum of the contents of B ₂ O ₃ and Al ₂ O ₃ (SiO ₂ /Al ₂ O ₃ + B ₂ O ₃ ) is preferably not more than 2.0, more preferably not more than 1.5.

In one embodiment of the invention, the glass comprises all three components, SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ . If all three components are present, in particular in the above-mentioned ratio, the glass has a particularly high degree of crosslinking and thus a particularly high devitrification stability, in particular when reheating. The addition of all three components is advantageous because it crosslinks in different ways in the glass and thus ensures a particularly high devitrification stability.

The sum of the 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 in the glass of the present invention is from 0 to 10 mol% . It is preferably not more than 5 mol%, more preferably not more than 3 mol%, still more preferably not more than 2 mol%, and particularly preferably not more than 1 mol%. In preferred embodiments, no more than 5 mole percent should be exceeded, as otherwise devitrification will occur after the reheating process. However, it is preferred to add at least one alkali metal oxide (especially Na ₂ O) in an amount of at least 0.1 mol%, since the alkali metal oxide can optimize the melting behavior, i.e., it acts as a flux. In addition, it helps to lower the transition temperature _Tg and can be used to fine tune the Abbe number.

In a specific embodiment of the invention, the glass does not contain Li ₂ O and/or Cs ₂ O. Surprisingly, Cs ₂ O can lead to devitrification of the glass system of the invention. Li ₂ O lowers the refractive index and is therefore not as good as a glass component. The glass is preferably free of Li ₂ O.

In order to adjust the viscosity-temperature behavior in a flexible manner, the glass of the present invention may optionally comprise one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO and/or BaO. The proportion of individual components should not exceed 10 mol%, preferably 7 mol%, and particularly preferably 6 mol%. The glass of the present invention may comprise MgO, CaO, SrO or BaO in an amount of at least 0.5 mol%, preferably at least 1 mol%. Alkaline earth metal oxides contribute to steep viscosity curves. The maximum ratio of 10% by mole should not be exceeded, as a higher proportion of the glass will result in loss of vitrification, especially when reheating.

The glass of the present invention may have a ZnO ratio of no more than 10 mol%, preferably no more than 7 mol%, and particularly preferably no more than 5 mol%. ZnO contributes to the desired viscosity-temperature behavior ("short" glass) over a viscosity range from 10 ^7.6 to 10 ¹³ dPas.

However, in a variant of the invention, the glass has a divalent oxide RO ratio of less than 5 mol% (covering alkaline earth metal oxides and ZnO) or even no RO. The addition of the component RO can surprisingly result in a decrease in the refractive index of the glass of the invention and is therefore undesirable.

In a specific 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 comprises an amount of from 0.01 to 20 mol%, preferably at least 0.03 mol%, more preferably at least 0.1 mol%, most preferably 0.3 mol%, and/or preferably no more than 10 mol%, more Preferably no more than 7 mole %, even more preferably no more than 8 mole %, optimally no more than 4 mole % of one or more other components. These other components stabilize the glass from devitrification (ie, crystallization or separation), especially when reheating. In addition, the fine-tuning optical position can be achieved by such components. Preferably, the other components are selected from the group consisting of 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 individually at an individual ratio of at least 0.01 mol%, preferably at least 0.05 mol%, unless otherwise indicated below. The glass of the present invention preferably comprises at least three, more preferably at least four of the other components mentioned above.

The glass of the present invention may have a La ₂ O ₃ content of at least 0.01 and/or no more than 6 mol%, preferably no more than 5 mol%, more preferably no more than 4 mol%. WO ₃ and/or Nb ₂ O ₅ may be present in at least 0.01 mol% in each case and/or in any case no more than 6 mol%, preferably 5 mol%, particularly preferably no more than 4 mol%. In the glass. The optical position can be adjusted by such components. However, if the ratio is large, the glass viscosity will be high.

The glass may comprise TiO ₂ . It may be at least 0.01 mol%, preferably at least 0.2 mol%, more preferably at least 0.5 mol%, and/or no more than 6 mol%, preferably no more than 3 mol%, and particularly preferably no more than 2 mol. The amount of % exists. The addition of TiO ₂ has a positive effect on the high refractive index and can improve the stability of the glass upon reheating. However, this component causes an increase in _Tg and viscosity. Furthermore, it can lead to an increase in the dispersion of the glass and an adverse effect on the transmission of the glass due to absorption in the UV range. Therefore, the content of more than 6 mol% is not good.

ZrO _{2 is} preferably present in a small amount in the glass of the invention, for example at least 0.01 mol%, more preferably 0.04 mol%, and/or preferably no more than 2 mol%, more preferably no more than 1 mol%, The best is no more than 0.05% by mole. When the glass composition is melted in the ZAC tank, ZrO ₂ from the bath material is introduced into the glass melt in a small amount. In a particular embodiment, the glass is free of ZrO ₂ .

In one variation of the glass, the glass comprises at least one of the components TiO ₂ or ZrO ₂ , preferably two components. The total content of TiO ₂ +ZrO ₂ should preferably be at least 0.04 mol%, more preferably at least 0.1 mol%, particularly preferably 0.2 mol%, and/or preferably no more than 5 mol%, more preferably no more than 3. Mole% and best no more than 2 mol%. These components can act as nucleating agents, and therefore the amount is higher than indicated, which is undesirable because of the increased amount which causes the glass to crystallize. However, if it is present in a small amount in the glass, crystallization will only occur under certain conditions, and it can be used in the melting process in a targeted manner, so that, for example, a glass shell is produced on the tank or a crucible wall is generated in the cooling bath. , or use HF during melting and thus avoid contamination of the glass by the trough or crucible material.

The glass may additionally comprise GeO ₂ , preferably in an amount of at least 0.01 mol%, more preferably at least 0.5 mol%, and/or no more than 5 mol%. Cerium oxide has a beneficial effect on the stability of the glass upon reheating. However, the addition of larger amounts of cerium oxide is less preferred and the components are rather expensive. In a particular embodiment, the glass does not contain GeO _2.

Ta ₂ O ₅ may be at least 0.01 mol%, preferably at least 0.05 mol%, more preferably at least 0.1 mol%, and/or no more than 3 mol%, preferably no more than 2 mol%, optimally no more than The proportion of 1 mole is stored in the glass. The glass preferably does not contain Ta ₂ O ₅ .

The 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 no more than 2 mol%, preferably no more 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 may also comprise Ga ₂ O ₃ , preferably in an amount of at least 0.01 mol% and/or no more than 5 mol%. In particular, the total content of Al ₂ O ₃ +Ga ₂ O ₃ does not exceed 11 mol%, more preferably does not exceed 10 mol%.

HfO ₂ may be at least 0.01 mol%, preferably at least 0.03 mol%, particularly preferably at least 0.04 mol%, and/or no more than 1 mol%, preferably no more than 0.5 mol%, and particularly preferably no more than 0.25 mol. The amount of ear % is stored in the glass. This component can be added to adjust the refractive index and Abbe number, and it can be used with other additional components to stabilize the glass to such an extent that the glass does not separate in the reheating process (eg, re-pressing).

Furthermore, the glass may comprise TeO ₂ , preferably at least 0.5 mol%, more preferably at least 1 mol%, even more preferably at least 2 mol%, and/or preferably no more than 10 mol%, more preferably no More than 6% by mole.

Cerium oxide can be present in the glass to adjust the oxidation state. CeO ₂ may preferably be present in a proportion of no more than 1 mol%, more preferably no more than 0.5 mol%, still more preferably no more than 0.25 mol%. However, since this component causes slight discoloration of the glass, the glass is preferably free of CeO ₂ .

In one embodiment, the glass may comprise As ₂ O ₃ , preferably no more than 0.2 mol%, more preferably no more than 0.1 mol%, and/or preferably at least 0.05 mol%, more preferably at least 0.02 mol. %, more preferably at least 0.01 mol%. This component, alone or with a refining agent as described below together with the refining agent, but also to maintain the proper redox state Bi ₂ O ₃ of.

The glass of the present invention may contain small amounts of conventional refining agents. The sum of the addition of the refining agent is preferably not more than 1.0 mol%, more preferably not more than 0.5 mol%. At least one of the following components may be present in the glass of the present invention as a refining agent (in % of moles):

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

In one embodiment, 91% by mole of glass, preferably 95% by mole, is composed of the components Bi ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ and R ₂ O (especially Na ₂ O )composition.

In another embodiment of the invention, preferably at least 95 mole percent, more preferably at least 98 mole percent of the glass of the invention is comprised of the components Bi ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , La ₂ O ₃ , Ta ₂ O ₅ , TiO ₂ , ZrO ₂ , HfO ₂ , GeO ₂ and R ₂ O (especially Na ₂ O).

In one embodiment of the invention, preferably at least 90 mole percent, more preferably at least 95 mole percent, and most preferably at least 99 mole percent of the glass of the invention consists of the above components.

In a specific embodiment of the present invention, the glass of the present invention preferably does not contain other components not mentioned in the scope of the patent application, that is, in this specific example, the glass is substantially composed of the components mentioned. composition. The expression "consisting essentially of" means that the other components are present as impurities at most, and are not intentionally added as an individual component to the glass composition.

The glass preferably contains no components not mentioned above.

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

The invention further relates to high refractive index glasses having improved internal transmission τ _i , especially in the range from λ(τ _ip ) to λ(τ _ip +400 nm) and/or especially after reheating. τ _ip is the internal transmission of the range in the pass range or the extent of internal transmission through the range, and λ(τ _ip ) is above the wavelength at which the glass passes or transmits, for example, the internal transmission is not lower than τ _ip The scope. The variation of the internal transmission τ _i of the glass in the wavelength range from λ(τ _ip ) to λ(τ _ip +400 nm) is preferably not more than 2%, preferably not more than 1%, more preferably not more than 0.9%.

The glass of the present invention preferably has an internal transmission level τ _{ip of} at least 95%, more preferably at least 98% at 600 nm and/or 700 nm.

The inventors have found that in the case of glasses having a high Bi ₂ O ₃ content (ie, a content of at least 40 mol%), the transmission of the glass ranges from λ(τ _ip ) to λ(τ _ip +400 nm). Slightly degraded, that is, after the internal transmission degree τ _ip has been reached at the wavelength λ(τ _ip ), the internal transmission is again slightly reduced in the direction of the longer wavelength to λ (τ _ip +400 nm). This "sag" in the internal transmission curve increases after the glass is reheated to a temperature above the transition temperature. Even if the degradation of internal transmission is only relatively small, specifically 3% or less, the use of glass is still unsatisfactory and should be avoided.

In the case of optical glass, Cr as a coloring substance is not added as a component to the glass unless the glass is a colored glass. However, Cr is present in small amounts in some glass materials. In the prior art, it has been stated so far that Cr, which is present as an impurity in a normal amount, does not cause a problem in bismuth oxide glass. However, the inventors have found that normal Cr contamination of glass can surprisingly affect internal transmission, and if glass has a low Cr content, transmission degradation can be avoided.

Although Cr has an absorption band in the region, the tape cannot explain the "pitching" width in a large wavelength range or the transmission deterioration after reheating. Without wishing to be bound by theory, it is speculated that multivalent Cr interacts with the Bi ions of the glass, and that Cr becomes involved in the redox mechanism of Bi and results in additional transmission degradation. This effect appears to occur especially in glasses with a high cerium oxide content.

Accordingly, the glass of the present invention preferably has a Cr content of not more than 4 ppm, preferably not more than 3 ppm, more preferably not more than 2 ppm.

1 shows the internal transmission curve of a glass according to the present invention according to Example 1, using a conventional material and having a 6 ppm Cr content variant (solid line) and a variant having less than 2 ppm Cr content (dashed line).

Furthermore, the glass of the present invention preferably comprises no more than 3 ppm of platinum component, more preferably no more than 2 ppm and most preferably less than or less than 1 ppm. In order to achieve such preferred values of platinum content, the glass of the present invention is preferably melted in a Pt-free melting apparatus (e.g., in a molten vermiculite tank or ZAC tank). The preferred platinum component so that it can achieve low levels of UV 440 nm of the edge position lower than or equal to (τ _c), unusual for this system in terms of high refractive index glass of the tool.

Fluorine and fluorine-containing compounds also tend to evaporate during the melting or melting process, and thus make it difficult to precisely shape the glass composition. Therefore, the glass of the present invention is preferably also free of fluorine.

The invention further provides a 440 nm, preferably 430 nm, better 425 nm of glass that absorbs edge τ ₅ .

The glass of the present invention has good chemical resistance. In particular, it is possible to achieve an acid resistance AR according to ISO 8424 below grade 52.3 and/or an alkali resistance according to ISO 10629 below 4.3.

The glass of the present invention has an anomalous relative partial dispersion ΔP _g,F of a measurement sample cooled from a cooling rate of about 20 K/hour from 0 to 60 × 10 ^-4 .

The glass of the present invention has a coefficient of thermal expansion of not more than 11 × 10 ^-6 /K, more preferably not more than 10 × 10 ^-6 /K. This avoids thermal stress problems in rework and bonding techniques.

Further, the combination of the crystal stability and the viscosity-temperature distribution of the glass of the present invention substantially allows for problem-free thermal (re)treatment of the glass (pressing or re-pressing and hot rolling).

In particular, such glasses are suitable for near net shape processing, such as the manufacture of precision micelles, as well as precision molding to produce optical components having an exact final shape. In this case, the viscosity-temperature distribution and processing temperature of the glass of the present invention are preferably set such that such a near-final geometry or near-net shape thermoforming can also be performed using a sensitive precision machine.

The invention further provides for the use of the glass of the invention for imaging, projection, communication, optical information technology, mobile hard disk and laser applications.

The present invention further provides an optical component obtained from the glass molding, in particular, an optical component produced by precision molding, and a method of manufacturing an optical component by precision molding the glass.

The invention further provides an optical component comprising the glass of the invention. In particular, the optical element can be a lens, an aspheric component, a crucible and a compact component. In accordance with the present invention, the term "optical element" also encompasses preforms of such an optical element, such as spheres, micelles, precision micelles, and the like.

The invention further provides a method of making the glass of the invention comprising the step of directly inductively heating the mixture and/or oxidizing the molten glass using an alternating electromagnetic field.

For the purposes of the present invention, coupling a melt to an alternating electromagnetic field (especially in the form of a high frequency field) means that the energy input into the melt by inductive coupling is greater than the energy output from the melt by removal of heat. In this way, the melt can only be heated or maintained by high frequency (HF) heating.

Pair of B ₂ O ₃ and SiO ₂ molar ratio is preferably B ₂ O ₃ based sum is at least 0.5. In the case of low alkali or alkali free glass, this ratio is especially needed to ensure coupling to high frequencies. In addition, the low viscosity of glass with a high cerium oxide content facilitates the use of HF heated melt.

Preferably, the method further comprises the following steps: Fragments or mixtures of the foregoing compositions are introduced into a skull crucible.

Preferably, the crucible is made of aluminum. The cold heading makes it possible to melt in the same material, so that a particularly pure glass can be obtained. The mixture can be melted batchwise or continuously in the apparatus.

The method preferably further comprises the steps of: . Liquefaction of a mixture or glass shard by a burner or a Kanthal heater. The high frequency field is coupled to the molten material such that the remaining mixture or debris is melted by heat input.

The glass is then further processed continuously or batch by batch.

This further processing can be carried out in a conventional manner (in platinum) or in the case of particularly aggressive glass, in the second plant using HF heating for refining.

A preferred method is described in DE 10257049 A.

The invention will now be illustrated by a series of examples. However, the invention is not limited to the embodiment.

[Examples]

The following examples show preferred glasses in accordance with the present invention and are not intended to limit the scope of protection to such glasses.

Weigh the raw materials of oxides, addition of one or more refining agents (e.g., Sb ₂ O _3), and subsequently mixed components. The glass mixture is melted in a continuous melting apparatus at about 900 ° C and oxygen is bubbled therethrough (ie, oxygen is introduced into the melt), which is then refined (920 ° C) and homogenized. At a casting temperature of about 890 ° C, the glass can be cast and processed to the desired size. In a large volume continuous device, the temperature can be reduced by at least about 100 K based on experience, and the material can be processed by a profiling process that is close to the final geometry.

The properties of the glass obtained in this manner are shown in Table 2 under Example 1.

In Tables 2 to 4, all the amounts given for the glass are based on the oxides in % by mole.

All glasses according to the invention have a Cr content of less than 2 ppm, a glass transition temperature T _{g of} less than or equal to 420 ° C, 2.05 refractive index n _d , at 10 v _d The Abbe's value v _{d in the} range of 21, the absorption edge τ _{5 of} not more than 430 nm, can be easily processed, reheated to a temperature higher than T _g , and is considerably resistant to acid and alkali. Furthermore, none of the glasses according to the present invention exhibit a deterioration in glass transmission of more than 0.9% in the wavelength range from λ(τ _ip ) to λ(τ _ip +400 nm), and both have an internal transmission of at least 95%.

All transmissions were measured on glass samples having a thickness of 10 mm.

In the table, RHT(T ₁ ) refers to a test that reheats the glass to a temperature at which the glass has a viscosity of 10 ⁹ dPas for at least 20 minutes (preferably 2 hours), and RHT(T ₂ ) refers to reheating the glass to The glass has a temperature test with a viscosity of 10 ⁵ dPas. The abbreviation "p." means passing this test, that is, the glass shows neither devitrification nor turbidity after the test. The abbreviation "np" means that the test has not passed, that is, the glass loses vitrification upon reheating or exhibits turbidity after the test. The reheat test is not carried out under non-oxidizing conditions and is carried out in a normal atmosphere (air).

1 shows the internal transmission curve of the glass according to Example 1, wherein the solid line shows the internal transmission of the glass variant having a 6 ppm Cr content and the dashed line shows the internal transmission of the glass variant having a Cr content of less than 2 ppm.

Figure 2 shows the viscosity curve of the glass according to the invention in accordance with the description of the glass 2. In FIG. 2, vertical lines show the viscosity of this glass 10 from ^7.6 down to a temperature range of 10 ¹³ dPas △ T. In this case ΔT is from 440 to 386 ° C, i.e. it has a value of 54K.

Claims (10)

An optical glass comprising Bi ₂ O ₃ , SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ and comprising the following composition (in mole %, based on oxide): The glass of claim 1, wherein the glass has a Cr content of no more than 3 ppm. The glass of claim 1, wherein 8 to 25 mol% of SiO ₂ , 18 to 34 mol% of B ₂ O ₃ and/or 3 to 11 mol% of Al ₂ O are present in the glass. ₃ . The glass of claim 1, wherein the glass comprises one or more other components selected from the group consisting of 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 Ta ₂ O ₅ , the content of which is 0.03 to 10 ear%. A glass according to claim 1 which comprises As ₂ O _{3 in} an amount of from 0.01 to 0.20 mol% and/or Sb ₂ O _{3 in an} amount of from 0.02 to 0.50 mol%. For example, the glass of claim 1 of the patent scope has The absorption edge τ _{5 of} 430 nm (internal transmission is 5% wavelength). The glass of claim 1, wherein the reduction in internal transmittance of the glass in the wavelength range from λ(τ _ip ) to λ(τ _ip +400 nm) does not exceed 1%. For example, the glass of claim 1 of the patent scope has a n _d 2.2 the refractive index n _d and / or make 10 v _d Abbe number v _{d of} 21 and/or it has a glass transition temperature T _{g of} not more than 420 °C. A use of the glass of any one of claims 1 to 8 in the field of imaging, projection, communication, optical information technology, mobile hard disk and/or laser technology and/or for the manufacture of optical components. A method of producing an optical glass according to any one of claims 1 to 8, which comprises the step of directly inductively heating the mixture and/or oxidizing the molten glass by an alternating electromagnetic field.