DE4032566A1 - Lead-free glass resistant to devitrification - contg. oxide(s) of boron, barium, zirconium, titanium, niobium, tantalum and opt. germanium, silicon phosphorus etc. - Google Patents

Abstract

Lead-free optical glass (I) with negatively deviating anomalous partial dispersion in the blue region of the spectrum, a refractive index nd of 1.69-1.75, an Abbe number of 36-40 and a composition of (in wt.% based on oxide): 0-7 SiO2; 0-3 GeO2; with a total of 0-7 SiO2 + Ge02; 28-38 B203; 0-3 P205; 0-5 R2O, where R20 is 0-3 Li20; 0-0.45 Na2O; and/or 0-0.45 K20; 19-35 RO; where RO is 0-7.5 MgO, 0-10 CaO, 0-10 SrO, 10-35 BaO; and/or 0-10 ZnO; 0-2 Al203; 0-3 La203; 0-3 Y203; 0-3 Gd203; with 0-3 La203 + Y203 + Gd203; 3-11 Zr02; 0-8 Ti02; 0-6 Nb205; with 3-10 Ti02 : Nb205; 15-25 Ta205; 0-2 WO3; 0-1 Hf02; and opt. purification agents. The ratio (Si02+GeO2+B203(/(Ta205+Zr02) is less than 2. ADVANTAGE - (I) is easily melted and has a high stability against devitrification so that it can be reproducibly manufactured in large melt aggregates

Description

The invention relates to a lead-free optical glass with a negative deviating anomalous partial dispersion in the blue region of the spectrum, a refractive index n _d of 1.69-1.75 and a number ν _d of 36-40.

In recent years, optical systems in which the secondary spectrum is greatly reduced have become increasingly important, with the reduction in the blue area in particular taking on an important role. In this area of the spectrum of visible light, the optical behavior of a glass can be characterized by the partial dispersion P ^- _{g, F.}

In order to characterize the dependence of a refractive index on the wavelength of an optical glass, in addition to the refractive index n _d at the wavelength d = 587.56 nm, the dispersion characterized by the Abbe number ν _{d is also} given. The Abbe number is defined as follows:

Here n _{F represents} the refractive index at the wavelength 486.13 nm and n _c the refractive index at the wavelength 656.27 nm. The partial dispersion in the blue region is expressed by the size P ′ _{g, F ′} ′, which are composed of the quantities n _{F ′} (refractive index at 479.99 nm), n _{c ′} (refractive index at 643.85 nm) and n _g (refractive index at 435.83 nm):

The majority of all optical glasses, the so-called "normal glasses", meet approximately the relationship:

P _{x, y} ≈ a _{x, y} + b _{x, y} · ν _d = _{x, y} (3)

The straight line defined by glasses K 7 and F 2 in the diagram P _{x, y} / ν _d , the so-called "normal line", is in the blue region of the spectrum by the equation:

described. Glasses whose partial dispersion does not meet this equation are called glasses with a different partial dispersion. The difference Δ P ′ _{g, F ′} = P ′ _{g, F ′} - ′ _{g, F ′ is} given as a measure of the deviation. If the difference Δ P ′ _{g, F ′} <0, these glasses are referred to as glasses with a negatively differing partial dispersion.

The use of such glasses with a negatively differing partial dispersion is combined with glasses with positive deviating partial dispersion important for the Reduction of the secondary spectrum of lenses. The use of glasses with strongly negative deviating partial dispersions, it allows in imaging Optics greatly reduce the secondary spectrum and so the state of correction to improve the lenses.  

The object of the invention is to find a composition range for optical glasses with a negatively deviating partial dispersion in the blue region of the spectrum, in which the refractive index n _d between the values 1.69 and 1.75 and the Abbe number ν _d between the values 36 and 40 can be varied without losing the negatively deviating partial dispersion in the blue area. Furthermore, the glass should be lead-free in order to keep the density of the glass as low as possible. The glass should be easy to melt and have a high stability against devitrification, so that it can be easily and reproducibly produced even in large melting units.

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

Glasses with similar compositions are already from the prior art known, the generally no negative deviating partial dispersion have. Among these glasses, there are also those that are like this have wide compositional range that the occurrence of a negative Partial dispersion cannot always be excluded. A technical Teaching on the selection of glass compositions with a negative anomalous Partial dispersion is, however, not apparent from these documents.

For example, in DE-PS 28 09 409 a glass with a minimum CaO content of 25 wt .-% described. A negative anomalous partial dispersion is not mentioned, they probably have the glasses because of their high calcium oxide content also not, especially since they are used for ophthalmology will.

DE-PS 14 21 931 describes glasses with anomalous partial dispersion, which on the ternary systems B₂O₃-ZnO-WO₃ / MoO₃ and B₂O₃-CdO-WO₃ / MoO₃ build up and are characterized by particularly high zinc or cadmium oxide contents. Almost all known oxides can be widely used in these basic glasses Limits can be built in without difficulty. A concrete lesson which of these glasses have a negatively differing partial dispersion, is not specified.  

In JP-AS 53-25 323 (07.26.78) an optical glass is described that a high lanthanum oxide content and a minimum amount of ytterbium oxide got to. Glasses containing ytterbium oxide are strong Absorption band at 800-1100 nm and can therefore only be used to a very limited extent.

The glass system according to the invention is built up from the network formers SiO₂ and B₂O₃ and the network converters BaO, ZrO₂, TiO₂ and Nb₂O₅ and Ta₂O₅, whereby Ta₂O₅ in combination with ZrO₂ is responsible for the negative deviating partial dispersion in this glass system. The share of SiO₂ is not absolutely necessary for the existence of the glasses, but leads to small amounts for easier meltability and higher devitrification stability of the glass. At a content above 7 wt .-% SiO₂ there is a risk that the negatively deviating partial dispersion will disappear and the tendency of the glasses to crystallize begins to increase. Prefers are therefore contents between 3 and 7 wt .-% SiO₂, the content of SiO₂ can be replaced without disadvantages up to 3 wt .-% by the related GeO₂. Because of the high cost of germanium oxide, however, one only becomes make use of them in exceptional cases. The glass can continue without noticeable Obtaining disadvantages, have a share of up to 3 wt .-% P₂O₅.

The B₂O₃ content is between 28 and 38% by weight. You also get glassy melting products outside this range, but then the risk that the negatively deviating partial dispersion disappears large. In addition, stability falls below the lower limit of the glass.

To improve the meltability, the glass can contain up to 5% by weight of alkali oxides contain, of the individual alkali oxides not more than 3 wt .-% Li₂O, 4.5 wt .-% Na₂O and 4.5 wt .-% K₂O may be included. The use of other alkali oxides such as Rb₂O and Cs₂O is also possible. However, if a total alkali oxide (R₂O) content of 5% by weight is exceeded, the negatively deviating partial dispersion can disappear. Even the chemical one The resistance of the glass then drops. An alkali oxide content is therefore preferred by Max. 3 wt .-%, wherein it is further preferred if as  Alkaline oxides within this sum limit only lithium oxide in one Amount up to 1.5% by weight and sodium oxide in an amount up to 3 wt .-% are used.

The sum of the alkaline earth oxides + zinc oxide (sum RO) should be between 19 and 35% by weight, the barium oxide content being between 10 and 35% by weight lies. Barium oxide in the range according to the invention has on the glass composition a stabilizing effect and enables high devitrification stability of these glasses. From the total content of the divalent Therefore, the BaO portion of metal oxides can only be partially by others replace divalent metal oxides such as MgO, CaO, SrO or ZnO, the Maximum amount for MgO 7.5% by weight and the maximum amounts for CaO, SrO and ZnO are each 10% by weight. However, preference is given to only BaO is present in the glass in amounts of 19-35% by weight.

A content of 3-11% by weight of zirconium dioxide is necessary to achieve the desired one Partial dispersion required, in addition increases the content of Zirconium dioxide the chemical resistance of the glass. A is preferred Minimum ZrO₂ content of 4% by weight. However, it increases with increasing ZrO₂ content the tendency to crystallize the glass, so that with 11 wt .-% the maximum limit has been reached.

The glass also contains 15-25 wt .-% Ta₂O₅, which is also required is to achieve the desired partial dispersion. It is preferred a minimum content of Ta₂O₅ of 15.5 wt .-%, especially 16 wt .-%.

By adding titanium dioxide of up to 8 wt .-%, the chemical Increase the durability of the glass. In the same way, Nb₂O₅, which can be present in the glass in an amount of at most 6% by weight. With increasing content of TiO₂ or Nb₂O₅, however, the melting temperature increases and the tendency of the glass to crystallize, so that the sum of these two oxides should not exceed 10% by weight. To make sure sufficient chemical resistance, it is also necessary a minimum total content of 3% by weight of these two oxides in the glass to provide.  

A proportion of up to 2 wt .-% Al₂O₃ can be easily introduced into the glass, but it should be noted that the introduction of Al₂O₃ increases the tendency of the glass to crystallize, so that an upper limit of 1.7 wt .-% for the Al₂O₃ content is preferred. La₂O₃ and Y₂O₃ each serve to achieve sufficiently high n _d / ν _d values. La₂O₃, Y₂O₃ and Gd₂O₃ can each be used in amounts of up to 3% by weight, but the total content of these three oxides should not exceed 3% by weight. It is preferred if only La₂O₃ is used. The glass can also get up to 2 wt .-% WO₃ and up to 1 wt .-% HfO₂.

Another is essential to achieve the desired partial dispersion balanced ratio of the proportions of (SiO₂ + GeO₂ + B₂O₃) to (ZrO₂ + Ta₂O₅). If this ratio exceeds the value of 2, the influence becomes the network former SiO₂ and B₂O₃, which the partial dispersion to positive Influence values, no longer by the influence of the oxides Ta₂O₅ and ZrO₂ compensated. A value of less than 2 is preferred for this ratio. Due to the selected limits of SiO₂, B₂O₃, Ta₂O₅, TiO₂ (or Nb₂O₅) and ZrO₂ is also excluded, however, the risk that the The proportion of network formers in the glass composition becomes so low that the desired stability of the glass can no longer be achieved.

The glass can also be used in the usual amounts for optical glass Refining agents included. The oxides of Arsenic, antimony, cerium (IV) compounds and halogens in the form of halides, which are normally used in amounts of up to 1% in total Find. The refining aids can be obtained from the state of the art Technology known compounds (z. B. as BaF₂, LaF₃, BaSiF₆, etc.) in the Glass melt are introduced without the desired optical values in undesirably affect.

It should be particularly emphasized that the glass according to the invention is free of any PbO additives that most other glasses stand out a negative deviating partial dispersion in this optical position area distinguish, have to own. Due to the lack of PbO, the manufacture relieved by low density glass.  

The choice of the borate-containing glass system with low additions of SiO₂ has the advantage that due to the relatively low content SiO₂ the glasses despite the contents of Ta₂O₅ and ZrO₂ at relatively low Melting temperatures can be produced. The melting temperatures play an important role in the attack of the glass melt on the melting vessel Role as this attack has a very strong impact on glass quality and has the production cost. Can attack the melting vessel through a reduction in the melting temperature can be reduced, this leads to an improved glass quality and in addition to saving considerable Amounts of energy.

Examples

The glasses listed in the table were made from common raw materials (Oxides, carbonate, fluorides, etc.) at temperatures from about 1250 ° C to 1300 ° C melted, then refined and homogenized. Then was the melt at a temperature of about 1170 ° C in a preheated Cast mold. The composition and properties of the glasses are listed in the table.  

Table 1

Compositions

Table 1 (continued)

Claims (5)

1. Lead-free optical glass with a negative deviating anomalous partial dispersion in the blue region of the spectrum, a refractive index n _d from 1.69 to 1.75, an Abbe number ν _d from 36 to 40 and a composition (in% by weight based on oxide) of 0-7 SiO₂
0-3 GeO₂
0-7 ΣSiO₂ + GeO₂28-38 B₂O₃
0-3 P₂O₅
0-3 Li₂O
0-4.5 Na₂O
0-4.5 K₂O
0-5 ΣR₂O0-7.5 MgO
0-10 CaO
0-10 SrO
10-35 BaO
0-10 ZnO
19-35 ΣRO0-2 Al₂O₃
0-3 La₂O₃
0-3 Y₂O₃
0-3 Gd₂O₃
0-3 ΣLa₂O₃ + Y₂O₃ + Gd₂O₃3-11 ZrO₂
0-8 TiO₂
0-6 Nb₂O₅
3-10 ΣTiO₂ + Nb₂O₅15-25 Ta₂O₅
0-2 WO₃
0-1 HfO₂ as well as a content of conventional refining aids, with the proviso that the ratio of is 2. Optical glass according to claim 1, characterized by a composition (in wt .-% on an oxide basis) of 3-7 SiO₂
28-38 B₂O₃0-1.5 Li₂O
0-3 Na₂O
0-3 ΣLi₂O + Na₂O
19-35 BaO0-1.7 Al₂O₃
0-3 La₂O₃
4-8 TiO₂
15-25 Ta₂O₅4-11 ZrO₂ as well as a content of conventional refining aids, with the proviso that the ratio of is 3. Optical glass according to claims 1 or 2, marked by a content of 15.5-25 Ta₂O₅. 4. Optical glass according to at least one of claims 1-3, marked by a content of 4-10.5 ZrO₂.   5. Optical glass according to at least one of claims 1-4, marked by a content of 16-25 wt .-% Ta₂O₅.