GB2337046A

GB2337046A - Lead-free lanthanum crown or flint glasses

Info

Publication number: GB2337046A
Application number: GB9909134A
Authority: GB
Inventors: Danuta Grabowski; Uwe Kolberg; Silke Wolff; Magdalena Winkler-Trudewig
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 1998-05-06
Filing date: 1999-04-21
Publication date: 1999-11-10
Anticipated expiration: 2019-04-21
Also published as: DE19820072C1; MY122335A; FR2778398B1; CN1234376A; FR2778398A1; JP4213293B2; CN1200898C; GB9909134D0; GB2337046B; JP2000026133A

Abstract

Lead-free lanthanum crown or flint glasses have a refractive index n d of between 1.66 and 1.76 and an Abbe number v d of between 46 and 57, and have a composition (in % by weight, based on oxide) of SiO 2 1 - 9; B 2 O 3 29 - 43.5; La 2 O 3 27 - 40; CaO 5.5- 10; SrO 0 - 3.5; MgO 0 - 4.5; ZnO 3.5 - 10; TiO 2 0.1 - 3.5; ZrO 2 3.5 - 9; and, optionally, one or more fining agents.

Description

- 1 2337046 Lead-f ree lanthanum crown glasses and lanthanum f lint

glasses The invention relates to lead-free lanthanum crown glasses and lanthanum flint glasses which have refractive indices nd of between 1.66 and 1.76 and Abbe numbers Vd of between 46 and 57.

Since the glass components PbO and AS203 have come into public discussion as being environmental pollutants, there is a need amongst the manufacturers of optical instruments for Pbofree and preferably also AS203 - f ree glasses having the respective optical properties.

Simple replacement of lead oxide by one or more constituents does not generally result in reproduction of the desired optical and glass -technology properties affected by Pbo. Instead, new developments or extensive modifications to the glass composition are necessary.

The prior art can be regarded as being, in particular, the specifications discussed below, which describe lead-free glasses having optical values from these and adjacent regions, but which have a wide variety of disadvantages:

DE-Bl 061 976 describes a basic glass from the B203 - Si02 - La203 system which has a high La203 content, and glasses made from this basic glass with addition of aluminium oxide and/or yttrium oxide and metal oxides, in particular alkaline earth metal oxides, zirconium oxide, zinc oxide and/or cadmium oxide or which have only low B203 contents in the only optional presence of A1203 and Y203 and other additives. These glasses are very expensive, owing to these components, are difficult to melt or have inadequate devitrification stability.

British Patent 1,136,239 describes an electro luminescence lamp containing a glass comprising an oxide of a rare-earth metal, a glass former oxide and a divalent metal oxide in which the phosphor is embedded. The possible components and their proportions by weight, including further additives, vary over a very broad range. Such glasses do not meet the high demands 5 of optical glasses.

JP 55-121925 A discloses lanthanum dense flint glasses, i.e. glasses having high refractive indices and low Abbe numbers, which contain ZnO and Sro and/or BaO as divalent metal oxides. Further possible additives are MgO and small amounts of CaO. Si02 is also only an optional constituent. These glasses, which have a different optical position to that desired here, likewise do not exhibit good devitrification stability.

German Patent 22 65 703 C2 discloses optical glasses comprising the B203 Gd203 - La203 system. For stabilization against devitrification, the glasses require at least 2% by weight and up to 50% by weight of Gd203. The presence of this expensive component in these large amounts makes the glasses much more expensive.

JP 62-100449 A discloses glasses which require up to 2% by weight of Sb203. If this component is used in such amounts, increased safety precautions are necessary during production to protect the personnel involved, and the transmission of the glasses is greatly reduced. The glasses furthermore necessarily contain Li20, which increases their devitrification tendency.

The glasses of JP 60-221 338 A likewise neces- sarily contain Li20. In addition, they require up to 20% by weight of the very expensive component Y203 in addition to La203 in order to modify the refractive index. The high ZnO-content glasses of JP 54-6243 B also contain Y203.

The glasses mentioned in JP 53-4023 A require Hf02. This component, which is used as a replacement for La203, also makes the glasses much more expensive.

It is an object of the invention to find leadfree optical lanthanum crown glasses and lanthanum flint glasses having a refractive index nd of between 1.66 and 1.76 and an Abbe number Vd of between 46 and 57 which have good melting and processing properties and are inexpensive to produce. This also includes the requirement for adequate crystallization stability.

This object is achieved by the glasses

Claims

described in Claim 1.

The glasses contain from 29 to 43.5% by weight (preferably at most 43% by weight) of the glass former B203. At higher contents, the chemical resistance would be impaired. Owing to the high minimum B203 content, the content of the glass former Si02 can remain restricted to 1 - 9% by weight. This only 1OW Si02 content firstly has a positive effect on the melting properties of the batch, i.e. the melting point is reduced, and the melting time drops. Secondly, the introduction of relatively large amounts of lanthanum oxide is facilitated.

This is because the glasses contain from 27 to 40% by weight (preferably from 29 to 40% by weight) of La203. This range facilitates the desired optical position, in particular moderate Abbe numbers at the same time as high refractive indices. In addition, La203 increases the transmission of glasses and promotes their crystallization stability. A further increase in the La203 content would result in different nd and Vd values and an unnecessary increase in the cost of the batch.

The glasses contain from 0.1 to 3.5% by weight (preferably from 0.1 to 3% by weight) of Ti02 and from 3.5 to 9% by weight (preferably from 4 to 9% by weight) of Zr02. In these minimum contents, these two com ponents improve the chemical resistance. They thus not only facilitate said high B203 content, but also even result, surprisingly, in improved alkali and acid resistance of the glasses, compared with the conventional lead-containing glasses having the optical position.

same The glasses contain from 3.5 to 10% by weight (preferably from 4 to 10% by weight) of ZnO. In this minimum content, the staining resistance is improved and the devitrification tendency reduced.

Although an increase in the contents of Ti02, Zr02 and ZnO above the maximum value given in each case would initially have a further positive effect on the devitrification properties, i.e. further improve the devitrification stability, it would, however, adversely affect the melting properties of the batch.

In order instead to achieve high devitrifi cation stability substantially independently of the melting properties, the glasses contain CaO in amounts of between 5.5 and 10% by weight (preferably between 5.5 and 9.5% by weight) At a lower content, the devitrification stability of the glasses would be reduced, while at a higher content, the chemical resistance would be reduced.

In order to improve the devitrification stability further, the glasses may contain up to 3.5% by weight (preferably up to 3% by weight) of SrO and up to 4.5% by weight (preferably up to 4% by weight) of MgO. If the respective maximum contents were exceeded, the chemical resistance would again be impaired.

In a specific embodiment of the invention, the lanthanum crown glasses and lanthanum flint glasses contain no SrO or MgO. These glasses contain relatively little ZnO (at most 6% by weight) and relatively little CaO (at most 7.5% by weight) and at least 35% by weight of La203.

They therefore preferably contain (in % by weight, based on oxide) Si02 1 9; B203 29 43; La203 - 40; CaO 5.5 - 7.5; ZnO 4 6; Ti02 0.1 3; Zr02 4 9, and have refractive indices nd of between 1.69 and 1.76 and Abbe numbers Vd of between 46 and 54.

In another specific embodiment of the invention, the glasses contain Sro and/or MgO, more precisely at least 0. 1% by weight of SrO + MgO. Such glasses have the advantage over MgO- and SrO-free glasses of somewhat improved devitrification stability and lower density. within this group of glasses, firstly SrOcontaining, MgO-free glasses represent a specific variant of the invention. They differ from the Srofree, Mgo-containing glasses described below through lower density and a lower coefficient of thermal expansion and preferably have the following composition (in % by weight, based on oxide):

Si02
2.5 - 4. 5 (preferably 2.5 - 4); B203 35 (preferably > 35) - 42 (preferably 37 - 40) La203 31 - 40 (preferably 32 - 38) Cao 6 - 8 (preferably 7 - 8); Sro 0.1 - 2 (preferably 0.5 - 1.5); Zno 4.5 - 7.5 (preferably 5 - 7); Ti02 0.5 - 2. 5 (pref erably 1 2. 5) Zr02 5 - 9 (pref erably 6 7) The glasses have refractive indices nd of between 1.69 and 1.75 and Abbe numbers Vd of between 48 and 54. The optical data of the glasses having the preferred compositions are 1.70:! nd:5 1.72 and 48:5 Vd:5 51.

Secondly, the abovementioned Mgo-containing, Srofree glasses represent a specific embodiment of the invention. They preferably have the following composition (in % by weight, based on oxide): Si02, 5 (preferably > 5) 7.5; B203 30 - 39: La203 30 30 39; CaO 6 - 8; MgO 1 3; ZnO 6 - 9; Ti02 0.5 - 2.5; Zr02 5 - 8.

The glasses have refractive indices nd of between 1.69 and 1.75 and Abbe numbers Vd of between 48 and 54.

Within the composition range mentioned in the main claim, there are furthermore two preferred groups of glasses which differ in their Ti02 content.

These are firstly Mgo-containing glasses having Ti02 contents in the upper region of the range claimed overall, namely glasses having the composition (in % by - 6 weight, based on oxide): Si02
3. 5
4. 5; B203 41 43; La203 27 - 41; CaO 8 - 10; MgO 3.
5 4.5; ZnO 3.5 - 4.5; Ti02 2.5 - 3.5; Zr02 3.5 4.5. The glasses have refractive indices nd of between 1.68 and 1.70 and Abbe numbers Vd of between 49 and 51.

The second group comprises MgO- and SrOcontaining glasses having low Ti02 contents. These glasses having the composition (in % by weight, based on oxide) Si02 3.5 - 4.5; B203 41 - 43; La203 27 31; CaO 8.5 - 9.5; SrO 2.5 3.5; MgO 3.5 - 4.5; ZnO 3.5 4.5; Ti02 0.1 - 1; Zr02 3.5 - 4.5 are lanthanum crown glasses having Abbe numbers Vd of between 54 and 56 and refractive indices nd of between 1.66 and 1.69.

In order to improve the glass quality, one or more f ining agents known per se can be added to the batch in conventional amounts for fining the glass. The glass thus has particularly good internal glass quality with respect to freedom from bubbles and streaks.

If the fining agent used is not AS203, but instead, for example, Sb203, preferably in amounts of up to 0.3% by weight, which is possible without losses in respect to the glass quality, the lead-free glasses according to the invention in addition contain no arsenic.

The invention manages to produce glasses which have the desired optical properties and are also free from alkali metal oxides, BaO, A1203, Nb205, Y203 and Ta203, apart from the usual impurities. This has various advantages, for example for the melting properties and the crystallization stability and for low production costs of the glasses.

The novel glasses have the following advantages:

The glasses contain no Pbo and in a preferred embodiment also contain no AS203. Compared with conventional PbO-containing glasses but the same optical position, they are "longer", i.e. the temperature range in which the glasses can be processed is greater.

is - 7 The glasses have high chemical resistance, especially very high alkali resistance. Thus, compared with conventional Pbo-containing glasses of the same optical position, they have both improved acid resistance (for example glass No. 8 [see Examples and Table 2] has acid resistance class 52.0 instead of 52.3 [Pbo-containingl) and improved alkali resistance (for example glass No. 8 has alkali resistance class 1.0 instead of 1.2 [Pbo-containingl). The high chemical resistance of the glasses is important for their further mechanical treatment, such as grinding and polishing.

The glasses have high crystallization stability. This enables the glasses to be produced in relatively large melting equipment, for example in an optical tank furnace. A measure of the crystallization stability is the upper devitrification limit or the viscosity at this temperature. For continuous production, it should be: 1000 dPas. This is achieved by the novel glasses.

The glasses are easy to melt and process. The 3 density of the glasses, at:5 4.0 g/cm, is relatively low.

Examples:

Eight examples of novel glasses were produced from conventional raw materials.

Table 2 shows the respective composition (in % by weight, based on oxide), the refractive index nd, the Abbe number Vd, the density p [g/CM3], the coefficient of thermal expansion (X201300 [ 10-
6 /K] and the glass transition temperature Tg [OCI of the glasses.
The novel glasses were produced as follows: the raw materials for oxides, preferably carbonates and oxides, were weighed out. The fining agent was added, and the components were then mixed well. The glass batch was melted at about 1200 - 13600C, then fined and homogenized well. The casting temperature was 1000 10800C.
8 Table 1 shows a melt example.

Table 1 oxide melt example for 100 kg of calculated glass % by weight Raw material Initial weight [kg] 5i02 1.0 Si02 1.00 B203 42.9 H3B03 76.23 CaO 5.5 CaC03 9.75 Ti02 0.1 Ti02 0.10 ZnO 5.00 ZnO 5.01 ZrO2 5.4 Zr02 5.51 La203 40.0 La203 40.08 Sb203 0.10 Sb203 0.10 The properties of the resultant glass are shown in Table 2, Example 1.
9 - Table 2 Glass compositions (in % by weight, based on oxide) and main properties of the glasses 2 3 4 5 6 7 8 Si02 1.0 8.9 3.9 9.0 3.9 2.9 3.7 6.2 B203 42.9 29.0 42.9 29.9 43.0 38.8 38.8 34.6 CaO 5.5 9.0 9.0 5.5 9.0 7.5 7.5 7.5 Sro - 3.0 3.0 - - 1.0 1.0 - M90 - 4.0 4.0 - 4.0 - - 2.0 ZnO 5.0 10.0 4.0 4.0 4.0 5.9 5.9 7.5 Ti02 0.1 0.1 0.1 3.0 3.0 2.5 1.5 1.4 Zr02 5.4 6.9 4.0 8.5 4.0 6.1 6.4 6.5 La203 40.0 29.0 29.0 40.0 29.0 35.2 35.1 34.3 Sb203 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Vd p[g/cir] 3.66 (X201300 6.50 [10-'/K1 Tg[OCI 1.7033 1.7086 1.6752 1.7481 1.6898 1.7144 1.7091 1.7182 53.78 51.47 55.39 46.43 50.55 48.20 50.1050.16 3.70 3.41 3.88 3.39 3.02 3.00 3.70 7.56 6.99 6.87 6.73 4.86 4.81 6.98 646 615 634 652 634 713 713 622 CLAIMS 1. A lead-free lanthanum crown glass or lanthanum flint glass, said glass having a refractive index nd of between 1.66 and 1.76 and an Abbe number Vd of between 46 and 57, characterized by the following composition (in % by weight, based on oxide) 5i02 1 - 9 B203 29 - 43.5 1a203 27 - 40 CaO 5.5 - 10 SrO 0 - 3.5 Mgo 0 - 4.5 ZnO 3.5 - 10 Ti02 0.1 3.5 Zr02 3.5 - 9 and, optionally, one or more fining agents.

2. A glass according to claim 1, characterized by the following composition (in % by weight, based on oxide) Si02 B203 La203 CaO SrO Mgo ZnO 1 - 9 29 29 5.5 0 0 4 - 10 43.5 9.5 - 3 11 T'02 Zr02 0.1 3 4 9 and, optionally, one or more fining agents.

3. A glass according to claim 1 or 2, having a refractive index nd Of between 1.69 and 1.76 and an Abbe number vd of between 46 and 54, characterized by the following composition (in % by weight, based on oxide) S'02 1 - 9 B203 1a203 CaO ZnO Ti02 Zr02 29 5.5 4 6 0.1 3 4 9 43 40 7.5 and, optionally, one or more fining agents.

4. A glass according to claim 1 or 2, characterized in that it contains a total of at least 0. 1 % by weight of SrO and/or MgO.

e 5. A glass according to claim 1, 2 or 4, having a refractive index nd Of between 1.69 and 1.75 and an Abbe number vd of between 48 and 54, characterized by the following composition (in % by weight, based on oxide) 12 Si02 B203 La203 CaO SrO ZnO Ti02 Zr02 and, optionally, one or more fining agents.

2.5 4.5 42 40 31 6 8 0.1 2 4.5 0.5 7.5 2.5 - 9 6. A glass according to claim 5, having a refractive index ndof between 1. 70 and 1.72 and an Abbe numberVdof between 48 and 51, characterized by the following composition (in % by weight, based on oxide) S'02 B203 La203 CaO SrO ZnO Ti02 Zr02 2.5 37 32 38 7 8 0.5 1.5 7 1 2.5 6 and. optionally, one or more fining agents.

7 7. A glass according to claim 1, 2 or 4, having a refractive index nd Of between 1.69 and 1.75 and an Abbe numberVdof between 48 and 54, 13 characterized by the following composition (in % by weight, based on oxide) Si02 B203 La203 CaO Mgo ZnO T'02 Zr02 and, optionally, one or more fining agents.

7.5 30 39 30 39 6 1 6 8 3 9 0.5 - 2.5 - 8 8. A glass according to claim 1, having a refractive index nd of between 1.68 and 1.70 and an Abbe number Vd of between 49 and 51, characterized by the following composition (in % by weight, based on oxide) S'02 3.5 - 4.5 B203 41 - 43 1a203 27 - 31 CaO 8 - 10 Mgo 3.5 - 4.5 ZnO 3.5 - 4.5 Ti02 2.5 - 3.5 Zr02 3.5 - 4.5 and, optionally, one or more fining agents.

14 9. A glass having a refractive index nd of between 1.66 and 1.69 and an Abbe number Vd of between 54 and 56, characterized by the following composition (in % by weight, based on oxide) Si02 3.5 - 4.5 B203 41 - 43 La203 27 - 31 CaO 8.5 - 9.5 SrO 2.5 - 3.5 Mgo 3.5 - 4.5 ZnO 3.5 - 4.5 Ti02 0.1 - 1 Zr02 3.5 - 4.5 and, optionally, one or more fining agents.
10. A glass according to any one of claims 1 to 9, containing 0 - 0.3% by weight of Sb203.
11. A glass according to any one of claims 1 to 10, containing no arsenic oxide, apart from unavoidable impurities.
12. A glass according to any one of claims 1 to 11, containing no niobium oxide, aluminium oxide, barium oxide and alkali metal oxides, apart from usual impurities.