GB2321640A

GB2321640A - Lead-free dense and extra-dense optical barium crown glass

Info

Publication number: GB2321640A
Application number: GB9727436A
Authority: GB
Inventors: Danuta Grabowski; Uwe Dr Kolberg; Alwin Weitzel
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 1997-01-30
Filing date: 1997-12-31
Publication date: 1998-08-05
Anticipated expiration: 2017-12-31
Also published as: JPH10212133A; CN1168682C; GB2321640A8; CN1197042A; DE19703391C1; FR2760234A1; GB2321640B; FR2760234B1; JP3148175B2; GB9727436D0

Abstract

Lead-free optical dense and extra-dense barium crown glasses have a refractive index n d of between 1.60, and 1.65 an Abbe number # d of between 49 and 60, and have the following composition (in % by weight, based on oxide): SiO 2 38 - 45; B 2 O 3 5 - 10; BaO 29 - 42; ZnO 0 - 10; CaO 0 - 5; where BaO + ZnO + CaO 35 - 50; TiO 2 1 - 5; ZrO 2 0.5 - 3; where (SiO 2 + TiO 2 + ZrO 2 )/(BaO + ZnO + CaO) 0.84 - 1.35; La 2 O 3 0 - 2.5; Al 2 O 3 1 - 3.5; where La 2 O 3 + Al 2 O 3 2.5 - 3.5; Na 2 O 0 - 2; K 2 O 0 - 6 where Na 2 O + K 2 O 0 - 7. The glasses have very good chemical resistance and very high crystallization stability. Fining agents such as Sb 2 O 3 and/or fluoride may be present in amount up to 0.5 wt%.

Description

2321640 Lead-free dense and extra-dense optical barium crmm glass The

invention relates to lead-free dense and extra-dense optical barium crown glass which has a refractive index nd of between 1.60 and 1.65 and an Abbe number Yd of between 49 and 60.

Since the glass components PbO and As.03 have in recent years come under public discussion as environmentally polluting, some producers of consumer products and optical instruments will go over to using only glasses which are free from PbO and also from As,03. Such glasses having the particular optical properties should therefore be available to the market.

It is also desirable to avoid PbO in the produc- is tion of lightweight glass parts, i.e. from low-density glass.

Simple replacement of lead oxide by one or more constituents generally does not enable reproduction of the desired optical and glass-engineering properties affected by PbO. Instead, new developments or extensive changes in glass composition are necessary.

The patent literature has already revealed numerous documents describing lead-free glasses having the above optical values. However, these glasses have a wide variety of disadvantages.

For example, JP 60-221338 A describes glasses comprising predominantly Y. 031 La203# B.03 and Li.0, while, for example, SiO, is only an optional constituent. The Y.03 and La.03 contents, which can be up to 20% by weight and up to 52% by weight respectively, make the glasses expensive and uneconomic for a continuous production process. The. in a=e cases, very high B203 content (up to 50% by weight) and also the presence of Li20 give the glasses poor chemical resistance, which both makes further treatment more difficult and also restricts their use. The same also applies to the L'20-containing glasses from JP 53-92816 A and JP 54159428 A. Li20 reduces the is crystallization stability of the glasses. The glasses described in JP 3- 5341 A also require L1.0 and in addition relatively high proportions of La203.

A similar situation as for La.03 and Y203 also applies to Nb205. This oxide increases the price of the glass hatch and thus the production costs enormously. It in a crucial constituent of the glasses described in DE 1 496 524 and JP 6-107425 A. The former glasses have fairly high refractive indices (at least l.'65). In the latter glasses, the optical values vary over a broad range; Nb.o. in necessary in these glasses to ameliorate the extremely adverse effects of the in some cases very high alkali metal oxide content (up to 30% by weight) on the chemical resistance and crystallization stability.

The glasses proposed in JP 5-17176 A require SrO. They contain this component in amounts of up to 20% by weight. Since the effect of SrO on the optical properties corresponds approximately to that of BaO and CaO, but the latter components can be incorporated into glass via much cheaper raw materials, it is advantageous for economic production to omit SrO.

It is an object of the invention to find a leadfree dense or extra-dense optical barium crown glass having a refractive index nd of between 1.60 and 1.65 and an Abbe number Yd of between 49 and 60 which has good melting and processing properties, good chemical resistance and such high crystallization stability that the viscosity at the upper devitrification limit is a 1000 dPa.s.

Claims

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

The glass contains 38 - 45% by weight of the glass former SiO.. At lower contents, the crystallization stability and transformation temperature of the glass are reduced, while at higher contents fusibility is impaired and the refractive index is reduced.

Another glass former present is B.03 in an amount of f rom 5 to 10% by weight. This minimum content is necessary to ensure adequate fusibility of the glasses.

The maximum amount mentioned should not be exceeded, since otherwise the refractive index is not achieved and the chemical resistance is adversely affected.

The glass also contains 29 - 42% by weight of BaO. At lower contents, the Abbe number is not achieved, while at higher contents the tendency toward devitrification increases.

In order to improve the crystallization stability and chemical resistance, the glass may also contain up to 5% by weight of Cao and up to 10% by weight of ZnO, although the sum of BaO, ZnO and CaO should be between 35 and 50% by weight, since otherwise the crystallization stability and chemical resistance properties mentioned above are again adversely affected. This sum is particu- is larly preferably limited to a maximum of 49% by weight.

In order to achieve the desired optical values, the glass contains Ti02 in an amount of f rom 1 to 5% by weight and Zr02 in an amount of from 0.5 to 3% by weight.

in addition to the absolute amounts of the individual components, an essential feature of the invention is the weight ratio between the sum of S102P Tú02 and Zr02 and the sum of BaO, ZnO and CaO ((SiO, + T'02 + ZrO,) / (BaO + ZnO + CaO)). This ratio in crucial for the very good chemical resistance of the novel glasses and should be between 0.84 and 1.35. At a weight ratio of < 0.84, the chemical resistance, in particular the acid resistance, drops. The novel glasses are thus very acidresistant (see working examples 7 and 9: acid resistance = 1.0). BY contrast, the commercially available extra dense barium crown glass SSK2, which has a comparable basic glass composition but contains PbO, and has a value of 0.81 for said ratio, belongs to acid resistance class 51.3 with comparatively low acid resistance. At a value of > 1.35, the fusibility of the glass decreases. Although this could be compensated by increasing the contents of B203 and Na.0 andlor K20. this would, however, have the consequence that, firstly, the crystallization stability would be impaired and secondly the desired optical properties would only be achievable at the - 4 expense of other disadvantages. it is particularly preferred to restrict the upper limit of said ratio to 1.34.

The glass contains from 1 to 3.5% by weight of A1203. The minimurn content of this component is necessary both for good crystallization stability and also for good chemical resistance of glass. Exceeding the maximum content impairs fusibility.

In addition, the glass may contain up to 2.'5% by weight of La203. This also improves the chemical resis tance. At a content of > 2.5% by weight, the glass would be difficult to melt. in addition, an excessively high content of the expensive component La.03 would make the glass unnecessarily expensive.

is For these reasons, the sum of La203 and A1,03 should be not more than 3.5% by weight and not less than 2.5% by weight.

This sum is particularly preferably between 2.7 and 3.4% by weight.

in order to improve fusibility, the glass may furthermore contain up to 2% by weight of Na.0 and up to 6% by weight of R20 although the SUM Of X20 and Na20 should not exceed 7% by weight, since otherwise the chemical resistance and crystallization stability would be reduced. Li.0 is omitted entirely. The sum of Na20 and X20 is particularly preferably between 0 and 6.4% by weight.

The balanced contents of S102 and B203 together on the one hand and La203, A1,03. X.0 and Na20 together on the other hand give the glasses excellent crystallization stability. For example, in a preferred embodiment of the invention, the sum S'02 + B203 in between 45 and 50% by weight and at the same time the sum La203 + A1203 + Na20 + K20 should not exceed 10% by weight. This gives glasses which have particularly good crystallization stability.

Within the range claimed in the main claim, there is a preferred glass composition range whose glasses, owing to their balanced combination of components, are notable for good melting and processing properties. This is the following composition range (in % by weight, based on oxide): Si02 38-43; B203 5-9; BaO 29-40; Zno 09; CaO 0-5; T'02 1_ S; Zr02 0.5-3; La203 0-2.5; A1203 1-3.5; Na20 0-2; X20 O-S'S with the above sums BaO + ZnO + CaO 35-50; La.03 + A1203 2.5-3.5; Na20 + X20 0-7 and the above ratio (S'02 + T'02 + ZrO.MBaO + ZnO + CaO) 0.84-1.35. These glasses are extra- dense barium crown glasses having refractive indices n. of between 1.60 and 1.63 and Abbe 10 numbers Yd of between 49.5 and 54. In order to improve the glass quality, one or more fining agents known per se can be added to the batch in conventional amounts in order to refine the glass. This gives the glass particularly good internal quality is regarding freedom from bubbles and streaks. If the f ining agent used is not A5203. but instead, for example, Sb203. which is possible without any reduction in glass quality, the novel lead-free glasses are additionally free from arsenic. 20 in a further preferred embodiment of the invention, the glass contains the following fining agents: 0.1 - 0.5% by weight of Sb203 + F- with 0 0.5% by weight of Sb203 and 0 - 0. 5% by weight of F-, which gives excellent internal glass quality. F- is added, for example, as KF. 25 The novel glass composition range thus provides a further group of lead-free dense and extra-dense barium crown glasses having the above optical properties. These glasses have the following advantages: they have very good chemical resistance, which in of crucial importance 30 for further treatment, such as grinding and polishing, and for the potential uses of glasses, very high crystallization stability, which enables the glasses to be produced in larger melting units, for example in an optical tank, and good ninternalw glass quality. In 35 addition, the glasses are inexpensive to produce, partly because it in unnecessary to use some expensive components. The freedom of the glasses from PbO is important not only for the environmental protection reasons mentioned, but also has a beneficial effect by reducing the 6 - density of the glasses and increasing their transformation temperature. It in furthermore advantageous that the glasses are not only f ree f rom PbO, but also, in a preferred embodiment, are free from As.03.

9 Examples of novel glasses in the preferred composition range were produced from conventional raw materials. Table 2 shows the compositions (in % by weight, based on oxide) and the retractive indices and Abbe numbers, and also examples of further properties of the glasses.

Novel glasses were produced as follows: the raw materials for the oxides, preferably carbonates and nitrates, were weighed out. The fining agent Sb203 Was is added, and the components were then mixed thc.,roughly. The glass batch was fused at about 1300 - 13500C in a con tinuous melter, then refined and homogenized thoroughly.

The glass was converted into the desired dimensions at a casting temperature of 1220C.

Table 1 shows a melt example.

Table 1 Melt example for 100 kg of calculated glass is oxide by wt. Raw material Amount weighed [kg] Si02 41.5 S'02 41.51 B203 8.0 H3BO 3 14.19 BaO 29.6 Ba (N03) 2 33.46 BaC03 13.04 ZnO 3.s ZnO 3.50 CaO 2.1 CaC03 3.71 A1203 1.1 AI(OE)3 1.69 La203 1.8 La.C)3 1.80 T102 4.8 TiO 4.82 Zr02 0.9 ZrO, 0.91 Na20 1.7 NaRC03 4.60 K20 4.7 K2C03 6.90 Sb203 0.3 Sb203 0.29 Sum 100 130.42 The properties of the resultant glass are shown in Table 2, Example 9.

Table 2 Glass composition (in % by weight, based on oxide) and essential properties of glasses:

1 2 3 4 5 6 7 a 9 5102 38.5 39.0 41.20 38.7 38.34 38.99 42.7 41.0 41.5 B'03 6.5 7.1 8.22 6.3 7.31 7.41 5.0 8.0 0.0 BaO 39.6 39c 75 29.64 39.6 38.93 38.40 35.5 29.9 29.6 ZnO 8.5 8.9 3.51 8.5 8.40 8.28 - 3.5 3.5 CaO - 2.01 - - - 4.4 2.0 2.1 A110, 3.0 2.7 1.05 3.0 2.77 2.73 3.0 1.1 1.1 La2O3 - - 2.06 - - - - 2.2 1.8 TIO2 1.1 1.4 4.71 1.3 1.48 1.46 2.5 4.7 4.8 ZrO, 2.5 0.9 0.95 2.3 2.47 2.44 0.9 0.9 0.9 Nalo - - 1.65 - - - 0.5 1.7 1.7 K30 - - 4.71 - - - 5.2 4.7 4.7 Sb20, 0.3 0.3 0.30 0.3 0.3 0.29 0.3 0.3 0.3 (SiO,+TIO,+ZrO.,) (BaO+ZnO+CaO) 0. 875 0.85 1.33 0.88 0.89 0.92 1.155 1.

32 1.34 % 1.62245 1.61912 1.61600 1.62272 1.62226 1.61920 1.60246 1.61679 1.61540 53.48 53.72 49.87 53.17 52.98 53.28 53.54 49.86 49.80 Acid resistance 1.0 1.0 Alkali resistance 2.3 1.3 Density P (q/cmI 3.274 3.263 3.258 Viocoeity at the upper 1500 6500 c 3500 c 1300 devitrification lirait [dPa-al Ir, 125 0.860 0.907 0.919 0.914 0.8671 Key:

Tg: Acid resistance:

Alkali resistance:

r.... =/25 M:

--d Transformation temperature Acid resistance measured in accordance with ISO 8424 Alkali resistance measured in accordance with ISO draft 10629 Net internal spectral transmittance at wavelength X = 400 nm and sample thickness d = 25 mm.

o CIIAIMS is Lead-free dense or extra-dense optical barium crown glass having a refractive index nd of between 1.60 and 1.65 and an Abbe number Yd of between 49 and 60, characterized by the following composition (in % by weight, based on oxide):

S'02 B203 BaO ZnO CaO where BaO + ZnO + CaO 35 - so Ti02 Zr02 where 38 45 29 0 - 0 - 5 42 10 0.5 (Si02 + Ti02 + ZrO,) 0.84 (BaO + Zno + Cao) La203 A1203 where La203 + A1203 Na20 K20 where Na20 + X20 1.35 0 - 2.5 3.5 3.5 2.5 - 0 - 0 - 6 0 - 7 and, if desired, fining agents in conventional amounts.

2) Lead-free dense or extra-dense optical barium crown glass according to Claim 1, characterized in that the sum of La203, A12031 Na.0 and K.0 is less than or equal to 10% by weight, and that the sum of S'02 and B.03 is between 45 and tk 50% by weight.

3) Lead-free dense or extra-dense optical barium crown glass according to Claim 1 or 2, having a refractive index n. of between 1.60 and 1.63 and an Abbe number v,, of between 49.5 and 54, characterized by the following composition (% by weight, based on oxide):

Si02 38 - 43 B203 5 - 9 BaO 29 - 40 ZnO 0 - 9 Cao 0 - 5 TIO2 1 - 5 is Zr02 0.5 - 3 La203 0 - 2.5 A1203 1 - 3.5 Na20 0 - 2 X20 0 - 5.5 and, if desired, fining agents in conventional amounts.

4) Lead-free dense or extra-dense optical barium crown glass according to at least one of Claims 1 to 3, characterized in that the sum of BaO, ZnO and CaO is between 35 and 49% by weight.

5) Lead-free dense or extra-dense optical barium crown glass according to at least one of Claims 1 to 4, characterized in that the sum of La.03 and A1,03 is between 2.7 and 3.4% by weight.

6) Lead-free dense or extra-dense optical barium crown glass according to at least one of Claims 1 to 5, 111-, characterized in that the sum of Na.0 and X.0 is between 0 and 6.4% by weight.

7) Lead-free dense or extra-dense optical barium crown glass according to at least one of Claims 1 to 6, characterized in that the weight ratio (Si02 + Ti02 + zr02) (Bao + ZnO + CaO) is between 0.84 and 1.34.

8) Lead-free dense or extra-dense optical barium crown glass according to at least one of Claims 1 to 7, characterized in that it contains, as fining agents (in % by weight):

Sb203 0 - 0.5 p- 0 - 0.5 where Sb.03 + F- 0.1 - 0.5 9) ...i A Lead-free dense or extra-dense optical barium crown glass according to at least one of Claims 1 to 8, characterized in that it in free from arsenic oxide, apart from unavoidable impurities.

10) Lead-free dense or extra-dense optical barium crown glass according to claim 1, substantially as hereinbefore described in any one of Examples 1 to 9.