GB2342918A

GB2342918A - Lead-free optical glasses

Info

Publication number: GB2342918A
Application number: GB9922412A
Authority: GB
Inventors: Uwe Kolberg; Danuta Grabowski; Magdalena Winkler-Trudewig; Silke Wolff
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 1998-10-19
Filing date: 1999-09-23
Publication date: 2000-04-26
Anticipated expiration: 2019-09-23
Also published as: HK1029098A1; FR2784676A1; GB9922412D0; JP2000128568A; MY124408A; JP3347106B2; GB2342918B; DE19848077C1; CN1252391A; FR2784676B1; CN1152836C

Abstract

Lead-free optical glasses having a refractive index n<SB>d</SB> of between 1.64 and 1.83 and an Abbe number n <SB>d</SB> of between 36 and 56, have a composition (in % by weight, based on oxide) of SiO<SB>2</SB> 10-25; B<SB>2</SB>O<SB>3</SB> 8-20; ZrO<SB>2</SB> 1-5; TiO Þ 1-5; La<SB>2</SB>O<SB>3</SB> 10-30; BaO 30-50; ZnO 0.1-2; CaO 0.5-2; WO<SB>3</SB> 0.1-2; Nb<SB>2</SB>O<SB>5</SB> 0.1-5; Y<SB>2</SB>O<SB>3</SB> 0.1-3; Gd<SB>2</SB>O<SB>3</SB> 0-1; Na<SB>2</SB>O 0-1; K<SB>2</SB>O 0-1 and optionally at least one refining agent such as 0.1-5 wt % Sb<SB>2</SB>O<SB>3</SB> or 0-0.5 wt % fluoride.

Description

2342918 Lead-free optical glasses The invention relates to lead-free

optical glasses which have refractive indices nd of between 1.64 and 1.83 and Abbe numbers Vd of between 36 and 56.

Since the glass components PbO and AS203 have entered public debate as being environmental pollutants, there is a demand amongst the manufacturers of optical equipment for Pbo-free and preferably also AS203-free glasses having the respective optical properties.

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

The patent literature reveals some specifications which also describe lead-free glasses having optical values from the above range and having similar compositions. However, the glasses have a wide variety of disadvantages.

The patent specifications DE 22 65 703 C2 and US

3,958,999 disclose optical glasses comprising the system B203 - Gd203 La203. The glasses require at least 2% by weight and up to 50% by weight of Gd203 for stabilization against devitrification. The presence of this expensive component in these large quantities makes the glasses much more expensive. In specific embodiments, the glasses of US 3,958,999 additionally contain at least 2% by weight of the likewise expensive component Ta,20.5.

The glasses of JP 61-146" j'30 A and JP 60-221 338 A necessarily contain Li20, which increases their devitrification tendency. The glasses of the last- 2 mentioned specification additionally require up to 20% by weight Of Y203 and up to 52% by weight of La203, both likewise expensive components, in order to achieve the desired refractive indices; this makes the glasses 5 expensive and uneconomic for tank production.

The German Patent Specification DE 32 01 344 C2 discloses high-refractiveindex glasses which, with 15-22% by weight of Ti02 + Nb205 + Y203, contain high proportions of meltability-impairing (Ti02) and expensive components (Nb205, Y203) and a large amount of CaO (4 - 18% by weight), while BaO is only an optional component with a maximum of 14% by weight.

The object of the invention is to find lead-free optical glasses having a refractive index nd of between 1.64 and 1.83 and an Abbe number Vd of between 36 and 56 which ate inexpensive to produce and have good melt and processing properties. This also includes the requirement for adequate cr ystallization stability.

Claims

- This object is achieved by the glasses described in Claim 1. 25 The

glasses contain the glass formers Si02 (10-25% by weight) and B203 (8-20% by weight) in balanced proportions. Thus, both the meltability of the glasses, which improves with increasing B203 content and worsens with increasing SiO2 content, and their chemical 30 resistance, which would be impaired at an excessive B203 content, are good. A reduction in said minimum B203 content would result in the devitrification tendency increasing excessively. 35 The glasses contain 30-50% by weight of BaO. This content of BaO is needed in order to achieve the desired Abbe number range.- Especially due to the balanced contents of B203 and Si02 in relation to the

BaO content, the meltability of the glasses is particularly good. In addition to BaO, the glasses contain 0.5-2W by weight of CaO and 0.1-2% by weight of ZnO. Their presence alongside BaO improves the crystallization stability of the glasses.

The glasses contain both Ti02 and Zr02 in proportions of from 1 to 5% by weight each. These two components improve the chemical resistance, in particular the alkali resistance. At higher contents, the crystallization stability would be reduced.

It is particularly preferred for the glasses to contain Zr02 and Ti02 in similar proportions; this can be expressed by a preferred Zr02/TiO2 weight ratio of from 0.8 to 1.0.

The glasses contain 10-30% by weight of La203. This range facilitates the desired optical position, in particular moderate Abbe numbers with high refractive indices. In addition, La203 increases the transmission of the glasses and promotes their crystallization stability. A further increase in the La203 content would result in different rid and Vd values and make the batch unnecessarily more expensive.

For variation and precise tuning of the low Abbe number at high refractive index, the glasses contain 0.1-2% by weight of W03, 0.1-5% by weight of Nb205 and 0.1-3% by weight Of Y203 and can also contain up to 1% by weight of Gd203. The total amount of these four components is preferably greater than 5% by weight.

In order further to improve the meltability, the glasses can also contain up to 1% by weight of Na20 and up to 1% by weight of K20. At higher contents, the crystallization tendency would be increased. For the same reason, Li20 is omitted entirely.

Within said composition range, a distinction can be made between two groups of glasses, depending on the refractive index:

These are firstly glasses having refractive indices nd of between 1.64 and 1.75, which contain at least 25% by weight of Si02 + B203 and at most 60% by weight of Bao + La203, with the maximum amount of La203 being 25% by weight.

The second group consists of glasses having refractive indices nd of between 1.75 and 1.83. They contain a maximum of 25% by weight Of Si02 + B203, 10-17% by weight Of Si02 and 8-15% by weight Of B203 and at least 15 60% by weight of BaO + La203, the amount of La203 being at least 15% by weight. Within the composition range of the main claim, there is Pne group of glasses having refractive indices nd of 20 between 1.71 and 1.75 and Abbe numbers Vd of between 42 and- 46 which are distinguished by their chemical resistance and their crystallization stability. These glasses have the following compositions:

Sio, 15-21 (particularly preferably 15 -17) B203 10-15 (particularly preferably 12-15); Zr02 1-4 (particularly preferably 2-3); TiO, 1-4 (particularly preferably 2 -3); preferably where Si02+ Zr02 + Ti02 19-23; La203 15-25 (particularly preferably 19-22); BaO 30-43 (particularly preferably 37-39); ZnO 0.1-1; CaO 0.5-1; where BaO + ZnO + CaO: 31 (preferably 37.6-41); Nb205 2-5 (particularly preferably 2 -4) Y20, 0.1-2 (particularly preferably 0.5-1-5); Gd203 0-1; where Y,03 + Gd,O, 2! 0.2 (preferably Z 0.6-2.5); Na20 0-1; K20 0-1; The optical data of glasses having the respective compositions mentioned as preferred are nd between 1.73 and 1.75 and Vd between 44 and 46.

The weight ratio between the sum of Si02 and B203 and the sum of BaO, ZnO and CaO ( (Si02 + 13203) / (BaO + ZnO + Cao)) is preferably between 0.5 and 1. In this range, the crystallization stability of the glasses is particularly good. In particular for the glasses described as preferred (1.71:5 nd:5 1.75, 42:5 Vd:5 46), - a ratio of:5 1 is particularly advantageous; the preferred minimum value of at least 0.5 is satisfied in them. The glasses described as particularly preferred (1.73:5 Vd:5 1.75; 44:5 Vd:5 46) already have such balanced amounts of these components that this preferred range indication is satisfied for this ratio.- In order to improve the glass quality, one or more refining agents known per se can be added in conventional amounts to the batch in order to refine the glass. In this way, the glass has particularly good internal glass quality with respect to freedom from bubbles and streaks.

If the refining agent used is not AS203, but instead, for example, Sb203, which is possible without losses with respect to the glass quality, the lead-free glasses according to the invention are in addition arsenic-free.

The Sb203 content is preferably between 0.1 and 0.5% by weight. It is furthermore preferred for the glasses, optionally in addition to Sb203, to contain up to 0.5% by weight of fluoride, which likewise has a refining action. Fluoride is added, for example, as CaF2 or NaF.

Besides the desired optical properties, the glasses according to the invention have the following advantages:

The glasses are PbO-free and in a preferred embodiment also As203-free. The glasses have good crystallization stability. This enables production in a continuous melter. A measure of adequate crystallization stability for such production is the viscosity of the upper devitrification limit. For continuous production, it should be Z: 1000 dPas. This is satisfied in the glasses according to the invention. Such crystallization stability of the glasses also enables further thermal treatment of the glasses, such as pressing or re- pressing.

The glasses not only have good processing properties, but also good melting properties. This is also shown by their melting point of about 13000C.

The glasses have excellent alkali resistance, documented by their presence in alkali resistance class AR = 1, at the same time as adequate general chemical resistance. The chemical resistance of the glasses is important for their further treatment, such as grinding and polishing.

Examples:

Nine examples of glasses according to the invention 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 partial dispersion in the blue region of the spectrum P,,V -and the anomalous partial dispersion A Pg, F [10-'], the density p [g/CM3], the - 7 coefficient of thermal expansion a20,300 [10-6/K] and the glass transition temperature T. [OCI of the glasses.

The glasses according to the invention were produced as follows: the refining agent was added to theraw materials for the oxides, preferably carbonates or nitrates, and the batch was subsequently mixed well.

The batch was melted in a batch melter at melting temperatures between 12200C and 13600C, then refined and well homogenized. The casting temperature was about 10500C.

Table 1 shows a melt example.

Table 1 Melt example for 100 kg of calculated glass Oxide % by wt. Raw Weight material (kg) Si02 10.0 Si02 9.22 B203 12.0 H3BO3 19.64 La203 15.0 La203 13.85 Gd203 0.45 Gd203 0.42 Y203 0.1 Y203 0.09 Ti02 5.0 Ti02 4.63 ZrO2 3.0 Zr02 2.82 CaO 0.7 CaCO.3 1.14 ZnO o.3 ZnO 0.28 BaO 50.0 BaCO:3 40.14 Ba W03) 2 26.22 2.75 Nb205 2.54 o.2 Sn203 0.2 The properties of the resultant glass are shown in Table 2, Example 3. Examples 6 and 7 are compositions close to the limits of the claimed composition range and also represent the extremes amongst the examples - 8 with respect to refractive index and Abbe number. However, their physical properties correspond with those of the glasses from the narrower preferred composition ranges.

9 Table 2 Glass compositions (in % by weight, based on oxide) and essential properties of the glasses 1 2 3 4 5 6 7 a 9 Si02 16.15 20.0 10.0 20.0 16.25 11.0 24.9 10.0 16.55 B203 13.0 20.0 12.0 20.0 13.0 9.0 20.0 9.0 13.05 La203 20.8 25.0 15.0 15.0 20.7 29.0 10.0 30.0 21.8 Gd203 0.5 0.45 0.45 0-.45 0.5 0.45 0.45 0.45 - Y203 1.15 0.1 0.1 0.1 1.15 1.0 0.1 0.1 0.2 Ti02 2.7 1.0 5.0 5.0 2.7 5.0 1.0 2.0 2.75 ZrO2 2.3 1.65 3.0 2.75 2.3 5.0 1.5 2.25 2.4 CaO 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 ZnO 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 BaO 38.2 30.0 50.0 30.0 38.2 32.75 40.0 39.5 38.1 W03 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Nb205 3.4 0.1 2.75 5.0 3.4 5.0 0.25 5.0 3.45 Sb203 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 nd 1.7434 1.6868 1.7682 1.7130 1.7427 1.8231 1.6574 1.7952 1.7440 Vd 44.59 52.82 40.52 42.81 44.56 37.84 54.74 41.22 44.85 P9, F 0.5659 0.5509 0.5732 0.5685 0.5659 0.5773 0.5491 0.5700 0.5656 APq, F [ 10 -4 -29 -41 -24 -33 -30 -29 -26 -45 -27 P [g/CM3] 3.74 3.95 4.50 3.80 3.73 4.26 3.74 4.77 4.30 C420/300 [10- 6] /K1 8.05 7.85 10.51 7.25 8.02 9.25 7.64 10.47 9.10 Tq[OCI 676 645 596 646 676 695 648 643 653 CLAIMS 1. A lead-free optical glass having a refractive index ndof between 1.64 and 1.83 and an Abbe numberVdof between 36 and 56, characterized by the following composition (in % by weight, based on oxide):

Si02 10-25 B203 8-20 Zr02 1-5 Ti02 1-5 La203 10-30 BaO 30-50 ZnO 0.1-2 CaO 0.5-2 Nb205 0.1-5 Y203 0.1-3 Gd203 0-1 Na20 0-1 K20 0-1 and, optionally, at least one refining agent.
2. A lead-free optical glass according to claim 1, having a refractive index nd of between 1.64 and 1.75, characterized by the following composition (in % by weight, based on oxide):

-1 Si02 10-25 B203 8-20 whereSi02 + B203: 25 Zr02 1 -5 Ti02 1 -5 La203 10-25 BaO 30 - 50 where La203+BaO,60 -< ZnO 0.1-2 CaO 0.5-2 Nb205 0.1-5 Y203 0.1-3 Gd203 0-1 Na20 0-1 K20 0-1 and, optionally, at least one refining agent.
3. A lead-free optical glass according to claim 1, having a refractive index ndof between 1.75 and 1.83, characterized by the following composition (in % by weight, based on oxide):

Si02 10-17 B203 8-15 whereSi02 + B203 < 25 Zr02 1 -5 Ti02 1-5 La203 15-30 BaO 30-50 where La203+ BaO: 60 ZnO 0.1-2 CaO 0.5-2 Nb20.5 0.1-5 Y203 0.1-3 Gd203 0-1 Na20 0-1 K20 0-1 and, optionally, at least one refining agent.
4. A lead-free optical glass according to claim 1, having a refractive index ndof between 1.71 and 1.75 and an Abbe numberVdof between 42 and 46, characterized by the following composition (in % by weight, based on oxide):

Si02 15-21 B203 10-15 Zr02 1-4 Ti02 1 -4 La203 15-25 BaO 30-43 ZnO 0.1-1 CaO 0.5-1 where BaO + ZnO + CaO > 31 Nb205 2-5 Y203 0.1-2 Gd203 0-1 whereY203 + Gd203: 0.2 Na20 0-1 K20 0-1 and, optionally, at least one refining agent.
5. A lead-free optical glass according to claim 4, characterized in that the weight ratio SiO2 + B2 03 BaO + ZnO + CaO
6. A lead-free optical glass according to claim 4, having a refractive index ndof between 1.73 and 1.75 and an Abbe numberVdof between 44 and 46, characterized by the following composition (in % by weight, based on oxide):

Si02 15-17 B203 12-15 Zr02 2-3 Ti02 2-3 La203 19-22 BaO 37-39 ZnO 0.1-1 CaO 0.5-1 Nb205 2-4 Y203 0.5-1.5 Gd203 0-1 whereY203+ Gd203! 0.6
7. A lead-free optical glass according to at least one of claims 1 to 6, characterized in thatW03 + Nb205 + Y203 + Gd203> 5% by weight.
8. A lead-free optical glass according to at least one of claims 1 to 7, characterised in that the weight ratio ZrO)TiO2 is between 0.8 and 1.0.
9. A lead-free optical glass according to at least one of claims 1 to 8, characterized in that the glass contains from 0.1 to 0.5% by weight of Sb203-
10. A lead-free optical glass according to at least one of claims 1 to 9, characterized in that the glass contains up to 0.5% by weight of fluoride.
11. A lead-free optical glass according to at least one of claims 1 to 10, characterized in that it is free from arsenic oxide., apart from unavoidable impurities.
12. A lead-free optical glass as claimed in claim 1, substantially as hereinbefore described in any one of Examples 1 to 9 in Table 2.