GB2318576A

GB2318576A - Lead-free optical light and double-light flint glasses

Info

Publication number: GB2318576A
Application number: GB9720752A
Authority: GB
Inventors: Danuta Grabowski; Uwe Kolberg; Alwin Weitzel
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 1996-10-28
Filing date: 1997-10-01
Publication date: 1998-04-29
Anticipated expiration: 2017-10-01
Also published as: JP3073474B2; FR2755125B1; CN1171817C; GB9720752D0; JPH10139473A; DE19644736C1; MY122044A; GB2318576B; FR2755125A1; CN1182721A

Abstract

Lead-free optical light flint and double-light flint glasses having a refractive index n d of between 1.52 and 1.57 and an Abbe coefficient v d of between 43 and 52 are described, which have the following composition (in % by weight based on oxides): SiO 2 48-55, B 2 O 3 7-9, K 2 O 18-20, Al 2 O 3 7-9, La 2 O 3 0.1-2, ZrO 2 0-1, # La 2 O 3 +ZrO 2 0.5-2, TiO 2 5.5-12, F<SP>-</SP> 1.5-6, (Al 2 O 3 +La 2 O 3 )/(TiO 2 +ZrO 2 ) = 0.73-1.15. The glasses show outstanding crystallization stability and very good chemical resistance. Fining agents Sb 2 O 3 and/or Cl<SP>-</SP> may be present in amount up to 0.5wt%.

Description

2318576 Lead-free optical light flint and double-light flint glasses The

invention relates to lead-free optical light flint and double-light flint glasses having refractive 5 indices nd of between 1. 52 and 1. 57 and Abbe coef f icients Yd of between 43 and 52. Since, in recent years, the glass components Pbo and As.03 have come into public discussion as being pollutants of the environment, some manufacturers of consumer products and of optical instruments will change over to the use of only glasses which are free of PbO and also of A9,03. Such glasses having the specific optical properties should therefore be available on the market.

For the production of light glass coimponents, is that is to say of glasses having a low density, it is also desirable to dispense with PbO.

Simple replacement of the load oxide by one or more constituents an a rule does not succeed in reproducing the desired optical and glasstechnological pro- perties which are subject to the influence of PbO. instead, new developments or far-reaching changes in the glass composition are necessary.

Specifications can already be found in the patent literature in which lead-free glasses having the optical values mentioned are described. However, these glasses show considerable disadvantages.

Thus, in the specification JP 1-133,956 A, optical-fibre glasses are described which belong to an Sú02-A1203-Y'20-p- glass system and in which Pbo is an optional constituent. To obtain adequate crystallization stability, tle glasses require high A1203 Contents' but this reduces the fusibility. In order to rove the latter, they can contain up to 25 mol% of LI.O. Such high Li.0 contents, however, in turn entail a reduction in the crystallization stability.

The glasses described in JP 6-107,425 A, whose optical values vary over a wide range, contain B&O. Together with the sometimes high B202. contents and also M.0 contents, chemically unstable and crystallizationunstable glasses will be obtained, but this can be censated by using up to 25% by weight of Nb.O.. However, this expensive component enormously increases the 5 price of the mixture and hence the production coats.

The glasses described in the patent specification EP 0,645,349 Bl also contain Nb.O.. They are free of B203To improve the fusibility of the glasses, they contain up to 40% by weight of alkali metal oxides, which, in the case of P- contents of up to 8% by weight, will have the result that the glasses have a low crystallization stability and an inadequate chemical resistance.

The glasses of German patent specification DE 973,350 belong to the SiO,M.0-F glass system. These glasses contain neither La.03 nor ZrO.. PbO is an optional constituent. These glasses also show a broadband width of the optical values. At the abovementioned values, the glasses have a high Fcontent. Owing to their composition, the glasses will not show good chemical stability and, in particular, will not have adequate resistance to acid and alkali. They will also tend to segregate (opacity) and show an unfavourable viscosity curve at the upper devitrification limit. In the specification JP 6-92,674 A, optical 25 glasses from the Si02-M-P205 glass system are described. Na20 (at least 12.5% by weight) an an alkali metal oxide must be present. Owing to high M20 contents and the P20. content (up to 15% by weight), these glasses will also not have an adequate crystallization stability and show poor chemical resistance.

It in the object of the invention to provide a lead-free light flint or double-light flint glass having a ref ractive index nd of between 1. 52 and 1. 57 and an Abbe coef f icient of between 43 and 52, which has a low density (p s 2.60 g/c&) and good melting and processing properties, also including very good crystallization stability and a viscosity which allows production in relatively large melting units, for example in an optical tank, that is to say a viscosity of a 1000 dPas at the 3

Claims

upper devitrification limit. Moreover, the glass should have good chemical

resistances, which is very important for further working such an grinding and polishing, and it should be producible at low costs. 5 This object is achieved by the glass described in Patent Claim 1. The glass contains 48 to 55% by weight of the glass former SiO.. At lower contents, the tendency to crystallize increases and the chemical resistance decreases and, at higher contents, the glasses become more difficult to melt. The range between 50 and 52% by weight in preferred.

B203 is present an a further glass f ormer in a content of between 7 and 9% by weight. The given minimum is content In necessary to improve the fusibility of the glasses and to minimize vaporization of fluoride. The given maximilm content should not be exceeded since otherwise the hydrolysis resistance decreases. A maximum content of 8% by weight in preferred.

The glass contains 7 to 9% by weight of A120 The crystallization stability and the chemical resistance are improved by the minimurn content of this component. At higher contents. the viscosity of the glass increases unduly. It is preferred to restrict the maximum content to 8.5% by weight.

To imp rove the melting properties and to obtain good transmission, the glass contains 18 to 20% by weight, preferably 19 to 20% by weight, of K20.

In order to obtain the desired optical values and to achieve high chemical resistance, the glass contains 0.1 to 2% by weight of La203. At higher contents, the desired optical position in not reached and the price of the mixture is unnecessarily increased.

Zr02 also has a strong influence on the optical values. This oxide can be present in quantities of up to 1% by weight, since, at higher contents, the refractive index in unduly increased.

The total of La.03 and Zr02 should be between 0.5 and 2% by weight, since the disadvantages discussed for the individual oxides arise already above or below these limits. In a particularly preferred embodiment, the sum of the two oxides is between 0.6 and 1.4% by weight.

The fact that these glasses show very good crystallization stability in spite of the fairly high X20 content in due to the balanced ratio of A1203 and La203 to B203' In a preferred embodiment of the invention, the weight ratio (A1203 + La203)/B203 should be greater than 1.

it has been f ound that the S'02 content should then be at least 49% by weight, so that sufficient glass-formiing oxides are present.

To reach the given optical values, the glass comprises, an a further component, T'02 at a content of 5.5 to 12% by weight. Moreover, at lower contents, the is chemical resistance is decreased and, at higher contents, the transmission in reduced. A content of between 8 and 11% by weight is preferred.

in addition to the absolute quantities, the decisive factor for the outstanding chemical resistance of the glasses according to the invention Is the specific ratio of A1203 and La203 to T'02 and ZrO2 ( (A-1203 + La203MTi02 + Zr0j). This should be between 0.73 and 1.15. At a weight ratio of < 0.73, the chemical resis tance, in particular the acid and alkali resistance, decreases. At a value of > 1.15, the fusibility decreases. Although it would be possible to compensate this by increasing the contents of 1C.0 and B203. this would in turn entail a deterioration in the crystalli zation stability. Moreover, it would then be very diffi cult, that is to say associated with other disadvantages, to adjust the desired optical values, in particular the Abbe coef f Icient. In a particularly pref erred embodl maint, the (A1203 + La203) 1 (T102 + ZrO.) weight ratio is between 0.77 and 1.10.

in addition, the glass contains fluoride Ions, namely between 1.5 and 6% by weight, preferably between 2 and 5.5% by weight. In this way, a very good ainternalw glass quality (with respect to freedom from bubbles and striations) and the very good light transmission r,,;.

(that is to say at a specimen thickness of 25 n=) in the wavelength range between 400 and 1600 nm of at least 80% are achieved. Exceeding the maximum P- content of 6% by weight leads to segregation and hence to opacity of the 5 glasses.

Glasses in which all the components are within the given preferred composition ranges represent doublelight flint glasses having refraction indices of between 1.52 and 1.55 and Abbe coefficients of between 45 and 50.

For a further Improvement of the glass quality, one or more fining agents known per se, can he added in the usual quantities to the mixture for fining the glass.

If no As.03 but, for example, Sb203 15 then used instead, which is possible without losses relating to the is glass quality, the glasses which are lead-free according to the invention are additionally free of arsenic. In a further preferred embodiment of the invention, the glass contains the following fining agents: 0.1-0.5% by weight of Sb203 + Cl- at 0-0.5% by weight of 20 Sb203 and 0-0.5% by weight of Cl-. The range of glass compositions according to the invention thus makes a further group of lead-free light flint and/or double-light flint glasses having the given optical properties available. In comparison with the conventional light flint and double-flint glasses, it Is distinguished by low density (p s 2.6 g/c&) and by the following properties: the glasses show very good chemical resistance and outstanding crystallization stability, very high ninternalw glass quality, a high transformation temperature and very good light transmission in the wavelengths ranged between 400 and 1600 =.. Additionally, they can he produced at low costs, inter alia because the expensive Nb.O. component can he omitted. it in a further advantage that the glasses are not only free of PbO but, in a preferred embodiment, also free of A0203- Exffin lea:

7 examples of glasses according to the invention within the preferred composition range were smelted from conventional raw materials. The compositions (in % by weight based on oxides) and, partially by way of example, essential properties of the glasses are listed in Table 2.

The glasses according to the invention were produced in the following way: the raw materials for the oxides and fluoride, preferably carbonates, nitrates and fluorides, were weighed; one or more fining agents, for example Sb203. were added followed by good mixing. The glass mixture was fused at about 1250-1300C in a con tinuous melting unit, then fined and well homogenized.

The glass is cast at 12000C, placed at 550C into a cooling oven and cooled down to room temperature, in order to reach a stress-free state.

Table 1 shows a melting example:

oxide % by weight Raw material Amount weighed (kg) Si02 51.60 Sio, 51.61 AJL203 8.10 A10ME) 10.33 B203 7.79 113B03 13.83 1C20 19.60 KN03 36.79 p2.00 KEF2 4.14 0.10 L%03 0.10 La203 TIO2 10.12 Ti02 10.17 ZrO, 0.51 Zr02 0.52 Sb203 0.18 Sh203 0.20 Total 100 127.69 The properties of the glass thus obtained are indicated in Table 2, Example 7.

7 Table 2 Glass composition (in % by weight based on oxides) and essential properties of the glasses 1 2 3 4 5 6 7 Sio, 51.08 51.08 51.59 50.98 50.85 51.35 51.60 B'o' 7.37 7.37 7.44 7.35 7.68 7.75 7.79 x, 0 19.06 19.06 19.25 19.02 19.34 19.54 19.60 A120, 7.56 7.56 7.64 7.55 7.90 8.00 8.10 La203 0.79 1.18 1.19 1.37 0.15 0.17 0.10 TIO, 8.55 8.15 8.23 8.14 9.97 10.08 10.12 Zr02 - - - - 0.50 0.51 0.51 p- 5.40 5.40 4.46 5.39 3.48 2.50 2.00 sh20, 0.20 0.20 0.20 0.20 0.13 0.10 0.18 La,O,+ZrO, 0.79 1.18 1.19 1.37 0.65 0.68 0.61 A1,0,+La.,0, TiO,+ZrO2 0.98 1.07 1.07 1.10 0.77 0.77 0.77 A1 0 1.13 1.19 1.19 1.21 1.05 1.05 1.05 __,+La,O, B201 n, 1.5315 1.5285 1.5304 1.5287 1.5425 1.5448 1.5460 Y, 48.19 48.94 49.12 49.04 45.94 46.03 46.06 p [g.CZ01 2.500 2.498 2.502 2.501 2.493 2.504 2.496 P5F. p 0.5670 0.5658 0.5659 0.5656 0.5712 0.5705 0.5700 AP!F.F 0.0043 0.0043 0.0042 0.0042 0.0047 0.0041 0.0036 SR 1.0 1.0 1.0 AR 1.0 1.0 1.0 0.84 0.85 0.86 0.86 0.82 0.83 0.84 Viscosity at 1550 1600 1700 1500 3000 14000 3200 the upper de vitrification limit [dP&ol is wherein:

Tg: Transformation twWerature AR: Alkali resistance according to draft ISO 10,629 SR: Acid resistance according to ISO 8424 P,.,: Relative partial dispersion at the wavelengths stated AP51.7: Deviation of the relative partial dispersion f rom the Onormal straight line 7400Zsm: Spectral transmission ratio at wavelengths X = 400 n= and a sample thickness of d = 25 =m 1 Lead-free optical light flint and double-light flint glasses having a refractive index rld of between 1.52 and 1.57 and an Abbe coefficient v. of between 43 and 5 2, characterized by the following composition (in % by weight based on oxides):

Si02 48-55 B203 7-9 K20 18-20 A1203 7-9 LaP3 0.1-2 Zr02 0-1 with La203+Zr02.0.5-2 is T102 5.5-12 F- 1.5-6 A1 2,-±L-a,03 0.73-1.15 Ti02+Zr02 and, if appropriate, fining agents in the customary quantities.
2. Lead-free optical light flint and double-flint glasses according to Claim 1, characterized in that the weight ratio A1,23+La,03 is greater than 1 B203 and that the SiO, content is at least 49% by weight.
3. Lead-free optical double-light flintglasses according to Claim 1 or 2 having a refractive index nd of between 1.52 and 1.55 and an Abbe coefficient Yd Of between 45 and 50, characterized by the following com position (in % by weight based on oxides):

Si02 50-52 B203 7-8 K20 19-20 A1203 7-8.5 La.03 0.1-2 Zr02 0-1 with La203+Zr02 0.5-2 Ck TiO2 8-11 F- 2-5.5 A1,20-, Aa-203 0.73-1.15 Ti02+ZrO2 and, if appropriate, fining agents in the customary quantities.
4. Lead-free optical light flint and double-light flint glasses according to at least one of Claims 1 to 3, characterized in that the sum of La.03+ ZrO, is between 0.6 10 and 1.4% by weight.
5. Lead-free optical light flint and double-light flint glasses according to at least one of Claims 1 to 4, characterized in that the weight ratio A1,23+La,03 is Ti02+ZrO, is between 0.77 and 1.10.
6. Lead-free optical light flint and double-light f lint glasses according to at least one of Claims 1 to 5, characterized in that they contain, an fining agents (in by weight):

Sb203 0-0.5 Cl- 0-0.5 with Sb203+Cl- 0.1-0.5
7. Lead-free optical light flint and double-light f lint glasses according to at least one of Claims 1 to 6, characterized in that they are free of arsenic oxide except for unavoidable contaminations.