DE973350C - Optical silicate glasses with a refractive index that is low in relation to the mean dispersion or the ª † value - Google Patents

Description

Issued on the basis of the First Transitional Act of July 8, 1949

(WiGBl. P. 175)

FEDERAL REPUBLIC OF GERMANY

ISSUED JANUARY 28, 1960

GERMAN PATENT OFFICE

PATENT LETTERING

CLASS 32 b GROUP 1 INTERNAT. CLASS C 03c

J 7843 IVc132b

Dr. Edwin Berger f, Jena, and Otto Freundel, Mainz

have been named as inventors

Jenaer Glaswerk Schott & Gen., Mainz

Optical silicate glasses with a refractive index that, based on the mean dispersion or the r-value,

is low

Patented in the territory of the Federal Republic of Germany on June 11, 1940 The period from May 8, 1945 up to and including May 7, 1950 is not counted towards the patent term

(Ges. Of 15.7.1951)

Patent application published on July 15, 1954 Patent granted on January 14, 1960

It is known to be special for the production of lens systems with the best correction at the highest light intensity advantageous, converging lenses made of glasses with the highest possible refraction and as low as possible Dispersion with diverging lenses made of glasses with the lowest possible refraction and the highest possible dispersion to combine.

The present invention aims to provide such low refraction and high refraction glasses ίο dispersion.

In ordinary optical crown and flint glasses, the Abbe's number ν is a function

the refraction a lower limit, which is represented by the straight connection of the following pairs of values can be,

nd = 1.48
nd = 1.49
nd = 1.51
nd = 1.53
nd = 1.55
nd = 1.57

Table 1

ν = 67.4
ν - 62.4
ν = 54.8
ν = 49.3
ν = 45.1
ν = 41.8

nd = i, 59 nd = i, 6i nd - 1.63 nd = 1.65 nd - 1.67 nd = 1.69

ν = 39.1 ν = 36.9 ν = 35.0 ν = 33.4 ν = 3i, 4 ν = 29.9

909 702/19

where for nd <1.65 the specified pairs of numbers satisfy the following condition

nd - ι ".-

13,815

ν =

nd - 1.3815

or equivalent to it
nd - 1.3815

ν -10

ν - 13.815 '

According to the invention, it is possible to significantly fall below the specified limits for the nd and for the v values in the entire area and thereby create glasses that have a similar meaning for negative lenses as the lanthanum crown for positive lenses.

The glasses according to the invention have the following composition in percent by weight:

Alkali metal oxides 5 to 30 ° / ₀

SiO ₂ + B ₂ O ₃ 30 to 70%.

F 0.15 to 25%

also up to 5 percent by weight of alkaline earth oxides and at least one of the substances Al ₂ O ₃ , TiO ₂ , Sb ₂ O ₃ , As ₂ O ₃ and PbO, the Al ₂ O ₃ and TiO ₂ content not exceeding 30%, the PbO not more than 55%, the Sb ₂ O ₃ not more than 35% and the As ₂ O ₈ not more than 5% and these substances otherwise meet the condition Al ₂ O ₃ + TiO ₂ + alkali oxides + Sb ₂ O ₃ + As ₂ O ₃ + PbO = 35 to 69.85%.

If one wishes to obtain a v value> 63.5, then it is expedient to choose the content of Al ₂ O ₃ + Sb ₂ O ₃ + As ₂ O ₃ > B ₂ O ₃ .

_{Glasses which contain alkali oxides, SiO 2} and B ₂ O ₃ within the specified limits, and also small amounts of fluorine and alkaline earth oxides between 11 and 15%, are known. These glasses have good ultraviolet transmittance. However, they do not show the desired low refractive index, based on the mean dispersion.

Furthermore, glasses are known which contain 5 to 25% alkali metal oxides and, in addition to SiO _2, a total of 15 to 35% B ₂ O ₃ + Al ₂ O ₃ and up to 9% fluorine. For these glasses the lower limit of the! »Value is 63.5. The glasses according to the invention, on the other hand, generally have v values which are below this limit. In those cases where the glasses according to the invention also have a?>Value> 63.5 (cf. Table 2, Examples 1 to 14), the glasses according to the invention have a better optical position, since they have a lower limit for the «< ?-Value of

1.3815 -

V IO

v - 13.815

-0.017

exhibit. For ν = 66, at least the «iZ value of 1.464 is obtained. The example in Table 2 gives a «^ value of 1.4465.

The fluorides are particularly important for lowering the refraction. The glasses according to the invention have the further advantage that the fluorides are incorporated into the glass in a relatively stable manner, so that excretions, which otherwise usually occur in the form of milky opacities due to liquid droplets or crystals, are avoided. The alkali content is particularly important for combating the tendency to excretion. However, since the alkali metals Na ₂ O and Li ₂ O cause only a small reduction in the value related to the v- nd- values, is suitably at least half of the content of alkali of potassium oxide. The difficulty with the introduction of fluorides is that they easily evaporate during the entire melting process. For this reason, an analysis should not find much more than 70% of the fluorine added to the mixture in the glass. This must be taken into account in Table 2, which specifies the synthetic fluorine content of the glasses in the symbols O -> - F. This symbolism is based on the principle that you can no longer tell in the finished glass in which compound the fluorine was introduced and to which atom of the finished glass is attached as a partner and to which fluorine. So you act as if you were looking at a glass made of pure oxides, from which some of the oxygen was subsequently replaced by fluorine. O -> - F is therefore defined as that amount of oxygen in percent by weight of the sum of the oxides that is replaced by the equivalent amount, i.e. 2.36 times the amount of fluorine. This naturally increases the total weight by (2.36 - 1) · (O -> - F). The fluorine content of the finished glass is 2.36 (O ^ - F) if it is related to 100 g of the oxides. However, if you relate it to 100 g of the total glass, the fluorine content is evidently through

2.36 (O- ^ F)

"100 + 1.36 (O -» · F)

shown.

Thus, in Example 16 of Table 2, an O -y F content of 12% is given. The fluorine content, based on 100 g of oxides, is 28.4 g, i.e. the percentage of fluorine in the glass

28.4

100 +16.3

= 24.5 percent by weight.

Example 31 contains 10% O
there is also fluorine in the glass

F. The percentage

23.6

100 +13.6

= 20.8 percent by weight.

The examples therefore give an upper limit for the fluorine content of around 25 percent by weight.

In addition to the alkali mentioned, there is also the introduction Boric anhydride and aluminum oxide are suitable to counteract the tendency of fluorine to precipitate. The introduction of titanium oxide works in the same way. The titania content, however, finds practical a limit at about 30%, otherwise apart from crystallization and turbidity one for the use as optical glass makes harmful brown discoloration too noticeable. Regarding crystallization and Coloring the most favorable composition is obtained when boric anhydride, aluminum oxide and titanium oxide together amount to at least 5 and at most 45%. At the same time, however, boron

anhydride and alumina together more than 40 ° / ₀ account. The higher the titanium oxide content, the less the aluminum oxide content may exceed that of boric anhydride, because the brown color is particularly noticeable when the aluminum oxide content is high. The content of antimony and arsenic oxide should also be selected to be low with higher titanium oxide contents, because they also strongly favor the brown color. If the content of titanium oxide io ° / ₀ or more, we therefore provide appropriate that the content of antimony oxide and Arsenoxyd together is at most 10%. Alkaline earth oxides lead to cloudiness even in the presence of titanium oxide in molten metal containing molten metal. Their content should therefore be as small as possible and under no circumstances exceed 5% of the initial glass batch. Divalent metal oxides will also not be used as far as possible because they favor the tendency to precipitate and counteract the lowering of the refractive index. Lead oxide is most favorable in both respects.

If you want to produce glasses with a very large average dispersion and a reduced refractive index, it is even advisable to introduce lead oxide in addition to antimony and arsenic oxide in order to make it brown to be avoided despite larger amounts of titanium. The resulting increase in the refractive index can be reduced by reducing the boric acid content partially encounter.

The general rules for achieving optical glasses with a lower refractive index, based on the scattering, according to the invention, are to be applied in different ways, depending on the area in which the optical glasses are located. The first area is the one where the v-value is above 63.5; the second the one for which ν is greater than 63.5 and the refractive index is at most 1.65; the third is finally the one in which the refractive index is greater than 1.65. The following applies within the first area: Pure alkali-silicic acid-fluoride glasses produce crystal precipitates with low fluorine contents, and cloudiness with higher fluorine contents, both to a greater extent the lower the alkali content. Potassium glasses behave more favorably than sodium or lithium glasses. As already mentioned above, the tendency to precipitate can be sufficiently suppressed by introducing boric anhydride and aluminum oxide, so one can replace larger amounts of oxygen with fluorine and still melt crystal-free and opaque-free glasses.

The investigations on which the invention is based have now shown that boric anhydride weakens the refraction-reducing effect of fluorides to a greater or lesser extent, whereas aluminum oxide strengthens them, i.e. leads to greater reductions in the refractive index. However, the effect of boric anhydride and, albeit less so, of aluminum oxide is not additive, but depends on the amount introduced. For smaller contents boric anhydride weakens the brechungsvermindemde effect of fluorides from very strong, with larger contents of about io ° / ₀ of the initial glass set of the action for the same growth is much weaker. But if aluminum oxide is present in a larger amount than boric anhydride, the same increase in boric anhydride can even increase the effect mentioned. In addition, it is then possible to increase the amount of fluoride further to over 4 ° / ₀ O -> - F. It is therefore possible to increase the lowering of the refractive index to over 0.018 if the content of aluminum oxide is chosen to be at least equal to the content of boric anhydride and lets the sum of the two be 10 to 45%.

If one wants to get into the second of the above-mentioned areas and for this purpose one tries the Medium dispersion of the fluorine glasses due to the introduction of alkaline earths or divalent metal oxides to increase above 0.0073, a pronounced result is obtained even with low levels of such additives Tendency to cloudiness. This tendency falls in the order BeO, MgO, CaO, SrO, BaO, ZnO, CdO, PbO clearly decrease, but even with PbO it is still so strong that it is necessary to achieve less turbidity Glasses would have to reduce the content of fluoride so much that the refraction-reducing Effect of the fluoride weakening effect of boric anhydride and also of divalent oxides even the desired lowering of the refractive index cannot be achieved. According to the invention, it succeeds however, by introducing antimony oxide, the mean dispersion can be increased above 0.0073 and Obtain glasses with a reduced refractive index. It is true that antimony oxide itself has a somewhat opposite effect Meaning, if noticeably less than boric anhydride or divalent oxides, it performs but in the presence of fluorine to a much lesser extent than the divalent oxides for crystallization and Cloudiness. With the same tendency to precipitate, antimony oxide can even be used in the presence of larger amounts significantly increase the absorption capacity for fluoride and aluminum oxide. However, since these amendments the fluorine-alumino-borosilicate glasses are practical must be done at the expense of the silica content, one obtains glasses with reduced in this way chemical resistance, in particular greater acid solubility and increased swelling capacity by exposure to water. Such glasses form when polished surfaces dry out then easily fine hairline cracks. Larger contents of antimony oxide should also be avoided because they give rise to optically harmful yellow or brown discolorations. Similar to antimony oxide behaves Arsenic oxide.

However, it has shown that these difficulties, largely through the introduction of titanium oxide addition to or instead of antimony, in amounts of at least 0.2 ° / ₀ have it removed and that this is therefore particularly favorable because titanium oxide which even in small amounts The mean dispersion is greatly increased and, at the same time, the refractive index related to the dispersion is lowered and the acid solubility and swelling capacity are reduced.

Boric acid and clay are also conveniently present in the glasses, but at least as much Aluminum oxide such as boric anhydride. Advantage-

one chooses here the glass set so that the glasses on aluminum oxide, titanium oxide, antimony oxide and Arsenic oxide together contain at least as much as boric anhydride and any alkaline earth oxides together.

Since the effect of fluorine, expressed by% O -v F, on the lowering of the refractive index corresponds on average to about five times the opposite effect of boric acid, the should be equivalent

ίο parts by weight of oxygen replaced by fluorine amount to at least one fifth of the boric anhydride and alkaline earth oxyden content of the starting glassware together.
In order to obtain glasses within the third of the above-mentioned areas, i.e. those with a refractive index above 1.65, the sum of the percentages of antimony oxide, arsenic oxide, lead oxide and other divalent oxides must be increased by twice the percentage in the glasses corresponding to the invention in the initial glass batch titanium oxide exceed 50 ° / _0th To lower the refractive index related to the dispersion, it is advisable to introduce titanium oxide in amounts of 0.2 to 30%. Other tetravalent titanium oxides as well as pentavalent and hexavalent metal oxides seem to reduce the reduction in the refractive index related to the scattering, in any case they do not intensify it as much as titanium oxide. The total content of aluminum oxide, titanium oxide and of the oxides of antimony and arsenic, which have practically no effect on the lowering of the refractive index, is expediently at least equal to that of boric anhydride and alkaline earths combined. Since high titanium oxide contents give rise to brown discolouration and clouding, it is advisable to produce glasses with a very high refractive index by introducing lead oxide, which of all divalent oxides increases the refractive index related to the dispersion the least. Because of the content of lead oxide and other divalent oxides, such glasses show only small reductions in the refractive index despite the low content of boric anhydride and despite the introduction of fluorine in amounts of more than 0.1% O - * - F, but this is also the case in this area a small reduction is practically of the greatest importance for the achievement of new optical constructions. Table 2 lists the glass sets for a number of the glasses according to the invention and their optical position.

The components of the starting glass sets are indicated as oxides, but nothing stands in the way of importing the raw materials in the appropriate quantities in a different form. So you can z. B. instead of boric anhydride (B ₂ O ₃ ) use crystallized boric acid (B ₃ HO ₃ ) and instead of sodium bicarbonate (Na ₂ O) use calcined soda (Na ₂ CO ₃ ).

As can be seen from the information on the optical position, the glasses with the serial number 1 to 14 belong in the first of the above-mentioned areas, the glasses with the numbers 15 to 34 in the second and the glasses with the designation 35 to 41 in the third of the mentioned areas. The value α given in the last column is the amount by which the refractive index nd is reduced compared to the lowest refractive index occurring in ordinary optical glasses with the same average dispersion, as listed in Table 2.

Tabel

ho ö

CO

O
'm 6 '
κ ' d ο
ti * ο PbO <P
Vi

nd

n _c -n _F

4th
5
6th

7th 8th

9
10

II
12th
13th

! 4

15th
16

17th
18th

* 9
20th

21

47.1 13.5 20.3 19.1 o, 3 8.3 1.4443 67.6 0.00657 41.7 18.0 20.0 - 20.0 - - 0.3 - - 8.0 1.4380 67.7 0647 46.2 13.5 21.0 - 19.0 - - - - - 8.0 1.4395 67.5 0651 37.5 20.0 20.0 - 20.0 - - ■ - - 2.5 BaO 8.0 1.4484 67.4 0665 37.5 20.0 20.0 - 20.0 2.5 - - - • - ■ 8.0 1.4465 66.0 0676 37.5 20.0 20.0 • - 20.0 - 2.5 - - - 8.0 1.4469 65.2 0685 35.0 20.0 20.0 ■ - 20.0 - 5.0 - - - 8.0 i, 4507 63.2 0713 45.0 10.0 20.0 - 20.0 - 5, o - - - 8.0 1.4454 64.8 0687 37.5 20.0 20.0 20.0 - ■ - - - 2.5 GeO ₂ 8.0 1.4402 66.6 0661 37.5 20.0 20.0 - 20.0 - - - -. 2.5 P ₂ O ₅ 8.0 1.4483 67.6 0663 37.5 20.0 20.0 - 20.0 - - 03 - 2.5 WO ₃ 8.0 1.4459 65.8 0678 41.7 15.0 20.0 ■ - 20.0 - · - 2.5 ■ - ■ 3.0 Tl ₂ O ₃ 6.0 1.4470 67.0 0667 37.5 20.0 20.0 - 20.0 - - - -. - 8.0 1.4454 65.8 0677 45.0 15.0 20.0 2.5 I7.5 - - - ■ - - 6.0 i, 45i6 66.1 0683 30.0 15.0 15.0 - 20.0 - 20.0 - - - 8.0 1.5000 52.9 0945 15.0 15.0 20.0 - 20.0 - 30.0 - - - 12.0 i, 5037 46.4 1085 20.0 25.0 15.0 - 20.0 - 20.0 0.3 - - 8.0 1.5032 5i, 4 0979 34.7 12.0 22.0 2.0 l6.0 - 13.0 0.3 - - 3.5 1.4939 54.8 0902 35.7 12.0 22.0 • - 18.0 - 9.0 0.3 - 3.0 CdO 4.0 1.4837 57.3 0844 29.7 15.0 25.Q 20.0 - 10.0 5.0 - - 4.0 1.4991 56.8 0878 25.0 15.0 20.0 20.0 - 15.0 - - 8.0 1.4772 56.5 0844

0.0280

329 319 250

284 no

292

293 310 326 248

293

267 296

243

121

277

I3I

122

144

Ο37

209

continuation

description O
W. d
«Ff O
< O
I. O PbO 0 " 0
4 " d
H CD
+
O nd V n _c -n _F a 22nd 25.0 15.0 20.0 20.0 ,. 15.0 5.0 - 6.0 1.4902 54, i 0906 165 23 26.7 18.0 25.0 - 20.0 - 10.0 0.3 - - 8.0 1.4583 61.3 0748 265 24 69.7 - - - 20.0 ■ - - 0.3 10.0 - 2.0 1.5287 48.0 HOI O49 25th 49> 7 15.0 5, o - 20.0 - - 0.3 10.0 - 4, o 1.5253 47.4 II08 O93 26th 49.5 10.0 10.0 • - 20.0 - - 0.5 10.0 - 4, o 1.5214 45.5 1146 IiS ₄ 27 54, i 7.9 8.5 - ■ 20.0 1.2 - 0.5 7.8 - 4, o 1.51281 50.5 IOI5 O89 28 51.6 7.9 8.5 - 20.0 1.2 • - 0.5 10.3 - 3, o 1.53358 46.0 II60 082 29 49.2 8.0 9.0 - 23.0 - · - 0.5 10.0 - 3, o 1.5269 48.1 1095 O59 30th 49.5 - 5, o - 20.0 - - 0.5 25.0 - 2.0 1.6142 32.9 1867 252 31 5i, 9 7.9 8.5 - 20.0 1.2 - 0.5 10.0 - 10.0 1.50794 46.1 HOI 257 32 49.8 10.0 8.5 - 20.0 1.2 - 0.5 10.0 2.5 BaO 10.0 1.51348 45.7 1123 260 33 47.5 10.0 10.0 2.0 18.0 - 3.0 2.0 5, o - 3, o 1.5106 54, i O943 012 34 37.9 - - 11.6 40.0 0.5 10.0 - 4, o 1.64176 32.6 I966 "3 35 37.2 - i, 5 1.0 6.5 48.3 - 0.5 5, o - 1.0 1.67756 31.2 2171 039 36 39.5 - 5, o - 15.0 20.0 - 0.5 20.0 - 2.0 1.65378 30.9 2II5 199 37 33.5 - 5, o - 15.0 30.0 5, o 1.5 10.0 - 2.0 1.66375 31.2 2126 115 38 37.9 - - - 11.6 40.0 - 0.5 10.0 - 2.0 1.67770 30.5 2220 105 39 37, o - · - 1.5 6.0 5o, o - 0.5 5.0 - 1.0 1.6942 28.9 24OO 189 40 34.5 - 2.5 i, 5 6.0 50.0 - 0.5 5, o - 2.0 1.6686 3i, 3 2135 079 41 31.8 - 2.5 i, 5 8.7 50.0 - 0.5 5, o 4, o 1.66950 31.6 2122 052

Claims (11)

PATENT CLAIMS: 1. Optical glasses with a refractive index that is low in relation to the mean dispersion, characterized by the following composition in percent by weight: Alkali oxides 5 to 30% SiO ₂ + B ₂ O ₃ 30 to 70% F 0.15 to 25% also up to 5 percent by weight of alkaline earth oxides and at least one of the substances Al ₂ O ₃ , TiO ₂ , Sb ₂ O ₃ , As ₂ O ₃ and PbO, the Al ₂ O ₃ and TiO ₂ content not exceeding 30% of PbO is not more than 55%, of not more than 35% ^u ^ <i ^{he of} as ₂ O _{3 3} not to be more than 5% Sb ₂ O and satisfy these substances in the rest condition Al ₂ O ₃ + TiO ₂ + alkali oxides + Sb ₂ O ₃ + As ₂ O ₃ + PbO = 35 -69.85%. 2. Optical glasses according to claim 1 with an r value> 63.5, characterized in that the content of Al ₂ O ₃ + Sb ₂ O ₃ + As ₂ O ₃ > B ₂ O ₃ . 3. Optical glasses according to claim 1, characterized in that at least half of the Alkali consists of potassium oxide. 4. Optical glasses according to claim 1, characterized in that the sum of the percentages by weight of B ₂ O ₃ -f Al ₂ O ₃ + TiO _{2 is} between 5 and 45. 5. Optical glasses according to claim 4, characterized in that the content of B ₂ O ₃ + Al ₂ O ₃ together is at most 40 percent by weight. 6. Optical glasses according to claim 1 with a TiO ₂ content of 10 to 30 percent by weight, characterized in that the sum of the contents of As ₂ O ₃ + Sb ₂ O _{3 is} less than 10 percent by weight. 7. Optical glasses according to claim 1 and 5 with an r value of at least 63.5, characterized in that the content of B ₂ O ₃ + Al ₂ O _{3 is} 10 to 45 percent by weight. 8. Optical glasses according to claim 1 with a v value of less than 63.5, characterized in that they contain _{at least 0.2 percent by weight of TiO 2.} 9. Optical glasses according to claim 1, characterized in that the content of Al ₂ O ₃ + TiO ₂ + Sb ₂ O ₃ + As ₂ O ₃ 5: B ₂ O ₃ + alkaline earth oxides. 10. Optical glasses according to claim 1, characterized in that the content of O -> F is at least one fifth of the content of B ₂ O ₃ and alkaline earth oxides together. 11. Optical glasses according to claim 1 having a refractive index greater than 1.65, characterized in that the sum of the contents of Sb ₂ O ₃ + As ₂ O ₃ -f · PbO + other divalent oxides double + TiO ₂ content of more than 50 Weight percent is. Considered publications:
U.S. Patent No. 2,056,627. > 909 702/19 1.60