United States Patent (19) 11 3,929,495 Broemer et al. (45) Dec. 30, 1975 54) OPTICAL BORATE GLASS OF HIGH 3,149,984 9/1964 Faulstich........................... 106/47 R CHEMICAL RESISTANCE AND PROCESS 3,307,929 3/1967 Trap.................................. 106/47 R 3,480,453 it 1/1969 Reid et al.......................... 106/47 R OF MAKING SAME 3,486,915 12/1969 Broemer et al................... 106/47 R (75) Inventors: Heinz Broemer, Hermannstein; 3,510,325 5/1970 Broemer et al................... 106/47 R Norbert Meinert, Wetzlar, both of FOREIGN PATENTS OR APPLICATIONS Germany 863,352 3/1961 United Kingdom............... 106/47 Q 73 Assignee: Ernst Leitz G.m.b.H., Wetzlar, 4,424,420 10/1969 Japan................................ 106/47 Q Germany Filed: May 15, 1973 Primary Examiner-Winston A. Douglas 22) Assistant Examiner-Mark Bell 21 Appl. No.: 360,418 Attorney, Agent, or Firm-Erich M. H. Radde 30 Foreign Application Priority Data 57 ABSTRACT May 15, 1972 Germany............................ 2223564 An optical borate glass of high chemical resistance, with negative anomalous partial dispersion, refraction 52) U.S. Cl. ............................. 106/47 Q; 106/47 R index n between 1,65 and 1,79, and Abbe number ve 51 Int. CI..... C03C 3/14: CO3C 3/00; C03C 3/30 between 40 and 30 is composed of boron trioxide, 58) Field of Search......................... 106/47 O, 47 R lead oxide, and aluminum oxide. It may additionally contain lithium, sodium, and/or potassium oxides, zinc (56) References Cited oxide, zirconium dioxide, tantalum pentoxide, and, if UNITED STATES PATENTS desired, antimony trioxide and/or bismuthum trioxide. 2,511,228 6/1950 Sun et al........................... 106/47 O 2,996,392 8/1961 Broemer et al................... 106/47 O 23 Claims, No Drawings 3,929,495 2 between 2.0 and 6.0 percent, b y weight, of zirconium OPTICAL BORATE GLAss OF HIGH CHEMICAL oxide (ZrO), . ." ; : " . ; RESISTANCE AND PROCESS OF MAKING SAME between 2 and 15 percent, by weight, of tantalum oxide (Ta2O5), and . .. BACKGROUND OF THE INVENTION 5 between 8 and f6 percent, by weight, of antimony l Field of the Invention oxide (SbOs) and/or bismuthum oxide (BiO3). The present invention relates to an optical borate The process of manufacturing the glasses of the pres glass and more particularly to an optical borate glass of ent invention is characterized by melting down mix high chemical resistance with negative anomalous par tures which consist of the chemical components indi tial dispersion, refractive indices n between 1.65 and 10 cated in the preceding paragraphs in the weight per 1.79, and Abbe numbers v between 40 and 30, and to centages also indicated therein. a method or manufacturing same. The glasses according to the present invention have 2 Description of the Prior Art the advantage that they are of superior chemical resis Recently the need for optical glass of a high index of tance so that the possibilities of their use in modern refraction and a low Abbe number which, as additional parameter, have a negative anomalous partial disper optical systems are considerably broadened. In addi sion, has increased greatly due to recalculations of tion thereto the glasses can be worked much more optical systems. In this connection, it is of decisive easily. This results in a simplification of manufacture importance to improve the possibilities of correction of which, in the final analysis, leads to lower manufactur the optical systems by the use of optical glasses of pre 20 ing costs. determined anomalous partial dispersion. Details con DESCRIPTION OF THE PREFERRED cerning the importance, the use, and the nomenclature EMBODIMENTS of glasses having anomalous partial dispersion values The following examples serve to illustrate the present are set forth in German Pat. No. 1,496,563. 25 invention without, however, limiting the same thereto. However, it has proven to be very difficult to pro Thus a number of glasses according to the present duce, by melting, glasses having the aforesaid physical invention are given in the following Tables, The refrac properties because they do not possess other properties tive index ne, the Abbe number ve (reciprocal of the which are absolutely required for utilizing them in high dispersion), and the amount of the anomalous partial grade optical systems, such as, for instance, lack of 30 dispersion Ave are also indicated in said Tables. color and high chemical resistance. In Table 1, examples are given for the pure ternary Glasses of this type which have become known here tofore either have insufficient chemical resistance or system BO -Pbo Al2O3. else a disturbing color cast. Due to their insufficient Table 1 chemical resistance, they are not only unsuitable for 35 (weight%) use as outer lenses in modern optical systems, but they Glass No.: 1 2 3 are also responsible for causing a very high percentage BOs 38.5 38.5 38.5 of rejects when mechanically assembling them. PbO 56.5 515 46.5 AlOs 5.0 10.0 15.0 SUMMARY OF THE INVENTION 40 ne 1.724.1 1.6938 16709 It is one object of the present invention to provide an e 34.5 36.4 38.2 optical borate glass of superior chemical resistance Ave -2.6 -3.3 -3.5 which, in addition to a refractive index n between 1.65 and 1.79 and an Abbe number we between 40 and 30, also has a negative anomalous partial dispersion but 45 In these compositions the proportion of boron triox which is free of the disadvantages of the known glasses. ide (BO) was left constant in each case while that of Another object of the present invention is to provide aluminum oxide (AlOs) was increased at the expense a simple and effective process of making such a valu of the proportion of lead oxide (PbO) by 5 percent, by able optical borate glass. weight, each time. Thereby, in addition to a decrease in Other objects of the present invention and advanta 50 the refractive index and a corresponding increase in the geous features thereof will become apparent as the Abbe number, the absolute value of the anomalous description proceeds. partial dispersion increases. In principle these objects are achieved by providing a In Table 2, the example given in Table 1 under Glass glass which contains No. 3 is modified by partially replacing lead oxide by an between 26 and 39 percent, by weight, of boron 55 alkali metal oxide. trioxide (BO), Table 2 between 32 and 57 percent, by weight, of lead oxide (weight%) (PbO), and Glass No.: 4. S. 6 between 5 and 19 percent, by weight, of aluminum B0s 38.5 38.5 38.5. oxide (AlO4). 60 PbO 44.5 44.5 44.5 According to a specific embodiment of the present AlOs 15.0 15.0 15.0 LiO 2.0 - - invention the glass can, in addition, contain the follow NaO 2.0 - ing components in the quantities indicated: 'KO ... 2.0 Between 0.2 and 3.0 percent, by weight, of at least 65 le 1,6686 1,6563 1.654 one of the oxides of the alkali metals lithium e 38.5 38.7 38.7 (LiO), sodium (NaO), and potassium (KO), AV. -3.7 -3.7 -3.5 between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), 3,929,495 3. 4. predeterminedIt is evident finethat adjustmentwith such partialof the opticalsubstitutions, position a - - Table 5-continued- parameters can be effected. " i.e. 'Na . (weight%) Of course, it is understood that the use of the alkali Glass No. - s 16 17 alkalimetal metaloxides oxide is not only; limited rather, to theit is additionalso possible of a tosingle add 5 g44- - - - 335 7609 two or more oxides together for partially replacing the A. 3.3 3.8 3.0 lead oxide. ' ' ' , nentIn startingTable 3, glass. zinc Inoxide this is case added also to thestarting three from compo- the 10 Thereby,.. the total. proportion. of the... ' ' sum, , of zirco composition given as Glass No. 3 in Table 1- the zinc nium, dioxide plus tantalum pentoxide (ZrO,--Tagos) oxide (ZnO) is substituted in part for equal percent- has been increased from 10.0 percent, by weight, in the ages, by weight, of lead oxide (PbO). composition of Example 15, to 14.0 percent, by weight, Table 3 15 percent,in the composition by weight, ofin Examplethe composition 16, and of finally Example to 16.0 17, Glass No.: 7 (weight%) 8 9. whereby the zirconium dioxide and tantalum pentoxide are substituted for the same proportion, by weight, of : 6: m boron trioxide (BOs). On the other, hand, the weight AlO 15.0 150 so percentages of lead oxide (PbO) and aluminum oxide ZnO 4.0 6.0 8.0 20 (Al...O.) were left constant. ne m 1669 1.6689 1.6659 Finally, in Table 6, in addition to the replacement e 39.2 39.7 4.0.1 compounds zirconium dioxide (ZrO.) and tantalum Ave -4.2 -3.6 -3.9 pentoxide. (Taos) mentioned heretofore, there are furthermore also used in addition antimony trioxide 25 (SbO) and bismuthum trioxide (BiO), alone or in Glass No.7 has the greatest negative anomalous par- combination. As a result thereof further possibilities of tial dispersion of all the examples given. However, this combinations for the three optical parameters ne, we, does not mean that higher negative values for the Av - and Ave are made available. s Table 6 s. (weight%) Glass No 18 19 20 21 . 22, B.O. 33.5 33.5 3.0 31.0 31.0 PbO 42.5 42.5 40.0 40.0 32.0.