Optical glass
An optical glass that is an oxide glass having a very high refractive index in spite of its low-dispersion property, having excellent glass stability and having less susceptibility to coloring.
1. An optical glass that is an oxide glass and that comprises, by cationic %,
0 to 30% of Si 4+ ,
10 to 55% of B 3+ ,
less than 5% of total of Li + , Na + and K + ,
less than 5% of total of Mg 2+ , Ca 2+ and Sr 2+ ,
0 to 8% of Ba 2+ ,
0.1 to 15% of Zn 2+ ,
10 to 50% of La 3+ ,
0 to 20% of Gd 3+ ,
0.25 to 15% of Y 3+ ,
0 to 10% of Yb 3+ ,
0 to 20% of Zr 4+ ,
0.1 to 22% of Ti 4+ ,
0 to 20% of Nb 5+ ,
0 to 8% of Ta 5+ ,
0 to 5% of W 6+ ,
0 to 8% of Ge 4+ ,
0 to 10% of Bi 3+ , and
0 to 10% of Al 3+ ,
the cationic ratio of the content of Si 4+ to the content of B 3+ , Si 4+ /B 3+ , being less than 1.0, the total content of Nb 2 O 5 and Ta 2 O 5 as oxides being determined so as to achieve a liquidus temperature of 1,220° or lower, the optical glass having a refractive index nd of 1.930 to 2.2, an Abbe's number νd of 25 to 45 and a glass transition temperature Tg of 630° C. or higher.
2. The optical glass of claim 1 , which has a coloring degree λ70 of less than 470 nm.
3. The optical glass of claim 1 , which has a partial dispersion ratio Pg,F and an Abbe's number νd which satisfy the relationship of the following expression (1),
Pg,F≦− 0.0017 ×νd+ 0.660 (1).
4. A press-molding glass gob formed of the optical glass recited in claim 1 .
5. An optical element which is formed of the optical glass recited in claim 1 .
6. A process for producing an optical element blank to be completed into an optical element by grinding and polishing, which comprises softening the press-molding glass gob recited in claim 4 by heating, and press-molding it.
7. A process for producing an optical element blank to be completed into an optical element by grinding and polishing, which comprises melting a glass raw material and press-molding the thus-obtained molten glass to produce an optical element blank formed of the optical glass recited in claim 1 .
8. A process for producing an optical element, which comprises grinding and polishing the optical glass blank recited in claim 6 .
9. A process for producing an optical element, which comprises grinding and polishing the optical glass blank recited in claim 7 .
10. The optical glass of claim 1 , comprising less than 2% of total of Mg 2+ , Ca 2+ and Sr 2+ .
11. The optical glass of claim 1 , comprising 0 to 2% of W 6+ .
12. The optical glass of claim 1 , comprising 0 to 4% of Ge 4+ .
13. The optical glass of claim 10 , comprising 0 to 5% of Ba 2+ .
14. The optical glass of claim 10 , comprising 0 to 3% of Ba 2+ .
15. The optical glass of claim 1 , comprising less than 2% of total of Mg 2+ , Ca 2+ and Sr 2+ , 0 to 2% of W 6+ , 0 to 4% Ge 4+ and 0 to 5% of Ba 2+ .