Abstract This invention is directed to the production of glasses especially suitable for use as ophthalmic lenses which exhibit indices of refraction between about 1.699-1.703, Abbe numbers equal to or greater than 41.0, densities less than 3.25 g/cm 3 , and good resistance to attack by acids. The glasses are essentially free of Al 2 O 3 and consist essentially, in weight percent on the oxide basis, of: ______________________________________ SiO 2 33-37 CaO 8-9.5
B 2 O 3 7.5-13 SrO 2-4
SiO 2 + B 2 O 3 44-48 La 2 O 3 12.3-14.5
Li 2 O 5-8 ZrO 2 4-6
Na 2 O 0-2.5 Nb 2 O 5 8-10.5
K 2 O 0-2 TiO 2 5-7
Li 2 O + Na 2 O + K 2 O
5-8 As 2 O 3 0-0.8.
______________________________________
Glasses useful in the production of ophthalmic lenses having an index of refraction between about 1.699-1.703, an Abbe number equal to or greater than 41.0, a density less than 3.25 g/cm 3 , and good chemical durability in an acid medium, characterized in that they are essentially free of Al 2 O 3 and consist essentially, expressed in terms of weight percent on the oxide basis, of: ______________________________________
SiO.sub.2 33-37 CaO 8-9.5
B.sub.2 O.sub.3
7.5-13 SrO 2-4
SiO.sub.2 + B.sub.2 O.sub.3
44-48 La.sub.2 O.sub.3
12.3-14.5
Li.sub.2 O 5-8 ZrO.sub.2
4-6
Na.sub.2 O 0-2.5 Nb.sub.2 O.sub.5
8-10.5
K.sub.2 O 0-2 TiO.sub.2
5-7
Li.sub.2 O + Na.sub.2 O + K.sub.2 O
5-8 As.sub.2 O.sub.3
0-0.8.
______________________________________
Claim 2
Dependent Claim
114 words
Glasses useful in the production of ophthalmic lenses having an index of refraction between about 1.699-1.703, an Abbe number equal to or greater than 41.0, a density less than 3.25 g/cm 3 , and good chemical durability in an acid medium, characterized in that they are essentially free of Al 2 O 3 and consist essentially, expressed in terms of weight percent on the oxide basis, of: ______________________________________
SiO.sub.2 33-37 CaO 8-9.5
B.sub.2 O.sub.3
7.5-13 SrO 2-4
SiO.sub.2 + B.sub.2 O.sub.3
44-48 La.sub.2 O.sub.3
12.3-14.5
Li.sub.2 O 5-8 ZrO.sub.2
4-6
Na.sub.2 O 0-2.5 Nb.sub.2 O.sub.5
8-10.5
K.sub.2 O 0-2 TiO.sub.2
5-7
Li.sub.2 O + Na.sub.2 O + K.sub.2 O
5-8 As.sub.2 O.sub.3
0-0.8.
______________________________________
Claim 3
Dependent Claim
63 words
Glasses according to claim 1 characterized in that they consist essentially, expressed in terms of weight percent on the oxide basis, of: ______________________________________
SiO.sub.2 33.5-35 SrO 2.4-3.4
B.sub.2 O.sub.3
9-12.5 La.sub.2 O.sub.3
12.8-14.3
SiO.sub.2 + B.sub.2 O.sub.3
44.5-47 ZrO.sub.2
4.5-5.5
Li.sub.2 O 5.5-7.8 Nb.sub.2 O.sub.5
9-10
Na.sub.2 O 0-2 TiO.sub.2
5.5-6.5
Li.sub.2 O + Na.sub.2 O
5.5-7.8 As.sub.2 O.sub.3
0.1-0.3
CaO 8.5-9.2
______________________________________