Abstract The present invention is drawn to glasses suitable for the fabrication of segments or buttons for multifocal ophthalmic lenses. The inventive glasses have refractive indices ranging between about 1.745-1.771, an Abbe number greater than 29 for a refractive index of 1.771 and greater than 31 for a refractive index of 1.745, a softening point between about 640°-700° C., a coefficient of thermal expansion (25°-300° C.) between about 90-98×10 -7 /°C., and satisfactory chemical durability. The glasses consist essentially, expressed in terms of weight percent on the oxide basis, of ______________________________________ SiO 2 28-32.5
Na 2 O 2-9
K 2 O 0-4
Li 2 O 0-1
K 2 O + Na 2 O + Li 2 O
4-10.5
BaO 0-22
La 2 O 3 0-20
BaO + La 2 O 3 14-22
PbO 28.5-34
ZnO 0-4
TiO 2 0-9
ZrO 2 2-6.5
Nb 2 O 5 0-10
TiO 2 + Nb 2 O 5 4.5-12
ZrO 2 + TiO 2 + Nb 2 O 5 6-17
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A glass suitable for the fabrication of segments or buttons for multifocal ophthalmic lenses having a refractive index between 1.745-1.771, an Abbe number greater than 29 for a refractive index of 1.771 and greater than 31 for a refractive index of 1.745, a softening temperature between approximately 640°-700° C., a coefficient of thermal expansion (25°-300° C.) of approximately 90-98×10 -7 /°C. and satisfactory chemical durability, which consists essentially, espressed in terms of weight percent on the oxide basis, of ______________________________________
SiO.sub.2 28-32.5
Na.sub.2 O 2-9
K.sub.2 O 0-4
Li.sub.2 O 0-1
K.sub.2 O + Na.sub.2 O + Li.sub.2 O
4-10.5
BaO 0-22
La.sub.2 O.sub.3 0-20
BaO + La.sub.2 O.sub.3
14-22
PbO 28.5-34
ZnO 0-4
TiO.sub.2 0-9
ZrO.sub.2 2-6.5
Nb.sub.2 O.sub.5 0-10
TiO.sub.2 + Nb.sub.2 O.sub.5
4.5-12
ZrO.sub.2 + TiO.sub.2 + Nb.sub.2 O.sub.5
6-17
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Claim 2
Dependent Claim
134 words
A glass suitable for the fabrication of segments or buttons for multifocal ophthalmic lenses having a refractive index between 1.745-1.771, an Abbe number greater than 29 for a refractive index of 1.771 and greater than 31 for a refractive index of 1.745, a softening temperature between approximately 640°-700° C., a coefficient of thermal expansion (25°-300° C.) of approximately 90-98×10 -7 /°C. and satisfactory chemical durability, which consists essentially, espressed in terms of weight percent on the oxide basis, of ______________________________________
SiO.sub.2 28-32.5
Na.sub.2 O 2-9
K.sub.2 O 0-4
Li.sub.2 O 0-1
K.sub.2 O + Na.sub.2 O + Li.sub.2 O
4-10.5
BaO 0-22
La.sub.2 O.sub.3 0-20
BaO + La.sub.2 O.sub.3
14-22
PbO 28.5-34
ZnO 0-4
TiO.sub.2 0-9
ZrO.sub.2 2-6.5
Nb.sub.2 O.sub.5 0-10
TiO.sub.2 + Nb.sub.2 O.sub.5
4.5-12
ZrO.sub.2 + TiO.sub.2 + Nb.sub.2 O.sub.5
6-17
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Claim 3
Dependent Claim
59 words
A glass according to claim 1 consisting essentially, expressed in terms of weight percent on the oxide basis, of ______________________________________
SiO.sub.2 29-32
Na.sub.2 O 5-8
BaO 0-22
La.sub.2 O.sub.3 0-14
BaO + La.sub.2 O.sub.3
18-22
PbO 30-33
ZnO 0-3
TiO.sub.2 5-9
ZrO.sub.2 2-4
Nb.sub.2 O.sub.5 0-6
TiO.sub.2 + Nb.sub.2 O.sub.5
5-11
ZrO.sub.2 + TiO.sub.2 + Nb.sub.2 O.sub.5
8-14
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Claim 4
Dependent Claim
39 words
A glass according to claim 1 consisting essentially, expressed in terms of weight percent on the oxide basis, of ______________________________________
SiO.sub.2
30.9
Na.sub.2 O
6.7
BaO 8.0
ZnO 2.7
La.sub.2 O.sub.3
11.5
ZrO.sub.2
3.3
PbO 31.6
TiO.sub.2
5.3
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