Optical glass

Details Optical glass Optical glass

2002-01-29

2004-06-01

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S045000, C501S046000, C501S902000, C501S903000

Reexamination Certificate

active

06743743

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical glass that has a medium to high refractive index and high dispersion characteristics, can be pressed at relative low temperature, and has a relatively low sag temperature and liquidus temperature.
2. Description of Related Art
A number of glasses having medium to high refractive indexes and high dispersion characteristics are known.
For example, Japanese Patent Un-examined Publication No. Hei 07-97234 describes a low melting point optical glass having a medium to high refractive index and high dispersion characteristics and comprising prescribed quantities of P
2
O
5
, Na
2
O, Nb
2
O
5
, and WO
3
. This optical glass is described as having a refractive index of 1.69-1.83, a dispersion ratio of 21-32, and a sag temperature of not more than 570° C. However, when comparison is conducted between the examples described in Japanese Patent Un-examined Publication No. Hei 07-97234 having a refractive index of not greater than 1.73, those glasses characterized by having a sag temperature Ts exceeding 520° C. are numerous. This is attributed to an Li
2
O content of 0-0.5 weight percent. Further, there are also examples (Examples 6, 7, and 8) in which Ts is less than 520° C. even with an Li
2
O content within the range of 0-0.5 weight percent. In that case, there is the problem of the use of expensive GeO
2
as a glass starting material. When the GeO
2
is removed from the glasses of these examples, the liquidus temperature (also referred to hereinafter as “LT”) ends up exceeding 900° C. This is attributed to a P
2
O
5
content of not greater than 32 percent.
Japanese Patent Un-examined Publication No. Hei 05-270853 describes an optical glass having a medium to high refractive index and high dispersion characteristics and comprising prescribed quantities of SiO
2
, B
2
O
3
, P
2
O
5
, Nb
2
O
5
, and Na
2
O+K
2
O. In the glasses described in this publication, all the glasses described in the examples having a refractive index of 1.64-1.73 have liquidus temperatures exceeding 900° C. This is attributed to a P
2
O
5
content of not greater than 32 weight percent. Further, these glasses also have a Ts exceeding 520° C. This is attributed to an Na
2
O content of not greater than 5 weight percent.
Japanese Patent Un-examined Publication No. Sh{overscore (o)} 52-132012 describes an optical glass having a medium to high refractive index and high dispersion characteristics and comprising prescribed quantities of B
2
O
3
, P
2
O
5
, and Nb
2
O
5
. The glasses described in the examples of this publication, which have refractive indexes of 1.64-1.73, all have a Ts exceeding 520° C. This is attributed to an Na
2
O content not exceeding 5 weight percent. Excluding the glasses described in Examples 2 and 3, the lack of Li
2
O is thought to result in a Ts exceeding 520° C. Even in the glasses of Examples 2 and 3 which comprise Li
2
O in a quantity exceeding 0.5 weight percent, the Ts exceeds 520° C. and the liquidus temperature exceeds 900° C. This is attributed to a P
2
O
5
content of not more than 32 weight percent and an Nb
2
O
5
content exceeding 30 weight percent.
The press-molding of glass is normally conducted within a high temperature range exceeding the sag temperature temperature Ts of the glass by about 20-60° C. When the yield temperature of the glass exceeds 520° C., the press temperature becomes at least 540° C. Thus, the glass has a strong tendency to react with the molding surface of the mold, shortening the service life of the mold and rendering the glass unsuited to mass production.
When the liquidus temperature is high, the glass tends to lose transparency in the vicinity of its softening point, that is, in the vicinity of the molding temperature in press-molding.
Further, the glass preforms employed in reheating presses are required not to have variation in shape and weight. Thus, when forming preforms by shaping molten glass, the shaping is conducted at a prescribed viscosity where there tends not to be variation in shape and weight. Thus, when the glass is at a temperature at which the viscosity is suited to shaping, it must not tend to lose transparency, that is, the liquidus temperature must be lower than the temperature at which viscosity is suited to shaping. From these perspectives, the liquidus temperature is required to be 800-900° C.
However, in the above-described glasses, almost all of those glasses having a refractive index falling within a range of 1.64-1.72 and an Abbé number of 29-36 have a sag temperature temperature exceeding 520° C. and a liquidus temperature exceeding 900° C. In glasses used in press-molding, when the life of the mold and the tendency of the glass to lose transparency are considered, a sag temperature of not greater than 520° C. and a relatively low liquidus temperature, particularly one not greater than 900° C., are desirable.
Accordingly, the object of the present invention is to provide an optical glass having a medium to high refractive index and high dispersion characteristics, the liquidus temperature of which is comparatively low, specifically not greater than 900° C., and more particularly, an optical glass the refractive index of which falls within the range of 1.64-1.72 and the Abbé number of which falls within the range of 29-36.
SUMMARY OF THE INVENTION
The invention relates to an optical glass comprising, by means of weight percentages, more than 32 percent and not more than 45 percent P
2
O
5
, more than 0.5 percent and not more than 6 percent Li
2
O, more than 5 percent and not more than 22 percent Na
2
O, 6-30 percent Nb
2
O
5
, 0.5-10 percent B
2
O
3
, 0-35 percent WO
3
, 0-14 percent K
2
O, and 10-24 percent Na
2
O+K
2
O, and the total of all the above components is not less than 80 percent.
With the above optical glass, the glass preferably comprises, by means of weight percentages, more than 32 percent and not more than 40 percent P
2
O
5
, 1-4 percent Li
2
O, 10-19 percent Na
2
O, 10-28 percent Nb
2
O
5
, 1-5 percent B
2
O
3
, 0-8 percent K
2
O, and 12-22 percent Na
2
O+K
2
O, and the total of all the above components is not less than 80 percent. With this optical glass, the glass more preferably comprises 12-17 percent Na
2
O, 15-26 percent Nb
2
O
5
, 0-4 percent K
2
O, and 14-19 percent Na
2
O+K
2
O.
With the above optical glasses, the glass may further comprise, by means of weight percentages, 0-2 percent SiO
2
, 0-5 percent Al
2
O
3
, not less than 0 percent but less than 8 percent TiO
2
, 0-15 percent ZnO, 0-12 percent BaO, 0-18 percent WO
3
, not less than 0 percent but less than 1 percent Sb
2
O
3
, and 0-1 percent SnO
2
, and the total of all of the above components and the components listed in any one of claims
1
to
3
is not less than 95 percent. With this optical glass, the glass preferably comprises, by means of weight percentages, 0-3 percent Al
2
O
3
, 0-6 percent TiO
2
, and 0-9 percent ZnO, where the total of all of the components listed is not less than 95 weight percent; and the glass preferably comprises 0-1 percent SiO
2
.
With the above optical glasses, the glass may comprise not less than 0 percent but less than 0.5 percent SiO
2
, 0-5 percent TiO
2
, 0-5 percent ZnO, and the total of all of the components listed is not less than 98 percent; and the glass may further comprise 3-15 weight percent WO
3
.
The invention further relates to an optical glass comprised phosphate glass which comprises, by means of weight percentages, more than 0.5 percent and but not more than 6 percent Li
2
O, more than 5 percent but not more than 22 percent Na
2
O, 0-14 percent K
2
O, 10-24 percent Na
2
O+K
2
O, 6-30 percent Nb
2
O
5
, and not more than 45 percent P
2
O
5
, and exhibits a refractive index (nd) of 1.64-1.72, an Abbé number (vd) of 29-36, and a sag temperature (Ts) of not greater than 520° C.; and an optical glass comprised of phosphate glass which comprises, by means of weight percentages, more than 0.5 percent but not more than 6 percent Li
2
O, more than 5 percent but not more than 22

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