Optical glass and its use

Details Optical glass and its use Optical glass and its use

1999-04-27

2001-06-26

Sample, David R. (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S079000, C501S900000, C501S901000, C501S902000, C501S903000

Reexamination Certificate

active

06251813

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an optical glass, a precision-press shapeable material formed of the optical glass, and an optical part formed of the optical glass. More specifically, it relates to an optical glass suitable for producing a high-refractivity low-dispersion optical part by press shaping, a precision-press shapeable material formed of the optical glass and an optical part formed of the optical glass.
PRIOR ART OF THE INVENTION
A method of precision-press shaping a glass is a method in which a glass preform is shaped, under pressure and at a high temperature, into a glass product having a form of an end product or a form very close thereto and having a surface accuracy by means of a shaping mold having a predetermined cavity. In the above precision-press shaping method, shaped articles having a predetermined form can be produced with high productivity. Therefore, various optical parts of glass such as a spherical lens, a non-spherical lens, a diffraction grating, etc., have come to be produced by precision-press shaping, and various optical glasses suitable for precision-press shaping have been accordingly developed.
For producing an optical part of a glass by precision-press shaping, it is required to press-shape a glass preform at a high temperature as described above, and a shaping mold used for the above production is therefore also exposed to a high temperature and a high pressure exerted thereon. It is therefore desired to decrease the sag temperature T
s
of the glass preform to the lowest level possible, in view of prevention of damage which is caused on the shaping mold per se and a release film provided on the internal surface of the shaping mold by a high-temperature environment during the press shaping.
When a glass preform for precision-press shaping is produced, a glass having a high liquidus temperature L.T. is liable to devitrify and is therefore poor in mass-productivity, so that it is desirable that the liquidus temperature L.T. of the glass should be as low as possible.
As an optical glass with a high refractivity (used to refer to a refractive index n
d
of at least 1.675 in the present specification), a low dispersion (used to refer to an Abbe's number &ngr;
d
of at least 50 in the present specification) and a low sag temperature T
s
, there are known (1) a glass of SiO
2
—B
2
O
3
—(Li
2
O, Na
2
O, K
2
O)—ZnO—La
2
O
3
system (see JP-A-8-259257), (2) a glass of SiO
2
—B
2
O
3
—La
2
O
3
—Gd
2
O
3
—Li
2
O—CaO—BaO system (see Japanese Patent No. 2,616,958), and the like.
However, the above glass (1) has a defect that when it is attempted to produce a glass having an Abbe's number &ngr;
d
of at least 50, the glass shows a liquidus temperature L.T. of as high as approximately 1,000° C. so that the glass is poor in mass-productivity, or that the glass easily devitrifies so that it is poor in mass-productivity.
The above glass (2) has a defect that when it is attempted to produce a glass having a refractive index n
d
of at least 1.675, it shows a liquidus temperature L.T. of over 1,000° C. so that it is poor in mass-productivity.
SUMMARY OF THE INVENTION
Under the circumstances, it is a first object of the present invention to provide an optical glass which can be easily obtained as an optical glass having the properties of a high refractive index and low dispersion and having both a low sag temperature T
s
and a low liquidus temperature L.T.
It is a second object of the present invention to provide a precision-press shapeable material which can easily give a precision-press shaped article formed of an optical glass having properties of a high refractive index and low dispersion.
It is a third object of the present invention to provide an optical part formed of an optical glass having properties of a high refractive index and low dispersion, by precision-press shaping with high productivity.
The present inventors have made diligent studies to achieve the above objects, and have found that an optical glass comprising specific amounts of specific components as essential components and optional components can fulfill the above objects. On the basis of the above finding, the present invention has been completed.
That is, according to the present invention, the first object of the present invention is achieved by an optical glass comprising, as essential components, boron oxide, lanthanum oxide, yttrium oxide, silicon oxide, lithium oxide, calcium oxide, zinc oxide and at least one of gadolinium oxide and zirconium oxide, the contents of these essential components by % by weight being 25 to 42% of boron oxide, 14 to 30% of lanthanum oxide, 2 to 13% of yttrium oxide, 2 to 20% of silicon oxide, greater than 2% but up to 9% of lithium oxide, 0.5 to 20% of calcium oxide, 2 to 20% of zinc oxide, 0 to 8% of gadolinium oxide and 0 to 8% of zirconium oxide, the total content of gadolinium oxide and zirconium oxide being 0.5 to 12%, the total content of these essential components being at least 90%, the optical glass further comprising, as optional components, by % by weight, 0 to 5% of sodium oxide, 0 to 5% of potassium oxide, 0 to 5% of magnesium oxide, 0 to 5% of strontium oxide, 0 to 10% of barium oxide, 0 to 5% of tantalum oxide, 0 to 5% of aluminum oxide, 0 to 5% of ytterbium oxide, 0 to 5% of niobium oxide, 0 to 2% of arsenic oxide and 0 to 2% of antimony oxide.
According to the present invention, the above second object of the present invention is achieved by a precision-press shapeable material formed of the above optical glass.
According to the present invention, the above third object of the present invention is achieved by an optical part produced by precision-press shaping a material formed of the above optical glass into the part in a mold comprising an upper mold member and a lower mold member and having a predetermined cavity.


REFERENCES:
patent: 4057435 (1977-11-01), Boudot et al.
patent: 4128432 (1978-12-01), Komorita et al.
patent: 4166746 (1979-09-01), Ishibashi et al.
patent: 4469800 (1984-09-01), Boudot et al.
patent: 4732875 (1988-03-01), Sagara et al.
patent: 35 35575 (1996-04-01), None
patent: 61-146721 (1986-07-01), None
patent: 62-100449 (1987-05-01), None
patent: 7-51446 (1995-06-01), None
patent: 8-059282 (1996-03-01), None
patent: 8-259257 (1996-10-01), None
patent: 2616958 (1997-03-01), None
patent: 10-226533 (1998-08-01), None

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