JP6675772B2 - Optical glass, preform and optical element - Google Patents

Description

  The present invention relates to an optical glass, a preform, and an optical element.

  Optical systems such as digital cameras and video cameras, although large or small, include blurs called aberrations. This aberration is classified into monochromatic aberration and chromatic aberration. In particular, chromatic aberration strongly depends on the material properties of a lens used in an optical system.

  Generally, chromatic aberration is corrected by a combination of a low-dispersion convex lens and a high-dispersion concave lens. However, this combination can only correct aberrations in the red and green regions, and leaves aberrations in the blue region. This aberration in the blue region that cannot be completely removed is called a secondary spectrum. In order to correct the secondary spectrum, it is necessary to perform optical design in consideration of the trend of the g-line (435.835 nm) in the blue region. At this time, the partial dispersion ratio (θg, F) is used as an index of the optical characteristic that is noticed in the optical design. In the above-described optical system in which a low dispersion lens and a high dispersion lens are combined, an optical material having a large partial dispersion ratio (θg, F) is used for the low dispersion lens, and the partial dispersion ratio (θg) is used for the high dispersion lens. By using an optical material having a small θg, F), the secondary spectrum is favorably corrected.

The partial dispersion ratio (θg, F) is represented by the following equation (1).
_{θg, F = (n g -n} F) / (n F -n C) ······ (1)

The optical glass has a substantially linear relationship between the partial dispersion ratio (θg, F) representing the partial dispersion in the short wavelength region and the Abbe number (ν _d ). A straight line representing this relationship is obtained by plotting the partial dispersion ratio of NSL7 and PBM2 and the Abbe number on rectangular coordinates using the partial dispersion ratio (θg, F) on the vertical axis and the Abbe number (ν _d ) on the horizontal axis. It is represented by a straight line connecting two points and is called a normal line (see FIG. 1). The normal glass used as the standard for the normal line differs depending on the optical glass manufacturer, but each company defines the glass with substantially the same inclination and intercept. (NSL7 and PBM2 are optical glasses manufactured by OHARA CORPORATION. The Abbe number (ν _d ) of PBM2 is 36.3, the partial dispersion ratio (θg, F) is 0.5828, and the Abbe number of NSL7 (ν _d ) Is 60.5, and the partial dispersion ratio (θg, F) is 0.5436.)

  Here, as a glass having an Abbe number (νd) of 20 or more and 35 or less, for example, optical glasses as disclosed in Patent Documents 1 to 3 are known.

JP 2000-016830 A JP 2013-234104 A JP 2012-206891 A

  However, the glasses disclosed in Patent Literatures 1 and 2 have a small partial dispersion ratio and are not sufficient for use as a lens for correcting the secondary spectrum. Further, although the glass disclosed in Patent Document 3 has a relatively small partial dispersion ratio, it has a large Abbe number, and thus a glass having a smaller Abbe number has been required.

The present invention has been made in view of the above-described problems, and has as its object to reduce the partial dispersion ratio (n _d ) and Abbe number (ν _d ) within desired ranges. (θg, F) is to obtain an optical glass having a small value.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, in a glass containing a SiO ₂ component and a Nb ₂ O ₅ component, a high refractive index and a low Abbe number (high Dispersion) and that a glass having a low partial dispersion ratio can be obtained, thereby completing the present invention.
Specifically, the present invention provides the following.

(1) In mass%, the SiO ₂ component contains 5.0 to 40.0%, and the Nb ₂ O ₅ component contains 15.0% or more and 60.0% or less, and 1.70 or more and 2.00 or less. An optical glass having a refractive index (n _d ), an Abbe number (ν _d ) of 20 or more and 35 or less, and a partial dispersion ratio (θg, F) of less than 0.610.

(2) In mass%,
ZrO ₂ component 0-20.0%
TiO ₂ component 0-20.0%
Li ₂ O component 0 to 15.0%
The optical glass according to (1), wherein

(3) In mass%,
La ₂ O ₃ component 0-20.0%
Gd ₂ O ₃ component 0 to 10.0%
Y ₂ O ₃ component from 0 to 20.0%
Yb ₂ O ₃ component 0 to 10.0%
MgO component 0-10.0%
CaO component 0-25.0%
SrO component 0-15.0%
BaO component 0-30.0%
ZnO component 0-15.0%
Na ₂ O component 0 to 15.0%
K ₂ O component from 0 to 10.0%
P ₂ O ₅ component 0-10.0%
B ₂ O ₃ component 0 to 15.0%
GeO ₂ component 0-10.0%
Ta ₂ O ₅ component 0-10.0%
WO ₃ components 0-10.0%
Al ₂ O ₃ component 0 to 10.0%
Ga ₂ O ₃ component 0 to 10.0%
Bi ₂ O ₃ component 0-10.0%
TeO ₂ component 0-10.0%
SnO ₂ component 0-5.0%
Sb ₂ O ₃ component 0-1.0%
The optical glass according to (1) or (2), wherein

(4) The mass sum of the Ln ₂ O ₃ component (where Ln is one or more selected from the group consisting of Y, La, Gd, and Yb) is 20.0% or less (1) to (3). The optical glass according to any one of the above.

(5) The optical glass according to any one of (1) to (4), wherein the mass ratio (Nb ₂ O ₅ + ZrO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + ZrO ₂ + Ln ₂ O ₃ ) is 0.50 or more.

(6) The optical glass according to any one of (1) to (5), wherein a mass ratio (ZrO ₂ ) / (Nb ₂ O ₅ + ZrO ₂ ) is 0.05 or more and 0.50 or less.

  (7) Any of (1) to (6), wherein the mass sum of the RO component (where R is at least one selected from the group consisting of Mg, Ca, Sr, and Ba) is 40.0% or less. The optical glass as described.

(8) Any of (1) to (7), wherein the mass sum of the Rn ₂ O component (where Rn is at least one selected from the group consisting of Li, Na and K) is 30.0% or less. The optical glass as described.

  (9) Any one of (1) to (8), wherein the refractive index (nd) and Abbe number (νd) satisfy the relationship of (−0.02νd + 2.35) ≦ nd ≦ (−0.02νd + 2.50). Optical glass.

(10) The optical glass according to any one of (1) to (9), wherein the wavelength (λ ₇₀ ) at which the spectral transmittance indicates 70% is 460 nm or less.

  (11) An optical element comprising the optical glass according to any one of (1) to (9).

  (12) A preform for polishing and / or precision press molding, comprising the optical glass according to any one of (1) to (9).

  (13) An optical element obtained by precision-pressing the preform according to (11).

According to the present invention, the refractive index (n _d) and Abbe number ([nu _d) is while remaining within the desired range to give the smaller optical glass having the partial dispersion ratio ([theta] g, F).

FIG. 7 is a diagram showing a normal line in which a partial dispersion ratio (θg, F) is represented on a vertical axis and an Abbe number (ν _d ) is represented on a rectangular coordinate on a horizontal axis. FIG. 4 is a diagram illustrating a relationship between a partial dispersion ratio (θg, F) and an Abbe number (ν _d ) for an example of the present application. FIG. 4 is a diagram illustrating a relationship between a refractive index (nd) and an Abbe number (ν _d ) for an example of the present application.

The optical glass of the present invention contains 5.0 to 40.0% of a SiO ₂ component and 15.0% or more and 60.0% or less of a Nb ₂ O ₅ component by mass%, and with .00 following refractive index _{(n d),} 20 or more 35 or less the Abbe number of the (ν _d), a partial dispersion ratio of less than 0.610 and (θg, F).
In the glass containing the SiO ₂ component and the Nb ₂ O ₅ component, a glass having a high refractive index, a low Abbe number (high dispersion) and a low partial dispersion ratio within a desired range can be obtained.
Therefore, it is possible to obtain desired while having a high refractive index (n _d) and low Abbe number ([nu _d), the partial dispersion ratio ([theta] g, F) useful optical glass in reducing chromatic aberration is small optical system .
In addition, low specific gravity can contribute to the weight reduction of optical equipment, high transmittance for visible light allows it to be used suitably for applications that transmit visible light, and press molding due to low glass transition point An optical glass suitable for molding by the above method can also be obtained.

  Hereinafter, embodiments of the optical glass of the present invention will be described in detail, but the present invention is not limited to the following embodiments at all, and can be implemented with appropriate changes within the scope of the present invention. . In addition, although the description may be omitted as appropriate for portions where the description is duplicated, the purpose of the invention is not limited.

[Glass component]
The composition range of each component constituting the optical glass of the present invention will be described below. In the present specification, unless otherwise specified, the contents of the respective components are all represented by mass% with respect to the total mass of the glass in terms of oxide. Here, the `` composition in terms of oxides '' refers to oxides, composite salts, metal fluorides, and the like used as raw materials of the glass constituent components of the present invention, assuming that they are all decomposed at the time of melting and change to oxides. The composition is a composition in which each component contained in the glass is described, with the total mass of the generated oxide being 100% by mass.

<About essential and optional components>
The SiO ₂ component is an essential component that promotes stable glass formation and reduces undesired devitrification (formation of crystals) as optical glass.
In particular, by setting the content of the SiO ₂ component to 5.0% or more, a glass having excellent devitrification resistance can be obtained without significantly increasing the partial dispersion ratio. This can also reduce devitrification and coloring during reheating. Therefore, the content of the SiO ₂ component is preferably 5.0% or more, more preferably more than 8.0%, further preferably more than 10.0%, further preferably more than 15.0%, and still more preferably 17. More than 0%.
On the other hand, when the content of the SiO ₂ component is set to 40.0% or less, a desired high refractive index can be easily obtained because the refractive index does not easily decrease, and an increase in the partial dispersion ratio can be suppressed. In addition, a decrease in the melting property of the glass raw material can be suppressed. Therefore, the upper limit of the content of the SiO ₂ component is preferably 40.0%, more preferably 35.0%, further preferably less than 30.0%, and further preferably less than 25.0%.
As the SiO ₂ component, SiO ₂ , K ₂ SiF ₆ , Na ₂ SiF _6, or the like can be used as a raw material.

The Nb ₂ O ₅ component is an essential component that, when contained at 15.0% or more, can increase the refractive index, lower the Abbe number and the partial dispersion ratio, and increase the devitrification resistance. Therefore, the content of the Nb ₂ O ₅ component is preferably 15.0% or more, more preferably more than 20.0%, further preferably more than 22.0%, further more preferably more than 25.0%, and still more preferably. It may be more than 29.0%, more preferably more than 31.0%.
On the other hand, by reducing the content of the Nb ₂ O ₅ component to 60.0% or less, the material cost of the glass can be reduced. In addition, it is possible to suppress an increase in the melting temperature during glass production and reduce devitrification due to excessive Nb ₂ O ₅ component content. Therefore, the content of the Nb ₂ O ₅ component is preferably 60.0% or less, more preferably 55.0% or less, and further preferably less than 50.0%.
As the Nb ₂ O ₅ component, Nb ₂ O ₅ or the like can be used as a raw material.

The ZrO ₂ component is an optional component that, when contained more than 0%, can increase the refractive index and Abbe number of the glass, lower the partial dispersion ratio, and increase the devitrification resistance. This can also reduce devitrification and coloring during reheating. Therefore, the content of the ZrO ₂ component is preferably more than 0%, more preferably more than 1.0%, more preferably more than 3.0%, still more preferably more than 5.0%, and still more preferably 6.0%. It may be super.
On the other hand, by setting the content of the ZrO ₂ component to 20.0% or less, devitrification can be reduced and more uniform glass can be easily obtained. Therefore, the upper limit of the content of the ZrO ₂ component is preferably 20.0%, more preferably 15.0%, further preferably 12.0%, and still more preferably 9.0%.
As the ZrO ₂ component, ZrO ₂ , ZrF ₄ or the like can be used as a raw material.

The TiO ₂ component is an optional component that increases the refractive index, lowers the Abbe number, and increases the devitrification resistance when it contains more than 0%. Therefore, the content of the TiO ₂ component may be preferably more than 0%, more preferably more than 1.0%, further preferably more than 2.0%, and still more preferably more than 2.4%.
On the other hand, by setting the content of the TiO ₂ component to 20.0% or less, the coloring of the glass can be reduced and the internal transmittance can be increased. Further, this makes it difficult for the partial dispersion ratio to increase, so that a desired low partial dispersion ratio close to a normal line can be easily obtained. Therefore, the content of the TiO ₂ component is preferably 20.0% or less, more preferably less than 17.0%, further preferably less than 14.0%, further preferably 10.0% or less, and further preferably 6. 2% or less.
As the TiO ₂ component, TiO ₂ or the like can be used as a raw material.

The Li ₂ O component is an optional component that can lower the partial dispersion ratio, lower the glass transition point, and enhance the melting property of the glass raw material when it contains more than 0%. Therefore, the content of the Li ₂ O component is preferably more than 0%, more preferably more than 0.5%, furthermore preferably more than 1.0%, further preferably 1.2% or more, and still more preferably 1.6. %.
On the other hand, when the content of the Li ₂ O component is 15.0% or less, a decrease in the refractive index can be suppressed, the chemical durability can be hardly deteriorated, and devitrification due to excessive content can be reduced.
Therefore, the content of the Li ₂ O component is preferably 15.0% or less, more preferably less than 10.0%, and still more preferably less than 8.0%.
As the Li ₂ O component, Li ₂ CO ₃ , LiNO ₃ , LiF, or the like can be used as a raw material.

La ₂ O ₃ component, Gd ₂ O ₃ component, Y ₂ O ₃ component, and Yb ₂ O ₃ component contain at least any one of more than 0%, so that the refractive index can be increased and the partial dispersion ratio can be reduced. Component.
On the other hand, when the content of each of the La ₂ O ₃ component and the Y ₂ O ₃ component is 20.0% or less, an increase in Abbe number can be suppressed, specific gravity can be reduced, devitrification can be reduced, and Material cost can be reduced. Therefore, the content of each of the La ₂ O ₃ component and the Y ₂ O ₃ component is preferably 20.0% or less, more preferably less than 10.0%, further preferably less than 5.0%, and still more preferably 3%. 0.0% or less.
Further, by setting the content of each of the Gd ₂ O ₃ component and the Yb ₂ O ₃ component to 10.0% or less, an increase in Abbe number can be suppressed, specific gravity can be reduced, devitrification can be reduced, and the material can be reduced. Cost can be reduced. Therefore, the content of each of the Gd ₂ O ₃ component and the Yb ₂ O ₃ component is preferably 10.0% or less, more preferably less than 5.0%, and still more preferably less than 3.0%.
La ₂ O ₃ component, Gd ₂ O ₃ component, Y ₂ O ₃ component and Yb ₂ O ₃ component are La ₂ O ₃ , La (NO ₃ ) ₃ .XH ₂ O (X is an arbitrary integer) as raw materials, Y ₂ O ₃ , YF ₃ , Gd ₂ O ₃ , GdF ₃ , Yb ₂ O _3, or the like can be used.

The MgO component is an optional component that can lower the melting temperature of glass when it contains more than 0%.
On the other hand, by setting the content of the MgO component to 10.0% or less, devitrification can be reduced while suppressing a decrease in the refractive index. Therefore, the content of the MgO component is preferably 10.0% or less, more preferably less than 5.0%, and further preferably less than 3.0%.
As the MgO component, MgO, MgCO ₃ , MgF ₂ or the like can be used as a raw material.

The CaO component is an optional component that, when contained in more than 0%, can reduce the Abbe number, reduce the devitrification, and enhance the melting property of the glass raw material while reducing the material cost of the glass. Therefore, the content of the CaO component may be preferably more than 0%, more preferably more than 1.0%, and even more preferably more than 2.0%.
On the other hand, by setting the content of the CaO component to 25.0% or less, a decrease in the refractive index, an increase in the Abbe number, and an increase in the partial dispersion ratio can be suppressed, and devitrification can be reduced. Therefore, the content of the CaO component is preferably 25.0% or less, more preferably less than 20.0%, further preferably less than 17.0%, further preferably less than 14.0%, and still more preferably 12.0%. %.
As the CaO component, CaCO ₃ , CaF ₂ or the like can be used as a raw material.

The SrO component is an optional component that can increase the refractive index and increase the devitrification resistance when it contains more than 0%.
In particular, by setting the content of the SrO component to 15.0% or less, deterioration of chemical durability can be suppressed. Therefore, the content of the SrO component is preferably 15.0% or less, more preferably less than 10.0%, further preferably less than 5.0%, further preferably less than 3.0%, and still more preferably 1.0%. %.
As the SrO component, Sr (NO ₃ ) ₂ , SrF ₂ or the like can be used as a raw material.

When the BaO component contains more than 0%, the refractive index can be increased, the partial dispersion ratio can be reduced, the devitrification resistance can be increased, the melting property of the glass raw material can be increased, and other alkaline earth components can be used. It is an optional component that can reduce the material cost of glass as compared with. Therefore, the content of the BaO component may be preferably more than 0%, more preferably more than 1.0%, further preferably more than 2.0%, and still more preferably more than 5.0%.
On the other hand, by setting the content of the BaO component to 30.0% or less, deterioration of chemical durability and devitrification can be suppressed. Therefore, the upper limit of the content of the BaO component is preferably 30.0%, more preferably 25.0%, still more preferably 22.0%, and still more preferably 19.0%.
As the BaO component, BaCO ₃ , Ba (NO ₃ ) ₂ or the like can be used as a raw material.

The ZnO component is an optional component that, when contained at more than 0%, can lower the partial dispersion ratio, increase the devitrification resistance, and lower the glass transition point. Therefore, the content of the ZnO component may be preferably more than 0%, more preferably more than 0.5%, further preferably more than 1.0%, and still more preferably 1.4% or more.
On the other hand, by reducing the content of the ZnO component to 15.0% or less, chemical durability can be enhanced while reducing devitrification and coloring at the time of reheating glass. Therefore, the content of the ZnO component is preferably 15.0% or less, more preferably less than 12.0%, further preferably less than 9.0%, further preferably less than 4.0%, and still more preferably 2.5%. %.
As the ZnO component, ZnO, ZnF ₂ or the like can be used as a raw material.

The Na ₂ O component is an optional component that can lower the partial dispersion ratio, lower the glass transition point, and enhance the melting property of the glass raw material when it contains more than 0%. Therefore, the content of the Li ₂ O component may be preferably more than 0%, more preferably more than 0.5%, and still more preferably more than 1.0%.
On the other hand, when the content of the Na ₂ O component is 15.0% or less, a decrease in the refractive index can be suppressed, chemical durability can be hardly deteriorated, and devitrification due to excessive content can be reduced.
Therefore, the content of the Na ₂ O component is preferably 15.0% or less, more preferably 12.0% or less, further preferably less than 10.0%, and still more preferably less than 7.0%.
As the Na ₂ O component, Na ₂ CO ₃ , NaNO ₃ , NaF, Na ₂ SiF ₆ or the like can be used as a raw material.

The K ₂ O component is an optional component that can increase the melting property of the glass raw material and lower the glass transition point when at least one of them exceeds 0%.
On the other hand, when the content of the K ₂ O component is 10.0% or less, an increase in the partial dispersion ratio can be suppressed, devitrification can be reduced, and chemical durability can be hardly deteriorated. Therefore, the content of the K ₂ O component is preferably 10.0% or less, more preferably less than 5.0%.
As the K ₂ O component, K ₂ CO ₃ , KNO ₃ , KF, KHF ₂ , K ₂ SiF ₆ or the like can be used as a raw material.

The P ₂ O ₅ component is an optional component that can enhance the stability of the glass when it contains more than 0%.
On the other hand, by setting the content of the P ₂ O ₅ component to 10.0% or less, the devitrification due to the excessive content of the P ₂ O ₅ component can be reduced. Therefore, the content of the P ₂ O ₅ component is preferably 10.0% or less, more preferably less than 5.0%, and still more preferably less than 3.0%.
As the P ₂ O ₅ component, Al (PO ₃ ) ₃ , Ca (PO ₃ ) ₂ , Ba (PO ₃ ) ₂ , BPO ₄ , H ₃ PO ₄ or the like can be used as a raw material.

The B ₂ O ₃ component is an optional component that, when contained in more than 0%, promotes stable glass formation to enhance devitrification resistance and enhance the melting property of the glass raw material. Therefore, the content of the B ₂ O ₃ component may preferably have a lower limit of more than 0%, more preferably 1.0%, and still more preferably 2.0%.
On the other hand, by setting the content of the B ₂ O ₃ component to 15.0% or less, a decrease in the refractive index and an increase in the partial dispersion ratio can be suppressed. Therefore, the content of the B ₂ O ₃ component is preferably 15.0% or less, more preferably less than 14.0%, further preferably less than 12.0%, further preferably less than 10.0%, and still more preferably. It is less than 8.0%, more preferably less than 6.0%.
As the B ₂ O ₃ component, H ₃ BO ₃ , Na ₂ B ₄ O ₇ , Na ₂ B ₄ O ₇ .10H ₂ O, BPO ₄ or the like can be used as a raw material.

The GeO ₂ component is an optional component that can increase the refractive index and reduce devitrification when it contains more than 0%.
On the other hand, by setting the content of the GeO ₂ component to 10.0% or less, the amount of the expensive GeO ₂ component used is reduced, so that the material cost of the glass can be reduced. Therefore, the content of the GeO ₂ component is preferably 10.0% or less, more preferably less than 5.0%, and further preferably less than 3.0%.
As the GeO ₂ component, GeO ₂ or the like can be used as a raw material.

The Ta ₂ O ₅ component is an optional component that, when contained more than 0%, can increase the refractive index, decrease the Abbe number and the partial dispersion ratio, and increase the devitrification resistance.
On the other hand, by reducing the content of the Ta ₂ O ₅ component to 10.0% or less, the use amount of the Ta ₂ O ₅ component, which is a rare mineral resource, is reduced, and the glass is easily melted at a lower temperature. Glass production costs can be reduced. In addition, this can reduce the devitrification of the glass due to the excessive content of the Ta ₂ O ₅ component. Therefore, the content of the Ta ₂ O ₅ component is preferably 10.0% or less, more preferably less than 5.0%, further preferably less than 3.0%, and still more preferably less than 1.0%. In particular, from the viewpoint of reducing the material cost of the glass, the Ta ₂ O ₅ component need not be contained.
As the Ta ₂ O ₅ component, Ta ₂ O ₅ or the like can be used as a raw material.

The WO ₃ component is an optional component that, when contained in more than 0%, can increase the refractive index, lower the Abbe number, increase the devitrification resistance, and enhance the melting property of the glass raw material.
On the other hand, by setting the content of the WO ₃ component to 10.0% or less, it is possible to make it difficult to increase the partial dispersion ratio of the glass, and to reduce the coloring of the glass to increase the internal transmittance. Therefore, the content of WO ₃ component is preferably 10.0% or less, more preferably less than 5.0%, more preferably less than 3.0%, more preferably the upper limit of less than 1.0%.
As the WO ₃ component, WO ₃ or the like can be used as a raw material.

The Al ₂ O ₃ component and the Ga ₂ O ₃ component are optional components that can enhance chemical durability and improve devitrification resistance when at least one of them exceeds 0%.
On the other hand, by setting the content of each of the Al ₂ O ₃ component and the Ga ₂ O ₃ component to 10.0% or less, devitrification due to excessive content of the Al ₂ O ₃ component and the Ga ₂ O ₃ component is reduced. it can. Therefore, the content of each of the Al ₂ O ₃ component and the Ga ₂ O ₃ component is preferably 10.0% or less, more preferably less than 5.0%, and further preferably less than 3.0%.
As the Al ₂ O ₃ component and the Ga ₂ O ₃ component, Al ₂ O ₃ , Al (OH) ₃ , AlF ₃ , Ga ₂ O ₃ , Ga (OH) _{3 and the} like can be used as raw materials.

The Bi ₂ O ₃ component is an optional component that, when contained more than 0%, can increase the refractive index to lower the Abbe number and lower the glass transition point.
On the other hand, by setting the content of the Bi ₂ O ₃ component to 10.0% or less, the partial dispersion ratio can be hardly increased, and the coloring of the glass can be reduced to increase the internal transmittance. Therefore, the content of the Bi ₂ O ₃ component is preferably 10.0% or less, more preferably less than 5.0%, further preferably less than 3.0%, and still more preferably less than 1.0%.
As the Bi ₂ O ₃ component, Bi ₂ O ₃ or the like can be used as a raw material.

The TeO ₂ component is an optional component that can increase the refractive index, lower the partial dispersion ratio, and lower the glass transition point when containing more than 0%.
On the other hand, by setting the content of the TeO ₂ component to 10.0% or less, the coloring of the glass can be reduced and the internal transmittance can be increased. Further, by reducing the use of expensive TeO ₂ components, a glass with lower material cost can be obtained. Therefore, the content of the TeO ₂ component is preferably 10.0% or less, more preferably less than 5.0%, further preferably less than 3.0%, and still more preferably less than 1.0%.
As the TeO ₂ component, TeO ₂ or the like can be used as a raw material.

The Sb ₂ O ₃ component is an optional component capable of promoting defoaming from the molten glass and refining the glass when contained in an amount of more than 0%.
On the other hand, by the content of _Sb 2 _{O 3} ingredient 1.0% or less, it is possible to hardly cause excessive foaming during glass melting, melting facilities _Sb 2 _{O 3} component (especially Pt, etc. Alloy with noble metals). Therefore, the upper limit of the content of the Sb ₂ O ₃ component is preferably 1.0%, more preferably 0.5%, and still more preferably 0.1%. However, when importance is placed on the environmental influence of the optical glass, the Sb ₂ O ₃ component may not be contained.
Sb ₂ O ₃ component can be used _{Sb 2 O 3, Sb 2 O} 5, Na 2 H 2 Sb 2 O 7 · 5H 2 O and the like as raw materials.

In addition, the component which clarifies and defoams glass is not limited to the above-mentioned Sb ₂ O ₃ component, and a known fining agent or defoaming agent in the field of glass production, or a combination thereof can be used. .

The sum (mass sum) of the contents of Ln ₂ O ₃ components (where Ln is at least one selected from the group consisting of La, Gd, Y, and Yb) is preferably 20.0% or less. Thereby, devitrification of glass can be reduced, increase in Abbe number can be suppressed, and material cost of glass can be reduced. Therefore, the mass sum of the Ln ₂ O ₃ component is preferably 20.0% or less, more preferably less than 15.0%, further preferably less than 10.0%, further preferably less than 7.0%, further preferably less than 7.0%. It is less than 4.0%, more preferably less than 2.0%.

Nb _{2 with} respect to the total amount of the Nb ₂ O ₅ component, the TiO ₂ component, the ZrO ₂ component, and the Ln ₂ O ₃ component (where Ln is at least one selected from the group consisting of Y, La, Gd, and Yb) O ₅ component and the total amount of the ratio of the ZrO ₂ component is preferably 0.50 or more. Thereby, the partial dispersion ratio can be made smaller while obtaining a desired high refractive index. Therefore, the mass ratio (Nb ₂ O ₅ + ZrO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + ZrO ₂ + Ln ₂ O ₃ ) is preferably 0.50, more preferably 0.60, further preferably 0.75, The lower limit is preferably 0.80, and more preferably 0.86.
The upper limit of the mass ratio (Nb ₂ O ₅ + ZrO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + ZrO ₂ + Ln ₂ O ₃ ) may be 1, but from the viewpoint of suppressing a decrease in the melting property of the glass raw material. It may be less than one.

The total amount of nb ₂ O ₅ component and ZrO ₂ component, the ratio of the content of the ZrO ₂ component is preferably 0.05 or more. Thereby, while obtaining a desired high refractive index, the material cost of the glass can be reduced, and the partial dispersion ratio can be further reduced. Therefore, the lower limit of the mass ratio (ZrO ₂ ) / (Nb ₂ O ₅ + ZrO ₂ ) is preferably 0.05, more preferably 0.10, and still more preferably 0.13.
The upper limit of the mass ratio (ZrO ₂ ) / (Nb ₂ O ₅ + ZrO ₂ ) may be 1, but may be less than 1 from the viewpoint of further improving the devitrification resistance, and may be 0.50 or less. There may be.

The sum (mass sum) of the contents of the RO components (where R is at least one selected from the group consisting of Mg, Ca, Sr, and Ba) is preferably 40.0% or less. Thereby, the devitrification of the glass due to excessive content of these components can be reduced. Therefore, the mass sum of the RO component is preferably 40.0% or less, more preferably 35.0% or less, and further preferably less than 32.0%.
On the other hand, the mass sum of the RO component is preferably more than 0%, more preferably 1.0% or more, and still more preferably 1.8% or more, from the viewpoint of enhancing the meltability of the glass raw material and reducing the devitrification. It may be.

The sum (mass sum) of the contents of Rn ₂ O components (where Rn is at least one selected from the group consisting of Li, Na and K) is preferably 30.0% or less. This makes it difficult to lower the refractive index of the glass and reduces the devitrification during glass formation. Therefore, the total content of the Rn ₂ O component is preferably 30.0% or less, more preferably 25.0%, further preferably 20.0%, and further preferably 16.0%.
On the other hand, the mass sum of the Rn ₂ O component is preferably more than 0%, more preferably more than 1.0%, and still more preferably 1.0%, from the viewpoint of increasing the melting property of the glass raw material and lowering the glass transition point. It may be 9% or more.

The total amount (mass sum) of the B ₂ O ₃ component and the Ln ₂ O ₃ component (where Ln is one or more selected from the group consisting of Y, La, Gd, and Yb) is 30.0% or less. preferable. Thereby, specific gravity can be reduced and high transmittance can be obtained. Therefore, the mass sum (B ₂ O ₃ + La ₂ O ₃ ) is preferably 30.0%, more preferably 25.0%, further preferably 20.0%, still more preferably 15.0%, and still more preferably. The upper limit is 11.0%, more preferably 7.0%, and still more preferably 4.0%.

The ratio of the total amount of the B ₂ O ₃ component and the Ln ₂ O ₃ component (where Ln is one or more selected from the group consisting of Y, La, Gd and Yb) to the content of the ZrO ₂ component is as follows: It is preferably 3.00 or less. Thereby, the specific gravity can be reduced, a high transmittance can be obtained, and the partial dispersion ratio can be further reduced. Therefore, the upper limit of the mass ratio ZrO ₂ / (B ₂ O ₃ + Ln ₂ O ₃ ) is preferably 3.00, more preferably 2.00, further preferably 1.00, and further preferably 0.50.

The ratio of the content of the Na ₂ O component to the content of the Li ₂ O component is preferably 0.01 or more and 10.00 or less.
In particular, by setting this ratio to 0.01 or more, devitrification of glass can be reduced. Therefore, the lower limit of the mass ratio Na ₂ O / Li ₂ O may preferably be 0.01, more preferably 0.02, and even more preferably 0.03.
On the other hand, by setting this ratio to 10.00 or less, the partial dispersion ratio can be further reduced. Therefore, the upper limit of the mass ratio Na ₂ O / Li ₂ O is preferably 10.00, more preferably 5.00, further preferably 3.00, and further preferably 1.50.

<Ingredients that should not be contained>
Next, components that should not be contained in the optical glass of the present invention and components that are not preferably contained will be described.

  Other components can be added as needed as long as the properties of the glass of the present invention are not impaired. However, each of transition metal components such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag, and Mo, excluding Ti, Zr, Nb, W, La, Gd, Y, Yb, and Lu, is used alone. Or, even when a small amount is contained in a complex, the glass is colored, and has a property of causing absorption at a specific wavelength in the visible region.In particular, in an optical glass using a wavelength in the visible region, it is preferable that the glass is not substantially contained. .

Further, lead compounds such as PbO and arsenic compounds such as As ₂ O ₃ are components that have a high environmental load, and therefore, should not substantially be contained, that is, should not be contained at all except for unavoidable contamination.

  Furthermore, each component of Th, Cd, Tl, Os, Be, and Se tends to refrain from using as harmful chemicals in recent years, and is used not only in the glass manufacturing process but also in the processing process and disposal after commercialization. Environmental measures are required to this extent. Therefore, when importance is placed on environmental influences, it is preferable that these are not substantially contained.

[Production method]
The optical glass of the present invention is produced, for example, as follows. That is, the above-mentioned raw materials are uniformly mixed so that each component is within a predetermined content range, and the prepared mixture is charged into a platinum crucible, a quartz crucible or an alumina crucible and roughly melted, and then a gold crucible, a platinum crucible , Placed in a platinum alloy crucible or an iridium crucible, melted in a temperature range of 1100 to 1400 ° C for 3 to 5 hours, homogenized by stirring, foamed out, etc., lowered to a temperature of 1000 to 1400 ° C, and then finished with stirring. It is manufactured by removing striae by casting, casting in a mold and gradually cooling.

<Physical properties>
The optical glass of the present invention has a high refractive index and an Abbe number in a predetermined range.
The lower limit of the refractive index ( _nd ) of the optical glass of the present invention is preferably 1.70, more preferably 1.72, further preferably 1.75, and further preferably 1.80. The upper limit of the refractive index may be preferably 2.00, more preferably 1.97, further preferably 1.95, further preferably 1.92, further preferably 1.90.
The Abbe number (ν _d ) of the optical glass of the present invention is preferably 35 or less, more preferably less than 32, and further preferably less than 30. On the other hand, the lower limit of the Abbe number (ν _d ) of the optical glass of the present invention is preferably 20, more preferably 22, and still more preferably 25.
The optical glass of the present invention having such a refractive index and Abbe's number is useful in optical design. In particular, it is possible to reduce the size of an optical system while achieving high imaging characteristics and the like. The degree can be expanded.

Here, the optical glass of the present invention preferably has a refractive index (nd) and an Abbe number (νd) satisfying a relationship of (−0.02νd + 2.35) ≦ nd ≦ (−0.02νd + 2.50). In the glass having the composition specified by the present invention, a more stable glass can be obtained by satisfying the relationship between the refractive index (nd) and the Abbe number (νd).
Therefore, in the optical glass of the present invention, the refractive index (nd) and Abbe number (νd) preferably satisfy the relationship of nd ≧ (−0.02νd + 2.35), and nd ≧ (−0.02νd + 2.36) More preferably, the relationship of nd ≧ (−0.02νd + 2.37) is satisfied.
On the other hand, in the optical glass of the present invention, the refractive index (nd) and Abbe number (νd) preferably satisfy the relationship of nd ≦ (−0.02νd + 2.50), and nd ≦ (−0.02νd + 2.49). ) Is more preferably satisfied, the relationship of nd ≦ (−0.02νd + 2.48) is more preferably satisfied, and the relationship of nd ≦ (−0.02νd + 2.47) is more preferably satisfied.

The optical glass of the present invention has a low partial dispersion ratio (θg, F).
More specifically, the partial dispersion ratio (θg, F) of the optical glass of the present invention is preferably less than 0.610, more preferably 0.605, and still more preferably 0.600. The lower limit of the partial dispersion ratio (θg, F) may be preferably 0.550, more preferably 0.560, and even more preferably 0.570.
In addition, the partial dispersion ratio (θg, F) of the optical glass of the present invention is (−0.0025 × νd + 0.645) ≦ (θg, F) ≦ (−0.05) with respect to the Abbe number (ν _d ). 0025 × νd + 0.695).
As a result, an optical glass having a low partial dispersion ratio (θg, F) can be obtained, and an optical element formed from this optical glass can be used to reduce chromatic aberration of an optical system.

Therefore, in the optical glass of the present invention, it is preferable that the partial dispersion ratio (θg, F) and the Abbe number (νd) satisfy the relationship of θg, F ≧ (−0.0025 × νd + 0.645). It is more preferable to satisfy the relationship of ≧ (−0.0025 × νd + 0.655), and it is more preferable to satisfy the relationship of θg, F ≧ (−0.0025 × νd + 0.660).
On the other hand, in the optical glass of the present invention, the partial dispersion ratio (θg, F) and Abbe number (νd) preferably satisfy the relationship of θg, F ≦ (−0.0025 × νd + 0.695). It is more preferable to satisfy the relationship of F ≦ (−0.0025 × νd + 0.685), and it is further preferable to satisfy the relationship of θg, F ≦ (−0.0025 × νd + 0.680).

In particular, in a region where the Abbe number (ν _d ) is small, the partial dispersion ratio (θg, F) of general glass is higher than that of the normal line, and the Abbe number (νd) is plotted on the horizontal axis and the partial axis is plotted on the vertical axis. When the dispersion ratio (θg, F) is taken, the relationship between the partial dispersion ratio (θg, F) of general glass and the Abbe number (ν _d ) is represented by a curve having a larger slope than the normal line. In the above-mentioned relational expression of the partial dispersion ratio (θg, F) and Abbe number (νd), by defining these relations using a straight line having a larger slope than the normal line, the partial dispersion ratio is more than that of general glass. This indicates that a glass having a small (θg, F) can be obtained.

It is preferable that the optical glass of the present invention has little coloring.
In particular, the optical glass of the present invention, when expressed in terms of glass transmittance, has a wavelength (λ ₇₀ ) showing a spectral transmittance of 70% in a sample having a thickness of 10 mm, preferably 460 nm or less, more preferably 430 nm or less, and further more preferably. It is 420 nm or less.
In the optical glass of the present invention, the wavelength (λ ₅ ) showing a spectral transmittance of 5% in a sample having a thickness of 10 mm is preferably 400 nm or less, more preferably 380 nm or less, and still more preferably 360 nm or less.
In the optical glass of the present invention, the wavelength (λ ₈₀ ) at which a sample having a thickness of 10 mm shows a spectral transmittance of 80% is preferably 550 nm or less, more preferably 520 nm or less, and still more preferably 500 nm or less.
As a result, the absorption edge of the glass is positioned near the ultraviolet region, and the transparency of the glass in the visible region is increased. Therefore, this optical glass can be preferably used as a material for an optical element such as a lens.

The optical glass of the present invention preferably has a low specific gravity. More specifically, the specific gravity of the optical glass of the present invention is preferably 5.00 [g / cm ³ ] or less. This reduces the mass of the optical element and the optical device using the same, which can contribute to the weight reduction of the optical device. Therefore, the specific gravity of the optical glass of the present invention is preferably 5.00, more preferably 4.80, further preferably 4.50, and further preferably 4.10. The specific gravity of the optical glass of the present invention is generally about 2.50 or more, more specifically 2.80 or more, and more specifically 3.00 or more in many cases.
The specific gravity of the optical glass of the present invention is measured based on Japan Optical Glass Industrial Association Standard JOGIS05-1975 “Method for measuring specific gravity of optical glass”.

The optical glass of the present invention preferably has a glass transition point of 650 ° C. or lower. As a result, the glass is softened at a lower temperature, so that the glass can be mold-pressed at a lower temperature. In addition, the life of the mold can be extended by reducing the oxidation of the mold used for mold press molding. Therefore, the upper limit of the glass transition point of the optical glass of the present invention is preferably 650 ° C, more preferably 630 ° C, and further preferably 620 ° C.
The lower limit of the glass transition point of the optical glass of the present invention is not particularly limited, but the glass transition point of the optical glass of the present invention is preferably 460 ° C, more preferably 480 ° C, and even more preferably 500 ° C. Good.

  It is preferable that the optical glass of the present invention has high devitrification resistance at the time of glass production (in the specification, it may be simply referred to as “devitrification resistance”). This suppresses a decrease in transmittance due to crystallization of the glass or the like at the time of glass production, so that the optical glass can be preferably used for an optical element such as a lens that transmits visible light. In addition, as a scale which shows that devitrification resistance at the time of glass preparation is high, a low liquidus temperature is mentioned, for example.

[Preform and optical element]
From the produced optical glass, a glass molded body can be produced by means of mold press molding such as reheat press molding and precision press molding. That is, a preform for mold press molding is produced from optical glass, and a reheat press molding is performed on the preform, and then a polishing process is performed to produce a glass molded body. Precision press molding is performed on the preform thus formed to produce a glass molded body. The means for producing the glass molded body is not limited to these means.

  The glass molded body produced in this way is useful for various optical elements, and among them, it is particularly preferable to use it for applications of optical elements such as lenses and prisms. Accordingly, color blur due to chromatic aberration in transmitted light of the optical system provided with the optical element is reduced. Therefore, when this optical element is used for a camera, an object to be photographed can be represented more accurately, and when this optical element is used for a projector, a desired image can be projected with higher definition.

The composition of the embodiment of the present invention (No.1~No.15) and Comparative Example (No. A), and a refractive index _(n d), Abbe number ([nu _d), the partial dispersion ratio ([theta] g, F), Tables 1 and 2 show the results of wavelengths (λ ₅ , λ ₇₀ , λ ₈₀ ) at which the spectral transmittances show 5%, 70% and 80%, the glass transition point (Tg), and the specific gravity. The following embodiments are for illustrative purposes only, and are not limited to these embodiments.

  The glasses of the Examples and Comparative Examples were used as ordinary raw materials for the respective components, such as oxides, hydroxides, carbonates, nitrates, fluorides, hydroxides, and metaphosphate compounds. High-purity raw materials are selected, weighed so as to have the composition ratios of the respective Examples and Comparative Examples shown in the table, uniformly mixed, and then charged into a platinum crucible, depending on the melting difficulty of the glass composition. After melting in an electric furnace in a temperature range of 1100 to 1400 ° C. for 3 to 5 hours, performing homogenization by stirring and homogenizing the foam, lowering the temperature to 1000 to 1400 ° C., homogenizing with stirring, and then casting into a mold. The glass was produced by slow cooling.

The refractive index of the glass of the Examples and Comparative Examples _(n d), Abbe number ([nu _d) and partial dispersion ratio ([theta] g, F) were measured according to Japan Optical Glass Industry Society Standard JOGIS01-2003.
Then, from the value of the refractive index obtained _{(n d)} and Abbe number ([nu _d), in relation _{(n d = -a × ν d} + b), the gradient a is calculated intercept b when 0.02 .
Also, when the slope a ′ in the relational expression (θg, F = −a ′ × ν _d + b ′) is 0.0025 from the obtained Abbe number (ν _d ) and the value of the partial dispersion ratio (θg, F). Was obtained.
In addition, the glass used for this measurement used what was processed in the annealing furnace with the annealing temperature falling rate of -25 degreeC / hr.

The transmittances of the glasses of the examples and the comparative examples were measured according to the Japan Optical Glass Industrial Association standard JOGIS02. In the present invention, the presence or absence and the degree of coloring of the glass were determined by measuring the transmittance of the glass. Specifically, a face-to-face parallel polished product having a thickness of 10 ± 0.1 mm was measured for spectral transmittance from 200 to 800 nm according to JISZ8722, and λ ₅ (wavelength at a transmittance of 5%), λ ₇₀ (transmittance) (Wavelength at 70%) and λ ₈₀ (wavelength at a transmittance of 80%) were obtained.

  The glass transition point (Tg) of each of the glasses of the examples and the comparative examples is determined by measuring the relationship between the temperature and the elongation of the sample in accordance with JOGIS08-2003 “Method for measuring the thermal expansion of optical glass” specified by the Japan Optical Glass Industrial Association. It was determined from the obtained thermal expansion curve.

  The specific gravities of the glasses of the examples and the comparative examples were measured based on JOGIS05-1975 “Method for measuring the specific gravity of optical glass” specified by Japan Optical Glass Industrial Association.

As shown in these tables, the optical glass of the example of the present invention had a partial dispersion ratio (θg, F) of less than 0.610, which was within a desired range.
Here, in the optical glass of the example of the present invention, the partial dispersion ratio (θg, F) and Abbe number (νd) are (−0.0025 × νd + 0.645) ≦ (θg, F) ≦ (−0. 0025 × νd + 0.695), and more specifically, the relationship of (−0.0025 × νd + 0.660) ≦ (θg, F) ≦ (−0.0025 × νd + 0.680). . That is, the relationship between the partial dispersion ratio (θg, F) and the Abbe number (ν _d ) of the glass of the example of the present application is as shown in FIG.
On the other hand, the glass of Comparative Example (No. A) of the present invention had a partial dispersion ratio (θg, F) of 0.610. Therefore, it became clear that the optical glass of the example of the present invention had a smaller partial dispersion ratio (θg, F) than the glass of the comparative example.

The optical glasses of Examples of the present invention are both refractive index _{(n d)} of 1.75 or more, with more particularly 1.80 or more, the refractive index _{(n d)} is 2.00 or less, more Specifically, it was 1.90 or less, which was within a desired range.
Further, the optical glasses of the examples of the present invention each have an Abbe number (ν _d ) of 20 or more, more specifically 26 or more, and an Abbe number (ν _d ) of 35 or less, more specifically 30. And within the desired range.
Here, in the optical glass of the example of the present invention, the refractive index (nd) and the Abbe number (νd) satisfy the relationship of (−0.02νd + 2.35) ≦ nd ≦ (−0.02νd + 2.50). More specifically, the relationship of (−0.02νd + 2.37) ≦ nd ≦ (−0.02νd + 2.47) was satisfied. FIG. 3 shows the relationship between the refractive index (nd) and Abbe number (νd) of the glass of the example of the present invention.

Therefore, the optical glass of the embodiment, there refractive index (n _d) and Abbe number ([nu _d) is within a desired range, and the partial dispersion ratio ([theta] g, F) found to be a small optical glass having Was.

In addition, each of the optical glasses of Examples of the present invention had λ ₇₀ (wavelength at a transmittance of 70%) of 460 nm or less, more specifically 420 nm or less.
Further, the optical glasses of the examples of the present invention each had λ ₅ (wavelength at a transmittance of 5%) of 400 nm or less, more specifically 360 nm or less.
Further, the optical glasses of the examples of the present invention each had λ ₈₀ (wavelength at a transmittance of 80%) of 550 nm or less, more specifically 500 nm or less.
Therefore, it became clear that the optical glass of the example of the present invention had high transmittance to visible light and was hardly colored.

  Further, the optical glasses of the examples each had a specific gravity of 5.00 or less, more specifically 4.00 or less, and were within a desired range.

  In addition, since the optical glass of the example has a glass transition point of 650 ° C. or lower, more specifically 620 ° C. or lower, it is presumed that the glass can be press-molded at a lower temperature.

  Furthermore, a lens preform was formed using the optical glass of the example, and the lens preform was subjected to mold press molding. As a result, various lens shapes could be stably processed.

  As described above, the present invention has been described in detail for the purpose of illustration. However, this example is for the purpose of illustration only, and many modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention. Will be understood.

Claims (11)

% By mass, containing more than 15.0% to 35.0% or less of SiO ₂ component and more than 25.0% or more of 55.0% of Nb ₂ O ₅ component,
ZrO ₂ component more than 3.0% to 7.25 %
CaO component 0 to less than 17.0% ZnO component more than 0.5% to less than 12.0% B ₂ O ₃ component 1.0 to 15.0%
Ta ₂ O ₅ component 0 to less than 1.0% TiO ₂ component More than 1.0% to 10.0%
Rn ₂ O component (where Rn is at least one selected from the group consisting of Li, Na and K) having a mass sum of more than 1.0% to 20.0 % ;
The mass ratio Na ₂ O / Li ₂ O is 0 to 1.50,
1.75 to 2.00 of the refractive index _{(n d),} 27.1 or more 35 or less the Abbe number of the (ν _d), a partial dispersion ratio of less than 0.610 (θg, F) an optical glass having. In mass%,
Li ₂ O component 0 to 15.0%
The optical glass according to claim 1, wherein In mass%,
La ₂ O ₃ component 0-20.0%
Gd ₂ O ₃ component 0 to 10.0%
Y ₂ O ₃ component from 0 to 20.0%
Yb ₂ O ₃ component 0 to 10.0%
MgO component 0-10.0%
SrO component 0-15.0%
BaO component 0-30.0%
Na ₂ O component 0 to 15.0%
K ₂ O component from 0 to 10.0%
P ₂ O ₅ component 0-10.0%
GeO ₂ component 0-10.0%
WO ₃ components 0-10.0%
Al ₂ O ₃ component 0 to 10.0%
Ga ₂ O ₃ component 0 to 10.0%
Bi ₂ O ₃ component 0-10.0%
TeO ₂ component 0-10.0%
SnO ₂ component 0-5.0%
Sb ₂ O ₃ component 0-1.0%
The optical glass according to claim 1, wherein The mass sum of Ln ₂ O ₃ components (where Ln is one or more selected from the group consisting of Y, La, Gd, and Yb) is 20.0% or less according to any one of claims 1 to 3. Optical glass. The weight ratio _{(Nb 2 O 5 + ZrO 2} ) / (Nb 2 O 5 + TiO 2 + ZrO 2 + Ln 2 O 3) is 0.50 or more either described optical glass of claims 1 to 4, which is. The optical glass according to claim 1, wherein a mass ratio (ZrO ₂ ) / (Nb ₂ O ₅ + ZrO ₂ ) is 0.05 or more and 0.50 or less.   The optical glass according to any one of claims 1 to 6, wherein a mass sum of an RO component (where R is at least one selected from the group consisting of Mg, Ca, Sr, and Ba) is 40.0% or less.   The optical glass according to any one of claims 1 to 7, wherein the refractive index (nd) and the Abbe number (νd) satisfy a relationship of (−0.02νd + 2.35) ≦ nd ≦ (−0.02νd + 2.50). The optical glass according to any one of claims 1 to 8, wherein a wavelength (λ ₇₀ ) at which the spectral transmittance indicates 70% is 460 nm or less.   An optical element comprising the optical glass according to claim 1.   A preform for polishing and / or precision press molding, comprising the optical glass according to claim 1.

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