JP2020172428A - Optical glass, preform and optical element - Google Patents

Abstract

To obtain an optical glass that has excellent reheat press moldability while its refractive index (nd), Abbe number (νd) and partial dispersion ratio (θg, F) are in desired ranges.SOLUTION: An optical glass contains, in mass%, SiO2 component 20.0-50.0%, Nb2O5 component 10.0-45.0%, TiO2 component 2.0-20.0%, ZrO2 component 1.0-15.0%, and Rn2O component 5.0-30.0%. The refractive index (nd) is 1.67 or more and 1.90 or less and the Abbe number is 23.0 or more and 38.0 or less. The relational expression of the refractive index (nd) and the Abbe number (νd), nd<-0.0125νd+2.175, is satisfied. The relational expression of the Abbe number (νd) and the partial dispersion ratio (θg, F), θg, F<-0.00257νd+0.6800, is satisfied.SELECTED DRAWING: None

Description

The present invention relates to optical glass and optical elements.

Optical systems such as digital cameras and video cameras, although they are large and small, contain bleeding called aberrations. This aberration is classified into monochromatic aberration and chromatic aberration, and in particular, chromatic aberration strongly depends on the material characteristics of the lens used in the optical system.

Generally, chromatic aberration is corrected by combining a low-dispersion convex lens and a high-dispersion concave lens, but this combination can only correct aberrations in the red region and the green region, and aberrations in the blue region remain. This aberration in the blue region that cannot be completely removed is called a quadratic spectrum. In order to correct the secondary spectrum, it is necessary to carry out an optical design that takes into account 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 characteristics attracting attention in the optical design. In the optical system combining the above-mentioned low-dispersion lens and high-dispersion lens, an optical material having a large partial dispersion ratio (θg, F) is used for the low-dispersion side lens, and a partial dispersion ratio (partial dispersion ratio) is used for the high-dispersion side lens. By using an optical material having a small θg, F), the secondary spectrum is satisfactorily corrected.

The partial dispersion ratio (θg, F) is expressed by the following equation (1).
θg, F = ( _ng −n _F ) / (n _F −n _C ) ・ ・ ・ ・ ・ ・ ・ ・ (1)

In optical glass, there is a substantially linear relationship between the partial dispersion ratio (θg, F) and the Abbe number (ν _d ), which represent the partial dispersibility in the short wavelength region. The straight line representing this relationship is a plot of the partial dispersion ratio and Abbe number of NSL7 and PBM2 on Cartesian coordinates with 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. The normal glass that is the standard of the normal line differs depending on the optical glass manufacturer, but each company defines it with almost the same inclination and section (NSL7 and PBM2 are optical glasses manufactured by O'Hara Co., Ltd., and Abbe of PBM2. The number (ν _d ) is 36.3, the partial dispersion ratio (θg, F) is 0.5828, the Abbe number (ν _d ) of NSL7 is 60.5, and the partial dispersion ratio (θg, F) is 0.5436. .).

In recent years, due to the needs in optical design, glass having an Abbe number (ν _d ) of 25 or more and 40 or less is often used as an optical material having a small partial dispersion ratio (θg, F).
The following documents are known as anomalous dispersive glass in the region of 25 to 40 Abbe numbers.

Japanese Unexamined Patent Publication No. 2013-028532 Although the glass of Patent Document 1 of JP-A-2017-154963 has both a high refractive index and a low partial dispersion ratio, there is a problem that devitrification is likely to occur during reheat pressing. The glass of Patent Document 2 has a high Abbe number value with respect to the refractive index, and a glass having a lower Abbe number (high dispersion side) has been required in terms of optical design.

The present invention was made in view of the above problems, it is an object of the refractive index (n _d), Abbe number ([nu _d) and partial dispersion ratio ([theta] g, F) is desired range The purpose is to obtain an optical glass having good reheat press moldability while being inside.

More specifically a refractive index _{(n d)} and Abbe number satisfies the relation n _d <-0.0125ν _d +2.150 of ([nu _d), and an Abbe number ([nu _d) and partial dispersion ratio ([theta] g, It is an object of the present invention to obtain an optical glass satisfying the relational expression θg and F <−0.003ν _d +0.6740 of F) and having good reheat press moldability.

As a result of intensive test and research to solve the above problems, the present inventor has found that the glass containing the SiO ₂ component, the TiO ₂ component and the Nb ₂ O ₅ component contains the TiO ₂ component and the Nb ₂ O ₅ component. By adjusting the relationship between the rates, it has been found that an optical glass capable of achieving both a high refractive index and a high dispersion, a low partial dispersion ratio, and good reheat press characteristics can be produced, and the present invention has been completed.

(1) By mass%
SiO ₂ component 20.0-50.0%,
Nb ₂ O ₅ component 10.0-45.0%
TiO ₂ component 2.0 to 20.0%,
ZrO ₂ component 1.0 to 15.0%
Rn ₂ O component 5.0 to 30.0%
Contains,
Refractive index _{(n d)} of 1.67 or more 1.90 or less, and the Abbe number is 23.0 or more 38.0 or less,
Satisfy the relation n _d <-0.0125ν _d +2.175 refractive index _{(n d)} and Abbe number (ν _d),
An optical glass characterized by satisfying the relational expressions θg and F <−0.00257ν _d +0.6800 of the Abbe number (ν _d ) and the partial dispersion ratio (θg, F).

(2) The optical glass according to (1), wherein the value of the mass ratio TiO ₂ / Nb ₂ O ₅ is in the range of 0.10 to 1.00.

(3) The optical glass according to (1) or (2), wherein the λ70 value is 420 nm or less.

(4) An optical glass for reheat pressing made of the optical glass according to any one of (1) to (3).

According to the present invention, the refractive index (n _d), has an Abbe number ([nu _d), and low partial dispersion ratio ([theta] g, F), and reheat press formability it is possible to obtain good optical glass.

An embodiment of the optical glass of the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the object of the present invention. In addition, although the description may be omitted as appropriate for the parts where the description is duplicated, the gist of the invention is not limited.

[Glass component]
The composition range of each component constituting the optical glass of the present invention is described below. Unless otherwise specified in the present specification, the content of each component shall be expressed as a mass% of the total mass of the glass in the oxide conversion composition. Here, the "oxide-equivalent composition" is based on the assumption that the oxides, composite salts, metal fluorides, etc. used as raw materials for the glass constituents of the present invention are all decomposed at the time of melting and changed to oxides. The composition is such that each component contained in the glass is described with the total mass of the produced oxide as 100% by mass.

<About essential ingredients and optional ingredients>
The SiO ₂ component is an essential component that promotes stable glass formation and reduces devitrification (generation of crystals) that is unfavorable for optical glass.
In particular, by setting the content of the SiO ₂ component to 20.0% or more, glass having excellent devitrification resistance can be obtained without significantly increasing the partial dispersion ratio. In addition, devitrification and coloring can be reduced. Therefore, the lower limit of the content of the SiO ₂ component is preferably 20.0% or more, more preferably 25.0% or more, still more preferably 30.0% or more.
On the other hand, by setting the content of the SiO ₂ component to 50.0% or less, the refractive index is less likely to decrease, so that a desired high refractive index can be easily obtained and an increase in the partial dispersion ratio can be suppressed. Further, this can suppress a decrease in the meltability of the glass raw material. Therefore, the content of the SiO ₂ component is preferably 50.0% or less, more preferably 48.0% or less, and most preferably 46.0% or less.
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 capable of increasing the refractive index and lowering the Abbe number and the partial dispersion ratio.
In particular, by setting the content of the Nb ₂ O ₅ component to 10.0% or more, the refractive index is increased to the target optical constant and adjusted within the range of the present invention to reduce the anomalous dispersibility. can do. Therefore, the lower limit of the content of the Nb ₂ O ₅ component is preferably 10.0% or more, more preferably 12.0% or more, still more preferably 15.0% or more.
On the other hand, by reducing the content of the Nb ₂ O ₅ component to 45.0%% or less, the temperature coefficient of the relative refractive index can be reduced and the material cost of glass can be reduced.
Further, the devitrification of the glass can be reduced. Therefore, the content of the Nb ₂ O ₅ component is preferably 45.0% or less, more preferably 43.0% or less, and most preferably 41.0% or less.
As the Nb ₂ O ₅ component, Nb ₂ O ₅ or the like can be used as a raw material.

The TiO ₂ component is an optional component that increases the refractive index and decreases the Abbe number. Therefore, the lower limit of the TiO ₂ component is preferably 2.0% or more, most preferably 3.0% or more.
On the other hand, when the TiO ₂ component is contained in a large amount, the partial dispersion ratio becomes large. Further, 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. In addition, this makes it difficult for the partial dispersion ratio to increase. Therefore, the content of the TiO ₂ component is preferably 20.0% or less, more preferably 19.0% or less, still more preferably 18.0% or less.
As the TiO ₂ component, TiO ₂ or the like can be used as a raw material.

The optical glass of the present invention not only has a predetermined high refractive index and high dispersion characteristic, but also has a feature that the partial dispersion ratio is within a predetermined range.
That is, satisfying the relation n _d <-0.0125ν _d +2.175 refractive index _{(n d)} and Abbe number ([nu _d), and Abbe's number ([nu _d) and partial dispersion ratio ([theta] g, F) relationship It is required to satisfy the equation θg, F <−0.00257ν _d +0.6800. The present inventor has found that it is effective that the mass ratio of TiO ₂ and Nb ₂ O ₅ is within a predetermined range in order to satisfy the above characteristics. Specifically, the value of the mass ratio TiO ₂ / Nb ₂ O ₅ is preferably 0.10 or more, more preferably 0.11 or more, most preferably 0.12 or more as the lower limit, and preferably 1.00 or less. , More preferably 0.95 or less, and most preferably 0.90 or less.

ZrO ₂ component, when containing more than 1.0%, increasing the refractive index of the glass and the Abbe number, which is an optional component that can be lowered partial dispersion ratio. Therefore, the content of the ZrO ₂ component is preferably 1.0% or more, more preferably 2.0% or more, most preferably from a lower limit of 3.0% or more.
On the other hand, by the content of the ZrO ₂ component below 15.0%, it is possible to reduce the devitrification and can be easy to obtain a more homogeneous glass. Therefore, the content of the ZrO ₂ component is preferably 15.0% or less, more preferably 12.0 percent or less, more preferably to a maximum of 10.0%.
As the ZrO ₂ component, ZrO ₂ , ZrF _4, or the like can be used as a raw material.

The Rn ₂ O component (in the formula, Rn is one or more selected from the group consisting of Li, Na, and K) is contained in the glass when the sum of the contents (mass sum) is 5.0% or more. It is an essential ingredient that can improve stability. Therefore, the lower limit of the sum of the Rn ₂ O components is preferably 5.0% or more, more preferably 7.0% or more, and more preferably 10.0% or more.
On the other hand, the sum (mass sum) of the contents of the Rn ₂ O component (in the formula, Rn is one or more selected from the group consisting of Li, Na, and K) is 30.0% or less. It is possible to suppress a decrease in the refractive index and reduce devitrification due to excessive content. Therefore, the upper limit is preferably 30.0% or less, more preferably 29.0% or less, still more preferably 28.0% or less.

The Li ₂ O component is an optional component that can lower the partial dispersion ratio when it contains more than 0%. Therefore, the content of the Li ₂ O component may be preferably more than 0%, more preferably 0.5% or more, and more preferably 1.0% or more as the lower limit.
On the other hand, by reducing the content of the Li ₂ O component to 10.0% or less, devitrification due to excessive content can be reduced, and devitrification of the reheat press can also be reduced.
Therefore, the content of the Li ₂ O component is preferably 10.0% or less, more preferably 9.0% or less, and most preferably 7.0% or less.
As the Li ₂ O component, Li ₂ CO ₃ , LiNO _3, or the like can be used as a raw material.

When the Na ₂ O component is contained in excess of 0%, it is an optional component that enhances the meltability of the glass raw material, reduces coloring, increases the coefficient of thermal expansion, and decreases the temperature coefficient of the relative refractive index. Therefore, the lower limit of the content of the Na ₂ O component is preferably more than 0%, more preferably 1.0% or more, still more preferably 3.0% or more.
On the other hand, by setting the content of the Na ₂ O component to 15.0% or less, a decrease in the refractive index can be suppressed and devitrification due to an excessive content can be reduced.
Therefore, the content of the Na ₂ O component is preferably 15.0% or less, more preferably 14.0% or less, still more preferably 13.0% or less.
As the Na ₂ O component, Na ₂ CO ₃ , Na NO _3, or the like can be used as a raw material.

K 2 _O component, when ultra containing 0%, an elevated melting property of the glass raw material, which is an optional component to reduce coloration.
On the other hand, by the content of K 2 _O component below 15.0%, suppressed the increase in the partial dispersion ratio, suppress the increase in the refractive index, it can be reduced devitrification. Therefore, the content of _{K 2} O component is preferably 15.0% or less, 12.0 percent and more preferably less, more preferably to a maximum of 10.0%.
As the K ₂ O component, K ₂ CO ₃ , KNO _3, or the like can be used as a raw material.

The RO component (in the formula, R is one or more selected from the group consisting of Mg, Ca, Sr, and Ba) is an optional component that can improve the stability of the glass.
On the other hand, the sum (mass sum) of the contents of the RO component (in the formula, R is one or more selected from the group consisting of Mg, Ca, Sr, and Ba) is 10.0% or less. It is possible to suppress an increase in the partial dispersion ratio and reduce devitrification due to excessive content. Therefore, the upper limit is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 1.0% or less.

The MgO component is an optional component that can improve the stability of the glass.
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 5.0% or less, and further preferably 1.0% or less.
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 can improve the stability of the glass. On the other hand, by reducing the content of the CaO component to 10.0% or less, an increase in the partial dispersion ratio can be suppressed. Therefore, the content of the CaO component is preferably 10.0% or less, more preferably 5.0% or less, and further preferably less than 1.0%.
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 improve the stability of the glass.
On the other hand, by reducing the content of the SrO component to 10.0% or less, an increase in the partial dispersion ratio can be suppressed. Therefore, the content of the SrO component is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 1.0% or less.
As the SrO component, Sr (NO ₃ ) ₂ , SrF _2, or the like can be used as a raw material.

The BaO component is an optional component whose refractive index can be increased.
On the other hand, by setting the content of the BaO component to 10.0% or less, an increase in the partial dispersion ratio can be suppressed and devitrification during reheat pressing can be reduced. Therefore, the content of the BaO component is preferably 10.0% or less, more preferably 5.0% or less, and most preferably 1.0% or less.
As the BaO component, BaCO ₃ , Ba (NO ₃ ) _2, or the like can be used as a raw material.

The B ₂ O ₃ component is an optional component that promotes stable glass formation, can lower the liquidus temperature, enhances devitrification resistance, and enhances the meltability of the glass raw material. By setting the content of the B ₂ O ₃ component to 10.0% or less, the decrease in the refractive index can be suppressed and the increase in the partial dispersion ratio can be suppressed. Therefore, the content of the B ₂ O ₃ component is preferably 10.0% or less, more preferably 8.0% or less, and more preferably 5.0% or less.
B ₂ O ₃ component can be used _H 3 _BO 3 as a starting _{material, Na 2 B 4 O 7,} Na 2 B 4 O 7 · 10H 2 O, the BPO ₄ and the like.

The ZnO component is an optional component that is inexpensive and can be adjusted to the high dispersion side. By setting the content of the ZnO component to 10.0% or less, devitrification and coloring can be reduced. Therefore, the content of the ZnO component is preferably 10.0% or less, more preferably 8.0% or less, and more preferably 5.0% or less.

The La ₂ O ₃ component, the Gd ₂ O ₃ component, the Y ₂ O ₃ component, and the Yb ₂ O ₃ component are optional components that can increase the refractive index and reduce the partial dispersion ratio by containing at least one of them. ..
In particular, by reducing the content of each of the La ₂ O ₃ component, Gd ₂ O ₃ component, Y ₂ O ₃ component, and Yb ₂ O ₃ component to 10.0% or less, the increase in the Abbe number can be suppressed and the loss can be achieved. Transparency can be reduced and coloring can be reduced. Therefore, the content of each of the La ₂ O ₃ component, the Gd ₂ O ₃ component, the Y ₂ O ₃ component, and the Yb ₂ O ₃ component is preferably 10.0% or less, more preferably 8.0% or less, and further. The upper limit is preferably 5.0% or less.
La ₂ O ₃ component, Gd ₂ O ₃ component, Y ₂ O ₃ component and Yb ₂ O ₃ component are used as raw materials for La ₂ O ₃ , La (NO ₃ ) ₃ , XH ₂ O (X is an arbitrary integer), Y ₂ O ₃ , YF ₃ , Gd ₂ O ₃ , GdF ₃ , Yb ₂ O _{3, and the} like can be used.

The Ta ₂ O ₅ component is an optional component capable of increasing the refractive index, lowering the Abbe number and the partial dispersion ratio, and increasing the devitrification resistance when the content exceeds 0%. By reducing the content of the Ta ₂ O ₅ component to 10.0% or less, the 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. The cost can be reduced. Further, 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 5.0% or less, still more preferably 1.0% or less. In particular, from the viewpoint of reducing the material cost of glass, it is not necessary to contain the Ta ₂ O ₅ component.
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 can increase the refractive index, reduce the Abbe number, and enhance the meltability of the glass raw material. 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 it is possible to reduce the coloring of the glass and increase the internal transmittance. Therefore, the content of the WO ₃ component is preferably 10.0% or less, more preferably 5.0% or less, and further preferably 1.0% or less.
As the WO ₃ component, WO ₃ 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. P ₂ O ₅ content of the component by 10.0% or _less, can be reduced devitrification due to excessive content of P 2 _{O 5} component. Therefore, the content of the P ₂ O ₅ component is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 3.0% or less.
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, and the} like can be used as raw materials.

The GeO ₂ component is an optional component that can increase the refractive index and reduce devitrification. By reducing the content of the GeO ₂ component to 10.0% or less, the amount of the expensive GeO ₂ component used can be 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 5.0% or less, still more preferably 3.0% or less.
As the GeO ₂ component, GeO ₂ 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 capable of increasing the refractive index and improving the devitrification resistance.
On the other hand, by reducing 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 the 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 5.0% or less, and further preferably 3.0% or less.
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 can increase the refractive index, reduce the Abbe number, and lower the glass transition point. By setting the content of the Bi ₂ O ₃ component to 10.0% or less, it is possible to make it difficult to increase the partial dispersion ratio, and it is possible to reduce the coloring of the glass and increase the internal transmittance. Therefore, the content of the Bi ₂ O ₃ component is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 1.0% or less.
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 capable of increasing the refractive index, lowering the partial dispersion ratio, and lowering the glass transition point. By reducing the content of the TeO ₂ component to 10.0 % or less, it is possible to reduce the coloring of the glass and increase the internal transmittance. Further, by reducing the use of the expensive TeO ₂ component, a glass having a lower material cost can be obtained. Therefore, the content of the TeO ₂ component is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 1.0% or less.
As the TeO ₂ component, TeO ₂ or the like can be used as a raw material.

The SnO ₂ component is an optional component that can clarify (defoam) the molten glass and increase the visible light transmittance of the glass. By setting the content of the SnO ₂ component to 1.0% or less, it is possible to prevent the glass from being colored or devitrified by the reduction of the molten glass. Further, since the alloying of the SnO ₂ component and the melting equipment (particularly noble metal such as Pt) is reduced, the life of the melting equipment can be extended. Therefore, the content of the SnO ₂ component is preferably 1.0% or less, more preferably 0.5% or less, and further preferably 0.1% or less.
As the SnO ₂ component, SnO, SnO ₂ , SnF ₂ , SnF _4, or the like can be used as a raw material.

The Sb ₂ O ₃ component is a component that promotes defoaming of the glass and clarifies the glass, and is an optional component in the optical glass of the present invention. By setting the content of the Sb ₂ O ₃ component to 1.0% or less of the total mass of the glass, it is possible to prevent excessive foaming during glass melting, and the Sb ₂ O ₃ component is a melting facility (particularly Pt). It can be made difficult to alloy with precious metals such as. Therefore, the content of the Sb ₂ O ₃ component with respect to the total mass of the glass in the oxide conversion composition is preferably 1.0% or less, more preferably 0.8% or less, still more preferably 0.6% or less. ..
Sb ₂ O ₃ component can be used _{Sb 2 O 3, Sb 2 O} 5, Na 2 H 2 Sb 2 O 7 · 5 H 2 O and the like as raw materials.

The component that clarifies and defoams the glass is not limited to the above Sb ₂ O ₃ component, and a clarifying agent, a defoaming agent, or a combination thereof known in the field of glass production can be used. ..

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

Other components can be added as needed without impairing the properties of the glass of the present invention. However, each transition metal component 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. Alternatively, even if it is compounded and contained in a small amount, the glass is colored and has a property of causing absorption at a specific wavelength in the visible region. Therefore, it is preferable that the glass is substantially not contained, especially in optical glass using a wavelength in the visible region. ..

Further, since lead compounds such as PbO and arsenic compounds such as As ₂ O ₃ are components having a high environmental load, it is desirable that they are not substantially contained, that is, they are not contained at all except for unavoidable contamination.

Furthermore, each component of Th, Cd, Tl, Os, Be, and Se has tended to refrain from being used as a harmful chemical substance in recent years, and is used not only in the glass manufacturing process but also in the processing process and disposal after commercialization. Up to this point, environmental measures are required. Therefore, when the environmental impact is important, 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 raw materials are uniformly mixed so that each component is within a predetermined content range, and the prepared mixture is put into a platinum crucible, a quartz crucible or an alumina crucible to be roughly melted, and then a gold crucible and a platinum crucible. , Platinum alloy crucible or iridium crucible, melt in a temperature range of 1000 to 1400 ° C for 2 to 5 hours, homogenize with stirring to break bubbles, etc., then lower to a temperature of 950 to 1250 ° C and then finish stirring. It is produced by removing the crucible, casting it in a mold, and slowly cooling it.

<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 1.67 or more, more preferably 1.69 or more, still more preferably 1.70 or more. The upper limit of the refractive index is preferably 1.90 or less, more preferably 1.85 or less, and more preferably 1.83 or less.

The Abbe number (ν _d ) of the optical glass of the present invention is preferably 23.0 or more, more preferably 25.0 or more, and further preferably 27.0 or more as the lower limit. On the other hand, the Abbe number (ν _d ) of the optical glass of the present invention is preferably 38.0 or less, more preferably 35.0 or less, still more preferably 33.0 or less.

The optical glass of the present invention having such a refractive index and Abbe number is useful in optical design, and the optical system can be miniaturized while achieving particularly high imaging characteristics, so that the optical design is free. You can increase the degree.

Here, the optical glass of the present invention is a refractive index _{(n d)} and Abbe number ([nu _{d) preferably} satisfy the relation of n _d <-0.0125ν d +2.175. With the glass having the composition specified in the present invention, stable glass can be obtained even if the refractive index ( _nd ) and the Abbe number (ν _d ) satisfy this relationship.
Accordingly, in the optical glass of the present invention refractive index _{(n d)} and Abbe number ([nu _{d) is,} it is preferable to satisfy the relation of _{n d <-0.0125ν d +2.175, n} d <-0.0125ν it is more preferable to satisfy the relationship _{d +2.160,} it is more preferable to satisfy the relation of n _d <-0.0125ν d +2.150.

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 satisfies the relationship of θg, F <−0.00257ν _d +0.6800 with the Abbe number (ν _d ). Is preferable.
Therefore, in the optical glass of the present invention, it is preferable that the partial dispersion ratio (θg, F) and the Abbe number (ν _d ) satisfy the relationship of θg, F <−0.00257ν _d + 0.6800, and θg, F <. it is more preferable to satisfy the relationship -0.00257ν _d +0.6790, θg, it is more preferable to satisfy the relation of F <-0.00257ν _d +0.6780.

It is preferable that the optical glass of the present invention has a high visible light transmittance, particularly a light transmittance on the short wavelength side of visible light, and thus less coloring.
In particular, the optical glass of the present invention has a wavelength (λ ₇₀ ) showing a spectral transmittance of 70% in a sample having a thickness of 10 mm, preferably 420 nm or less, more preferably 410 or less nm, and further preferably in terms of glass transmittance. The upper limit is 405 nm or less.
As a result, the absorbing edge of the glass becomes near the ultraviolet region, and the transparency of the glass with respect to visible light is enhanced. Therefore, this optical glass can be preferably used for an optical element such as a lens that transmits light.

[Preform and optical element]
From the produced optical glass, a glass molded body can be produced by using a mold press molding means such as reheat press molding or precision press molding. That is, a preform for mold press molding is produced from optical glass, and after reheat press molding is performed on this preform, a glass molded body is produced by polishing, or for example, it is produced by polishing. A glass molded body can be produced by performing precision press molding on the preform. The means for producing the glass molded product is not limited to these means.

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

The composition of Example (No.1~No.12) and Comparative Example A of the present invention, and a refractive index _(n d), Abbe number ([nu _d), the partial dispersion ratio ([theta] g, F), the transmittance λ70 The results are shown in Tables 1 and 2. The following examples are for purposes of illustration only, and are not limited to these examples.

The glasses of Examples and Comparative Examples are of high purity, which are used for ordinary optical glasses such as oxides, hydroxides, carbonates, nitrates, fluorides, and metaphosphate compounds, which correspond to each component as a raw material. After selecting the raw materials, weighing them so as to have the composition ratios of the examples and comparative examples shown in the table and mixing them uniformly, a stone crucible (depending on the meltability of the glass, a platinum crucible or an alumina crucible) is used. It does not matter), and after melting in an electric furnace in a temperature range of 1100 to 1400 ° C. for 0.5 to 5 hours depending on the degree of difficulty of melting the glass composition, it is transferred to a platinum crucible and stirred and homogenized to break bubbles, etc. After that, the temperature was lowered to 1000 to 1200 ° C. to homogenize by stirring, then cast into a mold and slowly cooled to prepare glass.

The refractive index of the glass of the Examples and Comparative Examples _{(n d)} Abbe's number (νd), JISB 7071-2: was measured according to 2018. The partial dispersion ratio (θg, F) is the refractive index (nC) at the C line (wavelength 656.27 nm), the refractive index (nF) at the F line (wavelength 486.13 nm), and the refraction at the g line (wavelength 435.835 nm). The rate (ng) was measured and calculated by the formula of θg, F = (ng-nF) / (nF-nC).
The transmittance (λ70) was measured according to JOJIS02-2003.

The optical glasses of Examples of the present invention are both refractive index (n _d) with at 1.67 or more, were within the desired range is 1.90 or less.
Further, all of the optical glasses of the examples of the present invention had an Abbe number (ν _d ) of 25 or more and 33 or less, which were within a desired range.

As these tables, the optical glasses of Examples of the present invention satisfies the relation n _d <-0.0125ν _d +2.175 refractive index _{(n d)} and Abbe number ([nu _d), and the Abbe number (Ν _d ) and the relational expression θg of the partial dispersion ratio (θg, F), F <−0.00257ν _d +0.6800 were satisfied.

As shown in the table, all of the optical glasses of the examples had a 70% transmittance wavelength (λ70) of 420 nm or less.

Further, when a glass block was formed using the optical glass of the example of the present invention and the glass block was reheat-pressed, devitrification during pressing did not occur.

Although the present invention has been described in detail above for the purpose of exemplification, the present embodiment is merely for the purpose of exemplification, and many modifications can be made by those skilled in the art without departing from the idea and scope of the present invention. Will be understood.

Claims (4)

By mass%
SiO ₂ component 20.0-50.0%,
Nb ₂ O ₅ component 10.0-45.0%
TiO ₂ component 2.0 to 20.0%,
ZrO ₂ component 1.0 to 15.0%
Rn ₂ O component 5.0 to 30.0%
Contains,
Refractive index _{(n d)} of 1.67 or more 1.90 or less, and the Abbe number is 23.0 or more 38.0 or less,
Satisfy the relation n _d <-0.0125ν _d +2.175 refractive index _{(n d)} and Abbe number (ν _d),
An optical glass characterized by satisfying the relational expressions θg and F <−0.00257ν _d +0.6800 of the Abbe number (ν _d ) and the partial dispersion ratio (θg, F). The optical glass according to claim 1, wherein the value of the mass ratio TiO ₂ / Nb ₂ O ₅ is in the range of 0.10 to 1.00. The optical glass according to claim 1 or 2, wherein the λ70 value is 420 nm or less. An optical glass for reheat pressing, which comprises the optical glass according to any one of claims 1 to 3.