JP7478889B2 - Optical glass, preforms and optical elements - Google Patents

Description

The present invention relates to optical glass, preforms, and optical elements.

In recent years, devices that use optical systems have rapidly become more digitalized and have higher definition, and there is a growing demand for improved processing yields in the field of various optical devices, such as photographic devices such as digital cameras and video cameras, and image reproduction (projection) devices such as projectors and projection televisions.

In addition, the partial dispersion ratio (θg, F) is used as an index of optical characteristics that are of interest in optical design, and optical materials with a large partial dispersion ratio are required for lenses on the low dispersion side in order to effectively correct secondary spectra.

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

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

In optical glasses, there is an approximately linear relationship between the partial dispersion ratio (θg, F) that represents the partial dispersion in the short wavelength region and the Abbe number (ν _d ). The line that represents this relationship is expressed as a line connecting two points on which the partial dispersion ratios and Abbe numbers of NSL7 and PBM2 are plotted on an orthogonal coordinate system with the partial dispersion ratio (θg, F) on the vertical axis and the Abbe number (ν _d ) on the horizontal axis, and is called the normal line (see FIG. 1). The normal glass that is the basis of the normal line varies depending on the optical glass manufacturer, but each company defines it with approximately the same slope and intercept (NSL7 and PBM2 are optical glasses manufactured by Ohara Co., Ltd., the Abbe number (ν _d ) of PBM2 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).

Furthermore, when processing in the manufacturing process of glass, if the processability of glass is poor, the surface of the glass is likely to become discolored or cloudy during grinding/polishing steps, cleaning steps, etc. In this case, the processing step requires an increased amount of time because an additional step is required to grind/polish the glass surface to prevent discoloration or clouding inside the glass.
In particular, optical glass containing _BaO, mainly composed of _P2O5 , in the low dispersion region (for example, Abbe number 50 or more and 70 or less) generally tends to have poor acid resistance and abrasion resistance, and the glass has poor workability, so there is a demand for optical glass with good acid resistance.

Furthermore, for optical elements incorporated in optical devices that generate heat, such as projectors, there is a demand for optical systems that are less susceptible to the effects of temperature fluctuations in the operating environment on the imaging characteristics of the optical system.

Among optical glasses for producing optical elements, there is a growing demand for glass materials having improved processability and large partial dispersion ratios for fluorine-free phosphate-based glasses having a refractive index (n _d ) of 1.57 to 1.65 and a high Abbe number (ν _d ) of 50 or more and 70 or less. As such fluorine-free phosphate-based glasses, glass compositions such as those shown in Patent Document 1 are known.

JP 2010-202418 A

Optical glass is polished and cleaned for use in various optical devices. Abrasives are used in the polishing process, and detergents are used in the cleaning process, so glass with poor chemical durability, especially acid resistance, is prone to scratches.
In addition, when designing an optical system, it is preferable that the partial dispersion ratio on the low dispersion side is large. Furthermore, in constructing an optical system in which temperature fluctuations are unlikely to affect imaging performance, etc., it is preferable to use an optical element made of glass whose refractive index decreases when the temperature increases and whose temperature coefficient of the relative refractive index is negative, and an optical element made of glass whose refractive index increases when the temperature increases and whose temperature coefficient of the relative refractive index is positive, in order to correct the effects of temperature changes on imaging performance, etc. It is known that the temperature coefficient of the relative refractive index is correlated with the linear expansion coefficient, and it is preferable that the phosphate glass on the low dispersion side has a small linear expansion coefficient.
However, it is difficult to say that the glass described in Patent Document 1 satisfactorily meets such demands.

The present invention was made in consideration of the above problems, and its purpose is to provide glass that is easy to process in the polishing and cleaning processes, and has the characteristics of a low refractive index and low dispersion in optical design, while also having a large partial dispersion ratio.

In order to solve the above problems, the present inventors have conducted extensive testing and research, and as a result have found that a glass having good acid resistance and a large partial dispersion ratio can be obtained by the _powder method by using a _P2O5 component as a main component and BaO and rare earth elements as essential components, and have thus completed the present invention.
Specifically, the present invention provides the following:

(1)
In mass percent,
_P2O5 component _20.0 to 60.0%,
BaO component 5.0 to 45.0%
Ln ₂ O ₃ component: over 0 to 15.0%
(In the formula, Ln is one or more selected from the group consisting of La, Gd, Y, and Yb).
Contains
Between the partial dispersion ratio (θg, F) and the Abbe number (νd),
The relationship of (−0.00162×ν _d +0.625)≦(θg,F)≦(−0.00162×ν _d +0.660) is satisfied,
Optical glass with chemical durability (acid resistance) of grades 1 to 5, produced using the powder method.

(2)
The optical glass according to (1), characterized in that the mass ratio Rn ₂ O/(P ₂ O ₅ +B ₂ O ₃ ) is less than 0.1 (wherein Rn is one or more selected from the group consisting of Li, Na and K).

(3)
The optical glass according to (1) or (2), having a refractive index ( _nd ) of 1.57 or more and 1.65 or less, and an Abbe number ( _vd ) of 50 or more and 70 or less.

(4)
A preform made of the optical glass according to any one of (1) to (3).

(5)
An optical element comprising the optical glass according to any one of (1) to (3).

(6)
(5) An optical device comprising the optical element according to (5).

According to the present invention, it is possible to obtain optical glass with good chemical durability (acid resistance) and a large partial dispersion ratio by the powder method.

FIG. 1 is a diagram showing a normal line represented on an orthogonal coordinate system with the partial dispersion ratio (θg, F) on the vertical axis and the Abbe number (νd) on the horizontal axis. FIG. 1 is a diagram showing the relationship between the partial dispersion ratio (θg, F) and the Abbe number (νd) for an example of the present application.

The optical glass of the present invention contains, by mass%, 20.0 to 60.0% of a P ₂ O ₅ component, 5.0 to 45.0% of a BaO component, and more than 0 to 10.0% of a Ln ₂ O ₃ component, and the partial dispersion ratio (θg, F) and Abbe number (νd) satisfy the relationship of (-0.00162×ν _d +0.625)≦(θg, F)≦(-0.00162×ν _d +0.660), and has chemical durability (acid resistance) of grades 1 to 5 by powder method.
According to the present invention, by using P ₂ O ₅ as the main component and BaO and rare earth elements as essential components, it is possible to obtain glass having good acid resistance and a large partial dispersion ratio by the powder method.

The following describes in detail the embodiments of the optical glass of the present invention, but the present invention is not limited to the following embodiments and can be modified as appropriate within the scope of the object of the present invention. Note that where explanations overlap, they may be omitted as appropriate, but this does not limit the spirit of the invention.

[Glass components]
The composition range of each component constituting the optical glass of the present invention is described below. In this specification, the content of each component is expressed as mass% relative to the total substance amount of the glass in terms of oxide composition unless otherwise specified. Here, "composition in terms of oxide" refers to a composition in which each component contained in the glass is expressed with the total substance amount of the generated oxide being 100 mass%, assuming that the oxides, composite salts, metal fluorides, etc. used as raw materials for the glass components of the present invention are all decomposed and converted to oxides during melting.

<Required and optional ingredients>
In the optical glass of the present invention, P ₂ O ₅ is an essential component, and is the main component that forms the glass, as well as a component that increases the viscosity of the glass and enhances the stability of the glass.
On the other hand, if the content of _{the P2O5} component is too low, the glass may become unstable and the viscosity may decrease, and the stability of the glass may deteriorate. Therefore, in the optical glass of the present invention, the content of _{the P2O5} component is preferably at least 20.0%, more preferably at least 25.0%, and even more preferably at least 30.0%.
On the other hand, if the content of the _P2O5 component is too high, the refractive index decreases and the partial _dispersion ratio also becomes small, so the content of _{the P2O5 component} is preferably 60.0% or less, more preferably 56.0% or less, more preferably 53.0% or less, and even more preferably 50.0% or less.
As the _P2O5 component, Al( _{PO3 ) 3} , Ca( _PO3 ) ₂ , Ba( _PO3 ) ₂ , _BPO4 , _{H3PO4 ,} etc. can be used as raw materials.

The BaO component has the effect of increasing the refractive index of the glass and enhancing the stability of the glass, and is an essential component in the present invention for increasing the partial dispersion ratio.
Therefore, the content of the BaO component is preferably 5.0% or more, more preferably 8.0% or more, and further preferably 10.0% or more.
On the other hand, if the content of the BaO component is too high, the acid resistance deteriorates and the linear expansion coefficient increases, making it difficult to improve the processability and produce a glass with low linear expansion, which are the aims of the optical glass of the present invention. Therefore, the content of the BaO component is preferably 45.0% or less, more preferably 40.0% or less, and even more preferably 36.0% or less.
As the BaO component, _BaCO3 , Ba( _NO3 ) ₂ , Ba( _PO3 ) ₂ , BaF2 _, etc. can be used as a raw material.

The sum of the contents (sum of mass) of the _three Ln ₂ O components (wherein Ln is one or more selected from the group consisting of La, Gd, Y and Yb) is preferably more than 0% and 15.0% or less.
In particular, by making this mass sum more than 0%, it is possible to reduce the weight loss rate of the _powder method acid resistance while maintaining the desired refractive index. The mass sum of the content of the _Ln2O3 component is preferably more than 0%, more preferably more than 1.0%, and even more preferably more than 3.0%.
On the other hand, by making the mass sum 15.0% or less, the partial dispersion ratio does not become too small, and the stability of the glass can be improved. Therefore, the mass sum of the content of _{the Ln2O3} component is preferably 15.0% or less, more preferably 10.0% or less, and further preferably 8.0% or less.

The mass ratio of the Rn ₂ O component (wherein Rn is at least one selected from the group consisting of Li, Na and K) to the sum of the P ₂ O ₅ component and the B ₂ O ₃ component is preferably less than 0.1.
By adjusting the ratio of Rn ₂ O/(P ₂ O ₅ +B ₂ O ₃ ), the decrease in the refractive index of the glass is suppressed, the glass becomes stable, and the weight loss rate of the powder method acid resistance is reduced.
Therefore, Rn ₂ O/(P ₂ O ₅ +B ₂ O ₃ ) is preferably less than 0.1, more preferably less than 0.08, and even more preferably less than 0.05.

_{The B2O3} component is an essential component as a glass-forming oxide in the optical glass of the present invention containing rare earth oxides. In particular, in the optical glass of the present invention, the meltability of the glass can be improved by containing more than 0% of _{the B2O3} component. Therefore, the content of _{the B2O3 component} is preferably more than 0%, more preferably 3.0% or more, and even more preferably more than 5.0%.
On the other hand, by making the content of the B ₂ O ₃ component 20.0% or less, deterioration of chemical durability can be suppressed. Therefore, the content of the B ₂ O ₃ component is preferably 20.0% or less, more preferably 18.0% or less, and further preferably less than 15.0%.
For _{the B2O3} component, _H3BO3 , _Na2B4O7 , _{Na2B4O7.10H2O , BPO4 , etc.} can be used _{as raw materials} .

When the SrO component is contained in an amount exceeding 0%, the partial dispersion ratio is increased while maintaining the desired refractive index and dispersion.
On the other hand, if the content of the SrO component is too high, the acid resistance deteriorates and the glass becomes unstable. Therefore, the content of the SrO component is preferably 35.0% or less, more preferably 30.0% or less, and more preferably 28.0% or less.
As the SrO component, Sr(NO ₃ ) ₂ , SrF _{2 ,} Sr(PO ₃ ) ₂ , etc. can be used as the raw material.

The _SiO2 component is an optional component that, when contained in an amount exceeding 0%, can increase the viscosity of the molten glass and can also increase the devitrification resistance.
On the other hand, by making the content of the _SiO2 component 10.0% or less, a stable glass can be obtained. Therefore, the content of the _SiO2 component is preferably 10.0% or less, more preferably less than 5.0%, and further preferably less than 3.0%.
As the _SiO2 component, _SiO2 , _K2SiF6 , _{Na2SiF6 , etc.} can be used as raw materials.

The MgO component is an optional component that, when contained in an amount exceeding 0%, can enhance the stabilization of the glass and increase the partial dispersion ratio.
On the other hand, by making the content of the MgO component 15.0% or less, it is possible to reduce the decrease in the refractive index and devitrification caused by the excessive inclusion of these components. Therefore, the content of the MgO component is preferably 15.0% or less, more preferably less than 13.0%, and further preferably less than 10.0%.
As the MgO component, MgCO ₃ , MgF ₂ , MgO, 4MgCO3.Mg(OH) 2 and the like can be used as raw materials.

The CaO component is an optional component that, when contained in an amount of more than 0%, can improve the meltability of the glass raw material and the devitrification resistance of the glass.
On the other hand, by making the CaO content 18.0% or less, it is possible to reduce the decrease in refractive index and devitrification caused by the excessive inclusion of these components. The CaO content is preferably 18.0% or less, more preferably less than 15.0%, and even more preferably less than 13.0%.
As the CaO component, CaCO ₃ , CaF ₂ , etc. can be used as a raw material.

The ZnO component is an optional component that, when contained in an amount of more than 0%, can increase the devitrification resistance, reduce the specific gravity, and increase the chemical durability. Therefore, the content of the ZnO component may be preferably more than 0%, more preferably more than 0.5%, and even more preferably more than 1.0%.
On the other hand, by setting the content of the ZnO component to 20.0% or less, low dispersion can be maintained. Therefore, the content of the ZnO component is preferably set to 20.0% or less, more preferably set to 15.0% or less, more preferably set to 10.0% or less, and further preferably set to 8.0% or less.
As the ZnO component, ZnO, _ZnF2 , etc. can be used as raw materials.

The _La2O3 component is an optional component that can reduce the acid resistance weight loss rate and increase _the refractive index by containing more than 0%. Therefore, the content of _{the La2O3 component} may be preferably more than 0%, more preferably more than 0.5%, and even more preferably more than 1.0%.
On the other hand, if the content is too high, the devitrification resistance deteriorates and the partial dispersion ratio decreases, so the content of _{the La2O3} component is preferably 10.0% or less, more preferably less than 8.0%, and even more preferably less than 5.0%.
As the La ₂ O ₃ component, La ₂ O ₃ , La(NO ₃ ) _{3.XH 2} O (X is any integer), etc. can be used as a raw material.

_{The Gd2O3} component is an optional component that has good devitrification resistance among rare earth elements and can reduce the weight loss rate due to acid resistance when contained in an amount of more than 0%. Therefore, the content of _{the Gd2O3 component} may be preferably more than 0%, more preferably more than 1.0%, and even more preferably more than 1.5%.
On the other hand, if the content is too high, the devitrification resistance deteriorates and the partial dispersion ratio decreases, so the content of the Gd ₂ O ₃ component is preferably 15.0% or less, more preferably less than 13.0%, and further preferably less than 8.0%.
As _{the Gd2O3 component} , _Gd2O3 , _{GdF3, etc.} can be used as raw materials.

The Y ₂ O ₃ component and the Yb ₂ O ₃ component are optional components that, when at least either one of them is contained in an amount exceeding 0%, can increase the refractive index of the glass while maintaining a desired Abbe number, and can also increase the devitrification resistance.
On the other hand, by making the content of each of _{the Y2O3} component and _{the Yb2O3} component 10.0% or less, it is possible to reduce devitrification due to the excessive content of these components, and to reduce the material cost of the glass. Therefore, the content of each of _{the Y2O3} component and _{the Yb2O3} component is preferably 10.0% or less, more preferably less than 5.0%, and further preferably less than 3.0%.
For the Y ₂ O ₃ component and the Yb ₂ O ₃ component, Y ₂ O ₃ , YF _{3 ,} Yb ₂ O _{3 ,} etc. can be used as raw materials.

The _ZrO2 component is an optional component that can reduce the weight loss rate due to acid resistance when the content exceeds 0%.
On the other hand, by making the content of the _ZrO2 component 10.0% or less, the desired Abbe number can be maintained and the deterioration of devitrification resistance due to the excessive content of the _ZrO2 component can be suppressed. Therefore, the content of the _ZrO2 component is preferably 10.0% or less, more preferably less than 5.0%, and further preferably less than 3.0%.
As the _ZrO2 component, _ZrO2 , _ZrF4 , etc. can be used as raw materials.

Nb ₂ O ₅ is an optional component that improves acid resistance and increases the partial dispersion ratio when the content exceeds 0%.
On the other hand, by making the content of _{the Nb2O5} component 10.0% or less, a low Abbe number can be maintained and the weight loss rate due to acid resistance can be reduced, so the content is preferably 10.0% or less, more preferably 8.0% or less, even more preferably less than 5.0%, and even more preferably less than 3.0%.
As the Nb ₂ O ₅ component, Nb ₂ O ₅ or the like can be used as a raw material.

The _WO3 component is an optional component that, when contained in excess of 0%, can increase the refractive index and partial dispersion ratio and can also increase resistance to devitrification.
On the other hand, by making the content of the _WO3 component 10.0% or less, it is possible to prevent the visible light transmittance of the glass from decreasing and to reduce material costs. Therefore, the content of the _WO3 component is preferably 10.0% or less, more preferably 8.0% or less, more preferably less than 5.0%, and even more preferably less than 3.0%.
As the _WO3 component, _WO3 or the like can be used as a raw material.

The _TiO2 component is an optional component that, when contained in an amount exceeding 0%, reduces the acid resistance weight loss rate and increases the partial dispersion ratio.
On the other hand, by making the content of the _TiO2 component 10.0% or less, it is possible to maintain a desired Abbe number and obtain a stable glass. Therefore, the content of the _TiO2 component is preferably 10.0% or less, more preferably less than 5.0%, and further preferably less than 3.0%.
As the _TiO2 component, _TiO2 or the like can be used as a raw material.

The Ta ₂ O ₅ component is an optional component which, when contained in an amount exceeding 0%, increases the refractive index, increases the resistance to devitrification, and increases the viscosity of the molten glass.
On the other hand, by making the content of the _Ta2O5 component 5.0% or less, the amount of _{the Ta2O5} component, which is a rare mineral resource, used is reduced, and the material cost of the glass can be reduced. Therefore, _the content of _{the Ta2O5} component is preferably 5.0% or less, more preferably less than 3.0%, even more preferably less than 1.0%, and most preferably not contained.
As the Ta ₂ O ₅ component, Ta ₂ O ₅ or the like can be used as a raw material.

The Li ₂ O component is an optional component that improves the meltability of the glass and increases the refractive index when contained in an amount of 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 even more preferably more than 1.0%.
On the other hand, by making the content of the Li ₂ O component 10.0% or less, devitrification can be reduced and the viscosity of the molten glass can be increased, thereby reducing the occurrence of striae in the glass. Therefore, the content of the Li ₂ O component is preferably 10.0% or less, more preferably less than 8.0%, more preferably less than 5.0%, and even more preferably less than 3.0%.
As the Li ₂ O component, Li ₂ CO ₃ , LiNO ₃ , LiF, etc. can be used as a raw material.

The Na ₂ O component and the K ₂ O component are optional components that can improve the meltability of the glass raw material and enhance the devitrification resistance when at least either of them is contained in an amount exceeding 0%.
On the other hand, by making the content of each of the Na ₂ O component and the K ₂ O component 10.0% or less, it is possible to make it difficult for the refractive index to decrease and to reduce devitrification due to excessive content. Therefore, the content of each of the Na ₂ O component and the K ₂ O component is preferably 10.0% or less, more preferably less than 8.0%, more preferably less than 5.0%, and even more preferably less than 3.0%.
For the _Na2O component and _K2O component, _{Na2CO3 , NaNO3} , _NaF , _Na2SiF6 , _K2CO3 , _KNO3 , KF, _KHF2 , _{K2SiF6 , etc.} can be used as raw materials.

The _GeO2 component is an optional component that, when contained in an amount exceeding 0%, can increase the refractive index of the glass and can also increase the devitrification resistance.
However, since the raw material price of GeO2 is high, a large amount of _GeO2 increases the material cost. Therefore, the content of _GeO2 component is preferably 10.0% or less, more preferably less than 5.0%, even more preferably less than 3.0%, even more preferably less than 1.0%, and most preferably not contained.
The _GeO2 component can use _GeO2 or the like as a raw material.

The Al ₂ O ₃ component is an optional component that, when contained in an amount of more than 0%, reduces the acid resistance weight loss rate and enhances devitrification resistance. Therefore, the content of the Al ₂ O ₃ component may be preferably more than 0%, more preferably more than 0.5%, and even more preferably more than 1.0%.
On the other hand, by making the content of the Al ₂ O ₃ component 10.0% or less, devitrification due to excessive content can be reduced. Therefore, the content of the Al ₂ O ₃ component is preferably 10.0% or less, more preferably less than 9.0%, and further preferably less than 8.0%.
As the Al ₂ O ₃ component, Al ₂ O ₃ , Al(OH) ₃ , AlF ₃ , etc. can be used as raw materials.

The Ga ₂ O ₃ component is an optional component that can improve chemical durability and devitrification resistance when the content exceeds 0%.
On the other hand, by making the content of _{the Ga2O3} component 10.0% or less, devitrification due to excessive inclusion can be reduced. Therefore, the content of _{the Ga2O3 component} is preferably 10.0% or less, more preferably less than 5.0%, even more preferably less than 3.0%, and even more preferably less than 1.0%.
The Ga ₂ O ₃ component can use Ga ₂ O ₃ or the like as a raw material.

The Bi ₂ O ₃ component is an optional component that, when contained in an amount exceeding 0%, can increase the refractive index, decrease the Abbe number, and decrease the glass transition point.
On the other hand, by making the content of _{the Bi2O3} component 10.0% or less, the devitrification resistance of the glass can be improved, and the coloring of the glass can be reduced to increase the visible light transmittance. Therefore, the content of _{the Bi2O3} component is preferably 10.0% or less, more preferably less than 5.0%, even more preferably less than 3.0%, and even more preferably less than 1.0%.
As _{the Bi2O3 component} , _Bi2O3 or _the like can be used as a raw material.

The _TeO2 component is an optional component that, when contained in an amount of more than 0%, can increase the refractive index and decrease the glass transition point.
On the other hand, by making the content of _TeO2 component 10.0% or less, the coloring of the glass can be reduced and the visible light transmittance can be increased. In addition, when melting glass raw materials in a platinum crucible or a melting tank whose part in contact with the molten glass is made of platinum, there is a problem that _TeO2 may be alloyed with platinum. Therefore, the content of _TeO2 component is preferably 10.0% or less, more preferably less than 5.0%, even more preferably less than 3.0%, and even more preferably less than 1.0%.
For the _TeO2 component, _TeO2 or the like can be used as a raw material.

The _SnO2 component is an optional component that, when contained in an amount of more than 0%, can promote the fining of the molten glass while suppressing the dissolution of platinum by reducing the oxidation of the molten glass.
On the other hand, by making the content of the _SnO2 component 3.0% or less, it is possible to reduce coloration of the glass due to reduction of the molten glass and devitrification of the glass. In addition, alloying of the _SnO2 component with the melting equipment (especially precious metals such as Pt) is reduced, so that the life of the melting equipment can be extended. Therefore, the content of the _SnO2 component is preferably 3.0% or less, more preferably less than 1.0%, and even more preferably less than 0.5%.
As the _SnO2 component, SnO, _SnO2 , _SnF2 , _SnF4 , etc. can be used as raw materials.

The Sb ₂ O ₃ component is an optional component that can degas the molten glass when its content exceeds 0%.
On the other hand, if the content of the Sb ₂ O ₃ component is too high, the transmittance in the short wavelength region of the visible light region is deteriorated. Therefore, the content of the Sb ₂ O ₃ component is preferably 1.0% or less, more preferably less than 0.5%, and further preferably less than 0.1%.
As the Sb ₂ O ₃ component, Sb ₂ O ₃ , Sb ₂ O ₅ , Na ₂ H ₂ Sb ₂ O _{7.5H 2} O, etc. can be used as raw materials.

The component for clarifying and defoaming the glass is not limited to the above Sb ₂ O ₃ component, and any known fining agent or defoaming agent in the field of glass manufacturing, or a combination thereof, can be used.

The F component is an optional component which, when contained in an amount of more than 0%, can increase the Abbe number of the glass, lower the glass transition point, and improve resistance to devitrification.
However, when the content of the F component, i.e., the total amount of F in the fluorides which have substituted a part or all of the oxides of one or more of the above-mentioned elements, exceeds 10.0%, the amount of volatilization of the F component increases, making it difficult to obtain stable optical constants and homogeneous glass, and the Abbe number increases more than necessary.
Therefore, the content of the F component is preferably 10.0% or less, more preferably less than 5.0%, even more preferably less than 3.0%, even more preferably less than 1.0%, and even more preferably none is contained.
The F component can be contained in the glass by using, for example, ZrF ₄ , AlF ₃ , NaF, CaF ₂ or the like as a raw material.

The sum of the contents (sum of mass) of RO components (wherein R is one or more selected from the group consisting of Mg, Ca, Sr, and Ba) is preferably 10.0% or more and 50.0% or less.
In particular, by making this sum 10.0% or more, the refractive index can be increased and the devitrification resistance of the glass can be improved. Therefore, the total content of the RO components is preferably 10.0% or more, more preferably 15.0% or more, more preferably 20.0% or more, even more preferably 25.0% or more, and still more preferably 28.0% or more.
On the other hand, by making this sum 50.0% or less, it is possible to reduce devitrification due to the excessive content of these components, and to obtain a glass with a small acid resistance weight loss rate and abrasion resistance. Therefore, the total content of the RO components is preferably 50.0% or less, more preferably less than 48.0%, and even more preferably less than 45.0%.

When the sum (mass sum) of the contents of Rn ₂ O components (wherein Rn is one or more selected from the group consisting of Li, Na, and K) exceeds 0%, the decrease in the refractive index of the glass can be suppressed and devitrification can be reduced. Therefore, the content of the Rn ₂ O component is preferably more than 0%, more preferably more than 0.05%, and even more preferably more than 0.10%.
On the other hand, by setting this sum to 10.0% or less, the weight loss rate of the powder method acid resistance is reduced. The mass sum of the content of the Rn ₂ O component is preferably 10.0% or less, more preferably less than 8.0%, more preferably less than 5.0%, and even more preferably less than 3.0%.

The mass ratio of the ZnO component to the BaO component is preferably 0.01 or more. This reduces the linear expansion coefficient. This mass ratio (ZnO/BaO) is preferably 0.01 or more, more preferably 0.025 or more, even more preferably 0.05 or more, and even more preferably more than 0.1.
On the other hand, by setting the mass ratio (ZnO/BaO) to 1.0 or less, it is possible to achieve a desired refractive index while maintaining low dispersion. Therefore, the mass ratio (ZnO/BaO) is preferably set to 1.0 or less, more preferably 0.8 or less, and even more preferably 0.5 or less.

The sum (mass sum) of _{the P2O5} component and _{the B2O3} component is preferably 30.0% or more. This stabilizes the glass _and makes it easier to introduce components that improve the _powder method acid resistance and components that increase the partial dispersion ratio. The mass sum of _P2O5 and _B2O3 is preferably 30.0% or more, more preferably 35.0% or more, and even more preferably 40.0% or more.
On the other hand, if this mass sum is too large, it becomes difficult to obtain the desired refractive index and Abbe number, so it is preferably less than 65.0%, more preferably less than 63.0%, more preferably less than 60.0%, and even more preferably less than 56.0%.

By setting the mass ratio of the SrO component to the BaO component to 2.00 or less, the weight loss rate of the powder method acid resistance is reduced and the linear expansion coefficient can be reduced. Therefore, the mass ratio (SrO/BaO) is preferably 2.00 or less, more preferably 1.80 or less, and even more preferably 1.60 or less.

The sum of the contents (mass sum) of _{the La2O3 component} and _Gd2O3 is preferably more than 0%. This allows for good acid resistance by the powder method to be obtained. It is preferably more than 0%, more preferably _more than 1.0%, and even more preferably more than 3.0%.
On the other hand, the mass sum ( _{La2O3 + Gd2O3} ) is preferably less than 15.0%. If _it is contained at 15.0% or more, the devitrification property deteriorates and it becomes difficult to obtain a stable glass. It is preferably less than 15.0%, more preferably less than 13.0%, and even more preferably less than 8.0%.

The mass ratio of the sum of the contents (mass sum) of the SrO component, the CaO component, and the MgO component to the BaO component is preferably 0.20 or more. This reduces the weight loss rate of the powder method acid resistance and the linear expansion coefficient. It is preferably 0.20 or more, more preferably 0.22 or more, and even more preferably 0.24 or more.
On the other hand, by making the mass ratio (SrO+CaO+MgO)/BaO 3.00 or less, the glass can be stabilized while having a desired refractive index, preferably 3.00 or less, more preferably 2.50 or less, and even more preferably 2.20 or less.

<Ingredients that should not be included>
Next, components that should not be contained in the optical glass of the present invention and components whose inclusion is undesirable will be described.

Other components may be added as necessary to the extent that they do not impair the properties of the glass of the present invention. However, 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, have the property of coloring the glass and absorbing specific wavelengths in the visible range even when contained in small amounts alone or in combination, so it is preferable that they are substantially absent, especially in optical glasses that use wavelengths in the visible range.

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

Furthermore, in recent years, there has been a trend to refrain from using the components Th, Cd, Tl, Os, Be, and Se as harmful chemical substances, and environmental measures are required not only in the glass manufacturing process, but also in the processing process and disposal after productization. Therefore, when environmental impact is important, it is preferable that these components are not substantially contained.

[Production method]
The optical glass of the present invention is produced, for example, as follows: the above-mentioned raw materials are mixed uniformly so that the contents of the respective components fall within the prescribed ranges, the mixture thus produced is charged into a platinum crucible, a quartz crucible, or an alumina crucible for rough melting, and then the mixture is placed into a platinum crucible, a platinum alloy crucible, or an iridium crucible for melting at a temperature range of 1100 to 1400°C for 1 to 5 hours, stirred to homogenize, and subjected to bubble removal and the like, and then the temperature is lowered to 900 to 1300°C, followed by finish stirring to remove striae, and then cast into a mold and slowly cooled.

<Physical Properties>
The optical glass of the present invention has a desired refractive index and a high Abbe number (low dispersion).
In particular, the lower limit of the refractive index (n _d ) of the optical glass of the present invention is preferably 1.57 or more, more preferably 1.58 or more, and even more preferably 1.59 or more.
On the other hand, the upper limit of this refractive index is preferably 1.65 or less, more preferably 1.64, and even more preferably 1.63. The lower limit of the Abbe number (ν _d ) of the optical glass of the present invention is preferably 50 or more, more preferably 52 or more, and even more preferably 54 or more. The upper limit of this Abbe number is preferably 70 or less, more preferably less than 68, and even more preferably 65 or less.
The optical glass of the present invention has such refractive index and Abbe number, and is therefore useful in optical design, and in particular makes it possible to miniaturize the optical system while achieving high imaging characteristics, thereby expanding the freedom of optical design.

The optical glass of the present invention preferably has a high partial dispersion ratio (θg,F).
More specifically, the partial dispersion ratio (θg, F) of the optical glass of the present invention preferably satisfies the relationship (−0.00162×ν _d +0.625)≦(θg, F)≦(−0.00162×ν _d +0.660) in relation to the Abbe number (ν _d ).
Thus, the optical glass of the present invention has a higher partial dispersion ratio (θg,F) than conventionally known glasses containing large amounts of rare earth elements, and therefore, while achieving a high refractive index and low dispersion for the glass, optical elements made from this optical glass can be preferably used to correct chromatic aberration.
Here, the lower limit of the partial dispersion ratio (θg, F) of the optical glass of the present invention is preferably (−0.00162×ν _d +0.625), more preferably (−0.00162×ν _d +0.630), and even more preferably (−0.00162×ν _d +0.632).
On the other hand, the upper limit of the partial dispersion ratio (θg,F) of the optical glass of the present invention is often not more than (−0.00162× _νd +0.660), more specifically not more than (−0.00162× _νd +0.658), and even more specifically not more than (−0.00162× _νd +0.656). With a glass having a composition specified in the present invention, a stable glass can be obtained even if the partial dispersion ratio (θg,F) and the Abbe number (νd) satisfy this relationship.

The optical glass of the present invention preferably has high acid resistance. In particular, the chemical durability (acid resistance) of the glass according to the powder method in accordance with JOGIS06-2009 is preferably at least grade 5, more preferably at least grade 4, and even more preferably at least grade 3.

Here, "acid resistance" refers to the durability of glass against corrosion by acid, and this acid resistance can be measured by the Japan Optical Glass Industry Association standard JOGIS06-2009 "Method for measuring chemical durability of optical glass (powder method)." Furthermore, "chemical durability (acid resistance) by the powder method is grade 1 to 3" means that the chemical durability (acid resistance) measured according to JOGIS06-2009 is less than 0.65% by mass, in terms of the loss in mass of the sample before and after the measurement.
In terms of chemical durability (acid resistance), "Grade 1" means that the mass loss of the sample before and after measurement is less than 0.20% by mass, "Grade 2" means that the mass loss of the sample before and after measurement is 0.20% by mass or more and less than 0.35% by mass, "Grade 3" means that the mass loss of the sample before and after measurement is 0.35% by mass or more and less than 0.65% by mass, "Grade 4" means that the mass loss of the sample before and after measurement is 0.65% by mass or more and less than 1.20% by mass, "Grade 5" means that the mass loss of the sample before and after measurement is 1.20% by mass or more and less than 2.20% by mass, and "Grade 6" means that the mass loss of the sample before and after measurement is 2.20% by mass or more.

The optical glass of the present invention preferably has an average linear thermal expansion coefficient α at 100 to 300° C. of 130 (10 ⁻⁷ ° C. ⁻¹ ) or less.
That is, the average linear thermal expansion coefficient α of the optical glass of the present invention at 100 to 300° C. is preferably 130 or less, more preferably 125 or less, and more preferably 120 or less as an upper limit.

It is preferable that the optical glass of the present invention has a high visible light transmittance, particularly a high transmittance for light on the short wavelength side of visible light, and therefore has little coloring.
In particular, the optical glass of the present invention, when expressed in terms of glass transmittance, has an upper limit of the wavelength (λ ₈₀ ) at which a sample having a thickness of 10 mm exhibits a spectral transmittance of 80%, preferably 420 nm, more preferably 400 nm, and even more preferably 380 nm.
In the optical glass of the present invention, the shortest wavelength (λ ₅ ) at which a sample having a thickness of 10 mm exhibits a spectral transmittance of 5% is preferably set to an upper limit of 380 nm, more preferably 370 nm, and even more preferably 360 nm.
These properties bring the absorption edge of the glass near the ultraviolet region, enhancing the transparency of the glass to visible light, and therefore this optical glass can be preferably used in optical elements that transmit light, such as lenses.

[Glass Molded Body and Optical Element]
From the produced optical glass, a glass molded body can be produced, for example, by using a polishing means or a mold press molding means such as reheat press molding or precision press molding. That is, a glass molded body can be produced by performing mechanical processing such as grinding and polishing on the optical glass, a glass molded body can be produced by performing reheat press molding on a preform produced from the optical glass and then polishing, or a glass molded body can be produced by performing precision press molding on a preform produced by polishing or a preform molded by known floating molding or the like. The means for producing the glass molded body are not limited to these means.

Thus, the glass molded body formed from the optical glass of the present invention is useful for various optical elements and optical designs, but is particularly preferably used for optical elements such as lenses and prisms. This makes it possible to form glass molded bodies with large diameters, so that while the optical elements can be made larger, high-definition, high-precision imaging and projection characteristics can be achieved when used in optical devices such as cameras and projectors.

Tables 1 to 6 show the compositions of the examples (No. 1 to No. 32) of the present invention and comparative examples A and B, as well as the refractive index (n _d ), Abbe number (ν _d ), partial dispersion ratio (θg, F), acid resistance, linear expansion coefficient of the glass (100-300° C.), and wavelengths (λ ₅ , λ ₈₀ ) showing spectral transmittances of 5% and 80%.
It should be noted that the following examples are merely illustrative and are not intended to be limiting.

For the glasses of the Examples and Comparative Examples, high-purity raw materials used in ordinary optical glass, such as the corresponding oxides, hydroxides, carbonates, nitrates, fluorides, and metaphosphate compounds, were selected as the raw materials for each component, and after weighing and mixing uniformly to obtain the composition ratios of each Example and Comparative Example shown in the table, they were placed in a quartz crucible or platinum crucible and melted in an electric furnace at a temperature range of 1100 to 1400°C for 1 to 5 hours depending on the melting difficulty of the glass composition. After stirring and homogenizing, and removing bubbles, the temperature was lowered to 1000 to 1300°C and stirred and homogenized, and the glass was cast into a mold and slowly cooled to produce the glass.

The refractive index (n _d ) and Abbe number (ν _d ) of the glasses in the examples and comparative examples are shown as measured values for the d-line (587.56 nm) of a helium lamp. The Abbe number (ν _d ) was calculated from the formula Abbe number (ν _d )=[(n d -1)/(n _F -n _C )] using the refractive index for the d-line, the refractive index (n F ) for the F-line (486.13 nm) of a hydrogen lamp, and the refractive index (n _C ) for the C-line ( _{656.27 nm} ) of a hydrogen lamp.
The partial dispersion ratio was calculated by measuring the refractive index n _C at C line (wavelength 656.27 nm), the refractive index n _F at F line (wavelength 486.13 nm), and the refractive index n _g at g line (wavelength 435.835 nm) using the formula (θg, F) = (n _g - n _F ) / (n _F - n _C ).

The acid resistance of the glass in the examples and comparative examples was measured in accordance with the Japan Optical Glass Industry Association standard "Method for measuring the chemical durability of optical glass (powder method)" JOGIS06-2009. That is, the glass samples crushed to particle sizes of 425 to 600 μm were taken in grams of specific gravity and placed in a platinum cage. The platinum cage was placed in a quartz glass round-bottom flask containing 0.01 N nitric acid aqueous solution and treated in a boiling water bath for 60 minutes. The weight loss rate (mass%) of the glass sample after treatment was calculated, and the weight loss rate (mass%) was classified as grade 1 if it was less than 0.20, grade 2 if it was 0.20 to 0.35, grade 3 if it was 0.35 to 0.65, grade 4 if it was 0.65 to 1.20, grade 5 if it was 1.20 to 2.20, and grade 6 if it was 2.20 or more. In this case, the smaller the class number, the better the acid resistance of the glass.

The linear expansion coefficient (100-300°C) of the glass in the examples and comparative examples was determined from a thermal expansion curve obtained by measuring the relationship between temperature and sample elongation in accordance with the Japan Optical Glass Industry Association standard JOGIS08-2003 "Method for measuring thermal expansion of optical glass."

The transmittance of the glasses in the examples and comparative examples was measured in accordance with the Japan Optical Glass Industry Association standard JOGIS02-2003. In the present invention, the presence and degree of coloration of the glass was determined by measuring the transmittance of the glass. Specifically, the spectral transmittance of a 10±0.1 mm thick parallel polished face-to-face product was measured in accordance with JIS Z8722 from 200 to 800 nm to determine λ ₅ (wavelength at 5% transmittance) and λ ₈₀ (wavelength at 80% transmittance).

As shown in these tables, the optical glasses of the examples of the present invention all had a refractive index (n _d ) of 1.57 or more and at the same time, this refractive index (n _d ) was 1.65 or less, which was within the desired range.

Furthermore, the optical glasses in the examples of the present invention all had an Abbe number (ν _d ) of 50 or more, and this Abbe number (ν _d ) was 70 or less, which was within the desired range.

Furthermore, in all of the optical glasses according to the examples of the present invention, the partial dispersion ratio (θg, F) and the Abbe number (νd) satisfied the relationship (−0.00162× _νd +0.625)≦(θg, F)≦(−0.00162× _νd +0.660).

The optical glasses in the examples of the present invention all had acid resistance of grade 5 or higher. On the other hand, the optical glass in Comparative Example A had acid resistance of grade 6, making it clear that the glass has poor workability.

In addition, the optical glass in the examples of the present invention all had a linear expansion coefficient (100-300°C) of 130 or less.

Moreover, the optical glasses of the examples of the present invention all had a λ ₈₀ (wavelength at transmittance of 80%) of 420 nm or less. Moreover, the optical glasses of the examples of the present invention all had a λ ₅ (wavelength at transmittance of 5%) of 380 nm or less. This demonstrates that the optical glasses of the examples of the present invention have a high transmittance to visible light and are difficult to color.

Moreover, the optical glasses of the examples of the present invention were stable glasses that did not devitrify.
On the other hand, the optical glass B of the comparative example was devitrified and was not vitrified.

Therefore, it has become clear that the optical glass according to the embodiments of the present invention has a partial dispersion ratio (θg, F) and Abbe number (νd) in the range of (−0.00162× _νd +0.625)≦(θg, F)≦(−0.00162× _νd +0.660), and has acid resistance of grades 3 to 5.

Although the present invention has been described in detail for purposes of illustration, it will be understood that the present embodiments are for illustrative purposes only and that numerous modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims (6)

In mass percent,
_P2O5 component _20.0 to 42.53%,
BaO component 5.0 to 40.0%,
_Ln2O3 component _: more than 0 to 15.0% (wherein Ln is one or more selected from the group consisting of La, Gd, Y, and Yb);
_B2O3 component _: over 0% to 7.86% or less ;
MgO content: 2.74% or less
_Al2O3 component _2.43 % or more,
ZnO content: 2.81% or less
Contains less than 1.0% _{of Ta2O5} component;
The mass ratio (SrO+CaO+MgO)/BaO is 0.28 or less,
Substantially does not contain _GeO2 component,
The refractive index (n _d ) is 1.604 or more;
The partial dispersion ratio (θg, F) and the Abbe number (ν _d ) are
The relationship of (−0.00162×ν _d +0.625)≦(θg,F)≦(−0.00162×ν _d +0.660) is satisfied,
Optical glass with chemical durability (acid resistance) of grades 1 to 5, produced using the powder method. 2. The optical glass according to claim 1, wherein the mass ratio Rn ₂ O/(P ₂ O ₅ +B ₂ O ₃ ) is less than 0.1 (wherein Rn is at least one element selected from the group consisting of Li, Na and K). 3. The optical glass according to claim 1, which has a refractive index ( _nd ) of 1.604 or greater and 1.65 or less, and an Abbe number ( _vd ) of 50 or greater and 70 or less. A preform made of the optical glass according to any one of claims 1 to 3. An optical element made of the optical glass according to any one of claims 1 to 3. An optical device comprising the optical element according to claim 5.

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