JP2024043490A - Optical glass and optical element - Google Patents

Abstract

To provide an optical glass having a refractive index nd in a range of 1.77 to 1.95 and an Abbe number νd in a range of 42 to 48, and having a reduced content of Ta2O5 and a reduced raw material cost, and to provide an optical element comprising the same.SOLUTION: In an optical glass, by mass%: a content of SiO2 is 3 to 13%; a content of B2O3 is 13 to 23%; a mass ratio [SiO2/B2O3] of the content of SiO2 to the content of B2O3 is 0.30 to 0.70; a content of La2O3 is 50% or less; a content of Gd2O3 is 30% or less; a content of Y2O3 is 13% or less; a total content [La2O3+Gd2O3+Y2O3] of La2O3, Gd2O3, and Y2O3 is 53 to 75%; a content of ZrO2 is 12% or less; a content of Nb2O5 is 7% or less; a total content [ZrO2+Nb2O5] of ZrO2 and Nb2O5 is 3.0% to 12.0%; a content of ZnO is 7.8% or less; a content of TiO2 is 7.8% or less; a content of WO3 is 7.8% or less; a total content [Nb2O5+ZnO+TiO2+WO3] of Nb2O5, ZnO, TiO2, and WO3 is 7.8% or less; a content of Ta2O5 is 4.9% or less; and a total content [SiO2+Al2O3+B2O3] of SiO2, Al2O3, and B2O3 is 24 to 32%. The optical glass has: a refractive index nd of 1.77 to 1.95; an Abbe number νd of 42 to 48; and a specific gravity of 4.40 to 5.20.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to optical glasses and optical elements.

Optical element materials constituting imaging optical systems installed in cameras, in-vehicle optical equipment, mobile devices, etc., and projection optical systems such as projectors, etc., with refractive index nd in the range of 1.77 to 1.95 and 42 to 42 A high refractive index, low dispersion optical glass having an Abbe number νd in the range of 48 is used.

Among glass components, rare earth oxides can increase the refractive index without significantly increasing dispersion (without significantly decreasing the Abbe number), so they are useful for creating optical glasses with high refractive index and low dispersion. It is a component. Among rare earth oxides, Ta ₂ O ₅ in particular is known as a component that can impart high refractive index and low dispersion properties to glass while suppressing coloring of the glass. However, Ta ₂ O ₅ is a particularly expensive raw material among glass components. In other words, the cost of glass raw materials increases significantly depending on the content of Ta ₂ O ₅ , so optical glasses with high refractive index and low dispersion that contain Ta ₂ O ₅ are expensive. Ta.

Patent documents 1 to 3 disclose optical glasses with a reduced content of Ta ₂ O _5. However, Patent documents 1 and 3 do not disclose optical glasses having a refractive index nd in the range of 1.77 to 1.95 and an Abbe number νd in the range of 42 to 48. Specifically, the optical glass of Patent document 1 has a small refractive index nd and a high Abbe number νd. Moreover, the optical glass of Patent document 3 has a refractive index nd that is too small. Therefore, Patent documents 1 and 3 do not propose optical glasses having the optical constants desired in the present invention, that is, the refractive index nd and Abbe number νd in the above range. And, in the optical glass of Patent document 2, the content of Ta ₂ O ₅ is reduced, while the content of Gd ₂ O ₃ , which is the same rare earth oxide as Ta ₂ O ₅ , is increased. Gd ₂ O ₃ is a very expensive component, like Ta ₂ O _5. That is, the optical glass of Patent document 2 does not sufficiently suppress the increase in the raw material cost of the glass.

JP 2007-106611 A JP 2007-269584 A China Patent Publication No. 110835227

The present invention provides an optical glass having a refractive index nd in the range of 1.77 to 1.95 and an Abbe number νd in the range of 42 to 48, with a reduced content of Ta ₂ O ₅ and reduced raw material cost. , and an optical element made of the optical glass described above.

(1) In mass % display,
SiO ₂ content is 3-13%,
B ₂ O ₃ content is 13-23%,
The mass ratio of the content of SiO ₂ to the content of B ₂ O ₃ [SiO ₂ /B ₂ O ₃ ] is 0.30 to 0.70,
The content of La ₂ O ₃ is 50% or less,
Gd ₂ O ₃ content is 30% or less,
The content of Y ₂ O ₃ is 13% or less,
The total content of La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ [La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ ] is 53 to 75%,
ZrO ₂ content is 12% or less,
Nb ₂ O ₅ content is 7% or less,
The total content of ZrO ₂ and Nb ₂ O ₅ [ZrO ₂ +Nb ₂ O ₅ ] is 3.0 to 12.0%,
ZnO content is 7.8% or less,
TiO ₂ content is 7.8% or less,
WO ₃ content is 7.8% or less,
The total content of Nb ₂ O ₅ , ZnO, TiO ₂ and WO ₃ [Nb ₂ O ₅ +ZnO+TiO ₂ +WO ₃ ] is 7.8% or less,
Ta ₂ O ₅ content is 4.9% or less,
The total content of SiO ₂ , Al ₂ O ₃ , and B ₂ O ₃ [SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ ] is 24 to 32%,
refractive index nd is 1.77 to 1.95,
Abbe number νd is 42 to 48,
Specific gravity is 4.40 to 5.20,
optical glass.

(2) An optical element made of the optical glass described in (1) above.

According to one aspect of the present invention, the refractive index nd is in the range of 1.77 to 1.95 and the Abbe number νd is in the range of 42 to 48, the content of Ta ₂ O ₅ is reduced, and the raw material cost is reduced. A reduced optical glass can be provided. Further, according to one aspect of the present invention, it is possible to provide an optical element made of the above optical glass.

In the present invention and this specification, the glass composition of optical glass is expressed on an oxide basis unless otherwise specified. Here, "oxide-based glass composition" refers to the glass composition obtained by converting the glass raw materials as if they were all decomposed during melting and existing as oxides in the optical glass, and the notation of each glass component is Following customary practice, they are written as SiO ₂ , TiO ₂ , etc. The content of the glass component and the total content are based on mass unless otherwise specified, and "%" means "% by mass".

The content of glass components can be quantified by known methods, such as inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). In this specification and the present invention, a content of 0% of a component means that the component is substantially not contained, and it is acceptable for the component to be present at an unavoidable impurity level.

An embodiment of the present invention will be described below.

In the optical glass according to this embodiment, the content of SiO ₂ is 3 to 13%. The lower limit of the content of SiO ₂ is preferably 3.5%, and more preferably 4.0%, 4.5%, and 5.0% in that order. Further, the upper limit of the content of SiO ₂ is preferably 12.5%, and more preferably 12.0%, 11.5%, and 11.0% in that order.

SiO ₂ is a network-forming component of glass, and is a component that has the function of improving the thermal stability and chemical durability of glass. By setting the content of SiO ₂ within the above range, the thermal stability of the glass is improved and devitrification during glass production can be suppressed. Additionally, chemical durability can be improved. Furthermore, molten glass having a viscosity suitable for molding can be prepared. On the other hand, if the content of SiO ₂ is too large, there is a risk that the refractive index nd will decrease, and the meltability will decrease, resulting in the possibility that unmelted raw materials will remain. Furthermore, there is also a possibility that the glass transition temperature Tg will rise excessively. Furthermore, if the content of SiO ₂ is too small, the thermal stability of the glass may decrease, and the viscosity of the molten glass may decrease, making it impossible to obtain the desired viscosity.

In the optical glass according to this embodiment, the content of B ₂ O ₃ is 13 to 23%. The lower limit of the content of B ₂ O ₃ is preferably 13.5%, and more preferably 14.0%, 14.5%, and 15.0% in that order. Further, the upper limit of the content of B ₂ O ₃ is preferably 22.5%, and more preferably 22.0%, 21.5%, and 21.0% in that order.

B ₂ O ₃ is a component that has the function of improving the thermal stability and meltability of glass. By setting the content of B ₂ O ₃ within the above range, the thermal stability of the glass can be improved and devitrification during glass production can be suppressed. Furthermore, the meltability is improved, the amount of unmelted glass raw materials is reduced, and a homogeneous glass can be obtained. On the other hand, if the content of B ₂ O ₃ is too large, the refractive index nd may decrease. Moreover, if the content of B ₂ O ₃ is too small, there is a risk that the thermal stability of the glass will decrease, and further, there is a risk that the meltability will decrease and unmelted raw materials will remain.

In the optical glass according to this embodiment, the mass ratio of the SiO ₂ content to the B ₂ O ₃ content [SiO ₂ /B ₂ O ₃ ] is 0.30 to 0.70. The lower limit of the mass ratio is preferably 0.35, and more preferably in the order of 0.40, 0.43, 0.44, 0.45, and 0.46. Further, the upper limit of the mass ratio is preferably 0.69, and more preferably in the order of 0.68, 0.67, and 0.66. By setting the mass ratio [SiO ₂ /B ₂ O ₃ ] within the above range, the thermal stability of the glass is improved and a molten glass having a viscosity suitable for molding can be prepared.

In the optical glass according to this embodiment, the content of La ₂ O ₃ is 50% or less. The upper limit of the content of La ₂ O ₃ is preferably 49%, and more preferably 48%, 47%, and 46% in that order. Further, the lower limit of the content of La ₂ O ₃ is preferably 0%, and more preferably in the order of 10%, 20%, 30%, 31%, 31.5%, 32.0%, and 32.5%. more preferred.

La ₂ O ₃ is a component that has the function of increasing the refractive index nd without significantly reducing the Abbe number νd. By setting the content of La ₂ O ₃ within the above range, an optical glass having desired optical constants can be obtained. Further, the thermal stability of the glass is improved, and devitrification during glass production can be suppressed. Furthermore, meltability is improved, and unmelted glass raw materials can be suppressed.
On the other hand, if the content of La ₂ O ₃ is too large, the specific gravity may increase and the thermal stability of the glass may decrease. Furthermore, there is also a possibility that the glass transition temperature Tg will rise excessively. Note that among the rare earth components, La ₂ O ₃ is a component that is less likely to increase the specific gravity of glass than Gd ₂ O ₃ and Yb ₂ O ₃ . Further, La ₂ O ₃ is also a component that can maintain the thermal stability of the glass even if it is contained in a relatively large amount. Furthermore, like Yb ₂ O ₃ , La ₂ O ₃ has no absorption in the near-infrared region, so it is also a component that can maintain near-infrared transmittance.

In the optical glass according to this embodiment, the content of Gd ₂ O ₃ is 30% or less. The upper limit of the Gd ₂ O ₃ content is preferably 29.0%, and more preferably 28.0%, 27.0%, and 26.0% in that order. Further, the lower limit of the content of Gd ₂ O ₃ is preferably 0%, more preferably 1.0%, 2.0%, 3.0%, 8.0%, 10.0%, 12.0%. The order of percentage is more preferable.

Gd ₂ O ₃ is a component that has the function of increasing the refractive index nd without significantly reducing the Abbe number νd. By setting the content of Gd ₂ O ₃ within the above range, an optical glass having desired optical constants can be obtained. Further, the thermal stability of the glass is improved, and devitrification during glass production can be suppressed. Furthermore, meltability is improved, and unmelted glass raw materials can be suppressed. In addition, coloring of the glass can be suppressed. On the other hand, since Gd ₂ O ₃ is an expensive component, if the content of Gd ₂ O ₃ is too large, the raw material cost may increase. Furthermore, if the content of Gd ₂ O ₃ is too large, the specific gravity of the glass may increase. Furthermore, since Gd ₂ O ₃ has the effect of reducing the transmittance of glass on the short wavelength side of the visible range, if the content of Gd ₂ O ₃ is too large, the transmittance of glass on the short wavelength side of the visible range decreases. There is a risk that it will decrease. If the content of Gd ₂ O ₃ is too large, the glass transition temperature Tg may increase.

In the optical glass according to this embodiment, the content of Y ₂ O ₃ is 13% or less. The upper limit of the content of Y ₂ O ₃ is preferably 12.0%, and more preferably 11.0%, 10.0%, and 9.0% in that order. Further, the lower limit of the content of Y ₂ O ₃ is preferably 0%, more preferably 0.5%, 1.0%, 1.5%, 2.0%, 3.0%, 4.0%. %, 5.0%, and 6.0% in that order.

_Y2O3 is a component that increases the refractive index nd without significantly decreasing _the Abbe number νd. By setting the content of _Y2O3 within the above range, an optical glass having the desired _optical constants can be obtained. In addition, the thermal stability of the glass is improved, and devitrification during glass production can be suppressed. Furthermore, the melting property is improved, and the unmelted glass raw material can be suppressed. On the other hand, if the content of _Y2O3 is too high, the glass transition temperature _Tg may increase. In addition, among the rare earth components, _Y2O3 is a component that can maintain the thermal stability of the glass even if it is contained _in a relatively large amount, but if the content is too high, the thermal stability of the glass may decrease.

In the optical glass according to this embodiment, the total content of La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ [La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ ] is 53 to 75%. The lower limit of the total content is preferably 54.0%, and more preferably 55.0%, 56.0%, and 56.5% in that order. Further, the upper limit of the total content is preferably 74.0%, and more preferably 73.0%, 72.0%, and 71.0% in that order. By setting the total content within the above range, the refractive index nd can be increased without greatly reducing the Abbe number νd, and an optical glass having desired optical constants can be obtained. Further, the thermal stability of the glass is improved, and devitrification during glass production can be suppressed.

In the optical glass according to this embodiment, the content of ZrO ₂ is 12% or less. The upper limit of the ZrO ₂ content is preferably 11.5%, and more preferably 11.0%, 10.5%, and 10.0% in that order. Further, the lower limit of the ZrO ₂ content is preferably 0%, and more preferably 0.5%, 1.0%, and 1.5% in that order.

_ZrO2 is a component that has the function of increasing the refractive index nd and improving the thermal stability of glass. By setting the content of _ZrO2 within the above range, an optical glass having desired optical constants and improved thermal stability can be obtained. On the other hand, if the content of _ZrO2 is too high, there is a risk that the thermal stability will decrease, the specific gravity will increase, and the glass transition temperature Tg will increase.

In the optical glass according to this embodiment, the content of Nb ₂ O ₅ is 7% or less. The upper limit of the content of Nb ₂ O ₅ is preferably 6.5%, and more preferably 6.0%, 5.5%, and 5.0% in that order. Further, the lower limit of the content of Nb ₂ O ₅ is preferably 0%, and more preferably 0.5%, 1.0%, and 1.5% in that order. The content of Nb ₂ O ₅ may be 0%.

Nb ₂ O ₅ is a component that has the function of increasing the refractive index nd and maintaining the thermal stability of the glass. It is also a component that can adjust the Abbe number νd. By setting the content of Nb ₂ O ₅ within the above range, an optical glass having desired optical constants and improved thermal stability can be obtained. On the other hand, if the content of Nb ₂ O ₅ is too large, there is a risk that the thermal stability will decrease, the specific gravity will increase, and the glass transition temperature Tg will increase.

In the optical glass according to this embodiment, the total content of ZrO ₂ and Nb ₂ O ₅ [ZrO ₂ +Nb ₂ O ₅ ] is 3.0 to 12.0%. The lower limit of the total content is preferably 3.1%, and more preferably 3.3%, 3.5%, and 3.6% in that order. Further, the upper limit of the total content is preferably 11.5%, and more preferably in the order of 10.5%, 9.3%, 9.2%, and 9.1%. By setting the total content within the above range, an optical glass having desired optical constants and improved thermal stability can be obtained. On the other hand, if the total content is too large, the Abbe number νd may decrease and an optical glass having desired optical constants may not be obtained.

In the optical glass according to this embodiment, the ZnO content is 7.8% or less. The upper limit of the ZnO content is preferably 7.5%, and more preferably in the order of 7.0%, 6.5%, 6.0%, 5.0%, and 3.0%. Further, the lower limit of the ZnO content may be 0%, 0.5%, 1.0%, or 1.5%. The content of ZnO may be 0%.

ZnO is a component that has the functions of improving meltability, suppressing an excessive increase in glass transition temperature Tg, and adjusting optical properties. It is also a component that can adjust the Abbe number νd. By setting the content of ZnO within the above range, an optical glass having desired optical constants and optical properties and improved meltability and thermal stability can be obtained. On the other hand, if the ZnO content is too large, the thermal stability of the glass may decrease.

In the optical glass according to this embodiment, the content of TiO ₂ is 7.8% or less. The upper limit of the TiO ₂ content is preferably 7.5%, and more preferably in the order of 7.0%, 6.5%, 6.0%, 5.0%, and 4.0%. Further, the lower limit of the TiO ₂ content may be 0%, and the TiO ₂ content is preferably 0%.

_TiO2 is a component that has the function of increasing the refractive index nd and maintaining the thermal stability of glass. By setting the content of _TiO2 within the above range, optical glass having desired optical constants can be obtained. On the other hand, if the content of _TiO2 is too high, the thermal stability of glass may decrease, and the coloring of glass may increase.

In the optical glass according to this embodiment, the content of WO ₃ is 7.8% or less. The upper limit of the content of WO ₃ is preferably 7.5%, and more preferably 7.0%, 6.5%, and 6.0% in that order. Further, the lower limit of the WO ₃ content may be 0%, and the WO ₃ content is preferably 0%.

WO ₃ is a component that has the function of increasing the refractive index nd and improving the thermal stability of the glass. It is also a component that has the function of suppressing crystallization during glass production. By setting the content of WO ₃ within the above range, an optical glass having desired optical constants can be obtained. On the other hand, if the content of WO ₃ is too large, the thermal stability may decrease and the specific gravity may increase. Furthermore, if the content of WO ₃ is too large, the light absorption edge on the short wavelength side of the spectral transmittance becomes longer wavelength, so there is a possibility that the transmittance of ultraviolet rays decreases.

In the optical glass according to this embodiment, the total content of Nb ₂ O ₅ , ZnO, TiO ₂ , and WO ₃ [Nb ₂ O ₅ +ZnO+TiO ₂ +WO ₃ ] is 7.8% or less. The upper limit of the total content is preferably 7.5%, and more preferably 7.0%, 6.5%, and 6.0% in that order. Further, the lower limit of the total content is preferably 0%, and more preferably 0.5%, 1.0%, and 1.5% in that order. The content of the total content may be 0%. By setting the total content within the above range, the refractive index nd can be increased and an optical glass having desired optical constants can be obtained.

In the optical glass according to this embodiment, the content of Ta ₂ O ₅ is 4.9% or less. The upper limit of the content of Ta ₂ O ₅ is preferably 4.0%, more preferably 3.5%, 3.0%, 2.5%, 2.2%, 2.1%, 2.0%. %, 1.70%, 1.65%, 1.60%, 1.55%, 1.50% in that order. The upper limit of the Ta ₂ O ₅ content can be set as 1.45%, 1.40%, 1.35%, etc. in 0.05% increments after 1.50%. That is, for example, the upper limit of the Ta ₂ O ₅ content can be 1.25%, 1.00%, 0.75%, or 0.50%. Further, the lower limit of the content of Ta ₂ O ₅ is preferably 0%. The content of Ta ₂ O ₅ may be 0%.

Ta ₂ O ₅ is a component that has the function of increasing the refractive index nd and improving the thermal stability of the glass. However, since Ta ₂ O ₅ is an extremely expensive component, if the content of Ta ₂ O ₅ is too large, the raw material cost may increase excessively. Therefore, by setting the content of Ta ₂ O ₅ within the above range, an optical glass with reduced raw material cost can be obtained. Moreover, if the content of Ta ₂ O ₅ is too large, the thermal stability of the glass may decrease, the specific gravity may increase, the coloring of the glass may increase, and the glass transition temperature Tg may increase. In this embodiment, by specifying the content of glass components other than Ta ₂ O ₅ , desired optical constants can be achieved even if the content of Ta ₂ O ₅ is reduced. Further, by setting the content of Ta ₂ O ₅ within the above range, it can contribute to reducing raw material costs.

In the optical glass according to this embodiment, the total content of SiO ₂ , Al ₂ O ₃ , and B ₂ O ₃ [SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ ] is 24 to 32%. The lower limit of the total content is preferably 24.5%, and more preferably 25.0%, 25.5%, and 25.7% in that order. Further, the upper limit of the total content is preferably 31.9%, and more preferably in the order of 31.8%, 31.7%, 31.6%, 30.0%, and 28.0%. SiO ₂ , Al ₂ O ₃ , and B ₂ O ₃ are all network forming components of the glass. By setting the total content within the above range, the thermal stability of the glass can be improved.

<Refractive index nd>
In the optical glass according to the present embodiment, the refractive index nd is 1.77 to 1.95. The lower limit of the refractive index nd is preferably 1.78), and more preferably in the order of 1.79, 1.80, and 1.81. Further, the upper limit of the refractive index nd is preferably 1.93, and more preferably in the order of 1.91, 1.90, and 1.88.

In the optical glass according to this embodiment, the refractive index nd can be controlled by adjusting the content, ratio, and total content of the above-mentioned glass components while considering the effects of each glass component. Unless otherwise specified, the refractive index refers to the refractive index nd at the d-line (helium wavelength: 587.56 nm).

<Abbe number νd>
From the same viewpoint, the Abbe number νd of the optical glass according to this embodiment is 42 to 48. The lower limit of the Abbe number νd is preferably 42.5, and more preferably in the order of 42.7, 42.9, and 43.0. Further, the upper limit of the Abbe number νd is preferably 47.9, and more preferably 47.8 and 47.7 in that order.

In the optical glass according to this embodiment, the Abbe number vd can be controlled by adjusting the contents, ratios, and total contents of the above-mentioned glass components while taking into consideration the action and effect of each glass component. Unless otherwise specified, the Abbe number vd is defined as follows, where nF and nC are the refractive indices at the F line (hydrogen wavelength 486.13 nm) and C line (hydrogen wavelength 656.27 nm), respectively:
νd=(nd−1)/(nF−nC)

<Specific gravity>
The optical glass according to this embodiment has a specific gravity of 4.40 to 5.20. The lower limit of the specific gravity is preferably 4.50, and more preferably 4.55, 4.60, and 4.65 in this order. Further, the upper limit of the specific gravity is preferably 5.15, and more preferably 5.10, 5.05, and 5.00 in this order.

For example, it is conceivable that the optical glass according to this embodiment is used in a lens with an autofocus function. If the specific gravity is too large, the mass of the lens increases, which may increase the power consumption during focusing and cause the battery to wear out faster. On the other hand, if the specific gravity is too small, the thermal stability of the glass may decrease. Therefore, by setting the specific gravity within the above range, an optical glass that is lightweight and maintains thermal stability can be obtained.

In the optical glass according to this embodiment, the specific gravity can be reduced by adjusting the content, ratio, and total content of the above-mentioned glass components while considering the effects of each glass component.

Non-limiting examples will be shown below regarding the contents, ratios, and glass properties of glass components other than those mentioned above in the optical glass according to the present embodiment.

In the optical glass according to the present embodiment, the upper limit of the total content of ZrO ₂ , Nb ₂ O ₅ , ZnO, TiO ₂ , and WO ₃ [ZrO ₂ +Nb ₂ O ₅ +ZnO+TiO ₂ +WO ₃ ] is 15.0, preferably It is 14.5%, and more preferably 14.0%, 13.5%, and 13.0% in that order. Further, the lower limit of the total content is preferably 3.0%, and more preferably 4.0%, 5.0%, and 6.0% in that order. From the viewpoint of increasing the refractive index nd and obtaining an optical glass having desired optical constants, it is preferable that the total content is within the above range.

In the optical glass according to this embodiment, the mass ratio of the total content of _{Ta 2 O 5} , Nb ₂ O ₅ , and WO _{3 to the total content of Gd 2 O 3 and} Y ₂ O ₃ [(Ta ₂ O ₅ +Nb ₂ O ₅ +WO ₃ )/(Gd ₂ O ₃ +Y ₂ O ₃ )] is 0.45, preferably 0.40, and more preferably 0.35, 0.30, and 0.25 in this order. . Further, the lower limit of the mass ratio is preferably 0, and more preferably 0.01, 0.02, and 0.03 in this order. From the viewpoint of obtaining an optical glass having desired optical constants and reduced raw material cost, it is preferable that the mass ratio is within the above range.

In the optical glass according to this embodiment, the upper limit of the mass ratio of the total content of _ZrO2 , _{Ta2O5 ,} and _Nb2O5 to the total content of _SiO2 and _B2O3 [( _ZrO2 + _Ta2O5 + _{Nb2O5 )} /( _{SiO2 + B2O3} )] is 0.465, preferably 0.450, more preferably 0.430 _, 0.410, and 0.390 in that order. The lower _limit of the mass ratio _is 0.145, preferably 0.150, more preferably 0.200, 0.250, and 0.300 in that order. From the viewpoint of obtaining an optical glass having desired optical constants and improved thermal stability, it is preferable that the mass ratio is within the above range.

In the optical glass according to the present embodiment, the upper limit of the mass ratio of the total content of ZnO and Y ₂ O ₃ to the content of La ₂ O ₃ [(ZnO+Y ₂ O ₃ )/La ₂ O ₃ ] is preferably 1. .0, and more preferably in the order of 0.8, 0.6, and 0.4. Further, the lower limit of the mass ratio is preferably 0, and more preferably 0.05, 0.10, and 0.15 in this order. From the viewpoint of obtaining an optical glass having desired optical constants and improved thermal stability, it is preferable that the mass ratio is within the above range.

In the optical glass according to this embodiment, the total content of BaO, La _{2 O 3 ,} Nb ₂ O ₅ , TiO ₂ , and ZrO 2 is greater than the total content of SiO ₂ , Al ₂ O ₃ , and B 2 O _{3 .} The upper limit of the mass ratio [(BaO+ _{La2O3 + Nb2O5} + _{TiO2+ZrO2)/(SiO2+Al2O3 + B2O3 ) ] is 2.80} , preferably _2.62 , and more preferably 2.80. The preferred order is 50, 2.30, and 2.00. Further, the lower limit of the mass ratio is preferably 0.35, and more preferably 0.40, 0.50, 1.00, and 1.50 in this order. From the viewpoint of obtaining an optical glass having desired optical constants and improved thermal stability, it is preferable that the mass ratio is within the above range.

In the optical glass according to the present embodiment, the mass ratio of the content of Gd 2 O ₃ to the total content of La ₂ O ₃ , Gd ₂ O ₃ , and Y _{2 O 3} [Gd ₂ O ₃ /(La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ )] is preferably 0.40, and more preferably in the order of 0.38, 0.36, and 0.32. The lower limit of the mass ratio is preferably 0.20, and more preferably 0.23, 0.26, and 0.29 in this order. From the viewpoint of obtaining an optical glass with improved thermal stability, it is preferable that the mass ratio is within the above range.

In the optical glass according to the present embodiment, the mass ratio of _the content of Y 2 O ₃ to the total content of La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ is [Y ₂ O ₃ /(La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ )] is preferably 0.23, and more preferably in the order of 0.21, 0.19, and 0.17. The lower limit of the mass ratio is preferably 0.07, and more preferably in the order of 0.09, 0.11, and 0.13. From the viewpoint of obtaining an optical glass with improved thermal stability, it is preferable that the mass ratio is within the above range.

In the optical glass according to this embodiment, the mass ratio of the content of Nb ₂ O ₅ to the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ , and Ta ₂ O ₅ is [Nb ₂ O ₅ /(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Ta ₂ O ₅ )] can be set to 1.00. The lower limit of the mass ratio is preferably 0, and more preferably 0.20, 0.40, and 0.60 in this order. From the viewpoint of obtaining an optical glass having desired optical constants and reduced raw material cost, it is preferable that the mass ratio is within the above range.

In the optical glass according to the present embodiment, the mass of the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ , and Ta 2 O ₅ with respect to the total content of La _{2 O 3} , Gd ₂ O ₃ , and Y ₂ O ₃ The upper limit of the ratio [(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Ta ₂ O ₅ )/(La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ )] is preferably 0.12, more preferably 0.10, The order of 0.08 and 0.06 is more preferable. The lower limit of the mass ratio is preferably 0, and more preferably in the order of 0.01, 0.02, and 0.03. From the viewpoint of obtaining an optical glass having desired optical constants, it is preferable that the mass ratio is within the above range.

In the optical glass according to this embodiment, the upper limit of the P ₂ O ₅ content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 3.0%. The order of percentage is more preferable. Further, the lower limit of the content of P ₂ O ₅ is preferably 0%. The content of P ₂ O ₅ may be 0%. P ₂ O ₅ is a component that lowers the refractive index nd, and is also a component that lowers the thermal stability of the glass. Therefore, it is preferable that the content of P ₂ O ₅ is within the above range.

In the optical glass according to this embodiment, the upper limit of the Al ₂ O ₃ content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 2.0%. The order of percentage is more preferable. The lower limit of the content of Al ₂ O ₃ is preferably 0%. The content of Al ₂ O ₃ may be 0%. In a small amount, Al ₂ O ₃ has the effect of improving the thermal stability and chemical durability of glass, but if the content of Al ₂ O ₃ is too large, the liquidus temperature LT increases and the thermal stability Stability tends to deteriorate. Therefore, the content of Al ₂ O ₃ is preferably within the above range.

In the optical glass according to this embodiment, the upper limit of the _Li2O content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 1.0%, in that order. The lower limit of the _Li2O content is preferably 0%. _{The Li2O} content may be 0%.

In the optical glass according to this embodiment, the upper limit of the Na ₂ O content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 1.0%. This order is more preferable. The lower limit of the Na ₂ O content is preferably 0%. The content of Na ₂ O may be 0%.

In the optical glass according to this embodiment, the upper limit of the K ₂ O content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 2.0%. This order is more preferable. The lower limit of the K ₂ O content is preferably 0%. The content of K ₂ O may be 0%.

Li ₂ O, Na ₂ O, and K ₂ O all have the function of lowering the liquidus temperature LT and improving the thermal stability of glass, but when their contents increase, the chemical durability and weather resistance deteriorate. There is a risk that performance may deteriorate. Therefore, it is preferable that the contents of Li ₂ O, Na ₂ O, and K ₂ O are each within the above ranges.

In the glass according to this embodiment, the upper limit of the Cs ₂ O content is preferably 10.0%, and more preferably 8.0%, 6.0%, and 4.0% in that order. The lower limit of the Cs ₂ O content is preferably 0%. The content of Cs ₂ O may be 0%.

Cs ₂ O is a component that has the function of improving the thermal stability of glass. On the other hand, when the content of Cs ₂ O increases, chemical durability and weather resistance may decrease. Therefore, the content of Cs ₂ O is preferably within the above range.

In the glass according to the present embodiment, the upper limit of the total content of Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O [Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O] is preferably 10.0%. , and more preferably in the order of 8.0%, 6.0%, 4.0%, and 2.0%. Further, the lower limit of the total content is preferably 0%. The total content may be 0%. From the viewpoint of suppressing deterioration of chemical durability and weather resistance of glass, the total content is preferably within the above range.

In the glass according to this embodiment, the upper limit of the MgO content is preferably 10.0%, and more preferably in the order of 8.0%, 6.0%, 4.0%, and 1.0%. preferable. Further, the lower limit of the MgO content is preferably 0%. The content of MgO may be 0%.

In the glass according to this embodiment, the upper limit of the CaO content is preferably 10.0%, and more preferably in the order of 8.0%, 6.0%, 4.0%, and 2.0%. preferable. Further, the lower limit of the CaO content is preferably 0%. The content of CaO may be 0%.

In the glass according to the present embodiment, the upper limit of the SrO content is preferably 10.0%, and more preferably in the order of 8.0%, 6.0%, 4.0%, and 3.0%. preferable. Further, the lower limit of the SrO content is preferably 0%. The content of SrO may be 0%.

In the glass according to this embodiment, the upper limit of the BaO content is preferably 10.0%, and more preferably 8.0%, 6.0%, and 4.0% in this order. Further, the lower limit of the BaO content is preferably 0%. The content of BaO may be 0%.

MgO, CaO, SrO, and BaO are all components that improve the thermal stability and devitrification resistance of glass. On the other hand, if the content of these components is too high, the specific gravity increases, high dispersion is lost, and the thermal stability and devitrification resistance of the glass may decrease. Therefore, it is preferable that the content of each of these glass components is within the above range.

In the optical glass according to this embodiment, the upper limit of the Bi ₂ O ₃ content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 1.0%. The order of percentage is more preferable. Moreover, the lower limit of the content of Bi ₂ O ₃ is preferably 0%. The content of Bi ₂ O ₃ may be 0%.

Bi ₂ O ₃ is a component that has the function of increasing the refractive index nd and improving the thermal stability of the glass. On the other hand, if the content of Bi ₂ O ₃ is too large, the absorption edge on the short wavelength side of the spectral transmittance may become short in wavelength. Therefore, the content of Bi ₂ O ₃ is preferably within the above range.

In the optical glass according to this embodiment, the upper limit of the Yb ₂ O ₃ content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 3.0%. The order of percentage is more preferable. Further, the lower limit of the content of Yb ₂ O ₃ is preferably 0%. The content of Yb ₂ O ₃ may be 0%.

Yb ₂ O ₃ is a component that has the function of increasing the refractive index nd without significantly reducing the Abbe number νd. It is also a component that improves the thermal stability of glass and suppresses devitrification during glass production. Furthermore, it is a component that improves meltability and suppresses unmelted glass raw materials. It is also a component that does not absorb in the near-infrared region. On the other hand, if the content of Yb ₂ O ₃ is too large, the specific gravity of the glass may increase and the glass transition temperature Tg may increase. Therefore, the content of Yb ₂ O ₃ is preferably within the above range.

In _the optical glass according to this embodiment, the content of _Sc2O3 is preferably 2% or less. The lower limit of _the content _{of Sc2O3} is preferably 0%. The content of _Sc2O3 may be 0%.

In the optical glass according to this embodiment, the content of HfO ₂ is preferably 2% or less. Further, the lower limit of the content of HfO ₂ is preferably 0%. The content of HfO ₂ may be 0%.

Sc ₂ O ₃ and HfO ₂ have the function of increasing the high dispersibility of glass, but are also expensive components. Therefore, the contents of Sc ₂ O ₃ and HfO ₂ are preferably within the above ranges.

In the optical glass according to this embodiment, the content of Lu ₂ O ₃ is preferably 2% or less. Further, the lower limit of the content of Lu ₂ O ₃ is preferably 0%. The content of Lu ₂ O ₃ may be 0%.

Lu ₂ O ₃ has the function of increasing the high dispersibility of glass, but since it has a large molecular weight, it is also a glass component that increases the specific gravity of glass. Therefore, the content of Lu ₂ O ₃ is preferably within the above range.

In the optical glass according to this embodiment, the _GeO2 content is preferably 2% or less. The lower limit of the _GeO2 content is preferably 0%. _{The GeO2} content may be 0%.

GeO ₂ has the function of increasing the high dispersibility of glass, but is a relatively expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the raw material cost of glass, the content of GeO ₂ is preferably within the above range.

The optical glass according to this embodiment mainly contains the above-mentioned glass components, that is, SiO ₂ and B ₂ O ₃ as essential components, and La ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ , ZrO ₂ as optional components. _Nb2O5 , _ZnO , _TiO2 , WO3, _Ta2O5 , _P2O5 , _Al2O3 , _Li2O , _Na2O , _K2O , _{Cs2O , MgO} , _CaO , _SrO , It is preferably composed of BaO, Bi ₂ O ₃ , Yb ₂ O ₃ , Sc ₂ O ₃ , HfO ₂ , Lu ₂ O ₃ , and GeO ₂ , and the total content of the above-mentioned glass components is 95% or more. is preferable, 98% or more is more preferable, 99% or more is even more preferable, and even more preferably 99.5% or more.

Although it is preferable that the optical glass according to the present embodiment is basically composed of the above-mentioned glass components, it is also possible to contain other components within a range that does not impede the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

(Other ingredients)
In addition to the above components, the optical glass according to this embodiment may contain small amounts of fining agents such as _Sb2O3 and _SnO2 . Note that in this specification, the content of the fining agent is expressed as _an exclusive percentage and is not included in the total content of all glass components expressed on an oxide basis.

In the optical glass according to the present embodiment, the content of Sb ₂ O ₃ is preferably 1% by mass or less, and more preferably 0.5% by mass when the total content of all glass components other than the fining agent is 100% by mass. It is preferably 5% by mass or less, and preferably 0.1% by mass or less. The content of Sb ₂ O ₃ may be 0% by mass. In addition to acting as a clarifying agent, Sb ₂ O ₃ also has the function of suppressing the decrease in light transmittance due to the inclusion of _impurities such as _Fe . Coloring may increase. Therefore, the content of Sb ₂ O ₃ is preferably within the above range.

In the optical glass according to the present embodiment, the SnO ₂ content is preferably 1% by mass or less, and more preferably 0.5% by mass when the total content of all glass components other than the fining agent is 100% by mass. % or less, preferably 0.1% by mass or less. The content of SnO ₂ may be 0% by mass. SnO ₂ has the function of a fining agent, but if the amount of SnO ₂ added is large, there is a risk that the coloring of the glass will increase. , Sn may serve as a starting point for crystal nucleation and the glass may become devitrified.

Pb, As, Cd, Tl, Be, and Se are all toxic. Therefore, it is preferable that the optical glass of this embodiment does not contain these elements as glass components.

U, Th, and Ra are all radioactive elements. Therefore, it is preferable that the optical glass of this embodiment does not contain these elements as glass components.

V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Ce increase the coloring of glass and can be a source of fluorescence. . Therefore, it is preferable that the optical glass of this embodiment does not contain these elements as glass components.

(Glass characteristics)
<Coloring degree λ5, λ70 and λ80>
Regarding the suppression of coloration of glass, the light transmittance of the glass, specifically, the suppression of the increase in wavelength of the light absorption edge on the short wavelength side can be evaluated by one or more of the degree of coloration λ5, λ70, and λ80. The degree of coloration λ5 represents a wavelength at which the spectral transmittance (including surface reflection loss) of glass with a thickness of 10±0.1 mm is 5% from the ultraviolet region to the visible region. λ70 represents a wavelength at which the spectral transmittance measured by the method described for λ5 is 70%. λ80 represents a wavelength at which the spectral transmittance measured by the method described for λ5 is 80%. λ5, λ70, and λ80 shown in Examples below are values measured in the wavelength range of 250 to 700 nm. Note that the spectral transmittance T (%) of glass in the present invention and this specification refers to the spectral transmittance T (%) of light that is perpendicularly incident on one of the two optically polished planes of the glass sample that is parallel to each other. When the intensity is I _in and the intensity of the light transmitted through the glass sample and emitted from the other side is I _out ,
T (%) = I _out / I _in × 100
It is expressed as

According to the coloring degrees λ5, λ70, and λ80, the absorption edge of the spectral transmittance on the short wavelength side can be quantitatively evaluated. For example, when joining lenses together using an ultraviolet curable adhesive to produce a cemented lens, the adhesive is irradiated with ultraviolet rays through an optical element to cure the adhesive. From the viewpoint of efficiently curing the ultraviolet curable adhesive, it is preferable that the absorption edge on the short wavelength side of the spectral transmittance is in a short wavelength range. As an index for quantitatively evaluating the absorption edge on the short wavelength side, one or more of the degree of coloration λ5, λ70, and λ80 can be used.

In the optical glass according to this embodiment, λ5 is preferably 350 nm or less, more preferably 340 nm or less, and still more preferably 330 nm or less. Moreover, λ70 is preferably 390 nm or less, more preferably 380 nm or less, and even more preferably 370 nm or less. Furthermore, λ80 is preferably 480 nm or less, more preferably 450 nm or less, and still more preferably 420 nm or less.

In the optical glass according to this embodiment, λ5, λ70, and λ80 can be reduced by adjusting the contents, ratios, and total contents of the above-mentioned glass components while taking into account the action and effect of each glass component.

<Glass transition temperature Tg>
From the viewpoint of reducing the burden on the annealing furnace and mold, the glass transition temperature Tg of the optical glass according to this embodiment is preferably 735°C or lower, more preferably 725°C or lower, and even more preferably 715°C or lower. It is. On the other hand, from the viewpoint of machinability (specifically, from the viewpoint that it is difficult to break when performing glass machining such as cutting, cutting, grinding, polishing, etc.), the glass transition temperature Tg of optical glass is preferably 670 ° C. The temperature is more preferably 680°C or more, and still more preferably 690°C or more. The glass transition temperature Tg is determined by the method described below. The glass transition temperature Tg can be controlled by adjusting the content, ratio, and total content of the above-mentioned glass components while taking into consideration the effects of each glass component.

(manufacture of optical glass)
The optical glass according to the present embodiment may be produced by blending glass raw materials to have the above-mentioned predetermined composition, and using the blended glass raw materials according to a known glass manufacturing method. For example, a plurality of compounds are prepared and sufficiently mixed to form a batch raw material, and the batch raw material is put into a quartz crucible or a platinum crucible and roughly melted (rough melted). The molten material obtained by rough melting is rapidly cooled and pulverized to produce cullet. Further, the cullet is placed in a platinum crucible, heated and remelted to obtain a molten glass, and the molten glass is clarified and homogenized, then molded, and slowly cooled to obtain an optical glass. A known method may be applied to forming and slowly cooling the molten glass.

Note that the compound used when preparing the batch raw material is not particularly limited as long as the desired glass component can be introduced into the glass in a desired content. Such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, and the like.

(Manufacture of optical elements, etc.)
In order to produce an optical element using the optical glass according to this embodiment, a known method may be applied. For example, in the production of the optical glass described above, molten glass is poured into a mold and formed into a plate shape to produce a glass material made of the optical glass according to the present invention. The obtained glass material is appropriately cut, ground, and polished to produce cut pieces of a size and shape suitable for press molding. The cut piece is heated, softened, and press-molded (reheat-pressed) by a known method to produce an optical element blank that approximates the shape of the optical element. An optical element blank is annealed, ground and polished by a known method to produce an optical element.

The optically functional surface of the manufactured optical element may be coated with an antireflection film, a total reflection film, etc. depending on the purpose of use.

According to one aspect of the present invention, an optical element made of the optical glass described above can be provided. Examples of the types of optical elements include lenses such as spherical lenses and aspheric lenses, prisms, and diffraction gratings. Examples of the shape of the lens include various shapes such as a biconvex lens, a plano-convex lens, a biconcave lens, a plano-concave lens, a convex meniscus lens, and a concave meniscus lens. The optical element can be manufactured by a method including a process of processing a glass molded body made of the optical glass. Examples of processing include cutting, cutting, rough grinding, fine grinding, and polishing. By using the above-mentioned glass during such processing, breakage can be reduced and high-quality optical elements can be stably supplied.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the embodiments shown in the examples.

Oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass are prepared as raw materials, and the glass composition of the resulting optical glass is as shown in Tables 1 (1) to (7). The above raw materials were weighed and prepared, and the raw materials were thoroughly mixed. The blended raw material (batch raw material) thus obtained was placed in a platinum crucible, heated in a furnace set at 1400°C, and melted for 2 hours to obtain molten glass. The molten glass was stirred to homogenize and poured into a preheated mold. After the cast glass is allowed to cool to around the glass transition temperature, it is immediately put into an annealing furnace, kept at a temperature around the glass transition temperature for about 30 minutes, and then slowly cooled for 4 hours at a slow cooling rate of -30°C/hour. Then, it was allowed to cool to room temperature in the furnace. Optical glass samples having the compositions shown in Tables 1 (1) to (7) were obtained.

[Confirmation of glass component composition]
Regarding the obtained optical glass sample, the content of each glass component was measured by inductively coupled plasma emission spectroscopy (ICP-AES), and it was confirmed that the content of each glass component was as shown in Table 1 (1) to (7). confirmed.

[Evaluation of the physical properties]
For the obtained optical glass sample, the refractive index nd, Abbe number νd, glass transition temperature Tg, specific gravity, and degree of coloration λ5, λ70, and λ80 were measured. The results are shown in Tables 2 (1) to (7).

(1) Refractive index nd, Abbe number νd
The refractive index nd and Abbe number νd of the obtained optical glass sample were measured by the refractive index measurement method specified by the Japan Optical Glass Industry Association.

(2) Glass transition temperature Tg
The obtained optical glass sample was thoroughly pulverized in a mortar to prepare a specimen, and the glass transition temperature Tg was measured at a heating rate of 10° C./min using a differential scanning calorimeter (DSC8270) manufactured by Rigaku Corporation.

(3) Specific gravity Specific gravity was measured by the Archimedes method.

(4) Coloring degree λ5, λ70, λ80
Using a glass sample with a thickness of 10±0.1 mm having two optically polished planes facing each other, the spectral transmittance T (%) at a wavelength of 250 to 700 nm was measured using a spectrophotometer. The wavelength (nm) at which T becomes 5% is defined as λ5, the wavelength (nm) at which T becomes 70% is defined as λ70, and the wavelength (nm) at which T becomes 80% is defined as λ80.

(Example 2)
Using each optical glass produced in Example 1, a lens blank was produced by a known method, and the lens blank was processed by a known method such as polishing to produce various lenses.

The optical lenses produced include various types of lenses, such as biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses.

Because the glass has a low specific gravity, each lens weighs less than lenses with the same optical characteristics and size, making it suitable for use in various imaging devices, especially autofocus imaging devices due to its energy saving potential. . Similarly, prisms were produced using the various optical glasses produced in Example 1.

The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

For example, by adjusting the composition of the glass compositions exemplified above within the ranges described in the specification, an optical glass according to one aspect of the present invention can be produced.
Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims (2)

In mass % display,
SiO ₂ content is 3-13%,
B ₂ O ₃ content is 13-23%,
The mass ratio of the content of SiO ₂ to the content of B ₂ O ₃ [SiO ₂ /B ₂ O ₃ ] is 0.30 to 0.70,
The content of La ₂ O ₃ is 50% or less,
Gd ₂ O ₃ content is 30% or less,
The content of Y ₂ O ₃ is 13% or less,
The total content of La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ [La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ ] is 53 to 75%,
ZrO ₂ content is 12% or less,
Nb ₂ O ₅ content is 7% or less,
The total content of ZrO ₂ and Nb ₂ O ₅ [ZrO ₂ +Nb ₂ O ₅ ] is 3.0 to 12.0%,
ZnO content is 7.8% or less,
TiO ₂ content is 7.8% or less,
WO ₃ content is 7.8% or less,
The total content of Nb ₂ O ₅ , ZnO, TiO ₂ and WO ₃ [Nb ₂ O ₅ +ZnO+TiO ₂ +WO ₃ ] is 7.8% or less,
Ta ₂ O ₅ content is 4.9% or less,
The total content of SiO ₂ , Al ₂ O ₃ , and B ₂ O ₃ [SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ ] is 24 to 32%,
refractive index nd is 1.77 to 1.95,
Abbe number νd is 42 to 48,
Specific gravity is 4.40 to 5.20,
optical glass. An optical element comprising the optical glass according to claim 1.