TW202413300A - Optical glass and optical components - Google Patents

Abstract

The present invention provides an optical glass having an nd of 1.77 to 1.95 and a νd of 42 to 48, wherein the Ta ₂ O ₅ content is reduced and the raw material cost is reduced, and an optical element including the same. The optical glass is expressed by mass%, SiO ₂ is 3~13%, B ₂ O ₃ is 13~23%, SiO ₂ /B ₂ O ₃ is 0.30~0.70, La ₂ O ₃ ≤50%, Gd ₂ O ₃ ≤30%, Y ₂ O ₃ ≤13%, La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ is 53~75%, ZrO ₂ ≤12%, Nb ₂ O ₅ ≤7%, ZrO ₂ +Nb ₂ O ₅ is 3.0~12.0%, ZnO, TiO ₂ , WO ₃ , Nb ₂ O ₅ +ZnO+TiO ₂ +WO ₃ are all ≤7.8%, Ta ₂ O ₅ ≤4.9%, SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ is 24~32%, and the specific gravity is 4.40~5.20.

Description

Optical glass and optical components

The present invention relates to optical glass and optical elements.

As optical element materials constituting imaging optical systems and projection optical systems such as projectors installed in cameras, vehicle-mounted optical equipment, and mobile devices, high refractive index/low dispersion optical glasses with 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 are used.

Among glass components, rare earth oxides can increase the refractive index without significantly increasing dispersion (without significantly reducing the Abbe number), and are therefore useful components for producing high refractive index/low dispersion optical glass. Among rare earth oxides, Ta ₂ O ₅ is particularly known as a component that can impart high refractive index/low dispersion characteristics to glass while suppressing coloring of the glass. However, Ta ₂ O ₅ is a component whose raw materials are significantly expensive among glass components. That is, the content of Ta ₂ O ₅ leads to a significant increase in the raw material cost of the glass, and therefore, in high refractive index/low dispersion optical glass containing Ta ₂ O ₅ , there is a problem that the price becomes high.

Patent documents 1 to 3 disclose optical glasses with reduced Ta ₂ O ₅ content. 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, in the optical glass of Patent document 1, the refractive index nd is small and the Abbe number νd is high. In addition, in the optical glass of Patent document 3, the refractive index nd 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 the Abbe number νd in the above range. In addition, in the optical glass of Patent document 2, the content of Ta ₂ O ₅ is reduced, but on the other hand, the content of Gd ₂ O _3, which is a rare earth oxide like Ta ₂ O _5, is increased. Gd ₂ O ₃ and Ta ₂ O ₅ are both very expensive components. That is, the optical glass of Patent Document 2 cannot sufficiently suppress the increase in the cost of glass raw materials. [Prior Art Document] [Patent Document]

Patent document 1: Japanese Patent Publication No. 2007-106611 Patent document 2: Japanese Patent Publication No. 2007-269584 Patent document 3: Chinese Patent Publication No. 110835227

[Problem to be solved by the invention]

The object of the present invention is to provide 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, wherein the content of Ta ₂ O ₅ is reduced and the raw material cost is reduced, and an optical element including the optical glass. [Solution to the Problem]

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

(2) An optical element comprising the optical glass described in (1) above. [Effect of the invention]

According to one embodiment of the present invention, 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, wherein the content of _Ta2O5 is reduced and the raw material cost is reduced _, can be provided. In addition, according to one embodiment of the present invention, an optical element including the optical glass can be provided.

In the present invention and this specification, unless otherwise specified, the glass composition of optical glass is expressed on an oxide basis. Here, "glass composition on an oxide basis" refers to a glass composition obtained by converting the glass raw materials into substances that are present in the form of oxides in the optical glass after they are completely decomposed during melting, and each glass component is usually expressed as SiO ₂ , TiO ₂ , etc. Unless otherwise specified, the content and total content of the glass component are on a mass basis, and "%" means "mass %".

The content of the glass component can be quantified by a known method, such as inductively coupled plasma emission spectroscopy (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), etc. In addition, in this specification and the present invention, the content of a constituent component of 0% means that the constituent component is not substantially contained, and the inclusion of the constituent component at an unavoidable impurity level is allowed.

Hereinafter, an implementation mode of the present invention will be described.

In the optical glass of the present embodiment, the content of _SiO2 is 3-13%. The lower limit of the content of _SiO2 is preferably 3.5%, and more preferably in the order of 4.0%, 4.5%, and 5.0%. In addition, the upper limit of the content of _SiO2 is preferably 12.5%, and more preferably in the order of 12.0%, 11.5%, and 11.0%.

_SiO2 is a network-forming component of glass, and is a component that has the effect of improving the thermal stability of glass and improving chemical durability. By setting the content of _SiO2 to the above range, the thermal stability of glass is improved, and devitrification during glass manufacturing can be suppressed. In addition, chemical durability can be improved. Moreover, molten glass with a viscosity suitable for molding can be prepared. On the other hand, when the content of _SiO2 is too high, there is a risk of a decrease in the refractive index nd, a decrease in solubility, and a risk of generating molten residues of the raw materials. In addition, there is a risk of excessive increase in the glass transition temperature Tg. In addition, when the content of _SiO2 is too low, there is a risk of a decrease in the thermal stability of glass, and there is a risk that the viscosity of the molten glass decreases and the desired viscosity cannot be obtained.

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

B ₂ O ₃ is a component that improves the thermal stability and solubility of glass. By setting the content of B ₂ O ₃ to the above range, the thermal stability of glass is improved, and devitrification during glass production can be suppressed. In addition, solubility can be improved, and the molten residue of glass raw materials can be reduced, so that homogeneous glass can be obtained. On the other hand, when the content of B ₂ O ₃ is too high, there is a risk of lowering the refractive index nd. In addition, when the content of B ₂ O ₃ is too low, there is a risk of lowering the thermal stability of glass, and there is also a risk of lowering the solubility and generating molten residue of the raw materials.

In the optical glass of the present embodiment, 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 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. In addition, 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 ] to the above range, the thermal stability of the glass can be improved, and a molten glass having a viscosity suitable for molding can be prepared.

In the optical glass of the present embodiment, the content of _La2O3 is 50% or less _. The upper limit _{of the content of La2O3 is} preferably 49%, and more preferably in the order of 48%, 47%, and 46%. In addition, the lower limit of the content of _La2O3 is preferably 0%, and more preferably in the order of 10%, 20%, 30%, 31%, 31.5%, 32.0%, _and 32.5%.

La ₂ O ₃ is a component that has the effect of increasing the refractive index nd without causing a significant decrease in the Abbe number νd. By setting the content of La ₂ O ₃ to the above range, an optical glass with desired optical constants can be obtained. In addition, the thermal stability of the glass is improved, and devitrification during glass manufacturing can be suppressed. In addition, the solubility can be improved and the melting residue of the glass raw material can be suppressed. On the other hand, when the content of La ₂ O ₃ is too high, there is a risk of an increase in specific gravity, and there is also a risk of a decrease in the thermal stability of the glass. In addition, there is also a risk of excessive increase in the glass transition temperature Tg. It should be noted that among the rare earth components, La ₂ O ₃ is a component that is less likely to cause an increase in the specific gravity of the glass than Gd ₂ O ₃ and Yb ₂ O _3. In addition, La ₂ O ₃ is also a component that can maintain the thermal stability of the glass even if the content is relatively high. Furthermore, La ₂ O ₃ , like Yb ₂ O ₃ , has no absorption in the near-infrared region and is therefore also a component capable of maintaining near-infrared transmittance.

In the optical glass _of the present embodiment, the content of _Gd2O3 is 30% or less _. The upper limit of the content of _Gd2O3 is preferably 29.0%, and more preferably in the order of 28.0%, 27.0%, and 26.0%. In addition, the lower limit of the content of _Gd2O3 is preferably 0%, and more preferably in the order of 1.0%, 2.0%, 3.0%, 8.0%, 10.0%, _and 12.0%.

Gd ₂ O ₃ is a component that has the effect of increasing the refractive index nd without causing a significant decrease in the Abbe number νd. By setting the content of Gd ₂ O ₃ to the above range, an optical glass with desired optical constants can be obtained. In addition, the thermal stability of the glass is improved, and devitrification during glass manufacturing can be suppressed. In addition, the meltability can be improved, and the melting residue of the glass raw material can be suppressed. Moreover, the coloring of the glass can be suppressed. On the other hand, Gd ₂ O ₃ is an expensive component, so when the content of Gd ₂ O ₃ is too high, there is a risk of increasing the cost of raw materials. In addition, when the content of Gd ₂ O ₃ is too high, there is a risk of increasing the specific gravity of the glass. In addition, Gd ₂ O ₃ has the effect of reducing the transmittance of the glass on the short wavelength side of the visible light region, so when the content of Gd ₂ O ₃ is too high, there is a risk of reducing the transmittance of the glass on the short wavelength side of the visible light region. Furthermore, when the content of Gd ₂ O ₃ is too high, there is a risk that the glass transition temperature Tg may rise.

In the optical glass of the present embodiment, the content of _Y2O3 is 13% or less _. The upper limit _{of the content of Y2O3 is} preferably 12.0%, and more preferably in the order of 11.0%, 10.0%, and 9.0%. In addition, the lower limit of the content of _Y2O3 is preferably 0%, and more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%, 3.0%, 4.0%, 5.0%, _and 6.0%.

_Y2O3 is a component that has the effect of increasing the refractive index _{nd without causing a significant decrease in the Abbe number νd. By setting the content of Y2O3 to 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 manufacturing can be suppressed. In addition, the meltability can be improved, and the melting residue of the glass raw materials can be suppressed. On the other hand, when the content of _Y2O3 is too high, there is _{a risk that the glass transition temperature Tg will rise. In addition, among the rare earth components, Y2O3 is a} component that can maintain the thermal stability of the glass even if its content is relatively high, but when its content is too high, there is a risk that the thermal stability of the glass will decrease.

In the optical glass of the present 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 53-75%. The lower limit of the total content is preferably 54.0%, and more preferably in the order of 55.0%, 56.0%, and 56.5%. In addition, the upper limit of the total content is preferably 74.0%, and more preferably in the order of 73.0%, 72.0%, and 71.0%. By setting the total content to the above range, the refractive index nd can be increased without causing a significant decrease in the Abbe number νd, thereby obtaining an optical glass having desired optical constants. In addition, the thermal stability of the glass is improved, and devitrification during glass manufacturing can be suppressed.

In the optical glass of the present embodiment, the content of _ZrO2 is 12% or less. The upper limit of the content of _ZrO2 is preferably 11.5%, and more preferably in the order of 11.0%, 10.5%, and 10.0%. In addition, the lower limit of the content of _ZrO2 is preferably 0%, and more preferably in the order of 0.5%, 1.0%, and 1.5%.

ZrO ₂ 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 ZrO ₂ to the above range, an optical glass having the desired optical constants and improved thermal stability can be obtained. On the other hand, when the content of ZrO ₂ is too high, there is a risk of reducing thermal stability, increasing specific gravity, and increasing the glass transition temperature Tg.

In the optical glass of the present embodiment, the content of _Nb2O5 is 7 _{% or less. The upper limit of the content of Nb2O5 is preferably} 6.5%, and more preferably in the order of 6.0%, 5.5%, and 5.0%. In addition, the lower limit of the content of _Nb2O5 is preferably 0%, and more preferably in the order of 0.5%, _1.0 %, and _{1.5%. The content of Nb2O5 may} also be 0%.

_Nb2O5 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 _Nb2O5 to the above range, an optical glass having the desired optical constants and improved thermal stability can be obtained. On the other hand, when the content _{of Nb2O5} is _too high, there is a risk of lowering the thermal stability, increasing the specific gravity, and raising the glass transition temperature Tg.

In the optical glass of the present embodiment, the total content of ZrO ₂ and Nb ₂ O ₅ [ZrO ₂ +Nb ₂ O ₅ ] is 3.0~12.0%. The lower limit of the total content is preferably 3.1%, and more preferably in the order of 3.3%, 3.5%, and 3.6%. In addition, 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 to the above range, an optical glass having the desired optical constants and improved thermal stability can be obtained. On the other hand, when the total content is too much, there is a risk that the Abbe number νd is reduced and an optical glass having the desired optical constants cannot be obtained.

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

ZnO is a component that has the functions of improving melting properties, suppressing excessive rise of the glass transition temperature Tg, and adjusting optical properties. In addition, it is also a component that can adjust the Abbe number νd. By setting the ZnO content to the above range, an optical glass having desired optical constants and optical properties, improved melting properties and thermal stability can be obtained. On the other hand, when the ZnO content is too high, there is a risk that the thermal stability of the glass will be reduced.

In the optical glass of the present embodiment, the content of _TiO2 is 7.8% or less. The upper limit of the content of _TiO2 is preferably 7.5%, and further preferably in the order of 7.0%, 6.5%, 6.0%, 5.0%, and 4.0%. In addition, the lower limit of the content of _TiO2 may also be 0%, and the content of _TiO2 is preferably 0%.

_TiO2 is a component that has the function of increasing the refractive index nd and maintaining the thermal stability of the glass. By setting the content of _TiO2 to the above range, an optical glass having the desired optical constants can be obtained. On the other hand, when the content of _TiO2 is too high, there is a risk that the thermal stability of the glass will be reduced, and there is also a risk that the coloring of the glass will increase.

In the optical glass of the present 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 in the order of 7.0%, 6.5%, and 6.0%. In addition, the lower limit of the content of WO ₃ may also be 0%, and the content of WO ₃ 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. In addition, it is also a component that has the function of inhibiting crystallization during glass manufacturing. By setting the content of WO ₃ to the above range, an optical glass with desired optical constants can be obtained. On the other hand, when the content of WO ₃ is too high, there is a risk of reduced thermal stability and increased specific gravity. In addition, when the content of WO ₃ is too high, the spectral transmittance at the light absorption end on the short-wave side becomes longer wavelength, so there is a risk of reduced transmittance of ultraviolet rays.

In the optical glass of the present 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 in the order of 7.0%, 6.5%, and 6.0%. In addition, the lower limit of the total content is preferably 0%, and more preferably in the order of 0.5%, 1.0%, and 1.5%. The total content may also be 0%. By setting the total content to 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 of the present embodiment, the content of Ta ₂ O ₅ is less than 4.9%. The upper limit of the content of Ta ₂ O ₅ is preferably 4.0%, and further preferably in the order of 3.5%, 3.0%, 2.5%, 2.2%, 2.1%, 2.0%, 1.70%, 1.65%, 1.60%, 1.55%, and 1.50%. The upper limit of the content of Ta ₂ O ₅ can be set to 1.45%, 1.40%, 1.35%... at intervals of 0.05% after 1.50%. That is, for example, the upper limit of the content of Ta ₂ O ₅ can be set to 1.25%, 1.00%, 0.75%, or 0.50%. In addition, the lower limit of the content of Ta ₂ O ₅ is preferably 0%. The content of Ta ₂ O ₅ can also 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, Ta ₂ O ₅ is a significantly expensive component, so when the content of Ta ₂ O ₅ is too high, there is a risk that the raw material cost will increase excessively. Therefore, by setting the content of Ta ₂ O ₅ to the above range, an optical glass with reduced raw material cost can be obtained. In addition, when the content of Ta ₂ O ₅ is too high, there is a risk that the thermal stability of the glass will decrease, the specific gravity will increase, the coloring of the glass will increase, and the glass transition temperature Tg will increase. In this embodiment, by limiting the content of glass components other than Ta ₂ O ₅ , the desired optical constants can be achieved even if the content of Ta ₂ O ₅ is reduced. In addition, by setting the content of Ta ₂ O ₅ to the above range, it can help reduce the cost of raw materials.

In the optical glass of the present 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 24-32%. The lower limit of the total content is preferably 24.5%, and more preferably in the order of 25.0%, 25.5%, and 25.7%. In addition, 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 glass. By setting the total content to the above range, the thermal stability of the glass can be improved.

<Refractive index nd> In the optical glass of the present embodiment, the refractive index nd is 1.77 to 1.95 from the perspective of usefulness as an optical element material constituting an optical system such as an imaging optical system and a projection optical system, and more specifically, from the perspective of chromatic aberration correction and high functionality of the optical system. 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. In addition, 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 of the present 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 under d-rays (helium wavelength 587.56nm).

<Abbe number νd> From the same point of view, in the optical glass of this embodiment, the Abbe number νd 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. In addition, the upper limit of the Abbe number νd is preferably 47.9, and more preferably in the order of 47.8 and 47.7.

In the optical glass of the present embodiment, the content, ratio and total content of the above-mentioned glass components can be adjusted while considering the effects of each glass component to control the Abbe number νd. Unless otherwise specified, the Abbe number νd is defined as follows when the refractive index under F rays (hydrogen wavelength 486.13nm) and C rays (hydrogen wavelength 656.27nm) are set to nF and nC respectively. νd＝(nd－1)／(nF－nC)

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

For example, imagine that the optical glass of this embodiment is used in a lens with an autofocus function. If the specific gravity is too large, there is a risk that the mass of the lens increases, the power consumption during focusing increases, and the battery is consumed earlier. On the other hand, if the specific gravity is too small, there is a risk that the thermal stability of the glass decreases. Therefore, by setting the specific gravity to the above range, a lightweight optical glass with maintained thermal stability can be obtained.

In the optical glass of the present embodiment, the specific gravity can be reduced by adjusting the content, ratio, and total content of the above-mentioned glass components while taking the effects of the respective glass components into consideration.

Regarding the contents, ratios, and glass properties of the glass components other than those described above in the optical glass of the present embodiment, non-limiting examples are shown below.

In the optical glass of 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 14.5%, more preferably 14.0%, 13.5%, 13.0% in this order. In addition, the lower limit of the total content is preferably 3.0%, more preferably 4.0%, 5.0%, 6.0% in this order. From the viewpoint of increasing the refractive index nd and obtaining an optical glass having desired optical constants, it is preferred that the total content be within the above range.

In the optical glass of the present embodiment, the upper limit of 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, more preferably in the order of 0.35, 0.30, and 0.25. In addition, the lower limit of the mass ratio is preferably 0, 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 and reduced raw material costs, it is preferred that the mass ratio be within the above range.

In the optical glass of the present embodiment, the mass ratio of the total content of ZrO ₂ , Ta ₂ O ₅ and Nb ₂ O ₅ to the total content of SiO ₂ and B ₂ O ₃ [(ZrO ₂ +Ta ₂ O ₅ +Nb ₂ O ₅ )/(SiO ₂ +B ₂ O ₃ )] has an upper limit of 0.465, preferably 0.450, more preferably in the order of 0.430, 0.410, and 0.390. The lower limit of the mass ratio is 0.145, preferably 0.150, more preferably in the order of 0.200, 0.250, and 0.300. From the viewpoint of obtaining an optical glass having desired optical constants and improved thermal stability, the mass ratio is preferably set to the above range.

In the optical glass of the present embodiment, the upper limit of the mass ratio of the total content of _{ZnO and Y2O3 to} the content of _La2O3 [(ZnO+ _Y2O3 )/ _La2O3 ] is preferably 1.0, more preferably in the order of 0.8, 0.6 _{, and 0.4} . In addition, the lower limit of the mass ratio is preferably 0, more preferably in the order of 0.05, 0.10, and 0.15. From the viewpoint of obtaining an optical glass having desired optical constants and improved thermal stability, it is preferred that the mass ratio be within the above range.

In the optical glass of the present embodiment, the mass ratio of the total content of BaO, _La2O3 , _Nb2O5 , _{TiO2 and ZrO2} to the total content of _SiO2 , _Al2O3 and _B2O3 [(BaO+ _La2O3 + _Nb2O5 + _TiO2 + _ZrO2 )/( _SiO2 + _Al2O3 + _B2O3 )] is 2.80, preferably 2.62, more preferably _in the order of 2.50 _{, 2.30 and 2.00 .} The lower limit of the mass ratio is _preferably 0.35, more preferably in the order of 0.40, 0.50, 1.00 and 1.50. From the viewpoint of obtaining an optical glass having desired optical constants and improved thermal stability, it is preferable to set the mass ratio to the above range.

In the optical glass of the present embodiment, the upper limit _of the mass ratio of the content of _Gd2O3 to _the total content of _{La2O3 , Gd2O3 ,} and _Y2O3 [ _Gd2O3 /( _La2O3 + _Gd2O3 + _Y2O3 )] is preferably 0.40, more preferably in the order of 0.38 _, 0.36 _{, and 0.32} . The lower limit of the mass ratio is preferably 0.20, more preferably in the order of 0.23, 0.26, and 0.29. From the viewpoint of obtaining an optical glass having improved thermal stability, it is preferred that the mass ratio be within the above range.

In the optical glass of the present embodiment, the upper limit of the mass ratio of _{the content of Y2O3 to} the total content of _{La2O3 , Gd2O3 ,} and _Y2O3 [ _Y2O3 /( _La2O3 + _Gd2O3 + _Y2O3 )] is preferably 0.23, more preferably in the order of 0.21 _, 0.19 _{, and 0.17} . The lower limit of the mass ratio is preferably 0.07, more preferably in the order of 0.09, 0.11, _and 0.13. From the viewpoint of obtaining an optical glass having improved thermal stability, the mass ratio is preferably set to the above range.

In the optical glass of the present embodiment, the upper limit of 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 [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 in the order of 0.20, 0.40, and 0.60. From the viewpoint of obtaining an optical glass having desired optical constants and reduced raw material costs, it is preferred that the mass ratio be set to the above range.

In the optical glass of the present embodiment, the upper limit of the mass ratio of the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Ta ₂ O ₅ to the total content of La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ [(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 in the order of 0.10, 0.08 and 0.06. The lower limit of the mass ratio is preferably 0, 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, the mass ratio is preferably set to the above range.

In the optical glass of the present embodiment, the upper limit of the content of _P2O5 is preferably 10.0%, _and more preferably in the order of 8.0%, 6.0%, 4.0%, _and 3.0%. In addition, the lower limit of the content of _P2O5 is preferably 0%. The content of _P2O5 may also be 0%. _P2O5 is a component that causes a decrease in the refractive index nd, and is also a component that causes a decrease in the thermal stability of the glass. Therefore, it is preferred _{that the content of P2O5 be set within} the above range.

In the optical glass of the present embodiment, the upper limit of the content of Al ₂ O ₃ is preferably 10.0%, and more preferably in the order of 8.0%, 6.0%, 4.0%, and 2.0%. The lower limit of the content of Al ₂ O ₃ is preferably 0%. The content of Al _{2 O 3 may also be 0%. If Al 2 O 3 is in} a small amount, it has the effect of improving the thermal stability and chemical durability of the glass, but when the content of Al ₂ O ₃ is too high, there is a tendency to cause the liquidus temperature LT to rise and the thermal stability to deteriorate. Therefore, it is preferred to set the content of Al ₂ O ₃ to the above range.

In the optical glass of the present embodiment, the upper limit of the content of Li ₂ O is preferably 10.0%, more preferably 8.0%, 6.0%, 4.0%, and 1.0%, in this order. The lower limit of the content of Li ₂ O is preferably 0%. The content of Li ₂ O may be 0%.

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

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

Li ₂ O, Na ₂ O and K ₂ O all have the effect of lowering the liquidus temperature LT and improving the thermal stability of glass, but when their contents are increased, there is a possibility of reducing chemical durability and weather resistance. Therefore, the contents of Li ₂ O, Na ₂ O and K ₂ O are preferably within the above ranges.

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

Cs ₂ O is a component that improves the thermal stability of glass. On the other hand, if the content of Cs ₂ O increases, there is a possibility that chemical durability and weather resistance may be reduced. Therefore, the content of Cs ₂ O is preferably within the above range.

In the glass of 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%, more preferably 8.0%, 6.0%, 4.0%, and 2.0% in this order. In addition, the lower limit of the total content is preferably 0%. The total content may also be 0%. From the viewpoint of suppressing the reduction of the chemical durability and weather resistance of the glass, it is preferred that the total content be within the above range.

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

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

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

In the glass of the present embodiment, the upper limit of the BaO content is preferably 10.0%, and more preferably 8.0%, 6.0%, and 4.0%, in that order. In addition, the lower limit of the BaO content is preferably 0%. The BaO content may also be 0%.

MgO, CaO, SrO, and BaO are components that improve the thermal stability and devitrification resistance of glass. On the other hand, if their contents are too high, there is a risk that the specific gravity increases, the high dispersion property is impaired, and the thermal stability and devitrification resistance of the glass decrease. Therefore, the contents of each of these glass components are preferably within the above ranges.

In the optical glass of the present embodiment, the upper limit of the content of _Bi2O3 is preferably 10.0%, _and more preferably 8.0%, 6.0%, 4.0%, _and 1.0%, in this order. In addition, the lower limit of the content of _Bi2O3 is preferably 0%. The content _{of Bi2O3 may} also be 0%.

Bi ₂ O ₃ is a component that increases the refractive index nd and improves the thermal stability of glass. On the other hand, if the content of Bi ₂ O ₃ is too high, there is a risk that the spectral transmittance may be shortened at the absorption end on the short-wave side. Therefore, it is preferred that the content of Bi ₂ O ₃ be within the above range.

In the optical glass of the present embodiment _, the upper limit of the content of _Yb2O3 is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, _and 3.0%, in this order. In addition, the lower limit of the content of _Yb2O3 is preferably 0%. The content _{of Yb2O3 may} also be 0%.

_Yb2O3 is a component that increases 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 manufacturing. It is also a component that improves meltability and suppresses the melting residue of glass raw materials. It is also a component that does not have absorption in the near-infrared region. On the other hand, if the content of _Yb2O3 is too high, there is a risk that the specific gravity of the glass increases and _the glass _transition temperature Tg rises. Therefore, it is preferable to set the content of _Yb2O3 to the above range.

In the optical glass of the present embodiment, the content of Sc ₂ O ₃ is preferably 2% or less. In addition, the lower limit of the content of Sc ₂ O ₃ is preferably 0%. The content of Sc ₂ O ₃ may also be 0%.

In the optical glass of the present embodiment, the content of HfO ₂ is preferably 2% or less. In addition, the lower limit of the content of HfO ₂ is preferably 0%. The content of HfO ₂ may also be 0%.

Sc ₂ O ₃ and HfO ₂ have the effect of improving the high dispersion of glass, but are also expensive components. Therefore, it is preferred that the contents of Sc ₂ O ₃ and HfO ₂ be within the above ranges.

In the optical glass of the present embodiment, the content of Lu ₂ O ₃ is preferably 2% or less. In addition, the lower limit of the content of Lu ₂ O ₃ is preferably 0%. The content of Lu ₂ O ₃ may also be 0%.

Lu ₂ O ₃ has the effect of improving the high dispersion of glass, but it is also a glass component that increases the specific gravity of glass due to its large molecular weight. Therefore, it is preferred that the content of Lu ₂ O ₃ be within the above range.

In the optical glass of the present embodiment, the content of GeO ₂ is preferably 2% or less. In addition, the lower limit of the content of GeO ₂ is preferably 0%. The content of GeO ₂ may also be 0%.

GeO ₂ has the effect of improving the high dispersion of glass, but it is a relatively expensive component in the glass components generally used. Therefore, from the perspective of reducing the cost of raw materials for glass, it is preferred to set the content of GeO ₂ to the above range.

The optical glass of the present embodiment is preferably mainly composed of the above-mentioned glass components, _that is _{, SiO2} and _B2O3 as essential components, and _La2O3 , _Gd2O3 , _Y2O3 , _ZrO2 , _Nb2O5 , _ZnO , _TiO2 , _WO3 , _{Ta2O5 , P2O5 ,} Al2O3 _{, Li2O} , _Na2O , _K2O , _{Cs2O ,} MgO, CaO, _SrO , BaO, _{Bi2O3 , Yb2O3} , _Sc2O3 , _HfO2 , _Lu2O3 and _GeO2 as optional components, _and the total content of the above _- mentioned glass components is preferably 95% or more, more preferably ₉₈ % _or more, further preferably 99% or more, and further preferably 99.5% or more.

The optical glass of the present embodiment is preferably basically composed of the above-mentioned glass components, but may also contain other components within the scope of not hindering the effects of the present invention. In addition, in the present invention, it is not excluded to contain inevitable impurities.

(Other components) In addition to the above components, the optical glass of the present embodiment may contain a small amount of _{Sb2O3 , SnO2} , etc. as a fining agent. In this specification, the content of the fining agent is expressed as an additional ratio and is not included in the total content of all glass components expressed on an oxide basis.

In the optical glass of the present embodiment, when the total content of all glass components except the clarifier is set to 100 mass%, the content of Sb ₂ O ₃ is preferably 1 mass% or less, and more preferably 0.5 mass% or less, or 0.1 mass% or less. The content of Sb ₂ O ₃ may also be 0 mass%. In addition to its role as a clarifier, Sb ₂ O ₃ also has the effect of suppressing the reduction of light transmittance caused by the mixing of impurities such as Fe. However, when the amount of Sb ₂ O ₃ added increases, there is a risk that the coloring of the glass will increase due to the light absorption of Sb itself. Therefore, it is preferred that the content of Sb ₂ O ₃ be set within the above range.

In the optical glass of the present embodiment, when the total content of all glass components except the clarifier is set to 100 mass%, the content of _SnO2 is preferably 1 mass% or less, and more preferably 0.5 mass% or less, or 0.1 mass% or less. The content of _SnO2 may also be 0 mass%. _SnO2 has a function as a clarifier, but when the amount of _SnO2 added increases, there is a risk of increasing the coloring of the glass. In addition, when the glass is heated, softened, and re-molded by press molding, there is a risk that Sn becomes a starting point for the generation of crystal nuclei and causes the glass to lose clarity.

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

U, Th, and Ra are all radioactive elements. Therefore, the optical glass of the preferred 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, and Ce increase the coloring of the glass and become a source of fluorescence. Therefore, the optical glass of the preferred embodiment does not contain these elements as glass components.

(Glass properties) <Coloring indices λ5, λ70 and λ80> Regarding the suppression of coloring of glass and the light transmittance of glass, specifically, whether the long-wavelength shift of the light absorption end on the short-wavelength side is suppressed can be evaluated based on one or more of the coloring indices λ5, λ70 and λ80. The coloring indices λ5 refer to the wavelength at which the spectral transmittance (including surface reflection loss) of glass with a thickness of 10±0.1mm from the ultraviolet region to the visible region reaches 5%. λ70 indicates the wavelength at which the spectral transmittance measured by the method described for λ5 reaches 70%. λ80 indicates the wavelength at which the spectral transmittance measured by the method described for λ5 reaches 80%. The λ5, λ70 and λ80 shown in the embodiments described below are values measured in the wavelength range of 250~700nm. It should be noted that the spectral transmittance T(%) of the glass in the present invention and this specification can be expressed as follows: for a glass sample having two parallel planes after optical polishing, the intensity of light perpendicularly incident on one of such planes is set to I _in , and the intensity of light emitted from the other surface after passing through the glass sample is set to I _out , and it is expressed as T(%) = I _out /I _in × 100.

The absorption end of the spectral transmittance on the short wavelength side can be quantitatively evaluated based on the chromaticity λ5, λ70, and λ80. For example, when lenses are bonded together using a UV-curing adhesive to produce a bonded lens, the adhesive is cured by irradiating UV light through an optical element. From the perspective of efficiently curing the UV-curing adhesive, the absorption end of the spectral transmittance on the short wavelength side is preferably in a short wavelength range. As an indicator for quantitatively evaluating the absorption end on the short wavelength side, one or more of the chromaticity λ5, λ70, and λ80 can be used.

In the optical glass of the present embodiment, λ5 is preferably 350 nm or less, more preferably 340 nm or less, and further preferably 330 nm or less. In addition, λ70 is preferably 390 nm or less, more preferably 380 nm or less, and further preferably 370 nm or less. In addition, λ80 is preferably 480 nm or less, more preferably 450 nm or less, and further preferably 420 nm or less.

In the optical glass of the present embodiment, λ5, λ70, and λ80 can be reduced by adjusting the content, ratio, and total content of the above-mentioned glass components while taking the effects of the respective glass components into consideration.

<Glass transition temperature Tg> From the perspective of reducing the burden on the annealing furnace and the molding die, the glass transition temperature Tg of the optical glass of the present embodiment is preferably 735°C or less, more preferably 725°C or less, and further preferably 715°C or less. On the other hand, from the perspective of machinability (specifically, from the perspective of not being easily broken during mechanical processing of the glass such as cutting, cutting, grinding, and polishing), the glass transition temperature Tg of the optical glass is preferably 670°C or more, more preferably 680°C or more, and further preferably 690°C or more. The glass transition temperature Tg can be obtained 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 considering the effects of each glass component.

(Manufacturing of optical glass) For the optical glass of this embodiment, glass raw materials are prepared in a manner to achieve the above-mentioned given composition, and the prepared glass raw materials are used to manufacture it according to a known glass manufacturing method. For example, a plurality of compounds are prepared and fully mixed to make a batch of raw materials, and the batch of raw materials is placed in a quartz crucible or a platinum crucible for rough melting. The molten material obtained by the rough melting is quenched and crushed to produce cullet. The cullet is further placed in a platinum crucible for heating and remelting to produce molten glass. After the molten glass is clarified and homogenized, it is formed and slowly cooled to obtain optical glass. The forming and slow cooling of the molten glass can be carried out by known methods,

It should be noted that there is no particular limitation on the compounds used in preparing the batch raw materials as long as the desired glass components can be introduced into the glass in a manner that achieves the desired content. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, and the like.

(Manufacturing of optical elements, etc.) When optical glass of the present embodiment is used to manufacture optical elements, known methods may be used. For example, in the manufacture of the above optical glass, molten glass is poured into a casting mold and formed into a plate to manufacture a glass material formed of the optical glass of the present invention. The obtained glass material is appropriately cut, ground, and polished to manufacture fragments of a size and shape suitable for press molding. The fragments are heated and softened, and press molded (re-hot pressing) is performed by a known method to manufacture an optical element blank of a shape similar to that of an optical element. The optical element blank is annealed, and is ground and polished by a known method to manufacture an optical element.

Depending on the purpose of use, the optical functional surface of the manufactured optical element may be coated with an anti-reflection film, a total reflection film, etc.

According to one embodiment of the present invention, an optical element formed of the above optical glass can be provided. As the type of optical element, lenses such as spherical lenses and aspherical lenses, prisms, diffraction gratings, etc. can be exemplified. As the shape of the lens, various shapes such as biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses can be exemplified. The optical element can be manufactured by a method including a procedure of processing a glass molded body formed of the above optical glass. As processing, cutting, machining, rough grinding, fine grinding, polishing, etc. can be exemplified. When performing such processing, by using the above glass, breakage can be reduced, and high-quality optical elements can be stably supplied.

Embodiments The present invention is described in more detail below in conjunction with embodiments. However, the present invention is not limited to the solutions shown in the embodiments.

Oxides, hydroxides, carbonates and nitrates corresponding to the constituent components of the glass are prepared as raw materials, and the above raw materials are weighed and blended in such a manner that the glass composition of the obtained optical glass reaches the respective compositions shown in Table 1 (1) to (7), and the raw materials are fully mixed. The blended raw materials (batch raw materials) thus obtained are placed in a platinum crucible, heated and melted in a furnace set at 1400°C for 2 hours, and molten glass is obtained. The molten glass is stirred and homogenized, and cast into a preheated casting mold. The cast glass is naturally cooled to near the glass transition temperature and immediately placed in an annealing furnace. After being kept at a temperature around the glass transition temperature for about 30 minutes, it is slowly cooled at a slow cooling rate of -30°C/hour for 4 hours, and then naturally cooled in the furnace to room temperature. Optical glass samples having the compositions shown in Table 1(1) to (7) were obtained.

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

[Physical property evaluation] The refractive index nd, Abbe number νd, glass transition temperature Tg, specific gravity and coloration λ5, λ70, λ80 of the obtained optical glass samples were measured. The results are shown in Table 2 (1) to (7).

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

(2) Glass transition temperature Tg The obtained optical glass sample was fully ground in a mortar or the like and used as a sample. 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 The specific gravity was measured by the Archimedean method.

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

(Example 2) Using the optical glasses prepared in Example 1, lens blanks were prepared by a known method, and the lens blanks were processed by a known method such as polishing to prepare various lenses.

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

Glass has a low specific gravity, so each lens weighs less than a lens of the same optical characteristics and size, and can be used in various imaging devices, especially in autofocus imaging devices for energy saving reasons. Similarly, prisms were made using various optical glasses made in Example 1.

It should be understood that the embodiments disclosed herein are exemplary in all respects and are not intended to be limiting. The scope of the invention is defined by the claims, not the above description, and is intended to include all variations within the meaning and scope equivalent to the claims.

For example, for the glass composition exemplified above, by adjusting the composition within the range described in the specification, an optical glass of one embodiment of the present invention can be produced. In addition, of course, any combination of two or more items exemplified in the specification or described as a preferred range can be used.

without

without

Claims (2)

An optical glass, wherein, expressed in mass%, the content of SiO ₂ is 3-13%, the content of B ₂ O ₃ 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 0.30-0.70, the content of La ₂ O ₃ is 50% or less, the content of Gd ₂ O ₃ 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 53-75%, the content of ZrO ₂ is 12% or less, the content of Nb ₂ O ₅ is 7% or less, the total content of ZrO ₂ and Nb ₂ O ₅ [ZrO ₂ +Nb ₂ O ₅ ] is 3.0~12.0%, the content of ZnO is less than 7.8%, the content of TiO ₂ is less than 7.8%, the content of WO ₃ is less than 7.8%, the total content of Nb ₂ O ₅ , ZnO, TiO ₂ and WO ₃ [Nb ₂ O ₅ +ZnO+TiO ₂ +WO ₃ ] is less than 7.8%, the content of Ta ₂ O ₅ is less than 4.9%, 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 24~32%, the refractive index nd of the optical glass is 1.77~1.95, the Abbe number νd is 42~48, and the specific gravity is 4.40~5.20. An optical element comprising the optical glass as described in claim 1.