TWI891725B - Optical glass and optical components - Google Patents

Abstract

The subject of the present invention is to provide optical glass and optical components with high internal transmittance and high refractive index at a wavelength of 460nm. The solution provided by the present invention is an optical glass, wherein the mass ratio of the total content _of BaO, _La2O3 , _Gd2O3 and _WO3 to _the total content of CaO, SrO and _Y2O3 [( _BaO + _{La2O3 +Gd2O3 + WO3} )/ ₍ CaO+SrO+ _Y2O3 )] is 2.0 or _less , the mass ratio of the total content of _B2O3 and _P2O5 to the total content of _SiO2 and _Al2O3 [( _B2O3 + _{P2O5 )} / _{( SiO2 + Al2O3} )] is 0.10 or less, the total content of _Li2O , _{Na2O and K2O} [ _Li2O + _Na2O + _K2O ] is 10% by mass or _less , _and the content of _Al2O3 and SiO2 _are 10% by mass or less. The mass ratio of the total content of Al 2 O ₃ and ZrO ₂ [Al ₂ O ₃ /(SiO ₂ +ZrO ₂ )] is greater than 0.

Description

Optical glass and optical components

The present invention relates to optical glass and optical components.

In recent years, with the advancement of AR (augmented reality) technology, goggle-type and spectacles-type displays have been developed as AR devices. For example, goggle-type displays use flat lenses, and there is a growing demand for lenses with high refractive index, high transmittance, and low specific gravity, and for glass suitable for such lenses. Transmittance refers to the internal transmittance of light when it passes through the glass, as distinguished from external transmittance, which includes reflection loss.

The refractive index of general glass increases as the interaction between light passing through it and the electron cloud within it increases. Therefore, to increase the refractive index, the glass composition is selected to pack more electrons into the glass. Specifically, glass compositions with large atomic numbers but small ionic radii and high electron content are selected to increase the electron density per unit volume of the glass (mostly oxygen number density). Borate-lumbernium glass is an example of this. However, borate-lumbernium glass has a high specific gravity, which poses a problem when used in goggle-type AR displays due to the increased lens weight.

_Examples of glass components that increase the refractive index while maintaining a low specific gravity include _Nb₂O₅ and _TiO₂ , which absorb in the near-ultraviolet region. However, increasing the content of such glass components raises the problem of expanding the absorption range beyond the near-ultraviolet region to include the visible short-wavelength region (blue region). Furthermore, increasing the _content of _Nb₂O₅ or _TiO₂ reduces the proportion of other ions that can donate oxygen to Nb or Ti ions, causing some of the Nb or Ti ions to be reduced and discolored, thus reducing the glass's internal transmittance for visible light.

Furthermore, one of the main reasons for the decrease in glass transmittance is the incorporation of platinum (Pt) from the glass melting furnace. For example, to increase the refractive index of glass, by increasing the content _{of Nb2O5} or _TiO2 , the melting temperature of the glass rises, and the glass raw materials need to be heated to high temperatures. At this time, the high-temperature molten glass comes into contact with platinum (Pt), and the Pt ions dissolve into the molten glass, forming a solid solution in the glass. Pt absorbs light in the ultraviolet region, but as the amount of Pt in the glass increases, the absorption range of light expands beyond the ultraviolet region to include the visible light region. This results in a decrease in the internal transmittance of the glass in the visible light region.

On the other hand, melting glass in a melting furnace using refractory bricks can suppress the incorporation of platinum (Pt) from the melting furnace. An example of glass that can be melted in a melting furnace using refractory bricks is _SiO2 - _TiO2 -based glass. This type of glass is known to increase the refractive index nd to approximately 1.85, reduce the specific gravity to approximately 3.5, and exhibit relatively good transmittance (Patent Document 1).

The term "refractory brick" here refers to bricks primarily composed of _ZrO2 , _Al2O3 , _and /or _SiO2 (e.g., Patent 2). The ratio of these components can range from 4: ₅ : ₁ to ₃ :6: ₁ , as shown in https://www.an.shimadzu.co.jp/apl/material/chem0502005.htm _. There are also refractory bricks that contain virtually no _Al2O3 or _SiO2 . However, as described in Patent 2, to enhance thermal shock resistance or corrosion resistance, a certain amount _{of Al2O3} is often incorporated.

However, to be suitable for use in AR display device lenses, the refractive index needs to be further increased. For example, Patent Document 3 discloses SiO2 _- TiO2 _-based glass with a refractive index nd in the range of 1.86-1.99 and an Abbe number νd in the range of 21-29. However, the high melting temperature of this glass will corrode the glassy portion of the refractory bricks in the melting furnace, resulting in the problem that the components of the refractory bricks are easily mixed into the glass. In glass, if components derived from refractory bricks are dissolved, especially if a large amount of _ZrO2 or _SiO2 is dissolved in the glass, the glass composition will change, making it difficult to maintain the stability of the glass or maintain a high refractive index. In addition, the crystallized components of the main components of the _refractory bricks, such as _Al2O3 or _ZrO2, mixed into the glass as foreign matter will damage the homogeneity of the glass. Therefore, such glass needs to be melted in a platinum container. However, when the glass is melted in a platinum container, Pt is introduced into the glass as described above, which has the problem of reducing the internal transmittance.

_SiO2- based glass containing _Nb2O5 or _TiO2 , melted in a refractory furnace, can maintain a high _refractive index and improve transmittance. This glass is useful for lenses in AR displays.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent No. 2535407

[Patent Document 2] Japanese Patent Publication No. 2018-537387

[Patent Document 3] Japanese Patent Application Laid-Open No. 2012-229135

This invention was developed in light of this reality, with the goal of providing optical glass and optical components with high internal transmittance and high refractive index at a wavelength of 460nm.

The main points of the present invention are as follows.

(1) An optical glass, wherein the mass ratio of the total content of BaO, _{La2O3 , Gd2O3 , and WO3} to _the total content _of CaO, SrO, and _Y2O3 [(BaO+ _{La2O3 + Gd2O3} + _WO3 )/(CaO+SrO+ _Y2O3 )] is 2.0 or less, the mass ratio of the total content of _{B2O3 and P2O5 to} the total content _{of SiO2} and _Al2O3 [ _{( B2O3} + _P2O5 )/ _{( SiO2} + _Al2O3 )] is 0.10 or less, the total content of _Li2O , _Na2O , and _K2O [ _Li2O + _Na2O + _K2O ] _is 10 mass% or less, and _the content of _Al2O3 and the total content _{of SiO2} and ZrO3 are 10 mass% or less. The mass ratio of the _total content of [Al ₂ O ₃ /(SiO ₂ +ZrO ₂ )] is greater than 0.

(2) An optical glass having a total content _{of TiO2 and Nb2O5 [ TiO2 + Nb2O5} ] of ₂₀ mass% or more and a mass ratio of the _total content of _Al2O3 to the total content of _{SiO2 and ZrO2} [ _Al2O3 /( _SiO2 + _ZrO2 )] greater than zero.

(3) The optical glass according to (2), wherein the mass ratio _of the total content _{of B2O3} and _P2O5 to the total content _{of SiO2} and _Al2O3 [ _{( B2O3} + _P2O5 ) / _{( SiO2} + _Al2O3 )] is _0.15 or less.

(4) The optical glass according to (2) or (3), wherein the mass ratio of the total content of TiO ₂ , Nb ₂ O ₅ and ZrO ₂ to the total content of B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ and GeO ₂ [(TiO ₂ + Nb ₂ O ₅ + ZrO ₂ )/(B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ + GeO ₂ )] is 1.8 or more, and the mass ratio of the total content of BaO, La ₂ O ₃ , Gd ₂ O ₃ and WO ₃ to the total content of CaO, SrO and Y ₂ O ₃ [(BaO + La ₂ O ₃ + Gd ₂ O ₃ + WO ₃ )/(CaO + SrO + Y ₂ O ₃ )] is 3.0 or less.

(5) The optical glass according to any one of (2) to (4), wherein the mass ratio of the total content of TiO ₂ , Nb ₂ O ₅ and ZrO ₂ to the total content of B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ and GeO ₂ [(TiO ₂ +Nb ₂ O ₅ +ZrO ₂ )/(B ₂ O ₃ +SiO ₂ +Al ₂ O ₃ +GeO ₂ )] is 1.8 or more, and the mass ratio of the total content of B ₂ O ₃ , ZnO, La ₂ O ₃ , Gd ₂ O ₃ and WO ₃ to the total content of SiO ₂ , CaO, TiO ₂ and Nb ₂ O ₅ [(B ₂ O ₃ +ZnO +La ₂ O ₃ +Gd ₂ O ₃ +WO ₃ )/(SiO ₂ +CaO +TiO ₂ +Nb ₂ O ₅ )] is 0.15 or less.

(6) An optical element composed of any one of the optical glasses listed in (1) to (5).

According to the present invention, optical glass and optical components with high internal transmittance and high refractive index at a wavelength of 460nm can be provided.

Figure 1 is a graph showing the internal transmittance of an example of optical glass according to this embodiment, indicating the wavelength λτ90 at which the internal transmittance is 90%.

Figure 2 shows a photograph of the corrosion test results of the brick sample in Example 2.

Figure 3 shows the location where the brick sample diameter was measured during the erosion test in Example 2.

The following describes one aspect of the present invention. In this invention and this specification, glass compositions are expressed on an oxide basis unless otherwise specified. "Glass composition on an oxide basis" refers to the glass composition resulting from the complete decomposition of the glass raw materials during melting, calculated as the oxides present in the glass. The individual glass components are described as _SiO₂ , _TiO₂ , etc., following conventional practice. The content and total content of glass components are expressed by mass unless otherwise specified, and "%" means "mass %."

The content of glass components can be quantified using conventional methods, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). In this specification and the present invention, a 0% content of a component means that the component is substantially absent; however, the presence of such a component as an unavoidable impurity level is permitted.

The optical glass of the present invention will be described below, divided into a first embodiment and a second embodiment. The functions and effects of the various glass components in the second embodiment are the same as those in the first embodiment. Therefore, any overlapping descriptions of the second embodiment will be omitted as appropriate.

First implementation form

In the optical glass of the first embodiment, the mass ratio of the total content _of BaO, _La2O3 , _Gd2O3 and _WO3 to _the total content of CaO, SrO _{and Y2O3} [(BaO+ _La2O3 + _Gd2O3 + _WO3 )/ ₍ CaO+SrO+ _Y2O3 )] is 2.0 or less, _the mass ratio of the total content of _{B2O3 and P2O5} to the total content of _{SiO2 and Al2O3} [( _B2O3 + _{P2O5 )} / _{( SiO2 + Al2O3} )] is 0.10 or less, the total content _{of Li2O} , _Na2O and _K2O [ _{Li2O + Na2O} + _K2O ] is 10 mass% or less, the content _{of Al2O3} and SiO The mass ratio of the total content of Al 2 O ₃ and ZrO ₂ [Al ₂ O ₃ /(SiO ₂ +ZrO ₂ )] is greater than 0.

In the optical glass of the first embodiment, the mass ratio of the total content _of BaO, _La₂O₃ , _{Gd₂O₃ ,} and _WO₃ to _the total content _of CaO, SrO, and _Y₂O₃ [(BaO + _La₂O₃ + _Gd₂O₃ + _WO₃ ) / (CaO + SrO + _Y₂O₃ )] is 2.0 or less. The upper limit of this mass ratio is preferably 1.9, more preferably 1.8 _, 1.7, _and 1.6. The lower limit of this mass ratio is preferably 0.0, more preferably 0.3, 0.5, 0.8, 1.0, and 1.2.

By maintaining the mass ratio [(BaO + La ₂ O ₃ + Gd ₂ O ₃ + WO ₃ ) / (CaO + SrO + Y ₂ O ₃ )] within the above range, the specific gravity of the glass can be reduced by suppressing the content of high-refractive-index components with excessive atomic weights, particularly elements from the sixth period and later that have a relatively high refractive-index-raising effect, or by limiting the amount of high-refractive-index components that promote oxygen incorporation. On the other hand, if this mass ratio is too high, the increased specific gravity of the glass reduces the dynamic viscosity of the molten glass, making it difficult to control the glass flow and potentially degrading productivity. Furthermore, there is a risk of increased erosion of refractory bricks.

In the optical glass of the first embodiment, the mass ratio _of the total content _{of B2O3} and _P2O5 to the total content of _SiO2 and _Al2O3 [( _B2O3 + _P2O5 ) / ( _SiO2 + _Al2O3 )] is 0.10 or less. The upper limit of this mass ratio is preferably _0.09 , and more preferably 0.08, 0.07, _and 0.06. The lower limit of this mass ratio is preferably 0.00, and more preferably 0.01, 0.02, 0.03, _0.04 , _and 0.05.

By keeping the mass ratio [( _B2O3 + _P2O5 )/( _SiO2 + _Al2O3 )] within the above range, erosion of the _glass quality of _the refractory bricks during glass melting _can be suppressed. If the mass ratio is too high, erosion of the refractory bricks may increase, reducing the homogeneity of the molten glass and the devitrification resistance.

In the optical glass of the first embodiment, the total content of _Li₂O , _Na₂O , and _K₂O ( _Li₂O + _Na₂O + _K₂O ) is 10% or less. The upper limit of this total content is preferably 8.0%, with 6.0%, 5.0%, and 4.0% being more preferred. The lower limit of this total content is preferably 0.01%, with 0.5%, 1.0%, 1.5%, 2.0%, and 3.0% being more preferred.

By keeping the combined content [ _Li2O + _Na2O + _K2O ] within the above range, the glass viscosity can be appropriately maintained, thereby improving glass productivity. Furthermore, by suppressing light absorption from reducing components generated by Ti or Nb, and by promoting the elimination of electronic defects in the glass by lowering the melting temperature or slow cooling, the internal transmittance at 460nm can be increased. Furthermore, the corrosion of refractory bricks during glass melting can be suppressed. On the other hand, if the combined content is too low, the solubility of the glass raw materials will deteriorate, and it will be necessary to increase the melting temperature of the raw materials. As a result, the deterioration of refractory bricks will be promoted, and productivity will deteriorate. Conversely, if the combined content is too high, the viscosity of the glass will decrease, and this will cause a decrease in thermal stability, which may worsen productivity. Furthermore, the specific resistance of the molten glass decreases, which reduces the heating efficiency when the molten glass is heated by applying electricity, resulting in a decrease in the solubility of the glass and a risk of deteriorating productivity.

In the optical glass of the first embodiment, the mass ratio of _{the Al₂O₃} content to the total content of _SiO₂ and _{ZrO₂ [ Al₂O₃} /( _SiO₂ + _ZrO₂ )] is greater than 0. The lower limit of this mass ratio is preferably 0.0001, and more preferably 0.0003, 0.0006, 0.0010, 0.0020, 0.0030, 0.0040, 0.0050, and 0.0060. The upper limit of this mass ratio is preferably 0.3000, and more preferably 0.2000, 0.1500, 0.1000, 0.0500, 0.0300, and 0.0150.

By keeping the mass ratio [ _Al₂O₃ /( _SiO₂ + _ZrO₂ )] within the above range, erosion of refractory _bricks during molten glass can be suppressed. Furthermore, this ratio has the effect of improving thermal stability and devitrification during heating, and delaying crystallization during cooling of molten glass, compared to glass outside the above range. On the other hand, if this mass ratio is too high, not only will the refractive index nd be reduced, but thermal stability may also be impaired, potentially leading to devitrification.

The following describes preferred aspects of the optical glass according to the first embodiment.

In the optical glass of the first embodiment, the lower limit _of the combined content of _TiO₂ and _Nb₂O₅ ( _TiO₂ + _{Nb₂O₅ )} is preferably 20%, with 24%, 28%, 33%, 37%, 40%, and 42% being more preferred. Furthermore, the upper limit of the combined content is preferably 70%, with 60%, 55%, 50%, and 46% being more preferred.

_TiO2 and _Nb2O5 are components that contribute to a higher refractive index without significantly increasing _the specific gravity. Therefore, in order to obtain glass with a desired refractive index without excessively increasing the specific gravity of the glass, the combined content of _TiO2 and _{Nb2O5 is} preferably within the above range.

In the optical glass of the first embodiment, the mass ratio of the total content of _TiO2 , _{Nb2O5 ,} and _ZrO2 to the total content of _B2O3 , _SiO2 , _{Al2O3 ,} and _GeO2 [( _TiO2 + _Nb2O5 + _ZrO2 ) / ( _B2O3 + _SiO2 + _Al2O3 + GeO2)] is preferably 1.8, with _2.0 , _2.1 , 2.2, and 2.3 being more preferred. Furthermore, _the upper limit of this mass ratio is preferably 7.0, with 6.0, 5.0, 4.0 _{, 3.5} , and 3.0 being more preferred.

By maintaining the mass ratio [( _TiO2 + _Nb2O5 + _ZrO2 ) / ( _{B2O3 + SiO2} + _Al2O3 + _GeO2 )] within _the above range, the refractive index can be increased, enabling a wide viewing angle when used as a display lens for AR devices. Furthermore, optical glass with _a further reduced specific gravity can be obtained. On the other hand, if the mass ratio is too low, the refractive index relative to specific gravity decreases, making it unsuitable for the purposes of the present invention. Furthermore, if the mass ratio is too high, the stability of the glass may be reduced, and there is also the risk of lowering transmittance.

In the optical glass of the first embodiment, _the upper limit of the mass ratio of the total content of _B2O3 , _ZnO , _La2O3 , _Gd2O3 , _{and WO3} to the total content of _SiO2 , CaO, _TiO2 , and _Nb2O5 [( _B2O3 + ZnO _{+ La2O3} + _Gd2O3 + _WO3 ) / ( _SiO2 + CaO + _TiO2 + _Nb2O5 )] is preferably _0.15 , and more preferably 0.12, 0.10 _, and _0.08 , respectively. The lower limit of this mass ratio is preferably 0.01, and more preferably 0.02, 0.03, 0.04, 0.05, _and 0.06, respectively.

By maintaining the mass ratio [( _B2O3 + ZnO + _La2O3 + _Gd2O3 + _{WO3 )} / ( _SiO2 + CaO + _TiO2 + _Nb2O5 )] within _{the above} range, the content of glass components, which are often found in glasses using boric acid as a network _former , can be suppressed. Consequently, erosion of refractory bricks during glass melting can be suppressed. This in turn prevents contact between glass and platinum, improving the internal transmittance of the glass. Furthermore, maintaining this mass ratio within the above range limits the use of components with excessively large atomic weights or high-refractive-index components that promote oxygen filling, thereby reducing the specific gravity at the same refractive index. Furthermore, by suppressing a decrease in the dynamic viscosity of the glass, productivity can be improved.

In the optical glass of the first embodiment, the lower limit of _{the Al₂O₃} content is preferably 0.001%, and more preferably 0.002%, 0.003%, 0.005%, 0.007%, 0.010%, 0.025%, 0.050%, 0.075%, 0.100%, 0.125%, 0.150%, 0.175%, and 0.200%. The upper limit of _{the Al₂O₃} content is preferably 10.0%, and more preferably 6.0%, 3.0%, 1.00%, and 0.50%.

When melting glass in a refractory furnace, _Al₂O₃ from the bricks is introduced into _the molten glass. Therefore, even when the glass raw materials do not contain _Al₂O₃ , the glass produced in a refractory furnace _will contain trace amounts of _Al₂O₃ . When _{the Al₂O₃ content} is within the above range, compared _{to Al₂O₃} contents outside this range, thermal stability is improved, devitrification during heating is suppressed, and crystallization during cooling of the molten glass is suppressed. However, since _Al₂O₃ has a minimal effect on reducing specific _gravity and is a component that lowers the refractive index, a lower _Al₂O₃ content is preferred for obtaining glass with a high refractive index _and low specific _gravity . Furthermore, if the _Al2O3 content is too high, the devitrification resistance of the glass will be reduced, the glass transition temperature (Tg) will be increased, and there is a risk of reduced thermal stability. On the other hand, if the _Al2O3 content is too low, there is a risk of increased corrosion of _the refractory _bricks .

The following are non-limiting examples of the contents and ratios of glass components other than those described above in the optical glass according to the first embodiment.

In the optical glass of the first embodiment, the lower limit of the mass ratio of the total content of TiO ₂ , CaO, SrO and Y ₂ O ₃ to the total content of BaO, MgO, Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , La ₂ O ₃ and Gd ₂ O ₃ [(TiO ₂ +CaO +SrO +Y ₂ O ₃ )/(BaO + MgO +Nb ₂ O ₅ +Ta ₂ O ₅ +WO ₃ +Bi ₂ O ₃ +La ₂ O ₃ +Gd ₂ O ₃ )] is preferably 0.5, and more preferably 0.6, 0.7, 0.8, 0.9, and 1.0, in this order. In addition, the upper limit of the mass ratio is preferably 4.0, and further preferably 3.0, 2.5, 2.0, and 1.5.

By keeping the mass ratio [( _TiO2 + CaO + SrO + _Y2O3 ) / ( _BaO + MgO + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 + _{La2O3 + Gd2O3} ) _] within the _above range, optical glass with _a high refractive index _nd and a low specific gravity can be obtained. If this mass ratio is too low, it may be impossible to achieve both a high refractive index and a low specific gravity. If this mass ratio is too high, the stability of the glass may be reduced.

In the optical glass of the first embodiment, the mass ratio of _TiO₂ to _Nb₂O₅ ( _TiO₂ / _{Nb₂O₅ )} is preferably 0.5, with 0.53, 0.54, 0.55, 0.6, 0.7, 0.8, 0.9 _, and 1.0 being more preferred. Furthermore, the upper limit of the mass ratio is preferably 4.0, with 3.0 _, 2.5, _{2.0, and} 1.5 being more preferred.

By keeping the mass ratio [ _TiO₂ / _Nb₂O₅ ] within the above range, _the specific gravity of the glass can be reduced while improving its stability. On the other hand, if the mass ratio is too low, the liquidus temperature may rise, impairing solubility and increasing the risk of erosion of refractory bricks during glass melting. This may also increase manufacturing costs. Furthermore, if the mass ratio is too high, the glass's resistance to devitrification may be reduced, potentially lowering its transmittance.

In the optical glass of the first embodiment, the lower limit of the total content of MgO, CaO, SrO, and BaO [MgO + CaO + SrO + BaO] is 5.0%, and more preferably 10.0%, 15.0%, 18.0%, 22.0%, and 25.0%. Furthermore, the upper limit of the total content is preferably 50.0%, and more preferably 45.0%, 40.0%, 36.0%, 33.0%, and 30.0%, respectively.

By keeping the combined content of [MgO + CaO + SrO + BaO] within the above range, the solubility of the glass can be improved, and the thermal stability of the glass can be enhanced. On the other hand, if the combined content is too low, the glass's solubility may be deteriorated, and there is a risk of increased erosion of refractory bricks during glass melting. Furthermore, if the combined content is too high, the desired optical properties may not be achieved, and stability may be reduced.

In the optical glass of the first embodiment, the lower limit of the mass ratio of the total content of _Li2O , _Na2O , and _K2O to the total content of MgO, CaO, SrO, and BaO [( _Li2O + _Na2O + _K2O )/(MgO+CaO+SrO+BaO)] is preferably 0.00020, and more preferably 0.001, 0.005, 0.010, 0.050, and 0.100, respectively. The upper limit of this mass ratio is preferably 2.0, and more preferably 1.5, 1.0, 0.5, 0.3, and 0.2, respectively.

By keeping the mass ratio [( _Li₂O + _Na₂O + _K₂O )/(MgO+CaO+SrO+BaO)] within the above range, the specific gravity of the glass can be easily reduced. Furthermore, by suppressing the reduction of the glass, the internal transmittance can be easily increased. On the other hand, if this mass ratio is too low, the glass's meltability may be impaired, and erosion of refractory bricks during melting may be increased. Furthermore, if this mass ratio is too high, the homogeneity of the glass may be reduced due to volatility of glass components or vascularization, and stability may be reduced due to a decrease in viscosity.

In the optical glass of the first embodiment, the lower limit of the ratio of the value obtained by dividing the _Li2O content by 29.9 to the sum of the value obtained by dividing _{the B2O3 content} by 69.6, the value obtained by dividing the _Li2O content by 29.9, the value obtained by dividing the _Na2O content by 62.0, and the value obtained by dividing the _K2O content by 94.2 [( _Li2O /29.9)/{( _{B2O3 /} 69.6+ _Li2O /29.9+Na2O/62.0+ _K2O / _94.2 )}] is preferably 0.10, and more preferably 0.20, 0.30, 0.40, 0.45, and 0.50, respectively. The upper limit of this ratio is preferably 1.00, with 0.90, 0.80, 0.70, 0.60, and 0.55 being more preferred. Since the divisor of the content of each glass component is equivalent to the molecular weight of each oxide, this ratio represents the ratio of the number of Li ions in the glass to the total number of Li ions, B ions, Na ions, and K ions.

By keeping the ratio [( _Li2O /29.9)/( _B2O3 / _69.6 + _Li2O /29.9+ _Na2O /62.0+ _K2O /94.2)] within the above range, the glass can be densely packed, without introducing high-melting-point, high-refractive-index components that would otherwise raise the glass's melting temperature, resulting in a low-specific-gravity, high-refractive-index glass. Furthermore, the increased number of Li ions improves the heating efficiency of the molten glass when heated by electrical heating, and also enhances the fluidity of the molten glass. Furthermore, keeping this ratio within the above range ensures the solubility of the glass while suppressing reduction discoloration that can occur during glass melting, thereby improving internal transmittance. On the other hand, if the ratio is too small, the specific resistance of the molten glass will increase, requiring a higher voltage to be applied during electric melting, which may increase the erosion of refractory bricks during glass melting. Conversely, if the ratio is too large, the stability of the glass may be reduced.

In the optical glass of the first embodiment, the lower limit of the SiO ₂ content is 5.0%, and more preferably 8.0%, 11.0%, 13.0%, and 15.0%. In addition, the upper limit of the SiO ₂ content is 35.0%, and more preferably 30.0%, 27.0%, 25.0%, 23.0%, and 21.0%.

_SiO₂ is a network-forming component of glass, improving its thermal stability, chemical durability, and weather resistance, while also increasing the viscosity of molten glass. Too little _SiO₂ tends to reduce the glass's resistance to devitrification. Too much _SiO₂ can lower the refractive index nd, increase viscosity, and potentially increase the partial dispersion ratios Pg and F.

In the optical glass of the first embodiment, the lower limit of the _ZrO2 content is preferably 0%, and more preferably 0.0005%, 0.0010%, 0.0050%, 0.0100%, 0.0500%, 0.1%, 0.5%, 1.0%, and 1.5%. Furthermore, the upper limit of the _ZrO2 content is preferably 15.0%, and more preferably 10.0%, 7.0%, 5.0%, 3.0%, and 2.0%.

When melting glass in a melting furnace using refractory bricks, _ZrO₂ from the bricks tends to be introduced into the molten glass. Therefore, even when the glass raw materials do not contain _ZrO₂ , the glass produced by melting in a melting furnace using refractory bricks may contain trace amounts of _ZrO₂ . Furthermore, _Zr may be introduced into the glass to strengthen the contact between platinum and the molten glass. Too little _ZrO₂ may increase erosion of the refractory bricks. Too much ZrO₂ may deteriorate the glass's meltability. By keeping the _ZrO₂ content within the above range, it is possible to obtain glass with a high refractive index while suppressing brick erosion. Furthermore, the glass's meltability and thermal stability can be maintained.

In the optical glass of the first embodiment, the upper limit of _{the P₂O₅} content is preferably 5.0%, with 4.0%, 3.0%, 2.0%, 1.0%, and 0.6% being more preferred. A lower _P₂O₅ content is preferred, with a lower limit of 0.0%. However, to adjust the stability and liquidus temperature of the glass, a _P₂O₅ content of 0.20% or higher, or 0.40% or higher, may be used. _{The P₂O₅} content is preferably 0.0%.

By setting _the content of _P2O5 within the above range, devitrification of the glass can be suppressed, and erosion of the refractory bricks during melting of the glass can be suppressed.

In the optical glass of the first embodiment, the upper limit of _{the B2O3} content is preferably 15.0%, and more preferably 10.0%, 6.0%, 3.0%, 2.0%, and 1.0%. The lower limit of _{the B2O3} content is preferably 0.0%, and more preferably 0.1%, 0.2%, 0.4%, and 0.7%.

_B2O3 improves the thermal stability of glass and enhances its solubility. Furthermore, among the network-forming components of glass, _it has a relatively high refractive index and can reduce specific gravity. By keeping _{the B2O3 content} within the above range, the solubility _of the glass can be improved, and optical glass with a high refractive index and low specific gravity can be obtained. On the other hand, if the _B2O3 content is too low, the high refractive index properties may be compromised, and the specific gravity may increase. Furthermore, if _{the B2O3} content is too high, the volatility of the glass components may increase during melting. Furthermore, this may hinder high dispersion and tend to reduce resistance to devitrification.

In the optical glass of the first embodiment, the lower limit of the combined content _{of SiO₂} and _{Al₂O₃ [ SiO₂} + _Al₂O₃ ] is preferably 5%, with 8%, 11%, and 13% being more preferred. Furthermore, the upper limit of the combined content _{[ SiO₂} + _Al₂O₃ ] is preferably 40%, with 35%, 30%, 25%, 23%, 21%, and 15% being more preferred.

By keeping the total content [SiO ₂ +Al ₂ O ₃ ] within the above range, erosion of the refractory bricks during glass melting can be suppressed. However, if the total content is too high, the specific gravity does not decrease much while the refractive index decreases significantly, and the refractive index required by the present invention may not be obtained.

In the optical glass of the first embodiment, the lower limit _of the combined content _{of B2O3} and _{P2O5 [ B2O3} + _P2O5 ] is preferably 0.1%, with _0.2 %, 0.4%, 0.7%, and 1% being more preferred. Furthermore, the upper limit of _the combined content _{[ B2O3} + _P2O5 ] is preferably 10%, with 6%, 3%, and 2% being more preferred.

By setting the total content [B ₂ O ₃ +P ₂ O ₅ ] within the above range, the viscosity of the glass can be maintained, the stability can be improved, and the erosion of the refractory bricks during glass melting can be suppressed.

In the optical glass of the first embodiment, the lower limit of the _TiO2 content is preferably 5.0%, and more preferably 10.0%, 14.0%, 14.2%, 14.5%, 14.8%, 15.0%, 18.0%, and 20.0%. Furthermore, the upper limit of the _TiO2 content is preferably 40.0%, and more preferably 35.0%, 30.0%, 25.0%, and 22.0%.

By keeping the _TiO₂ content within the above range, glass with a high refractive index and low specific gravity can be obtained. It also has the effect of reducing UV transmittance. On the other hand, too little _TiO₂ may lower the refractive index and increase the specific gravity. Furthermore, too much _TiO₂ may reduce the internal transmittance of the glass in the visible range, particularly in the short-wavelength range, and may also reduce devitrification resistance.

In the optical glass of the first embodiment, the lower limit of _{the Nb₂O₅} content is preferably 0.0%, with 5.0%, 10.0%, 13.0%, and 15.0% being more preferred. Furthermore, the upper limit of the _Nb₂O₅ content is preferably _40.0 %, with 35.0%, 30.0%, 28.0%, 27.0%, 26.0%, 25.0%, 20.0%, and 17.0% being more preferred.

By keeping the _Nb2O5 content within the above range, an optical glass _with a high refractive index and a relatively low specific gravity can be obtained. On the other hand, if the _Nb2O5 content is too low, the refractive index _may decrease and the specific gravity may increase. If _{the Nb2O5} content is too high, the devitrification resistance may be reduced.

In the optical glass of the first embodiment, the lower limit of the total content of _TiO₂ , _Nb₂O₅ , and _ZrO₂ ( _TiO₂ + _Nb₂O₅ + _ZrO₂ ) is preferably 25%, with 30%, 35%, 40%, _and 45% being more preferred. Furthermore, the upper limit _of this total content is preferably 75%, with 70%, 60%, 55%, 52.5%, and 50% being more preferred.

By setting the total content of [TiO ₂ +Nb ₂ O ₅ +ZrO ₂ ] within the above range, an optical glass having a high refractive index and high internal transmittance at a predetermined wavelength can be obtained while suppressing an increase in specific gravity.

In the optical glass of the first embodiment, the upper limit of the WO ₃ content is preferably 5.0%, and more preferably 3.0%, 2.0%, 1.0%, and 0.5% in this order. The lower limit of the WO ₃ content is preferably 0.0%. The _{WO 3} content may also be 0.0%.

By keeping the _WO3 content within the above range, optical glass with a lower specific gravity and reduced UV transmittance can be obtained. On the other hand, excessive _WO3 content may increase the partial dispersion ratios Pg and F, reduce internal transmittance, and increase specific gravity. Furthermore, transmittance in the visible range, particularly in the short-wavelength range, may be reduced, potentially making the glass unstable.

In the optical glass of the first embodiment, the upper limit of _{the Bi2O3} content is preferably 5.0%, and more preferably 3.0%, 2.0%, 1.0%, and 0.5%. The lower limit of _{the Bi2O3} content is preferably 0.0%. _{The Bi2O3} content may also be 0.0%.

By keeping _{the Bi₂O₃} content within the above range, optical glass _with a lower specific gravity and reduced UV transmittance can be obtained. On the other hand, excessive _Bi₂O₃ content increases the partial dispersion ratios Pg and F, increasing the specific gravity. Furthermore, since Bi ions absorb light of specific wavelengths, combined with reduced transmittance in the short-wavelength region, there is a risk of lowering internal transmittance. Furthermore, there is a risk of increased platinum erosion by the glass, leading to increased glass coloration.

In the optical glass of the first embodiment, the total content _{of WO3} and _Bi2O3 [ _WO3 + _Bi2O3 ] is preferably 3 _% or less, more preferably 2.4% or less, 1.9% or less, 1.4% or less, 0.9% or less, and 0.4% or less, in this order. It is particularly preferred that _{neither WO3} nor _Bi2O3 be _contained .

By setting the total content [WO ₃ +Bi ₂ O ₃ ] within the above range, a decrease in internal transmittance in the visible light region can be suppressed.

In the optical glass of the first embodiment, the upper limit of the Li ₂ O content is preferably 15.0%, and more preferably 10.0%, 7.0%, 5.0%, 3.0%, and 2.0%. The lower limit of the _{Li 2} O content is preferably 0.0%, and more preferably 0.1%, 0.5%, 1.0%, and 1.5%.

By keeping the _Li₂O content within the above range, the filling factor of the glass structure can be increased, resulting in optical glass with a high refractive index and low specific gravity. Furthermore, the glass's meltability can be improved, reducing the specific resistivity of the molten glass. Furthermore, it also has the effect of suppressing the reduction discoloration that may occur during melting of the glass. On the other hand, too little _Li₂O may reduce the glass's transmittance. Too much _Li₂O may reduce chemical durability, weather resistance, and stability during reheating.

In the optical glass of the first embodiment, the upper limit of the Na ₂ O content is preferably 15.0%, and more preferably 10.0%, 7.0%, 5.0%, 3.0%, and 2.0%. The lower limit of the _{Na 2} O content is preferably 0.0%, and more preferably 0.1%, 0.5%, 1.0%, and 1.5%.

By keeping the Na ₂ O content within the above range, optical glass with a reduced specific gravity can be obtained. Furthermore, the glass's solubility can be improved, reducing the specific resistivity of the molten glass. On the other hand, too little Na ₂ O can reduce the glass's solubility. Too much Na ₂ O can lower the refractive index.

In the optical glass of the first embodiment, the upper limit of the K ₂ O content is preferably 15.0%, and more preferably 10.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The _{K 2} O content is preferably lower, and the lower limit is preferably 0.0%, and more preferably 0.1%, 0.3%, 0.6%, and 0.9%.

By setting the K ₂ O content within the above range, the stability of the glass containing TiO ₂ is improved. In addition, the meltability of the glass can be enhanced. On the other hand, if the K ₂ O content is too high, the refractive index may be significantly lowered.

In the optical glass of the first embodiment, the upper limit of the Cs ₂ O content is preferably 15.0%, and more preferably 10.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the _{Cs 2} O content is preferably 0.0%. The _{Cs 2} O content may also be 0.0%.

Cs ₂ O enhances the meltability of glass and improves its thermal stability. However, excessive Cs ₂ O content can significantly lower the refractive index and deteriorate the chemical durability of the glass.

In the optical glass of the first embodiment, the upper limit of the MgO content is preferably 10.0%, with 5.0%, 4.0%, 3.0%, 2.0%, and 1.0% being more preferred. Furthermore, the lower the MgO content, the better, with the lower limit being 0.0%. The MgO content may also be 0.0%.

By keeping the MgO content within the above range, the stability of the glass can be improved and coloration can be reduced. On the other hand, if the MgO content is too high, there is a risk that a high refractive index and low specific gravity will not coexist.

In the optical glass of the first embodiment, the upper limit of the CaO content is preferably 30.0%, with 25.0%, 20.0%, 16.0%, and 13.0% being more preferred. Furthermore, the lower limit of the CaO content is preferably 0.0%, with 3.0%, 6.0%, 8.0%, and 10.0% being more preferred.

By keeping the CaO content within the above range, optical glass with a high refractive index, low specific gravity, and improved solubility can be obtained. On the other hand, if the CaO content is too low, it may not be possible to achieve both a high refractive index and a low specific gravity. Furthermore, if the CaO content is too high, it may increase the amount of brick erosion, making it impossible to maintain high dispersibility, and may also reduce the thermal stability of the glass and its resistance to devitrification.

In the optical glass of the first embodiment, the upper limit of the SrO content is preferably 10.0%, with 7.0%, 5.0%, 3.0%, 2.5%, and 2.0% being more preferred. Furthermore, the lower the SrO content, the better. The lower limit is preferably 0.0%, with 0.1%, 0.5%, 1.0%, and 1.5% being more preferred.

By keeping the SrO content within the above range, meltability can be improved. On the other hand, excessive SrO content increases the specific gravity, making it difficult to maintain high dispersibility, reducing the thermal stability of the glass, and potentially decreasing devitrification resistance.

In the optical glass of the first embodiment, the upper limit of the BaO content is preferably 30.0%, with 25.0%, 20.0%, 16.0%, and 13.0% being more preferred. Furthermore, the lower limit of the BaO content is preferably 0.0%, with 3.0%, 6.0%, 8.0%, and 10.0% being more preferred. The BaO content may also be 0.0%.

By keeping the BaO content within the above range, meltability can be improved. On the other hand, too little BaO can reduce glass stability. Furthermore, too much BaO can significantly increase the specific gravity, making it impossible to maintain high dispersibility, resulting in a decrease in the thermal stability of the glass and a reduction in devitrification resistance.

In the optical glass of the first embodiment, the upper limit of the ZnO content is preferably 10.0%, with 5.0%, 4.0%, 3.0%, 2.0%, and 1.0% being more preferred. Furthermore, the ZnO content is preferably lower, with the lower limit being preferably 0.0%. The ZnO content may also be 0.0%.

A ZnO content within the above range can lower the glass transition temperature (Tg). On the other hand, excessive ZnO content not only increases the specific gravity but also may impair glass stability.

In the optical glass of the first embodiment, the upper limit of the La ₂ O ₃ content is preferably 10.0%, and more preferably 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. In addition, the lower limit of the La ₂ O ₃ content is preferably 0.0%.

By keeping the _La₂O₃ content within the above range, _a high-refractive-index optical glass can be obtained without degrading _the internal transmittance of the glass. On the other hand, a low _La₂O₃ content tends to lower the refractive index. Furthermore, an excessively _{high La₂O₃} content increases the specific gravity, potentially reducing the thermal stability of the glass.

In the optical glass of the first embodiment, the upper limit of _{the Gd2O3} content is preferably 10.0%, and more preferably 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. Furthermore, the lower _{the Gd2O3} content, the better, and the lower limit is preferably 0.0%.

By keeping the _Gd2O3 content within the above range, _high -refractive-index optical glass can be obtained without degrading the internal transmittance of the glass. On the other hand, excessive _Gd2O3 content _may reduce the thermal stability of the glass, increase its specific gravity, and increase the manufacturing cost of the glass.

In the optical glass of the first embodiment, the upper limit of the Y ₂ O ₃ content is preferably 10.0%, and more preferably 8.0%, 5.0%, 3.0%, 2.0%, and 1.5%. The lower limit of the Y ₂ O ₃ content is preferably 0.0%.

By introducing _Y₂O₃ within the above range, for example, instead _{of ZrO₂} or _Nb₂O₅ , it is possible to obtain optical glass _with a high refractive index and low specific gravity _without degrading the internal transmittance of the glass. On the other hand, low _Y₂O₃ contents tend to lower the refractive index. Furthermore, excessive _Y₂O₃ contents may reduce the thermal stability of the glass and decrease _its resistance to devitrification.

In the optical glass of the first embodiment, the upper limit of the _GeO2 content is preferably 10.0%, with 6.0%, 4.0%, 3.0%, 2.0%, and 1.0% being more preferred. Furthermore, the lower the _GeO2 content, the better, with a lower limit of 0.0%.

_GeO2 is an expensive glass component, so excessive _GeO2 content may increase manufacturing costs.

In the optical glass of the first embodiment, the upper limit of the Ta ₂ O ₅ content is preferably 5%, more preferably 3%, 2%, and 1%. The lower limit of the Ta ₂ O ₅ content is preferably 0%.

_Ta₂O₅ is _a glass component that increases the refractive index without degrading the internal transmittance of the glass. It also reduces the partial dispersion ratio of Pg and F. However, _Ta₂O₅ is an expensive glass component, _and increasing _its content may increase manufacturing costs and _the specific gravity. Therefore, the _Ta₂O₅ content is preferably within the _above range.

In the optical glass of the first embodiment, the content of Sc ₂ O ₃ is preferably 2% or less. The lower limit of the content of Sc ₂ O ₃ is preferably 0%.

Sc ₂ O ₃ has the effect of increasing the refractive index of glass, but it is an expensive component. Therefore, the Sc ₂ O ₃ content is preferably within the above range.

In the optical glass of the first embodiment, the upper limit of the _HfO2 content is preferably 2%, with 1.5%, 1.0%, 0.5%, and 0.3% being more preferred. Furthermore, the lower limit of the _HfO2 content is preferably 0%, with 0.005%, 0.01%, 0.03%, 0.05%, 0.07%, and 0.09% being more preferred.

Furthermore, _HfO₂ may be contained in a certain amount in the _ZrO₂ raw material. Therefore, glass containing _ZrO₂ may also contain a certain amount of _HfO₂ . Therefore, in the optical glass of the first embodiment, the mass ratio of the _HfO₂ content to the _ZrO₂ content [ _HfO₂ / _ZrO₂ ] may also be within a predetermined range. For example, the lower limit of this mass ratio [ _HfO₂ / _ZrO₂ ] may be 0.005, and further, it may be 0.010, 0.013, or 0.015. On the other hand, the upper limit of this mass ratio may be 0.05, and further, it may be 0.040, 0.030, 0.020, or 0.018. From the perspective of suppressing the melting of refractory brick components in the glass, it is preferred that the glass contain a small amount of _ZrO2 , and for this purpose, the content of _HfO2 is preferably within the above range.

In the optical glass of the first embodiment, the content of Lu ₂ O ₃ is preferably 2% or less. The lower limit of the content of Lu ₂ O ₃ is preferably 0%.

Lu ₂ O ₃ has the function of adjusting the refractive index of glass, but due to its high molecular weight, it is a glass component that increases the specific gravity of the glass. Therefore, the Lu ₂ O ₃ content is preferably within the above range.

In the optical glass of the first embodiment, the Yb ₂ O ₃ content is preferably 2% or less, more preferably 1% or less, and even more preferably 0.5% or less. Furthermore, the lower limit of the Yb ₂ O ₃ content is preferably 0%.

_Yb2O3 adjusts the refractive index of glass, but its high molecular weight increases the specific gravity of the glass. This increases the weight of optical components. Therefore, it's best to reduce _{the Yb2O3} content to minimize the increase in _the specific gravity of the glass.

Furthermore, excessive _Yb2O3 content can reduce the thermal stability of the glass. Furthermore, it can cause absorption in the infrared region. To prevent a decrease in _the thermal stability of the glass and suppress an increase in specific gravity, _{the Yb2O3} content is preferably within the above range.

Regarding the optical glass of the first embodiment, it is preferably composed mainly of the above- _mentioned glass components _, namely _{, Al2O3} , _SiO2 , _ZrO2 , _P2O5 , _B2O3 , _TiO2 , _Nb2O5 , _{WO3, Bi2O3, Li2O, Na2O , K2O , Cs2O , MgO} , CaO, SrO, BaO, ZnO, _La2O3 , _Gd2O3 , _Y2O3 , _GeO2 , _Ta2O5 , _Sc2O3 , _HfO2 , _Lu2O3 and _Yb2O3 , 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 even more preferably 99.5% _or more _.

Furthermore, the optical glass of the first embodiment is preferably composed primarily of the aforementioned glass components, but may contain other components as long as they do not hinder the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

(Other ingredients)

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

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

V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase glass coloration and may become a source of fluorescence. Therefore, the optical glass of this embodiment preferably does not contain these elements as glass components. However, elements that do not degrade the transmittance around 460 nm, the target of this invention, may be introduced within a range that solves the problem of this invention.

Sb (Sb ₂ O ₃ ) and Ce (CeO ₂ ) are elements that can be added arbitrarily as clarifiers. Sb (Sb ₂ O ₃ ) is the most effective clarifier. Ce (CeO ₂ ) has a lesser clarification effect than Sb (Sb ₂ O ₃ ). Adding large amounts of Ce (CeO ₂ ) tends to enhance the coloring of the glass.

The _Sb2O3 content is expressed as an external _percentage . That is, when the total content of all glass components other _{than Sb2O3} and _CeO2 is taken as 100% by mass, _{the Sb2O3} content is preferably 1.0% by mass or less, and more preferably 0.4% by mass or less, 0.2% by mass or less, 0.1% by mass or less, 0.05% by mass or less, 0.03% by mass or less, 0.02% by mass or less, and 0.01% by mass _or less. The _Sb2O3 content may also be 0% by mass.

The _CeO2 content is also expressed as an external percentage. Specifically, when the total content of all glass components other than _{CeO2 and Sb2O3} is taken as 100% by mass, the _CeO2 content is preferably 2% by mass or less, more preferably 1% by mass or less, further preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. The _CeO2 content may also be 0% by mass. By maintaining the _CeO2 content within the above range, the clarity of the glass can be improved.

(Characteristics of glass)

<Refractive index nd>

In the optical glass of the first embodiment, the upper limit of the refractive index nd can be 2.50, or further 2.20, 2.10, 2.05, 2.00, or 1.98. Furthermore, the lower limit of the refractive index nd can be 1.85, or further 1.87, 1.89, or _1.90 . The refractive index can be controlled by adjusting the content of glass components that contribute to a higher _refractive index, such as _TiO₂ , _Nb₂O₅ , _ZrO₂ , _{and Y₂O₃} , or by adjusting the content of low-refractive-index components such as _SiO₂ , _Al₂O₃ , _{and B₂O₃} , or by introducing modifying components such as _Li₂O and CaO.

<Abbe number νd>

In the optical glass of the first embodiment, the upper limit of the Abbe number νd can be 30.0, and can be further preferably 28.0, 26.0, 25.0, or 24.5. Furthermore, the lower limit of the Abbe number νd can be 15.0, and can be further preferably 18.0, 20.0, 22.0, or 23.0. An Abbe number νd within the above range can produce glass with desired dispersion properties. The Abbe number νd can be controlled by adjusting the contents of _TiO₂ , _Nb₂O₅ , _WO₃ , _ZrO₂ , and _{Bi₂O₃ , glass} components that contribute to high dispersion.

<Specific Gravity of Glass>

Although the optical glass of the first embodiment is high-refractive-index glass, its specific gravity is not high. Reducing the specific gravity of the glass can reduce the weight of the lens. On the other hand, an excessively low specific gravity can lead to a decrease in thermal stability.

Therefore, in the optical glass of the first embodiment, the upper limit of the specific gravity is preferably 7.0, and more preferably 6.0, 5.0, 4.5, and 4.0, in that order. The lower limit of the specific gravity is preferably 2.5, and more preferably 3.0 and 3.5, in that order.

Specific gravity depends on the atomic weight of the constituent components of the glass and the volume occupied by those atoms. For example, the introduction of oxides containing Period VI elements or elements with large atomic numbers above 57 tends to increase the specific gravity. However, if the volume occupied by those elements is also large, the increase in specific gravity can sometimes be suppressed.

However, if the volume of an element is too large, the refractive index decreases. Furthermore, the volume of an element is not inherent and varies slightly depending on the presence of other glass components. The specific gravity can be controlled by adjusting the total amount and ratio of these components. Furthermore, the volume of each element also varies slightly depending on the cooling conditions of the glass.

<Glass transition temperature Tg>

In the optical glass of the first embodiment, the upper limit of the glass transition temperature (Tg) is not particularly limited. Considering productivity factors such as the time required for slow cooling, 850°C is preferred, with 800°C, 750°C, 700°C, and 650°C being more preferred. Furthermore, the lower limit of the glass transition temperature (Tg) is not particularly limited. From the perspective of achieving heat resistance suitable for optical glass, 100°C is preferred, with 200°C, 300°C, 400°C, and 500°C being more preferred.

The glass transition temperature (Tg) can be controlled by adjusting the increase or decrease of glass-forming components and the ratio of each component, in addition to introducing components such as Li and Zn, which are known to lower the Tg, into the introduced glass components.

By ensuring that the upper limit of the glass transition temperature (Tg) meets the above-mentioned requirements, increases in the forming and annealing temperatures during reheating and pressing of the glass can be suppressed, thereby reducing thermal damage to the reheating and pressing forming and annealing equipment.

By ensuring that the lower limit of the glass transition temperature (Tg) satisfies the above conditions, it is possible to easily maintain the desired Abbe number and refractive index while also maintaining good reheat pressing formability and thermal stability of the glass.

<Liquid phase temperature LT>

The upper limit of the liquidus temperature (LT) of the optical glass of the first embodiment is preferably 1450°C to minimize the energy required for glass melting, with 1400°C, 1350°C, 1300°C, 1250°C, and 1200°C being more preferred. The lower limit of the liquidus temperature is not particularly limited, but is preferably 800°C to achieve a certain level of stability, with 900°C, 1000°C, 1050°C, and 1100°C being more preferred. By keeping the liquidus temperature within this range, erosion of refractory bricks during glass melting can be suppressed.

The liquidus temperature is determined as follows. 10cc (10ml) of glass is placed in a platinum crucible and melted at 1250°C to 1450°C for 20-30 minutes. The glass and platinum crucible are then cooled to below the glass transition temperature (Tg). The glass and platinum crucible are then placed in a melting furnace at a predetermined temperature and held for two hours. The temperature is maintained above 800°C in 5°C or 10°C increments for two hours, followed by cooling. The glass is then observed under a 100x optical microscope to detect the presence of crystals. The lowest temperature at which no crystals are observed is defined as the liquidus temperature.

<Pt content>

In the optical glass of the first embodiment, the upper limit of the Pt content is preferably 10.0 mass ppm, with 8.0 mass ppm, 7.0 mass ppm, 6.0 mass ppm, and 5.0 mass ppm being more preferred. The lower the Pt content, the better. The lower limit is preferably 4.0 mass ppm, with 3.0 mass ppm, 2.0 mass ppm, and 0.0 mass ppm being the most preferred.

Glass produced in a furnace that uses refractory bricks in a portion of the melting furnace, particularly where the batch of raw materials is heated and melted, can have a lower Pt content than glass produced in a platinum furnace. By keeping the Pt content within the above range, optical glass with excellent transmittance can be obtained.

<τ460, τ440>

Regarding the optical glass of the first embodiment, the lower limit of the internal transmittance τ460 at a wavelength of 460 nm with a thickness of 10.0 mm ± 0.1 mm is preferably 88.0%, with 90.0%, 91.0%, 92.0%, 93.0%, 94.0%, and 95.0% being more preferred. The higher the internal transmittance, the better, with 100.0% being preferred. The upper limit is preferably 99.0%, 98.0%, 97.0%, and 96.0%, respectively. Furthermore, the thickness (optical path length) of a glass product using the optical glass of this embodiment can be appropriately selected according to its intended use and is not limited to 10.0 mm. For example, it can be 15 mm or greater, and further can be 20 mm or greater, or 30 mm or greater. Depending on the intended use, it can also be 8 mm or less, 6 mm or less, or 4 mm or less.

Furthermore, for the optical glass of the first embodiment, the lower limit of the internal transmittance τ440 at a wavelength of 440 nm with a thickness of 10.0 mm ± 0.1 mm is preferably 85.0%, with 88.0%, 90.0%, 91.0%, 92.0%, 93.0%, and 94.0% being more preferred. The higher the internal transmittance, the better, with 100.0% being preferred. The upper limit is preferably 99.0%, 98.0%, 97.0%, 96.0%, and 95.0%, respectively.

Internal transmittance (τ) is the transmittance after removing surface reflection loss on the incident and exit sides. For two glass samples of different thicknesses, the internal transmittance was calculated using the following formula using the measured transmittance values including surface reflection loss at wavelengths of 460nm and 440nm, respectively. The thicknesses of the glass samples, d ₁ and d ₂ , were 2.0mm±0.1mm and 10.0mm±0.1mm, respectively.

Here

τ: internal transmittance of glass at sample thickness _d2

△d: Thickness difference of sample [d ₂ -d ₁ ]

T1: Transmittance including surface reflection loss obtained with sample thickness _d1

T2: Transmittance including surface reflection loss obtained with the sample thickness _d2

Internal transmittance is the transmittance of a material that is independent of its refractive index. It can be controlled by adjusting the intrinsic light absorption of elements contained in the glass, light absorption from impurities such as Pt, and even absorption by coloring centers generated within the glass framework.

From this perspective, for example, by adjusting the contents of components that reduce internal transmittance, such as _WO₃ and _{Bi₂O₃ ,} the internal transmittance can be controlled within the above range. Adjusting the contents of trace components such as _Sb₂O₃ and Pt is also effective. Furthermore, adjusting the contents of alkaline components such as βOH, _Li₂O , _Na₂O , and _K₂O is also effective in reducing reduction coloration.

<λτ90、λτ80、λτ5>

Regarding the optical glass of the first embodiment, light transmittance can also be evaluated using λτ90, λτ80, and λτ5. For example, λτ90 is the wavelength at which internal transmittance reaches 90%, as shown in Figure 1. Similarly, λτ80 and λτ5 are the wavelengths at which internal transmittance reaches 80% and 5%, respectively. Internal transmittance can be calculated using the above formula.

In the optical glass of the first embodiment, the upper limit of λτ90 is preferably 500 nm, with 470 nm, 450 nm, 430 nm, and 420 nm being more preferred, in order of increasing transmittance at the desired wavelength. There is no particular restriction on the lower limit of λτ90; however, from the perspective of reducing transmittance of short-wavelength light that may adversely affect the human body, 150 nm is preferred, with 200 nm, 250 nm, 300 nm, and 350 nm being more preferred, in order of decreasing transmittance.

In the optical glass of the first embodiment, the upper limit of λτ80 is preferably 450 nm, with 440 nm, 430 nm, 420 nm, and 410 nm being more preferred, from the perspective of improving transmittance at the desired wavelength. There is no particular restriction on the lower limit of λτ80, but from the perspective of reducing transmittance of short-wavelength light that may adversely affect the human body, 150 nm is preferred, with 200 nm, 250 nm, 300 nm, and 350 nm being more preferred, from the perspective of reducing transmittance of short-wavelength light that may adversely affect the human body.

In the optical glass of the first embodiment, the upper limit of λτ5 is preferably 390 nm, with 380 nm, 370 nm, 365 nm, and 360 nm being more preferred, in order of increasing transmittance at the desired wavelength. There is no particular restriction on the lower limit of λτ5; however, from the perspective of reducing transmittance of short-wavelength light that may adversely affect the human body, 150 nm is preferred, with 250 nm, 300 nm, 330 nm, 350 nm, and 355 nm being more preferred, in order of decreasing transmittance.

<λ70>

In the optical glass of the first embodiment, the upper limit of λ70 is preferably 435 nm, with 430 nm, 425 nm, 420 nm, 415 nm, 410 nm, 405 nm, and 400 nm being more preferred, from the perspective of improving transmittance at the desired wavelength. There is no particular restriction on the lower limit of λ70, but from the perspective of achieving both a high refractive index and a high refractive index, 300 nm is preferred, with 310 nm, 320 nm, 330 nm, 340 nm, and 350 nm being more preferred, from the perspective of achieving both a high refractive index and a high refractive index.

λ70, which indicates an external transmittance of 70%, is not the best indicator of the properties of the glass of the present invention because it depends on the internal transmittance and refractive index of the glass. However, a λ70 within the above range is preferred as a standard.

(Manufacturing of optical glass)

The optical glass of the embodiments of the present invention can be produced by blending glass raw materials into the aforementioned predetermined composition and using the blended glass raw materials in accordance with conventional glassmaking methods. For example, a plurality of compounds can be blended and thoroughly mixed to form a batch of raw materials. This batch of raw materials is then placed in a crucible made of refractory bricks and heated to form molten glass. After further clarification and homogenization, the molten glass is shaped and slowly cooled to produce the optical glass. The clarification or homogenization steps can also be performed by melting in a suitable platinum crucible. When melting in a platinum crucible, the melting can be performed in a non-oxidizing atmosphere, such as nitrogen or steam, to suppress oxidation of the platinum. Forming and slowly cooling the molten glass can be performed using conventional methods. Furthermore, cullet obtained by rapidly cooling molten glass roughly melted in refractory bricks or quartz crucibles can be used as the raw glass raw materials.

Furthermore, as long as the desired glass components can be introduced into the glass at the desired content, the compounds used in preparing the batch raw materials are not particularly limited. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, hydrates, fluorides, chlorides, and the like.

Furthermore, as a means of suppressing oxidation of glass components caused by Pt, which may be introduced from the platinum crucible, the amount of hydroxyl groups in the glass can be controlled. In the optical glass of this embodiment, since it is primarily composed of silicate, the introduction of excessive hydroxyl groups disrupts the glass structure and may reduce the thermal stability of the glass. This thermal stability affects not only the degree of crystallization during slow cooling of the molten glass, but also the degree of crystallization during reheating. In the case of the optical glass of this embodiment, the latter effect is more pronounced, so appropriately controlling the amount of hydroxyl groups is preferred.

The amount of hydroxyl groups in the glass can be expressed as a βOH value. In the optical glass of the first embodiment, the lower limit of the βOH value represented by the following formula (1) is preferably 0.1 mm ^-1 , more preferably 0.2 mm ^-1 , 0.3 mm ^-1 , and 0.4 mm ^-1 . Furthermore, the upper limit of the βOH value is preferably 1.5 mm ^-1 , more preferably 1.2 mm ^-1 , 1.0 mm ^-1 , 0.9 mm ^-1 , 0.8 mm ^-1 , 0.7 mm ^-1 , and 0.6 mm ^-1 .

βOH=-[ln(B/A)]/t...(1)

Here, in formula (1), t represents the thickness (mm) of the glass used to measure the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to the thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to the thickness direction. In addition, 1n represents the natural logarithm.

Furthermore, the so-called "external transmittance" is the ratio of the intensity of the transmitted light through the glass, I _out , to the intensity of the incident light entering the glass, I _in (I _out /I _in ). This is the transmittance that also takes into account the surface reflection of the glass surface. The transmittance can be obtained by measuring the transmission spectrum using a spectrometer.

By evaluating βOH, the water (and/or hydroxide ions, hereinafter simply referred to as "water") content in the glass can be evaluated. In other words, glass with a high βOH content means a high water content.

By keeping the βOH value within the above range, devitrification can be suppressed, resulting in optical glass with high transmittance. On the other hand, in the present invention, if the βOH value is too high, the thermal stability of the glass when reheated above the glass transition point tends to be reduced. Furthermore, during the cooling step of the glass, maintaining the glass at a temperature higher than near the strain point but below the yield point for minutes or hours may accelerate the clouding and devitrification of the glass.

There are no particular limitations on the method for controlling the βOH value. Examples include using water-containing raw materials as glass feedstock and adding water vapor to the molten atmosphere during the melting step. Furthermore, when melting glass in a melting furnace using refractory bricks, the molten glass is indirectly heated by a gas burner. Water generated by the combustion of the gas burner is introduced into the molten glass. This can appropriately increase the moisture content in the molten glass, thereby maintaining the βOH value within the aforementioned range.

(Manufacturing of optical components, etc.)

Optical components can be manufactured using the optical glass of embodiments of the present invention using known methods. For example, in manufacturing the optical glass, molten glass is poured into a mold and formed into a plate, thereby producing a glass material comprising the optical glass of the present invention. The resulting glass material is then appropriately cut, ground, and polished to produce slices of a size and shape suitable for press molding. The slices are heated to soften them and then pressed (and then heated and pressed) using known methods to produce an optical component blank with a shape similar to that of an optical component. The optical component blank is then annealed and then ground and polished using known methods to produce an optical component.

The optically functional surfaces of the manufactured optical components can also be coated with anti-reflection coatings, total reflection coatings, etc. depending on the intended use.

According to one aspect of the present invention, an optical element composed of the aforementioned optical glass can be provided. Examples of optical element types include lenses such as plane lenses, spherical lenses, and aspherical lenses, prisms, and diffraction gratings. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. The optical element can be manufactured by a method comprising processing a glass molded body composed of the aforementioned optical glass. Examples of such processing include cutting, machining, rough grinding, fine grinding, and polishing. Using the aforementioned glass during such processing can reduce breakage and consistently provide high-quality optical elements.

Second implementation form

In the optical glass of the second embodiment of the present invention, the total content _{of TiO2} and _{Nb2O5 [ TiO2} + _Nb2O5 ] is 20% or more, and the mass ratio of the _total content of _Al2O3 to the total content of _{SiO2 and ZrO2} [ _Al2O3 /( _SiO2 + _ZrO2 )] is greater than zero.

In the optical glass of the second embodiment, the combined content of _TiO₂ and _Nb₂O₅ ( _TiO₂ + _{Nb₂O₅ )} is 20% or greater. The lower limit of this combined content is preferably 22%, with 24%, 26%, 28%, ₃₃ %, 37%, 40%, and 42% being more preferred. The upper limit of this combined content is preferably 70%, with 60%, 57%, 55%, 53%, 50%, and 46% being more preferred.

_TiO2 and _Nb2O5 are components that contribute to a high refractive index without significantly increasing _the specific gravity. Therefore, in order to obtain glass with the desired specific gravity and refractive index properties, the combined content _{of TiO2} and _Nb2O5 is preferably within the above range.

In the optical glass of the second embodiment, the mass ratio of _{the Al₂O₃} content to the total content of _SiO₂ and _ZrO₂ [ _Al₂O₃ /( _SiO₂ + _ZrO₂ )] is greater than 0. The lower limit of this mass ratio [ _Al₂O₃ /( _SiO₂ + _ZrO₂ )] is preferably 0.0001, and more preferably 0.0003, 0.0005, 0.0007, 0.0010 _, 0.0050, 0.0100, 0.0200, 0.0250, 0.0350, _and 0.0450. The upper limit of this mass ratio is preferably 0.3000, and more preferably 0.2500, 0.2000, 0.1500, and 0.1000.

By keeping _the mass ratio [ _Al₂O₃ /( _SiO₂ + _ZrO₂ )] within the above range, erosion of refractory bricks during molten glass can be suppressed. Furthermore, compared to glass with this ratio outside the above range, this ratio improves thermal stability and devitrification during heating, and delays crystallization during cooling of the molten glass. On the other hand, if this mass ratio is too high, not only will the refractive index nd be reduced, but thermal stability may also be impaired, potentially leading to devitrification.

The following describes preferred aspects of the optical glass according to the second embodiment.

In the optical glass of the second embodiment, the upper limit _of the mass ratio of the total content _{of B2O3} and _P2O5 to the total content of _SiO2 and _Al2O3 [( _B2O3 + _P2O5 ) / ( _SiO2 + _Al2O3 )] is preferably 0.30, and more preferably _0.26 , _0.21 , 0.18, 0.16, 0.15, 0.14, 0.12, 0.10, 0.90, _and 0.08. The lower limit of this mass ratio is preferably 0.00, and more preferably 0.01, 0.02, 0.03, _0.04 , and 0.05.

By keeping the mass ratio [( _B2O3 + _P2O5 )/( _SiO2 + _Al2O3 )] within the above range, erosion of the _glass quality of _the refractory bricks during glass melting _can be suppressed. If the mass ratio is too high, erosion of the refractory bricks may increase, reducing the homogeneity of the molten glass and the devitrification resistance.

In the optical glass of the second embodiment, _{the upper limit of the mass ratio of the total content of BaO, La2O3, Gd2O3 , and WO3} to _the total content of CaO, SrO, and _Y2O3 [(BaO+ _La2O3 + _Gd2O3 + _{WO3 )} /(CaO+SrO+ _Y2O3 )] is preferably _3.0 , and more preferably 2.7, 2.0, 1.9, 1.8, _1.7 , and 1.6, respectively. The lower limit of this mass ratio is preferably 0.0, and more preferably 0.5, 0.8, 1.0, and 1.2, respectively.

By maintaining the mass ratio [(BaO + La ₂ O ₃ + Gd ₂ O ₃ + WO ₃ ) / (CaO + SrO + Y ₂ O ₃ )] within the above range, the use of components with excessively large atomic weights or high-refractive-index components that promote oxygen incorporation can be limited, thereby reducing the specific gravity of the glass. On the other hand, if this mass ratio is too high, the increased specific gravity of the glass reduces the dynamic viscosity of the molten glass, making it difficult to control the glass flow and potentially degrading productivity. Furthermore, there is a risk of increased erosion of refractory bricks.

In the optical glass of the second embodiment, the upper limit of the total content of _Li₂O , _Na₂O , and _K₂O [ _Li₂O + _Na₂O + _K₂O ] is preferably 13%, with 11%, 10%, 8.0%, 6.0%, 5.0%, and 4.0% being more preferred. Furthermore, the lower limit of the total content is preferably 0.00%, with 0.01%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, and 3.0% being more preferred.

By keeping the combined content [ _Li2O + _Na2O + _K2O ] within the above range, the glass viscosity can be appropriately maintained, thereby improving glass productivity. Furthermore, by suppressing light absorption from reducing components generated by Ti or Nb, and by promoting the elimination of electronic defects in the glass by lowering the melting temperature or slow cooling, the internal transmittance at 460nm can be increased. Furthermore, the corrosion of refractory bricks during glass melting can be suppressed. On the other hand, if the combined content is too low, the solubility of the glass raw materials will deteriorate, and it will be necessary to set the melting temperature of the raw materials higher. As a result, the deterioration of refractory bricks will be promoted, and productivity will deteriorate. Conversely, if the combined content is too high, the viscosity of the glass will decrease, and this will cause a decrease in thermal stability, which may worsen productivity. Furthermore, the specific resistivity of the molten glass decreases, reducing the heating efficiency when heating the molten glass by applying electricity, resulting in a decrease in the glass's solubility and the risk of deteriorating productivity. The higher _{the Al2O3} content in the glass, the better it is to adjust the content to avoid excessive levels.

In the optical glass of the second embodiment, the lower limit of _{the Al₂O₃} content is preferably 0.01%, and more preferably 0.05%, 0.08%, 0.10%, 0.13%, 0.16%, 0.20%, 0.30%, 0.50%, 0.70%, and 1.0%. The upper limit of _{the Al₂O₃} content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 2.0%.

When melting glass in a refractory furnace, _Al₂O₃ from the bricks is introduced into _the molten glass. Therefore, even when the glass raw materials do not contain _Al₂O₃ , the glass produced in a refractory furnace _will contain trace amounts of _Al₂O₃ . When _{the Al₂O₃ content} is within the above range, compared _{to Al₂O₃} contents outside this range, thermal stability is improved, devitrification during heating is suppressed, and crystallization during cooling of the molten glass is suppressed. However, since _Al₂O₃ has a minimal effect on reducing specific _gravity and is a component that lowers the refractive index, a lower _Al₂O₃ content is preferred for obtaining glass with a high refractive index _and low specific _gravity . Furthermore, if the _Al2O3 content is too high, the devitrification resistance of the glass will be reduced, the glass transition temperature (Tg) will be increased, and there is a risk of reduced thermal stability. On the other hand, if the _Al2O3 content is too low, there is a risk of increased corrosion of _the refractory _bricks .

Regarding the optical glass of the second embodiment, the contents and ratios of the glass components other than those described above can be the same as those of the first embodiment. Furthermore, the glass properties, production of the optical glass, and production of optical elements in the second embodiment can also be the same as those of the first embodiment.

[Example]

The present invention is described in more detail below using examples. However, the present invention is not limited to the embodiments shown in the examples.

(Example 1)

In the following steps, glass samples with the glass compositions shown in Tables 1 and 2 were prepared and various evaluations were performed.

[Production of optical glass]

First, oxides, hydroxides, carbonates, and nitrates corresponding to the glass's constituents are prepared as raw materials. These raw materials are weighed and blended to produce the optical glass compositions shown in Tables 1 and 2, and the raw materials are thoroughly mixed. The resulting blended raw materials (batch raw materials) are placed in a crucible made of refractory oxides and heated at 1150°C to 1450°C for one hour to form a molten glass. The molten glass is then transferred to a platinum crucible and stirred for homogenization. Once clear, the molten glass is cast into a preheated metal mold. The cast glass is heat treated at a temperature 100°C below the glass transition temperature (Tg) for 30 minutes and then cooled to room temperature in the furnace to obtain a glass sample.

Furthermore, in the embodiment, the amount of raw materials is approximately 150g based on oxide.

[Confirmation of glass composition]

The glass samples obtained were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to determine the contents of the various glass components, confirming the compositions shown in Tables 1 and 2.

[Measurement of optical properties]

The resulting glass sample was further annealed near the glass transition temperature (Tg) for approximately 30 minutes to 2 hours, then cooled in a furnace at a rate of -30°C/hour to room temperature to obtain an annealed sample. The refractive indices nd, ng, nF, and nC, as well as the Abbe numbers νd, τ460, τ440, λτ90, λτ80, λτ5, and λ70 of the annealed sample were measured. The results are shown in Table 3.

(i) Refractive index nd, ng, nF, nC and Abbe number νd

For the annealed sample described above, the refractive indices nd, ng, nF, and nC were measured according to the JIS standard JIS B 7071-1 refractive index measurement method, and the Abbe number νd was calculated using the following formula.

νd=(nd-1)/(nF-nC)

(ii) τ460, τ440

Measure internal transmittance (τ460, τ440) at wavelengths of 460nm and 440nm.

For two glass samples of different thicknesses, the internal transmittance was calculated using the following formula using the measured transmittance values including surface reflection loss at wavelengths of 460 nm and 440 nm. The thicknesses of the glass samples, d ₁ and d ₂ , were 2.0 mm ± 0.1 mm and 10.0 mm ± 0.1 mm, respectively.

Here

τ: internal transmittance of glass at sample thickness _d2

△d: Thickness difference of sample [d ₂ -d ₁ ]

T1: Transmittance including surface reflection loss obtained with sample thickness _d1

T2: Transmittance including surface reflection loss obtained with the sample thickness _d2

(iii)λτ90, λτ80, λτ5, λ70

The wavelength at which internal penetration is 90% (λτ90), the wavelength at which internal penetration is 80% (λτ80), the wavelength at which internal penetration is 5% (λτ5), and the wavelength at which external penetration is 70% (λ70) are measured. Internal penetration is calculated using the above formula.

[Specific Gravity]

Specific gravity was measured using the Archimedean method. The results are shown in Table 3.

[Glass transition temperature Tg]

The glass transition temperature (Tg) was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH JAPAN Co., Ltd. at a heating rate of 10°C/min. The results are shown in Table 3.

[Liquidus Temperature LT]

The liquidus temperature (LT) is determined as follows. 10cc (10ml) of glass is placed in a platinum crucible and melted at 1250°C to 1450°C for 20-30 minutes. The mixture is then cooled to below the glass transition temperature (Tg). The glass and platinum crucible are then placed in a melting furnace at a predetermined temperature and held for two hours. The temperature is maintained at or above 800°C, with intervals of 5°C or 10°C for two hours. After cooling, the glass is observed under a 100x optical microscope to detect the presence of crystals. The lowest temperature at which no crystals precipitate is defined as the liquidus temperature. The results are shown in Table 3.

[Pt content]

The Pt content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The results are shown in Table 3.

(Example 2)

[Erosion test of refractory bricks]

Glass samples composed of glass compositions No. 13, 26, 27, 28 in Table 1 and Comparative Example A were prepared using the same steps as Example 1 and evaluated for refractory brick erosion using the following procedure.

A 40cc glass sample was melted in a platinum crucible at 1280°C for 30 minutes. A cylindrical brick sample (AGC Ceramics ZB-1711VF, _SiO₂ : _ZrO₂ : _Al₂O₃ ratio approximately 1:4:5, diameter 20mm, length 100mm ₎ was immersed in the melted glass sample in the platinum crucible and heated at 1280°C for 72 hours. After heating, the brick sample was removed.

The removed brick sample was cut in half longitudinally through the center of the sample. The width of the sample in the cross section was equivalent to its diameter. A photograph of the cross section is shown in Figure 1. As shown in Figure 1, the comparative example exhibits damage resembling a necking at the liquid surface of the molten glass sample during immersion. Furthermore, the portion of the sample immersed in the molten glass was eroded overall, reducing its diameter. On the other hand, the brick sample in the example exhibited no noticeable damage resembling a necking, and erosion was minimal at the portion immersed in the molten glass sample.

The removed brick samples were evaluated as follows. First, the diameter of the cross-section before the corrosion test, as shown in Figure 2, was measured. The minimum diameter near the contact point with the glass liquid surface after the corrosion test (diameter at the neckline) and the diameter 25 mm below the neckline were measured. The increase or decrease in diameter (%) and the average increase or decrease (ΔD) after the corrosion test were evaluated based on the following formula. The diameter does not include glass adhering to the brick sample surface or any deteriorated glass.

Increase/decrease rate _DN (%) = ([minimum diameter (diameter at the neck position)] - [diameter before erosion test]) / [diameter before erosion test] × 100

Increase/decrease rate D ₂₅ (%) = ([Diameter 25 mm below the neck position after the erosion test] - [Diameter before the erosion test]) / [Diameter before the erosion test] × 100

Average increase/decrease rate △D = (increase/decrease rate _DN + increase/decrease rate _D25 )/2

In the above formula, the brick sample diameter was measured three times using a digital vernier caliper capable of displaying to 0.01 mm. The average value (unit: mm) was rounded to the second decimal place to obtain the first decimal place. Based on the absolute value of the average increase or decrease rate ΔD (|ΔD|), the degree of corrosion was determined using the classification shown in Table 4. The results are shown in Table 5.

(Example 3)

Using the optical glasses produced in Example 1, lens blanks were prepared using conventional methods. The lens blanks were then processed using conventional methods such as grinding to produce various lenses.

The optical lenses produced include various types of lenses, such as plane lenses, biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses. Components obtained by cutting optical glass without heat softening can also be used as lens blanks.

Various lenses, when combined with lenses composed of other optical glass compositions, can effectively correct secondary chromatic aberration.

Furthermore, because glass has a low specific gravity, each lens weighs less than lenses with comparable optical properties and size, making it suitable for use in goggle- or spectacles-type AR displays. Similarly, prisms can be made using the various optical glasses produced in Example 1.

The embodiments disclosed herein are to be construed in all respects as illustrative only and not restrictive. The scope of the present invention is defined not by the above description but by the scope of the patent application, and is intended to encompass all modifications within the meaning and scope equivalent to those of the patent application.

For example, by adjusting the composition of the glass composition described in the specification, an optical glass according to one embodiment of the present invention can be produced.

Furthermore, it is of course possible to combine two or more items exemplified or described as preferred scopes in the description.

Claims (13)

An optical glass having a refractive index nd of 1.87 or greater, a _TiO2 content of 10.0 mass% or greater, a mass ratio of the total content of BaO, _La2O3 , _Gd2O3 , _{and WO3} to the total content _of CaO, _SrO , and _{Y2O3 [} (BaO+ _La2O3 + _Gd2O3 + _WO3 )/(CaO+ _{SrO + Y2O3} )] of 2.0 or less, a mass ratio of the total content _{of B2O3} and _P2O5 to the total content _{of SiO2} and _Al2O3 [( _B2O3 + _P2O5 )/( _SiO2 + _Al2O3 )] of 0.10 or less, _and a total content of _Li2O , _Na2O , and _K2O [ _Li2O + _Na2O +K2O _] of _{0.10 or less} . O] is 10 mass% or less, and the mass ratio of the content of Al ₂ O ₃ to the total content of SiO ₂ and ZrO ₂ [Al ₂ O ₃ /(SiO ₂ +ZrO ₂ )] is greater than 0. An optical glass having a refractive index nd of 1.87 or greater, a _TiO2 content of 10.0 mass% or greater, a combined content of _{TiO2 and Nb2O5} [ _TiO2 + _Nb2O5 ] _of 20 mass% or _greater , a mass ratio of _{the Al2O3} content to the combined content of _SiO2 and _ZrO2 [ _Al2O3 /( _SiO2 + _ZrO2 )] greater than 0, and _a mass ratio of _the combined content of _B2O3 and _P2O5 to the combined content of _{SiO2 and Al2O3} [ _{( B2O3} + _P2O5 )/ _{( SiO2} + _Al2O3 )] of _0.15 or less. The optical glass of claim 2, wherein the mass ratio of the total content of TiO ₂ , Nb ₂ O ₅ and ZrO ₂ to the total content of B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ and GeO ₂ [(TiO ₂ + Nb ₂ O ₅ + ZrO ₂ )/(B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ + GeO ₂ )] is 1.8 or more, and the mass ratio of the total content of BaO, La ₂ O ₃ , Gd ₂ O ₃ and WO ₃ to the total content of CaO, SrO and Y ₂ O ₃ [(BaO + La ₂ O ₃ + Gd ₂ O ₃ + WO ₃ )/(CaO + SrO + Y ₂ O ₃ )] is 3.0 or less. The optical glass of claim 2, wherein the mass ratio of the total content of TiO ₂ , Nb ₂ O ₅ and ZrO ₂ to the total content of B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ and GeO ₂ [(TiO ₂ +Nb ₂ O ₅ +ZrO ₂ )/(B ₂ O ₃ +SiO ₂ +Al ₂ O ₃ +GeO ₂ )] is 1.8 or more, and the mass ratio of the total content of B ₂ O ₃ , ZnO, La ₂ O ₃ , Gd ₂ O ₃ and WO ₃ to the total content of SiO ₂ , CaO, TiO ₂ and Nb ₂ O ₅ [(B ₂ O ₃ +ZnO +La ₂ O ₃ +Gd ₂ O ₃ +WO ₃ )/(SiO ₂ +CaO +TiO ₂ +Nb ₂ O ₅ )] is less than 0.15. The optical glass of claim 3, wherein the mass ratio of the total content of TiO ₂ , Nb ₂ O ₅ and ZrO ₂ to the total content of B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ and GeO ₂ [(TiO ₂ +Nb ₂ O ₅ +ZrO ₂ )/(B ₂ O ₃ +SiO ₂ +Al ₂ O ₃ +GeO ₂ )] is 1.8 or more, and the mass ratio of the total content of B ₂ O ₃ , ZnO, La ₂ O ₃ , Gd ₂ O ₃ and WO ₃ to the total content of SiO ₂ , CaO, TiO ₂ and Nb ₂ O ₅ [(B ₂ O ₃ +ZnO +La ₂ O ₃ +Gd ₂ O ₃ +WO ₃ )/(SiO ₂ +CaO +TiO ₂ +Nb ₂ O ₅ )] is less than 0.15. The optical glass of claim 1, wherein the total content of Li ₂ O, Na ₂ O, and K ₂ O [Li ₂ O + Na ₂ O + K ₂ O] is not less than 0.5 mass % and not more than 10 mass %. The optical glass of claim 1, wherein the content of Al ₂ O ₃ is 0.005% by mass or greater. The optical glass of claim 1, wherein the total content of TiO ₂ and Nb ₂ O ₅ [TiO ₂ +Nb ₂ O ₅ ] is 20 mass % or more. The optical glass of claim 1, wherein the total content of _Al2O3 , _SiO2 , _ZrO2 , _{P2O5, B2O3 , TiO2, Nb2O5 , WO3} , _Bi2O3 , _Li2O , _Na2O , _K2O , _Cs2O , _MgO , _CaO , _SrO , BaO, _ZnO , _La2O3 , _Gd2O3 , _Y2O3 , _GeO2 , _Ta2O5 , _Sc2O3 , _HfO2 , _{Lu2O3 , and Yb2O3 is 95 % by mass or more} . The optical glass of claim 1 satisfies any one or more of the following: a SiO ₂ content of 35.0 mass % or less; a Al ₂ O ₃ content of 6.0 mass % or less; a MgO content of 5.0 mass % or less; a total SiO ₂ and Al ₂ O ₃ content [SiO ₂ +Al ₂ O ₃ ] of 40 mass % or less; a mass ratio of the Al ₂ O ₃ content to the total SiO ₂ and ZrO ₂ content [Al ₂ O ₃ /(SiO ₂ +ZrO ₂ )] of 0.1500 or less; a mass ratio of the total TiO ₂ , Nb ₂ O ₅ , and ZrO ₂ content to the total B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , and GeO ₂ content [(TiO ₂ +Nb ₂ O ₅ +ZrO ₂ )/(B ₂ O ₃ +SiO ₂ +Al ₂ O ₃ +GeO ₂ )] is 1.8 or more; the total content of TiO ₂ , Nb ₂ O ₅ and ZrO ₂ [TiO ₂ +Nb ₂ O ₅ +ZrO ₂ ] is 25 mass % or more; and the mass ratio of the TiO ₂ content to the Nb ₂ O ₅ content [TiO ₂ /Nb ₂ O ₅ ] is 4.0 or less. The optical glass of claim 1 satisfies any one or more of the following: a SiO ₂ content of 25.0 mass % or less; a Al ₂ O ₃ content of 3.0 mass % or less; a B ₂ O ₃ content of 3.0 mass % or less; a Li ₂ O content of 5.0 mass % or less; a Na ₂ O content of 3.0 mass % or less; a MgO content of 5.0 mass % or less; a CaO content of 6.0 mass % or more; a La ₂ O ₃ content of 11.76 mass % or less; a TiO ₂ content of 14.5 mass % or more; a Nb ₂ O ₅ content of 10.0 mass % or more; a total SiO ₂ and Al ₂ O ₃ content [SiO ₂ +Al ₂ O ₃ ] of 25 mass % or less; a total B ₂ O ₃ and P ₂ O ₅ content [B ₂ O ₃ +P ₂ O ₅ ] is 0.1% by mass or more; the _total content _{of B2O3 and P2O5 [ B2O3 + P2O5} ] is 3% by mass or less; the total content of _Li2O , _Na2O , and _K2O [ _Li2O + _Na2O + _K2O ] is 8.0% by mass or less _{; the mass ratio of the total content of B2O3 and P2O5 to the total content of SiO2 and Al2O3 [(B2O3 +P2O5 ) / ( SiO2 + Al2O3 ) ] is 0.03 or more ; the mass} ratio of the content of _Al2O3 to the total content _{of SiO2} and _ZrO2 [ _Al2O3 / _{(SiO2 + ZrO2} )] is 0.1500 or less; _TiO2 and _Nb2O the total content of TiO ₂ , Nb ₂ O _{5 , and ZrO 2 [TiO 2 + Nb 2 O 5 ] is 33} mass % or more; the mass ratio of the total content of TiO ₂ , Nb 2 O ₅ , and ZrO ₂ to the total content of B ₂ O ₃ , SiO ₂ , Al ₂ O 3 , and GeO ₂ [(TiO ₂ + Nb ₂ O ₅ + ZrO ₂ ) / (B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ + GeO ₂ )] is 1.8 or more; the total content of TiO ₂ , Nb ₂ O ₅ , and ZrO ₂ [TiO ₂ + Nb ₂ O ₅ + ZrO ₂ ] is 40 mass % or more; the total content of B ₂ O ₃ , ZnO, La ₂ O ₃ , Gd ₂ O ₃ , and WO ₃ to the total content of SiO ₂ , CaO, TiO ₂ , and Nb The mass ratio of the total content _{of B2O3} + ZnO + _La2O3 + _{Gd2O3 + WO3} / _{( SiO2} + CaO + _TiO2 + _Nb2O5 )] is 0.01 or more; the mass ratio of the total content of _B2O3 , _ZnO , _La2O3 , _Gd2O3 and _WO3 to the total content _{of SiO2} , CaO, _TiO2 and _Nb2O5 [( _{B2O3 +} ZnO _{+ La2O3} + _Gd2O3 + _WO3 ) / ( _SiO2 + _CaO + _TiO2 + _Nb2O5 )] _is 0.19 or less; _the mass ratio of the total content _{of TiO2} , CaO, SrO and _Y2O3 to _the total _{content of} BaO _{, MgO} , _Nb2O5 The mass ratio of the total content of _Ta2O5 , _WO3 , _{Bi2O3 , La2O3} and _Gd2O3 [( _{TiO2 +} CaO+SrO+ _Y2O3 ) _/ ( _BaO +MgO+ _Nb2O5 +Ta2O5+WO3+ _Bi2O3 +La2O3+ _Gd2O3 )] _is 0.7 or _more ; the mass ratio of the _content of _TiO2 to the content _{of Nb2O5} [ _TiO2 / _Nb2O5 ] is _3.0 or less; the total content of MgO, CaO, _SrO , and _BaO [ _MgO +CaO+SrO+ _BaO ] is 18.0 mass% or more; _Li2O , Na2O and _K2O are 0.5% by weight or less; the total content of _MgO , CaO, _SrO , and BaO _{is 1 ...} The mass ratio of the total content of O to the total content of MgO, CaO, SrO, and BaO [( _Li2O + _Na2O + _K2O )/(MgO+CaO+SrO+BaO)] is 0.5 or less; the ratio of the total value of the value obtained by dividing the content of _Li2O by 29.9, the value obtained by dividing the content of _B2O3 by 69.6, the value obtained by dividing the content of _Li2O by 29.9, the value obtained by dividing the content of _Na2O by 62.0, and the value obtained by dividing the content of _K2O by 94.2 [( _Li2O /29.9)/{(B2O3/69.6+Li2O/29.9+Na2O/62.0+K2O/94.2)}] is 0.45 or more; the ratio of the total value obtained by dividing the content of _{Li2O by} 29.9, the value obtained by dividing the _{content of B2O3} by 69.6, the value obtained by dividing the content of _Li2O by 29.9, the value obtained by dividing the content of _Na2O by 62.0, and the value obtained by dividing the content of K2O by _94.2 The ratio of the total value of the O ₃ content divided by 69.6, the value of the Li ₂ O content divided by 29.9, the value of the Na ₂ O content divided by 62.0, and the value of the K ₂ O content divided by 94.2 [(Li ₂ O/29.9)/{(B ₂ O ₃ /69.6 + Li ₂ O/29.9 + Na ₂ O/62.0 + K ₂ O/94.2)}] is 0.90 or less; and the Abbe number νd is 30.0 or less. The optical glass of claim 1 satisfies at least one of the following: a _SiO2 content of not less than 5.0 mass% and not more than 25 mass%; _{a Al2O3} content of not less than 0.005 mass% and not more than 3.0 mass%; _{a B2O3} content of not less than 0.4 mass% and not more than 3.0 mass%; a _Li2O content of not less than 0.5 mass% and not more than 5.0 mass%; a CaO content of not less than 6.0 mass% and not more than 30.0 mass%; a _TiO2 content of not less than 10.0 mass% and not more than 40.0 mass%; and a _Nb2O5 content of _not less than 10.0 mass% and not more than 35.0 mass%. An optical element is composed of the optical glass according to any one of claims 1 to 12.