JP2023053164A - Optical glass and optical element - Google Patents

Abstract

An object of the present invention is to provide an optical glass and an optical element with reduced reduction color. SOLUTION: It contains 1 to 45% by mass of B2O3, 10 to 60% by mass of La2O3, and at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3 and Bi2O3, and is represented by the following formula (2): An optical glass having a βOH value of 0.1 to 2.0 mm -1 . βOH=-[ln(B/A)]/t … (2) [Selection] None

Description

The present invention relates to optical glasses and optical elements.

2. Description of the Related Art In recent years, as devices such as imaging optical systems and projection optical systems have become more sophisticated and compact, the demand for optical glass with a high refractive index has increased as an effective material for optical elements.

A high-refractive-index optical glass such as that described in Patent Document 1 usually contains a large amount of high-refractive-index components such as Ti, Nb, W, and Bi as glass components. These components are easily reduced during the melting process of the glass, and these reduced components absorb light on the short wavelength side of the visible light range, resulting in the coloring of the glass (hereinafter sometimes referred to as "reduction color"). ).

JP 2007-112697 A

An object of the present invention is to provide an optical glass and an optical element with reduced reduction color.

The gist of the present invention is as follows.
[1] containing 1 to 45% by mass of B ₂ O ₃ and 10 to 60% by mass of La ₂ O ₃ ,
comprising _{at least} one oxide selected from the group consisting of _TiO2 , _Nb2O5 , _WO3 and _Bi2O3 ;
An optical glass having a βOH value of 0.1 to 2.0 mm ^-1 represented by the following formula (2).
βOH=-[ln(B/A)]/t (2)
[In formula (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, and A represents the external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with the thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is the natural logarithm. ]

[2] The optical glass of [1], containing 0.1 to 25% by mass of SiO ₂ .

[3] The optical glass of [1], containing 0.5 to 15% by mass of SiO ₂ , 1 to 30% by mass of B ₂ O ₃ and 20 to 60% by mass of La ₂ O ₃ .

[4] The optical glass according to any one of [1] to [3], wherein the content of B ₂ O ₃ is greater than the content of SiO ₂ in % by mass.

[5] The mass ratio of the content of TiO ₂ to the total content of B ₂ O ₃ and La ₂ O ₃ [TiO ₂ /(B ₂ O ₃ +La ₂ O ₃ )] is 0.030 or more, [1 ] to [4].

[6] Abbe number νd is 20 to 45,
The optical glass according to any one of [1] to [5], which has a refractive index nd of 1.75 to 2.50.

[7] An optical element made of the optical glass described in any one of [1] to [6] above.

ADVANTAGE OF THE INVENTION According to this invention, the optical glass and optical element which reduced the reduction color can be provided.

One embodiment of the present invention is described below. In the present invention and this specification, unless otherwise specified, glass compositions are indicated on the basis of oxides. Here, "glass composition based on oxides" refers to the glass composition obtained by conversion assuming that the glass raw materials are all decomposed during melting and exist as oxides in the glass, and the notation of each glass component is customary. It is described as SiO ₂ , TiO ₂ and the like, following the standard. The content and total content of the glass components are based on mass unless otherwise specified, "%" means "mass %" and "ppm" means "mass ppm".

The content of the glass component can be quantified by known methods such as inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Further, in the present specification and the present invention, the content of a component of 0% means that the component is not substantially contained, and the component is allowed to be contained at the level of unavoidable impurities.

In this specification, the refractive index refers to the refractive index nd at the helium d-line (wavelength 587.56 nm), unless otherwise specified.

The Abbe number νd is used as a value representing properties related to dispersion, and is represented by the following formula (1). Here, nF is the refractive index of blue hydrogen at the F-line (wavelength 486.13 nm), and nC is the refractive index of red hydrogen at the C-line (656.27 nm).
νd=(nd−1)/(nF−nC) (1)

An optical glass according to an embodiment of the present invention is
1 to 45% by mass of B ₂ O ₃ and 10 to 60% by mass of La ₂ O ₃ ,
comprising _{at least} one oxide selected from the group consisting of _TiO2 , _Nb2O5 , _WO3 and _Bi2O3 ;
The value of βOH shown in the following formula (2) is 0.1 to 2.0 mm ^-1 .
βOH=-[ln(B/A)]/t (2)
[In formula (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, and A represents the external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with the thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is the natural logarithm. ]

The optical glass (hereinafter sometimes simply referred to as "glass") according to the present embodiment will be described in detail below.

The glass according to this embodiment contains 1 to 45% B ₂ O ₃ . The lower limit of the B ₂ O ₃ content is preferably 2%, more preferably 3%, 4% and 6% in that order. Also, the upper limit of the B ₂ O ₃ content is preferably 30%, more preferably 25%, 20% and 15% in that order.

B ₂ O ₃ is a network forming component of the glass, and has the function of maintaining low dispersion and improving the thermal stability of the glass. On the other hand, if the content of B ₂ O ₃ is high, the volatilization amount of the glass component may increase during melting of the glass. Also, the devitrification resistance tends to decrease. Therefore, the content of B ₂ O ₃ is preferably within the above range.

The glass according to this embodiment contains 10 to 60% La ₂ O ₃ . The lower limit of the La ₂ O ₃ content is preferably 20%, more preferably 22%, 24%, 27% and 30% in that order. The upper limit of the La ₂ O ₃ content is preferably 57%, more preferably 55% and then 53% in that order.

La ₂ O ₃ has the function of increasing the refractive index nd. It also has a function of enhancing chemical durability. On the other hand, when the content of La ₂ O ₃ increases, the specific gravity increases and the thermal stability of the glass decreases. Therefore, it is preferable to set the content of La ₂ O ₃ within the above range.

The glass according to this _embodiment contains at least one oxide selected from _the group consisting of _TiO2 , _Nb2O5 , _WO3 and _Bi2O3 . TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ are all components that contribute to increasing the refractive index.

In the glass according to this embodiment, the value of βOH represented by the following formula (2) is 0.1 to 2.0 mm ^-1 . The lower limit of the value of βOH is preferably 0.2 mm ^-1 , more preferably 0.25 mm ^-1 , 0.3 mm ^-1 and 0.35 mm ^-1 in that order. Also, the upper limit of the value of βOH is preferably 1.8 mm ^-1 , more preferably 1.6 mm ^-1 , 1.5 mm ^-1 , 1.4 mm ^-1 and 1.2 mm ^-1 in that order.
βOH=-[ln(B/A)]/t (2)

Here, in the above formula (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, and A is the wavelength 2500 nm when light is incident on the glass in parallel with the thickness direction. and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Moreover, ln is a natural logarithm in said Formula (2). The unit of βOH is mm ⁻¹ .

The "external transmittance" is the ratio of the intensity Iout of the transmitted light that has passed through the glass to the intensity Iin of the incident light that enters the glass (Iout/Iin), that is, the transmittance that also considers the surface reflection on the surface of the glass. and the transmittance is obtained by measuring the transmission spectrum using a spectrophotometer.

βOH represented by the above formula (2) means absorbance due to hydroxyl groups. Therefore, by evaluating βOH, the water (and/or hydroxide ion, hereinafter simply referred to as "water") content in the glass can be evaluated. That is, a high βOH glass means a high water content in the glass.

By increasing the water content in the glass to increase the value of βOH, the reduction color can be reduced and the annealing time can be shortened. In addition, defoaming and clarification effects can be obtained. On the other hand, if the value of βOH is too high, the amount of volatiles from the molten glass tends to increase. Therefore, it is preferable to set the value of βOH within the above range.

The method for increasing the βOH of the glass is not particularly limited, but for example, an operation for increasing the water content in the molten glass in the melting process can be mentioned. The operation for increasing the water content in the molten glass includes, for example, a process of adding water vapor to the melting atmosphere and a process of bubbling a gas containing water vapor into the melt.

(glass component)
Glass components other than the above in this embodiment will be described in detail below.

In the glass according to the present embodiment, the lower limit of the SiO ₂ content is preferably 0.1%, more preferably 0.5%, 1%, 1.5%, 2%, 3% in this order. . The upper limit of the SiO ₂ content is preferably 25%, more preferably 15%, 10%, 8% and 7% in that order.

SiO ₂ is a network-forming component of glass and works to improve the thermal stability, chemical durability and weather resistance of glass. On the other hand, when the SiO ₂ content is high, the devitrification resistance of the glass may deteriorate. Therefore, it is preferable to set the content of SiO ₂ within the above range.

In the glass according to the present embodiment, the P ₂ O ₅ content is preferably less than 7%, more preferably 5% or less, 4% or less, 3% or less, 2% or less, and 1% or less in that order. . The content _{of P2O5} may be 0%.

P ₂ O ₅ is a component that lowers the refractive index nd and is also a component that lowers the thermal stability of the glass. Therefore, it is preferable to set the content of P ₂ O ₅ within the above range.

In the glass according to the present embodiment, the content of Al ₂ O ₃ is preferably 5% or less, more preferably 4% or less, 3% or less, 2% or less, and 1% or less in this order. The content of Al ₂ O ₃ may be 0%.

Al ₂ O ₃ is a glass component that works to improve the chemical durability and weather resistance of glass, and can be considered as a network-forming component. On the other hand, when the content of Al ₂ O ₃ increases, the devitrification resistance of the glass decreases. Moreover, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability tend to occur. Therefore, the content of Al ₂ O ₃ is preferably within the above range.

In the glass according to the present embodiment, the lower limit of the total content of SiO ₂ and B ₂ O ₃ [SiO ₂ +B ₂ O ₃ ] is preferably 2%, more preferably 4%, 6%, 8%, 10%. % order is preferred. Further, the upper limit of the total content [SiO ₂ +B ₂ O ₃ ] is preferably 35%,
Furthermore, the order of 30%, 26%, 24% and 22% is more preferable.

SiO ₂ and B ₂ O ₃ are network-forming components of glass, and are components that improve the thermal stability and devitrification resistance of glass. Therefore, the total content of SiO ₂ and B ₂ O ₃ [SiO ₂ +B ₂ O ₃ ] is preferably within the above range.

In addition, in the glass according to the present embodiment, the B ₂ O ₃ content [B ₂ O ₃ ] is preferably larger than the SiO ₂ content [SiO ₂ ] in terms of mass % ([B ₂ O ₃ ]> [ _SiO2 ]). More preferably, the B ₂ O ₃ content is greater than 1.3 times the SiO ₂ content ([B ₂ O ₃ ]>[SiO ₂ ]×1.3).
By making the content of B ₂ O ₃ larger than the content of SiO ₂ , the Abbe number can be increased.

In the glass according to the present embodiment, the upper limit of the ZnO content is preferably 30%, more preferably 25%, 20%, 15%, 10%, 7% and 5% in that order. Moreover, the content of ZnO is preferably more than 0%, and the lower limit thereof is more preferably 0.1%, and more preferably 0.3%, 0.5%, and 1% in this order.

ZnO is a glass component that works to improve the thermal stability of the glass, as well as the meltability and chemical durability of the glass. On the other hand, if the ZnO content is too high, the specific gravity increases. Therefore, the content of ZnO is preferably within the above range.

In the glass according to the present embodiment, the upper limit of the BaO content is preferably 20%, more preferably 19%, 18%, 17% and 16% in this order. Also, the lower limit of the BaO content is preferably 0%, more preferably 2%, 5%, and 10% in that order.

BaO is an effective glass component for maintaining a high refractive index, and also works to improve the thermal stability and devitrification resistance of the glass. On the other hand, when the content increases, the specific gravity increases and the devitrification resistance decreases. Therefore, the content of BaO is preferably within the above range.

In the glass according to the present embodiment, the upper limit of the MgO content is preferably 5%, more preferably 4%, 3%, 2% and 1% in this order. Also, the lower limit of the MgO content is preferably 0%.

In the glass according to the present embodiment, the upper limit of the CaO content is preferably 10%, more preferably 8%, 6%, 4% and 2% in this order. Also, the lower limit of the CaO content is preferably 0%.

In the glass according to the present embodiment, the upper limit of the SrO content is preferably 7%, more preferably 5%, 4%, 3% and 1% in this order. Also, the lower limit of the SrO content is preferably 0%.

MgO, CaO, and SrO are all glass components that work to improve the thermal stability and devitrification resistance of glass. On the other hand, when the content of these glass components increases, the specific gravity increases, the high dispersibility is impaired, and the thermal stability and devitrification resistance of the glass decrease. Therefore, it is preferable that the content of each of these glass components is within the above range.

In the glass according to the present embodiment, the upper limit of the Gd ₂ O ₃ content is preferably 35%, more preferably 30%, 25%, 20%, 17% and 12% in this order. The lower limit of the Gd ₂ O ₃ content is preferably 0%, more preferably 1%, 3%, 4% and 5% in that order.

In the glass according to this embodiment, the upper limit of the Y ₂ O ₃ content is preferably 25%, more preferably 20%, 15%, 10%, 7% and 5% in that order. The lower limit of the Y ₂ O ₃ content is preferably 0%, more preferably 1%, 2% and 3% in that order.

Both Gd ₂ O ₃ and Y ₂ O ₃ are components that contribute to improving the weather resistance of the glass and increasing the refractive index. On the other hand, if the content is too high, the thermal stability of the glass is lowered, and the glass tends to devitrify during production. Therefore, it is preferable that the content of each of these glass components is within the above range.

In the glass according to the present embodiment, the upper limit of the Yb ₂ O ₃ content is preferably 5%, more preferably 4%, 3%, 2% and 1% in that order. Also, the lower limit of the Yb ₂ O ₃ content is preferably 0%.

Yb ₂ O ₃ is a component that contributes to improving weather resistance and increasing the refractive index. On the other hand, Yb ₂ O ₃ has a higher molecular weight than La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ and thus increases the specific gravity of the glass. Increasing the specific gravity of the glass increases the mass of the optical element. For example, if a lens with a large mass is incorporated into an autofocus imaging lens, the power required to drive the lens during autofocus increases, resulting in rapid battery consumption. Therefore, it is desirable to reduce the content of Yb ₂ O ₃ to suppress an increase in the specific gravity of the glass.

In the glass according to this embodiment, the upper limit of the ZrO ₂ content is preferably 18%, more preferably 15%, 12%, 10%, 8% and 7% in this order. The lower limit of the ZrO ₂ content is preferably 0%, more preferably 1%, 2% and 3% in that order.

ZrO ₂ is a component that contributes to increasing the refractive index, and is a glass component that works to improve the thermal stability and devitrification resistance of the glass. On the other hand, if the ZrO ₂ content is too high, the thermal stability tends to decrease. Therefore, the content of ZrO ₂ is preferably within the above range.

In the glass according to the present embodiment, the content of TiO ₂ is preferably more than 0%, and the lower limit thereof is more preferably 0.1%, and furthermore 1%, 3%, 4%, 5%. is more preferable in that order. Also, the upper limit of the content of TiO ₂ is preferably 30%, more preferably 25%.
%, 23%, 21%, 20% in that order.

TiO ₂ is a component that contributes to increasing the refractive index and also works to improve chemical durability. On the other hand, if the content of TiO ₂ is too high, the devitrification resistance may deteriorate. Therefore, it is preferable to set the content of TiO ₂ within the above range.

In the glass according to the present embodiment, the lower limit of the Nb ₂ O ₅ content is preferably 0.1%, more preferably 1%, 3%, 4% and 5% in that order. The upper limit of the Nb ₂ O ₅ content is preferably 35%, more preferably 30%, 25%, 20%, 16%, 15%, 14% and 12% in that order.

Nb ₂ O ₅ is a component that contributes to increasing the refractive index, and also works to improve the thermal stability and chemical durability of the glass. On the other hand, if the content of Nb ₂ O ₅ is too high, the thermal stability of the glass may deteriorate, and the coloration of the glass tends to increase. Therefore, it is preferable to set the content of Nb ₂ O ₅ within the above range.

In the glass according to this embodiment, the lower limit of the total content of Nb ₂ O ₅ and TiO ₂ [Nb ₂ O ₅ +TiO ₂ ] is preferably 13%, more preferably 13.5%, 14%, 14.0%, The order of 5% and 15% is more preferred. The upper limit of the total content [Nb ₂ O ₅ +TiO ₂ ] is preferably 40%, more preferably 35%, 32%, 31% and 30% in that order.

Nb ₂ O ₅ and TiO ₂ are components that contribute to increasing the refractive index. On the other hand, if the content of Nb ₂ O ₅ is too high, the thermal stability and devitrification resistance of the glass are lowered. Therefore, the total content of Nb ₂ O ₅ and TiO ₂ is preferably within the above range.

In the glass according to the present embodiment, the upper limit of the _WO3 content is preferably 25%, more preferably 20%, 15%, 10% and 5% in this order. The lower limit of the _WO3 content is preferably 0%.

WO ₃ has the function of lowering the glass transition temperature Tg. On the other hand, if the _WO3 content is too high, the coloration of the glass increases and the specific gravity increases. Therefore, the content of _WO3 is preferably within the above range.

In the present embodiment, the upper limit of the Bi ₂ O ₃ content is preferably 20%, more preferably 15%, 10%, 5% and 3% in that order. Also, the lower limit of the content of Bi ₂ O ₃ is preferably 0%.

Bi ₂ O ₃ has the function of improving the thermal stability of the glass when contained in an appropriate amount. On the other hand, increasing the Bi ₂ O ₃ content increases the coloration of the glass and also increases the specific gravity. Therefore, the content of Bi ₂ O ₃ is preferably within the above range.

In the glass according to _the present embodiment, the upper limit of the total content of _Nb2O5 , _TiO2 , _WO3 and _Bi2O3 [ _Nb2O5 + _TiO2 + _{WO3 + Bi2O3 ]} is preferably 40 _% . Yes, and more preferably 37%, 35%, 33%, 32% in that order. Also, the lower limit of the total content [Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ ] is preferably 1.0%, more preferably 1.5%, 5%, 10%, 13%, 13.0%. The order of 5%, 14%, 14.5%, 15% is more preferred.

TiO ₂ , WO ₃ and Bi ₂ O ₃ are components that contribute to increasing the refractive index together with Nb ₂ O ₅ . Therefore, the total content [Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ ] is preferably within the above range.

In _{the glass according to the present embodiment, the mass ratio [TiO2/(B2O3 + La2O3 ) ] of the} content of _TiO2 to the total content of _B2O3 and _La2O3 is preferably small. , the lower limit of which is preferably 0.030, furthermore 0.035, 0.040, 0.045, 0.050, 0.055, 0.060, 0.065, 0.070, 0.075 , 0.080, 0.085, 0.090, 0.095, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0 Smaller in the order of .50 is preferred. Also, the upper limit of the mass ratio [TiO ₂ /(B ₂ O ₃ +La ₂ O ₃ )] is preferably 1.5, more preferably 1.0, 0.8 and 0.6 in that order.

Among Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ , TiO ₂ is the component having the greatest effect of increasing the refractive index nd per unit content in mass %. In addition, TiO ₂ is easily reduced during the glass melting process, and when TiO ₂ is reduced, the transmittance in the visible short wavelength region is likely to be significantly reduced. On the other hand, B ₂ O ₃ and La ₂ O ₃ , which are main components in the glass according to the present embodiment, do not cause such problems due to reduction. Therefore, the total content of B ₂ O ₃ and La ₂ O ₃ that does not cause such problems is large with respect to the content of TiO ₂ that significantly reduces the transmittance in the visible short wavelength region, that is, the mass ratio [TiO ₂ /(B ₂ O ₃ +La ₂ O ₃ )] is preferably as small as possible.

In the glass according to the present embodiment, the mass ratio of the content of TiO ₂ to the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ [TiO ₂ /(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )] is preferably 0.05, more preferably 0.25, 0.30, 0.40 and 0.45 in that order. The upper limit of the _mass ratio [ _TiO2 /( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is preferably 1.00, more preferably 0.90, 0.80, or 0.75 _. can also

As described above, TiO ₂ is easily reduced during the glass melting process, and when TiO ₂ is reduced, the transmittance in the visible short wavelength region tends to be significantly reduced. In the present embodiment, among the components that contribute to increasing the refractive index, such as Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ , the content of TiO ₂ that is particularly likely to cause coloration is high. Even when [TiO ₂ /(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )] is within the above range, coloring may occur by introducing a gas into the atmosphere in the melting process or by bubbling the gas into the melt. can suppress the increase in

In the glass according to the present embodiment, the upper limit of the Ta ₂ O ₅ content is preferably 25%, more preferably 20%, 16%, 12%, 8% and 4% in that order. Also, the lower limit of the Ta ₂ O ₅ content is preferably 0%.

Ta ₂ O ₅ is a component that contributes to increasing the refractive index and also works to improve the thermal stability of the glass. On the other hand, if the Ta ₂ O ₅ content is too high, the thermal stability of the glass is lowered, and the unmelted glass material tends to remain unmelted when the glass is melted. Therefore, the content of Ta ₂ O ₅ is preferably within the above range.

In the glass according to the present embodiment, the upper limit of the Li ₂ O content is preferably 10%, more preferably 7%, 5%, 4%, 3%, 2% and 1% in this order. The lower limit of the Li ₂ O content is preferably 0%.

In the glass according to the present embodiment, the upper limit of the Na ₂ O content is preferably 10%, more preferably 7%, 5%, 4%, 2% and 1% in this order. The lower limit of the Na ₂ O content is preferably 0%.

In the glass according to the present embodiment, the upper limit of the K ₂ O content is preferably 10%, more preferably 7%, 5%, 4%, 2% and 1% in this order. The lower limit of the K ₂ O content is preferably 0%.

Li ₂ O, Na ₂ O and K ₂ O all work to lower the liquidus temperature and improve the thermal stability of the glass. decreases. Therefore, the respective contents of Li ₂ O, Na ₂ O and K ₂ O are preferably within the above ranges.

In the glass according to the present embodiment, the upper limit of the Cs ₂ O content is preferably 5%, more preferably 4%, 3%, 2% and 1% in that order. The lower limit of the Cs ₂ O content is preferably 0%.

Cs ₂ O works to improve the thermal stability of the glass, but when the content of these elements increases, the chemical durability and weather resistance deteriorate. Therefore, each content of Cs ₂ O is preferably within the above range.

In the glass according to the present embodiment, the upper limit of the total content of Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O [Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O] is preferably 15%. is more preferred in the order of 10%, 7%, 5%, 3%, 1%. Also, the lower limit of the total content [Li ₂ O+Na ₂ O+K ₂ O+Cs ₂ O] is preferably 0%.

When the lower limit of the total content [Li ₂ O+Na ₂ O+K ₂ O+Cs ₂ O] satisfies the above, the meltability and thermal stability of the glass can be improved, and the liquidus temperature can be lowered. Further, when the upper limit of the total content [Li ₂ O+Na ₂ O+K ₂ O+Cs ₂ O] satisfies the above, a decrease in devitrification resistance can be suppressed.

In the glass according to this embodiment, the content of Sc ₂ O ₃ is preferably 2% or less. Moreover, the lower limit of the content of Sc ₂ O ₃ is preferably 0%.

In the glass according to this embodiment, the upper limit of the HfO ₂ content is preferably 2% or less, more preferably 1%, 0.5%, and 0.1% in that order. Also, the lower limit of the HfO ₂ content is preferably 0%.

Sc ₂ O ₃ and HfO ₂ have the function of increasing the high dispersibility of the glass, but they are expensive components. Therefore, each content of Sc ₂ O ₃ and HfO ₂ is preferably within the above range.

In the glass according to this embodiment, the content of Lu ₂ O ₃ is preferably 2% or less. Moreover, the lower limit of the content of Lu ₂ O ₃ is preferably 0%.

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

In the glass according to this embodiment, the content of GeO ₂ is preferably 2% or less.
Also, the lower limit of the GeO ₂ content is preferably 0%.

GeO ₂ has the function of increasing the high dispersion of glass, but it is by far the most expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of glass, the content of GeO ₂ is preferably within the above range.

The glass according to the present embodiment mainly contains the above-described components, that is, B ₂ O ₃ and La ₂ O ₃ as essential components, and SiO ₂ , P ₂ O ₅ , Al ₂ O ₃ , ZnO, BaO, MgO, _CaO , SrO, _Gd2O3 , _{Y2O3 , Yb2O3} , _{ZrO2 , TiO2 , Nb2O5 ,} WO3 _{, Bi2O3 , Ta2O5} , _Li2O , _Na2O , K ₂ O, Cs ₂ O, Sc ₂ O ₃ , HfO ₂ , Lu ₂ O ₃ and GeO ₂ , and the total content of the above glass components should be greater than 95%. is preferred, more preferably more than 98%, more preferably more than 99%, even more preferably more than 99.5%.

In this embodiment, as a further preferred aspect,
1-45% B ₂ O ₃ , 10-60% La ₂ O ₃ , more than 0% TiO ₂ , more than 0% ZnO,
The mass ratio [ _{TiO2 / ( Nb2O5} + _TiO2 + _WO3 + _Bi2O3 )] of the content of _TiO2 to the total _content of _{Nb2O5 , TiO2} , _WO3 and _Bi2O3 is 0. 4 or more,
Examples thereof include optical glasses having a βOH value of 0.1 to 2.0 mm ⁻¹ as represented by the following formula (2).
βOH=-[ln(B/A)]/t (2)
[In formula (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, and A represents the external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with the thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is the natural logarithm. ]

The contents of _{B2O3 , La2O3} , _TiO2 and ZnO _, the mass ratio _{[ TiO2} /( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )], and the content of βOH in the above more preferred _embodiment As for the values, the more preferable numerical ranges described above can be applied. In addition, the preferred numerical ranges described above can be appropriately applied to the contents and mass ratios of other glass components.

In the glass according to the present embodiment, the content of platinum Pt is preferably less than 10 ppm, more preferably 8 ppm or less, 7 ppm or less, and 5 ppm or less, in that order. Although the lower limit of the Pt content is not particularly limited, it is unavoidably included at about 0.001 ppm.

By setting the Pt content within the above range, it is possible to reduce the coloring of the glass caused by Pt and improve the transmittance.

In the manufacturing process of the glass according to this embodiment, glass raw materials are melted in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include inert gases such as nitrogen, carbon dioxide, argon and helium, and water vapor. Normally, oxygen in the melting atmosphere reacts with platinum, which is the material of the melting vessel (crucible, etc.) to produce platinum dioxide and platinum ions (Pt ⁴⁺ ), which melt into the molten glass, resulting in coloring. occur. In this embodiment, by reducing the oxygen partial pressure in the melting atmosphere, it is possible to suppress the oxidation of platinum and reduce the amount of Pt that melts into the molten glass. As a result, coloring derived from Pt can be reduced.

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

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

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

Sulfate is an optional oxidizing agent that functions as a fining agent. Sulfates are thermally decomposed to produce fine gases SO ₂ and O ₂ . Examples of sulfates include, but are not particularly limited to, zinc sulfate, zirconium sulfate, and the like.

Sulfate content shall be displayed on the outside. That is, the content of sulfate is preferably less than 1% by mass, more preferably less than 0.5% by mass, still more preferably less than 0.5% by mass, when the total content of all glass components other than sulfate is 100% by mass. It is in the range of less than 3% by mass. The sulfate content may be 0% by mass.

Sb (Sb ₂ O ₃ ) is also an optional element that functions as a refining agent. However, Sb (Sb ₂ O ₃ ) has a strong oxidizing property, and if the amount of addition is increased, there is a risk of accelerating the oxidation of platinum derived from the platinum crucible. In addition, during precision press molding, the Sb (Sb ₂ O ₃ ) contained in the glass oxidizes the molding surface of the press mold. may not be possible. As a result, the surface quality of the molded optical element is degraded. Therefore, the glass according to this embodiment preferably does not contain Sb (Sb ₂ O ₃ ).

The glass according to the present embodiment is preferably basically composed of the glass components described above, but may contain other components as long as the effects of the present invention are not impaired. Moreover, in the present invention, inclusion of unavoidable impurities is not excluded.

(Glass properties)
<Refractive index nd>
In the glass according to this embodiment, the refractive index nd is preferably 1.75 or more, and may be 1.77 or more and 1.80 or more. Also, the refractive index nd is preferably 2.50 or less, and may be 2.20 or less or 2.10 or less. The refractive index _nd can be increased by increasing the total content _{of Nb2O5} , _TiO2 , _WO3 and _{Bi2O3 [ Nb2O5} + _TiO2 + _WO3 + _{Bi2O3 ]} , and SiO It can be reduced by increasing the content of ₂ .

<Abbe number νd>
In the glass according to this embodiment, the Abbe number νd is 20 or more. The Abbe number νd may range from 20-45, or from 21-45. The Abbe number νd can be increased by increasing the content of La ₂ O ₃ and can be decreased by increasing the content of B ₂ O ₃ .

<Light transmittance of glass>
The light transmittance of the optical glass according to this embodiment can be evaluated by the coloring degree λ70.
The spectral transmittance of a glass sample having a thickness of 10.0 mm±0.1 mm is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 70% is defined as λ70.

λ70 of the optical glass according to the present embodiment is preferably 480 nm or less, more preferably 470 nm or less, still more preferably 450 nm or less, and particularly preferably 440 nm or less. λ70 can be reduced by reducing the platinum Pt content.

Further, λ70 of the optical glass according to this embodiment preferably satisfies the following formula (3).
λ70≦a×b+373 (3)
In formula (3), a is preferably 200, and more preferably 195, 190, 185, 180 and 175 in that order.
Also, b is the mass ratio of the content of TiO ₂ to the total content of B ₂ O ₃ and La ₂ O ₃ [TiO ₂ /(B ₂ O ₃ +La ₂ O ₃ )].

As the mass ratio [TiO ₂ /(B ₂ O ₃ +La ₂ O ₃ )] increases, the transmittance in the visible short wavelength region decreases and the coloring degree λ70 increases. In the optical glass according to this embodiment, the reduction color is reduced, and λ70 can be suppressed within the range shown by the above formula (3).

<T450>
The light transmittance of the optical glass according to this embodiment can be evaluated by T450.
In this embodiment, T450 is the external transmittance at a wavelength of 450 nm when converted to a thickness of 10.0 mm. "External transmittance" refers to the intensity of incident light, Iin, incident perpendicular to one of the optically polished planes of a glass sample processed so as to have optically polished planes parallel to each other. is the ratio (Iout/Iin) of the intensity Iout of , that is, the transmittance in consideration of the surface reflection on the surface of the glass. Transmittance is obtained by measuring the transmission spectrum using a spectrophotometer.
The thickness of the glass at the time of measurement may be 10.0 mm, but if the thickness is not 10.0 mm, the transmittance at a thickness of 10.0 mm may be converted by a well-known method.

The T450 of the optical glass according to this embodiment is preferably 65% or more, more preferably 70% or more, and still more preferably 75% or more. T450 can be increased by reducing the reduced color of the glass.

<T400>
The light transmittance of the optical glass according to this embodiment can also be evaluated by T400.
The external transmittance T400 at a wavelength of 400 nm is measured with a spectrophotometer for a glass sample having a thickness of 10.0 mm±0.1 mm. You may convert into the transmittance|permeability in thickness 10.0mm by a well-known method. A larger value of T400 means that the transmittance is excellent and the coloration of the glass is reduced.

The T400 of the optical glass according to this embodiment is preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. T400 can be increased by reducing the reduced color of the glass.

<τ400>
The light transmittance of the optical glass according to this embodiment can also be evaluated by τ400.
A glass sample having a thickness of 10.0 mm±0.1 mm is measured with a spectrophotometer for internal transmittance τ400 at a wavelength of 400 nm. You may convert into the transmittance|permeability in thickness 10.0mm by a well-known method. It means that the larger the value of τ400, the better the transmittance and the less the coloration of the glass.

The τ400 of the optical glass according to this embodiment is preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. τ400 can be enhanced by reducing the reduced color of the glass.

<Specific gravity of glass>
In the optical glass according to this embodiment, the specific gravity is preferably 7 or less, more preferably 6.5 or less, and 6 or less in that order. Also, the specific gravity is preferably 2.5 or more, more preferably 3 or more, and more preferably 3.5 or more in that order. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. As a result, it is possible to reduce power consumption for autofocus driving of a camera lens equipped with the lens. On the other hand, if the specific gravity is reduced too much, the thermal stability will be lowered.

<Glass transition temperature Tg>
The glass transition temperature Tg of the optical glass according to this embodiment is preferably 800° C. or lower, more preferably 770° C. or lower, and 750° C. or lower in that order. Also, the glass transition temperature Tg is preferably 300° C. or higher, more preferably 350° C. or higher, and 400° C. or higher in that order. The glass transition temperature Tg can be reduced by increasing the total content of _Li2O , _Na2O and _K2O [ _Li2O + _Na2O + _K2O ].

When the upper limit of the glass transition temperature Tg satisfies the above range, it is possible to suppress an increase in the molding temperature and the annealing temperature of the glass, and to reduce the thermal damage to press molding equipment and annealing equipment. Moreover, when the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easier to maintain good thermal stability of the glass while maintaining the desired Abbe number and refractive index.

(quality of optical glass)
Defects of optical glass generally include bubbles, bumps (foreign matter), and striae.
These defects are evaluated by measuring the amount of defects contained in the glass per unit amount. Depending on the amount of bubbles and grains present per unit cross-sectional area of the glass, the rate at which the light transmittance is inhibited changes.

However, when the unit for evaluating defects (evaluation unit) is extremely small, selecting a region where no bubbles or lumps are present means that there is no optical defect in that range. However, optical glass as a generally used industrial product does not have homogeneity in a minute range such as 1 mm×1 mm, but has homogeneity of glass having a cross-sectional area of, for example, about 100 mm×100 mm or a certain volume or more. requested.

And not only evaluation unit but also optical glass production unit should be discussed.
Even if the required homogeneity is the same between the case of producing 1 ml of glass and the case of producing 1000 kg of glass, there is a huge difference in the degree of difficulty of production. In other words, even when the same raw material is melted and vitrified, the amount of heat required varies depending on the amount of glass. can produce a melt (molten glass) without bubbles or lumps, but when producing 1000 kg of glass, even the raw material cannot be melted.

Depending on the amount of glass, not only the conditions necessary for vitrification change, but also the temperature and time required for defoaming (fining) need to be changed. If the amount of glass is increased, the amount of heat required for vitrification is increased, and the melting time and fining time are lengthened. As a result, the amount of platinum Pt forming the crucible eluted into the molten glass increases.

In other words, when producing optical glass, which is an industrial product, it is necessary to keep the glass capacity above a certain level. The amount of Pt mixed in also changes.

For striae, homogeneity is a further important characteristic. In the first place, the defect of "striae" is a defect that discusses the optical homogeneity of a certain volume (refractive index distribution in space), so naturally the evaluation unit needs to be above a certain level. . Even when the same glass of 1000 ml is produced, the homogeneity of the refractive index differs between the case of producing 1000 ml of glass melt at one time and the case of producing 100 ml of glass melt 100 times.
In general, when producing optical glass, it is possible to obtain a glass with excellent homogeneity by producing 1000 ml of glass melt at one time.

As described above, optical glass treated as an industrial product has been discussed in the case of manufacturing a certain volume or more. The characteristics and quality of optical glass are discussed inseparably.

Techniques discussed for glass melting on a very small scale (eg, small-scale experiments) are not directly applicable to industrial-grade glass melting. And when the scale of glass production is different, it is not possible to uniformly compare the properties and quality of the glass produced by each method.

In this embodiment, the concept of homogeneity of glass is introduced in order to distinguish between the properties and quality of glass at the experimental level and the properties and quality of glass at the industrial level. The homogeneity of glass can be evaluated by refractive index distribution.

<Refractive index distribution>
The refractive index distribution of the optical glass according to the present embodiment is preferably within 0.00050, more preferably within 0.00030, further preferably within 0.00010, further preferably within 0.00007, and further within 0.00005. preferable. The refractive index profile is measured on a continuum having a glass volume of 100 ml or more. Also, the glass volume of the sample used for refractive index measurement shall be 1 ml or more.
The volume of the glass may be calculated from the measurement result and the specific gravity after measuring the mass of the glass, for example.

Specifically, a glass a of 100 ml or more is prepared, and the refractive index is measured at two points, an arbitrary point A and a point B opposite to A.
If there is a portion with a known refractive index, that portion is set to A, and the refractive index of the portion B farthest from A is measured. A total of two or more pieces of glass are obtained from the glass a, and the refractive index is measured.
In this embodiment, the refractive index distribution is evaluated using the refractive index nd, but the evaluation may be performed using the refractive index at another wavelength as appropriate.

(Manufacture of optical glass)
The glass according to the embodiment of the present invention may be produced by blending glass raw materials so as to have the above-described predetermined composition, and using the blended glass raw materials according to a known glass manufacturing method. For example, a plurality of types of compounds are prepared, sufficiently mixed to form a batch raw material, and the batch raw material is placed in a platinum crucible and roughly melted (melting step).

In the glass melting process according to the present embodiment, a reducing agent can be added to the glass raw material. The reducing agent is not particularly limited, but examples thereof include Al, Si, Ti, W, H ₂ , CO, C and other substances exhibiting reducing properties. More specifically, a carbon compound and activated carbon C can be exemplified as the substance exhibiting reducing properties. By adding a reducing agent to the glass raw material, the reducing agent reacts with highly reactive oxygen generated when the glass raw material is vitrified, and the oxidation reaction of platinum derived from the platinum crucible is suppressed. As a result, the Pt content in the glass can be reduced.

The melting atmosphere in the glass melting process according to the present embodiment is preferably a non-oxidizing atmosphere. By performing the melting step in a non-oxidizing atmosphere, the partial pressure of oxygen in the melting atmosphere is reduced, the oxidation of platinum derived from the platinum crucible is suppressed, and the amount of Pt dissolved in the molten glass can be reduced.

Examples of the non-oxidizing atmosphere include, but are not limited to, inert gas atmospheres such as nitrogen, carbon dioxide, argon, and helium, and steam added atmospheres. In order to increase the βOH of the finally obtained glass, a water vapor added atmosphere is preferred.

By adding water vapor to the melting atmosphere, the βOH value of the finally obtained optical glass can be increased, the melting of Pt and the like into the glass can be effectively prevented, and the deaeration and clarification properties can be improved. sufficient dissolved gas to be supplied to the glass.

The method of adding steam to the melting atmosphere is not particularly limited. The method of supplying to space, etc. are mentioned.

The melting step can be accompanied by bubbling for the purpose of stirring the melt. Bubbling during melting may continue after the compounded material has been melted. Stirring the melt in the melting step promotes oxidation of the glass component while suppressing oxidation of platinum derived from the platinum crucible. This is because glass components tend to be more easily oxidized than platinum. As a result, the reductive reaction of the glass component is suppressed to reduce the reduction color, and the dissolution of platinum into the molten material is suppressed to reduce the coloring derived from platinum.

Gases used for bubbling are not necessarily limited, and known gases can be used. Examples include nitrogen, carbon dioxide, inert gases such as argon and helium, air, and these gases including water vapor.

By using a gas containing water vapor as the gas used for bubbling, the βOH value of the finally obtained optical glass can be increased, the melting of platinum into the glass can be effectively prevented, and the defoaming property and clarification property can be improved. sufficient dissolved gas to be supplied to the glass.

The content of water vapor in such water vapor-containing gas is preferably 10% by volume or more, more preferably 20% by volume or more, still more preferably 30% by volume or more, still more preferably 40% by volume or more, and even more preferably 50% by volume or more, more preferably 60% by volume or more, even more preferably 70% by volume or more, particularly preferably 80% by volume or more, and even more preferably 90% by volume or more. The higher the water vapor content, the better. By setting the water vapor content in the above range, the βOH value of the finally obtained optical glass can be increased.

A melt obtained by rough melting is rapidly cooled and pulverized to produce cullet. Further, the cullet is placed in a platinum crucible, heated and re-melted to obtain a molten glass, further clarified and homogenized, the molten glass is shaped, and slowly cooled to obtain an optical glass. A known method may be applied to the molding and slow cooling of the molten glass.

The compounds used in preparing the batch raw materials are not particularly limited as long as the desired glass components can be introduced into the glass so as to have the desired content. salts, nitrates, hydroxides, fluorides and the like.

(Manufacture of optical elements, etc.)
A known method may be applied to produce an optical element using the optical glass according to the embodiment of the present invention. For example, the molten glass is poured into a mold and molded into a plate to produce a glass material made of the optical glass according to the present invention. The obtained glass material is appropriately cut, ground, and polished to produce a cut piece having a size and shape suitable for press molding.

The cut piece is heated, softened, and press-molded (reheat pressed) by a known method to produce an optical element blank that approximates the shape of the optical element. annealing the optical element blank;
An optical element can be produced by grinding and polishing by a known method.

The cut piece is rough-polished (barrel-polished) to equalize the weight and make it easy to adhere a mold release agent to the surface, reheat, and press the softened glass into a shape that approximates the shape of the desired optical element. An optical element can also be manufactured by molding and finally grinding and polishing.

Alternatively, a predetermined weight of molten glass may be separated onto a mold, directly press-molded, and finally ground and polished to produce an optical element.

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

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

Glass samples having the glass compositions shown in Table 1 were produced by the following procedure, and various evaluations were performed.

[Manufacture of optical glass]
(Example 1-A)
First, oxides, hydroxides, carbonates, and nitrates corresponding to the components of glass are prepared as raw materials, and the raw materials are weighed so that the resulting optical glass has the glass composition shown in Table 1. , to mix the raw materials thoroughly. The prepared raw material (batch raw material) thus obtained is put into a platinum crucible, heated at 1250° C. to 1400° C. for 2 hours to be melted to form a molten glass (melting step), and stirred at 1300 to 1400° C. for 1 to 2 hours. It was homogenized and clarified (homogenization/clarification process). The molten glass was cast into a mold preheated to a suitable temperature. The cast glass was heat-treated for 30 minutes at a temperature lower than the glass transition temperature Tg by 100° C. and allowed to cool to room temperature in a furnace to obtain a glass sample.

The following operations were performed in the melting process and the homogenization/clarification process.

A platinum pipe was inserted into a platinum crucible placed in the furnace from outside the melting furnace, and steam was supplied to the space inside the platinum crucible through the platinum pipe. The flow rate of supplied steam was 25 cc/min.

Further, nitrogen was supplied to the space inside the platinum crucible through the platinum pipe, and water vapor was bubbled into the melt from a pipe installed at the bottom of the crucible. The flow rates of supplied nitrogen and water vapor were 30 L/min for nitrogen and 0.1 cc/min for water vapor.

Furthermore, glass samples were prepared by changing the presence or absence of additives, and the conditions in the melting process and the homogenization/clarification process as shown in Tables 2 to 4. Specifically, it is as follows.

(Example 1-B)
No. described in Table 1. The prepared raw material corresponding to 1 is put into a platinum crucible together with the additive shown in Table 2, heated and melted under each of conditions 1-1 to 1-9 shown in Table 2 to form molten glass (melting step). A glass sample was obtained in the same manner as in Example 1-A except that the mixture was stirred to homogenize and clarified (homogenization/clarification step).

(Example 1-C)
No. described in Table 1. The prepared raw material corresponding to 2 is put into a platinum crucible together with the additives shown in Table 3, heated and melted under each of conditions 2-1 to 2-4 shown in Table 3 to form molten glass (melting process). A glass sample was obtained in the same manner as in Example 1-A except that the mixture was stirred to homogenize and clarified (homogenization/clarification step).

(Example 1-D)
No. described in Table 1. The prepared raw material corresponding to 4 is put into a platinum crucible together with the additive shown in Table 4, heated and melted under each of the conditions 4-1 to 4-5 shown in Table 4 to form molten glass (melting step). A glass sample was obtained in the same manner as in Example 1-A except that the mixture was stirred to homogenize and clarified (homogenization/clarification step).

[Confirmation of glass component composition]
The content of each glass component in the resulting glass sample was measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES), and it was confirmed that each composition had the composition shown in Table 1.

[Measurement of Pt amount in glass]
The content of platinum Pt in the glass was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The quantitative results are shown in Tables 1-4.

[Confirmation of defoaming and clarification effect]
For the obtained glass sample, the number of bubbles observed inside the glass was counted, and the number of bubbles (residual bubbles) contained per unit mass (kg) was calculated. The calculation results are shown in Tables 2-4.

[Measurement of optical properties]
βOH, λ70, T400 and T450 were measured for the obtained glass samples. Further, after annealing the obtained glass sample at 710° C. for 72 hours,
An annealed sample was prepared by cooling to room temperature at a cooling rate of −30° C./hour in a furnace, and the refractive indices nd, ng, nF and nC, Abbe number νd, λ70 and T400 were measured.

(i) refractive indices nd, ng, nF, nC and Abbe number νd
The refractive indices nd, ng, nF, and nC of the annealed sample were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number νd was calculated based on the formula (1). Table 1 shows the results.
νd=(nd−1)/(nF−nC) (1)

(ii) βOH
The above glass samples were processed into plate glass samples with a thickness of 1 mm and planes parallel to each other and optically polished. Light is incident on the polished surface of this plate-shaped glass sample from a vertical direction, and the external transmittance A at a wavelength of 2500 nm and the external transmittance B at a wavelength of 2900 nm are measured using a spectrophotometer, respectively, and the following formula (2) βOH was calculated by The results are shown in Tables 1-4.
βOH=-[ln(B/A)]/t (2)

In the above equation (2), ln is the natural logarithm and the thickness t corresponds to the distance between the two planes. The external transmittance includes reflection loss on the surface of the glass sample, and is the ratio of the intensity of transmitted light to the intensity of incident light incident on the glass sample (transmitted light intensity/incident light intensity).

(iii) λ70
The glass sample obtained in Example 1-A was processed to have a thickness of 10 mm and flat surfaces parallel to each other and optically polished, and the spectral transmittance in the wavelength range from 280 nm to 700 nm was measured. The spectral transmittance B/A was calculated by setting the intensity A to the intensity of light incident perpendicularly to one optically polished plane and the intensity B to the intensity of light emitted from the other plane. The wavelength at which the spectral transmittance becomes 70% was defined as λ70. Note that the spectral transmittance also includes the reflection loss of light on the sample surface. Table 1 shows the results.

For the glass samples obtained in Examples 1-B to 1-D, λ70 before annealing treatment (before heat treatment) and after annealing treatment (after heat treatment) were measured in the same manner as described above. Tables 2 to 4 show λ70 before annealing (before heat treatment) and after annealing (after heat treatment).

(iv) T400
For the glass sample obtained in Example 1-B, T400 was measured before annealing treatment (before heat treatment) and after annealing treatment (after heat treatment). Specifically, a glass sample or an annealed sample was processed to have flat surfaces parallel to each other and optically polished with a thickness of 10 mm, and the spectral transmittance at a wavelength of 400 nm was measured. Note that the spectral transmittance also includes the reflection loss of light on the sample surface.
Table 2 shows T400 before annealing (before heat treatment) and after annealing (after heat treatment).

(v) T450
The glass sample obtained in Example 1-A was processed to have a thickness of 10 mm and flat surfaces parallel to each other and optically polished, and the spectral transmittance at a wavelength of 450 nm was measured. Note that the spectral transmittance also includes the reflection loss of light on the sample surface. Table 1 shows the results.

From the results in Table 1, as a result of increasing the value of βOH by introducing water vapor into the melting atmosphere or by bubbling water vapor into the molten glass, optical glass with little coloration and high transmittance at a wavelength of 450 nm can be obtained. did it.

From the results in Tables 2 to 4, by increasing the βOH value of the glass, it is possible to obtain an optical fiber with little coloration and high transmittance in the visible region without heat treatment for a long time in an oxidizing atmosphere after glass molding. It turns out that you can get glass.

(Example 2)
No. shown in Table 1. A glass block of 15 mm × 175 mm × 1500 mm made of glass having a composition of 1 and made according to conditions 1-1 in Table 2 is prepared, cut into 5 equal parts, and a glass block of 15 mm × 175 mm × 300 mm. Got 5. Five samples 1 to 5 for refractive index measurement were prepared using each glass block divided into 5 equal parts, and the refractive index nd of each sample was measured. Based on the refractive index nd of sample 1 at one of the two ends before cutting, the refractive index profiles of samples 2-5 were as follows.

The difference between the refractive index nd of the sample 2 sampled from a portion adjacent to the sample 1 and the refractive index nd of the sample 1 is +0.00001. The difference is +0.00002, the difference between the refractive index of sample 4 taken from a site adjacent to sample 3 and the refractive index of sample 1 is 0.00000, the end of the opposite electrode of sample 1 among the two ends before cutting The difference between the refractive index of Sample 5 and the refractive index of Sample 1, which were sampled more, was -0.00003.
As described above, the refractive index distribution at five locations was 0.00005.

No. shown in Table 1. When the refractive index profile of the glass having the composition of No. 1 and produced under conditions 1-2 to 1-9 in Table 2 was measured in the same manner, the refractive index profile at five locations was within 0.00005. rice field.

Furthermore, No. shown in Table 1. The refractive index profiles of the glasses having respective compositions of 2 to 17 and produced under the conditions of Example 1-A were measured in the same manner, and the refractive index profiles at five locations were within 0.00005.

(Example 3)
Using each optical glass produced in Examples 1-A to 1-D, lens blanks were produced by a known method, and various lenses were produced by processing the lens blanks by a known method such as polishing.
The manufactured optical lenses are various lenses such as a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens.
By combining various lenses with lenses made of other types of optical glass, secondary chromatic aberration could be satisfactorily corrected.

In addition, since the glass has a low specific gravity, each lens is lighter in weight than a lens having the same optical characteristics and size, and is suitable for various imaging equipment, especially autofocus imaging equipment for the reason that it can save energy. be. Similarly, prisms were produced using various optical glasses produced in Examples 1-A to 1-D.

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

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

Claims (1)

1 to 45% by mass of B ₂ O ₃ and 10 to 60% by mass of La ₂ O ₃ ,
comprising _{at least} one oxide selected from the group consisting of _TiO2 , _Nb2O5 , _WO3 and _Bi2O3 ;
An optical glass having a βOH value of 0.1 to 2.0 mm ^-1 represented by the following formula (2).
βOH=-[ln(B/A)]/t (2)
[In formula (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, and A represents the external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with the thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is the natural logarithm. ]