JP7445037B2 - Optical glass and optical elements - Google Patents

Description

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

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

High refractive index optical glass as 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 glass melting process, and these reduced components absorb light in the short wavelength range of the visible light range, resulting in coloring of the glass (hereinafter sometimes referred to as "reduced color"). ).

Japanese Patent Application Publication No. 2007-112697

The present invention was made in view of the above circumstances, and an object of the present invention is to provide an optical glass and an optical element with reduced reduced color.

The gist of the present invention is as follows.
[1] Contains 1 to 45% by mass of B ₂ O ₃ and 10 to 60% by mass of La ₂ O ₃ ,
Containing at least one oxide selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ ,
An optical glass having a βOH value of 0.1 to 2.0 mm ⁻¹ as shown in the following formula (2).
βOH=-[ln(B/A)]/t...(2)
[In formula (2), t represents the thickness (mm) of the glass used to measure the external transmittance, and A is the external transmission at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel to its thickness direction. Moreover, ln is a natural logarithm. ]

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

[3] The optical glass according to [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 larger than the content of SiO ₂ in 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]. The optical glass according to any one of [4].

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

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

According to the present invention, it is possible to provide an optical glass and an optical element with reduced reduced color.

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

The content of the glass component can be determined by a known method, for example, inductively coupled plasma optical emission spectroscopy (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), or the like. Furthermore, in this 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 an unavoidable impurity level.

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

The Abbe number νd is used as a value representing properties related to dispersion, and is expressed 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)

The optical glass according to the embodiment of the present invention is
Contains 1 to 45% by mass of B ₂ O ₃ and 10 to 60% by mass of La ₂ O ₃ ,
Containing at least one oxide selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ ,
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 to measure the external transmittance, and A is the external transmission at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel to its thickness direction. Moreover, ln is a natural logarithm. ]

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

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

B ₂ O ₃ is a network-forming component of glass, and has the function of maintaining low dispersion and improving the thermal stability of glass. On the other hand, if the content of B ₂ O ₃ is large, the amount of volatilization of glass components during glass melting may increase. Furthermore, 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 content of La ₂ O ₃ is preferably 20%, and more preferably 22%, 24%, 27%, and 30% in that order. Further, the upper limit of the content of La ₂ O ₃ is preferably 57%, and more preferably 55% and 53% in that order.

La ₂ O ₃ has the function of increasing the refractive index nd. It also has the function of increasing 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 that the content of La ₂ O ₃ is within the above range.

The glass according to this embodiment contains at least one oxide selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ . TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ are all components that contribute to increasing the refractive index, and by including these components, an optical glass with a high refractive index can be obtained.

In the glass according to this embodiment, the value of βOH shown in 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 , and more preferably in the order of 0.25 mm ⁻¹ , 0.3 mm ⁻¹ , and 0.35 mm ⁻¹ . Further, the upper limit of the value of βOH is preferably 1.8 mm ⁻¹ , and more preferably in the order of 1.6 mm ⁻¹ , 1.5 mm ⁻¹ , 1.4 mm ⁻¹ , and 1.2 mm ⁻¹ .
βOH=-[ln(B/A)]/t...(2)

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

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

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

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

A method for increasing the βOH of the glass is not particularly limited, and examples thereof include performing an operation to increase the water content in the molten glass in the melting process. Examples of operations for increasing the water content in the molten glass include adding water vapor to the melting atmosphere, bubbling gas containing water vapor into the melt, and the like.

(Glass component)
Glass components other than those mentioned above in this embodiment will be explained in detail below.

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

SiO ₂ is a network forming component of glass and has the function of improving the thermal stability, chemical durability, and weather resistance of glass. On the other hand, if the content of SiO ₂ is large, the devitrification resistance of the glass may be reduced. Therefore, it is preferable that the content of SiO ₂ is within the above range.

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

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

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

Al ₂ O ₃ is a glass component that has the function of improving 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. Further, problems such as an increase in glass transition temperature Tg and a decrease in thermal stability are likely to occur. Therefore, the content of Al ₂ O ₃ is preferably within the above range.

In the glass according to this 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%. The order of percentage is more preferable. Further, the upper limit of the total content [SiO ₂ +B ₂ O ₃ ] is preferably 35%,
More preferably, it is 30%, 26%, 24%, and 22% in that order.

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.

Furthermore, 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 ] ([B ₂ O ₃ ]> [ _SiO2 ]). More preferably, the content of B ₂ O ₃ is greater than 1.3 times the content of SiO ₂ ([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%, and more preferably in the order of 25%, 20%, 15%, 10%, 7%, and 5%. Further, 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 that order.

ZnO is a glass component that has the function of improving the thermal stability of glass, as well as the melting properties and chemical durability of glass. On the other hand, if the ZnO content is too large, the specific gravity will increase. Therefore, the content of ZnO is preferably within the above range.

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

BaO is an effective glass component for maintaining a high refractive index, and also has the function of improving 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 this embodiment, the upper limit of the MgO content is preferably 5%, and more preferably 4%, 3%, 2%, and 1% in this order. Further, the lower limit of the MgO content is preferably 0%.

In the glass according to this embodiment, the upper limit of the CaO content is preferably 10%, and more preferably 8%, 6%, 4%, and 2% in this order. Further, 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%, and more preferably 5%, 4%, 3%, and 1% in this order. Further, the lower limit of the SrO content is preferably 0%.

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

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

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

Gd ₂ O ₃ and Y ₂ O ₃ are both components that contribute to improving the weather resistance and increasing the refractive index of glass. On the other hand, if the content is too large, the thermal stability of the glass will decrease and the glass will be more likely to devitrify during production. Therefore, the content of each of these glass components is preferably within the above range.

In the glass according to this embodiment, the upper limit of the content of Yb ₂ O ₃ is preferably 5%, and more preferably 4%, 3%, 2%, and 1% in that order. Further, the lower limit of the content of Yb ₂ O ₃ 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, since Yb ₂ O ₃ has a larger molecular weight than La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ , it increases the specific gravity of the glass. As the specific gravity of the glass increases, the mass of the optical element increases. For example, if a lens with a large mass is incorporated into an autofocus type 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%, and more preferably 15%, 12%, 10%, 8%, and 7% in that order. Further, the lower limit of the ZrO ₂ content is preferably 0%, and 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 has the function of improving the thermal stability and devitrification resistance of the glass. On the other hand, if the ZrO ₂ content is too high, thermal stability tends to decrease. Therefore, the content of ZrO ₂ is preferably within the above range.

In the glass according to this 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%, and 5%. This order is more preferable. Further, the upper limit of the content of TiO ₂ is preferably 30%, and more preferably 25%.
%, 23%, 21%, 20% in that order.

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

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

Nb ₂ O ₅ is a component that contributes to increasing the refractive index, and also has the function of improving the thermal stability and chemical durability of glass. On the other hand, if the content of Nb ₂ O ₅ is too large, the thermal stability of the glass may decrease, and the glass tends to become more colored. Therefore, it is preferable that the content of Nb ₂ O ₅ is 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. The order of 5% and 15% is more preferable. Further, the upper limit of the total content [Nb ₂ O ₅ +TiO ₂ ] is preferably 40%, and 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 large, the thermal stability and devitrification resistance of the glass will decrease. Therefore, the total content of Nb ₂ O ₅ and TiO ₂ is preferably within the above range.

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

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

In this embodiment, the upper limit of the content of Bi ₂ O ₃ is preferably 20%, and more preferably 15%, 10%, 5%, and 3% in that order. Moreover, 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 glass by containing it in an appropriate amount. On the other hand, when the content of Bi ₂ O ₃ is increased, the coloring of the glass increases and the specific gravity also increases. Therefore, the content of Bi ₂ O ₃ is preferably within the above range.

In the glass according to this embodiment, the upper limit of the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ [Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ ] is preferably 40%. Yes, and more preferably 37%, 35%, 33%, and 32% in that order. Further, 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. The order of 5%, 14%, 14.5%, and 15% is more preferable.

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 this embodiment, the mass ratio of the TiO ₂ content 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 preferably smaller. , the lower limit thereof is preferably 0.030, more preferably 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 The smaller the value in the order of .50, the better. Further, the upper limit of the mass ratio [TiO ₂ /(B ₂ O ₃ +La ₂ O ₃ )] is preferably 1.5, and more preferably in the order of 1.0, 0.8, and 0.6.

Among Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ , TiO ₂ is the component that has the largest effect of increasing the refractive index nd per unit content expressed in mass %. Further, 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 decrease significantly. On the other hand, B ₂ O ₃ and La ₂ O ₃ , which are the main components in the glass according to this embodiment, do not suffer from such a problem 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, that is, _the mass ratio [TiO ₂ /(B ₂ O ₃ +La ₂ O ₃ )] is preferably smaller.

In the glass according to this 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, and more preferably in the order of 0.25, 0.30, 0.40, and 0.45. Further, the upper limit of the mass ratio [TiO ₂ /(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )] is preferably 1.00, and more preferably 0.90, 0.80, and 0.75. You can also do that.

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 range tends to decrease significantly. In this embodiment, among the components contributing to a high refractive index such as Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ , the content of TiO ₂ which is particularly likely to cause coloring is high, that is, the mass ratio Even when [TiO ₂ /(Nb ₂ O ₅ + TiO ₂ + WO ₃ + Bi ₂ O ₃ )] is within the above range, coloring can be caused by introducing gas into the atmosphere during the melting process or bubbling 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%, and more preferably 20%, 16%, 12%, 8%, and 4% in that order. Further, the lower limit of the content of Ta ₂ O ₅ is preferably 0%.

Ta ₂ O ₅ is a component that contributes to increasing the refractive index and also has the function of improving the thermal stability of glass. On the other hand, when the content of Ta ₂ O ₅ increases, the thermal stability of the glass decreases, and unmelted glass raw materials tend to remain when melting the glass. Therefore, the content of Ta ₂ O ₅ is preferably within the above range.

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

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

In the glass according to the present embodiment, the upper limit of the Cs ₂ O content is preferably 5%, and 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 has the function of improving the thermal stability of glass, but when its content increases, chemical durability and weather resistance decrease. Therefore, each content of Cs ₂ O is preferably within the above range.

In the glass according to this 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%, and The preferred values are 10%, 7%, 5%, 3%, and 1% in that order. Further, 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, it is possible to suppress a decrease in devitrification resistance.

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

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

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

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

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

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

GeO ₂ has the function of increasing the high dispersibility of glass, but 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 this embodiment mainly contains the above-mentioned 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, and optional components. _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-mentioned glass components should be more than 95%. is preferable, more preferably more than 98%, even more preferably more than 99%, even more preferably more than 99.5%.

In this embodiment, as a further preferred aspect,
Contains 1 to 45% of B ₂ O ₃ , 10 to 60% of La ₂ O ₃ , more than 0% of TiO ₂ , and more than 0% of ZnO,
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 0. 4 or more,
Examples include optical glasses having a βOH value of 0.1 to 2.0 mm ⁻¹ as shown in the following formula (2).
βOH=-[ln(B/A)]/t...(2)
[In formula (2), t represents the thickness (mm) of the glass used to measure the external transmittance, and A is the external transmission at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel to its thickness direction. Moreover, ln is a natural logarithm. ]

In the above-mentioned more preferred embodiment, the content of B ₂ O ₃ , La ₂ O ₃ , TiO ₂ and ZnO, the mass ratio [TiO ₂ /(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )], and the content of βOH Regarding the value, the more preferable numerical range described above can be applied. Moreover, the above-mentioned preferred numerical ranges can be applied as appropriate 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, and more preferably in the order of 8 ppm or less, 7 ppm or less, and 5 ppm or less. The lower limit of the Pt content is not particularly limited, but it inevitably includes about 0.001 ppm.

By setting the content of Pt within the above range, coloring of the glass due to Pt can be reduced and transmittance can be improved.

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 container (crucible, etc.), to produce platinum dioxide and platinum ions (Pt ⁴⁺ ), which dissolve into the molten glass and cause coloring. arise. In this embodiment, by reducing the oxygen partial pressure in the molten atmosphere, oxidation of platinum can be suppressed and the amount of Pt dissolved in the molten glass can be reduced. As a result, coloring derived from Pt can be reduced.

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

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

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

Sulfate is an optionally added oxidizing agent that functions as a clarifying agent. The sulfate is thermally decomposed to produce clear gases SO ₂ and O ₂ . Examples of the sulfate include, but are not limited to, zinc sulfate, zirconium sulfate, and the like.

The content of sulfate shall be expressed as a percentage. That is, the content of sulfate is preferably less than 1% by mass, more preferably less than 0.5% by mass, and still more preferably 0.5% by mass, when the total content of all glass components other than sulfate is 100% by mass. The content is less than 3% by mass. The content of sulfate may be 0% by mass.

Sb (Sb ₂ O ₃ ) is also an optionally addable element that functions as a refining agent. However, Sb (Sb ₂ O ₃ ) has strong oxidizing properties, and increasing the amount added may accelerate the oxidation of platinum derived from a platinum crucible. In addition, during precision press molding, Sb (Sb ₂ O ₃ ) contained in glass oxidizes the molding surface of the press mold, so as precision press molding is repeated, the molding surface deteriorates significantly, causing precision press molding to deteriorate. There is a risk that you will not be able to. 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 ).

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

(Glass characteristics)
<Refractive index nd>
In the glass according to this embodiment, the refractive index nd is preferably 1.75 or more, and may also be 1.77 or more, or 1.80 or more. Further, the refractive index nd is preferably 2.50 or less, and further may be 2.20 or less, or 2.10 or less. The refractive index nd can be increased by increasing the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ [Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ ], 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 be in the range of 20-45, or 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 degree of coloration λ70.
The spectral transmittance of a glass sample with 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.

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

Moreover, 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 in the order of 195, 190, 185, 180, and 175.
Moreover, 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 range decreases and the degree of coloring λ70 increases. In the optical glass according to this embodiment, reduced 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 transmitted light that passes through the glass for the intensity Iin of incident light that is perpendicular to one of the optically polished planes for a glass sample that has been processed to have parallel and optically polished planes. It is the ratio of the intensity Iout (Iout/Iin), that is, the transmittance that also takes into account surface reflection on the surface of the glass. Transmittance is obtained by measuring the transmission spectrum using a spectrophotometer.
Note that 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 may be converted to the transmittance at a thickness of 10.0 mm using 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.
External transmittance T400 at a wavelength of 400 nm is measured using a spectrophotometer for a glass sample having a thickness of 10.0 mm±0.1 mm. It may be converted into transmittance at a thickness of 10.0 mm using a well-known method. The larger the value of T400, the better the transmittance and the lower the coloring of the glass.

The T400 of the optical glass according to this embodiment is preferably 50% or more, more preferably 60% or more, and even 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.
For a glass sample having a thickness of 10.0 mm±0.1 mm, the internal transmittance τ400 at a wavelength of 400 nm is measured using a spectrophotometer. It may be converted into transmittance at a thickness of 10.0 mm using a well-known method. The larger the value of τ400, the better the transmittance and the lower the coloring of the glass.

The optical glass according to the present embodiment preferably has a τ400 of 50% or more, more preferably 60% or more, and even more preferably 70% or more. τ400 can be increased by reducing the reduced color of the glass.

<Specific gravity of glass>
In the optical glass according to the present embodiment, the specific gravity is preferably 7 or less, more preferably 6.5 or less, and 6 or less, in that order. Further, the specific gravity is preferably 2.5 or more, and more preferably 3 or more, then 3.5 or more. 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 a lens. On the other hand, reducing the specific gravity too much leads to a decrease in thermal stability.

<Glass transition temperature Tg>
The glass transition temperature Tg of the optical glass according to the present embodiment is preferably 800°C or lower, more preferably 770°C or lower, and then 750°C or lower, in that order. Further, the glass transition temperature Tg is preferably 300°C or higher, and 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 Li ₂ O, Na ₂ O and K ₂ O [Li ₂ O+Na ₂ O+K ₂ O].

When the upper limit of the glass transition temperature Tg satisfies the above range, increases in the molding temperature and annealing temperature of the glass can be suppressed, and thermal damage to press molding equipment and annealing equipment can be reduced. Further, when the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easy to maintain good thermal stability of the glass while maintaining a desired Abbe number and refractive index.

(Quality of optical glass)
Generally, the disadvantages of optical glass include bubbles, lumps (foreign objects), and striae.
These defects are evaluated by measuring the amount of defects contained in the glass per unit amount. The rate at which light transmittance is inhibited changes depending on the amount of bubbles and particles present per unit cross-sectional area of the glass.

However, when the unit for evaluating defects (evaluation unit) is extremely small, selecting an area where no bubbles or lumps are present means that no optical defects exist within that range. However, optical glass as a commonly used industrial product does not have homogeneity in a small area such as 1 mm x 1 mm, but rather has homogeneity in glass having a cross-sectional area of 100 mm x 100 mm or a volume above a certain level. required.

In addition to the evaluation unit, the production unit of optical glass should also be discussed.
Even if the homogeneity required is the same when producing 1 ml of glass and when producing 1000 kg of glass, there is a huge difference in the degree of difficulty of production. In other words, even if the same raw materials are melted and vitrified, the amount of heat required will vary depending on the amount of glass.For example, even if the melting temperature is 1250°C and the melting time is 2 hours, when producing 1ml of glass. While it is possible to produce a molten liquid (molten glass) without bubbles or lumps, when producing 1000 kg of glass, the raw materials cannot even be melted.

Not only will the conditions necessary for vitrification change depending on the amount of glass, but it will also be necessary to change the temperature and time required for defoaming (clarification). When the amount of glass is increased, the amount of heat required for vitrification increases, and the melting time and fining time also become longer. As a result, the amount of platinum Pt constituting the crucible eluted into the molten glass increases.

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

Regarding striae, homogeneity is an even more 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 it naturally follows that the evaluation unit must be of a certain size or more. . Even when the same 1000 ml of glass is produced, the uniformity of the refractive index is different depending on whether 1000 ml of glass melt is produced at one time or when 10 ml of glass melt is produced 100 times.
Generally, when producing optical glass, glass with excellent homogeneity can be obtained by producing 1000 ml of glass melt at one time.

As mentioned above, optical glass, which is treated as an industrial product, has been discussed in the case of manufacturing with a capacity above a certain level, and the difficulty of producing high-quality optical glass in this range and the difficulty in producing it depending on the manufacturing method are discussed. The characteristics and quality of optical glass are inseparable and are being discussed.

The techniques discussed for glass melting on an extremely small scale (for example, small-scale experiments) cannot be directly applied to glass melting on an industrial product level. When glass production scales are different, it is not possible to uniformly compare the characteristics and quality of glasses produced by each method.

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

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

Specifically, a glass a of 100 ml or more is prepared, and the refractive index at two locations, an arbitrary location A and a location B opposite to A, is measured.
Further, if there is a part whose refractive index is known, that part is set as A, and the refractive index of part B, which is farthest from A, is measured. A total of two or more pieces of glass are obtained from glass a, and the refractive index is measured.
In this embodiment, the refractive index distribution was evaluated using the refractive index nd, but the evaluation may be performed using the refractive index at other wavelengths as appropriate.

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

In the glass melting process according to this embodiment, a reducing agent can be added to the glass raw material. Examples of the reducing agent include, but are not limited to, substances exhibiting reducing properties such as Al, Si, Ti, W, H ₂ , CO, and C. More specifically, carbon compounds and activated carbon C can be exemplified as the substance exhibiting reducing properties. By adding a reducing agent to the glass raw material, the highly reactive oxygen generated when the glass raw material is vitrified reacts with the reducing agent, 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 this embodiment is preferably a non-oxidizing atmosphere. By performing the melting step in a non-oxidizing atmosphere, the oxygen partial pressure in the melting atmosphere is reduced, 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 particularly limited to, an atmosphere of an inert gas such as nitrogen, carbon dioxide, argon, helium, etc., and an atmosphere containing water vapor. In order to increase the βOH of the glass finally obtained, a water vapor added atmosphere is preferred.

By adding water vapor to the melting atmosphere, it is possible to increase the βOH value of the final optical glass, effectively prevent Pt etc. from dissolving into the glass, and improve defoaming and clarity. Sufficient dissolved gas can be supplied to the glass to

The method of adding water vapor to the melting atmosphere is not particularly limited, but for example, a connecting pipe is inserted into the crucible from an opening provided in the melting device, and water vapor is added to the melting atmosphere through this pipe as necessary. Examples include a method of supplying it to a space.

In the melting step, bubbling may be included for the purpose of stirring the melt. Bubbling during melting may continue even after the compounded material is melted. By stirring the melt in the melting step, oxidation of the glass components progresses, while oxidation of platinum derived from the platinum crucible is suppressed. This is because glass components tend to be more easily oxidized than platinum. As a result, the reduction reaction of the glass components is suppressed to reduce reduced coloring, and the dissolution of platinum into the melt is suppressed, thereby reducing platinum-derived coloring.

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

By using a gas containing water vapor as the gas used for bubbling, it is possible to increase the βOH value of the final optical glass, effectively prevent platinum from dissolving into the glass, and improve defoaming and clarity. Sufficient dissolved gas can be supplied to the glass.

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

The molten material obtained by rough melting is rapidly cooled and pulverized to produce cullet. Further, the cullet is placed in a platinum crucible, heated and remelted to obtain molten glass, and after further clarification and homogenization, the molten glass is shaped and slowly cooled to obtain optical glass. A known method may be applied to forming and slowly cooling the molten glass.

Note that the compounds used when preparing the batch raw materials are not particularly limited as long as the desired glass components can be introduced into the glass at the desired content, but examples of such compounds include oxides, carbonates, etc. Examples include salts, nitrates, hydroxides, fluorides, and the like.

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

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

The cut pieces are roughly polished (barrel polishing) to equalize their weight and make it easier for the mold release agent to adhere to the surface, then reheated and the softened glass is pressed into a shape that approximates the shape of the desired optical element. Optical elements can also be manufactured by molding and finally grinding and polishing.

Alternatively, an optical element may be manufactured by separating a predetermined weight of molten glass onto a mold, directly press-molding it, and finally grinding and polishing.

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

EXAMPLES Below, the present invention will be explained in more detail with reference to Examples. However, the present invention is not limited to the embodiments shown in the examples.

Glass samples having the glass composition shown in Table 1 were prepared according to the following procedure, and various evaluations were performed.

[Manufacture of optical glass]
(Example 1-A)
First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of glass are prepared as raw materials, and the raw materials are weighed so that the glass composition of the resulting optical glass is as shown in Table 1. , blended and mixed the raw materials thoroughly. The blended raw materials (batch raw materials) obtained in this way are put into a platinum crucible, heated at 1250 to 1400 °C for 2 hours to melt them into molten glass (melting process), and stirred at 1300 to 1400 °C for 1 to 2 hours. to homogenize and clarify (homogenization/clarification process). Molten glass was poured into a mold that had been preheated to an appropriate temperature. A glass sample was obtained by heat-treating the cast glass at a temperature 100° C. lower than the glass transition temperature Tg for 30 minutes and allowing it to cool to room temperature in a furnace.

In the melting step and homogenization/clarification step, the following operations were performed.

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

In addition, 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 nitrogen and steam supplied were 30 L/min for nitrogen and 0.1 cc/min for steam.

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

(Example 1-B)
No. listed in Table 1. The blended raw materials corresponding to 1 were put into a platinum crucible together with the additives shown in Table 2, and heated and melted under each of the conditions 1-1 to 1-9 shown in Table 2 to form molten glass (melting process). A glass sample was obtained in the same manner as in Example 1-A, except that it was stirred for homogenization and clarified (homogenization/clarification step).

(Example 1-C)
No. listed in Table 1. The blended raw materials corresponding to 2 were put into a platinum crucible together with the additives shown in Table 3, and heated and melted under the 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 it was stirred for homogenization and clarified (homogenization/clarification step).

(Example 1-D)
No. listed in Table 1. The blended raw materials corresponding to 4 were put into a platinum crucible together with the additives shown in Table 4, and heated and melted under the conditions 4-1 to 4-5 shown in Table 4 to form molten glass (melting process). A glass sample was obtained in the same manner as in Example 1-A, except that it was stirred for homogenization and clarified (homogenization/clarification step).

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

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

[Confirmation of defoaming/clarification effect]
Regarding 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 to 4.

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

(i) Refractive index nd, ng, nF, nC and Abbe number νd
Regarding the annealed sample, the refractive indexes nd, ng, nF, and nC were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number νd was calculated based on equation (1). The results are shown in Table 1.
νd=(nd-1)/(nF-nC)...(1)

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

In the above formula (2), ln is a natural logarithm, and the thickness t corresponds to the distance between the two planes. The external transmittance also includes reflection loss at the surface of the glass sample, and is the ratio of the intensity of transmitted light to the intensity of incident light that enters 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, parallel to each other and optically polished planes, 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 of the light beam perpendicularly incident on one optically polished plane as intensity A, and the intensity of the light beam emerging from the other plane as intensity B. The wavelength at which the spectral transmittance was 70% was defined as λ70. Note that the spectral transmittance also includes reflection loss of light rays on the sample surface. The results are shown in Table 1.

Regarding 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) was measured in the same manner as above. Tables 2 to 4 show λ70 before annealing treatment (before heat treatment) and after annealing treatment (after heat treatment).

(iv)T400
Regarding 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 annealed sample was processed to have a thickness of 10 mm, parallel to each other, and optically polished planes, and the spectral transmittance at a wavelength of 400 nm was measured. Note that the spectral transmittance also includes reflection loss of light rays on the sample surface.
Table 2 shows T400 before annealing treatment (before heat treatment) and after annealing treatment (after heat treatment).

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

From the results in Table 1, it is possible to obtain optical glass with less coloring and high transmittance at a wavelength of 450 nm by introducing water vapor into the melting atmosphere or bubbling water vapor into the molten glass to increase the value of βOH. did it.

From the results in Tables 2 to 4, it was found that by increasing the βOH value of glass, optical fibers with less coloring and high transmittance in the visible range can be produced without the need for long-term heat treatment in an oxidizing atmosphere after glass forming. It turns out that you can get glass.

(Example 2)
No. shown in Table 1. A 15 mm x 175 mm x 1500 mm glass block was prepared from glass having the composition of 1 and prepared according to conditions 1-1 in Table 2, and this was cut into 5 equal parts to obtain a 15 mm x 175 mm x 300 mm glass block. Obtained 5 pieces. Five samples 1 to 5 for refractive index measurement were prepared using each glass block divided into five equal parts, and the refractive index nd of each sample was measured. The refractive index distributions of Samples 2 to 5 were as follows, based on the refractive index nd of Sample 1 at one of the two ends before cutting.

The difference between the refractive index nd of sample 2 taken from the adjacent part of sample 1 and the refractive index nd of sample 1 is +0.00001, and the difference between the refractive index nd of sample 3 taken from the central part and the refractive index nd of sample 1 is +0.00001. The difference is +0.00002, and the difference between the refractive index of sample 4 and sample 1 taken from the area adjacent to sample 3 is 0.00000, the opposite end 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 collected from the sample was −0.00003.
As described above, the refractive index distribution at the five locations was 0.00005.

No. shown in Table 1. When the refractive index distribution of glasses having the composition No. 1 and prepared under conditions 1-2 to 1-9 in Table 2 was measured in the same manner, the refractive index distribution at five locations was within 0.00005. Ta.

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

(Example 3)
Using each of the optical glasses produced in Examples 1-A to 1-D, a lens blank was produced by a known method, and the lens blank was processed by a known method such as polishing to produce various lenses.
The produced 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 aberrations could be corrected well.

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

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

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

Claims (14)

Contains ₃ to 45% by mass of B ₂ O 3 and 20 to 60% by mass of La ₂ O ₃ ,
Containing at least one oxide selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ ,
The content of P ₂ O ₅ is 2% by mass or less,
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 0.080 or more,
An optical glass having a βOH value of 0.1 to 2.0 mm ⁻¹ as shown in the following formula (2).
βOH=-[ln(B/A)]/t...(2)
[In formula (2), t represents the thickness (mm) of the glass used to measure the external transmittance, and A is the external transmission at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel to its thickness direction. Moreover, ln is a natural logarithm. ] The optical glass according to claim 1, containing 0.1 to 25% by mass of SiO ₂ . The optical glass according to claim 1, containing 0.5 to 15% by mass of SiO ₂ , 3 to 30% by mass of B ₂ O ₃ , and 20 to 60% by mass of La ₂ O ₃ . The optical glass according to any one of claims 1 to 3, wherein the content of B ₂ O ₃ is larger than the content of SiO ₂ in mass %. Claims 1 to 4, wherein 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 0.090 or more. Optical glass according to any of the above. Abbe number νd is 20 to 37.37,
The optical glass according to any one of claims 1 to 5, having a refractive index nd of 1.90043 to 2.50. The optical glass according to any one of claims 1 to 6, wherein the total content of Nb ₂ O ₅ and TiO ₂ is 13% by mass or more. The optical glass according to any one of claims 1 to 7, wherein the total content of Nb ₂ O ₅ and TiO ₂ is 40% by mass or less. The optical glass according to any one of claims 1 to 8, wherein the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ is 40% by mass or less. The optical glass according to any one of claims 1 to 9, wherein the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ is 1.0% by mass or more. _B2O3 , _{La2O3 , SiO2} , _P2O5 , _Al2O3 , _ZnO , BaO, MgO, _CaO , _SrO , _{Gd2O3 , Y2O3 , Yb2O3 , ZrO2} , TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , Ta ₂ O ₅ , Li ₂ O, Na ₂ O, K 2 O, Cs ₂ O, Sc ₂ O ₃ , HfO _{2 ,} Lu ₂ O ₃ Optical glass according to any one of claims 1 to 10, wherein the total content of and GeO ₂ is more than 95% by mass. The optical glass according to any one of claims 1 to 11, wherein the content of platinum Pt is less than 10 mass ppm. The optical glass according to any one of claims 1 to 12, which has a volume of 100 ml or more and a refractive index distribution of 0.00050 or less. An optical element made of the optical glass according to any one of claims 1 to 13.