JP6517411B2 - Optical glass and optical element - Google Patents

Description

  The present invention relates to an optical glass and an optical element.

  In recent years, with the advancement of functions and compactness of apparatuses such as imaging optical systems and projection optical systems, the demand for optical glasses of high refractive index as materials of effective optical elements is increasing.

  The 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 in the melting process of the glass, and these reduced components absorb light on the short wavelength side of the visible light range, so the glass may be colored (hereinafter referred to as "reduced color" ) Cause.

JP 2007-112697 A

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an optical glass and an optical element with reduced reduced color.

The gist of the present invention is as follows.
[1] _B 2 _{O 3} and 1 to 45 wt%, wherein the _La 2 _{O 3} 10 to 60 wt%,
At least one oxide selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ ,
Optical glass whose value of (beta) OH shown to following formula (2) is 0.1-2.0 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 represents external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with its thickness direction Represents a percentage (%), and B represents an external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, 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], in which the content of B ₂ O ₃ is greater than the content of SiO ₂ in terms of 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 ] The optical glass in any one of-[4].

[6] The Abbe number d d is 20 to 45,
Optical glass in any one of [1]-[5] whose refractive index nd is 1.75-2.50.

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

  According to the present invention, an optical glass and an optical element with reduced color can be provided.

Hereinafter, one embodiment of the present invention will be described. In the present invention and in the present specification, the glass composition is indicated on an oxide basis unless otherwise specified. Here, "a glass composition based on oxide" refers to a glass composition obtained by converting all the glass raw materials to be decomposed and existing as an oxide in the glass during melting, and the notation of each glass component is customary It is described as SiO ₂ , TiO ₂ and so on. The content and total content of the glass component are on a mass basis unless otherwise specified, "%" means "mass%", and "ppm" means "mass ppm".

  The content of the glass component can be quantified by a known method such as inductively coupled plasma emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and the like. Further, in the present specification and the present invention, the content of the component of 0% means that the content of the component is substantially free, and the component is included at an unavoidable impurity level.

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

The Abbe number dd is used as a value representing the property relating to dispersion, and is represented by the following formula (1). Here, nF is the refractive index at the blue hydrogen F line (wavelength 486.13 nm), and nC is the refractive index at the red hydrogen C line (656.27 nm).
d d = (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 ,
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 (beta) OH shown to following formula (2) is 0.1-2.0 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 represents external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with its thickness direction Represents a percentage (%), and B represents an external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is a natural logarithm. ]

  Hereinafter, the optical glass (it may only be described as "glass" hereafter) which concerns on this embodiment is demonstrated in detail.

The glass according to the present embodiment contains 1 to 45% of B ₂ O ₃ . The lower limit of the B ₂ O ₃ content is preferably 2%, and more preferably 3%, 4%, 6% in this order. The upper limit of the content of B ₂ O ₃ is preferably 30%, and more preferably 25%, 20%, and 15% in this 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 the glass. On the other hand, when the content of B ₂ O ₃ is large, the volatilization amount of the glass component may increase at the time of glass melting. In addition, the devitrification resistance tends to decrease. Therefore, the content of B ₂ O ₃ is preferably in the above range.

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

La ₂ O ₃ works to increase the refractive index nd. It also has the 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, the content of _La 2 _{O 3} is preferably in the above range.

The glass according to the present embodiment includes 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 contributing to the high refractive index, and by including these components, optical glass with a high refractive index can be obtained.

The glass which concerns on this embodiment WHEREIN: The value of (beta) OH shown to following formula (2) is 0.1-2.0 mm < ^-1 >. The lower limit of the value of βOH is preferably 0.2 mm ⁻¹ , and more preferably 0.25 mm ⁻¹ , 0.3 mm ⁻¹ , and 0.35 mm ⁻¹ in this order. 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 the external transmittance, and A represents 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. Moreover, in said Formula (2), ln is a natural logarithm. The unit of βOH is mm ⁻¹ .

  The term "external transmittance" refers to the ratio of the intensity Iout of transmitted light transmitted through the glass to the intensity Iin of incident light incident on the glass (Iout / Iin), that is, the transmittance in consideration of surface reflection on the surface of the glass The transmittance is obtained by measuring the transmission spectrum using a spectrophotometer.

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

  By increasing the water content in the glass to increase the value of βOH, the reduced color can be reduced and the annealing time can be shortened. In addition, defoaming and clarifying effects can be obtained. On the other hand, when 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 to the above range.

  Although the method to raise (beta) OH of glass is not specifically limited, For example, performing operation which raises the moisture content in molten glass in a fusion | melting process etc. is mentioned. Examples of the operation to increase the amount of water in the molten glass include a process of adding water vapor to the melting atmosphere and a process of bubbling a gas containing water vapor in the molten material.

(Glass composition)
The glass components other than the above in the present embodiment will be described in detail below.

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

SiO ₂ is a network forming component of glass, and has the function of improving the thermal stability, chemical durability, and weather resistance of the glass. On the other hand, if the content of SiO ₂ is large, the devitrification resistance of the glass may be reduced. Therefore, the content of SiO ₂ is preferably in 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 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less. . The content of P ₂ O ₅ may be 0%.

P ₂ O ₅ is a component to reduce the refractive index nd, and is also a component to reduce the thermal stability of the glass. Therefore, it is preferable that the above range the content of P ₂ O _5.

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, or 1% or less. The content of Al ₂ O ₃ may be 0%.

Al ₂ O ₃ is a glass component having the function of improving the chemical durability and the 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. In addition, problems such as an increase in glass transition temperature Tg and a decrease in thermal stability tend to occur. Therefore, it is preferable that the content of _Al 2 _{O 3} is within the above range.

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

SiO ₂ and B ₂ O ₃ are network forming components of glass and are components improving the thermal stability and devitrification resistance of glass. Therefore, it is preferable that the total content of SiO ₂ and _{B 2 O 3 [SiO 2 +} B 2 O 3] is in the above range.

Further, in the glass according to the present embodiment, represented by mass%, preferably the content of _{B 2 O 3 [B 2 O} 3] is the content of SiO ₂ [SiO _2] is greater than _([B 2 _{O 3]>} [SiO ₂ ]). More preferably, the content of B ₂ O ₃ is more than 1.3 times the content of SiO ₂ ([B ₂ O ₃ ]> [SiO ₂ ] × 1.3).
The content of B ₂ O ₃ is made larger than the content of SiO _2, it is possible to increase the Abbe number.

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

  ZnO is a glass component having the function of improving the thermal stability of glass and improving the meltability and chemical durability of the glass. On the other hand, when the content of ZnO is too large, the specific gravity is increased. Therefore, the content of ZnO is preferably in the above range.

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

  BaO is a glass component effective to maintain a high refractive index, and also has the function of improving the thermal stability and the devitrification resistance of the glass. On the other hand, when the content is increased, the specific gravity is increased and the devitrification resistance is decreased. Therefore, the content of BaO is preferably in the above range.

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

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

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

  MgO, CaO and SrO are all glass components having the function of improving the thermal stability and devitrification resistance of the glass. On the other hand, when the content of these glass components is increased, the specific gravity is increased, the high dispersibility is impaired, and the thermal stability and the devitrification resistance of the glass are reduced. Therefore, it is preferable that each content of these glass components is the said range, respectively.

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

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%, 5% in this order. The lower limit of the content of Y ₂ O ₃ is preferably 0%, and more preferably in the order of 1%, 2%, and 3%.

Both Gd ₂ O ₃ and Y ₂ O ₃ are components that contribute to the improvement of the weather resistance of the glass and the increase of the refractive index. On the other hand, when the content is too large, the thermal stability of the glass is reduced, and the glass tends to be devitrified during manufacture. Therefore, it is preferable that each content of these glass components is the said range, respectively.

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

Yb ₂ O ₃ is a component that contributes to the improvement of the weather resistance and the increase of the refractive index. On the other hand, Yb ₂ O ₃ has a larger molecular weight than La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ and therefore increases the specific gravity of glass. As the specific gravity of the glass increases, the mass of the optical element increases. For example, when a lens with a large mass is incorporated into an autofocusing imaging lens, the power required to drive the lens during autofocusing increases, and battery consumption becomes severe. Therefore, it is desirable to reduce the content of Yb ₂ O ₃ to suppress the increase in specific gravity of the glass.

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

ZrO ₂ is a component that contributes to increasing the refractive index, and is a glass component having the function of improving the thermal stability and the devitrification resistance of the glass. On the other hand, when the content of ZrO ₂ is too large, the thermal stability tends to decrease. Therefore, the content of ZrO ₂ is preferably in 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 is more preferably 0.1%, and further 1%, 3%, 4%, 5% The order is more preferable. The upper limit of the content of TiO ₂ is preferably 30%, and more preferably 25%, 23%, 21%, and 20% in this order.

TiO ₂ is a component that contributes to increasing the refractive index, and also a component that works to improve the chemical durability. On the other hand, if the content of TiO ₂ is too large, the devitrification resistance may be reduced. Therefore, the content of TiO ₂ is preferably in the above range.

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

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 the glass. On the other hand, if the content of Nb ₂ O ₅ is too large, the thermal stability of the glass may be reduced, and the coloring of the glass tends to be intensified. Therefore, the content of _Nb 2 _{O 5} is preferably in the above range.

In the glass according to the present embodiment, the lower limit of the total content [Nb ₂ O ₅ + TiO ₂ ] of Nb ₂ O ₅ and TiO ₂ is preferably 13%, and further 13.5%, 14%, 14. It is more preferable in the order of 5% and 15%. 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 this order.

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

In the glass according to the present embodiment, the upper limit of the content of WO ₃ 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 a function to lower the glass transition temperature Tg. On the other hand, when the content of WO ₃ is too large, the coloration of the glass increases and the specific gravity also increases. Therefore, the content of WO ₃ is preferably in the above range.

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

Bi ₂ O ₃ works to improve the thermal stability of the glass by containing 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 increases. Therefore, the content of Bi ₂ O ₃ is preferably in the above range.

In the glass according to the present embodiment, the upper limit of the total content [Nb ₂ O ₅ + TiO ₂ + WO ₃ + Bi ₂ O ₃ ] of the total content of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ is preferably 40%. Furthermore, it is more preferable in the order of 37%, 35%, 33% and 32%. The lower limit of the total content [Nb ₂ O ₅ + TiO ₂ + WO ₃ + Bi ₂ O ₃ ] is preferably 1.0%, and further 1.5%, 5%, 10%, 13%, 13. It is more preferable in the order of 5%, 14%, 14.5% and 15%.

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

In the glass according to the present embodiment, the mass ratio [TiO ₂ / (B ₂ O ₃ + La ₂ O ₃ )] of the content of TiO ₂ to the total content of B ₂ O ₃ and La ₂ O ₃ is preferably smaller. The lower limit thereof is preferably 0.030, and 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 one is preferable in the order of .50. 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 , the component having the largest effect of increasing the refractive index nd per unit content in mass% is TiO ₂ . In addition, TiO ₂ is easily reduced in the process of glass melting, and when TiO ₂ is reduced, the transmittance in the visible short wavelength range tends 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 a problem due to the reduction. Therefore, the total content of B ₂ O ₃ and La ₂ O ₃ which does not cause such problems is large relative to the content of TiO ₂ which significantly reduces the transmittance in the visible short wavelength region, ie, the mass ratio The smaller [TiO ₂ / (B ₂ O ₃ + La ₂ O ₃ )] is preferable.

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 The lower limit of ₂ O ₃ )] is preferably 0.05, and more preferably 0.25, 0.30, 0.40, and 0.45 in this order. 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, 0.75. It can also be done.

As described above, TiO ₂ is easily reduced in the process of glass melting, and when TiO ₂ is reduced, the transmittance in the visible short wavelength range tends to be significantly reduced. In the present embodiment, among the components contributing to the increase of the 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 in the above range, coloring is performed by introducing a gas into the atmosphere or bubbling a gas into the melt in the melting step. Can be suppressed.

In the glass according to the present embodiment, the upper limit of the content of Ta ₂ O ₅ is preferably 25%, and more preferably in the order of 20%, 16%, 12%, 8%, 4%. 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 the glass. On the other hand, when the content of Ta ₂ O ₅ is increased, the thermal stability of the glass is lowered, and when melting the glass, a residue of the glass material tends to be generated. Therefore, the content of Ta ₂ O ₅ is preferably in the above range.

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

In the glass according to the present embodiment, the upper limit of the content of Na ₂ O is preferably 10%, and more preferably 7%, 5%, 4%, 2%, and 1% in this order. The lower limit of the content of Na ₂ O 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 this order. The lower limit of the content of K ₂ O 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 the glass, but when their contents increase, the chemical durability and the weather resistance Decreases. Therefore, each content of Li ₂ O, Na ₂ O and K ₂ O is preferably in the above range.

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

Cs ₂ O has the function of improving the thermal stability of glass, but when the content of Cs ₂ O is increased, the chemical durability and the weather resistance decrease. Therefore, each content of Cs ₂ O is preferably in the above range.

In the glass according to the present embodiment, the upper limit of the total content [Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O] of the total content of Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O is preferably 15%, and further Is more preferable in the order of 10%, 7%, 5%, 3% and 1%. 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 decreased. The upper limit of the total content _{[Li 2 O + Na 2 O} + K 2 O + Cs 2 O] is to satisfy the above, it is possible to suppress the deterioration of the devitrification resistance.

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

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

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

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

Lu ₂ O ₃ has the function of enhancing the high dispersion of glass, but is also a glass component which increases the specific gravity of glass because of its large molecular weight. Therefore, it is preferable that the content of _Lu 2 _{O 3} is within the above range.

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

GeO ₂ works to increase the high dispersion of glass, but is a prominent and expensive component among the commonly used glass components. Therefore, from the viewpoint of reducing the production cost of glass, the content of GeO ₂ is preferably in the above range.

The glass according to the present embodiment mainly includes the above components, ie, B ₂ O ₃ and La ₂ O ₃ as essential components, SiO ₂ , P ₂ O ₅ , Al ₂ O ₃ , ZnO, BaO, MgO, as optional components. _{CaO, SrO, Gd 2 O 3} , Y 2 O 3, Yb 2 O 3, ZrO 2, 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 and GeO ₂ , and the total content of the above glass components is more than 95%. Is more preferably more than 98%, still more preferably more than 99%, and even more preferably more than 99.5%.

In the embodiment, as a further preferable aspect,
₁ to 45% of B ₂ O ₃ , 10 to 60% of La ₂ O ₃ , more than 0% of TiO ₂ , 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,
The optical glass whose value of (beta) OH shown to following formula (2) is 0.1-2.0 mm < ^-1 > is mentioned.
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 represents external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with its thickness direction Represents a percentage (%), and B represents an external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is a natural logarithm. ]

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 βOH in the above-mentioned further preferred embodiments As the value, the above-mentioned more preferable numerical range can be applied. Moreover, the preferable numerical range mentioned above is suitably applicable also about content and mass ratio of another glass component.

  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 content of Pt is not particularly limited, but it is unavoidably contained in about 0.001 ppm.

  By making content of Pt into the said range, coloring of the glass resulting from Pt can be reduced and the transmittance | permeability can be improved.

The glass according to the present embodiment melts the glass material in a non-oxidizing atmosphere in the manufacturing process. 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 a material of the melting vessel (such as crucible), to generate platinum dioxide and platinum ions (Pt ⁴⁺ ), which dissolves in the molten glass to cause coloring. . In the present embodiment, by reducing the oxygen partial pressure in the melting atmosphere, the oxidation of platinum can be suppressed, and the amount of Pt dissolved in the molten glass can be reduced. As a result, the color derived from Pt can be reduced.

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

  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 a glass component.

  V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Ce can increase the color of the 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 a glass component.

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

  The content of sulfate is indicated on an external basis. That is, when the total content of all glass components other than sulfate is 100% by mass, the content of sulfate is preferably less than 1% by mass, more preferably less than 0.5% by mass, still more preferably 0. It is a range of less than 3% by mass. The content of sulfate may be 0% by mass.

Sb (Sb ₂ O ₃ ) is also an optionally added element that functions as a fining agent. However, Sb (Sb ₂ O ₃ ) is strongly oxidizing, and there is a possibility of promoting the oxidation of platinum derived from platinum crucible if the addition amount is increased. Also, during precision press molding, Sb (Sb ₂ O ₃ ) contained in the glass oxidizes the molding surface of the press mold, so while the precision press molding is repeated, the molding surface is significantly degraded, and precision press molding May not be able to As a result, the surface quality of the molded optical element is degraded. Therefore, the glass according to the present embodiment preferably does not contain Sb (Sb ₂ O ₃ ).

  In addition, although it is preferable that the glass which concerns on this embodiment is fundamentally comprised with the said glass component, it is also possible to contain another component in the range which does not prevent the effect of this invention. Moreover, in the present invention, the inclusion of unavoidable impurities is not excluded.

(Glass characteristics)
<Refractive index nd>
In the glass according to the present embodiment, the refractive index nd is preferably 1.75 or more, and may be 1.77 or more and 1.80 or more. The refractive index nd is preferably 2.50 or less, and may be 2.20 or less and 2.10 or less. The refractive index nd can be increased by increasing the total content [Nb ₂ O ₅ + TiO ₂ + WO ₃ + Bi ₂ O ₃ ] of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ , and also SiO _It can be reduced by increasing the content of ₂ .

<Abbe number dd>
In the glass according to the present embodiment, the Abbe number dd is 20 or more. The Abbe number dd may be in the range of 20 to 45, or 21 to 45. The Abbe number dd can be increased by increasing the content of La ₂ O ₃ , and can be reduced by increasing the content of B ₂ O ₃ .

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

  The 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. The λ 70 can be reduced by reducing the platinum Pt content.

Further, λ70 of the optical glass according to the present 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.
Further, b is a 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 coloring degree λ70 increases. In the optical glass according to the present embodiment, the reduced color is reduced, and λ70 can be suppressed to the range indicated by the above equation (3).

<T450>
The light transmittance of the optical glass according to the present embodiment can be evaluated by T450.
In the present embodiment, T450 is the external transmittance at a wavelength of 450 nm when converted to a thickness of 10.0 mm. The “external transmittance” is a transmitted light transmitted through a glass with respect to the intensity Iin of incident light perpendicularly incident on one optically polished plane, for a glass sample processed to have mutually parallel and optically polished planes. The ratio of intensity Iout (Iout / Iin), that is, the transmittance in consideration of surface reflection on the surface of the glass. The transmittance is obtained by measuring the transmission spectrum using a spectrophotometer.
In addition, although the thickness of the glass at the time of measurement may be 10.0 mm, when thickness is not 10.0 mm, you may convert into the transmittance | permeability in thickness 10.0 mm by a well-known method.

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

<T400>
The light transmittance of the optical glass according to the present 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. It may be converted to the transmittance at a thickness of 10.0 mm by a known method. The larger the value of T400, the better the transmittance, meaning that the coloration of the glass is reduced.

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

<Τ400>
The light transmittance of the optical glass according to the present embodiment can also be evaluated by τ400.
The internal transmittance τ 400 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. It may be converted to the transmittance at a thickness of 10.0 mm by a known method. The larger the value of τ400, the better the transmittance, meaning that the coloration of the glass is reduced.

  The τ 400 of the optical glass according to the present embodiment is preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. τ 400 can be enhanced 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, and more preferably 6.5 or less and 6 or less. The specific gravity is preferably 2.5 or more, and more preferably 3 or more and 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 the power consumption of the autofocus drive of the camera lens on which the lens is mounted. On the other hand, if the specific gravity is reduced too much, the thermal stability is reduced.

<Glass transition temperature Tg>
The glass transition temperature Tg of the optical glass according to this embodiment is preferably 800 ° C. or less, and more preferably 770 ° C. or less and 750 ° C. or less in this 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 this 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].

  By the upper limit of glass transition temperature Tg satisfy | filling the said range, the raise of the shaping | molding temperature and annealing temperature of glass can be suppressed, and the thermal damage to the installation for press molding and the annealing installation can be reduced. In addition, when the lower limit of the glass transition temperature Tg satisfies the above range, the thermal stability of the glass can be easily maintained while maintaining the desired Abbe number and the refractive index.

(Quality of optical glass)
In general, defects of optical glass include bubbles, bumps (foreign bodies) and cords.
These defects are evaluated by measuring the degree of defects contained in the glass per unit amount. Depending on the amount of bubbles and bumps per unit cross-sectional area of the glass, the rate at which the light transmission is inhibited changes.

  However, if the unit for evaluating the defect (evaluation unit) is extremely small, selecting a region in which no bubbles or bumps are present means that there is no optical defect in that range. However, optical glass as a commonly used industrial product is not homogeneous in a minute range such as 1 mm × 1 mm, for example, the homogeneity of glass having a cross-sectional area of about 100 mm × 100 mm or a certain volume or more is Required

And not only evaluation units but also production units of optical glass should be discussed.
Even in the case of producing 1 ml of glass and the case of producing 1000 kg of glass, even if the required homogeneity is identical, there is a difference in the degree of difficulty of production. That is, even when the same raw material is melted and vitrified, the necessary heat quantity changes according to the amount of glass, for example, when 1 ml of glass is produced even under conditions of a melting temperature of 1250 ° C. and a melting time of 2 hours While it is possible to produce melts (melted glass) free of bubbles and bumps, in the case of producing 1000 kg of glass, melting of the raw materials does not remain.

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

  That is, in the case of producing optical glass which is an industrial product, it is necessary to make the glass volume a certain level or more, and compared with experiments and small-scale glass production, melt and refining conditions and production equipment (such as crucible) The amount of Pt mixed in also changes.

For striae, homogeneity is a further important characteristic. Since the defect of "streak" is the defect that argues the optical homogeneity of a certain volume (refractive index distribution in space), the unit of evaluation must naturally have a certain value or more. . Even in the case of producing the same 1000 ml of glass, the uniformity of refractive index differs between the case of producing 1000 ml of glass melt at a time and the case of producing 10 ml of glass melt 100 times.
Generally, in the case of producing an optical glass, it is possible to obtain a glass excellent in homogeneity by producing 1000 ml of glass melt at one time.

  As described above, optical glass to be treated as an industrial product has been discussed in the case of producing a certain volume or more, and it is possible to meet the difficulty of producing high quality optical glass in this range and the production method thereof. The properties and qualities of optical glass are inseparably discussed.

  The techniques discussed for very small scale (eg, small scale experiments) glass melting are not directly applicable to industrial product level glass melting. And when glass preparation scales differ, the characteristic of the glass produced by each method and quality can not be compared uniformly.

  In the present embodiment, the concept of the degree of homogeneity of glass is introduced in order to distinguish between the characteristics and quality of glass of these experimental levels, and the characteristics and quality of glass of industrial level. The degree of homogeneity of the 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 0.00050 or less, more preferably 0.00030 or less, still more preferably 0.00010 or less, still more preferably 0.00007 or less, and further preferably 0.00005 or less. preferable. The refractive index profile is measured on a continuum having a glass volume of 100 ml or more. Moreover, the glass volume of the sample used for refractive index measurement shall be 1 ml or more.
In addition, what is necessary is just to measure the mass of glass, for example, and just to calculate the volume of glass from a measurement result and specific gravity.

Specifically, a glass a of 100 ml or more is prepared, and the refractive indexes at two places of an arbitrary place A and a place B at the opposite electrode are measured.
In addition, if there is a site whose refractive index is known, the site is taken as A, and the refractive index of the site B which is the farthest from A is measured. Obtain a total of two or more glass pieces from the glass a, and measure the refractive index.
In the present embodiment, the evaluation of the refractive index distribution is performed using the refractive index nd, but the evaluation may be performed using refractive indexes at other wavelengths as appropriate.

(Manufacturing of optical glass)
The glass according to the embodiment of the present invention may be prepared according to a known glass manufacturing method by blending glass raw materials so as to obtain the above-described predetermined composition and using the prepared glass raw materials. For example, a plurality of compounds are prepared and thoroughly mixed to make a batch material, and the batch material is placed in a platinum crucible and roughly melted (dissolution step).

In the glass melting step according to this embodiment, a reducing agent can be added to the glass material. The reducing agent is not particularly limited, and examples thereof include substances showing reducibility such as Al, Si, Ti, W, H ₂ , CO, C and the like. More specifically, a carbon compound and activated carbon C can be illustrated as a substance which shows reducibility. By adding a reducing agent to the glass material, oxygen having a high reaction activity generated when the glass material is vitrified reacts with the reducing agent, and the oxidation reaction of platinum derived from platinum crucible is suppressed. As a result, the Pt content in the glass can be reduced.

  The melting atmosphere in the glass melting step 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, the oxidation of platinum derived from the platinum crucible is suppressed, and the amount of Pt dissolved in the molten glass can be reduced.

  The non-oxidizing atmosphere is not particularly limited, and examples thereof include inert gas atmospheres such as nitrogen, carbon dioxide, argon, helium and the like, and a water vapor addition atmosphere. In order to increase the βOH of the finally obtained glass, a water vapor addition atmosphere is preferred.

  By adding water vapor to the melting atmosphere, the value of βOH of the finally obtained optical glass can be increased, and the dissolution of Pt etc. into the glass can be effectively prevented, and the defoaming property and the clarity are improved. Can provide enough dissolved gas to the glass.

  The method of adding water vapor to the melting atmosphere is not particularly limited. For example, a connecting pipe is inserted into the crucible through an opening provided in the melting apparatus, and if necessary, the water vapor is stored in the crucible through this pipe The method of supplying to space etc. are mentioned.

  In the melting step, bubbling may be accompanied for the purpose of stirring the melt. Bubbling at the time of melting may be continued after melting the compound material. By stirring the melt in the dissolution step, the oxidation of the glass component proceeds while the oxidation of platinum derived from the platinum crucible is suppressed. This is because the glass component tends to be more easily oxidized than platinum. As a result, the reduction reaction of the glass component is suppressed and the reduced color is reduced, and the dissolution of platinum in the melt is suppressed and the coloration derived from platinum is also reduced.

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

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

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

  The melt obtained by rough melting is quenched and crushed to prepare cullet. Further, the cullet is put in a platinum crucible and heated to be remelted (remelted) to form molten glass, and after clarifying and homogenizing, the molten glass is shaped and gradually cooled to obtain an optical glass. A known method may be applied to forming and annealing of the molten glass.

  In addition, the compound used when preparing a batch raw material is not particularly limited as long as a desired glass component can be introduced into the glass so as to have a desired content, but as such a compound, an oxide, carbonate, etc. And salts, nitrates, hydroxides, fluorides and the like.

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

The cut piece is heated and softened, and press molding (reheat press) by a known method to produce an optical element blank which approximates the shape of the optical element. Anneal the optical element blank
The optical element can be manufactured by grinding and polishing by a known method.

  The cut pieces are rough-polished (barrel-polished) to equalize the weight and facilitate adhesion of the mold release agent to the surface, and reheat and press the softened glass into a shape approximate to the desired optical element The optical element can also be manufactured by molding, and finally grinding and polishing.

  Alternatively, a predetermined weight of molten glass may be separated on a mold and directly pressed, and finally ground and polished to manufacture an optical element.

  The optical functional surface of the produced optical element may be coated with an antireflective film, a total reflection film or the like according to the purpose of use.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the embodiments shown in the examples.

  The glass sample which has a glass composition shown in Table 1 was produced in the following procedures, and various evaluation was performed.

[Manufacturing of optical glass]
Example 1-A
First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituents of glass are prepared as raw materials, and the raw materials are weighed so that the glass composition of the obtained optical glass becomes each composition shown in Table 1. Mix and mix the ingredients thoroughly. The mixed raw material (batch raw material) thus obtained is put into a platinum crucible and heated at 1250 ° C. to 1400 ° C. for 2 hours to melt it to a molten glass (melting step) and stir at 1300 to 1400 ° C. for 1 to 2 hours The mixture was homogenized and clarified (homogenization and clarification process). The molten glass was cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated at a temperature 100 ° C. lower than the glass transition temperature Tg for 30 minutes, and allowed to cool to room temperature in a furnace to obtain a glass sample.

  The following operations were performed in the melting step and the homogenization / fining step.

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

  In addition, nitrogen was supplied to the space in 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 water vapor supplied were 30 L / min of nitrogen and 0.1 cc / min of water vapor.

  Furthermore, the conditions in the presence or absence of the additive, the melting step and the homogenization / fining step were changed as shown in Tables 2 to 4 to produce glass samples. Specifically, it is as follows.

Example 1-B
No. 1 described in Table 1 A blended raw material corresponding to 1 is put into a platinum crucible together with additives shown in Table 2, heated under various conditions 1-1 to 1-9 shown in Table 2, and melted to obtain molten glass (melting process) The mixture was stirred to homogenize, and clarified (homogenization / clarification step) and others were obtained as in Example 1-A.

(Example 1-C)
No. 1 described in Table 1 Preparation materials corresponding to No. 2 are put into a platinum crucible together with additives shown in Table 3, heated under various conditions 2-1 to 2-4 shown in Table 3, and melted to obtain molten glass (melting process) The mixture was stirred to homogenize, and clarified (homogenization / clarification step) and others were obtained as in Example 1-A.

Example 1-D
No. 1 described in Table 1 Blended raw materials corresponding to No.4 are put into a platinum crucible together with additives shown in Table 4 and heated under various conditions 4-1 to 4-5 shown in Table 4 and melted to form molten glass (melting process) The mixture was stirred to homogenize, and clarified (homogenization / clarification step) and others were obtained as in Example 1-A.

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

[Measurement of amount of Pt 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 to 4.

[Confirmation of defoaming and clarification effect]
The number of bubbles observed inside the glass was counted for the obtained glass sample, 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 characteristics]
About the obtained glass sample, (beta) OH, (lambda) 70, T400, and T450 were measured. Further, the obtained glass sample is further annealed at 710 ° C. for 72 hours, and then cooled to room temperature at a temperature lowering rate of −30 ° C./hour in a furnace to prepare an annealed sample; refractive indices nd, ng, nF and nC, Abbe number 数 d, λ70 and T400 were measured.

(I) refractive index nd, ng, nF, nC and Abbe number d d
About the said annealing sample, refractive index nd, ng, nF, nC were measured with the refractive index measuring method of JIS specification JISB 707-1, and Abbe's number (nu) d was computed based on Formula (1). The results are shown in Table 1.
d d = (nd-1) / (nF-nC) (1)

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

  In the above equation (2), ln is a natural logarithm, and the thickness t corresponds to the distance between the two planes. The external transmittance also includes the reflection loss on the surface of the glass sample, and is the ratio of the intensity of the transmitted light to the intensity of the 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 plane parallel to each other and optically polished at a thickness of 10 mm, and the spectral transmittance in the wavelength range of 280 nm to 700 nm was measured. The spectral transmittance B / A was calculated by setting the intensity of a light beam incident perpendicularly to one of the optically polished planes as the intensity A and the intensity of the light beam emitted from the other plane as the intensity B. The wavelength at which the spectral transmittance is 70% is λ70. The spectral transmittance also includes the reflection loss of light on the sample surface. The results are shown in Table 1.

  For the glass samples obtained in Examples 1-B to 1-D, λ70 before annealing (before heat treatment) and after annealing (after heat treatment) was 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
With respect to the glass samples obtained in Example 1-B, T400 was measured before annealing (before heat treatment) and after annealing (after heat treatment). Specifically, a glass sample or an annealed sample was processed to have a plane parallel to each other and optically polished at a thickness of 10 mm, and the spectral transmittance at a wavelength of 400 nm was measured. 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 plane parallel to each other and optically polished at a thickness of 10 mm, and the spectral transmittance at a wavelength of 450 nm was measured. The spectral transmittance also includes the reflection loss of light on the sample surface. The results are shown in Table 1.

  According to the results in Table 1, as a result of introducing water vapor into the melting atmosphere or bubbling water vapor into the molten glass to increase the value of βOH, it is possible to obtain an optical glass having a small color and a high transmittance at a wavelength of 450 nm. did it.

  According to the results in Tables 2 to 4, by increasing the value of βOH of glass, after performing glass forming, without performing heat treatment for a long time in an oxidative atmosphere, optical with less coloring and high transmittance in the visible region It turned out that glass can be obtained.

(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 prepared according to condition 1-1 in Table 2 is prepared, cut into five, and divided into 15 mm × 175 mm × 300 mm glass blocks I got 5 pieces. Five refractive index measurement samples 1 to 5 were prepared using each of the five equally divided glass blocks, 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 that was at one of the two ends before cutting.

The difference between the refractive index nd of the sample 2 collected from the portion adjacent to the sample 1 and the refractive index nd of the sample 1 is +0.00001, and the refractive index nd of the sample 3 collected from the central portion and the refractive index nd of the sample 1 The difference is +0.00002, the difference between the refractive index of the sample 4 and the refractive index of the sample 1 taken from the portion adjacent to the sample 3 is 0.00000, and the end of the counter electrode of the sample 1 of the two ends before cutting The difference between the refractive index of sample 5 and the refractive index of sample 1 was −0.00003.
As described above, the five refractive index distributions were 0.00005.

  No. shown in Table 1 The refractive index distribution of the glass having the composition of 1 and prepared according to conditions 1-2 to 1-9 in Table 2 in the same manner was found to have a refractive index distribution of 0.00005 or less at five locations. The

  Furthermore, No. 1 shown in Table 1 The refractive index distribution of the glass having each composition of 2 to 17 and prepared under the conditions of Example 1-A was measured by the same method, and the refractive index distribution at five locations was within 0.00005.

(Example 3)
A lens blank was produced by a known method using each of the optical glasses produced in Examples 1-A to 1-D, 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 planoconvex lens, a planoconcave 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 corrected well.

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

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all the modifications within the meaning and scope equivalent to the claims.

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

Claims (15)

B ₂ O ₃ and 3-45 wt%, comprises _La 2 _{O 3} 20 _~60 wt%,
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,
Optical glass whose value of (beta) OH shown to following formula (2) is 0.1-2.0 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 represents external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with its thickness direction Represents a percentage (%), and B represents an external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is a natural logarithm. ] Containing SiO ₂ 0.1 to 25 wt%, the optical glass according to claim 1. The optical glass according to claim 1, comprising 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 . Represented by _mass%, the content is larger than the content of SiO ₂ in B 2 _{O 3,} the optical glass according to any one of claims 1 to 3. The mass ratio [TiO ₂ / (B ₂ O ₃ + La ₂ O ₃ )] of the content of TiO ₂ to the total content of B ₂ O ₃ and La ₂ O ₃ is 0.030 or more. Optical glass according to any of the above. The Abbe number d d is 20 to 45,
The optical glass according to any one of claims 1 to 5, wherein the refractive index nd is 1.75 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 total content of Nb ₂ O ₅ and TiO ₂ is not more than 40 wt%, the optical glass according to any one of claims 1 to 7. Nb ₂ O _5, the total content of _TiO 2, WO ₃ and _Bi 2 _{O 3} is not more than 40 wt%, the optical glass according to any one of claims 1 to 8. Nb ₂ O _5, the total content of _TiO 2, WO ₃ and _Bi 2 _{O 3} is not less than 1.0 wt%, the optical glass according to any one of claims 1 to 9. B ₂ O ₃ , La ₂ O ₃ , SiO ₂ , P ₂ O ₅ , Al ₂ O ₃ , ZnO, BaO, MgO, CaO, SrO, Gd ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , ZrO ₂ , 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 The optical glass according to any one of claims 1 to 10 , wherein the total content of GeO ₂ and GeO ₂ is more than 95% by mass. B ₂ O ₃ and 3-45 wt%, the _La 2 _{O 3} 20 _~60 wt%, the TiO ₂ 0 weight percent, ZnO and contains ultra 0 wt%,
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,
The content of P ₂ O ₅ is 2% by mass or less,
Optical glass whose value of (beta) OH shown to following formula (2) is 0.1-2.0 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 represents external transmission at a wavelength of 2500 nm when light is incident on the glass in parallel with its thickness direction Represents a percentage (%), and B represents an external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass in parallel with its thickness direction. Also, ln is a natural logarithm. ] The optical glass according to any one of claims 1 to 12 , wherein the content of platinum Pt is less than 10 ppm by mass. The optical glass according to any one of claims 1 to 13 , which has a volume of 100 ml or more and a refractive index distribution of 0.00050 or less. The optical element which consists of an optical glass in any one of Claims 1-14 .