JP2022021586A - Optical glass, and optical element - Google Patents

Abstract

To provide an optical glass big in a temperature coefficient (dn/dT) of a relative refractive index by temperature variation, and big in a mean linear thermal expansion coefficient, and an optical element comprising the optical glass.SOLUTION: The optical glass is an optical glass where the content of P2O5 is 25-50 mass%, the content of Nb2O5 is 14-40 mass%, the total content [TiO2+Nb2O5+WO3+Bi2O3+Ta2O5] of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 is 35-60 mass%, the mass ratio [TiO2/(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] of a content of TiO2 to a total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 is 0.25 or more, the mass ratio [B2O3/P2O5] of a content of B2O3 to a content of P2O5 is 0.05-0.39, the total content [Li2O+Na2O+K2O+Cs2O] of Li2O, Na2O, K2O and Cs2O is 10 mass% or more, and the mass ratio [Na2O/K2O] of a content of Na2O to a content of K2O is 1.50 or more.SELECTED DRAWING: None

Description

The present invention relates to optical glass and optical elements.

Optical elements incorporated in in-vehicle optical equipment and optical elements incorporated in heat-generating optical equipment such as projectors, copiers, laser printers, and broadcasting equipment are used in environments with large temperature changes. Fluctuations in optical characteristics such as the refractive index due to temperature changes affect the imaging characteristics of the optical system.

Here, it is known that the influence of temperature change on the imaging characteristics of the optical system can be reduced by combining an optical element having a negative temperature coefficient (dn / dT) of the relative refractive index and an optical element having a positive temperature coefficient (dn / dT). Has been done.

The temperature coefficient of the relative refractive index (dn / dT) represents the change in the refractive index with respect to the temperature change. In an optical element whose refractive index decreases as the temperature rises, the temperature coefficient of relative refractive index becomes negative. On the contrary, in an optical element in which the refractive index increases as the temperature rises, the temperature coefficient of the relative refractive index becomes positive.

In addition, when the melting temperature and the forming temperature of the glass are high, the productivity is inferior, and the glass melting equipment (for example, a pit, a stirring equipment for the molten glass, etc.) in the melting process is eroded, and the economy is also inferior. Therefore, a glass having a low liquidus temperature LT, that is, a glass having a low melting temperature and molding temperature of the glass is required.

Patent Document 1 discloses an optical glass in which the temperature coefficient (dn / dT) of the relative refractive index is negative. However, it has been found that the glass of Patent Document 1 has a high liquidus temperature LT and is inferior in productivity and economy.

In addition, the average coefficient of linear thermal expansion of the optical element is important in the optical design. When a low refractive index low dispersion glass material and a high refractive index high dispersion glass material are combined, the smaller the difference in the average linear thermal expansion coefficient of the glass material, the better the bonding. For example, a low refractive index low dispersion glass material containing fluorine usually has a large average linear thermal expansion coefficient. Therefore, the high-refractive index, high-dispersion glass material to be combined with it is also required to have a high average linear thermal expansion coefficient. The optical glass disclosed in Patent Document 2 has a high refractive index but a low dispersion and a small average linear thermal expansion coefficient. Therefore, there is a demand for optical glass having a high refractive index and high dispersion and a large average linear thermal expansion coefficient.

Japanese Unexamined Patent Publication No. 2019-1697 JP-A-2007-106611

Therefore, an object of the present invention is to provide an optical glass having a low temperature coefficient (dn / dT) of a relative refractive index due to a temperature change and a large average linear thermal expansion coefficient, and an optical element made of the optical glass.

The gist of the present invention is as follows.
(1) The content of P ₂ O ₅ is 25 to 50% by mass, and the content is 25 to 50% by mass.
The Nb ₂ O ₅ content is 14-40% by mass,
The total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TIM ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ ] is 35 to 60% by mass. ,
The mass ratio of the content of TiO ₂ to the total content of TIM ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TIO ₂ / (TIO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ) + Ta ₂ O ₅ )] is 0.25 or more,
The mass ratio of the content of B ₂ O ₃ to the content of P ₂ O ₅ [B ₂ O ₃ / P ₂ O ₅ ] is 0.05 to 0.39.
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 10% by mass or more.
An optical glass having a mass ratio [Na ₂ O / K ₂ O] of the content of Na ₂ O to the content of K ₂ O of 1.50 or more.

(2) The optical glass according to (1), which does not substantially contain F.

(3) The optical glass according to (1) or (2), wherein the average linear thermal expansion coefficient α at 100 to 300 ° C. is 100 × 10 ^-7 to 200 × 10 ^-7 ° C. ^-1 .

(4) The temperature coefficient dn / dT of the relative refractive index at the wavelength (633 nm) of the He-Ne laser is −0.1 × 10 ^-6 to -13.0 × 10 ^-6 ° C ^-1 in the range of 20 to 40 ° C. The optical glass according to any one of (1) to (3).

(5) An optical element made of the optical glass according to any one of (1) to (4) above.

According to the present invention, it is possible to provide an optical glass having a low temperature coefficient (dn / dT) of a relative refractive index due to a temperature change and a large average linear thermal expansion coefficient, and an optical element made of the optical glass.

Unless otherwise specified, the glass composition of optical glass in the present invention and the present specification is expressed on an oxide basis. Here, the "oxide-based glass composition" refers to a glass composition obtained by converting all glass raw materials into those that are decomposed at the time of melting and exist as oxides in optical glass, and the notation of each glass component is Following the custom, it is described as SiO ₂ , TiO ₂ , and the like. Unless otherwise specified, the content and total content of glass components are based on mass, and "%" means "% by mass".

The content of the glass component can be quantified by a known method, for example, an inductively coupled plasma emission spectroscopic analysis method (ICP-AES), an inductively coupled plasma mass spectrometry method (ICP-MS), or the like. Further, in the present specification and the present invention, the content of the constituent component is 0%, which means that the constituent component is substantially not contained, and the component is allowed to be contained at an unavoidable impurity level.

As used herein, the thermal stability and devitrification resistance of glass both refer to the difficulty of crystal precipitation in glass. In particular, thermal stability refers to the difficulty of crystal precipitation when the molten glass solidifies, and devitrification resistance refers to the crystal precipitation when the solidified glass is reheated, as in the case of reheat pressing. It shall refer to the difficulty.

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

Further, the Abbe number νd is used as a value representing the property related to the variance, and is expressed by the following equation. 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 this embodiment will be described in detail.
The optical glass according to this embodiment is
The content of P ₂ O ₅ is 25 to 50%,
The Nb ₂ O ₅ content is 14-40%,
The total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TIM ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ ] is 35 to 60%.
The mass ratio of the content of TiO ₂ to the total content of TIM ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TIO ₂ / (TIO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ) + Ta ₂ O ₅ )] is 0.25 or more,
The mass ratio of the content of B ₂ O ₃ to the content of P ₂ O ₅ [B ₂ O ₃ / P ₂ O ₅ ] is 0.05 to 0.39.
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 10% or more.
The mass ratio [Na ₂ O / K ₂ O] of the content of Na ₂ O to the content of K ₂ O is 1.50 or more.

In the optical glass according to this embodiment, the content of P2 O ₅ is 25 to ₅₀ %. The lower limit of the content of P ₂ O ₅ is preferably 26%, more preferably 26.5% and 26.7 in that order. The upper limit of the content of P ₂ O ₅ is preferably 42%, more preferably 40%, 38%, 37%, and 36% in that order.

P ₂ O ₅ is a network-forming component of glass, and is an essential component for containing a large amount of highly dispersed components in glass. By setting the content of P ₂ O ₅ in the above range, an optical glass having high thermal stability and a desired optical constant can be obtained.

In the optical glass according to this embodiment, the content of Nb ₂ O ₅ is 14 to 40%. The lower limit of the content of Nb ₂ O ₅ is preferably 16%, more preferably 17%, 18%, 19%, and 20% in that order. The upper limit of the content of Nb ₂ O ₅ is preferably 38%, more preferably 36%, 34%, and 32% in that order.

Nb ₂ O ₅ is a component that contributes to high refractive index and high dispersion. Therefore, by setting the content of Nb ₂ O ₅ in the above range, an optical glass having a desired optical constant can be obtained. On the other hand, if the content of Nb ₂ O ₅ is too large, the coloring of the glass may be strengthened.

In the optical glass according to the present embodiment, the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ ] Is 35 to 60%. The lower limit of the total content is preferably 36%, more preferably 37%, 38%, and 39% in that order. The upper limit of the total content is preferably 55%, more preferably 50%, 48%, 47%, and 46% in that order.

TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ are components that contribute to high dispersion of glass. Therefore, by setting the total content [TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ ] in the above range, an optical glass having a desired optical constant can be obtained. In addition, the thermal stability of the glass can be improved. On the other hand, if the total content is too large, an optical glass having a desired optical constant may not be obtained, the thermal stability of the glass may be lowered, and the coloring of the glass may be strengthened.

In the optical glass according to the present embodiment, the mass ratio of the content of TiO ₂ to the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TIO ₂ / (TIO ₂ + Nb). ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ )] is 0.25 or more. The lower limit of the mass ratio is preferably 0.26, more preferably 0.27, 0.28, 0.29, 0.30 in that order. The upper limit of the mass ratio is preferably 0.65, and more preferably 0.60, 0.58, 0.56, 0.54, 0.52, 0.50, 0.48 in that order. ..

TiO ₂ is a component having a particularly large effect of high dispersion among the components for increasing the refractive index. Therefore, from the viewpoint of obtaining a desired optical constant, the mass ratio [TiO ₂ / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ )] is preferably in the above range.

In the optical glass according to the present embodiment, the mass ratio of the content of B ₂ O ₃ to the content of P ₂ O ₅ [B ₂ O ₃ / P ₂ O ₅ ] is 0.05 to 0.39. The upper limit of the mass ratio is preferably 0.30, and more preferably 0.25, 0.22, 0.20, 0.19, and 0.18. The lower limit of the mass ratio is preferably 0.06, and more preferably 0.07, 0.08, and 0.09.

By setting the mass ratio [B ₂ O ₃ / P ₂ O ₅ ] in the above range, it becomes easy to obtain an optical glass having a desired optical constant, high thermal stability, and high devitrification resistance. ..

In the optical glass according to the present embodiment, 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 10% or more. The lower limit of the total content is preferably 12%, more preferably 14%, 16%, and 17% in that order. The upper limit of the total content is preferably 35%, more preferably 30%, 28%, 26%, and 25% in that order.

Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O all have a function of improving the thermal stability of the glass. However, if these contents are high, the chemical durability and weather resistance may decrease. Therefore, 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 in the above range.

In the optical glass according to the present embodiment, the mass ratio [Na ₂ O / K ₂ O] of the content of Na ₂ O to the content of K ₂ O is 1.50 or more. The lower limit of the mass ratio is preferably 1.70, and more preferably 1.90, 2.10, 2.30 in that order. The upper limit of the mass ratio is preferably 10.0, and more preferably 8.50, 7.50, 7.00, and 6.50 in that order.

Na ₂ O and K ₂ O are components that contribute to lowering the specific density of glass, and have a function of improving the meltability of glass and increasing the average coefficient of linear thermal expansion. However, as the _K2O content increases, thermal stability, devitrification resistance, chemical durability, and weather resistance decrease. Therefore, the mass ratio [Na ₂ O / K ₂ O] is preferably in the above range.

Non-limiting examples of the content and ratio of glass components other than the above in the optical glass according to the present embodiment are shown below.

In the optical glass according to the present embodiment _, the upper limit of the content of B2O3 is preferably ₁₀ %, more preferably 9%, 8%, 7%, and 6% in that order.

B ₂ O ₃ is a network-forming component of glass and has a function of improving the thermal stability of glass. On the other hand, if the content of B ₂ O ₃ is large, the devitrification resistance tends to decrease. Therefore, the content of B ₂ O ₃ is preferably in the above range.

In the optical glass according to the present embodiment, the mass ratio of the content of B ₂ O ₃ to the total content of P ₂ O ₅ and B ₂ O ₃ [B ₂ O ₃ / (P ₂ O ₅ + B ₂ O ₃ )]. The upper limit of is preferably 0.18, and more preferably 0.17, 0.16, and 0.15. The lower limit of the mass ratio is preferably 0, and more preferably 0.01, 0.03, and 0.05 in that order.

From the viewpoint of improving the thermal stability and devitrification resistance of the glass, the mass ratio [B ₂ O ₃ / (P ₂ O ₅ + B ₂ O ₃ )] is preferably in the above range.

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

Al ₂ O ₃ is a glass component having a 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 is large, the devitrification resistance of the glass is lowered. In addition, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability are likely to occur. From the viewpoint of avoiding such a problem, the upper limit of the content of Al ₂ O ₃ is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the content of SiO ₂ is preferably 5%, more preferably 3%, 2%, and 1%. The content of SiO ₂ may be 0%.

A quartz glass melting instrument such as a quartz glass crucible may be used to melt the glass. In this case, since a small amount of SiO ₂ is melted from the melting instrument into the glass melt, the glass produced even if the glass raw material does not contain SiO ₂ contains a small amount of SiO ₂ . The amount of SiO ₂ mixed into the glass from the quartz glass melting instrument depends on the melting conditions, but is, for example, about 0.5 to 1% by mass with respect to the total content of all glass components. The amount of SiO ₂ increases by about 0.5 to 1% by mass while the content ratio of the glass component other than SiO ₂ remains constant. The above amount may increase or decrease depending on the melting conditions. Since the optical characteristics such as the refractive index and the Abbe number change depending on the content of SiO ₂ , the content of the glass component other than SiO ₂ is finely adjusted to obtain an optical glass having desired optical characteristics.

SiO ₂ is a network-forming component of glass, and has a function of improving thermal stability, chemical durability, and weather resistance of glass, increasing the viscosity of molten glass, and facilitating molding of molten glass. On the other hand, when the content of SiO ₂ is large, the devitrification resistance of the glass tends to decrease. Therefore, the upper limit of the content of SiO ₂ is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the total content of P ₂ O ₅ , B ₂ O ₃ and SiO ₂ [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ ] is preferably 50%, and further. It is more preferable in the order of 45%, 43%, 42%, 41%. The lower limit of the total content is preferably 25%, more preferably 27%, 28%, and 29%.

By setting the total content [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ ] in the above range, an optical glass having high thermal stability and a desired optical constant can be obtained.

In the optical glass according to the present embodiment, the mass ratio of the total content of P ₂ O ₅ and B ₂ O ₃ to the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ , and Al ₂ O ₃ [( The lower limit of P ₂ O ₅ + B ₂ O ₃ ) / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is preferably 0.80, and further 0.90, 0.93, 0. It is more preferable in the order of .96 and 0.98. The upper limit of the mass ratio is preferably 1.00. The mass ratio may be 1.00.

From the viewpoint of obtaining a glass having high thermal stability and a desired optical constant, the mass ratio [(P ₂ O ₅ + B ₂ O ₃ ) / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )) ] Is preferably in the above range.

In the optical glass according to the present embodiment, the lower limit of the TiO ₂ content is preferably 10%, more preferably 11%, 12%, and 13% in that order. The upper limit of the TiO ₂ content is preferably 50%, more preferably 40%, 35%, 30%, 28%, 26%, 23%, and 21% in that order.

TiO ₂ greatly contributes to high dispersion. On the other hand, TiO ₂ tends to increase the coloring of the glass relatively easily, and may deteriorate the meltability. Therefore, the content of TiO ₂ is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the WO ₃ content is preferably 15%, more preferably 10%, 5%, 3%, 2%, and 1% in that order. The content of WO ₃ is preferably low, and the lower limit thereof is preferably 0%. The content of WO ₃ may be 0%.

By setting the content of WO ₃ in the above range, the transmittance can be increased and the increase in the specific gravity of the glass can be suppressed. Further, the temperature coefficient (dn / dT) of the relative refractive index can be lowered.

In the optical glass according to the present embodiment, the upper limit of the content of Bi ₂ O ₃ is preferably 15%, more preferably 10%, 7%, 5%, and 3% in that order. The lower limit of the Bi ₂ O ₃ content is preferably 0%.

Bi ₂ O ₃ has a function of improving the thermal stability of 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 is increased. Therefore, the content of Bi ₂ O ₃ is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the mass ratio [TiO ₂ / (P ₂ O ₅ + B ₂ O ₃ )] of the content of TiO ₂ to the total content of P ₂ O ₅ and B ₂ O ₃ is set. It is preferably 0.70, and more preferably 0.66, 0.64, 0.62, 0.60 in that order. The lower limit of the mass ratio is preferably 0.25, more preferably 0.27, 0.29, 0.31 in that order.

By setting the mass ratio [TIM ₂ / (P ₂ O ₅ + B ₂ O ₃ )] in the above range, it becomes easy to obtain an optical glass having a desired optical constant and high thermal stability.

In the optical glass according to the present embodiment, the upper limit of the mass ratio [TiO ₂ / P ₂ O ₅ ] of the content of TIO ₂ to the content of P ₂ O ₅ is preferably 0.70, and further 0. The order of 66, 0.64, 0.62 is more preferable. The lower limit of the mass ratio is preferably 0.25, more preferably 0.28, 0.31 and 0.34 in that order.

By setting the mass ratio [TIM ₂ / P ₂ O ₅ ] in the above range, it becomes easy to obtain an optical glass having a desired optical constant and high thermal stability.

In the optical glass according to the present embodiment, the lower limit of the total content of TiO ₂ and Nb ₂ O ₅ [TiO ₂ + Nb ₂ O ₅ ] is preferably 35.0%, and further 37.0%, 39. It is more preferable in the order of 0% and 40.0%. The upper limit of the total content is preferably 65.0%, more preferably 60.0%, 55.0%, 50.0%, 48.0%, and 46.0% in that order.

From the viewpoint of obtaining a glass having a high refractive index and a high dispersion and excellent thermal stability of the glass, the total content [TiO ₂ + Nb ₂ O ₅ ] is preferably in the above range.

In the optical glass according to the present embodiment, the lower limit of the mass ratio [Nb ₂ O ₅ / (Nb ₂ O ₅ + WO ₃ )] of the content of Nb ₂ O ₅ to the total content of Nb ₂ O ₅ and WO ₃ is set. It is preferably 0.70, and more preferably 0.80, 0.90, 0.95 in that order. The upper limit of the mass ratio is preferably 1.00. The mass ratio may be 1.00.

The mass ratio [Nb ₂ O ₅ / (Nb ₂ O ₅ + WO ₃ )] is The above range is preferable.

In the optical glass according to the present embodiment, the lower limit of the mass ratio of the content of TiO ₂ to the total content of TiO ₂ and WO ₃ [TiO ₂ / (TiO ₂ + WO ₃ )] is preferably 0.70. Further, it is more preferable in the order of 0.80, 0.90, 0.95. The upper limit of the mass ratio is preferably 1.00. The mass ratio may be 1.00.

From the viewpoint of obtaining a glass having a high dispersion and suppressing an increase in the temperature coefficient (dn / dT) of the relative refractive index, the mass ratio [TIM ₂ / (TiO ₂ + WO ₃ )] is preferably in the above range. ..

In the optical glass according to the present embodiment, the mass ratio of the total content of TiO ₂ and Nb ₂ O ₅ to the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ , and Bi ₂ O ₃ [(TiO ₂ + Nb ₂ ). The lower limit of O ₅ ) / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )] is preferably 0.70, and more preferably 0.80, 0.90, 0.95 in that order. The upper limit of the mass ratio is preferably 1.00. The mass ratio may be 1.00.

From the viewpoint of obtaining a glass having a high refractive index and a high dispersion and suppressed increase in the temperature coefficient (dn / dT) of the relative refractive index, the mass ratio [(TiO ₂ + Nb ₂ O ₅ ) / (TiO ₂ + Nb ₂ O) ₅ + WO ₃ + Bi ₂ O ₃ )] is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the content of Ta ₂ O ₅ is preferably 10%, more preferably 7%, 5%, and 3%. The lower limit of the content of Ta ₂ O ₅ is preferably 0%. The content of Ta ₂ O ₅ may be 0%.

Ta ₂ O ₅ is a glass component having a function of improving the thermal stability and devitrification resistance of glass. On the other hand, Ta ₂ O ₅ increases the refractive index and makes the glass highly dispersed. Further, when the content of Ta ₂ O ₅ is increased, the thermal stability of the glass is lowered, and when the glass is melted, unmelted glass raw materials are likely to occur. Therefore, the content of Ta ₂ O ₅ is preferably in the above range. Further, Ta ₂ O ₅ is an extremely expensive component as compared with other glass components, and the production cost of glass increases as the content of Ta ₂ O ₅ increases. Further, since Ta ₂ O ₅ has a larger molecular weight than other glass components, it increases the specific gravity of the glass, and as a result, increases the weight of the optical element.

In the optical glass according to the present embodiment, the upper limit of the Li ₂ O content is preferably 5%, more preferably 3%, 2%, and 1%. The lower limit of the Li ₂ O content is preferably 0%. The content of Li ₂ O may be 0%.

Li ₂ O is a component that contributes to lowering the specific density of glass, and has a function of improving the meltability of glass and increasing the average coefficient of linear thermal expansion. On the other hand, as the content of Li ₂ O increases, the devitrification resistance decreases. Therefore, the Li ₂ O content is preferably in the above range.

In the optical glass according to the present embodiment, the lower limit of the Na ₂ O content is preferably 6%, more preferably 10%, 12%, and 13% in that order. The upper limit of the Na ₂ O content is preferably 30%, more preferably 22%, 20%, 19%, and 18% in that order.

Na ₂ O is a component that contributes to lowering the specific density of glass, and has a function of improving the meltability of glass and increasing the average coefficient of linear thermal expansion. On the other hand, as the content of Na ₂ O increases, the devitrification resistance decreases. Therefore, the Na ₂ O content is preferably in the above range.

In the optical glass according to the present embodiment, the lower limit of the K2O content is preferably 1%, more preferably ₂ %, 3%, and 4%. The upper limit of the K ₂ O content is preferably 13%, more preferably 12%, 11%, and 10% in that order.

K ₂ O is a component that contributes to lowering the specific density of glass, and has a function of improving the thermal stability of glass. It also has the function of increasing the average coefficient of linear thermal expansion. _On the other hand, when the content of K2O is increased, the thermal stability, the devitrification resistance, the chemical durability, and the weather resistance are lowered. Therefore, the content of _K2O is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the total content [Li ₂ O + Na ₂ O + K ₂ O] of Li ₂ O, Na ₂ O and K ₂ O is preferably 35%, further 30% and 28. %, 26%, and 25% are more preferable. The lower limit of the total content is preferably 10%, more preferably 14%, 15%, 16%, and 17% in that order.

Li ₂ O, Na ₂ O and K ₂ O all have a function of improving the thermal stability of the glass. However, if these contents are high, the chemical durability and weather resistance may decrease. Therefore, the total content of Li ₂ O, Na ₂ O and K ₂ O [Li ₂ O + Na ₂ O + K ₂ O] is preferably in the above range.

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

Cs ₂ O has a function of improving the meltability of glass, but when the content is high, the thermal stability and refractive index nd of the glass decrease, and the volatilization of the glass component increases during melting. The desired glass cannot be obtained. Therefore, the content of Cs ₂ O is preferably in the above range.

In the optical glass according to the present embodiment, the mass ratio of the content of Na ₂ O to the total content of Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O [Na ₂ O / (Li ₂ O + Na ₂ O + K ₂ ). The lower limit of O + Cs ₂ O)] is preferably 0.20, more preferably 0.50, 0.55, 0.60, 0.65. The upper limit of the mass ratio is preferably 0.98, and more preferably 0.95, 0.92, 0.90, 0.88.

From the viewpoint of obtaining a glass having excellent devitrification resistance and thermal stability, the mass ratio [Na ₂ O / (Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O)] is preferably in the above range.

In the optical glass according to the present embodiment, the mass ratio of the total content of P ₂ O ₅ , B ₂ O ₃ and SiO ₂ to the total content of Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O [(( The upper limit of P ₂ O ₅ + B ₂ O ₃ + SiO ₂ ) / (Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O)] is preferably 2.50, and further 2.40, 2.35, 2.30, The order of 2.27 and 2.25 is more preferable. The lower limit of the mass ratio is preferably 1.20, and more preferably 1.30, 1.35, 1.38, and 1.40 in that order.

By setting the mass ratio [(P ₂ O ₅ + B ₂ O ₃ + SiO ₂ ) / (Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O)] in the above range, the thermal stability is high and the temperature coefficient of relative refractive index ( An optical glass having a low dn / dT) and a large average coefficient of linear thermal expansion can be obtained.

In the optical glass according to the present embodiment, the content of MgO is preferably 5% or less, more preferably 3% or less, and more preferably 1% or less. The lower limit of the MgO content is preferably 0%. The content of MgO may be 0%.

In the optical glass according to the present embodiment, the CaO content is preferably 5% or less, more preferably 3% or less, and more preferably 1% or less. The lower limit of the CaO content is preferably 0%. The CaO content may be 0%.

In the optical glass according to the present embodiment, the SrO content is preferably 6% or less, more preferably 5% or less, 3% or less, and 1% or less in that order. The lower limit of the SrO content is preferably 0%.

In the optical glass according to the present embodiment, the BaO content is preferably 8% or less, more preferably 5% or less, 3% or less, and 1% or less in that order. The lower limit of the BaO content is preferably 0%.

In the optical glass according to the present embodiment, the upper limit of the total content [MgO + CaO + SrO + BaO] of MgO, CaO, SrO, and BaO is preferably 8.0%, and further, 5.0%, 4.0%, and so on. It is more preferable in the order of 3.0%, 1.5%, 1.0% and 0.5%. The lower limit of the total content is preferably 0%. The total content may be 0%.

MgO, CaO, SrO, and BaO are all glass components having a function of improving the thermal stability and devitrification resistance of the glass. However, when the content of these glass components is high, the high dispersibility is impaired, and the thermal stability and devitrification resistance of the glass are lowered. Further, if the content of BaO is too large, the specific gravity of the glass increases. Therefore, the content and total content of each of these glass components are preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the ZnO content is preferably 10%, more preferably 6%, 4%, and 3%. The ZnO content is preferably low, and the lower limit thereof is preferably 0%. The ZnO content may be 0%.

ZnO is a glass component having a function of improving the thermal stability of glass. However, if the ZnO content is too high, the specific gravity of the glass will increase. Further, the temperature coefficient (dn / dT) of the relative refractive index becomes high. Therefore, the ZnO content is preferably in the above range.

In the optical glass according to the present embodiment, the lower limit of the mass ratio [Na ₂ O / (Na ₂ O + Zn O)] of the content of Na ₂ O to the total content of Na ₂ O and Zn O is preferably 0.50. Further, it is more preferable in the order of 0.60, 0.70, 0.90. The upper limit of the mass ratio is preferably 1.00. The mass ratio may be 1.00.

The mass ratio [Na ₂ O / (Na ₂ O + ZnO)] is in the above range from the viewpoint of suppressing the increase in the specific gravity of the glass and suppressing the increase in the temperature coefficient (dn / dT) of the relative refractive index. Is preferable.

In the optical glass according to the present embodiment, the lower limit of the mass ratio [TiO ₂ / (TiO ₂ + ZnO)] of the content of TiO ₂ to the total content of TiO ₂ and ZnO is preferably 0.70, and further. The order of 0.80, 0.90, 0.95 is more preferable. The upper limit of the mass ratio is preferably 1.00. The mass ratio may be 1.00.

From the viewpoint of obtaining a glass having a high dispersion and suppressing an increase in the temperature coefficient (dn / dT) of the relative refractive index, the mass ratio [TiO ₂ / (TiO ₂ + ZnO)] is preferably in the above range.

In the optical glass according to the present embodiment, the mass ratio of the total content of TiO ₂ and Nb ₂ O ₅ to the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and ZnO [(TIO ₂ + Nb). The lower limit of ₂ O ₅ ) / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + ZnO)] is preferably 0.70, more preferably 0.80, 0.90, 0.95 in that order. .. The upper limit of the mass ratio is preferably 1.00. The mass ratio may be 1.00.

From the viewpoint of obtaining a glass having a high refractive index and a high dispersion and suppressed increase in the temperature coefficient (dn / dT) of the relative refractive index, the mass ratio [(TiO ₂ + Nb ₂ O ₅ ) / (TiO ₂ + Nb ₂ O) ₅ + WO ₃ + Bi ₂ O ₃ + ZnO)] is preferably in the above range.

In the optical glass according to the present embodiment, TIO ₂ for the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O, Mass ratio of total content of Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [(TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ ) / (P ₂ O ₅ + B) ₂ O ₃ + SiO ₂ + Al ₂ O ₃ + Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O)] is preferably 1.10 or less. The upper limit of the mass ratio is preferably 1.00, more preferably 0.95, 0.90, 0.85, 0.82, 0.80. The lower limit of the mass ratio is more preferably 0.50, and further preferably 0.60, 0.65, 0.68, 0.70 in that order.

The mass ratio [(TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ ) / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ + Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O)] is described above. By setting the range, it becomes easy to obtain an optical glass having a desired optical constant.

In the optical glass according to the present embodiment, the content of ZrO ₂ is preferably 5% or less, more preferably 3% or less, and more preferably 1% or less. The lower limit of the content of ZrO ₂ is preferably 0%.

ZrO ₂ is a glass component having a function of improving the thermal stability and devitrification resistance of glass. However, if the content of ZrO ₂ is too high, the thermal stability tends to decrease. Therefore, the content of ZrO ₂ is preferably in the above range.

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

In the optical glass according to the present embodiment, the upper limit of the HfO ₂ content is preferably 2%. The lower limit of the HfO ₂ content is preferably 0%.

Sc ₂ O ₃ and HfO ₂ both have a function of increasing the refractive index nd and are expensive components. Therefore, the contents of Sc ₂ O ₃ and HfO ₂ are preferably in the above range.

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

Lu ₂ O ₃ has a function of increasing the refractive index nd. In addition, 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 in the above range.

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

GeO ₂ has a function of increasing the refractive index nd, and is a prominently 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 in the above range.

In the optical glass according to the present embodiment, the upper limit of the content of La ₂ O ₃ is preferably 2%. The lower limit of the content of La ₂ O ₃ is preferably 0%. The content of La ₂ O ₃ may be 0%.

When the content of La ₂ O ₃ is increased, the thermal stability and devitrification resistance of the glass are lowered, and the glass is easily devitrified during production. Therefore, the content of La ₂ O ₃ is preferably in the above range from the viewpoint of suppressing deterioration of thermal stability and devitrification resistance.

In the optical glass according to the present embodiment, the upper limit of the content of Gd ₂ O ₃ is preferably 2%. The lower limit of the content of Gd ₂ O ₃ is preferably 0%.

If the content of Gd ₂ O ₃ becomes too large, the thermal stability and devitrification resistance of the glass will decrease, and the glass will easily devitrify during production. Further, if the content of Gd ₂ O ₃ becomes too large, the specific gravity of the glass increases, which is not preferable. Therefore, the content of Gd ₂ O ₃ is preferably in the above range from the viewpoint of suppressing an increase in specific gravity while maintaining good thermal stability and devitrification resistance of the glass.

In the optical glass according to the present embodiment _, the upper limit of the content of Y2O3 is preferably ₂ %. The lower limit of the content of Y ₂ O ₃ is preferably 0%. The content of Y ₂ O ₃ may be 0%.

If the content of Y2O3 is too _{high ,} the thermal stability and devitrification resistance of the glass will decrease. Therefore _, the content of _Y2O3 is preferably in the above range from the viewpoint of suppressing deterioration of thermal stability and devitrification resistance.

In the optical glass according to the present embodiment, the upper limit of the content of Yb ₂ O ₃ is preferably 2%. The lower limit of the content of Yb ₂ O ₃ is preferably 0%.

Since Yb ₂ O ₃ has a higher 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 having a large mass is incorporated into an autofocus type image pickup lens, the power required to drive the lens during autofocus increases, and the battery consumption increases. Therefore, it is desirable to reduce the content of Yb ₂ O ₃ to suppress the increase in the specific gravity of the glass.

Further, if the content of Yb ₂ O ₃ is too large, the thermal stability and devitrification resistance of the glass are lowered. The content of Yb ₂ O ₃ is preferably in the above range from the viewpoint of preventing a decrease in the thermal stability of the glass and suppressing an increase in the specific gravity.

The optical glass according to the present embodiment mainly has the above-mentioned glass components, that is, P ₂ O ₅ , Nb ₂ O ₅ , B ₂ O ₃ , TIO ₂ , Na ₂ O, K ₂ O as essential components, and Al as optional components. ₂ O ₃ , SiO ₂ , WO ₃ , Bi ₂ O ₃ , Ta ₂ O ₅ , Li ₂ O, Cs ₂ O, MgO, CaO, SrO, BaO, ZnO, ZrO ₂ , Sc ₂ O ₃ , HfO ₂ , Lu It is preferably composed of ₂ O ₃ , GeO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ , and Yb ₂ O ₃ , and the total content of the above-mentioned glass components is 95% or more. It is preferably 98% or more, more preferably 99% or more, and even more preferably 99.5% or more.

In the optical glass according to the present embodiment, the upper limit of the content of TeO ₂ is preferably 2%. The lower limit of the content of TeO ₂ is preferably 0%.

Since TeO ₂ is toxic, it is preferable to reduce the content of TeO ₂ . Therefore, the content of TeO ₂ is preferably in the above range.

In the optical glass according to the present embodiment, the content of fluorine F is preferably 3% or less, and the upper limit thereof is more preferably 1%, 0.5%, and 0.3% in that order. The content of F is preferably small, and the lower limit thereof is preferably 0%. The content of F may be 0%. Further, preferably, it does not substantially contain fluorine F.

By setting the content of F in the above range, it is possible to suppress volatilization during melting of the glass, and it is possible to suppress fluctuations in the refractive index and pulse.

It is preferable that the optical glass according to the present embodiment is basically composed of the above glass components, but other components may be contained as long as the effects of the present invention are not impaired. Further, in the present invention, the inclusion of unavoidable impurities is not excluded.

<Other ingredient composition>
Pb, As, Cd, Tl, Be and Se are all toxic. Therefore, it is preferable that the optical glass according to the present 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 according to the present 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 increase the coloring of the glass and can be a source of fluorescence. Therefore, it is preferable that the optical glass according to the present embodiment does not contain these elements as a glass component.

Sb (Sb ₂ O ₃ ) and Ce (CeO ₂ ) are arbitrarily addable elements that function as finings. Of these, Sb (Sb ₂ O ₃ ) is a clarifying agent having a large clarifying effect. However, Sb (Sb ₂ O ₃ ) is highly oxidizing, and if the amount of Sb (Sb ₂ O ₃ ) added is increased, the coloration of the glass increases due to light absorption by Sb ions, which is not preferable. Further, when the glass is melted, if Sb is present in the melt, the elution of platinum constituting the glass melting crucible into the melt is promoted, and the platinum concentration in the glass becomes high. The presence of platinum as ions in the glass increases the coloration of the glass due to the absorption of light. Further, when platinum exists as a solid substance in the glass, it becomes a light scattering source and deteriorates the quality of the glass. Ce (CeO ₂ ) has a smaller clarification effect than Sb (Sb ₂ O ₃ ). When Ce (CeO ₂ ) is added in a large amount, the coloring of the glass is strengthened. Therefore, when adding a clarifying agent, it is preferable to add Sb (Sb ₂ O ₃ ) while paying attention to the amount of addition.

The content of Sb ₂ O ₃ shall be indicated by external division. That is, when the total content of all glass components other than Sb ₂ O ₃ and CeO ₂ is 100% by mass, the content of Sb ₂ O ₃ is preferably less than 1% by mass, more preferably 0.1% by mass. Is less than. Further, is preferably less than 0.05% by mass, less than 0.03% by mass, less than 0.02% by mass, and less than 0.01% in this order. The content of Sb ₂ O ₃ may be 0% by mass.

The content of CeO ₂ is also indicated by external division. That is, when the total content of all glass components other than CeO ₂ and Sb ₂ O ₃ is 100% by mass, the content of CeO ₂ is preferably less than 2% by mass, more preferably less than 1% by mass, and even more preferably. Is in the range of less than 0.5% by mass, more preferably less than 0.1% by mass. The content of CeO ₂ may be 0% by mass. By setting the content of CeO ₂ in the above range, the clarity of the glass can be improved.

(Glass characteristics)
Next, the characteristics of the optical glass according to the present embodiment will be described.

<Refractive index nd>
In the optical glass according to the present embodiment, the refractive index nd is preferably 1.63 to 1.80. The lower limit of the refractive index nd may be 1.65, 1.67, 1.69, 1.71 or 1.73, and the upper limit of the refractive index nd may be 1.79, 1.78, or 1.77.

The refractive index nd can be set to a desired value by appropriately adjusting the content of each glass component. The components having the function of relatively increasing the refractive index nd (high-refractive index-increasing component) are Nb ₂ O ₅ , TiO ₂ , WO ₃ , Bi ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , La ₂ O ₃ , etc. Is. On the other hand, the components having a function of relatively lowering the refractive index nd (lower refractive index component) are P ₂ O ₅ , SiO ₂ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O and the like. be.

<Abbe number νd>
In the optical glass according to the present embodiment, the Abbe number νd is preferably 20 to 30. The lower limit of the Abbe number νd may be 22, 22.5, 23, or 23.2, and the upper limit of the Abbe number νd may be 28, 26, or 25.

The Abbe number νd can be set to a desired value by appropriately adjusting the content of each glass component. The components that relatively lower the Abbe number νd, that is, the highly dispersed components, are Nb ₂ O ₅ , TiO ₂ , WO ₃ , Bi ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , and the like. On the other hand, the components that relatively increase the Abbe number νd, that is, the low dispersion components, are P ₂ O ₅ , SiO ₂ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, La ₂ O ₃ , BaO, CaO, SrO and the like.

<Average coefficient of linear thermal expansion α>
In the optical glass according to the present embodiment, the lower limit of the average coefficient of linear thermal expansion α at 100 to 300 ° C. is preferably 100 × 10 ^-7 ° C ^-1 , and further 102 × 10 ^-7 ° C ^-1 , 104 ×. The order of ^10-7 ° C ^-1 , 106 × ^10-7 ° C ^-1 , 108 × ^10-7 ° C ^-1 is more preferable. The upper limit of the average coefficient of linear thermal expansion α is more preferably 200 × 10 ^-7 ° C ^-1 , and further 190 × 10 ^-7 ° C ^-1 , 180 × 10 ^-7 ° C ^-1 , 170 × 10 ⁻ . ⁷ ° C ^-1 , 160 × 10 ^-7 ° C ^-1 , 150 × 10 ^-7 ° C ^-1 , 145 × 10 ^-7 ° C ^-1 is more preferable.

By setting the average linear expansion coefficient α of 100 to 300 ° C. in the above range, it is possible to suppress the change in the refractive index due to the thermal expansion of the glass, that is, the increase in the temperature coefficient dn / dT of the relative refractive index.

The average linear expansion coefficient α is measured based on the provisions of JOBIS08-2003. However, the sample shall be a round bar with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm, and with a load of 98 mN applied to the sample, it shall be heated to a constant rate of 4 ° C / min and the temperature shall be increased. And measure the elongation of the sample.
In this specification, the average linear expansion coefficient α is expressed in the unit of [° C ^-1 ], but the numerical value of the average linear expansion coefficient α is the same even when [K ^-1 ] is used as the unit.

<Temperature coefficient of relative refractive index dn / dT>
In the optical glass according to the present embodiment, the temperature coefficient dn / dT of the relative refractive index at the wavelength (633 nm) of the He-Ne laser is in the range of 20 to 40 ° C., preferably −1.0 × ^10-6 to −−. It is 13.0 × 10 ^-6 ° C ^-1 , and further −1.0 × 10 ^-6 to -10.0 × 10 ^-6 ° C ^-1 , -1.3 × 10 ^-6 to -9.0 ×. ^10-6 ° C ^-1 , -1.3 x ^10-6 to -8.0 x ^10-6 ° C ^-1 , -1.5 x ^10-6 to -7.0 x ^10-6 ° C ^-1 ,- It is more preferable in the order of 1.6 × 10 ^-6 to −6.5 × 10 ^-6 ° C ^-1 .

By setting dn / dT in the above range and combining it with an optical element having a positive dn / dT, the fluctuation of the refractive index becomes small even in an environment where the temperature of the optical element fluctuates greatly. The optical characteristics of can be exhibited with high accuracy.

The temperature coefficient dn / dT of the relative refractive index is measured based on the interferometry of JOBIS18-2008.
In this specification, the temperature coefficient dn / dT is expressed in the unit of [° C ^-1 ], but the numerical value of the temperature coefficient dn / dT is the same even when [K ^-1 ] is used as the unit.

<Glass transition temperature Tg>
The glass transition temperature Tg of the optical glass according to the present embodiment is preferably 600 ° C. or lower, more preferably 590 ° C. or lower, 580 ° C. or lower, 570 ° C. or lower, and 560 ° C. or lower.

When the upper limit of the glass transition temperature Tg satisfies the above range, it is possible to suppress an increase in the glass molding temperature and the annealing temperature, and it is possible to reduce thermal damage to the press molding equipment and the annealing equipment. 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.

<Specific gravity of glass>
In the optical glass according to the present embodiment, the specific gravity is preferably 3.40 or less, more preferably 3.30 or less, and more preferably 3.20 or less. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. As a result, the power consumption of the autofocus drive of the camera lens on which the lens is mounted can be reduced.

<Light transmission of glass>
The light transmittance of the optical glass according to this embodiment can be evaluated by the degree of coloring λ5.
The spectral transmittance of a glass sample having a thickness of 10.0 mm ± 0.1 mm is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 5% is defined as λ5.

The λ5 of the optical glass according to the present embodiment is preferably 400 nm or less, more preferably 390 nm or less, and further preferably 385 nm or less.

By using an optical glass having a shorter wavelength of λ5, it is possible to provide an optical element capable of suitable color reproduction.

(Manufacturing of optical glass)
The optical glass according to the embodiment of the present invention may be produced by blending a glass raw material so as to have the above-mentioned predetermined composition and using the blended glass raw material according to a known glass manufacturing method. For example, a plurality of kinds of compounds are mixed and sufficiently mixed to obtain a batch raw material, and the batch raw material is placed in a quartz crucible or a platinum crucible for rough melting. The melt obtained by crude melting is rapidly cooled and crushed to prepare a 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 formed and slowly cooled to obtain an optical glass. A known method may be applied to the molding and slow cooling of the molten glass.

The compound used when formulating the 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 examples of such compounds include oxides and carbonates. Examples thereof include salts, nitrates, hydroxides and fluorides.

(Manufacturing 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, a glass raw material is melted to obtain molten glass, and the molten glass is poured into a mold to form a plate shape to produce a glass material made of optical glass according to the present invention. The obtained glass material is appropriately cut, ground, and polished to produce a cut piece having a size and shape suitable for press molding. The cut piece is heated and softened, and press-formed (reheat-pressed) by a known method to produce an optical element blank that approximates the shape of the optical element. An optical element blank is annealed, and the optical element is manufactured by grinding and polishing by a known method.

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

Examples of the optical element include various lenses such as spherical lenses, prisms, and diffraction gratings.

The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

(Example)
[Preparation of glass sample]
The sample No. shown in Table 1 Compound raw materials corresponding to each component, that is, raw materials such as phosphates, carbonates, and oxides, were weighed and sufficiently mixed to prepare a compounding raw material so as to form a glass having a composition of 1 to 8. The compounding raw material was put into a platinum crucible, heated to 900 to 1350 ° C. in an air atmosphere to melt, homogenized and clarified by stirring to obtain molten glass. The molten glass was cast into a molding die, molded, and slowly cooled to obtain a block-shaped glass sample.
The compounding raw material is put into a quartz glass crucible, melted, then transferred to a platinum crucible, further heated and melted, homogenized by stirring, and clarified, and the obtained molten glass is cast into a molding die and molded. , May be slowly cooled.

[Evaluation of glass sample]
For the obtained glass sample, the glass composition, refractive index nd, Abbe number νd, λ5, glass transition temperature Tg, average linear expansion coefficient α, relative refractive index temperature coefficient dn / dT, and specific gravity are determined by the methods shown below. It was measured. The results are shown in Table 1.

[1] Glass Composition With respect to the obtained glass sample, the content of each glass component was measured by inductively coupled plasma emission spectroscopy (ICP-AES). No. 1 shown in Table 1. In all the glass samples 1 to 8, the content of F was 0%.

[2] Relative density Measured based on the Japan Optical Glass Industry Association standard JOBIS-05.

[3] Refractive index nd and Abbe number νd
The measurement was performed based on the Japan Optical Glass Industry Association standard JOGIS-01.

[4] λ5
Glass samples were processed to a thickness of 10 mm and had planes parallel to each other and optically polished, and the spectral transmittance in the wavelength range from 280 nm to 700 nm was measured. The spectral transmittance B / A was calculated with the intensity A of the light beam perpendicularly incident on one of the optically polished planes as the intensity A and the intensity of the light rays emitted from the other plane as the intensity B. The wavelength at which the spectral transmittance is 5% was defined as λ5. The spectral transmittance also includes the reflection loss of light rays on the sample surface.

[5] Glass transition temperature Tg
The glass transition temperature Tg was measured at a heating rate of 4 ° C./min using a thermomechanical analyzer (TMA) (TMA-4000S manufactured by Mac Science).

[6] Measurement of Temperature Coefficient dn / dT of Relative Refractive Index The obtained glass sample was measured based on the interferometry of JOBIS18-2008. A He-Ne laser having a wavelength of 633 nm was used as a light source, and continuous measurement was performed in a temperature range of −70 to 150 ° C. Of the measurement results, Table 1 shows the dn / dT values in the range of 20 ° C to 40 ° C.

[7] Measurement of average linear expansion coefficient α The average linear expansion coefficient α at 100 to 300 ° C. was measured based on the provisions of JOBIS08-2003. However, the sample shall be a round bar with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm, and with a load of 98 mN applied to the sample, it shall be heated to a constant rate of 4 ° C / min and the temperature shall be increased. And the elongation of the sample was measured.

(Example 2)
The glass sample obtained in Example 1 was cut and ground to prepare a cut piece. The cut piece was press-molded by a reheat press to prepare an optical element blank. The optical element blank is precisely annealed, the refractive index is precisely adjusted to the required refractive index, and then ground and polished by a known method to obtain a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, and a concave meniscus lens. , Various lenses such as a convex meniscus lens were obtained.

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

For example, the optical glass according to one aspect of the present invention can be produced by adjusting the composition described in the specification with respect to the glass composition exemplified above.
In addition, it is of course possible to arbitrarily combine two or more of the items described in the specification as an example or a preferable range.

Claims (5)

The content of P ₂ O ₅ is 25 to 50% by mass, and the content is 25 to 50% by mass.
The Nb ₂ O ₅ content is 14-40% by mass,
The total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TIM ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ + Ta ₂ O ₅ ] is 35 to 60% by mass. ,
The mass ratio of the content of TiO ₂ to the total content of TIM ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and Ta ₂ O ₅ [TIO ₂ / (TIO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ) + Ta ₂ O ₅ )] is 0.25 or more,
The mass ratio of the content of B ₂ O ₃ to the content of P ₂ O ₅ [B ₂ O ₃ / P ₂ O ₅ ] is 0.05 to 0.39.
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 10% by mass or more.
An optical glass having a mass ratio [Na ₂ O / K ₂ O] of the content of Na ₂ O to the content of K ₂ O of 1.50 or more. The optical glass according to claim 1, which does not substantially contain F. The optical glass according to claim 1 or 2, wherein the average linear thermal expansion coefficient α of 100 to 300 ° C. is 100 × 10 ^-7 to 200 × 10 ^-7 ° C. ^-1 . The temperature coefficient dn / dT of the relative refractive index at the wavelength (633 nm) of the He-Ne laser is −0.1 × 10 ^-6 to -13.0 × 10 ^-6 ° C ^-1 in the range of 20 to 40 ° C. The optical glass according to any one of claims 1 to 3. The optical element made of the optical glass according to any one of claims 1 to 4.