JP7132884B2 - Optical glasses and optical elements - Google Patents

Description

The present invention relates to optical glasses and optical elements.

Examples of fluorophosphate glasses containing phosphorus, oxygen and fluorine are described, for example, in US Pat.

JP-A-2005-112717 JP 2013-151410 A JP-A-51-114412 JP-A-58-217451

Fluorophosphate glass has a high utility value as an optical element material for correcting chromatic aberration. An object of one aspect of the present invention is to further increase the utility value of such a fluorophosphate glass as an optical element material.

One aspect of the present invention is an optical glass that is a fluorophosphate glass having a refractive index temperature coefficient dn/dT of less than 0° C. ⁻¹ , a glass transition temperature Tg of 550° C. or less, and an Abbe number νd of less than 50. Regarding.

The optical glass has a refractive index temperature coefficient dn/dT of less than 0° C. ⁻¹ . That is, the temperature coefficient dn/dT of the refractive index of the optical glass is a negative (minus) value.
The temperature coefficient of refractive index dn/dT (hereinafter also simply referred to as “dn/dT”) in the present invention and this specification is defined by the Japanese Optical Glass Industry Standard JOGIS18-2008 “Temperature coefficient of refractive index of optical glass. It is the temperature coefficient of the relative refractive index at a wavelength of 632.8 nm specified in "Method of Measurement" and is a value measured by an interferometric method.
In various optical systems such as imaging device systems and projection optical systems, multiple lenses made of optical glass with different optical characteristics are manufactured to correct chromatic aberration, and these lenses are combined to form an optical system. It is If such an optical system is constructed using only lenses made of optical glass having a positive value of dn/dT, the refractive index of the optical glass constituting each lens shows a similar increase or decrease tendency with respect to temperature changes. , it is difficult for individual lenses to cancel out the effects of temperature changes in the entire optical system. On the other hand, a lens made of optical glass having a negative value of dn/dT is combined with a lens made of optical glass having a positive value of dn/dT. It can be possible to cancel with a lens. As a result, the performance of the optical system (for example, imaging performance) can be maintained in a favorable state against temperature changes. In this respect, the above optical glass having a negative value of dn/dT is useful as an optical element material. For example, in an optical system composed of a combination of multiple lenses with positive refractive power, if the temperature coefficient of the refractive index of all lenses is positive, the focal length will decrease as the temperature rises, causing defocusing. As a result, the imaging performance deteriorates. On the other hand, if a lens with a negative temperature coefficient of refractive index is included in a plurality of lenses, the focal length of this lens increases as the temperature rises. can be reduced.
Also, conventional fluorophosphate glasses have low dispersion. In contrast, the optical glass is a high-dispersion fluorophosphate glass having an Abbe number νd of less than 50. The above optical glass is also useful as an optical element material because it has high dispersion characteristics that have been difficult to achieve with conventional fluorophosphate glasses.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, it is possible to provide an optical glass that is fluorophosphate glass, which is highly useful as an optical element material, and an optical element made of such an optical glass.

[Optical glass]
The optical glass is fluorophosphate glass. In the present invention and in this specification, "fluorophosphate glass" means glass containing at least phosphorus, oxygen and fluorine as elements constituting the glass.
The optical glass will be described in more detail below.

<Temperature coefficient of refractive index dn/dT>
The optical glass has a refractive index temperature coefficient dn/dT of less than 0° C. ⁻¹ . If dn/dT is less than 0° C. ⁻¹ , i.e., a negative value, such optical glasses allow individual lenses to offset or reduce the effects of temperature changes in the overall optical system as described above. can be done. In one aspect, the dn/dT of the optical glass is −1.0×10 ⁻⁶ ° C. ⁻¹ or less, −2.0×10 ⁻⁶ ° C. ⁻¹ or less, −3.0×10 ⁻⁶ ° C. ⁻ 1 or less. -3.5×10 ^-6 ℃ ^-1 or less, -4.0×10 ^-6 ℃ ^-1 or less, -4.5×10 ^-6 ℃ ^-1 or less, or -5.0×10 ^-6 °C ^-1 or less. In one aspect, the lower limit of dn/dT of the optical glass is −10.0×10 ⁻⁶ ° C. ⁻¹ or more, −9.0×10 ⁻⁶ ° C. ⁻¹ or more, −8.0×10 ⁻ It can be ⁶ ° C. ⁻¹ or more, or −5.0×10 ⁻⁶ ° C. ⁻¹ or more. However, it may fall below the lower limit exemplified above.

<Abbe number νd>
The Abbe number νd is a value representing properties related to dispersion, and is expressed as νd=(nd−1)/(nF−nC) using respective refractive indices nd, nF, and nC for the d-line, F-line, and C-line. .
The Abbe number νd of the optical glass is less than 50, preferably 49 or less, more preferably 48 or less, still more preferably 47 or less, still more preferably 46 or less, and even more preferably 45 or less. is. The above optical glass is useful as an optical element material in that it is a high-dispersion glass having an Abbe number νd in the above range, which has been difficult to achieve with conventional fluorophosphate glass. The Abbe number νd of the optical glass can be, for example, 33 or more, 34 or more, 35 or more, or 36 or more from the viewpoint of maintaining good thermal stability of the glass.

<Glass transition temperature Tg>
The optical glass has a glass transition temperature Tg of 550° C. or lower. If the glass transition temperature is low, the heating temperature can be lowered when the glass is reheated, softened and press-molded. As a result, it becomes easier to suppress fusion between the glass and the press mold. Moreover, since the heating temperature can be lowered, the thermal consumption of the glass heating device, the press mold, etc. can be reduced. Furthermore, since the glass annealing temperature can be lowered, the life of the annealing furnace can be extended. The glass transition temperature is preferably 540°C or lower, more preferably 530°C or lower, and even more preferably 520°C or lower. Also, the glass transition temperature Tg can be, for example, 400° C. or higher, 450° C. or higher, or 480° C. or higher.

The dn/dT, Abbe number νd and glass transition temperature Tg within the above ranges can be achieved by adjusting the glass composition as detailed below.

<Glass composition>
In the present invention and this specification, the content and total content of cationic components are expressed in cation % unless otherwise specified, and the content and total content of anionic components are expressed in anion % unless otherwise specified.
Here, "cation %" is a value calculated by "(number of cations of interest/total number of cations of glass component) x 100", and is the molar percentage of the amount of cations of interest to the total amount of cation components. means.
In addition, "anion %" is a value calculated by "(number of anions of interest/total number of anions of glass component) x 100", and means the molar percentage of the amount of anions of interest with respect to the total amount of anion components. do.
The molar ratio of the contents of the cation components is equal to the ratio of the contents of the cation components of interest expressed in cation %, and the molar ratio of the contents of the anion components to each other is the ratio of the contents of the anion components of interest expressed in anion %. equal to the ratio.
The molar ratio of the content of the cationic component to the content of the anionic component is the ratio of the contents of the components of interest (expressed in mol%) when the total amount of all cationic components and all anionic components is 100 mol%. be.
The content of each component can be quantified by known methods such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), ion chromatography, and the like. .

^P5+ acts as a network forming component. Al ³⁺ is a component that maintains the thermal stability of glass and works to improve chemical durability and workability. The molar ratio of the Al ³⁺ content to the P ⁵⁺ content (Al ³⁺ /P ⁵⁺ ) is preferably 0.30 or more in order to maintain good thermal stability of the glass. In order to increase the refractive index while maintaining the Abbe number, it is effective to set the molar ratio (Al ³⁺ /P ⁵⁺ ) to 0.30 or more.
A preferable lower limit of the molar ratio (Al ³⁺ /P ⁵⁺ ) is 0.5. On the other hand, the preferable upper limit of the molar ratio (Al ³⁺ /P ⁵⁺ ) is 2, and the more preferable upper limit is 1, from the viewpoint of maintaining good thermal stability of the glass.

Nb ⁵⁺ is a useful component for imparting high dispersion characteristics to the optical glass. In addition, Nb ⁵⁺ works as a network-forming component together with P ⁵⁺ to maintain the thermal stability of the glass and increase the partial dispersion ratio. In order to obtain such effects, the content of Nb ⁵⁺ is preferably 8% or more. A more preferred lower limit for the Nb ⁵⁺ content is 9%, a still more preferred lower limit is 10%, a still more preferred lower limit is 11%, and a still more preferred lower limit is 12%. On the other hand, when the content of Nb ⁵⁺ is excessive, the volatility of the glass during melting becomes significant, and the homogeneity of the glass tends to deteriorate. Therefore, the preferred upper limit of the Nb ⁵⁺ content is 25%, the more preferred upper limit is 23%, and the still more preferred upper limit is 20%.

From the viewpoint of maintaining the thermal stability of the glass, the total content of P ⁵⁺ and Nb ⁵⁺ (P ⁵⁺ +Nb ⁵⁺ ) is preferably 35% or more, more preferably 38%, and still more preferably 40%. is. A preferred upper limit of the total content of P ⁵⁺ and Nb ⁵⁺ (P ⁵⁺ +Nb ⁵⁺ ) is 60%, a more preferred upper limit is 58%, a still more preferred upper limit is 55%, and a still more preferred upper limit is 53%. .

Both Al ³⁺ and Nb ⁵⁺ serve to improve the chemical durability of the glass. From the viewpoint of imparting excellent chemical durability to the glass, the total content of Al ³⁺ and Nb ⁵⁺ is preferably 15% or more, more preferably 20% or more, and preferably 25% or more. More preferably, it is more preferably 28% or more. The total content of Al ³⁺ and Nb ⁵⁺ is preferably 45% or less, more preferably 40% or less, from the viewpoint of maintaining thermal stability.

The content of O ²⁻ is preferably 80% or less, more preferably 78% or less, and even more preferably 75% or less, from the viewpoint of obtaining high dispersion characteristics. O ^2- also serves to maintain the thermal stability of the glass. From the viewpoint of maintaining the thermal stability of the glass, the O ²⁻ content is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more.

F- has a function of imparting anomalous dispersion ^to the glass, a function of lowering the glass transition temperature, and a function of improving chemical durability. From the viewpoint of obtaining these functions ^, the content of F.sup.- is preferably 20% or more anions, more preferably 23% or more, and even more preferably 25% or more. On the other hand, from the viewpoint of maintaining the thermal stability of the glass ^, the F 2 content is preferably 60% or less, more preferably 50% or less, and even more preferably 40% or less.

The molar ratio of the content of O ²⁻ to the total content of P ⁵⁺ and Nb ⁵⁺ (O ²⁻ /(P ⁵⁺ +Nb ⁵⁺ )) is 2.5 or more from the viewpoint of suppressing volatility during glass melting. is preferred, 2.6 or more is more preferred, and 2.7 or more is even more preferred. On the other hand, from the viewpoint of maintaining the thermal stability of the glass, the molar ratio (O ²⁻ /(P ⁵⁺ +Nb ⁵⁺ )) is preferably 3.5 or less, more preferably 3.4 or less. , 3.3 or less.

Alkaline earth metal components, that is, Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ are components that work to adjust the viscosity and refractive index of glass and improve thermal stability. In order to obtain the above effects, the total content R ²⁺ (Mg ²⁺ +Ca ²⁺ +Sr ²⁺ +Ba ²⁺ ) of the alkaline earth metal components is preferably 20% or more, more preferably 23% or more, and more preferably 25%. It is more preferable that it is above.
On the other hand, if the total content R ²⁺ of the alkaline earth metal components is excessive, the thermal stability tends to decrease, so the total content R ²⁺ of the alkaline earth metal components is preferably 50% or less. , is more preferably 45% or less, still more preferably 40% or less, and even more preferably 35% or less.

The optical glass may or may not contain one or more rare earth elements selected from the group consisting of La ³⁺ , Gd ³⁺ , Y ³⁺ , Lu ³⁺ and Yb ³⁺ .
The total content of La ³⁺ , Gd ³⁺ , Y ³⁺ , Lu ³⁺ and Yb ³⁺ with respect to the Al ³⁺ content (La ³⁺ +Gd ³⁺ +Y ³⁺ +Lu ³⁺ +Yb ³⁺ ) molar ratio ((La ³⁺ +Gd ³⁺ +Y ³⁺ +Lu ³⁺ +Yb ³⁺ )/Al ³⁺ ) is preferably 0.3 or less, more preferably 0.2 or less. , 0.1. The molar ratio ((La ³⁺ +Gd ³⁺ +Y ³⁺ +Lu ³⁺ +Yb ³⁺ )/Al ³⁺ ) may be zero.

Next, the content of each component will be explained.

P5 ⁺ is an essential component that forms a glass network in fluorophosphate glass. From the viewpoint of maintaining good thermal stability, the lower limit of the P ⁵⁺ content is preferably 5%, more preferably 10%, and even more preferably 20%. From the viewpoint of maintaining good chemical durability and maintaining low dispersibility and anomalous partial dispersibility, the upper limit of the P ⁵⁺ content is preferably 40%, more preferably 38%, and still more preferably 35%. be.

Al ³⁺ is a component that works to improve thermal stability, chemical durability and workability, and also works to increase the refractive index. From the above viewpoints, the preferred lower limit of the Al ³⁺ content is 5%, the more preferred lower limit is 7%, the still more preferred lower limit is 9%, and the much more preferred lower limit is 11%. From the above viewpoints, the upper limit of the Al ³⁺ content is preferably 40%, more preferably 38%, still more preferably 36%, and still more preferably 34%.

In the glass composition expressed in atomic %, the ratio O ²⁻ /Al ³⁺ of the content of O ²⁻ to the content of Al ³⁺ is preferably less than 12, more preferably less than 10, and 9 Less than is more preferred, and less than 8 is even more preferred. As the content of O ²⁻ increases, the content of F 2 ⁻ relatively decreases and the glass transition temperature tends to rise. On the other hand, as described above, Al ³⁺ is a useful component for improving thermal stability, chemical durability and workability, and providing desired optical properties. In order to suppress the increase in the glass transition temperature while sufficiently obtaining the effect of Al ³⁺ , the ratio of the content of O ²⁻ to the content of Al ³⁺ in the glass composition expressed in atomic % O ²⁻ /Al ³⁺ is preferably within the above range. Regarding the lower limit of the above ratio O ²⁻ /Al ³⁺ , from the viewpoint of suppressing a decrease in devitrification resistance due to a relative increase in the content of Al ³⁺ , for example, 2 or more or 3 or more is a standard. be able to.
The content of each component in the glass composition represented by atomic % is a value expressed as a mole percentage of the content of each component when the total content of all cationic components and all anionic components is 100 mol%. Calculated.

Preferred contents of the individual components of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ are as follows.
A preferred range for the Mg ²⁺ content is 0-10%, and a more preferred range is 0-8%.
A preferred range for the Ca ²⁺ content is 0-20%, and a more preferred range is 0-15%.
A preferred range for the Sr ²⁺ content is 0 to 40%, and a more preferred range is 0 to 30%.
The Ba ²⁺ content preferably has a lower limit of 5%, a more preferred lower limit of 10%, a preferred upper limit of 50%, and a more preferred upper limit of 40%.

Preferred individual contents of La ³⁺ , Gd ³⁺ , Y ³⁺ and Lu ³⁺ are as follows.
A preferred range for the La ³⁺ content is 0 to 5%, and a more preferred range is 0 to 3%.
A preferred range for the Gd ³⁺ content is 0-5%, and a more preferred range is 0-3%.
A preferred range for the Y ³⁺ content is 0 to 5%, and a more preferred range is 0 to 3%.
A preferred range for the Lu ³⁺ content is 0-5%, and a more preferred range is 0-3%.

Since Yb ³⁺ has light absorption in the infrared region, it is not suitable for use in imaging with infrared light. Therefore, the content of Yb ³⁺ is preferably limited as follows using the molar ratio (Yb ³⁺ /(La ³⁺ +Gd ³⁺ +Y ³⁺ +Lu ³⁺ +Yb ³⁺ )) to the total content of other rare earth components. . That is, the molar ratio of the content of Yb ³⁺ to the total content of La ³⁺ , Gd ³⁺ , Y ³⁺ , Lu ³⁺ and Yb ³⁺ (Yb ³⁺ /(La ³⁺ +Gd ³⁺ +Y ³⁺ +Lu ³⁺ +Yb ³⁺ )) is 0.5. It is preferably 0.1 or less, more preferably 0 (the Yb ³⁺ content is 0%).

Zn ²⁺ has the function of improving thermal stability while maintaining the refractive index, and its content is preferably in the range of 0 to 10%. A more preferred upper limit of the Zn ²⁺ content is 8%, and a still more preferred upper limit is 5%. The content of Zn ²⁺ may be 0%.

The alkali metal component is a cationic component that functions to adjust the viscosity of glass and improve thermal stability. If the total content R ⁺ of the alkali metal components is excessive, the thermal stability will decrease. Therefore, the total content R ⁺ of the alkali metal components is preferably 0 to 30%. In view of the above, a more preferred range for R ⁺ is 0 to 20%, and a more preferred range is 0 to 15%. More preferably, the upper limit for R ⁺ is 10%, even more preferably 8%, and even more preferably 7%. In addition, it is preferable to set R ⁺ within the above range also from the viewpoint of imparting excellent chemical durability to the glass.
On the other hand, from the viewpoint of lowering the glass transition temperature, the lower limit of R ⁺ is preferably 1%, more preferably 2%, and still more preferably 3%.
Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ can be mentioned as alkali metal components R ⁺ . Rb ⁺ and Cs ⁺ tend to increase the specific gravity of the glass compared to other alkali metal components.
Therefore, the content of Rb ⁺ is preferably 0 to 3%, more preferably 0 to 2%, even more preferably 0 to 1%, and may be 0%.
The content of Cs ⁺ is preferably 0 to 3%, more preferably 0 to 2%, even more preferably 0 to 1%, and may be 0%.
From the viewpoint of maintaining the thermal stability of the glass, the Li ⁺ content is preferably in the range of 0 to 30%, more preferably in the range of 2 to 20%, still more preferably in the range of 3 to 10%, and more preferably in the range of 3-7%, with a more preferred range of 3-5%.
From the viewpoint of maintaining the thermal stability of the glass, the Na ⁺ content is preferably in the range of 0 to 10%, more preferably in the range of 0 to 8%, and still more preferably in the range of 0 to 6%.
From the viewpoint of maintaining the thermal stability of the glass, the K ⁺ content is preferably in the range of 0-10%, more preferably in the range of 0-8%, and still more preferably in the range of 0-6%.

Si ⁴⁺ , Ti ⁴⁺ , W ⁶⁺ , Bi ³⁺ , and Zr ⁴⁺ can be contained in small amounts, but if they are contained excessively, meltability and thermal stability decrease. Therefore, the contents of Si ⁴⁺ , Ti ⁴⁺ , W ⁶⁺ and Zr ⁴⁺ are each preferably in the range of 0 to 5%, more preferably in the range of 0 to 3%, and 0 to 1%. It is more preferable to make it a range, and it may be 0%.

B ³⁺ exhibits significant volatility even at low contents. The content of B ³⁺ is preferably 2% or less so as not to promote volatilization. A preferred range of the B ³⁺ content is 0 to 1%, a more preferred range is 0 to 0.1%, and 0% is even more preferred.

When the molten glass flows out from a pipe attached to a glass melting apparatus, Cl ⁻ is contained in order to suppress the wetting of the glass melt onto the outer periphery of the pipe and to suppress the quality deterioration of the glass due to the wetting. is valid. The preferred range of the Cl ⁻ content is 0 to 1%, more preferred range is 0 to 0.5%, and still more preferred range is 0 to 0.3%. Cl ⁻ also has an effect as a fining agent.

In addition, a small amount of Sb ³⁺ , Ce ⁴⁺ or the like can be added as a clarifier. The total amount of fining agent can be 0% or more, preferably less than 1%. For example, the total content of Sb ³⁺ and Ce ⁴⁺ can be 0% or more, preferably less than 1%.

Pb, Cd, As, and Th are components of concern about environmental impact.
Therefore, the optical glass preferably does not substantially contain at least one of Pb, Cd, As and Th.
The content of Pb ²⁺ is preferably from 0 to 0.5%, more preferably from 0 to 0.1%, even more preferably from 0 to 0.05% ^. It is particularly preferred not to contain.
The content of Cd ²⁺ is preferably 0 to 0.5%, more preferably 0 to 0.1%, even more preferably 0 to 0.05%, and Cd ²⁺ is substantially It is particularly preferred not to contain.
The content of As ³⁺ is preferably 0 to 0.1%, more preferably 0 to 0.05%, even more preferably 0 to 0.01%, and the content of As ³⁺ is substantially It is particularly preferred not to contain.
The content of Th ⁴⁺ is preferably 0 to 0.1%, more preferably 0 to 0.05%, even more preferably 0 to 0.01%, Th ⁴⁺ is substantially It is particularly preferred not to contain.

The optical glass can preferably exhibit high transmittance over a wide visible region. In order to take advantage of these features, the optical glass preferably does not contain a coloring agent. Examples of coloring agents include Cu, Co, Ni, Fe, Cr, Eu, Nd, Er, V, and the like. Preferably, the optical glass does not substantially contain at least one of Cu, Co, Ni, Fe, Cr, Eu, Nd, Er and V. The content range of Cu, Co, Ni, Fe, Cr, Eu, Nd, Er, and V in terms of cation % is preferably less than 100 ppm, more preferably 0 to 80 ppm. , more preferably 0 to 50 ppm or less, and particularly preferably not substantially contained. Here, ppm means cation ppm.
Also, Hf, Ga, Ge, Te, and Tb are expensive components. Therefore, the optical glass preferably does not substantially contain at least one of Hf, Ga, Ge, Te and Tb. The content range of Hf, Ga, Ge, Te, and Tb in terms of cation % is preferably 0 to 0.1%, more preferably 0 to 0.05%, It is more preferably 0 to 0.01%, still more preferably 0 to 0.005%, even more preferably 0 to 0.001%, and particularly preferably not substantially contained. .
The above optical glass can exhibit various properties without introducing Hf, Ga, Ge, Te, and Tb.

<Glass characteristics>
With respect to glass properties, the optical glass has a dn/dT of less than 0° C. ⁻¹ , a glass transition temperature Tg of less than or equal to 550° C. and an Abbe number νd of less than 50. Glass properties that the optical glass may have are further described below.

(Partial dispersion ratio Pg, F)
The optical glass preferably has positive anomalous dispersion.
A partial dispersion ratio Pg,F is used as an index of positive anomalous dispersion. The partial dispersion ratio Pg,F uses the refractive index nF at the F line (wavelength 486.13 nm), nC at the C line (wavelength 656.27 nm) and the refractive index ng at the g line (wavelength 435.84 nm), is represented as
Pg, F = (ng-nF)/(nF-nC) (1)
In one aspect of the optical glass, the Abbe number νd and the partial dispersion ratio Pg,F preferably satisfy the following formula (2).
Pg,F>−0.0004νd+0.5718 (2)
An optical glass whose Abbe number νd and partial dispersion ratio Pg,F satisfy the above formula (2) is suitable as an optical glass for high-order chromatic aberration correction.

(Transmittance)
The optical glass is preferably very little colored, and is suitable as a material for imaging optical elements such as camera lenses and projection optical elements such as projectors.
A preferred embodiment of the optical glass is glass having an internal transmittance of 96.5% or more at a wavelength of 400 nm to 700 nm and a thickness of 10 mm.
A preferable range of the internal transmittance is 97% or more, a more preferable range is 98% or more, and a much more preferable range is 99% or more.
It should be noted that glass containing light-emitting ions such as glass for lasers, such as Nd, Eu, Er, V, etc., has absorption in the visible region. Not suitable for element materials.

(Liquidus temperature)
A preferred embodiment of the optical glass is an optical glass having a liquidus temperature of 1000° C. or less. If the liquidus temperature is low, the melting and forming temperature of the glass can be lowered. As a result, the volatility of the glass during melting and molding can be reduced, and the occurrence of striae and variations in optical properties can be suppressed.
A more preferable range of the liquidus temperature is 950° C. or lower, and a further preferable range is 900° C. or lower.

(specific gravity)
The above optical glass can increase the partial dispersion ratio mainly by containing Nb ⁵⁺ without relying on rare earth elements, which increase the partial dispersion ratio but also increase the specific gravity. can have a specific gravity.
A preferred embodiment of the optical glass is optical glass having a specific gravity of 4.3 or less. By reducing the specific gravity, the weight of the optical element can be reduced.
A more preferable range of specific gravity is 4.2 or less, and a further preferable range is 4.1 or less. The specific gravity can be, for example, 3.5 or higher.

(refractive index nd)
The refractive index nd of the optical glass is not particularly limited. In one aspect, the refractive index nd can be, for example, 1.58 or higher, preferably 1.60 or higher, more preferably 1.62 or higher. Also, the refractive index nd can be, for example, 1.70 or less, but can also exceed this.

<Glass manufacturing method>
The above optical glass can be obtained, for example, by blending, melting, and molding glass raw materials so as to obtain desired properties. As glass raw materials, for example, phosphates, fluorides, alkali metal compounds, alkaline earth metal compounds, and the like may be used. Known methods may be used for the melting method and molding method of the glass.

[Glass material for press molding, its manufacturing method, and manufacturing method of glass molding]
According to one aspect of the present invention, it is possible to provide a press-molding glass material made of the above optical glass, a glass molded product made of the above optical glass, and a method for producing them.
A glass material for press molding means a glass lump that is heated and subjected to press molding.
Examples of press-molding glass materials include glass lumps having a mass equivalent to the mass of press-molded products such as precision press-molding preforms and glass materials for press-molding optical element blanks (press-molding glass gobs). can be shown.
A glass material for press molding is produced through a process of processing a glass molded body. The glass molded body can be produced by heating and melting glass raw materials as described above and molding the obtained molten glass. Cutting, grinding, polishing and the like can be exemplified as a method for processing the glass molded body.

[Optical element blank and its manufacturing method]
According to one aspect of the present invention, it is possible to provide an optical element blank made of the above optical glass. An optical element blank is a molded glass body having a shape that approximates the shape of the optical element to be manufactured. The optical element blank may be produced by a method of molding glass into a shape obtained by adding a processing allowance to be removed by processing to the shape of the optical element to be manufactured. For example, a method of heating and softening a glass material for press molding and press molding (reheat press method), a method of supplying a molten glass lump to a press mold by a known method and press molding (direct press method), etc. can be used to form an optical element. Blanks can be made.

[Optical element and its manufacturing method]
According to one aspect of the present invention, an optical element made of the above optical glass can be provided. Examples of types of optical elements include lenses such as spherical lenses and aspherical lenses, prisms, and diffraction gratings. The shape of the lens includes various shapes such as biconvex lens, plano-convex lens, bi-concave lens, plano-concave lens, convex meniscus lens, and concave meniscus lens. An optical element can be manufactured by a method including a step of processing a glass molded body made of the above optical glass. Examples of processing include cutting, cutting, rough grinding, fine grinding, polishing, and the like. With the above optical element, it is possible to construct an optical system whose performance (for example, imaging performance) changes little with respect to temperature changes.

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

(Example 1)
In order to obtain the glass composition shown in Table 1, corresponding phosphates, fluorides, oxides, etc. were used as raw materials for introducing each component, and the raw materials were weighed and thoroughly mixed to obtain a prepared raw material. .
This prepared raw material was placed in a platinum crucible and heated to melt. After melting, the molten glass is poured into a mold, allowed to cool to near the glass transition temperature, immediately placed in an annealing furnace, annealed in the range of the glass transition temperature for about 1 hour, and then allowed to cool to room temperature in the furnace. , each optical glass shown in Table 1 was obtained.
When the obtained optical glass was observed under an enlarged optical microscope, precipitation of crystals, foreign matter such as platinum particles, bubbles, and striae were not observed.
Table 1 shows various characteristics of the optical glass thus obtained.
Various properties of the optical glass were measured by the methods described below.

(1) Refractive indices nd, ng, nF, nC and Abbe number νd
The refractive index nd, ng, nF, nC and Abbe number νd of the glass obtained by cooling at a cooling rate of −30° C./hour were measured by the refractive index measuring method specified by the Japan Optical Glass Industry Association.

(2) Partial dispersion ratio Pg, F
The partial dispersion ratio Pg, F was calculated from the refractive indices ng, nF, and nC obtained in (1) above.

(3) glass transition temperature Tg
A differential scanning calorimeter (DSC3300) manufactured by NETZSCH was used to measure the glass transition temperature Tg at a heating rate of 10°C/min.

(4) Temperature coefficient of refractive index dn/dT
A disc-shaped sample with a diameter of 20 mm and a thickness of 5 mm was prepared, and a He—Ne gas laser was used to measure the temperature coefficient of the refractive index of optical glass according to the Japan Optical Glass Industry Association Standard JOGIS18-2008. The temperature coefficient dn/dT of the relative refractive index at a wavelength of 632.8 nm was measured by interferometry. Specifically, the sample temperature was raised from −40° C. to 80° C. at intervals of 20° C. (heating rate: about 1° C./min), and the sample temperature and the number of movements of the interference fringes were continuously measured. From the results, the refractive index temperature coefficient dn/dT at a temperature of 20 to 40° C. was determined.

(5) Specific Gravity Specific gravity was measured by the Archimedes method.

(6) Liquidus temperature LT
50 g of glass was placed in a platinum crucible, and after melting at 1100° C. for 20 minutes with a platinum lid, the glass was held at a predetermined temperature for 2 hours. After holding for 2 hours, the glass was observed, and the liquidus temperature LT was obtained from the presence or absence of crystal precipitation.
For each glass shown in Table 1, the glass was held at 850° C. for 2 hours by the above method, and then visually observed and magnified observation (100×) using an optical microscope was performed. As a result, precipitation of crystals was not observed.
Therefore, the liquidus temperature LT of each glass shown in Table 1 is 1000° C. or less.

(7) Transmittance For each glass of the examples shown in Table 1, the internal transmittance at a thickness of 10 mm was measured according to the internal transmittance measurement (JOGIS-17) of the Japan Optical Glass Industry Association standard. The example glasses had a transmission of greater than 96.50%.

The above results are shown in Table 1 (Tables 1-1 and 1-2).

（注）正の値の場合は、下記式を満たす。
Ｐｇ，Ｆ＞－０．０００４νｄ＋０．５７１８

(Note) In the case of a positive value, the following formula is satisfied.
Pg,F>−0.0004νd+0.5718

（注）正の値の場合は、下記式を満たす。
Ｐｇ，Ｆ＞－０．０００４νｄ＋０．５７１８

(Note) In the case of a positive value, the following formula is satisfied.
Pg,F>−0.0004νd+0.5718

The glass compositions expressed in atomic % of the examples in Table 1 are shown in Table 2 (Tables 2-1 and 2-2).

(Example 2)
Using each optical glass of Example 1, a lens blank was produced by the known method described above. The produced lens blanks were ground and polished to produce various lenses (biconvex lens, convex meniscus lens, concave meniscus lens, biconcave lens, planoconvex lens, planoconcave lens).
Both lenses are lightweight and suitable for high-order chromatic aberration correction.
By combining each lens of Example 2 with a lens made of optical glass having a positive refractive index temperature coefficient dn/dT, compared with an optical system configured using only lenses made of optical glass having a positive dn/dT Therefore, it is possible to construct an optical system having stable imaging performance with little change in imaging performance with respect to temperature change.

Finally, each aspect described above is summarized.

According to one aspect, the optical glass is a fluorophosphate glass having a refractive index temperature coefficient dn/dT of less than 0° C. ⁻¹ , a glass transition temperature Tg of 550° C. or less, and an Abbe number νd of less than 50. provided.

The above optical glass is useful as an optical element material because it is a fluorophosphate glass having a negative temperature coefficient dn/dT of refractive index and a high dispersion characteristic that has been difficult to achieve with conventional fluorophosphate glasses. is. Furthermore, since the optical glass has a glass transition temperature Tg of 550° C. or less, it is suitable for press molding.

In one aspect, the content of Nb ⁵⁺ in the optical glass can be 8 cation % or more.

In one aspect, the total content of P ⁵⁺ and Nb ⁵⁺ (P ⁵⁺ +Nb ⁵⁺ ) in the optical glass can be 35 cation % or more.

In one aspect, the molar ratio (O ²⁻ /(P ⁵⁺ +Nb ⁵⁺ )) of the optical glass can be 3.5 or less.

According to one aspect, an optical element made of the above optical glass is provided.

It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the meaning and range of equivalents of the scope of the claims.
For example, the glass according to one aspect of the present invention can be obtained 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 matters described as examples or preferred ranges in the specification.

Claims (10)

P ⁵⁺ content of 5 to 40 cation %,
Al ³⁺ content of 5 to 40 cationic %,
Nb ⁵⁺ content of 8 to 25 cation %,
O ^2- content of 40 to 80 anion%,
F ^- content is 20 to 60 anion%,
The total content R ⁺ of the alkali metal components is 1 cation % or more,
An optical glass which is a fluorophosphate glass having a refractive index temperature coefficient dn/dT of less than 0° C. ⁻¹ , a glass transition temperature Tg of 550° C. or less, and an Abbe number νd of less than 50. 2. The optical glass according to claim 1, wherein the content of Pb ²⁺ is 0-0.5 cation %. The optical glass according to claim 1 or 2, wherein the total content of P ⁵⁺ and Nb ⁵⁺ (P ⁵⁺ +Nb ⁵⁺ ) is 35 cationic % or more. 4. The optical glass according to claim 1, wherein the molar ratio (O ²⁻ /(P ⁵⁺ +Nb ⁵⁺ )) is 3.5 or less. The optical glass according to any one of claims 1 to 4, wherein the total content of Al ³⁺ and Nb ⁵⁺ is 15-45 cationic %. The optical glass according to any one of claims 1 to 5, wherein the total content R ²⁺ (Mg ²⁺ +Ca ²⁺ +Sr ²⁺ +Ba ²⁺ ) of alkaline earth metal components is 20 to 50 cation %. ^{The molar} ratio (( ^{La 3+ + Gd 3+ + Y 3+ + Lu 3+ + Yb 3+} )/Al ³⁺ ) is 0.3 or less, the optical glass according to any one of claims 1 to 6. 8. The glass composition according to any one of claims 1 to 7, wherein the ratio of the content of O ²⁻ to the content of Al ³⁺ (O ²⁻ /Al ³⁺ ) is less than 12 in the glass composition expressed in atomic %. optical glass. a Mg ²⁺ content of 0 to 10 cation %,
a Ca ²⁺ content of 0 to 20 cationic %;
Sr ²⁺ content of 0 to 40 cation %,
Ba ²⁺ content of 5 to 40 cation %,
La ³⁺ content of 0 to 5 cationic %,
a Gd ³⁺ content of 0 to 5 cationic %;
Y ³⁺ content is 0 to 5 cationic %,
a Lu ³⁺ content of 0 to 5 cationic %;
Molar ratio of the content of Yb ³⁺ to the total content of La ³⁺ , Gd ³⁺ , Y ³⁺ , Lu ³⁺ and Yb ³⁺ (Yb ³⁺ /(La ³⁺ +Gd ³⁺ +Y ³⁺ +Lu ³⁺ +Yb ³⁺ )) 0.5 or less Zn ²⁺ The content of 0 to 10 cation%,
the total content R ⁺ of the alkali metal components is 1 to 30 cation %,
Rb ⁺ content of 0 to 3 cationic %,
Cs ⁺ content of 0 to 3 cation %,
Li ⁺ content of 0 to 30 cation %,
Na ⁺ content of 0 to 10 cation %,
K ⁺ content of 0 to 10 cation %,
a Si ⁴⁺ content of 0 to 5 cationic %,
The content of Ti ⁴⁺ is 0 to 5 cation %,
W ⁶⁺ content is 0 to 5 cationic %,
a Zr ⁴⁺ content of 0 to 5 cationic %,
B ³⁺ content is 2 cation % or less,
The optical glass according to any one of claims 1 to 8, wherein An optical element comprising the optical glass according to any one of claims 1 to 9.