JP2014024748A - Optical glass, glass raw material for press molding, and optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical glass with less coloring even when a large amount of a high refractive index component is included.SOLUTION: The optical glass has a refractive index nd of 1.9 or more and less than 1.97, has a total content of TiO, NbO, WOand BiOwithin the range from 30 mol% to 60 mol%, and shows a βOH value defined by formula (1):βOH=-ln(B/A)/t, of 0.1 mmor more. A glass raw material for press molding and an optical element using the optical glass are also provided. In formula (1), t represents the thickness (mm) of the optical glass used for the measurement of an external transmittance; A represents an external transmittance (%) at a wavelength of 2500 nm when the light is incident parallel to the thickness direction of the optical glass; B represents an external transmittance (%) at a wavelength of 2900 nm when the light is incident parallel to the thickness direction of the optical glass; and ln is a natural logarithm.

Description

  The present invention relates to an optical glass, a glass material for press molding, and an optical element.

  Optical glass with a high refractive index is required as a material for optical elements effective for enhancing the functions and compactness of imaging optical systems and projection optical systems. High refractive index optical glass contains a large amount of high refractive index components such as Ti, Nb, W and Bi as glass components. In an optical glass containing a large amount of high refractive index components, these components are reduced during the melting process, and light absorption on the short wavelength side in the visible light region is strengthened. For this reason, there exists a problem that coloring of optical glass increases. As a means for solving such a problem, a technique described in Patent Document 1 has been proposed.

In the technique described in Patent Document 1, the non-oxidizing gas is bubbled during glass melting to promote the discharge of excess oxygen components in the molten glass, thereby reducing the reduction of the Nb ₂ O ₅ component. A method of reducing the melting of noble metal materials such as platinum constituting the melting vessel into glass has been proposed. Here, as the bubbling gas, an inert gas such as helium, neon, argon, krypton, xenon and nitrogen, a reducing gas such as carbon monoxide and hydrogen, or a mixture of these gas species is considered preferable. .

Further, Patent Document 1 proposes to heat-treat the glass once obtained at a reheating temperature within a range of (glass transition temperature Tg−100) ° C. to (glass transition temperature Tg + 100) ° C. Has been. By this heat treatment, even when the reduced Nb ₂ O ₅ component is contained in the glass, coloring of the glass can be reduced by oxidizing the Nb ₂ O ₅ component.

JP 2011-246344 A

The technical idea of the technique described in Patent Document 1 is as follows: (1) A metal molten container that eliminates excess oxygen components in the molten glass as long as the Nb ₂ O ₅ component is reduced and does not adversely affect the coloration of the glass. (2) Even if the Nb ₂ O ₅ component is somewhat reduced, the glass is heat-treated to oxidize the Nb ₂ O ₅ component and reduce coloring. However, when an inert gas such as helium, neon, argon, krypton, xenon, or nitrogen is bubbled, the Nb ₂ O ₅ component is reduced, and it is difficult to significantly reduce the coloring of the glass even if heat treatment is performed after glass forming. .

  Further, when a glass containing a large amount of a high refractive index component such as Ti, Nb, W, or Bi is melted and bubbled with a reducing gas such as carbon monoxide or hydrogen described in Patent Document 1, a high refractive index is obtained. There is a problem that the components are reduced to be metallized to form an alloy with a metal material such as platinum constituting the melting vessel, and the strength and durability of the melting vessel are remarkably lowered. Therefore, even if the technique described in Patent Document 1 is used, it is still difficult to significantly reduce the coloring of the high refractive index optical glass.

  The present invention has been made in view of the above circumstances, and provides an optical glass with little coloring even when it contains a large amount of a high refractive index component, and a glass material for press molding and an optical element using the optical glass. For the purpose.

The above-mentioned subject is achieved by the following present invention. That is, the optical glass of the present invention has a refractive index nd of 1.9 or more and less than 1.97, and at least one selected from TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ as a glass component. The total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is in the range of 30 mol% to 60 mol%, and the following formula (1) The βOH value shown is 0.1 mm ⁻¹ or more.
Formula (1) βOH = −ln (B / A) / t
[In formula (1), t represents the thickness (mm) of the optical glass used for measuring the external transmittance, and A represents the external transmission at a wavelength of 2500 nm when light is incident on the optical glass in parallel with the thickness direction. B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the optical glass parallel to the thickness direction. In is a natural logarithm. ]

An embodiment of the optical glass of the present invention preferably contains a _P 2 _{O 5} as a glass component in the range of 15mol% ~35mol%.

It is preferable that other embodiment of the optical glass of this invention satisfy | fills the following Formula (2).
Formula (2) λτ80 <aX + b
[In formula (2), λτ80 is the measured internal transmittance after measuring the internal transmittance in the wavelength range of 280 to 700 nm when light is incident on the optical glass parallel to the thickness direction. The internal transmittance calculated based on the assumption that the thickness of the optical glass is 10 mm based on this represents a wavelength (nm) at which the internal transmittance is 80%, a represents a constant (1.8359 nm / mol%), b represents Represents a constant (351.06 nm), and X represents the total content (mol%) of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ . ]

Another embodiment of the optical glass of the present invention preferably contains less than 1000 ppm of antimony oxide in terms of Sb ₂ O ₃ .

  The glass material for press molding of the present invention includes the optical glass of the present invention.

  The optical element of the present invention includes the optical glass of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where a high refractive index component is contained abundantly, an optical glass with little coloring and a glass material for press molding and an optical element using the same can be provided.

No. having the composition shown in Table 1. No. 1 having a thickness of 5 mm with respect to the βOH value when the βOH value of 1 glass was changed. It is the graph which showed the change of the external transmittance (T450) in wavelength 450nm when light injects in parallel with the thickness direction with respect to 1 glass.

The optical glass of the present embodiment has a refractive index nd of 1.9 or more and less than 1.97, and at least one selected from TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ as a glass component. It is an oxide glass containing an oxide, the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is in the range of 30 mol% to 60 mol%, and is shown in the following formula (1) The βOH value is 0.1 mm ⁻¹ or more.
Formula (1) βOH = −ln (B / A) / t

  Here, in the formula (1), t represents the thickness (mm) of the optical glass used for measuring the external transmittance, and A represents the wavelength at 2500 nm when light is incident on the optical glass in parallel with the thickness direction. External transmittance (%) is represented, and B represents external transmittance (%) at a wavelength of 2900 nm when light is incident on the optical glass in parallel with the thickness direction. In is a natural logarithm.

  The “external transmittance” is a transmittance considering the surface reflection on the surface of the optical glass, and the “internal transmittance” described later is a transmittance when there is no surface reflection on the surface of the optical glass (that is, The transmittance of the glass material itself constituting the optical glass. Further, in the following description, “glass material for optical glass” is glass produced through a molding process for molding molten glass in a melting vessel into a predetermined shape, and is deeply colored before being subjected to heat treatment. It means the glass in the finished state. Furthermore, “optical glass” means glass obtained by heat-treating a glass material for optical glass in a deeply colored state. That is, “optical glass” is a glass whose coloring is reduced by heat treatment as compared with “glass material for optical glass”. Also, “glass material for optical glass” and “optical glass”, and “glass material for press molding”, “optical element” and “others” produced using “glass material for optical glass” or “optical glass” "Glass articles" are all amorphous glass, not crystallized glass.

In the optical glass of the present embodiment, a large amount of at least one high refractive index component selected from TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is within a range of 30 mol% to 60 mol% in total content. Despite being contained in, it is less colored. As for the reason why such an effect is obtained, the present inventor presumes that it is as follows.

First, when melting a high refractive index glass containing a high refractive index component such as TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ using a melting vessel made of a noble metal such as platinum, When melting on the reducing side, the melting of metal ions into the molten glass can be suppressed. However, if the molten glass is excessively reduced, the melting vessel is alloyed as described above. Also, if the coloring degree of the glass material for optical glass is strengthened by reducing the high refractive index component without reducing the molten glass excessively, the glass material for optical glass is subjected to a heat treatment in a later step. However, the degree of color reduction is small.

  In order to solve such problems, the metal material constituting the melting vessel is ionized and does not melt into the molten glass, and the glass material for optical glass once obtained is heat-treated to greatly reduce coloring. What is necessary is just to make the glass raw material for optical glass which can do.

The present inventor considered the phenomenon that the coloring of the glass material for optical glass is reduced by the heat treatment as follows. First, although the color of the optical glass obtained by heat-treating the glass material for optical glass in an oxidizing atmosphere is reduced, each of the ions such as Ti, Nb, W, Bi, etc. in the reduced state is oxidized, This is thought to be due to weak absorption of visible light. Even if the glass material for optical glass is heat-treated, if the speed of oxidizing Ti, Nb, W, and Bi is slow, the improvement in coloring is limited. In order to significantly reduce the coloring of the glass material for optical glass, the oxidation speed of Ti, Nb, W, and Bi during heat treatment should be increased. If there are ions that are likely to move through the glass material for optical glass, and these ions do not directly affect the coloration, such ions will move quickly through the glass material for optical glass during heat treatment and charge will be charged. It is possible to reduce coloring due to reduction of Ti, Nb, W, and Bi in a short time after delivery. H ⁺ is considered suitable as such an ion, but in order to make H ⁺ easier to move, OH ⁻ is introduced into the glass structure so that H ⁺ can be hopped starting from OH ^−. By doing so, it is considered that the oxidation speed during the heat treatment can be increased.

In order to introduce H ⁺ and OH ⁻ into the glass material for optical glass, H ₂ O may be introduced into the glass material for optical glass. Here, the amount of water in the glass material for optical glass can be indirectly quantified by measuring the intensity of infrared absorption by OH ⁻ for the optical glass with less coloring and improved transparency.

Therefore, the refractive index nd is 1.9 or more and less than 1.97, and an oxide containing at least one oxide selected from TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ as a glass component In the glass material for optical glass that is glass and the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is in the range of 30 mol% to 60 mol%, in other words, in the glass material for optical glass By setting the βOH value, which is an index of OH ⁻ content in the optical glass, to 0.1 mm ⁻¹ or more, coloring can be reduced.

Furthermore, when producing a glass material for optical glass containing a large amount of water so that the βOH value is 0.1 mm ⁻¹ or more, since molten glass having a high water content is melted, melting used for melting molten glass. An increase in coloring caused by the metal material (including the alloy material) constituting the container can also be suppressed. Note that the βOH value can be measured in the same manner as the optical glass for the glass material for optical glass in a deeply colored state. This is because the glass material for optical glass transmits infrared rays.

Next, the reason why the lower limit of the βOH value is set to 0.1 mm ⁻¹ in the optical glass of the present embodiment will be described. 1 shows No. 1 having the composition shown in Table 1. No. 1 having a thickness of 5 mm with respect to the βOH value when the βOH value of 1 glass was changed. It is the graph which showed the change of the external transmittance (T450) in wavelength 450nm when light injects in parallel with the thickness direction with respect to 1 glass. The value of external transmittance (T450) shown in FIG. One glass is a value after heat treatment in the atmosphere at 600 ° C. for 1 hour, and the βOH value is also a value after heat treatment. No. One glass has a refractive index nd of 1.9 or more, and the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is in the range of 30 mol% to 60 mol%. That is, no. One glass has the same refractive index nd and glass composition as the optical glass of this embodiment.

Further, the βOH values at the five points shown in FIG. 1 is a value set by adjusting the amount of water vapor introduced into the glass melting atmosphere when melting one glass. As is apparent from FIG. 1, it can be seen that the external transmittance (T450) increases with an increase in the βOH value. From the tendency of change in external transmittance (T450) with respect to the βOH value shown in FIG. 1, it is understood that the external transmittance (T450) surely exceeds 30% when the βOH value is 0.1 mm ⁻¹ or more. it can.

On the other hand, since the optical glass of this embodiment has a high refractive index, the thickness of the lens can be reduced. Here, considering the thinning of the lens, the transmittance characteristic suitable as a material of the optical element constituting the optical system such as the imaging optical system and the projection optical system is that the external transmittance (T450) is 30% or more. Conceivable. Therefore, in consideration of the matters described above, in the optical glass of the present embodiment, the lower limit value of the βOH value needs to be 0.1 mm ⁻¹ or more.

  By the way, when an optical element is fixed to a lens barrel or the like, workability is remarkably improved by using an ultraviolet curable adhesive. Until now, in optical elements using a high refractive index optical glass having a refractive index nd of 1.9 or more, light on the short wavelength side in the visible light region is cut by the optical glass, so that the adhesive is cured beyond the optical element. It was difficult to cure by irradiating light for use. However, by improving the transmittance on the short wavelength side in the visible light region, adhesion using an ultraviolet curable adhesive is also possible.

Therefore, considering the light transmittance of the optical element constituting the optical system and the convenience of the bonding operation when using the ultraviolet curable adhesive, the lower limit of the βOH value is 0.2 mm ⁻¹ , 0. It is more preferable that it becomes larger in the order of 3 mm ⁻¹ , 0.4 mm ⁻¹ , 0.5 mm ⁻¹ , 0.6 mm ⁻¹ , 0.7 mm ⁻¹ , 0.8 mm ⁻¹ . By increasing the βOH value in this way, the external transmittance (T450) increases and it becomes easier to reduce the color of the optical glass.

In addition, it is preferable that the optical glass of this embodiment is phosphate glass. Since phosphate-based glass is easier to take in moisture than borate-based glass, it is easier to reduce the coloration of the optical glass. In this case, the optical glass of the present embodiment preferably contains a _P 2 _{O 5} as a glass component in the range of 15mol% ~35mol%. By setting the content of P ₂ O ₅ to 15 mol% or more, it becomes easy to increase the water content in the optical glass and increase the βOH value. On the other hand, when the content of P ₂ O ₅ is 35 mol% or less, a high refractive index can be easily maintained. _A preferable lower limit of the content of P 2 _{O 5} is 17 mol%, preferably the upper limit is 33 mol%.

The degree of coloring of the optical glass can be quantified by λτ80, which is an index indicating the degree of coloring. λτ80 is the thickness of the optical glass based on the measured internal transmittance after measuring the internal transmittance in the wavelength range of 280 to 700 nm when light is incident on the optical glass parallel to the thickness direction. Means a wavelength (nm) at which the internal transmittance (internal transmittance τ) calculated on the assumption that it is 10 mm is 80%. Here, the internal transmittance τ is a transmittance excluding the surface reflection loss on the incident side and the emission side, and the transmittances T1 and T2 including the surface reflection loss of each sample using two samples having different thicknesses. Is a value calculated based on the following formula (2) using the measured values.
Formula (2) logτ = − (logT1−logT2) × 10 / Δd

  Here, in formula (2), T1 is the surface reflection loss measured in the wavelength range of 280 nm to 1550 nm when light is incident on the first sample having a thickness of d1 (mm) in parallel with the thickness direction. T2 is a wavelength of 280 nm when light is incident on the second sample made of the same glass as the first sample and having a thickness of d2 (mm) in parallel with the thickness direction. It represents the transmittance (%) including the surface reflection loss measured in the range of ˜1550 nm. Since λτ80 is calculated using the result of transmittance measurement at a wavelength of 280 to 700 nm, the transmittances T1 and T2 may be measured in the wavelength range of 280 to 700 nm. Δd represents the absolute value (mm) of the difference between the thickness d1 and the thickness d2, and the thickness d1 and the thickness d2 satisfy the relationship d1 ≠ d2.

λτ80 increases as the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ increases. If the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ in mol% is X, the water content in the glass material for optical glass is not increased prior to heat treatment. In an optical glass produced by heat-treating a glass material, the relationship between X and λτ80 is expressed by the following equation (3). For this reason, it is difficult to significantly improve λτ80.
Formula (3) λτ80> aX + b
In the formula (3), a represents a constant (1.8359 nm / mol%), and b represents a constant (351.06 nm).

On the other hand, in the optical glass of this embodiment, λτ80 can be reduced within a range that satisfies the following expression (4).
Formula (4) λτ80 <aX + b
In the formula (4), a represents a constant (1.8359 nm / mol%), and b represents a constant (351.06 nm).

In addition, as for the optical glass of this embodiment, it is more preferable to satisfy | fill the following Formula (5), and it is still more preferable to satisfy the following Formula (6).
Formula (5) λτ80 <aX + c
Formula (6) λτ80 <aX + d
Here, in formula (5), a represents a constant (1.8359 nm / mol%), and c represents a constant (348.06 nm). In formula (6), a represents a constant (1.8359 nm / mol%), and d represents a constant (345.06 nm).

  According to the optical glass of the present embodiment, in the wavelength range of λτ80 or more and 700 nm or less, the internal transmittance converted to a thickness of 10 mm is 80% or more, and preferably in the wavelength range of λτ80 or more and 1550 nm or less. The internal transmittance converted to 10 mm is 80% or more.

Conventionally, an antimony oxide having an oxidizing action has been added in order to suppress reduction of the high refractive index component during glass melting. However, when the optical glass of the present embodiment is manufactured, the coloring can be reduced without using the oxidation action of antimony oxide. Further, by adding antimony oxide, the metal material constituting the melting vessel is oxidized and becomes ions and melts into the glass material for optical glass, which becomes a factor of coloring the finally obtained optical glass. For this reason, in the optical glass of the present embodiment, the content of antimony oxide is preferably less than 1000 ppm, and more preferably less than 700 ppm in terms of Sb ₂ O ₃ . Note that the upper limit of the content of antimony oxide is more preferably less than these values in the order of 600 ppm, 500 ppm, 400 ppm, 300 ppm, 200 ppm, and 100 ppm. Furthermore, the optical glass of this embodiment may not contain antimony oxide.

In the optical glass of the present embodiment, a composition containing P ₂ O ₅ and at least one oxide selected from at least TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is preferable. In addition, a composition containing an alkali metal oxide, alkaline earth metal oxide, ZnO, B ₂ O ₃ , SiO ₂ or the like as an optional component is more preferable. Also in the optical glass having such a composition, the preferred range of the content of P ₂ O ₅ and the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is as described above.

Moreover, the optical glass of this embodiment may contain alkali metal oxides such as Li ₂ O. Here, when Li ₂ O is used as the alkali metal oxide, from the viewpoint of obtaining a high refractive index glass, the content is preferably more than 0 mol% and less than 10 mol%, more than 0 mol% and not more than 9 mol%. More preferably, it is more than 0 mol% and 8 mol% or less. Further, the optical glass of this embodiment may contain GeO ₂ and / or Ga ₂ O ₃ . However, since these oxides are expensive, Ga ₂ O ₃ may not be included in the optical glass at all. However, when included, it is preferable to reduce the content thereof as much as possible. Here, when GeO ₂ is contained in the optical glass, the content is preferably more than 0 mol% and 5 mol% or less, more preferably more than 0 mol% and 2 mol% or less, more than 0 mol% and more than 1 mol%. More preferably, it is as follows. Further, when Ga ₂ O ₃ is contained in the optical glass, the content is preferably more than 0 mol% and 0.5 mol% or less, more preferably more than 0 mol% and 0.2 mol% or less, more preferably 0 mol More preferably, it is more than 0.1% and 0.1 mol% or less. The optical glass of this embodiment may not contain Li ₂ O, may not contain GeO _2, and may not contain Ga ₂ O ₃ .

  In the optical glass of this embodiment, it is preferable not to contain Pb, As, Cd, U, and Th as glass components in consideration of environmental impact. Further, in order to prevent an increase in coloring, it is preferable not to include a component that absorbs visible light such as Cr, Ni, Eu, Er, Tb, Fe, Cu, and Nd. Te may be contained within a range that does not impair the object of the present invention, but it is preferably not contained as a glass component in consideration of the burden on the environment. In addition, in this specification, it does not exclude even if it does not contain as an impurity inevitably mixing.

Next, the manufacturing method of the optical glass of this embodiment is demonstrated. In the optical glass manufacturing method of the present embodiment, in order to obtain molten glass, a heating / melting step of heating / melting a glass raw material in a melting vessel, and molding for shaping the molten glass in the melting vessel into a predetermined shape And an oxide glass containing at least one oxide selected from TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ as a glass component by passing through at least the process, TiO ₂ , Nb _A glass material for optical glass in which the total content of ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is in the range of 30 mol% to 60 mol% is produced. Then, the optical glass of this embodiment is obtained by heat-processing this glass raw material for optical glasses in oxidizing atmosphere gas. Here, in the heating / melting step, the βOH value of the optical glass may be controlled to be 0.1 mm ⁻¹ or more by adjusting the amount of water contained in the molten glass in the melting vessel.

  In the production of the optical glass of the present embodiment, known methods can be appropriately employed as the glass raw material adjustment method, the glass raw material heating method, the melting method, and the molten glass forming method. Moreover, it is preferable that a melting container is comprised with a metal material from a viewpoint of obtaining homogeneous optical glass. Here, the metal material constituting the melting container is preferably a noble metal such as platinum or gold and a noble metal alloy such as platinum alloy or gold alloy because of excellent corrosion resistance and heat resistance.

  Here, as a method for adjusting the amount of moisture contained in the molten glass, a first moisture amount adjusting method for supplying water vapor into the atmosphere in which the molten glass is melted, and a method for supplying water vapor while bubbling into the molten glass. It is preferable to use one selected from the second moisture content adjusting method and the third moisture content adjusting method in which the first moisture content adjusting method and the second moisture content adjusting method are combined. The adjustment of the amount of moisture contained in the molten glass in the melting vessel means an operation for increasing the amount of moisture contained in the molten glass mainly as in the first to third methods for adjusting the amount of moisture described above.

  In addition, as a method for adjusting the amount of water contained in the molten glass in the melting vessel, a method using a compound containing moisture as a glass raw material, for example, using a glass raw material containing orthophosphoric acid or boric acid, A method for increasing the amount of water is also mentioned. However, in this method, moisture is evaporated in the process of melting the glass raw material, and it is difficult to secure a sufficient water content in the glass material for optical glass and the optical glass. Furthermore, in the method of preparing a raw material by compounding the raw material, making a cullet by roughly melting the raw material, remixing the cullet and re-melting it in the melting vessel, the moisture originally contained in the raw material is further lost. When remelting in a melting vessel, the water content is greatly reduced.

  Therefore, even when a compound containing water such as orthophosphoric acid or boric acid is used as the glass raw material, the water vapor partial pressure in the molten atmosphere can be increased in order to suppress the evaporation of water from the molten glass. preferable. Or when using the compound which contains a water | moisture content as a glass raw material, a melting container may be airtight and it may be made not to dissipate water vapor | steam outside a melting container by a heating and a melting process. Such an operation is also included in the adjustment of the amount of water contained in the molten glass in the melting vessel.

  In addition, the heating / melting process is usually performed by melting the glass raw material by heating it into a molten glass, a clarification process for promoting defoaming of the molten glass, and lowering the temperature of the molten glass after clarification. And a homogenization step of homogenizing by stirring. When cullet is used as the glass raw material, a culleting step of roughly melting the glass raw material prepared by compounding as described above, that is, a so-called batch raw material to form a cullet is performed before the melting step.

  Whether the cullet is made or the batch raw material is melted directly in the melting step, excessive reduction of Ti, Nb, W and Bi is suppressed and the melting vessel is made of a metal material. From the viewpoint of suppressing the ionization of the metal material and ensuring the water content in the glass material for optical glass and the optical glass, it is preferable to maintain the heating temperature of the glass during the heating and melting step at 1400 ° C. or lower. It is more preferable to maintain the temperature at not more than ° C. Furthermore, from the viewpoint of obtaining optical glass with less coloring while improving clarity, the heating temperature of the glass during the heating / melting process is set to be the highest in the fining process, that is, the glass is melted at the fining temperature or lower. It is preferable to do.

  In addition, if the time from the start to the end of the heating / melting process is lengthened, the reduction of the high refractive index component, the ionization of the metal material is promoted when the melting vessel is made of a metal material, and the water content in the optical glass is also reduced. Will show a trend. For this reason, it is preferable that the time from the start to the end of the heating / melting process be within 100 hours. The time from the start to the end of the heating / melting process may be adjusted as appropriate depending on the capacity of the melting container. By subjecting the glass material for optical glass thus melted and formed to heat treatment in an oxidizing atmosphere, the coloration of the optical glass can be reduced.

  As the oxidizing atmosphere gas, air, a gas obtained by adding oxygen to air, oxygen, or the like may be used. Further, the heat treatment temperature and the heat treatment time are preferably set so that λτ80 satisfies Equation (4), more preferably λτ80 satisfies Equation (5), and λτ80 satisfies Equation (6). More preferably, the setting is made as follows.

  The press-molding glass material of the present embodiment and the optical element of the present embodiment include the optical glass of the present embodiment, and are generally composed only of the optical glass of the present embodiment.

  The glass material for press molding is a glass material for obtaining a press-molded product, specifically, an optical element blank or an optical element, by heating and softening optical glass to perform press molding. As a method for producing a glass material for press molding, for example, a method of forming a molten glass lump by separating the flowing molten glass flow into a molten glass lump, and forming the molten glass lump in the process of cooling the molten glass lump, For example, a glass block is formed by casting into a mold, and the glass block is processed into a glass material for press molding.

  Examples of the optical element include various lenses such as a spherical lens and an aspheric lens, and a prism. The optical element of the present embodiment is manufactured through at least a post-processing step of post-processing the optical glass of the present embodiment. As post-processing, various known post-processing such as heat treatment, molding, and polishing can be appropriately performed, and two or more types of post-processing can be combined as necessary. As a method for producing an optical element by post-processing, optical glass (or a glass material for press molding) is heated and softened, press-molded to produce an optical element blank, and the optical element blank is processed to obtain an optical element. Method, method of heating and softening a glass material for press molding to obtain an optical element by precision press molding, method of press molding molten glass to produce an optical element blank, and processing the optical element blank to obtain an optical element Etc.

  In the production of the glass material for press molding and the optical element, the glass material for optical glass used for the production of the optical glass of this embodiment is subjected to various processing such as molding and polishing, and then the coloring is reduced. You may produce by performing the heat processing for this.

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

(Examples 1-6)
The batch raw material was roughly melted to produce a cullet, and the cullet was put into a platinum crucible and heated, melted and molded. 1, no. Each optical glass of 2 was produced in the following procedures. First, phosphates, orthophosphoric acid, oxides, carbonates, nitrates and sulfates are weighed and mixed thoroughly to prepare a raw material (batch raw material). It heated in the range of-1400 degreeC, it was set as the molten glass, and this molten glass was dripped in water and the cullet raw material was produced.

  Next, after the cullet raw material was dried, the cullet raw material was re-prepared and put into a platinum crucible (melting vessel) to cover the platinum. In this state, the cullet raw material in the platinum crucible was heated within the range of the liquidus temperature LT to 1300 ° C. of the glass composition of the cullet raw material, and the cullet raw material was melted to form a molten glass (melting step). Further, the molten glass is heated within the range of the liquidus temperature LT to 1400 ° C. and clarified (clarification step), and then the temperature is lowered within the range of the liquidus temperature LT to 1300 ° C. and stirred and homogenized (homogenized). The glass block was formed by flowing the clarified and homogenized molten glass out of the glass outflow pipe and casting it into the mold.

  When performing the melting process, the clarification process, and the homogenization process, a platinum pipe is inserted into the platinum crucible from the opening provided in the platinum lid, and steam is passed through the platinum pipe as necessary. It was supplied to the space inside the crucible. Table 2 shows the water vapor flow rate per unit time supplied into the platinum crucible. In addition, the water vapor | steam flow rate shown in Table 2 is the value converted into the flow rate in normal temperature, and a unit is a liter / min. In addition, when water vapor is not supplied into the crucible, the platinum crucible is sealed with a platinum lid without an opening, and the platinum crucible is hermetically sealed from the melting process to the homogenization process. To suppress the transpiration of moisture from the cullet raw material and molten glass in the melting process.

  Next, the glass block is heated from 25 ° C. to 600 ° C. in the air over 2 hours and annealed (heat treated) at 600 ° C. to reduce the color of the glass block (glass material for optical glass). It was. Thereafter, the glass block was cooled to room temperature at a temperature lowering rate of −30 ° C./hr. In addition, the time which hold | maintained the glass block at 600 degreeC is 1 hour.

  After annealing, the βOH value, λτ80, refractive index nd, Abbe number νd, and glass transition temperature Tg of the glass block (optical glass) were measured. No. For the optical glass of No. 1, the values of βOH value, T450, and λτ80 are shown in Table 2. 1 and no. Table 1 shows the refractive index nd, Abbe number νd, and glass transition temperature Tg of each optical glass.

  The measured values of refractive index nd and Abbe number νd shown in Table 1 are values measured using a sample cooled at a cooling rate of 30 ° C. per hour, and the measured values of liquidus temperature LT are After reheating and holding for 2 hours, it is cooled to room temperature, the presence or absence of crystal precipitation inside the glass is confirmed by an optical microscope, and the lowest temperature at which no crystal is observed is defined as the liquidus temperature.

  Examples 1 to 3 in Table 2 are data on optical glass prepared without introducing water vapor from the platinum pipe into the melting vessel, and Examples 4 to 6 are from the platinum pipe to the melting vessel. It is the data about the optical glass produced by introducing water vapor. In Examples 1 to 3, a normal phosphoric acid raw material is used and the airtightness of the melting vessel is increased, whereby moisture is introduced into the molten glass and the dissipation of water vapor from the melting vessel is suppressed. Furthermore, in Examples 4 to 6, the partial pressure of water vapor in the melting vessel is also actively increased.

  When T450 and λτ80 of the optical glass of Examples 1 to 3 and T450 and λτ80 of the optical glasses of Examples 4 to 6 were compared, Example 4 in which the water vapor partial pressure in the melting vessel was positively increased It can be seen that the optical glass of Example 6 has a larger βOH value, and the coloring degree is further greatly reduced. Thus, No. 1 of Table 1 with small coloring by heat treatment. An optical glass having the composition shown in 1 was obtained.

  In Examples 1 to 6, the optical glass to be produced is No. 1 shown in Table 1. No. 1 from the optical glass of No. 1 composition. Even if it changes to the optical glass of the composition shown in 2, coloring degree can be made small significantly. Moreover, in Examples 1-6, although the platinum crucible was used as a melting container, optical glass was produced using a platinum alloy crucible, a gold crucible, and a gold alloy crucible, and the obtained optical glass was heat-treated. Even so, it was possible to obtain an optical glass having a greatly reduced degree of coloring. Furthermore, in Examples 4-6, although water vapor | steam was supplied through the pipe in the platinum crucible covered, the same effect can be acquired even if it bubbles by blowing water vapor into the molten glass in a platinum crucible. No. 1 shows the composition of the optical glass to be produced in Table 1. The same applies when the composition is changed to 2.

  Moreover, in Examples 4-6, the water vapor | steam obtained by boiling water using a boiler was used as the water vapor | steam supplied in the platinum crucible. However, when producing a glass material for optical glass, water vapor obtained by other methods can be used as appropriate. For example, even if water vapor is injected into a refractory glass melting furnace containing a melting vessel such as a platinum crucible to vaporize it to increase the partial pressure of water vapor in the glass melting furnace and the atmosphere inside the melting vessel. Good. Alternatively, water may be supplied into the glass melting furnace using a pump, and the water may be boiled by the heat in the melting furnace, thereby steaming and increasing the water vapor partial pressure in the glass melting atmosphere. Even if these methods are used, the water content in the glass material for optical glass can be increased.

(Comparative Example 1)
A glass block (glass material for optical glass) was prepared in the same manner as in Examples 1 to 3 except that the platinum lid was removed and the melting vessel atmosphere was opened, and then heat treatment was performed in the same manner as in Examples 1 to 6. . However, the degree of coloring of the heat-treated glass block (optical glass) was greater than that of Examples 1-6.

  In addition, the glass composition of No. 1 described in Table 1 was used. No. 1 in place of No. 1 A glass block (glass material for optical glass) was prepared and heat-treated in the same manner as in Comparative Example 1 except that the composition was 2. However, the degree of coloring of the heat-treated glass block (optical glass) was greater than that of Examples 1-6.

(Comparative Example 2)
A glass block (glass material for optical glass) was produced in the same manner as in Examples 4 to 6 except that nitrogen gas was introduced into the melting vessel instead of water vapor, and then heat treatment was carried out in the same manner as in Examples 1 to 6. It was. The degree of coloring of the heat-treated glass block (optical glass) was much higher than that of the glass block (optical glass) of Comparative Example 1.

(Comparative Example 3)
A glass block (glass material for optical glass) was prepared in the same manner as in Examples 4 to 6 except that a reducing gas such as carbon monoxide gas was introduced into the melting vessel instead of water vapor. Heat treatment was performed in the same manner as described above. However, the degree of coloring of the heat-treated glass block (optical glass) was much higher than that of the glass block (optical glass) of Comparative Example 1.

  When the concentration of the reducing gas is increased, the reduced glass component is alloyed with the platinum crucible, and the crucible is broken. This is because the glass composition of No. The same applies to the case where the composition is changed to 2.

(Details of observation results of coloring degree of glass block before and after heat treatment)
In Table 3, the observation result of the coloring degree before and behind the heat processing of the glass block produced by each Example and the comparative example is shown. The degree of coloring was evaluated by placing a glass block having a substantially circular planar shape on white paper and visually observing it under room light. The glass blocks of any of the examples and comparative examples used for the observation have almost the same thickness. Moreover, the evaluation criteria of transparency shown in Table 3 are as follows.
A: Although the glass block (optical glass) is lightly colored, the transparency is high enough to recognize the whiteness of the paper located below the glass block (optical glass) (high transparency).
B: Although the glass block (optical glass) is colored, the paper located below the glass block (optical glass) has transparency enough to be recognized (medium transparency).
C: The glass block (optical glass) is darkly colored, and the paper located below the glass block (optical glass) has only a low transparency that can be recognized slightly (low transparency).
D: The glass block (optical glass) is completely opaque, and the presence of the paper located below the glass block (optical glass) cannot be recognized at all (opaque).

(Confirmation of platinum contamination)
Among the glass blocks after the heat treatment used in Examples 1 to 6 and Comparative Examples 1 to 3, the inside of the glass block was observed with an optical microscope except for those having a transparency evaluation of D. As a result, in any glass block, the mixed platinum foreign matter and precipitated crystals were not confirmed. Moreover, when the amount of platinum melt | dissolution in the glass block used in Examples 1-6 and Comparative Examples 1-3 was measured by ICP emission spectroscopy, all were less than 2 ppm.

(Example 7)
The optical glass produced in Examples 1-6 was processed into a glass material for press molding, heated and softened, and press molded to produce an optical element blank. Further, the optical element blank was processed to produce optical elements such as a spherical lens and a prism. Further, an antireflection film was coated on the lens surface and the prism surface to obtain a final product. No. described in Table 1 Similarly, the glass material for press molding, the optical element blank, and the optical element were prepared for the optical glass of No. 2.

Claims (6)

Refractive index nd is 1.9 or more and less than 1.97,
An oxide glass containing at least one oxide selected from TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ as a glass component;
The total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ is in the range of 30 mol% to 60 mol%, and
An optical glass having a βOH value represented by the following formula (1) of 0.1 mm ⁻¹ or more.
Formula (1) βOH = −ln (B / A) / t
[In the formula (1), t represents the thickness (mm) of the optical glass used for the measurement of external transmittance, and A represents a wavelength of 2500 nm when light is incident on the optical glass in parallel with the thickness direction. External transmittance (%) is represented, and B represents external transmittance (%) at a wavelength of 2900 nm when light is incident on the optical glass in parallel with the thickness direction. In is a natural logarithm. ] The optical glass according to claim 1,
An optical glass comprising P ₂ O ₅ in the range of 15 mol% to 35 mol% as the glass component. In the optical glass according to claim 1 or 2,
An optical glass characterized by satisfying the following formula (2).
Formula (2) λτ80 <aX + b
[In formula (2), λτ80 is the measured internal transmittance after measuring the internal transmittance in the wavelength range of 280 to 700 nm when light is incident on the optical glass in parallel with the thickness direction. Represents the wavelength (nm) at which the internal transmittance calculated assuming that the thickness of the optical glass is 10 mm based on the above formula is 80%, a represents a constant (1.8359 nm / mol%), b Represents a constant (351.06 nm), and X represents the total content (mol%) of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ . ] In the optical glass as described in any one of Claims 1-3,
An optical glass containing less than 1000 ppm of antimony oxide in terms of Sb ₂ O ₃ .   A glass material for press molding comprising the optical glass according to any one of claims 1 to 4.   An optical element comprising the optical glass according to claim 1.

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