JP6869482B2 - Optical glass and its manufacturing method - Google Patents

Description

The present invention relates to an optical glass, and particularly to an optical glass having a high refractive index and excellent transmittance in the visible region.

In recent years, with the miniaturization and weight reduction of optical systems used in cameras, microscopes, endoscopes, etc., the optical characteristics of glass used in the optical lenses used are higher refractive index and wider visible range ( It is required to transmit light in the short wavelength range).

In order to make the glass have a higher refractive index, the content of SiO ₂ and B ₂ O ₃ which are glass skeleton components is reduced, and rare earth oxides such as _{La 2} O ₃ , Gd ₂ O ₃ and Ta ₂ O _{5 are used.} Alternatively, it is necessary to contain a large amount of _{Nb 2} O ₅ and TiO _2. However, in this case, vitrification becomes difficult. This is because optical glass is generally produced by melting a raw material in a melting container such as a crucible and cooling it. Therefore, in a glass system having a small amount of glass skeleton components, crystallization occurs starting from the contact interface with the melting container. This is because it becomes easier to proceed.

Even if the composition is difficult to vitrify, it can be vitrified by eliminating the contact at the interface with the melting vessel. As such a method, a container-free floating method (container-free solidification method) in which a raw material is melted and cooled in a suspended state is known. When this method is used, since the molten glass hardly comes into contact with the molten container, crystallization starting from the interface with the molten container can be prevented and vitrification becomes possible. For example, in Patent Document 1, a glass containing _{La 2} O ₃ and TiO _{2 as a glass composition is produced by a container-free floating method.}

Japanese Patent No. 4953234

Since the glass described in Patent Document 1 is relatively easily devitrified, it is difficult to increase the diameter (for example, a diameter of 2 mm or more) even when the containerless floating method is used, and the visible light is particularly short. There is a problem that the transmittance in the wavelength range (about 380 to 400 nm) is low.

In view of the above, it is an object of the present invention to provide a novel optical glass having a high refractive index, a high transmittance particularly in a short wavelength region, and an easy increase in diameter.

As a result of diligent studies by the present inventors, it has been found that the above problem can be solved by an optical glass having a specific composition containing _{La 2} O ₃ , TiO ₂ and Nb ₂ O _5.

The optical glass of the present invention _{is characterized by containing La 2} O ₃ 23 to 35% (but not 35%), TiO _{2 to} 10 to 40%, and Nb ₂ O ₅ 25 to 67% in mol%. To do.

The optical glass of the present invention, further, in _{mol%, Al 2 O 3 0~20%} , Ta 2 O 5 0~20%, ZrO 2 0~20%, Gd 2 O 3 0~20%, Y 2 O It preferably contains _{30 to} 20%, or Yb ₂ O _{30 to 20%.}

The optical glass of the present invention preferably has a refractive index (nd) of 2.15 to 2.30.

The optical glass of the present invention preferably has a transmittance of 60% or more for light having a wavelength of 400 nm and a transmittance of 25% or more for light having a wavelength of 380 nm in a sample having a thickness of 1 mm.

The optical glass of the present invention has, for example, a spherical shape or a spheroidal shape.

The method for producing an optical glass of the present invention is a method for producing the above-mentioned optical glass, in which the raw material lump is suspended and held, and the raw material lump is heated and melted to obtain molten glass, and then melted. It is characterized by including a step of cooling the glass.

The optical glass of the present invention has a higher refractive index than the conventional one, a high transmittance especially in a short wavelength region, and an easy increase in diameter.

It is a schematic cross-sectional view which shows one Embodiment of the apparatus for manufacturing the optical glass of this invention.

The optical glass of the present invention _{is characterized by containing La 2} O ₃ 23 to 35% (but not 35%), TiO _{2 to} 10 to 40%, and Nb ₂ O ₅ 25 to 67% in mol%. To do. The reason for limiting the glass composition range in this way will be described below. In the following description of the content of each component, "%" means "mol%" unless otherwise specified. "

La ₂ O ₃ is a component that forms a glass skeleton, and is a component that increases the refractive index without lowering the transmittance. It also has the effect of improving weather resistance. The content of La ₂ O ₃ is 23 to 35% (but not including 35%), preferably 24 to 33%, and more preferably 25 to 30%. If _{the content of La 2} O ₃ is too small, it becomes difficult to obtain the above effect. On the other hand, _{if the content of La 2} O ₃ is too large, it becomes difficult to vitrify.

TiO ₂ is a component having a large effect of increasing the refractive index, and also has an effect of increasing chemical durability. The content of TiO ₂ is 10 to 40%, preferably 11 to 39%, and more preferably 15 to 35%. If _{the content of TiO 2} is too small, it becomes difficult to obtain the above effect. If _{the content of TiO 2} is too large, the absorption end shifts to the long wavelength side, so that the transmittance in the short wavelength region tends to decrease. In addition, it becomes difficult to vitrify.

Nb ₂ O ₅ is a component having a large effect of increasing the refractive index, and also has an effect of expanding the vitrification range. The content of Nb ₂ O ₅ is 25 to 67%, preferably 27 to 66%, and more preferably 30 to 65%. If _{the content of Nb 2} O ₅ is too small, it becomes difficult to obtain the above effect. On the other hand, _{if the content of Nb 2} O ₅ is too large, the absorption end shifts to the long wavelength side, so that the transmittance in the short wavelength region tends to decrease. In addition, it becomes difficult to vitrify.

In addition to the above components, the optical glass of the present invention may contain Al ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Gd ₂ O ₃ , Y ₂ O ₃ or Yb ₂ O ₃ . By introducing these components, a glass having desired optical properties can be easily produced.

Al ₂ O ₃ is a component that forms a glass skeleton and expands the vitrification range. However, _{if the content of Al 2} O ₃ is too large, the refractive index is lowered and it becomes difficult to obtain desired optical characteristics. Therefore, _{the content of Al 2} O ₃ is preferably 0 to 20%, more preferably 0 to 10%.

Ta ₂ O ₅ is a component having a large effect of increasing the refractive index, and also has an effect of increasing chemical durability. However, _{if the content of Ta 2} O ₅ is too large, it becomes difficult to vitrify. In addition, raw material costs tend to be high. Therefore, _{the content of Ta 2} O ₅ is preferably 0 to 20%, more preferably 0 to 15%.

ZrO ₂ is a component that increases the refractive index and also has the effect of increasing chemical durability. However, _{if the content of ZrO 2} is too large, it becomes difficult to vitrify. Therefore, _{the content of ZrO 2} is preferably 0 to 20%, more preferably 0 to 10%.

Gd ₂ O ₃ is a component that increases the refractive index. However, _{if the content of Gd 2} O ₃ is too large, it becomes difficult to vitrify. Therefore, _{the content of Gd 2} O ₃ is preferably 0 to 20%, more preferably 0 to 10%.

Y ₂ O ₃ is a component that increases the refractive index. However, _{if the content of Y 2} O ₃ is too large, it becomes difficult to vitrify. Therefore, _{the content of Y 2} O ₃ is preferably 0 to 20%, more preferably 0 to 10%.

Yb ₂ O ₃ is a component that increases the refractive index. However, _{if the content of Yb 2} O ₃ is too large, it becomes difficult to vitrify. In addition, raw material costs tend to be high. Therefore, _{the content of Yb 2} O ₃ is preferably 0 to 20%, more preferably 0 to 10%.

In addition to the above components, the optical glass of the present invention may contain various components as shown below.

SiO ₂ is a component that forms a glass skeleton and expands the vitrification range. It also has the effect of improving weather resistance. However, _{if the content of SiO 2} is too large, the refractive index is lowered and it becomes difficult to obtain desired optical characteristics. Therefore, _{the content of SiO 2} is preferably 0 to 10%, more preferably 0 to 5%.

B ₂ O ₃ is a component that forms a glass skeleton and expands the vitrification range. However, _{if the content of B 2} O ₃ is too large, the refractive index is lowered and it becomes difficult to obtain desired optical characteristics. Therefore, _{the content of B 2} O ₃ is preferably 0 to 10%, more preferably 0 to 5%.

GeO ₂ is a component that increases the refractive index and also has the effect of expanding the vitrification range. However, _{if the content of GeO 2} is too large, the raw material cost tends to be high. Therefore, _{the content of GeO 2} is preferably 0 to 20%, more preferably 0 to 10%.

WO ₃ has the effect of increasing the refractive index. In addition, since it forms a glass skeleton as an intermediate oxide, it also has the effect of expanding the vitrification range. However, _{if the content of WO 3} is too large, devitrification tends to occur and it tends to be difficult to increase the diameter. Therefore, _{the content of WO 3} is preferably 0 to 10%, more preferably 0 to 5%.

SnO ₂ is a component having a large effect of increasing the refractive index. However, it is easily reduced and causes coloring. Therefore, the SnO ₂ content is preferably 0 to 5%, more preferably 0 to 3%.

P ₂ O ₅ is a component constituting the glass skeleton and has the effect of expanding the vitrification range. However, if the content is too large, phase separation is likely to occur. Therefore, _{the content of P 2} O ₅ is preferably 0 to 10%, more preferably 0 to 3%.

ZnO, MgO, CaO, SrO and BaO have the effect of improving the stability of vitrification and increasing the chemical durability. However, if the content is too large, the refractive index is lowered and it becomes difficult to obtain desired optical characteristics. Therefore, the content of these components is preferably 0 to 10%, more preferably 0 to 5%, respectively.

Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O have the effect of lowering the melting temperature, but since they lower the refractive index, the total amount is preferably 0 to 10%, and more preferably the total amount is 0. ~ 5%.

_{Sb 2} O ₃ can be contained as a fining agent. However, in order to avoid coloring or in consideration of the environment, _{the content of Sb 2} O ₃ is preferably 0.1% or less, and more preferably substantially not contained.

Considering the load on the environment, it is preferable that PbO is substantially not contained.

In the present invention, "substantially not contained" means that it is intentionally not contained as a raw material, and does not exclude unavoidable contamination of impurities. More objectively, it means that the content is less than 0.1%.

The refractive index of the optical glass of the present invention is preferably 2.15 or more, more preferably 2.17 or more, still more preferably 2.19 or more. For example, when the optical glass of the present invention is used as a lens, the lens can be made thinner as the refractive index is increased, which is advantageous in reducing the size of the optical device. The upper limit of the refractive index is preferably 2.30 or less, more preferably 2.29 or less in consideration of the stability of vitrification.

In the optical glass of the present invention, the Abbe number is not particularly limited, and is appropriately adjusted in the range of, for example, 10 to 25.

The transmittance of the optical glass of the present invention at a wavelength of 400 nm in a sample having a thickness of 1 mm is preferably 60% or more, more preferably 63% or more, and the transmittance at a wavelength of 380 nm is preferably 25% or more, more preferably. Is more than 30%. In this way, the transmittance becomes high in a wide range of the visible range, which makes it suitable as an optical lens.

The optical glass of the present invention has, for example, a spherical shape or a spheroidal shape. In that case, the diameter (or major axis) is preferably 2 mm or more, 2.5 mm or more, and particularly preferably 3 mm or more. By doing so, it becomes easy to apply it as an optical element such as a lens.

The optical glass of the present invention can be produced, for example, by a container-free floating method. FIG. 1 is a schematic cross-sectional view showing an example of a manufacturing apparatus for manufacturing a glass material by a containerless floating method. Hereinafter, the method for producing the optical glass of the present invention will be described with reference to FIG.

The glass material manufacturing apparatus 1 has a molding die 10. The molding die 10 also serves as a melting container. The molding die 10 has a molding surface 10a and a plurality of gas ejection holes 10b that are open to the molding surface 10a. The gas ejection hole 10b is connected to a gas supply mechanism 11 such as a gas cylinder. Gas is supplied from the gas supply mechanism 11 to the molding surface 10a via the gas ejection hole 10b. The type of gas is not particularly limited, and may be, for example, air or oxygen, or may be an inert gas such as nitrogen gas, argon gas, or helium gas.

When manufacturing a glass material using the manufacturing apparatus 1, first, a glass raw material block 12 prepared so as to have a glass having the above composition is arranged on a molding surface 10a. The glass raw material mass 12 includes, for example, a raw material powder integrated by press molding or the like, a sintered body obtained by integrating the raw material powder by press molding or the like and then sintering, or a composition equivalent to the target glass composition. An aggregate of crystals having the same can be mentioned.

Next, the glass raw material mass 12 is suspended on the molding surface 10a by ejecting gas from the gas ejection hole 10b. That is, the glass raw material block 12 is held in a state where it is not in contact with the molding surface 10a. In that state, the laser light irradiation device 13 irradiates the glass raw material block 12 with laser light. As a result, the glass raw material block 12 is heated and melted to vitrify it, and molten glass is obtained. After that, the glass material can be obtained by cooling the molten glass. In the step of heating and melting the glass raw material block 12 and the step of cooling the molten glass and further the glass material until the temperature of the glass material becomes at least the softening point or less, at least gas ejection is continued, and the glass raw material block 12 and the molten glass are continued. Furthermore, it is preferable to suppress the contact between the glass material and the molded surface 10a. In addition to the method of irradiating the laser beam, the method of heating and melting may be radiant heating.

Hereinafter, the present invention will be described based on examples, but the present invention is not limited to these examples.

Tables 1 and 2 show examples and comparative examples of the present invention, respectively.

Each sample was prepared as follows. First, a raw material mass was prepared using the raw material powder prepared so as to have the glass composition shown in the table. The raw material mass was prepared by a method in which the raw material powder was press-molded and sintered at 1100 to 1400 ° C. for 12 hours. The raw material mass was roughly pulverized using a mortar and used in a state of 0.1 to 0.6 g of small pieces.

Using the raw material mass obtained above, a substantially spherical glass material (major axis 4.5 to 6 mm) was produced by a container-free floating method using an apparatus according to FIG. A 100 W CO ₂ laser oscillator was used as the heat source. Further, oxygen gas was used as a gas for suspending the glass raw material block, and the glass raw material was supplied at a flow rate of 1 to 15 L / min.

The refractive index (nd), Abbe number (νd), and transmittance of the obtained glass material were measured. The results are shown in Tables 1 and 2.

The refractive index was evaluated by adhering a glass material on a soda plate substrate having a thickness of 5 mm, performing right angle polishing, and using KPR-2000 manufactured by Shimadzu Corporation, as a measured value with respect to the d line (587.6 nm) of a helium lamp.

For the Abbe number, the refractive index for the d line and the refractive index values for the F line (486.1 nm) and the C line (656.3 nm) of the hydrogen lamp are used, and the Abbe number (νd) = {(nd-1). It was calculated from the formula of / (nF-nC)}.

The transmittance was measured in the wavelength range of 300 to 800 nm using a UV-3100 manufactured by Shimadzu Corporation after processing the glass material to a thickness of 1 mm and then performing double-sided mirror processing. The table shows the transmittance at wavelengths of 400 nm and 380 nm.

As shown in Tables 1 and 2, the samples of Examples 1 to 10 have a high refractive index of 2.1757 to 2.2779, a transmittance of 60.8 to 64.2% at a wavelength of 400 nm, and a transmittance at a wavelength of 380 nm. The transmittance was 28.6 to 53.2%, showing high transmittance in the short wavelength range of visible light.

On the other hand, the samples of Comparative Examples 1 and 2 had a low transmittance at a short wavelength of 57.2% or less at a wavelength of 400 nm and 22.3% or less at a wavelength of 380 nm. Moreover, the sample of Comparative Example 3 was not vitrified.

1: Glass material manufacturing device 10: Molding mold 10a: Molding surface 10b: Gas ejection hole 11: Gas supply mechanism 12: Glass raw material block 13: Laser light irradiation device

Claims (6)

In _mol% La ₂ O 3 (containing no However _{35%) 23~35%, TiO 2} 10~40%, Nb 2 O 5 containing 25 to 67%, der Rukoto diameter or major axis of 2mm or more Optical glass featuring. Furthermore, in _{mol%, Al 2 O 3 0~20%} , Ta 2 O 5 0~20%, ZrO 2 0~20%, Gd 2 O 3 0~20%, Y 2 O 3 0~20%, or The optical glass according to claim 1, wherein the optical glass contains Yb ₂ O _{30 to 20%.} The optical glass according to claim 1 or 2, wherein the refractive index (nd) is 2.15 to 2.30. The invention according to any one of claims 1 to 3, wherein the 1 mm-thick sample has a transmittance of 60% or more for light having a wavelength of 400 nm and 25% or more for light having a wavelength of 380 nm. Optical glass. The optical glass according to any one of claims 1 to 4, wherein the optical glass has a spherical shape or a spheroidal shape. The method for producing the optical glass according to any one of claims 1 to 5.
A method for producing optical glass, which comprises a step of cooling the molten glass after heating and melting the raw material mass to obtain molten glass while the raw material mass is suspended and held.

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