JP6701557B2 - Optical glass and manufacturing method thereof - Google Patents

Description

  The present invention relates to optical glass, and more particularly to optical glass having high refractive index characteristics.

  In recent years, as optical systems used in cameras, microscopes, endoscopes, and the like have become smaller and lighter, higher refractive index has been demanded as optical characteristics of glass used in optical lenses used.

In order to make the glass have a higher refractive index, the content of SiO ₂ or B ₂ O ₃ which is a glass skeleton component 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 or 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, so that in a glass system with a small glass skeleton component, crystallization starts from the contact interface with the melting container. This is because it becomes easier to proceed.

Even if the composition is difficult to vitrify, vitrification is possible by eliminating contact at the interface with the melting container. As such a method, a containerless solidification method (a containerless floating method) of melting and cooling a raw material in a suspended state is known. When this method is used, the molten glass hardly contacts the melting vessel, so that crystallization starting from the interface with the melting vessel can be prevented and vitrification becomes possible. For example, in Patent Document 1, a glass containing only TiO ₂ and BaO as a glass composition is produced by a containerless solidification method.

Japanese Patent No. 4789086

  Since the glass described in Patent Document 1 is relatively easily devitrified, it is difficult to increase the diameter (for example, longer diameter of 2 mm or more) even when the container-free coagulation method is used.

  In view of the above, it is an object of the present invention to provide a novel optical glass having a high refractive index, excellent devitrification resistance, and easily increasing the diameter.

As a result of intensive studies by the present inventors, it has been found that the above problems can be solved if the optical glass contains TiO ₂ , La ₂ O ₃ , Gd ₂ O ₃ and ZrO ₂ as essential components in a predetermined range, It is proposed as an invention.

That is, the optical glass of the present invention is, in mol %, TiO ₂ 50 to 85%, La ₂ O _{3 to} 25% (excluding 25%), Gd ₂ O _{3 to} 20% (however, 0% is includes _{not), La 2 O 3 + Gd} 2 O 3 8~25%, characterized in that it contains ZrO 2 0 to 25% (not including 0%). Incidentally, _{"La 2 O 3 + Gd 2 O} 3 " means total content of each component.

The optical glass of the present invention, in _{mol%, Nb 2 O 5 0~20%} , Ta 2 O 5 0~20%, Y 2 O 3 0~20%, or containing _Yb 2 _O 3 _0~20% Preferably.

  The optical glass of the present invention preferably has a refractive index (nd) of 2.15 to 2.40.

  The method for producing an optical glass of the present invention is a method for producing the above-mentioned optical glass, in a state where the glass raw material is suspended and held in the air, and after the glass raw material is melted by heating to obtain a molten glass. And a step of cooling the molten glass.

  The optical glass of the present invention has a higher refractive index than conventional ones, is excellent in devitrification resistance, and is easy to increase in diameter.

It is a typical sectional view showing one embodiment of the device for manufacturing the optical glass of the present invention.

The optical glass of the present invention is, in mol %, TiO ₂ 50 to 85%, La ₂ O ₃ 5 to 25% (excluding 25%), Gd ₂ O _{30 to} 20% (excluding 0%). _{), La 2 O 3 + Gd} 2 O 3 8~25%, characterized in that it contains ZrO 2 0 to 25% (not including 0%). 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.

TiO ₂ is a component that has a large effect of increasing the refractive index, and also has an effect of increasing the chemical durability. The content of TiO ₂ is 50 to 85%, preferably 55 to 83%, more preferably 60 to 81%, and further preferably 65 to 79%. If the content of TiO ₂ is too small, it becomes difficult to obtain the above effects. On the other hand, when the content of TiO ₂ is too large, devitrification is likely to occur and it becomes difficult to obtain a glass material having a desired size.

La ₂ O ₃ is a component that enhances the refractive index and enhances the stability of vitrification. It also has the effect of improving weather resistance. The content of La ₂ O ₃ is 5 to 25% (excluding 25%), preferably 6 to 18%, more preferably 7 to 14%, and further preferably 8 to 11%. If the content of La ₂ O ₃ is too small, it becomes difficult to obtain the above effects. On the other hand, when the content of La ₂ O ₃ is too large, it becomes difficult to vitrify.

Gd ₂ O ₃ is a component that enhances the refractive index and enhances the stability of vitrification. The content of Gd ₂ O ₃ is 0 to 20% (excluding 0%), preferably 0.1 to 18%, more preferably 1 to 15%, and further preferably 2 to 13%. If the content of Gd ₂ O ₃ is too small, it becomes difficult to obtain the above effects. On the other hand, when the content of Gd ₂ O ₃ is too large, it becomes rather difficult to vitrify.

The content of La ₂ O ₃ +Gd ₂ O ₃ is 8 to 25%, preferably 10 to 23%, more preferably 12 to 20%, and further preferably 13 to 18%. If La ₂ O ₃ +Gd ₂ O ₃ is too little or too much, vitrification becomes difficult.

ZrO ₂ is a component that raises the refractive index and forms a glass skeleton as an intermediate oxide, and therefore has the effect of expanding the vitrification range. It also has the effect of increasing chemical durability. The content of ZrO ₂ is 0 to 25% (excluding 0%), preferably 0.1 to 23%, more preferably 1 to 20%, further preferably 3 to 18%. If the content of ZrO ₂ is too small, it becomes difficult to obtain the above effects. On the other hand, when the content of ZrO ₂ is too large, it becomes rather difficult to vitrify.

The optical glass of the present invention may contain Nb ₂ O ₅ , Ta ₂ O ₅ , Y ₂ O ₃ or Yb ₂ O ₃ in addition to the above components. By introducing these components, a glass having desired optical characteristics can be easily produced.

Nb ₂ O ₅ is a component that has a large effect of increasing the refractive index. However, if the content of Nb ₂ O ₅ is too large, vitrification becomes difficult. Therefore, the content of Nb ₂ O ₅ is preferably 0 to 20%, more preferably 1 to 10%.

Ta ₂ O ₅ is a component that has a large effect of increasing the refractive index. However, if the content of Ta ₂ O ₅ is too large, vitrification tends to be difficult, and the raw material cost tends to increase. Therefore, the content of Ta ₂ O ₅ is preferably 0 to 20%, more preferably 1 to 5%.

Y ₂ O ₃ is a component that enhances the stability of vitrification and enhances the refractive index. However, if the content of Y ₂ O ₃ is too large, it becomes rather 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, vitrification becomes difficult. In addition, the raw material cost tends to increase. Therefore, the content of Yb ₂ O ₃ is preferably 0 to 20%, more preferably 0 to 10%.

  The optical glass of the present invention may contain the following components in addition to the above components.

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 decreases, and it becomes difficult to obtain desired optical characteristics. Therefore, the content of Al ₂ O ₃ is preferably 0 to 10%, more preferably 0 to 5%.

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 decreases, 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 decreases, 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 increase. Therefore, the content of GeO ₂ is preferably 0 to 10%, more preferably 0 to 5%.

WO ₃ has the effect of increasing the refractive index. Further, since it forms a glass skeleton as an intermediate oxide, it also has an 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 that has a large effect of increasing the refractive index. However, reduction tends to cause coloring. Therefore, the content of SnO ₂ is preferably 0 to 5%, more preferably 0 to 3%.

P ₂ O ₅ is a component that constitutes the glass skeleton, and has the effect of expanding the vitrification range. However, if the content is too large, phase separation tends 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 effects of increasing the vitrification stability and 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 each of these components is preferably 0 to 10%, and more preferably 0 to 5%.

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, they are preferably 0 to 10% in total, and 0 to 5%. Is more preferable.

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

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

  In the present invention, “substantially free from” means not intentionally added as a raw material, and does not exclude inclusion of unavoidable 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 2.20 or more. For example, when the optical glass of the present invention is used as a lens, it is possible to make the lens thinner as the refractive index is increased, which is advantageous in downsizing the optical device. The upper limit of the refractive index is preferably 2.40 or less, more preferably 2.35 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 within the range of 10 to 25, for example.

  The optical glass of the present invention has, for example, a spherical shape or a spheroidal shape. In that case, the 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 as an optical element such as a lens.

  The optical glass of the present invention can be produced, for example, by a containerless solidification method. FIG. 1 is a schematic cross-sectional view showing an example of a manufacturing apparatus for manufacturing a glass material by a container-free coagulation method. Hereinafter, the manufacturing method of 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 mold 10 also serves as a melting container. The molding die 10 has a molding surface 10a and a plurality of gas ejection holes 10b opening in 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 holes 10b. The type of gas is not particularly limited, and may be, for example, air or oxygen, or an inert gas such as nitrogen gas, argon gas, or helium gas.

  When manufacturing a glass material using the manufacturing apparatus 1, first, the glass raw material ingot 12 prepared so as to be glass having the above composition is placed on the molding surface 10a. Examples of the glass raw material ingot 12 include 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, or a composition equivalent to the target glass composition. Examples thereof include aggregates of crystals.

  Next, the glass raw material block 12 is floated on the molding surface 10a by ejecting gas from the gas ejection holes 10b. That is, the glass raw material lump 12 is held in a state where it is not in contact with the molding surface 10a. In this state, the laser light irradiation device 13 irradiates the glass raw material block 12 with laser light. Thereby, the glass raw material lump 12 is heated and melted to be vitrified to obtain molten glass. After that, the glass material can be obtained by cooling the molten glass. In the step of heating and melting the glass raw material lump 12 and the step of cooling the molten glass, and further, cooling 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 lump 12 and the molten glass are melted. Further, it is preferable to suppress contact between the glass material and the molding surface 10a. The method of heating and melting may be radiation heating, instead of the method of irradiating with laser light.

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

  Tables 1 to 4 show examples of the present invention and comparative examples, respectively.

  Each sample was prepared as follows. First, a glass raw material lump was prepared using raw material powders prepared so as to have the glass compositions shown in Tables 1 to 4. The glass raw material lump was produced by a method in which raw material powder was press-molded and sintered at 1100 to 1400° C. for 12 hours. The glass raw material lump was roughly crushed using a mortar and used in the state of small pieces of 0.1 to 0.5 g.

Using the glass raw material lump obtained above, a substantially spherical glass material (major axis 3 to 7.5 mm) was produced by a containerless solidification 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 raw material mass, and was supplied at a flow rate of 1 to 15 L/min.

  The refractive index (nd) and Abbe's number (νd) of the obtained glass material were measured. The results are shown in Tables 1-4.

  The refractive index was evaluated by measuring the d-line (587.6 nm) of a helium lamp using Shimadzu KPR-2000 after performing a right angle polishing after adhering a glass material to a 5 mm thick soda plate substrate.

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

  As shown in Tables 1 to 3, in Examples 1 to 15, glasses having a high refractive index of 2.29486 to 2.333133 were obtained. On the other hand, as shown in Table 4, the samples of Comparative Examples 1 to 5 were not vitrified.

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

Claims (5)

In mol %, TiO ₂ 50 to 85%, La ₂ O ₃ 5 to 25% (excluding 25%), Gd ₂ O _{3 to} 20% (excluding 0%), La ₂ O ₃ +Gd. ₂ O _{3 8~25%,} containing ZrO 2 3 ~25%, optical glass major axis, characterized in der Rukoto than 3 mm. The optical glass according to claim 1, which has a spherical shape or a spheroidal shape. Content by molar _{percent, Nb 2 O 5 0~20%,} Ta 2 O 5 0~20%, Y 2 O 3 0~20%, or _Yb 2 _O 3 0 to 20% der Rukoto The optical glass according to claim 1 or 2, which is characterized. Refractive index (nd) is 2.15-2.40, The optical glass as described in any one of Claims 1-3 characterized by the above-mentioned. A method for producing optical glass according to any one of claims 1-4,
A method for producing optical glass, comprising a step of cooling the molten glass after heating and melting the glass raw material to obtain molten glass in a state where the glass raw material is suspended and held in the air.